Quark interactions with topological gluon configurations can induce chirality imbalance and local parity violation in quantum chromodynamics. This can lead to electric charge separation along the strong magnetic field in relativistic heavy-ion collisions – the chiral magnetic effect (CME). We report measurements by the STAR collaboration of a CME-sensitive observable in <math><mi>p</mi><mo>+</mo><mtext>Au</mtext></math> and <math><mi>d</mi><mo>+</mo><mtext>Au</mtext></math> collisions at 200 GeV, where the CME is not expected, using charge-dependent pair correlations relative to a third particle. We observe strong charge-dependent correlations similar to those measured in heavy-ion collisions. This bears important implications for the interpretation of the heavy-ion data.

United States

J. Adam

Poland

L. Adamczyk

J.R. Adams

J.K. Adkins

JINR

G. Agakishiev

India

M.M. Aggarwal

Z. Ahammed

Russia

I. Alekseev

D.M. Anderson

Japan

R. Aoyama

A. Aparin

D. Arkhipkin

E.C. Aschenauer

China

M.U. Ashraf

F. Atetalla

A. Attri

G.S. Averichev

V. Bairathi

K. Barish

A.J. Bassill

A. Behera

R. Bellwied

A. Bhasin

A.K. Bhati

Czechia

J. Bielcik

J. Bielcikova

L.C. Bland

I.G. Bordyuzhin

J.D. Brandenburg

A.V. Brandin

J. Bryslawskyj

I. Bunzarov

J. Butterworth

H. Caines

M. Calderón de la Barca Sánchez

D. Cebra

I. Chakaberia

P. Chaloupka

B.K. Chan

Taiwan

F.H. Chang

Z. Chang

N. Chankova-Bunzarova

A. Chatterjee

S. Chattopadhyay

J.H. Chen

X. Chen

J. Cheng

M. Cherney

W. Christie

H.J. Crawford

Hungary

M. Csanád

S. Das

T.G. Dedovich

Germany

I.M. Deppner

A.A. Derevschikov

L. Didenko

C. Dilks

X. Dong

J.L. Drachenberg

J.C. Dunlop

T. Edmonds

N. Elsey

J. Engelage

G. Eppley

R. Esha

S. Esumi

O. Evdokimov

J. Ewigleben

O. Eyser

R. Fatemi

S. Fazio

P. Federic

J. Fedorisin

Y. Feng

P. Filip

E. Finch

Y. Fisyak

L. Fulek

C.A. Gagliardi

T. Galatyuk

F. Geurts

A. Gibson

K. Gopal

D. Grosnick

A. Gupta

W. Guryn

A.I. Hamad

Egypt

A. Hamed

J.W. Harris

L. He

S. Heppelmann

N. Herrmann

L. Holub

Y. Hong

S. Horvat

B. Huang

H.Z. Huang

S.L. Huang

T. Huang

Charge-dependent pair correlations relative to a third particle in + Au and + Au collisions at RHIC

<math><mi>J</mi><mo>/</mo><mi>ψ</mi></math> suppression has long been considered a sensitive signature of the formation of the Quark-Gluon Plasma (QGP) in relativistic heavy-ion collisions. In this letter, we present the first measurement of inclusive <math><mi>J</mi><mo>/</mo><mi>ψ</mi></math> production at mid-rapidity through the dimuon decay channel in Au+Au collisions at <math><msqrt><mrow><msub><mrow><mi>s</mi></mrow><mrow><mi>NN</mi></mrow></msub></mrow></msqrt><mo>=</mo><mn>200</mn></math> GeV with the STAR experiment. These measurements became possible after the installation of the Muon Telescope Detector was completed in 2014. The <math><mi>J</mi><mo>/</mo><mi>ψ</mi></math> yields are measured in a wide transverse momentum (<math><msub><mrow><mi>p</mi></mrow><mrow><mi>T</mi></mrow></msub></math>) range of 0.15 GeV/c to 12 GeV/c from central to peripheral collisions. They extend the kinematic reach of previous measurements at RHIC with improved precision. In the 0-10% most central collisions, the <math><mi>J</mi><mo>/</mo><mi>ψ</mi></math> yield is suppressed by a factor of approximately 3 for <math><msub><mrow><mi>p</mi></mrow><mrow><mi>T</mi></mrow></msub><mo>&gt;</mo><mn>5</mn></math> GeV/c relative to that in <math><mi>p</mi><mo>+</mo><mi>p</mi></math> collisions scaled by the number of binary nucleon-nucleon collisions. The <math><mi>J</mi><mo>/</mo><mi>ψ</mi></math> nuclear modification factor displays little dependence on <math><msub><mrow><mi>p</mi></mrow><mrow><mi>T</mi></mrow></msub></math> in all centrality bins. Model calculations can qualitatively describe the data, providing further evidence for the color-screening effect experienced by <math><mi>J</mi><mo>/</mo><mi>ψ</mi></math> mesons in the QGP.

Measurement of inclusive / suppression in Au+Au collisions at GeV through the dimuon channel at STAR

We present the first measurement of the proton–Ω correlation function in heavy-ion collisions for the central (0–40%) and peripheral (40–80%) Au + Au collisions at <math><msqrt><mrow><msub><mrow><mi>s</mi></mrow><mrow><mi>NN</mi></mrow></msub></mrow></msqrt><mo>=</mo><mn>200</mn></math> GeV by the STAR experiment at the Relativistic Heavy-Ion Collider (RHIC). Predictions for the ratio of peripheral collisions to central collisions for the proton–Ω correlation function are sensitive to the presence of a nucleon–Ω bound state. These predictions are based on the proton–Ω interaction extracted from <math><mo>(</mo><mn>2</mn><mo>+</mo><mn>1</mn><mo>)</mo></math>-flavor lattice QCD calculations at the physical point. The measured ratio of the proton–Ω correlation function between the peripheral (small system) and central (large system) collisions is less than unity for relative momentum smaller than 40 MeV/c. Comparison of our measured correlation ratio with theoretical calculation slightly favors a proton–Ω bound system with a binding energy of ∼ 27 MeV.

N.N. Ajitanand

X. Bai

D. Brown

J.M. Campbell

G. Contin

L.G. Efimov

P. Federicova

C.E. Flores

D.S. Gunarathne

Y. Guo

A. Harlenderova

The proton–Ω correlation function in Au + Au collisions at

We present three-particle mixed-harmonic correlations <math><mo>〈</mo><mi>cos</mi><mo>⁡</mo><mo>(</mo><mi>m</mi><msub><mrow><mi>ϕ</mi></mrow><mrow><mi>a</mi></mrow></msub><mo>+</mo><mi>n</mi><msub><mrow><mi>ϕ</mi></mrow><mrow><mi>b</mi></mrow></msub><mo>−</mo><mo>(</mo><mi>m</mi><mo>+</mo><mi>n</mi><mo>)</mo><msub><mrow><mi>ϕ</mi></mrow><mrow><mi>c</mi></mrow></msub><mo>)</mo><mo>〉</mo></math> for harmonics <math><mi>m</mi><mo>,</mo><mi>n</mi><mo>=</mo><mn>1</mn><mo>−</mo><mn>3</mn></math> for charged particles in <math><msqrt><mrow><msub><mrow><mi>s</mi></mrow><mrow><mi>N</mi><mi>N</mi></mrow></msub></mrow></msqrt><mo>=</mo><mn>200</mn></math> GeV Au+Au collisions at RHIC. These measurements provide information on the three-dimensional structure of the initial collision zone and are important for constraining models of a subsequent low-viscosity quark–gluon plasma expansion phase. We investigate correlations between the first, second and third harmonics predicted as a consequence of fluctuations in the initial state. The dependence of the correlations on the pseudorapidity separation between particles show hints of a breaking of longitudinal invariance. We compare our results to a number of state-of-the art hydrodynamic calculations with different initial states and temperature dependent viscosities. These measurements provide important steps towards constraining the temperature dependent viscosity and longitudinal structure of the initial state at RHIC.

P. Bhattarai

J. Bouchet

L.C. De Silva

R.R. Debbe

J. Deng

J.E. Draper

L.E. Dunkelberger

Z. Feng

D. Garand

M. Girard

S. Gupta

Constraining the initial conditions and temperature dependent viscosity with three-particle correlations in Au+Au collisions

We present a measurement of inclusive <math><mi>J</mi><mo>/</mo><mi>ψ</mi></math> production at mid-rapidity (<math><mo>|</mo><mi>y</mi><mo>|</mo><mo>&lt;</mo><mn>1</mn></math>) in <math><mi>p</mi><mo>+</mo><mi>p</mi></math> collisions at a center-of-mass energy of <math><msqrt><mrow><mi>s</mi></mrow></msqrt><mo>=</mo><mn>200</mn></math> GeV with the STAR experiment at the Relativistic Heavy Ion Collider (RHIC). The differential production cross section for <math><mi>J</mi><mo>/</mo><mi>ψ</mi></math> as a function of transverse momentum (<math><msub><mrow><mi>p</mi></mrow><mrow><mi>T</mi></mrow></msub></math>) for <math><mn>0</mn><mo>&lt;</mo><msub><mrow><mi>p</mi></mrow><mrow><mi>T</mi></mrow></msub><mo>&lt;</mo><mn>14</mn></math> <math><mrow><mi>GeV</mi><mo>/</mo></mrow><mi>c</mi></math> and the total cross section are reported and compared to calculations from the color evaporation model and the non-relativistic Quantum Chromodynamics model. The dependence of <math><mi>J</mi><mo>/</mo><mi>ψ</mi></math> relative yields in three <math><msub><mrow><mi>p</mi></mrow><mrow><mi>T</mi></mrow></msub></math> intervals on charged-particle multiplicity at mid-rapidity is measured for the first time in <math><mi>p</mi><mo>+</mo><mi>p</mi></math> collisions at <math><msqrt><mrow><mi>s</mi></mrow></msqrt><mo>=</mo><mn>200</mn></math> GeV and compared with that measured at <math><msqrt><mrow><mi>s</mi></mrow></msqrt><mo>=</mo><mn>7</mn></math> TeV, PYTHIA8 and EPOS3 Monte Carlo generators, and the Percolation model prediction.

/ Production Cross Section and its Dependence on Charged-particle Multiplicity in + Collisions at

Fluctuations of conserved quantities such as baryon number, charge, and strangeness are sensitive to the correlation length of the hot and dense matter created in relativistic heavy-ion collisions and can be used to search for the QCD critical point. We report the first measurements of the moments of net-kaon multiplicity distributions in Au+Au collisions at <math><msqrt><mrow><msub><mrow><mi>s</mi></mrow><mrow><mi>NN</mi></mrow></msub></mrow></msqrt><mo>=</mo><mn>7.7</mn></math>, 11.5, 14.5, 19.6, 27, 39, 62.4, and 200 GeV. The collision centrality and energy dependence of the mean (M), variance (<math><msup><mrow><mi>σ</mi></mrow><mrow><mn>2</mn></mrow></msup></math>), skewness (S), and kurtosis (κ) for net-kaon multiplicity distributions as well as the ratio <math><msup><mrow><mi>σ</mi></mrow><mrow><mn>2</mn></mrow></msup><mo>/</mo><mi>M</mi></math> and the products Sσ and <math><mi>κ</mi><msup><mrow><mi>σ</mi></mrow><mrow><mn>2</mn></mrow></msup></math> are presented. Comparisons are made with Poisson and negative binomial baseline calculations as well as with UrQMD, a transport model (UrQMD) that does not include effects from the QCD critical point. Within current uncertainties, the net-kaon cumulant ratios appear to be monotonic as a function of collision energy.

J. Fujita

Collision energy dependence of moments of net-kaon multiplicity distributions at RHIC

New measurements of directed flow for charged hadrons, characterized by the Fourier coefficient <math><msub><mrow><mi>v</mi></mrow><mrow><mn>1</mn></mrow></msub></math>, are presented for transverse momenta <math><msub><mrow><mi>p</mi></mrow><mrow><mi>T</mi></mrow></msub></math>, and centrality intervals in Au+Au collisions recorded by the STAR experiment for the center-of-mass energy range <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><mtext>–</mtext><mn>200</mn></math> GeV. The measurements underscore the importance of momentum conservation, and the characteristic dependencies on <math><msqrt><mrow><msub><mrow><mi>s</mi></mrow><mrow><mi>N</mi><mi>N</mi></mrow></msub></mrow></msqrt></math>, centrality and <math><msub><mrow><mi>p</mi></mrow><mrow><mi>T</mi></mrow></msub></math> are consistent with the expectations of geometric fluctuations generated in the initial stages of the collision, acting in concert with a hydrodynamic-like expansion. The centrality and <math><msub><mrow><mi>p</mi></mrow><mrow><mi>T</mi></mrow></msub></math> dependencies of <math><msubsup><mrow><mi>v</mi></mrow><mrow><mn>1</mn></mrow><mrow><mi>even</mi></mrow></msubsup></math>, as well as an observed similarity between its excitation function and that for <math><msub><mrow><mi>v</mi></mrow><mrow><mn>3</mn></mrow></msub></math>, could serve as constraints for initial-state models. The <math><msubsup><mrow><mi>v</mi></mrow><mrow><mn>1</mn></mrow><mrow><mi>even</mi></mrow></msubsup></math> excitation function could also provide an important supplement to the flow measurements employed for precision extraction of the temperature dependence of the specific shear viscosity.

Beam energy dependence of rapidity-even dipolar flow in Au+Au collisions

Flow harmonics (<math><msub><mrow><mi>v</mi></mrow><mrow><mi>n</mi></mrow></msub></math>) in the Fourier expansion of the azimuthal distribution of particles are widely used to quantify the anisotropy in particle emission in high-energy heavy-ion collisions. The symmetric cumulants, <math><mi>S</mi><mi>C</mi><mo>(</mo><mi>m</mi><mo>,</mo><mi>n</mi><mo>)</mo></math>, are used to measure the correlations between different orders of flow harmonics. These correlations are used to constrain the initial conditions and the transport properties of the medium in theoretical models. In this Letter, we present the first measurements of the four-particle symmetric cumulants 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>39</mn></math> and 200 GeV from data collected by the STAR experiment at RHIC. We observe that <math><msub><mrow><mi>v</mi></mrow><mrow><mn>2</mn></mrow></msub></math> and <math><msub><mrow><mi>v</mi></mrow><mrow><mn>3</mn></mrow></msub></math> are anti-correlated in all centrality intervals with similar correlation strengths from 39 GeV Au+Au to 2.76 TeV Pb+Pb (measured by the ALICE experiment). The <math><msub><mrow><mi>v</mi></mrow><mrow><mn>2</mn></mrow></msub></math>–<math><msub><mrow><mi>v</mi></mrow><mrow><mn>4</mn></mrow></msub></math> correlation seems to be stronger at 39 GeV than at higher collision energies. The initial-stage anti-correlations between second and third order eccentricities are sufficient to describe the measured correlations between <math><msub><mrow><mi>v</mi></mrow><mrow><mn>2</mn></mrow></msub></math> and <math><msub><mrow><mi>v</mi></mrow><mrow><mn>3</mn></mrow></msub></math>. The best description of <math><msub><mrow><mi>v</mi></mrow><mrow><mn>2</mn></mrow></msub></math>–<math><msub><mrow><mi>v</mi></mrow><mrow><mn>4</mn></mrow></msub></math> correlations at <math><msqrt><mrow><msub><mrow><mi>s</mi></mrow><mrow><mi>N</mi><mi>N</mi></mrow></msub></mrow></msqrt><mo>=</mo><mn>200</mn><mspace width="0.25em"></mspace><mtext>GeV</mtext></math> is obtained with inclusion of the system's nonlinear response to initial eccentricities accompanied by the viscous effect with <math><mi>η</mi><mo>/</mo><mi>s</mi><mo>&gt;</mo><mn>0.08</mn></math>. Theoretical calculations using different initial conditions, equations of state and viscous coefficients need to be further explored to extract <math><mi>η</mi><mo>/</mo><mi>s</mi></math> of the medium created at RHIC.

Correlation measurements between flow harmonics in Au+Au collisions at RHIC

An invariant differential cross section measurement of inclusive Ï0 and Î· meson production at mid-rapidity in pp collisions at s=8 Â TeV was carried out by the ALICE experiment at the LHC. The spectra of Ï0 and Î· mesons were measured in transverse momentum ranges of 0.3&lt;pT&lt;35 Â GeV/c and 0.5&lt;pT&lt;35 Â GeV/c , respectively. Next-to-leading order perturbative QCD calculations using fragmentation functions DSS14 for the Ï0 and AESSS for the Î· overestimate the cross sections of both neutral mesons, although such calculations agree with the measured Î·/Ï0 ratio within uncertainties. The results were also compared with PYTHIAÂ 8.2 predictions for which the MonashÂ 2013 tune yields the best agreement with the measured neutral meson spectra. The measurements confirm a universal behavior of the Î·/Ï0 ratio seen for NA27, PHENIX and ALICE data for pp collisions from s=27.5 Â GeV to s=8 Â TeV within experimental uncertainties. A relation between the Ï0 and Î· production cross sections for pp collisions at s=8 Â TeV is given by mT scaling for pT&gt;3.5 Â GeV/c . However, a deviation from this empirical scaling rule is observed for transverse momenta below pT&lt;3.5 Â GeV/c in the Î·/Ï0 ratio with a significance of 6.2Ï .