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8 pages, 668 KiB

Open AccessCommunication

Study of Very Forward Neutrons with the CMS Zero Degree Calorimeter

by Olivér Surányi

Universe 2019, 5(10), 210; https://0-doi-org.brum.beds.ac.uk/10.3390/universe5100210 - 09 Oct 2019

Cited by 2 | Viewed by 3247

Forward neutrons are studied in proton-lead collisions at the CMS experiment at the CERN LHC. They provide information on the centrality and event plane of collisions and provide an opportunity to study nuclear breakup. At the CMS experiment they are detected by the [...] Read more.

Forward neutrons are studied in proton-lead collisions at the CMS experiment at the CERN LHC. They provide information on the centrality and event plane of collisions and provide an opportunity to study nuclear breakup. At the CMS experiment they are detected by the Zero Degree Calorimeters (ZDCs) in the

| η | > 8.5

pseudorapidity range. The ZDCs are quartz fiber Cherenkov calorimeters using tungsten as absorber. Test beam data and events with a single spectator neutron are used for the calibration of these detectors. A Fourier-based method is used correct for the effect of multiple pPb collisions. The corrected ZDC energy distribution is used to calculate centrality percentiles and unfold the neutron multiplicity distribution. Full article

(This article belongs to the Special Issue The Zimányi School and Analytic Hydrodynamics in High Energy Physics)

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23 pages, 949 KiB

Open AccessArticle

Temperature Dependence of the Axion Mass in a Scenario Where the Restoration of Chiral Symmetry Drives the Restoration of the U_A(1) Symmetry

by Davor Horvatić, Dalibor Kekez and Dubravko Klabučar

Universe 2019, 5(10), 208; https://0-doi-org.brum.beds.ac.uk/10.3390/universe5100208 - 08 Oct 2019

Cited by 5 | Viewed by 2575

Abstract

The temperature (T) dependence of the axion mass is predicted for

T^{'}

s up to

\sim 2.3 \times

the chiral restoration temperature of QCD. The axion is related to the

U_{A} (1)

anomaly. The squared axion mass [...] Read more.

The temperature (T) dependence of the axion mass is predicted for

T^{'}

s up to

\sim 2.3 \times

the chiral restoration temperature of QCD. The axion is related to the

U_{A} (1)

anomaly. The squared axion mass

m_{a} {(T)}^{2}

is, modulo the presently undetermined scale of spontaneous breaking of Peccei–Quinn symmetry

f_{a}

(squared), equal to QCD topological susceptibility

χ (T)

for all T. We obtain

χ (T)

by using quark condensates calculated in two effective Dyson–Schwinger models of nonperturbative QCD. They exhibit the correct chiral behavior, including the dynamical breaking of chiral symmetry and its restoration at high T. This is reflected in the

U_{A} (1)

symmetry breaking and restoration through

χ (T)

. In our previous studies, such

χ (T)

yields the T-dependence of the

U_{A} (1)

-anomaly-influenced masses of

η^{'}

and

η

mesons consistent with experiment. This in turn supports our prediction for the T-dependence of the axion mass. Another support is a rather good agreement with the pertinent lattice results. This agreement is not spoiled by our varying u and d quark mass parameters out of the isospin limit. Full article

(This article belongs to the Special Issue The Zimányi School and Analytic Hydrodynamics in High Energy Physics)

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9 pages, 4051 KiB

Open AccessCommunication

Open-Charm Hadron Measurements in Au+Au Collisions at √^sNN = 200 GeV by the STAR Experiment

by Jan Vanek

Universe 2019, 5(9), 196; https://0-doi-org.brum.beds.ac.uk/10.3390/universe5090196 - 07 Sep 2019

Cited by 1 | Viewed by 2355

Abstract

Study of the open-charm hadron production in heavy-ion collisions is crucial for understanding the properties of the Quark-Gluon Plasma. In these papers, we report on a selection of recent STAR measurements of open-charm hadrons in Au+Au collisions at [...] Read more.

Study of the open-charm hadron production in heavy-ion collisions is crucial for understanding the properties of the Quark-Gluon Plasma. In these papers, we report on a selection of recent STAR measurements of open-charm hadrons in Au+Au collisions at

\sqrt{s_{NN}} = 200 GeV

, using the Heavy-Flavor Tracker. In particular, the nuclear modification factors of D

^{0}

and D

^{\pm}

mesons, elliptic and directed flow of D

^{0}

mesons, D

_{s}

/D

^{0}

and

Λ_{c} / D^{0}

yield ratios are discussed. The observed suppression of D

^{0}

and D

^{\pm}

mesons suggests strong interactions of the charm quarks with the QGP. The measured elliptic flow of D

^{0}

mesons is large and follows the NCQ scaling, suggesting that charm quarks may be close to thermal equilibrium with the QGP medium. Both D

_{s}

/D

^{0}

and

Λ_{c} / D^{0}

yield ratios are found to be enhanced in Au+Au collisions. The enhancement can be explained by models incorporating coalescence hadronization of charm quarks. In addition, the directed flow of the D

^{0}

mesons is measured to be negative and larger than that of light-flavor mesons which is in a qualitative agreement with hydrodynamic model predictions with a tilted QGP bulk. Full article

(This article belongs to the Special Issue The Zimányi School and Analytic Hydrodynamics in High Energy Physics)

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9 pages, 243 KiB

Open AccessEditor’s ChoiceArticle

A Particle Emitting Source From an Accelerating, Perturbative Solution of Relativistic Hydrodynamics

by Bálint Kurgyis and Máté Csanád

Universe 2019, 5(9), 194; https://0-doi-org.brum.beds.ac.uk/10.3390/universe5090194 - 04 Sep 2019

Viewed by 1888

Abstract

The quark gluon plasma is formed in heavy-ion collisions, and it can be described by solutions of relativistic hydrodynamics. In this paper we utilize perturbative hydrodynamics, where we study first order perturbations on top of a known solution. We investigate the perturbations on [...] Read more.

The quark gluon plasma is formed in heavy-ion collisions, and it can be described by solutions of relativistic hydrodynamics. In this paper we utilize perturbative hydrodynamics, where we study first order perturbations on top of a known solution. We investigate the perturbations on top of the Hubble flow. From this perturbative solution we can give the form of the particle emitting source and calculate observables of heavy-ion collisions. We describe the source function and the single-particle momentum spectra for a spherically symmetric solution. Full article

(This article belongs to the Special Issue The Zimányi School and Analytic Hydrodynamics in High Energy Physics)

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11 pages, 466 KiB

Open AccessCommunication

Compact Star Properties from an Extended Linear Sigma Model

by János Takátsy, Péter Kovács, Zsolt Szép and György Wolf

Universe 2019, 5(7), 174; https://0-doi-org.brum.beds.ac.uk/10.3390/universe5070174 - 15 Jul 2019

Cited by 4 | Viewed by 2327

Abstract

The equation of state provided by effective models of strongly interacting matter should comply with the restrictions imposed by current astrophysical observations of compact stars. Using the equation of state given by the (axial-)vector meson extended linear sigma model, we determine the mass–radius [...] Read more.

The equation of state provided by effective models of strongly interacting matter should comply with the restrictions imposed by current astrophysical observations of compact stars. Using the equation of state given by the (axial-)vector meson extended linear sigma model, we determine the mass–radius relation and study whether these restrictions are satisfied under the assumption that most of the star is filled with quark matter. We also compare the mass–radius sequence with those given by the equations of state of somewhat simpler models. Full article

(This article belongs to the Special Issue The Zimányi School and Analytic Hydrodynamics in High Energy Physics)

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8 pages, 401 KiB

Open AccessArticle

Lévy HBT Results at NA61/SHINE

by Barnabás Pórfy

Universe 2019, 5(6), 154; https://0-doi-org.brum.beds.ac.uk/10.3390/universe5060154 - 16 Jun 2019

Cited by 4 | Viewed by 1980

Abstract

Bose–Einstein (or Hanbury–Brown and Twiss (HBT)) momentum correlations reveal the space–time structure of the particle emitting source created in high energy nucleus–nucleus collisions. In this paper we present the latest NA61/SHINE measurements of Bose–Einstein correlations of identified pion pairs and their description based [...] Read more.

Bose–Einstein (or Hanbury–Brown and Twiss (HBT)) momentum correlations reveal the space–time structure of the particle emitting source created in high energy nucleus–nucleus collisions. In this paper we present the latest NA61/SHINE measurements of Bose–Einstein correlations of identified pion pairs and their description based on Lévy distributed sources in Be + Be collisions at 150A GeV/c. We investigate the transverse mass dependence of the Lévy source parameters and discuss their possible interpretations. Full article

(This article belongs to the Special Issue The Zimányi School and Analytic Hydrodynamics in High Energy Physics)

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10 pages, 1339 KiB

Open AccessArticle

Estimating the Variation of Neutron Star Observables by Dense Symmetric Nuclear Matter Properties

by Péter Pósfay, Gergely Gábor Barnaföldi and Antal Jakovác

Universe 2019, 5(6), 153; https://0-doi-org.brum.beds.ac.uk/10.3390/universe5060153 - 14 Jun 2019

Cited by 7 | Viewed by 2170

Abstract

Recent multi-channel astrophysics observations and the soon-to-be published new measured electromagnetic and gravitation data provide information on the inner structure of the compact stars. These macroscopic observations can significantly increase our knowledge on the neutron star enteriors, providing constraints on the microscopic physical [...] Read more.

Recent multi-channel astrophysics observations and the soon-to-be published new measured electromagnetic and gravitation data provide information on the inner structure of the compact stars. These macroscopic observations can significantly increase our knowledge on the neutron star enteriors, providing constraints on the microscopic physical properties. On the other hand, due to the masquarade problem, there are still uncertainties on the various nuclear-matter models and their parameters as well. Calculating the properties of the dense nuclear matter, effective field theories are the most widely-used tools. However, the values of the microscopical parameters need to be set consistently to the nuclear and astrophysical measurements. In this work, we investigate how uncertainties are induced by the variation of the microscopical parameters. We use a symmetric nuclear matter in an extended

σ

-

ω

model to see the influence of the nuclear matter parameters. We calculate the dense matter equation of state and give the mass-radius diagram for a simplistic neutron star model. We present that the Landau mass and compressibility modulus of the nuclear matter have definite linear relation to the maximum mass of a Schwarzschild neutron star. Full article

(This article belongs to the Special Issue The Zimányi School and Analytic Hydrodynamics in High Energy Physics)

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11 pages, 4696 KiB

Open AccessArticle

Averaging and the Shape of the Correlation Function

by Boris Tomášik, Jakub Cimerman and Christopher Plumberg

Universe 2019, 5(6), 148; https://0-doi-org.brum.beds.ac.uk/10.3390/universe5060148 - 13 Jun 2019

Cited by 3 | Viewed by 2093

Abstract

A brief pedagogical introduction to correlation femtoscopy is given. We then focus on the shape of the correlation function and discuss the possible reasons for its departure from the Gaussian form and better reproduction with a Lévy stable distribution. With the help of [...] Read more.

A brief pedagogical introduction to correlation femtoscopy is given. We then focus on the shape of the correlation function and discuss the possible reasons for its departure from the Gaussian form and better reproduction with a Lévy stable distribution. With the help of Monte Carlo simulations based on asymmetric extension of the Blast-Wave model with resonances we demonstrate possible influence of averaging over many events and integrating over wide momentum bins on the shape of the correlation function. We also show that the shape is strongly influenced by the use of the one-dimensional parametrisation in the

q_{i n v}

variable. Full article

(This article belongs to the Special Issue The Zimányi School and Analytic Hydrodynamics in High Energy Physics)

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9 pages, 1077 KiB

Open AccessCommunication

Multiplicity Dependence in the Non-Extensive Hadronization Model Calculated by the HIJING++ Framework

by Gábor Bíró, Gergely Gábor Barnaföldi, Gábor Papp and Tamás Sándor Biró

Universe 2019, 5(6), 134; https://0-doi-org.brum.beds.ac.uk/10.3390/universe5060134 - 01 Jun 2019

Cited by 3 | Viewed by 1881

Abstract

The non-extensive statistical description of the identified final state particles measured in high energy collisions is well-known by its wide range of applicability. However, there are many open questions that need to be answered, including but not limited to, the question of the [...] Read more.

The non-extensive statistical description of the identified final state particles measured in high energy collisions is well-known by its wide range of applicability. However, there are many open questions that need to be answered, including but not limited to, the question of the observed mass scaling of massive hadrons or the size and multiplicity dependence of the model parameters. This latter is especially relevant, since currently the amount of available experimental data with high multiplicity at small systems is very limited. This contribution has two main goals: On the one hand we provide a status report of the ongoing tuning of the soon-to-be-released HIJING++ Monte Carlo event generator. On the other hand, the role of multiplicity dependence of the parameters in the non-extensive hadronization model is investigated with HIJING++ calculations. We present cross-check comparisons of HIJING++ with existing experimental data to verify its validity in our range of interest as well as calculations at high-multiplicity regions where we have insufficient experimental data. Full article

(This article belongs to the Special Issue The Zimányi School and Analytic Hydrodynamics in High Energy Physics)

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11 pages, 1023 KiB

Open AccessArticle

Coulomb Final State Interaction in Heavy Ion Collisions for Lévy Sources

by Máté Csanád, Sándor Lökös and Márton Nagy

Universe 2019, 5(6), 133; https://0-doi-org.brum.beds.ac.uk/10.3390/universe5060133 - 28 May 2019

Cited by 10 | Viewed by 1946

Abstract

Investigation of momentum space correlations of particles produced in high energy reactions requires taking final state interactions into account, a crucial point of any such analysis. Coulomb interaction between charged particles is the most important such effect. In small systems like those created [...] Read more.

Investigation of momentum space correlations of particles produced in high energy reactions requires taking final state interactions into account, a crucial point of any such analysis. Coulomb interaction between charged particles is the most important such effect. In small systems like those created in

e^{+} e^{-} -

or

p + p

collisions, the so-called Gamow factor (valid for a point-like particle source) gives an acceptable description of the Coulomb interaction. However, in larger systems such as central or mid-central heavy ion collisions, more involved approaches are needed. In this paper we investigate the Coulomb final state interaction for Lévy-type source functions that were recently shown to be of much interest for a refined description of the space-time picture of particle production in heavy-ion collisions. Full article

(This article belongs to the Special Issue The Zimányi School and Analytic Hydrodynamics in High Energy Physics)

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8 pages, 330 KiB

Open AccessCommunication

Jet Structure Studies in Small Systems

by Zoltán Varga, Róbert Vértesi and Gergely Gábor Barnaföldi

Universe 2019, 5(5), 132; https://0-doi-org.brum.beds.ac.uk/10.3390/universe5050132 - 27 May 2019

Cited by 5 | Viewed by 2229

Abstract

A study investigating a possible jet shape dependence on the charged event multiplicity was performed on collision samples generated by Monte–Carlo (MC) event generators Pythia and Hijing++. We calculated the integral jet shape and found a significant modification caused by multiple-parton interactions. [...] Read more.

A study investigating a possible jet shape dependence on the charged event multiplicity was performed on collision samples generated by Monte–Carlo (MC) event generators Pythia and Hijing++. We calculated the integral jet shape and found a significant modification caused by multiple-parton interactions. By interchanging and enabling different model ingredients in the simulations and analyzing the results in several

p_{T}

bins and event multiplicity classes, we found a characteristic jet size measure that was independent of the chosen tunes, settings, and jet reconstruction algorithms. Full article

(This article belongs to the Special Issue The Zimányi School and Analytic Hydrodynamics in High Energy Physics)

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7 pages, 425 KiB

Open AccessCommunication

Heavy-Flavor Measurements with the ALICE Experiment at the LHC

by Róbert Vértesi

Universe 2019, 5(5), 130; https://0-doi-org.brum.beds.ac.uk/10.3390/universe5050130 - 25 May 2019

Cited by 1 | Viewed by 2459

Abstract

Heavy quarks (charm and beauty) are produced early in the nucleus–nucleus collisions, and heavy flavor survives throughout the later stages. Measurements of heavy-flavor quarks thus provide us with means to understand the properties of the Quark–Gluon Plasma, a hot and dense state of [...] Read more.

Heavy quarks (charm and beauty) are produced early in the nucleus–nucleus collisions, and heavy flavor survives throughout the later stages. Measurements of heavy-flavor quarks thus provide us with means to understand the properties of the Quark–Gluon Plasma, a hot and dense state of matter created in heavy-ion collisions. Production of heavy-flavor in small collision systems, on the other hand, can be used to test Quantum-chromodynamics models. After a successful completion of the Run-I data taking period, the increased luminosity from the LHC and an upgraded ALICE detector system in the Run-II data taking period allows for unprecedented precision in the study of heavy quarks. In this article we give an overview of selected recent results on heavy-flavor measurements with ALICE experiments at the LHC. Full article

(This article belongs to the Special Issue The Zimányi School and Analytic Hydrodynamics in High Energy Physics)

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5 pages, 425 KiB

Open AccessCommunication

Medical Applications of the ALPIDE Detector

by Monika Varga-Kofarago

Universe 2019, 5(5), 128; https://0-doi-org.brum.beds.ac.uk/10.3390/universe5050128 - 24 May 2019

Viewed by 2177

Abstract

The CERN Large Hadron Collider (LHC) ALICE detector is undergoing a major upgrade in the Second Long Shutdown of the LHC in 2019–2020. During this upgrade, the innermost detector, the Inner Tracking System, will be completely replaced by a new detector which is [...] Read more.

The CERN Large Hadron Collider (LHC) ALICE detector is undergoing a major upgrade in the Second Long Shutdown of the LHC in 2019–2020. During this upgrade, the innermost detector, the Inner Tracking System, will be completely replaced by a new detector which is built from the ALPIDE sensor. In the Bergen proton computer tomography (pCT) collaboration, we decided to apply these sensors for medical applications. They can be used for positioning in hadron therapies due to their good position resolution and radiation tolerance. Dose planning of hadron therapy is calculated currently from photon CT measurements, which results in large uncertainties in the planning and therefore in a necessary enlargement of the treatment area. This uncertainty can be reduced by performing the CT scan using protons. The current contribution shows the development of a sampling calorimeter built from the ALPIDE detector for proton CT measurements and describes the state of the project. Full article

(This article belongs to the Special Issue The Zimányi School and Analytic Hydrodynamics in High Energy Physics)

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8 pages, 3010 KiB

Open AccessArticle

Influence of Backside Energy Leakages from Hadronic Calorimeters on Fluctuation Measures in Relativistic Heavy-Ion Collisions

by Andrey Seryakov

Universe 2019, 5(5), 126; https://0-doi-org.brum.beds.ac.uk/10.3390/universe5050126 - 23 May 2019

Cited by 1 | Viewed by 1931

Abstract

The phase diagram of the strongly interacting matter is the main research subject for different current and future experiments in high-energy physics. System size and energy scan programs aim to find a possible critical point. One of such programs was accomplished by the [...] Read more.

The phase diagram of the strongly interacting matter is the main research subject for different current and future experiments in high-energy physics. System size and energy scan programs aim to find a possible critical point. One of such programs was accomplished by the fixed-target NA61/SHINE experiment in 2018. It includes six beam energies and six colliding systems: p + p, Be + Be, Ar + Sc, Xe + La, Pb + Pb and p + Pb. In this study, we discuss how the efficiency of centrality selection by forward spectators influences multiplicity and fluctuation measures and how this influence depends on the size of colliding systems. We use SHIELD and EPOS Monte-Carlo (MC) generators along with the wounded nucleon model, introduce a probability to lose a forward spectator and spectator energy loss. We show that for light colliding systems such as Be or Li even a small inefficiency in centrality selection has a dramatic impact on multiplicity scaled variance. Conversely, heavy systems such as Ar + Sc are much less prone to the effect. Full article

(This article belongs to the Special Issue The Zimányi School and Analytic Hydrodynamics in High Energy Physics)

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7 pages, 340 KiB

Open AccessCommunication

Correlations of High-p_T Hadrons and Jets in ALICE

by Filip Krizek

Universe 2019, 5(5), 124; https://0-doi-org.brum.beds.ac.uk/10.3390/universe5050124 - 22 May 2019

Viewed by 2115

Abstract

There are two prominent experimental signatures of quark–gluon plasma creation in ultra-relativistic heavy-ion collisions: the jet quenching phenomenon and the azimuthal-momentum space-anisotropy of final-state particle emission. Recently, the latter signature was also observed in lighter collision systems such as p–Pb or pp. This [...] Read more.

There are two prominent experimental signatures of quark–gluon plasma creation in ultra-relativistic heavy-ion collisions: the jet quenching phenomenon and the azimuthal-momentum space-anisotropy of final-state particle emission. Recently, the latter signature was also observed in lighter collision systems such as p–Pb or pp. This raises a natural question of whether in these systems, the observed collectivity is also accompanied by jet quenching. In this paper, we overview ALICE measurements of the jet quenching phenomenon studied using semi-inclusive distributions of track-based jets recoiling from a high-transverse momentum (

p_{T}

) hadron trigger in Pb–Pb and p–Pb collisions at LHC energies. The constructed coincidence observable, the per trigger normalized yield of associated recoil jets, is corrected for the complex uncorrelated jet background, including multi-partonic interactions, using a data-driven statistical subtraction method. In the p–Pb data, the observable was measured in events with different underlying event activity and was utilized to set an upper limit on the average medium-induced out-of-cone energy transport for jets with resolution parameter

R = 0.4

. The associated jet momentum shift was found to be less than 0.4 GeV/c at 90% confidence. Full article

(This article belongs to the Special Issue The Zimányi School and Analytic Hydrodynamics in High Energy Physics)

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9 pages, 1166 KiB

Open AccessCommunication

Hadron Spectra Parameters within the Non-Extensive Approach

by Keming Shen, Gergely Gábor Barnaföldi and Tamás Sándor Biró

Universe 2019, 5(5), 122; https://0-doi-org.brum.beds.ac.uk/10.3390/universe5050122 - 21 May 2019

Cited by 16 | Viewed by 2059

Abstract

We investigate how the non-extensive approach works in high-energy physics. Transverse momentum (

p_{T}

) spectra of several hadrons are fitted by various non-extensive momentum distributions and by the Boltzmann–Gibbs statistics. It is shown that some non-extensive distributions can be transferred one [...] Read more.

We investigate how the non-extensive approach works in high-energy physics. Transverse momentum (

p_{T}

) spectra of several hadrons are fitted by various non-extensive momentum distributions and by the Boltzmann–Gibbs statistics. It is shown that some non-extensive distributions can be transferred one into another. We find explicit hadron mass and center-of-mass energy scaling both in the temperature and in the non-extensive parameter, q, in proton–proton and heavy-ion collisions. We find that the temperature depends linearly, but the Tsallis q follows a logarithmic dependence on the collision energy in proton–proton collisions. In the nucleus–nucleus collisions, on the other hand, T and q correlate linearly, as was predicted in our previous work. Full article

(This article belongs to the Special Issue The Zimányi School and Analytic Hydrodynamics in High Energy Physics)

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9 pages, 884 KiB

Open AccessArticle

Production and Detection of Light Dark Matter at Jefferson Lab: The BDX Experiment

by Marzio De Napoli

Universe 2019, 5(5), 120; https://0-doi-org.brum.beds.ac.uk/10.3390/universe5050120 - 20 May 2019

Cited by 2 | Viewed by 2656

Abstract

The Beam Dump eXperiment (BDX) is a an electron-beam thick-target experiment aimed to investigate the existence of light Dark Matter particles in the MeV-GeV mass region at Jefferson Lab. The experiment will make use of a 10.6 GeV high-intensity electron-beam impinging on the [...] Read more.

The Beam Dump eXperiment (BDX) is a an electron-beam thick-target experiment aimed to investigate the existence of light Dark Matter particles in the MeV-GeV mass region at Jefferson Lab. The experiment will make use of a 10.6 GeV high-intensity electron-beam impinging on the Hall-A beam-dump to produce the Dark Matter particles (

χ

) through the Dark Photon portal. The BDX detector located at ∼20 m from the dump consists of two main components: an electromagnetic calorimeter to detect the signals produced by the

χ

-electron scattering and a veto system to reject background. The expected signature of the DM (Dark Matter) interaction in the Ecal (Electromagnetic calorimeter) is a ∼GeV electromagnetic shower paired with a null activity in the surrounding active veto counters. Collecting

10^{22}

electrons on target in 285 days of parasitic run at 65

μ

A of beam current, and with an expected background of O(5) counts, in the case of a null discovery, BDX will be able to lower the exclusion limits by one to two orders of magnitude in the parameter space of dark-matter coupling versus mass. This paper describes the experiment and presents a summary of the most significant results achieved thus far, which led to the recent approval of the experiment by JLab-PAC46. Full article

(This article belongs to the Special Issue The Zimányi School and Analytic Hydrodynamics in High Energy Physics)

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9 pages, 956 KiB

Open AccessArticle

Quarkonium Phenomenology from a Generalised Gauss Law

by David Lafferty and Alexander Rothkopf

Universe 2019, 5(5), 119; https://0-doi-org.brum.beds.ac.uk/10.3390/universe5050119 - 20 May 2019

Cited by 2 | Viewed by 2291

Abstract

We present an improved analytic parametrisation of the complex in-medium heavy quark potential derived rigorously from the generalised Gauss law. To this end we combine in a self-consistent manner a non-perturbative vacuum potential with a weak-coupling description of the QCD medium. The resulting [...] Read more.

We present an improved analytic parametrisation of the complex in-medium heavy quark potential derived rigorously from the generalised Gauss law. To this end we combine in a self-consistent manner a non-perturbative vacuum potential with a weak-coupling description of the QCD medium. The resulting Gauss-law parametrisation is able to reproduce full lattice QCD data by using only a single temperature dependent parameter, the Debye mass

m_{D}

. Using this parametrisation we model the in-medium potential at finite baryo-chemical potential, which allows us to estimate the

Ψ^{'}

/

J / Ψ

ratio in heavy-ion collisions at different beam energies. Full article

(This article belongs to the Special Issue The Zimányi School and Analytic Hydrodynamics in High Energy Physics)

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7 pages, 388 KiB

Open AccessCommunication

Correlation of Heavy and Light Flavors in Simulations

by Eszter Frajna and Róbert Vértesi

Universe 2019, 5(5), 118; https://0-doi-org.brum.beds.ac.uk/10.3390/universe5050118 - 20 May 2019

Cited by 1 | Viewed by 2252

Abstract

The ALICE experiment at the Large Hadron Collider (LHC) ring is designed to study the strongly interacting matter at extreme energy densities created in high-energy heavy-ion collisions. In this paper we investigate correlations of heavy and light flavors in simulations at LHC energies [...] Read more.

The ALICE experiment at the Large Hadron Collider (LHC) ring is designed to study the strongly interacting matter at extreme energy densities created in high-energy heavy-ion collisions. In this paper we investigate correlations of heavy and light flavors in simulations at LHC energies at mid-rapidity, with the primary purpose of proposing experimental applications of these methods. Our studies have shown that investigating the correlation images can aid the experimental separation of heavy quarks and help understanding the physics that create them. The shape of the correlation peaks can be used to separate the electrons stemming from b quarks. This could be a method of identification that, combined with identification in silicon vertex detectors, may provide much better sample purity for examining the secondary vertex shift. Based on a correlation picture it is also possible to distinguish between prompt and late contributions to D meson yields. Full article

(This article belongs to the Special Issue The Zimányi School and Analytic Hydrodynamics in High Energy Physics)

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9 pages, 730 KiB

Open AccessCommunication

Quarkonium Production in the QGP

by Alexander Rothkopf

Universe 2019, 5(5), 117; https://0-doi-org.brum.beds.ac.uk/10.3390/universe5050117 - 16 May 2019

Viewed by 2554

Abstract

We report on recent theory progress in understanding the production of heavy quarkonium in heavy-ion collisions based on the in-medium heavy-quark potential extracted from lattice QCD simulations. On the one hand, the proper in-medium potential allows us to study the spectral properties of [...] Read more.

We report on recent theory progress in understanding the production of heavy quarkonium in heavy-ion collisions based on the in-medium heavy-quark potential extracted from lattice QCD simulations. On the one hand, the proper in-medium potential allows us to study the spectral properties of heavy quarkonium in thermal equilibrium, from which we estimate the

ψ^{'}

to

J / ψ

ratio in heavy-ion collisions. On the other hand, the potential provides a central ingredient in the description of the real-time evolution of heavy-quarkonium formulated in the open-quantum-systems framework. Full article

(This article belongs to the Special Issue The Zimányi School and Analytic Hydrodynamics in High Energy Physics)

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7 pages, 469 KiB

Open AccessCommunication

Study of Jet Shape Observables in Au+Au Collisions at s N N = 200 GeV with JEWEL

by Veronika Agafonova

Universe 2019, 5(5), 114; https://0-doi-org.brum.beds.ac.uk/10.3390/universe5050114 - 11 May 2019

Cited by 2 | Viewed by 2484

Abstract

Nuclear–nuclear collisions at energies attainable at the large accelerators RHIC and the LHC are an ideal environment to study nuclear matter under extreme conditions of high temperature and energy density. One of the most important probes of such nuclear matter is the study [...] Read more.

Nuclear–nuclear collisions at energies attainable at the large accelerators RHIC and the LHC are an ideal environment to study nuclear matter under extreme conditions of high temperature and energy density. One of the most important probes of such nuclear matter is the study of production of jets. In this article, several jet shape observables in Au+Au collisions at the center of mass energy per nucleon–nucleon pair of

\sqrt{s_{N N}}

= 200 GeV simulated in the Monte Carlo generator JEWEL are presented. Jets were reconstructed using the anti-

k_{T}

algorithm and their shapes were studied as a function of the jet-resolution parameter R, transverse momentum

p_{T}

and collision centrality. Full article

(This article belongs to the Special Issue The Zimányi School and Analytic Hydrodynamics in High Energy Physics)

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7 pages, 856 KiB

Open AccessArticle

Viscous Hydrodynamic Description of the Pseudorapidity Density and Energy Density Estimation for Pb+Pb and Xe+Xe Collisions at the LHC

by Xiong-Tao Gong, Ze-Fang Jiang, Duan She and C. B. Yang

Universe 2019, 5(5), 112; https://0-doi-org.brum.beds.ac.uk/10.3390/universe5050112 - 10 May 2019

Viewed by 2081

Abstract

Based on the analytical solution of accelerating relativistic viscous fluid hydrodynamics and Buda–Lund model, the pseudorapidity distributions of the most central Pb+Pb and Xe+Xe collisions are presented. Inspired by the CNC model, a modified energy density estimation formula is presented to investigate the [...] Read more.

Based on the analytical solution of accelerating relativistic viscous fluid hydrodynamics and Buda–Lund model, the pseudorapidity distributions of the most central Pb+Pb and Xe+Xe collisions are presented. Inspired by the CNC model, a modified energy density estimation formula is presented to investigate the dependence of the initial energy density estimation on the viscous effect. This new energy density estimation formula shows that the bulk energy is deposited to the neighboring fluid cells in the presence of the shear viscosity and bulk viscosity. In contrast to the well-known CNC energy density estimation formula, a 4.9% enhancement of the estimated energy density at the LHC kinematics is shown. Full article

(This article belongs to the Special Issue The Zimányi School and Analytic Hydrodynamics in High Energy Physics)

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6 pages, 413 KiB

Open AccessCommunication

Another Approach to Track Reconstruction: Cluster Analysis

by Ferenc Siklér

Universe 2019, 5(5), 105; https://0-doi-org.brum.beds.ac.uk/10.3390/universe5050105 - 06 May 2019

Cited by 1 | Viewed by 2017

Abstract

A novel combination of data analysis techniques is introduced for the reconstruction of primary charged particles and of daughters of photon conversions, created in high energy collisions. Instead of performing a classical trajectory building or an image transformation, efficient use of both local [...] Read more.

A novel combination of data analysis techniques is introduced for the reconstruction of primary charged particles and of daughters of photon conversions, created in high energy collisions. Instead of performing a classical trajectory building or an image transformation, efficient use of both local and global information is undertaken while keeping competing choices open. The measured hits in silicon-based tracking detectors are clustered with the help of a k-medians clustering. It proceeds by alternating between the hit-to-track assignment and the track-fit update steps, until convergence. The clustering is complemented with the possibility of adding new track hypotheses or removing unnecessary ones. A simplified model of a silicon tracker is employed to test the performance of the proposed method, showing good efficiency and purity characteristics. Full article

(This article belongs to the Special Issue The Zimányi School and Analytic Hydrodynamics in High Energy Physics)

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8 pages, 702 KiB

Open AccessCommunication

Highlights from NA61/SHINE: Proton Intermittency Analysis

by Daria Prokhorova and Nikolaos Davis

Universe 2019, 5(5), 103; https://0-doi-org.brum.beds.ac.uk/10.3390/universe5050103 - 03 May 2019

Cited by 5 | Viewed by 2209

Abstract

The NA61/SHINE experiment at CERN SPS searches for the critical point of strongly interacting matter via scanning the phase diagram by changing beam momenta (13A–150A GeV/c) and system size (p + p, p + Pb, Be + Be, [...] Read more.

The NA61/SHINE experiment at CERN SPS searches for the critical point of strongly interacting matter via scanning the phase diagram by changing beam momenta (13A–150A GeV/c) and system size (p + p, p + Pb, Be + Be, Ar + Sc, Xe + La). An observation of local proton-density fluctuations that scale as a power law of the appropriate universality class as a function of phase space bin size would signal the approach of the system to the vicinity of the possible critical point. An investigation of this phenomenon was performed in terms of the second-scaled factorial moments (SSFMs) of proton density in transverse momentum space with subtraction of a noncritical background. New NA61/SHINE preliminary analysis of Ar + Sc data at 150A GeV/c revealed a nontrivial intermittent behavior of proton moments. A similar effect was observed by NA49 in “Si” + Si data at 158A GeV/c. At the same time, no intermittency signal was detected in “C” + C and Pb + Pb events by NA49, as well as in Be + Be collisions by NA61/SHINE. EPOS1.99 also fails to describe the power-law scaling of SSFMs in Ar + Sc. Qualitatively, the effect is more pronounced with the increase of collision-peripherality and proton-purity thresholds, but a quantitative estimate is to be properly done via power-law exponent fit using the bootstrap method and compared to intermittency critical index

ϕ_{2}

, derived from 3D-Ising effective action. Full article

(This article belongs to the Special Issue The Zimányi School and Analytic Hydrodynamics in High Energy Physics)

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13 pages, 578 KiB

Open AccessArticle

Polarized Baryon Production in Heavy Ion Collisions: An Analytic Hydrodynamical Study

by Bálint Boldizsár, Márton I. Nagy and Máté Csanád

Universe 2019, 5(5), 101; https://0-doi-org.brum.beds.ac.uk/10.3390/universe5050101 - 01 May 2019

Cited by 7 | Viewed by 2032

Abstract

In this paper, we utilize known exact analytic solutions of perfect fluid hydrodynamics to analytically calculate the polarization of baryons produced in heavy-ion collisions. Assuming local thermodynamical equilibrium also for spin degrees of freedom, baryons get a net polarization at their formation (freeze-out). [...] Read more.

In this paper, we utilize known exact analytic solutions of perfect fluid hydrodynamics to analytically calculate the polarization of baryons produced in heavy-ion collisions. Assuming local thermodynamical equilibrium also for spin degrees of freedom, baryons get a net polarization at their formation (freeze-out). This polarization depends on the time evolution of the Quark-Gluon Plasma (QGP), which can be described as an almost perfect fluid. By using exact analytic solutions, we can thus analyze the necessity of rotation (and vorticity) for non-zero net polarization. In this paper, we give the first analytical calculations for the polarization four-vector. We use two hydrodynamical solutions; one is the spherically symmetric Hubble flow (a somewhat oversimplified model, to demonstrate the methodology); and the other solution is a somewhat more involved one that corresponds to a rotating and accelerating expansion, and is thus well-suited for the investigation of some of the main features of the time evolution of the QGP created in peripheral heavy-ion collisions (although there are still numerous features of real collision geometry that are beyond the scope of this simple model). Finally, we illustrate and discuss our results on the polarization. Full article

(This article belongs to the Special Issue The Zimányi School and Analytic Hydrodynamics in High Energy Physics)

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15 pages, 4019 KiB

Open AccessArticle

Nuclear Physics at the Energy Frontier: Recent Heavy Ion Results from the Perspective of the Electron Ion Collider

by Astrid Morreale

Universe 2019, 5(5), 98; https://0-doi-org.brum.beds.ac.uk/10.3390/universe5050098 - 28 Apr 2019

Viewed by 2670

Abstract

Quarks and gluons are the fundamental constituents of nucleons. Their interactions rather than their mass are responsible for

99 %

of the mass of all visible matter in the universe. Measuring the fundamental properties of matter has had a large impact on our [...] Read more.

Quarks and gluons are the fundamental constituents of nucleons. Their interactions rather than their mass are responsible for

99 %

of the mass of all visible matter in the universe. Measuring the fundamental properties of matter has had a large impact on our understanding of the nucleon structure and it has given us decades of research and technological innovation. Despite the large number of discoveries made, many fundamental questions remain open and in need of a new and more precise generation of measurements. The future Electron Ion Collider (EIC) will be a machine dedicated to hadron structure research. It will study the content of protons and neutrons in a largely unexplored regime in which gluons are expected to dominate and eventually saturate. While the EIC will be the machine of choice to quantify this regime, recent surprising results from the heavy ion community have begun to exhibit similar signatures as those expected from a regime dominated by gluons. Many of the heavy ion results that will be discussed in this document highlight the kinematic limitations of hadron–hadron and hadron–nucleus collisions. The reliability of using as a reference proton–proton (pp) and proton–ion (pA) collisions to quantify and disentangle vacuum and Cold Nuclear Matter (CNM) effects from those proceeding from a Quark Gluon Plasma (QGP) may be under question. A selection of relevant pp and pA results which highlight the need of an EIC will be presented. Full article

(This article belongs to the Special Issue The Zimányi School and Analytic Hydrodynamics in High Energy Physics)

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6 pages, 2091 KiB

Open AccessCommunication

Study of Angular Correlations in Monte Carlo Simulations in Pb-Pb Collisions

by Balázs Endre Szigeti and Monika Varga-Kofarago

Universe 2019, 5(5), 97; https://0-doi-org.brum.beds.ac.uk/10.3390/universe5050097 - 28 Apr 2019

Viewed by 2461

Abstract

In two-particle angular correlation measurements, the distribution of charged hadron pairs are evaluated as a function of pseudorapidity (

Δ η

) and azimuthal (

Δ φ

) differences. In these correlations, jets manifest themselves as a near-side peak around [...] Read more.

In two-particle angular correlation measurements, the distribution of charged hadron pairs are evaluated as a function of pseudorapidity (

Δ η

) and azimuthal (

Δ φ

) differences. In these correlations, jets manifest themselves as a near-side peak around

Δ η = 0,

Δ φ = 0

. These correlations can be used to extract transverse momentum (

p_{T}

) and centrality dependence of the shape of the near-side peak in Pb-Pb collision. The shape of the near-side peak is quantified by the variances of the distribution. The variances are evaluated from a fit combining the peak and the background. In this contribution, identified and unidentified angular correlations are shown from Pb-Pb collisions at

\sqrt{s_{N N}} = 2.76

TeV from Monte Carlo simulations (AMPT, PYTHIA 8.235/Angantyr). Results show that transport models in AMPT give better results than PYTHIA 8.235/Angantyr when comparing to the experimental results of the ALICE collaboration. Full article

(This article belongs to the Special Issue The Zimányi School and Analytic Hydrodynamics in High Energy Physics)

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8 pages, 480 KiB

Open AccessArticle

Bose–Einstein Correlations in pp and pPb Collisions at LHCb

by Bartosz Malecki

Universe 2019, 5(4), 95; https://0-doi-org.brum.beds.ac.uk/10.3390/universe5040095 - 25 Apr 2019

Cited by 4 | Viewed by 2297

Abstract

Bose–Einstein correlations for same-sign charged pions from proton–proton collisions at

\sqrt{s} = 7 TeV

are studied by the Large Hadron Collider beauty (LHCb) experiment. Correlation radii and chaoticity parameters are determined for different regions of charged-particle multiplicity using a double-ratio technique and a [...] Read more.

Bose–Einstein correlations for same-sign charged pions from proton–proton collisions at

\sqrt{s} = 7 TeV

are studied by the Large Hadron Collider beauty (LHCb) experiment. Correlation radii and chaoticity parameters are determined for different regions of charged-particle multiplicity using a double-ratio technique and a Levy parametrization of the correlation function. The correlation radius increases with the charged-particle multiplicity, while the chaoticity parameter decreases, which is consistent with observations from other experiments. A similar study for proton-lead collisions at

\sqrt{s_{N N}} = 5.02 TeV

is proposed. These results can give valuable input for the theoretical models that describe the evolution of the particle source, probing both its potential dependence on pseudorapidity region and differences between proton–proton and proton–lead systems. Full article

(This article belongs to the Special Issue The Zimányi School and Analytic Hydrodynamics in High Energy Physics)

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8 pages, 1773 KiB

Open AccessArticle

Characterization of Highly Irradiated ALPIDE Silicon Sensors

by Valentina Raskina and Filip Křížek

Universe 2019, 5(4), 91; https://0-doi-org.brum.beds.ac.uk/10.3390/universe5040091 - 14 Apr 2019

Viewed by 2940

Abstract

The ALICE (A Large Ion Collider Experiment) experiment at CERN will upgrade its Inner Tracking System (ITS) detector. The new ITS will consist of seven coaxial cylindrical layers of ALPIDE silicon sensors which are based on Monolithic Active Pixel Sensor (MAPS) technology. We [...] Read more.

The ALICE (A Large Ion Collider Experiment) experiment at CERN will upgrade its Inner Tracking System (ITS) detector. The new ITS will consist of seven coaxial cylindrical layers of ALPIDE silicon sensors which are based on Monolithic Active Pixel Sensor (MAPS) technology. We have studied the radiation hardness of ALPIDE sensors using a 30 MeV proton beam provided by the cyclotron U-120M of the Nuclear Physics Institute of the Czech Academy of Sciences in Řež. In this paper, these long-term measurements will be described. After being irradiated up to the total ionization dose 2.7 Mrad and non-ionizing energy loss 2.7 × 10

^{13}

1 MeV n

_{eq} \cdot

cm

^{- 2}

, ALPIDE sensors fulfill ITS upgrade project technical design requirements in terms of detection efficiency and fake-hit rate. Full article

(This article belongs to the Special Issue The Zimányi School and Analytic Hydrodynamics in High Energy Physics)

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Review

Jump to: Research

16 pages, 2015 KiB

Open AccessReview

Higgs and BSM Studies at the LHC

by Dezso Horváth

Universe 2019, 5(7), 160; https://0-doi-org.brum.beds.ac.uk/10.3390/universe5070160 - 02 Jul 2019

Viewed by 3012

Abstract

The discovery and study of the Higgs boson at the Large Hadron Collider of CERN has proven the validity of the Brout–Englert–Higgs mechanism of mass creation in the standard model via spontaneous symmetry breaking. The new results obtained by the ATLAS and CMS [...] Read more.

The discovery and study of the Higgs boson at the Large Hadron Collider of CERN has proven the validity of the Brout–Englert–Higgs mechanism of mass creation in the standard model via spontaneous symmetry breaking. The new results obtained by the ATLAS and CMS Collaborations at the LHC show that all measured cross-sections agree within uncertainties with the predictions of the theory. However, the standard model has obvious difficulties (nonzero neutrino masses, hierarchy problem, existence of dark matter, non-existence of antimatter galaxies, etc.), which point towards more possible violated symmetries. We first summarize the present status of the studies of the Higgs boson, including the latest results at 13 TeV p-p collision energy, then enlist some of the problems with possible solutions and the experimental situation regarding them. Full article

(This article belongs to the Special Issue The Zimányi School and Analytic Hydrodynamics in High Energy Physics)

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