Due to their weak coupling to the strongly interacting matter produced in relativistic heavy-ion collisions, dileptons serve as a sensitive probe of the initial geometry of the colliding nuclei. In this study, we investigate the influence of initial nuclear quadrupole deformation, characterized by the parameter <italic>&#946;</italic> <inf>2</inf>, on dilepton production in <math altimg='si5.svg'><mrow><mtext>U</mtext><mo linebreak='goodbreak'>+</mo><mtext>U</mtext></mrow></math> collisions at <math altimg='si2.svg'><mrow><msqrt><msub><mi>s</mi><mrow><mi>N</mi><mi>N</mi></mrow></msub></msqrt><mo linebreak='goodbreak'>=</mo><mn>193</mn></mrow></math> GeV. The analysis is carried out using a modified multiphase transport model in which partonic interactions are described by the Nambu-Jona-Lasinio model. We observe a clear linear dependence of dilepton yields on <math altimg='si6.svg'><msubsup><mi>&#946;</mi><mn>2</mn><mn>2</mn></msubsup></math> in both the low-mass region (LMR, &#8239;&lt;&#8239;1&#8201;GeV/ <italic>c</italic> 2) and intermediate-mass region (IMR, <math altimg='si7.svg'><mrow><mn>1</mn><mo linebreak='goodbreak'>&#8722;</mo><mn>3</mn><mspace width='0.16em' /><mtext>GeV</mtext><mspace width='-0.16em' /><mo linebreak='goodbreak'>/</mo><msup><mi>c</mi><mn>2</mn></msup></mrow></math>) of the dilepton spectrum for the most central collisions. Also, dilepton production in the IMR region exhibits a stronger sensitivity to nuclear deformation than in the LMR, reflecting the dominance of earlier partonic processes in this mass range. These results suggest that precise measurements of dilepton yields in relativistic heavy-ion collisions can provide a complementary probe of the nuclear deformation parameter <italic>&#946;</italic> <inf>2</inf> of 238U, offering additional insights when combined with constraints from low-energy experiments and flow-related probes in high-energy experiments.

China

Wen-Hao Zhou

Lu-Meng Liu

United States

Che Ming Ko

Kai-Jia Sun

Jun Xu

Investigating 238U deformation via dilepton production in relativistic heavy-ion collisions

Jet-associated deuteron production in pp collisions at <math><msqrt><mrow><mi>s</mi></mrow></msqrt><mo>=</mo><mn>13</mn></math> TeV and p-Pb collisions at <math><msqrt><mrow><msub><mrow><mi>s</mi></mrow><mrow><mi>N</mi><mi>N</mi></mrow></msub></mrow></msqrt><mo>=</mo><mn>5.02</mn></math> TeV is studied in the coalescence model by using the phase-space information of proton and neutron pairs from a multiphase transport (AMPT) model at the kinetic freezeout. In the low transverse momentum (<math><msub><mrow><mi>p</mi></mrow><mrow><mi>T</mi></mrow></msub></math>) region <math><msub><mrow><mi>p</mi></mrow><mrow><mi>T</mi></mrow></msub><mo>/</mo><mi>A</mi><mo>&lt;</mo><mn>1.5</mn></math> GeV/c, where A is the mass number of a nucleus, the in-jet coalescence factor <math><msubsup><mrow><mi>B</mi></mrow><mrow><mn>2</mn></mrow><mrow><mtext>In-jet</mtext></mrow></msubsup></math> for deuteron production, given by the ratio of the in-jet deuteron number to the square of the in-jet proton number, is found to be larger than the coalescence factor <math><msub><mrow><mi>B</mi></mrow><mrow><mn>2</mn></mrow></msub></math> in the medium perpendicular to the jet by a factor of about 10 in pp collisions and of 25 in p−Pb collisions, which are consistent with the ALICE measurements at the LHC. Such large low-momentum enhancements mainly come from coalescence of nucleons inside the jet with the medium nucleons. Coalescence of nucleons inside the jet dominates deuteron production only at the higher <math><msub><mrow><mi>p</mi></mrow><mrow><mi>T</mi></mrow></msub></math> region of <math><msub><mrow><mi>p</mi></mrow><mrow><mi>T</mi></mrow></msub><mo>/</mo><mi>A</mi><mo>≳</mo><mn>4</mn></math> GeV/c, where both the yield ratio <math><mi>d</mi><mo>/</mo><mi>p</mi></math> of deuteron to proton numbers and the <math><msub><mrow><mi>B</mi></mrow><mrow><mn>2</mn></mrow></msub></math> are also significantly larger in the jet direction than in the direction perpendicular to the jet due to the strong collinear correlation among particles produced from jet fragmentation. Studying jet-associated deuteron production in relativistic nuclear collisions thus opens up a new window to probe the phase-space structure of nucleons inside jets.

Yi-Heng Feng

Yu-Gang Ma

Xin-Nian Wang

Zhong Yang

Song Zhang

Jet-induced enhancement of deuteron production in And -Pb collisions at the LHC

The Λ hyperon spin flip and non-flip cross sections are calculated in a simple hadronic model by including both the s-channel process involving the spin 3/2, positive parity <math><msup><mrow><mi>Σ</mi></mrow><mrow><mo>⁎</mo></mrow></msup><mo>(</mo><mn>1358</mn><mo>)</mo></math> resonance and the t-channel process via the exchange of a scalar σ meson. Because of its large mass, the Λ spin flip to non-flip cross sections is negligibly small in the t-channel process compared to the constant value of 1/3.5 in the s-channel process. With the s-channel <math><mi>Λ</mi><mo>−</mo><mi>π</mi></math> spin-dependent cross sections included in a schematic kinetic model, the effects of hadronic scatterings on the Λ spin polarization in Au-Au collisions at <math><msqrt><mrow><msub><mrow><mi>s</mi></mrow><mrow><mi>N</mi><mi>N</mi></mrow></msub></mrow></msqrt><mo>=</mo><mn>7.7</mn></math> GeV are studied. It is found that the Λ spin polarization only decreases by 7-12% during the hadronic stage of these collisions, which justifies the assumption in theoretical studies that compare the Λ polarization calculated at the chemical freezeout to the measured one at the kinetic freezeout.

South Korea

Haesom Sung

Su Houng Lee

Hadronic scattering effects on Λ polarization in relativistic heavy ion collisions

Understanding the properties of hypernuclei helps to constrain the interaction between hyperon and nucleon, which is known to play an essential role in determining the properties of neutron stars. Experimental measurements have suggested that the hypertriton (<math><mmultiscripts><mrow><mtext>H</mtext></mrow><mprescripts></mprescripts><mrow><mi>Λ</mi></mrow><mrow><mn>3</mn></mrow></mmultiscripts></math>), the lightest hypernucleus, exhibits a halo structure with a deuteron core encircled by a Λ hyperon at a distance of about 10 fm. This large <math><mi>Λ</mi><mo>−</mo><mi>d</mi></math> distance in <math><mmultiscripts><mrow><mtext>H</mtext></mrow><mprescripts></mprescripts><mrow><mi>Λ</mi></mrow><mrow><mn>3</mn></mrow></mmultiscripts></math> wave function is found to cause a suppressed <math><mmultiscripts><mrow><mtext>H</mtext></mrow><mprescripts></mprescripts><mrow><mi>Λ</mi></mrow><mrow><mn>3</mn></mrow></mmultiscripts></math> yield and a softening of its transverse momentum (<math><msub><mrow><mi>p</mi></mrow><mrow><mi>T</mi></mrow></msub></math>) spectrum in relativistic heavy-ion collisions. Within the coalescence model based on nucleons and Λ hyperons from a microscopic hybrid hydro model with a hadronic afterburner for nuclear cluster production in Pb-Pb collisions at <math><msqrt><mrow><msub><mrow><mi>s</mi></mrow><mrow><mi>N</mi><mi>N</mi></mrow></msub></mrow></msqrt></math>= 5.02 TeV, we show how this softening of the hypertriton <math><msub><mrow><mi>p</mi></mrow><mrow><mi>T</mi></mrow></msub></math> spectrum appears and leads to a smaller mean <math><msub><mrow><mi>p</mi></mrow><mrow><mi>T</mi></mrow></msub></math> for <math><mmultiscripts><mrow><mtext>H</mtext></mrow><mprescripts></mprescripts><mrow><mi>Λ</mi></mrow><mrow><mn>3</mn></mrow></mmultiscripts></math> than for helium-3 ($^{3}$He). The latter is opposite to the predictions from the blast-wave model which assumes that <math><mmultiscripts><mrow><mtext>H</mtext></mrow><mprescripts></mprescripts><mrow><mi>Λ</mi></mrow><mrow><mn>3</mn></mrow></mmultiscripts></math> and $^{3}$He are thermally produced at the kinetic freeze-out of heavy-ion collisions. The discovered quantum mechanical softening of the (anti-)hypertriton spectrum can be experimentally tested in relativistic heavy-ion collisions at different collision energies and centralities and used to obtain valuable insights to the mechanisms for light (hyper-)nuclei production in these collisions.

Dai-Neng Liu

Italy

Francesco Mazzaschi

CERN

Maximiliano Puccio

Qi-Ye Shou

Yuan-Zhe Wang

Softening of the hypertriton transverse momentum spectrum in heavy-ion collisions

Using the nucleon coalescence model based on kinetic freeze-out nucleons from the hybrid model of MUSIC hydrodynamics and UrQMD hadronic transport model, we study the production of antideuteron and its event-by-event fluctuation in Pb+Pb collisions at <math><msqrt><mrow><msub><mrow><mi>s</mi></mrow><mrow><mi>N</mi><mi>N</mi></mrow></msub></mrow></msqrt><mo>=</mo><mn>5.02</mn></math> TeV. We find a clear suppression of the antideuteron to antiproton yield ratio in peripheral collisions, which is in accordance with the measurements from the ALICE Collaboration. Also found is a Poissonian event-by-event fluctuation of the antideuteron multiplicity in all collision centralities, which is different from the prediction of a simple coalescence model calculation which assumes that all antiproton and antineutron pairs have the same probability to form an antideuteron. However, due to the lack of baryon number conservation at the particlization when the viscous fluid in the hydrodynamic stage of MUSIC is converted to a hadronic matter, our model fails to describe the net-proton number fluctuation and the negative correlation between the antiproton and antideuteron multiplicities at large pseudorapidity acceptance observed in ALICE experiments. Both can nevertheless be well reproduced after selecting a suitable subset of events to fit the measured net-proton number fluctuation.

Event-by-event antideuteron multiplicity fluctuation in Pb+Pb collisions at TeV

Using the isospin-dependent relativistic Vlasov-Uehling-Uhlenbeck (RVUU) model, we study charged pion (<math><msup><mrow><mi>π</mi></mrow><mrow><mo>±</mo></mrow></msup></math>) production in Au+Au collisions at <math><msqrt><mrow><msub><mrow><mi>s</mi></mrow><mrow><mi>N</mi><mi>N</mi></mrow></msub></mrow></msqrt><mo>=</mo></math> 2.4 GeV. By fitting the density dependence of the Δ resonance production cross section in nuclear medium to reproduce the experimental <math><msup><mrow><mi>π</mi></mrow><mrow><mo>±</mo></mrow></msup></math> multiplicities measured by the HADES Collaboration, we obtain a good description of the rapidity distributions and transverse momentum spectra of <math><msup><mrow><mi>π</mi></mrow><mrow><mo>±</mo></mrow></msup></math> in collisions at various centralities. Some shortcomings in the description of <math><msup><mrow><mi>π</mi></mrow><mrow><mo>±</mo></mrow></msup></math> production may indicate the need for including the strong potential on <math><msup><mrow><mi>π</mi></mrow><mrow><mo>±</mo></mrow></msup></math> in RVUU, which is at present absent. We also calculate the proton rapidity distribution in the most central collisions and compare with the coalescence invariant proton rapidity distribution extracted from preliminary HADES data.

Kyle Godbey

Zhen Zhang

Jeremy W. Holt

Charged pion production from Au + Au collisions at GeV in the relativistic Vlasov-Uehling-Uhlenbeck model

Using the nucleon coalescence model, which can naturally take into account the correlations in the nucleon density distribution, we study the effects of QCD critical point on light nuclei production in relativistic heavy-ion collisions. We find that the yield ratio <math><msub><mrow><mi>N</mi></mrow><mrow><mtext>t</mtext></mrow></msub><msub><mrow><mi>N</mi></mrow><mrow><mtext>p</mtext></mrow></msub><mo>/</mo><msubsup><mrow><mi>N</mi></mrow><mrow><mtext>d</mtext></mrow><mrow><mn>2</mn></mrow></msubsup></math> of proton (p), deuteron (d) and triton (t) increases monotonically with the nucleon density correlation length, which is expected to increase significantly near the critical point in the QCD phase diagram. Our study thus demonstrates that the yield ratio <math><msub><mrow><mi>N</mi></mrow><mrow><mtext>t</mtext></mrow></msub><msub><mrow><mi>N</mi></mrow><mrow><mtext>p</mtext></mrow></msub><mo>/</mo><msubsup><mrow><mi>N</mi></mrow><mrow><mtext>d</mtext></mrow><mrow><mn>2</mn></mrow></msubsup></math> can be used as a sensitive probe of the QCD critical phenomenon. We further discuss the relation between the QCD phase transitions in heavy-ion collisions and the possible non-monotonic behavior of <math><msub><mrow><mi>N</mi></mrow><mrow><mtext>t</mtext></mrow></msub><msub><mrow><mi>N</mi></mrow><mrow><mtext>p</mtext></mrow></msub><mo>/</mo><msubsup><mrow><mi>N</mi></mrow><mrow><mtext>d</mtext></mrow><mrow><mn>2</mn></mrow></msubsup></math> in its collision energy dependence.

Feng Li

Effects of QCD critical point on light nuclei production

Using the nucleon coalescence model based on kinetic freeze-out nucleons from the 3D MUSIC+UrQMD and the 2D VISHNU hybrid model with a crossover equation of state, we study the multiplicity dependence of deuteron (d) and triton (t) production from central to peripheral Au+Au collisions at <math><msqrt><mrow><msub><mrow><mi>s</mi></mrow><mrow><mi>NN</mi></mrow></msub></mrow></msqrt><mo>=</mo></math> 7.7, 14.5, 19.6, 27, 39, 62.4 and 200 GeV and Pb+Pb at <math><msqrt><mrow><msub><mrow><mi>s</mi></mrow><mrow><mi>NN</mi></mrow></msub></mrow></msqrt><mo>=</mo><mn>2.76</mn></math> TeV, respectively. It is found that the ratio <math><msub><mrow><mi>N</mi></mrow><mrow><mi>t</mi></mrow></msub><msub><mrow><mi>N</mi></mrow><mrow><mi>p</mi></mrow></msub><mo>/</mo><msubsup><mrow><mi>N</mi></mrow><mrow><mi>d</mi></mrow><mrow><mn>2</mn></mrow></msubsup></math> of the proton yield <math><msub><mrow><mi>N</mi></mrow><mrow><mi>p</mi></mrow></msub></math>, deuteron yield <math><msub><mrow><mi>N</mi></mrow><mrow><mi>d</mi></mrow></msub></math> and triton yield <math><msub><mrow><mi>N</mi></mrow><mrow><mi>t</mi></mrow></msub></math> exhibits a scaling behavior in its multiplicity dependence, i.e., decreasing monotonically with increasing charged-particle multiplicity. A similar multiplicity scaling of this ratio is also found in the nucleon coalescence calculation based on kinetic freeze-out nucleons from a multiphase transport (AMPT) model. The scaling behavior of <math><msub><mrow><mi>N</mi></mrow><mrow><mi>t</mi></mrow></msub><msub><mrow><mi>N</mi></mrow><mrow><mi>p</mi></mrow></msub><mo>/</mo><msubsup><mrow><mi>N</mi></mrow><mrow><mi>d</mi></mrow><mrow><mn>2</mn></mrow></msubsup></math> can be naturally explained by the interplay between the sizes of light nuclei and the nucleon emission source. We further argue that the multiplicity scaling of <math><msub><mrow><mi>N</mi></mrow><mrow><mi>t</mi></mrow></msub><msub><mrow><mi>N</mi></mrow><mrow><mi>p</mi></mrow></msub><mo>/</mo><msubsup><mrow><mi>N</mi></mrow><mrow><mi>d</mi></mrow><mrow><mn>2</mn></mrow></msubsup></math> can be used to validate the production mechanism of light nuclei, and the collision energy dependence of this yield ratio can further serve as a baseline in the search for the QCD critical point in relativistic heavy-ion collisions.

Wenbin Zhao

Kai-jia Sun

Xiaofeng Luo

Multiplicity scaling of light nuclei production in relativistic heavy-ion collisions

In the past two decades, pions created in the high density regions of heavy ion collisions have been predicted to be sensitive at high densities to the symmetry energy term in the nuclear equation of state, a property that is key to our understanding of neutron stars. In a new experiment designed to study the symmetry energy, the multiplicities of negatively and positively charged pions have been measured with high accuracy for central $^{132}$Sn+$^{124}$Sn, $^{112}$Sn+$^{124}$Sn, and $^{108}$Sn+$^{112}$Sn collisions at <math><mi>E</mi><mo>/</mo><mi>A</mi><mo>=</mo><mn>270</mn><mtext> MeV</mtext></math> with the SπRIT Time Projection Chamber. While individual pion multiplicities are measured to 4% accuracy, those of the charged pion multiplicity ratios are measured to 2% accuracy. We compare these data to predictions from seven major transport models. The calculations reproduce qualitatively the dependence of the multiplicities and their ratios on the total neutron and proton number in the colliding systems. However, the predictions of the transport models from different codes differ too much to allow extraction of reliable constraints on the symmetry energy from the data. This finding may explain previous contradictory conclusions on symmetry energy constraints obtained from pion data in Au+Au system. These new results call for still better understanding of the differences among transport codes, and new observables that are more sensitive to the density dependence of the symmetry energy.

G. Jhang

J. Estee

J. Barney

G. Cerizza

Japan

M. Kaneko

J.W. Lee

W.G. Lynch

T. Isobe

M. Kurata-Nishimura

T. Murakami

C.Y. Tsang

M.B. Tsang

R. Wang

D.S. Ahn

Germany

L. Atar

T. Aumann

H. Baba

K. Boretzky

Poland

J. Brzychczyk

N. Chiga

N. Fukuda

Croatia

I. Gasparic

B. Hong

A. Horvat

K. Ieki

N. Inabe

Y.J. Kim

T. Kobayashi

Y. Kondo

P. Lasko

H.S. Lee

Y. Leifels

J. Łukasik

J. Manfredi

A.B. McIntosh

P. Morfouace

T. Nakamura

N. Nakatsuka

S. Nishimura

R. Olsen

H. Otsu

P. Pawłowski

K. Pelczar

D. Rossi

H. Sakurai

C. Santamaria

H. Sato

H. Scheit

R. Shane

Y. Shimizu

H. Simon

Netherlands

A. Snoch

A. Sochocka

Z. Sosin

T. Sumikama

H. Suzuki

D. Suzuki

H. Takeda

S. Tangwancharoen

H. Toernqvist

Y. Togano

Z.G. Xiao

S.J. Yennello

J. Yurkon

Y. Zhang

Maria Colonna

Romania

Dan Cozma

Paweł Danielewicz

Hannah Elfner

Natsumi Ikeno

Justin Mohs

Dmytro Oliinychenko

Akira Ono

Jun Su

Yong Jia Wang

Hermann Wolter

Ying-Xun Zhang

Symmetry energy investigation with pion production from Sn+Sn systems

We develop for charmed hadron production in relativistic heavy-ion collisions a comprehensive coalescence model that includes an extensive set of s and p-wave hadronic states as well as the strict energy-momentum conservation, which ensures the boost invariance of the coalescence probability and the thermal limit of the produced hadron spectrum. By combining our hadronization scheme with an advanced Langevin-hydrodynamics model that incorporates both elastic and inelastic energy loss of heavy quarks inside the dynamical quark-gluon plasma, we obtain a successful description of the <math><msub><mrow><mi>p</mi></mrow><mrow><mi>T</mi></mrow></msub></math>-integrated and differential <math><msub><mrow><mi>Λ</mi></mrow><mrow><mi>c</mi></mrow></msub><mo>/</mo><msup><mrow><mi>D</mi></mrow><mrow><mn>0</mn></mrow></msup></math> and <math><msub><mrow><mi>D</mi></mrow><mrow><mi>s</mi></mrow></msub><mo>/</mo><msup><mrow><mi>D</mi></mrow><mrow><mn>0</mn></mrow></msup></math> ratios measured at RHIC and the LHC. We find that including the effect of radial flow of the medium is essential for describing the enhanced <math><msub><mrow><mi>Λ</mi></mrow><mrow><mi>c</mi></mrow></msub><mo>/</mo><msup><mrow><mi>D</mi></mrow><mrow><mn>0</mn></mrow></msup></math> ratio observed in relativistic heavy-ion collisions. We also find that the puzzling larger <math><msub><mrow><mi>Λ</mi></mrow><mrow><mi>c</mi></mrow></msub><mo>/</mo><msup><mrow><mi>D</mi></mrow><mrow><mn>0</mn></mrow></msup></math> ratio observed in Au+Au collisions at RHIC than in Pb+Pb collisions at the LHC is due to the interplay between the effects of the QGP radial flow and the charm quark transverse momentum spectrum at hadronization. Our study further suggests that charmed hadrons have larger sizes in medium than in vacuum.