The data on transverse momentum integrated hadron yields in different multiplicity classes of <math><mrow><mi>p</mi><mo>+</mo><mi>p</mi></mrow></math> collisions at <math><mrow><msqrt><mi>s</mi></msqrt><mo>=</mo><mn>7</mn></mrow></math> TeV have been analyzed to extract the chemical freeze-out parameters using a thermal model. The chemical freeze-out parameters have been extracted for three different freeze-out schemes: (i) unified freeze-out for all hadrons in complete thermal equilibrium (1CFO), (ii) unified freeze-out for all hadrons with an additional parameter <math><msub><mi>γ</mi><mi>S</mi></msub></math> which accounts for possible out-of-equilibrium production of strange hadrons (<math><mrow><mn>1</mn><mi>CFO</mi><mo>+</mo><msub><mi>γ</mi><mi>S</mi></msub></mrow></math>), and (iii) separate freeze-out for hadrons with and without strangeness content (2CFO). It has been observed that the <math><mrow><mn>1</mn><mi>CFO</mi><mo>+</mo><msub><mi>γ</mi><mi>S</mi></msub></mrow></math> scheme gives the best description of the hadronic yields at midrapidity when multiplicity (<math><mrow><mo>〈</mo><mi>d</mi><msub><mi>N</mi><mrow><mi>c</mi><mi>h</mi></mrow></msub><mo>/</mo><mi>d</mi><mi>η</mi><mo>〉</mo></mrow></math>) of the collision is less than 10. This indicates that the strangeness is out of equilibrium in most of the multiplicity classes of <math><mrow><mi>p</mi><mo>+</mo><mi>p</mi></mrow></math> collisions. All three parameters of this CFO scheme, temperature <math><mi>T</mi></math>, radius <math><mi>R</mi></math> of the fireball, and strangeness suppression factor <math><msub><mi>γ</mi><mi>S</mi></msub></math> increase with the increase of <math><mrow><mo>〈</mo><mi>d</mi><msub><mi>N</mi><mrow><mi>c</mi><mi>h</mi></mrow></msub><mo>/</mo><mi>d</mi><mi>η</mi><mo>〉</mo></mrow></math>. Furthermore, we have compared applicability of different CFO schemes considering two more colliding systems <math><mrow><mi>p</mi><mo>+</mo><mtext>Pb</mtext></mrow></math> at <math><mrow><msqrt><msub><mi>s</mi><mi>NN</mi></msub></msqrt><mo>=</mo><mn>5.02</mn></mrow></math> and <math><mrow><mtext>Pb</mtext><mo>+</mo><mtext>Pb</mtext></mrow></math> at <math><mrow><msqrt><msub><mi>s</mi><mi>NN</mi></msub></msqrt><mo>=</mo><mn>2.76</mn></mrow></math> TeV along with <math><mrow><mi>p</mi><mo>+</mo><mi>p</mi></mrow></math> collisions at <math><mrow><msqrt><mi>s</mi></msqrt><mo>=</mo><mn>7</mn></mrow></math> TeV. We observe a freeze-out volume (or multiplicity) dependence of CFO schemes regardless of colliding ions. The <math><mrow><mn>1</mn><mtext>CFO</mtext><mo>+</mo><msub><mi>γ</mi><mi>S</mi></msub></mrow></math>, 1CFO, and 2CFO schemes provide the best description of the data when the dimensionless quantity <math><mrow><mi>V</mi><msup><mi>T</mi><mn>3</mn></msup></mrow></math> approximately satisfies the conditions <math><mrow><mi>V</mi><msup><mi>T</mi><mn>3</mn></msup><mo>&lt;</mo><mn>50</mn></mrow><mo>,</mo><mo> </mo><mrow><mn>50</mn><mo>&lt;</mo><mi>V</mi><msup><mi>T</mi><mn>3</mn></msup><mo>&lt;</mo><mn>100</mn></mrow></math>, and <math><mrow><mi>V</mi><msup><mi>T</mi><mn>3</mn></msup><mo>&gt;</mo><mn>100</mn></mrow></math>, respectively, or the corresponding multiplicity satisfies the conditions <math><mrow><mo>〈</mo><mi>d</mi><msub><mi>N</mi><mrow><mi>c</mi><mi>h</mi></mrow></msub><mo>/</mo><mi>d</mi><mi>η</mi><mo>〉</mo><mo>&lt;</mo><mn>30</mn></mrow><mo>,</mo><mo> </mo><mrow><mn>30</mn><mo>&lt;</mo><mi>d</mi><msub><mi>N</mi><mrow><mi>c</mi><mi>h</mi></mrow></msub><mo>/</mo><mi>d</mi><mi>η</mi><mo>&lt;</mo><mn>60</mn></mrow></math>, and <math><mrow><mo>〈</mo><mi>d</mi><msub><mi>N</mi><mrow><mi>c</mi><mi>h</mi></mrow></msub><mo>/</mo><mi>d</mi><mi>η</mi><mo>〉</mo><mo>&gt;</mo><mn>100</mn></mrow></math>, respectively.

India

Susil Kumar Panda

Sandeep Chatterjee

Ajay Kumar Dash

Bedangadas Mohanty

Rita Paikaray

Poland

Subhasis Samanta

Ranbir Singh

Multiplicity dependence of freezeout scenarios in <math><mrow><mi>p</mi><mi>p</mi></mrow></math> collisions at <math><mrow><msqrt><mi>s</mi></msqrt><mo>=</mo><mn>7</mn></mrow></math> TeV

Rapidity-odd directed flow in heavy ion collisions can originate from two very distinct sources in the collision dynamics i. an initial tilt of the fireball in the reaction plane that generates directed flow of the constituents independent of their charges, and ii. the Lorentz force due to the strong primordial electromagnetic field that drives the flow in opposite directions for constituents carrying unlike sign charges. We study the directed flow of open charm mesons <math><msup><mrow><mi>D</mi></mrow><mrow><mn>0</mn></mrow></msup></math> and <math><mover><mrow><msup><mrow><mi>D</mi></mrow><mrow><mn>0</mn></mrow></msup></mrow><mo>‾</mo></mover></math> in the presence of both these sources of directed flow. The drag from the tilted matter dominates over the Lorentz force resulting in same sign flow for both <math><msup><mrow><mi>D</mi></mrow><mrow><mn>0</mn></mrow></msup></math> and <math><mover><mrow><msup><mrow><mi>D</mi></mrow><mrow><mn>0</mn></mrow></msup></mrow><mo>‾</mo></mover></math>, albeit of different magnitudes. Their average directed flow is about ten times larger than their difference. This charge splitting in the directed flow is a sensitive probe of the electrical conductivity of the produced medium. We further study their beam energy dependence; while the average directed flow shows a decreasing trend, the charge splitting remains flat from <math><msqrt><mrow><msub><mrow><mi>s</mi></mrow><mrow><mi>N</mi><mi>N</mi></mrow></msub></mrow></msqrt><mo>=</mo><mn>60</mn></math> GeV to 5 TeV.

Piotr Bożek

Interplay of drag by hot matter and electromagnetic force on the directed flow of heavy quarks

The data on hadron transverse momentum spectra in different centrality classes of p + Pb collisions at <math><mrow><msqrt><msub><mi>s</mi><mi>NN</mi></msub></msqrt><mo>=</mo><mn>5.02</mn></mrow></math> TeV have been analyzed to extract the freeze-out hypersurface within a simultaneous chemical and kinetic freeze-out scenario. The freeze-out hypersurface has been extracted for three freeze-out schemes that differ in the way strangeness is treated: (i) unified freeze-out for all hadrons at complete thermal equilibrium (1FO), (ii) unified freeze-out for all hadrons with an additional parameter <math><msub><mi>γ</mi><mi>S</mi></msub></math> which accounts for possible out-of-equilibrium production of strangeness (<math><mrow><mn>1</mn><mi>FO</mi><mo>+</mo><msub><mi>γ</mi><mi>S</mi></msub></mrow></math>), and (iii) separate freeze-out for hadrons with and without strangeness content (2FO). Unlike in heavy-ion collisions where 2FO performs best in describing the mean hadron yields as well as the transverse momentum spectra, with p + Pb we find that <math><mrow><mn>1</mn><mi>FO</mi><mo>+</mo><msub><mi>γ</mi><mi>S</mi></msub></mrow></math> with one fewer parameter than 2FO performs better. This confirms expectations based on previous analysis of system size dependence in the freeze-out scheme with mean hadron yields: while heavy-ion collisions that are dominated by constituent interactions prefer 2FO, smaller collision systems like proton + nucleus and proton + proton collisions with lesser constituent interaction prefer a unified freeze-out scheme with varying degrees of strangeness equilibration.

Chitrasen Jena

Role of system size in freeze-out conditions extracted from transverse momentum spectra of hadrons

We present the first estimates of isothermal compressibility (<math><msub><mrow><mi>k</mi></mrow><mrow><mi>T</mi></mrow></msub></math>) of hadronic matter formed in relativistic nuclear collisions (<math><msqrt><mrow><msub><mrow><mi>s</mi></mrow><mrow><mi>NN</mi></mrow></msub></mrow></msqrt><mo>=</mo><mn>7.7</mn><mtext> GeV</mtext></math> to 2.76 TeV) using experimentally observed quantities. <math><msub><mrow><mi>k</mi></mrow><mrow><mi>T</mi></mrow></msub></math> is related to the fluctuation in particle multiplicity, temperature, and volume of the system formed in the collisions. Multiplicity fluctuations are obtained from the event-by-event distributions of charged particle multiplicities in narrow centrality bins. The dynamical components of the fluctuations are extracted by removing the contributions to the fluctuations from the number of participating nucleons. From the available experimental data, a constant value of <math><msub><mrow><mi>k</mi></mrow><mrow><mi>T</mi></mrow></msub></math> has been observed as a function of collision energy. The results are compared with calculations from UrQMD, AMPT, and EPOS event generators, and estimations of <math><msub><mrow><mi>k</mi></mrow><mrow><mi>T</mi></mrow></msub></math> are made for Pb–Pb collisions at the CERN Large Hadron Collider. A hadron resonance gas (HRG) model has been used to calculate <math><msub><mrow><mi>k</mi></mrow><mrow><mi>T</mi></mrow></msub></math> as a function of collision energy. Our results show a decrease in <math><msub><mrow><mi>k</mi></mrow><mrow><mi>T</mi></mrow></msub></math> at low collision energies to <math><msqrt><mrow><msub><mrow><mi>s</mi></mrow><mrow><mi>NN</mi></mrow></msub></mrow></msqrt><mo>∼</mo><mn>20</mn><mtext> GeV</mtext></math>, beyond which the <math><msub><mrow><mi>k</mi></mrow><mrow><mi>T</mi></mrow></msub></math> values remain almost constant.

Maitreyee Mukherjee

United States

Sumit Basu

Arghya Chatterjee

Souvik Priyam Adhya

Sanchari Thakur

CERN

Tapan K. Nayak

Isothermal compressibility of hadronic matter formed in relativistic nuclear collisions

Md. Nasim

China

Shusu Shi

Subhash Singha

Victor Roy

Collectivity in High Energy Heavy-Ion Collisions

The two component Monte-Carlo Glauber model predicts a knee-like structure in the centrality dependence of elliptic flow v2 in Uranium + Uranium collisions at sNN=193Â GeV . It also produces a strong anti-correlation between v2 and dNch/dy in the case of top ZDC events. However, none of these features have been observed in data. We address these discrepancies by including the effect of nucleon shadowing to the two component Monte-Carlo Glauber model. Apart from addressing successfully the above issues, we find that the nucleon shadow suppresses the event by event fluctuation of various quantities, e.g. Îµ2 which is in accordance with expectation from the dynamical models of initial condition based on gluon saturation physics.

Sushant K. Singh

Snigdha Ghosh

Md Hasanujjaman

Jane Alam

Sourav Sarkar

Initial condition from the shadowed Glauber model

There is event by event geometric as well as quantum fluctuations in the initial condition of heavy-ion collisions. The standard technique of analysing heavy-ion collisions in bins of centrality obtained from final state multiplicity averages out the various initial configurations and thus restricts the study to only a limited range of initial conditions. In this paper, we propose an additional binning in terms of total spectator neutrons in an event. This offers us a key control parameter to probe events with broader range of initial conditions providing us an opportunity to peep into events with rarer initial conditions which otherwise get masked when analysed by centrality binning alone. We find that the inclusion of spectator binning allows one to vary ε2 and ε3 independently. We observe that the standard scaling relation between v2/ε2 and 1SdNchdη exhibited by centrality bins is strongly broken by the spectator neutron bins. Further, the acoustic scaling relation between ln⁡(vn/εn) and transverse system size is also broken- the strength of the breaking being sensitive to the binning procedure. The introduction of the spectator binning allows us to tune over a wide range viscosity driven effects for events with varying initial states but similar final state multiplicity.

Vipul Bairathi

Md. Rihan Haque

Probing Pb + Pb collisions at SNN=2760Â GeV with spectators

We review the chemical and kinetic freeze-out conditions in high energy heavy-ion collisions for AGS, SPS, RHIC, and LHC energies. Chemical freeze-out parameters are obtained using produced particle yields in central collisions while the corresponding kinetic freeze-out parameters are obtained using transverse momentum distributions of produced particles. For chemical freeze-out, different freeze-out scenarios are discussed such as single and double/flavor dependent freeze-out surfaces. Kinetic freeze-out parameters are obtained by doing hydrodynamic inspired blast wave fit to the transverse momentum distributions. The beam energy and centrality dependence of transverse energy per charged particle multiplicity are studied to address the constant energy per particle freeze-out criteria in heavy-ion collisions.

Sabita Das

Lokesh Kumar

D. Mishra

Raghunath Sahoo

Natasha Sharma

Freeze-Out Parameters in Heavy-Ion Collisions at AGS, SPS, RHIC, and LHC Energies