A precision measurement of the <italic>K</italic> &#8270;0 meson yield is reported in Au+Au collisions at <math altimg='si5.svg'><mrow><msqrt><msub><mi>s</mi><mrow><mi>N</mi><mi>N</mi></mrow></msub></msqrt><mo linebreak='goodbreak'>=</mo><mn>7.7</mn><mo>,</mo><mspace width='0.28em' /><mn>11.5</mn><mo>,</mo><mspace width='0.28em' /><mn>14.6</mn><mo>,</mo><mspace width='0.28em' /><mn>19.6</mn><mo>,</mo></mrow></math> and 27&#8201;GeV using the high-statistics data sample collected by the STAR experiment during the Beam Energy Scan II (BES-II) program at RHIC. The transeverse momentum ( <italic>p<inf>T</inf></italic>)-integrated yield ratios <math altimg='si6.svg'><mrow><mrow><mo>(</mo><msup><mi>K</mi><mrow><mo>*</mo><mn>0</mn></mrow></msup><mo linebreak='badbreak'>+</mo><mover><mrow><msup><mi>K</mi><mrow><mo>*</mo><mn>0</mn></mrow></msup></mrow><mo stretchy='true'>&#8254;</mo></mover><mo>)</mo></mrow><mo linebreak='goodbreak'>/</mo><mrow><mo>(</mo><msup><mi>K</mi><mo>+</mo></msup><mo linebreak='badbreak'>+</mo><msup><mi>K</mi><mo>&#8722;</mo></msup><mo>)</mo></mrow></mrow></math> in central collisions show a suppression relative to peripheral collisions at the (1.7&#8211;3.6)&#8201; <italic>&#963;</italic> level, while a thermal model without final-stage rescattering overpredicts this ratio with a deviation of (6.9&#8211;8.2)&#8201; <italic>&#963;</italic>. These results indicate a loss of the measured <italic>K</italic> &#8270;0 signal in central collisions due to re-scattering of its hadronic decay products in the hadronic phase. The <italic>p<inf>T</inf></italic>-integrated yield of charged kaons exhibits an approximate scaling with charged-particle multiplicity, independent of collision energy and system size. A similar trend is observed for the short-lived <italic>K</italic> &#8270;0 resonance, although significant deviations emerge at lower energies. At BES energies, the <italic>K</italic> &#8270;0/ <italic>K</italic> ratio shows stronger suppression than at the highest RHIC and LHC energies within a given multiplicity bin, particularly in central and mid-central collisions. This behavior is consistent with changes in the effective hadronic interaction cross section and is supported by transport model calculations, which indicate dominant meson&#8211;baryon interactions at lower energies and meson&#8211;meson interactions at higher energies.

B.E. Aboona

Czechia

J. Adam

JINR

G. Agakishiev

India

I. Aggarwal

M.M. Aggarwal

Z. Ahammed

A. Aitbayev

I. Alekseev

E. Alpatov

A.K. Alshammri

A. Aparin

S. Aslam

J. Atchison

G.S. Averichev

Chile

V. Bairathi

X. Bao

P. Barik

K. Barish

S. Behera

P. Bhagat

A. Bhasin

S. Bhatta

I.G. Bordyuzhin

J.D. Brandenburg

A.V. Brandin

C. Broodo

X.Z. Cai

H. Caines

M. Calderón de la Barca Sánchez

D. Cebra

J. Ceska

I. Chakaberia

Y.S. Chang

Z. Chang

A. Chatterjee

D. Chen

J.H. Chen

China

L. Chen

Q. Chen

W. Chen

Z. Chen

J. Cheng

Y. Cheng

W. Christie

X. Chu

S. Corey

H.J. Crawford

G. Dale-Gau

A. Das

D. De Souza Lemos

T.G. Dedovich

Germany

I.M. Deppner

A.A. Derevschikov

A. Deshpande

A. Dhamija

A. Dimri

P. Dixit

X. Dong

J.L. Drachenberg

E. Duckworth

J.C. Dunlop

Egypt

Y.S. El-Feky

J. Engelage

G. Eppley

Japan

S. Esumi

O. Evdokimov

O. Eyser

B. Fan

Y. Fang

R. Fatemi

Italy

S. Fazio

H. Feng

Y. Feng

E. Finch

Y. Fisyak

F.A. Flor

B. Fu

C. Fu

T. Fu

T. Gao

Y. Gao

G. Garcia

F. Geurts

A. Gibson

A. Giri

K. Gopal

X. Gou

D. Grosnick

A. Gu

J. Gu

A. Gupta

A. Hamed

R.J. Hamilton

J. Han

X. Han

M.D. Harasty

J.W. Harris

H. Harrison-Smith

L.B. Havener

X.H. He

Probing late-stage hadronic interactions at high baryon density via <italic>K</italic> &#8270;0 production in the RHIC beam energy scan program

The correlation between the mean transverse momentum, [ <italic>p</italic> <inf>T</inf>], and the squared anisotropic flow, <math altimg='si8.svg'><msubsup><mi>v</mi><mi>n</mi><mn>2</mn></msubsup></math>, on an event-by-event basis has been suggested to be influenced by the initial conditions in heavy-ion collisions. We present measurements of the variances and covariance of [ <italic>p</italic> <inf>T</inf>] and <math altimg='si8.svg'><msubsup><mi>v</mi><mi>n</mi><mn>2</mn></msubsup></math>, along with their dimensionless ratio, for Au+Au collisions at various beam energies: <math altimg='si9.svg'><msqrt><msub><mi mathvariant='italic'>s</mi><mrow><mi>N</mi><mi>N</mi></mrow></msub></msqrt></math> = 14.6, 19.6, 27, 54.4, and 200 GeV. Our measurements reveal a distinct energy-dependent behavior in the variances and covariances. In addition, the dimensionless ratio displays a similar behavior across different beam energies. We compare our measurements with hydrodynamic models and similar measurements from Pb+Pb collisions at the Large Hadron Collider (LHC). These findings provide valuable insights into the beam energy dependence of the specific shear viscosity ( <italic>&#951;</italic>/ <italic>s</italic>) and initial-state effects, allowing for differentiating between different initial-state models.

United States

Russia

M. Calderón De La Barca Sánchez

Beam-energy dependence of correlations between mean transverse momentum and anisotropic flow of charged particles in Au+Au collisions at RHIC

Rapidity-odd directed flow <italic>v</italic> <inf>1</inf> measurements are presented for <italic>K</italic> &#8239;&#177;&#8239; and <math altimg='si4.svg'><msubsup><mi>K</mi><mi>S</mi><mn>0</mn></msubsup></math> in Au + Au collisions for <math altimg='si5.svg'><msqrt><msub><mi>s</mi><mrow><mi>N</mi><mi>N</mi></mrow></msub></msqrt></math> from 3.0 to 3.9&#8239;GeV with the STAR experiment. For comparison, <italic>v</italic> <inf>1</inf> of <italic>&#960;</italic> &#8239;&#177;&#8239;, protons, and &#923; from the same collisions are also discussed. The mid-rapidity <italic>v</italic> <inf>1</inf> slope <math altimg='si9.svg'><mrow><mtext>d</mtext><msub><mi>v</mi><mn>1</mn></msub><msub><mrow><mo>/</mo><mtext>d</mtext><mi>y</mi><mo>|</mo></mrow><mrow><mi>y</mi><mo>=</mo><mn>0</mn></mrow></msub></mrow></math> for protons and &#923; is positive in these collisions. On the other hand, <italic>v</italic> <inf>1</inf> slope of kaons exhibits a strong <math altimg='si8.svg'><msub><mi>p</mi><mtext>T</mtext></msub></math> dependence: negative at <math altimg='si19.svg'><mrow><msub><mi>p</mi><mtext>T</mtext></msub><mo linebreak='goodbreak'>&lt;</mo></mrow></math> 0.6&#8239;GeV/ <italic>c</italic> and positive at higher <math altimg='si8.svg'><msub><mi>p</mi><mtext>T</mtext></msub></math>. A similar <math altimg='si8.svg'><msub><mi>p</mi><mtext>T</mtext></msub></math> dependence is also evident for the <italic>v</italic> <inf>1</inf> slope of charged pions. Compared to the spectator-removed calculations in Au+Au collisions at <math altimg='si20.svg'><mrow><msqrt><msub><mi>s</mi><mtext>NN</mtext></msub></msqrt><mo linebreak='goodbreak'>=</mo></mrow></math> 3.0&#8211;3.9&#8239;GeV, the JAM model demonstrates a pronounced shift of the <italic>v</italic> <inf>1</inf> slopes of mesons towards the negative direction. It suggests that the shadowing effect of the spectators plays an important role in the observed kaon anti-flow at low <math altimg='si8.svg'><msub><mi>p</mi><mtext>T</mtext></msub></math> in the high baryon density region of non-central collisions.

Measurement of kaon directed flow in Au+Au collisions in the high baryon density region

The nuclear modification factor <italic>R</italic> <inf>AA</inf> of charm jets, identified by the presence of a D 0 meson among the jet constituents, has been measured for the first time in Pb&#8211;Pb collisions at a centre-of-mass energy per nucleon pair <math altimg='si8.svg'><mrow><msqrt><msub><mi>s</mi><mtext>NN</mtext></msub></msqrt><mspace width='0.33em' /><mo linebreak='goodbreak'>=</mo><mspace width='0.33em' /><mn>5.02</mn></mrow></math> TeV with the ALICE detector at the LHC. The D 0 mesons and their charge conjugates are reconstructed from the hadronic decay D <math altimg='si9.svg'><mrow><msup><mrow /><mn>0</mn></msup><mo>&#8594;</mo><msup><mrow><mi mathvariant='normal'>K</mi></mrow><mo>&#8722;</mo></msup><msup><mi>&#960;</mi><mo>+</mo></msup></mrow></math>. Jets are reconstructed from D 0-meson candidates and charged particles using the anti- <italic>k</italic> <inf>T</inf> algorithm with jet resolution parameter <math altimg='si10.svg'><mrow><mi>R</mi><mspace width='0.33em' /><mo linebreak='goodbreak'>=</mo><mspace width='0.33em' /><mn>0.3</mn></mrow></math>, in the jet transverse momentum ( <italic>p</italic> <inf>T</inf>) range 5 <math altimg='si11.svg'><mrow><mo>&lt;</mo><msubsup><mi>p</mi><mrow><mi mathvariant='normal'>T</mi></mrow><mrow><mtext>ch</mtext><mspace width='0.33em' /><mtext>jet</mtext></mrow></msubsup><mo linebreak='goodbreak'>&lt;</mo></mrow></math> 50 GeV/ <italic>c</italic> and pseudorapidity | <italic>&#951;</italic> ch&#8201;jet|&#8239;&lt;&#8239;0.6. A hint of reduced suppression in the charm-jet <italic>R</italic> <inf>AA</inf> is observed in comparison to inclusive jets in central Pb&#8211;Pb collisions with a significance of about 2 <italic>&#963;</italic> in 20 <math altimg='si11.svg'><mrow><mo>&lt;</mo><msubsup><mi>p</mi><mrow><mi mathvariant='normal'>T</mi></mrow><mrow><mtext>ch</mtext><mspace width='0.33em' /><mtext>jet</mtext></mrow></msubsup><mo linebreak='goodbreak'>&lt;</mo></mrow></math> 50&#8239;GeV/ <italic>c</italic>, suggesting the in-medium energy loss to depend on both the difference between quark and gluon coupling strength (Casimir colour-charge effect) and quark mass (dead-cone effect). The data are compared with model calculations that include mass effects in the in-medium energy loss. Several state-of-the-art models are consistent with the data, with the LIDO model providing the best description of the data in the common kinematic range of inclusive and D 0-tagged jets, highlighting the role of mass effects in interpreting the results.

France

S. Acharya

A. Agarwal

Switzerland

G. Aglieri Rinella

L. Aglietta

M. Agnello

N. Agrawal

S. Ahmad

South Korea

S.U. Ahn

Slovakia

I. Ahuja

A. Akindinov

V. Akishina

M. Al-Turany

D. Aleksandrov

B. Alessandro

H.M. Alfanda

Mexico

R. Alfaro Molina

B. Ali

A. Alici

N. Alizadehvandchali

A. Alkin

Norway

J. Alme

G. Alocco

T. Alt

A.R. Altamura

I. Altsybeev

J.R. Alvarado

M.N. Anaam

Romania

C. Andrei

United Kingdom

N. Andreou

A. Andronic

E. Andronov

V. Anguelov

F. Antinori

P. Antonioli

N. Apadula

L. Aphecetche

H. Appelshäuser

C. Arata

S. Arcelli

R. Arnaldi

Brazil

J.G.M.C.A. Arneiro

I.C. Arsene

M. Arslandok

A. Augustinus

R. Averbeck

D. Averyanov

M.D. Azmi

H. Baba

A. Badalà

J. Bae

Y.W. Baek

X. Bai

R. Bailhache

Y. Bailung

R. Bala

A. Balbino

A. Baldisseri

Poland

B. Balis

Z. Banoo

V. Barbasova

F. Barile

L. Barioglio

Greece

M. Barlou

B. Barman

Hungary

G.G. Barnaföldi

L.S. Barnby

E. Barreau

V. Barret

L. Barreto

C. Bartels

Investigating charm quark energy loss in medium with the nuclear modification factor of D <bold>0</bold>-tagged jets