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J/ψproduction at low transverse momentum inp+pandd+ Au collisions at<sub>sNN</sub>=200GeV
Adamczyk, L.,Adkins, J. K.,Agakishiev, G.,Aggarwal, M. M.,Ahammed, Z.,Alekseev, I.,Aparin, A.,Arkhipkin, D.,Aschenauer, E. C.,Attri, A.,Averichev, G. S.,Bai, X.,Bairathi, V.,Bellwied, R.,Bhasin, A.,Bh American Physical Society 2016 Physical Review C Vol.93 No.6
<P>We report on the measurement of J/psi production in the dielectron channel at midrapidity (vertical bar y vertical bar < 1) in p + p and d + Au collisions at root s(NN) = 200 GeV from the STAR experiment at the Relativistic Heavy Ion Collider. The transverse momentum p(T) spectra in p + p for pT < 4 GeV/c and d + Au collisions for p(T) < 3 GeV/c are presented. These measurements extend the STAR coverage for J/psi production in p + p collisions to low p(T). The < p(T)(2)> from the measured J/psi invariant cross section in p + p and d + Au collisions are evaluated and compared to similar measurements at other collision energies. The nuclear modification factor for J/psi is extracted as a function of pT and collision centrality in d + Au and compared to model calculations using the modified nuclear parton distribution function and a final-state J/psi nuclear absorption cross section.</P>
Abelev, B.,Adamczyk, L.,Adkins, J. K.,Agakishiev, G.,Aggarwal, M. M.,Ahammed, Z.,Alekseev, I.,Aparin, A.,Arkhipkin, D.,Aschenauer, E. C.,Ashraf, M. U.,Attri, A.,Averichev, G. S.,Bai, X.,Bairathi, V.,B American Physical Society 2016 Physical Review C Vol.94 No.1
<P>We present measurements of the near side of triggered di-hadron correlations using neutral strange baryons ( A, (A) over bar) and mesons (K-s(0)) at intermediate transverse momentum ( 3 < p(T) < 6 GeV/c) to look for possible flavor and baryon-meson dependence. This study is performed in d+Au, Cu+Cu, and Au+Au collisions at root S-NN = 200 GeV measured by the STAR experiment at RHIC. The near-side di-hadron correlation contains two structures, a peak which is narrow in azimuth and pseudorapidity consistent with correlations from jet fragmentation, and a correlation in azimuth which is broad in pseudorapidity. The particle composition of the jet-like correlation is determined using identified associated particles. The dependence of the conditional yield of the jet-like correlation on the trigger particle momentum, associated particle momentum, and centrality for correlations with unidentified trigger particles are presented. The neutral strange particle composition in jet-like correlations with unidentified charged particle triggers is not well described by PYTHIA. However, the yield of unidentified particles in jet-like correlations with neutral strange particle triggers is described reasonably well by the same model.</P>
Beam-Energy Dependence of Directed Flow of Λ , Λ¯ , K± , Ks0 , and ϕ in Au+Au Collisions
Adamczyk, L.,Adams, J. R.,Adkins, J. K.,Agakishiev, G.,Aggarwal, M. M.,Ahammed, Z.,Ajitanand, N. N.,Alekseev, I.,Anderson, D. M.,Aoyama, R.,Aparin, A.,Arkhipkin, D.,Aschenauer, E. C.,Ashraf, M. U.,Att American Physical Society 2018 Physical Review Letters Vol.120 No.6
Adam, J.,Adamczyk, L.,Adams, J.R.,Adkins, J.K.,Agakishiev, G.,Aggarwal, M.M.,Ahammed, Z.,Ajitanand, N.N.,Alekseev, I.,Anderson, D.M.,Aoyama, R.,Aparin, A.,Arkhipkin, D.,Aschenauer, E.C.,Ashraf, M.U.,A North-Holland Pub. Co 2018 Physics letters. Section B Vol.786 No.-
<P><B>Abstract</B></P> <P>We present a measurement of inclusive J / ψ production at mid-rapidity ( | y | < 1 ) in p + p collisions at a center-of-mass energy of s = 200 GeV with the STAR experiment at the Relativistic Heavy Ion Collider (RHIC). The differential production cross section for J / ψ as a function of transverse momentum ( <SUB> p T </SUB> ) for 0 < <SUB> p T </SUB> < 14 GeV / c 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 J / ψ relative yields in three <SUB> p T </SUB> intervals on charged-particle multiplicity at mid-rapidity is measured for the first time in p + p collisions at s = 200 GeV and compared with that measured at s = 7 TeV, PYTHIA8 and EPOS3 Monte Carlo generators, and the Percolation model prediction.</P>
J / ψ polarization in p + p collisions at s = 200 GeV in STAR
Adamczyk, L.,Adkins, J.K.,Agakishiev, G.,Aggarwal, M.M.,Ahammed, Z.,Alekseev, I.,Alford, J.,Anson, C.D.,Aparin, A.,Arkhipkin, D.,Aschenauer, E.C.,Averichev, G.S.,Balewski, J.,Banerjee, A.,Barnovska, Z North-Holland Pub. Co 2014 Physics letters. Section B Vol.739 No.-
<P><B>Abstract</B></P> <P>We report on a polarization measurement of inclusive J / ψ mesons in the di-electron decay channel at mid-rapidity at 2 < <SUB> p T </SUB> < 6 GeV / c in p + p collisions at s = 200 GeV . Data were taken with the STAR detector at RHIC. The J / ψ polarization measurement should help to distinguish between different models of the J / ψ production mechanism since they predict different <SUB> p T </SUB> dependences of the J / ψ polarization. In this analysis, J / ψ polarization is studied in the helicity frame. The polarization parameter <SUB> λ θ </SUB> measured at RHIC becomes smaller towards high <SUB> p T </SUB> , indicating more longitudinal J / ψ polarization as <SUB> p T </SUB> increases. The result is compared with predictions of presently available models.</P>
Beam energy dependence of rapidity-even dipolar flow in Au+Au collisions
Adam, J.,Adamczyk, L.,Adams, J.R.,Adkins, J.K.,Agakishiev, G.,Aggarwal, M.M.,Ahammed, Z.,Ajitanand, N.N.,Alekseev, I.,Anderson, D.M.,Aoyama, R.,Aparin, A.,Arkhipkin, D.,Aschenauer, E.C.,Ashraf, M.U.,A North-Holland Pub. Co 2018 Physics letters. Section B Vol.784 No.-
<P><B>Abstract</B></P> <P>New measurements of directed flow for charged hadrons, characterized by the Fourier coefficient <SUB> v 1 </SUB> , are presented for transverse momenta <SUB> p T </SUB> , and centrality intervals in Au+Au collisions recorded by the STAR experiment for the center-of-mass energy range <SUB> s N N </SUB> = 7.7 – 200 GeV. The measurements underscore the importance of momentum conservation, and the characteristic dependencies on <SUB> s N N </SUB> , centrality and <SUB> p T </SUB> 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 <SUB> p T </SUB> dependencies of v 1 even , as well as an observed similarity between its excitation function and that for <SUB> v 3 </SUB> , could serve as constraints for initial-state models. The v 1 even 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.</P>
Correlation measurements between flow harmonics in Au+Au collisions at RHIC
Adam, J.,Adamczyk, L.,Adams, J.R.,Adkins, J.K.,Agakishiev, G.,Aggarwal, M.M.,Ahammed, Z.,Ajitanand, N.N.,Alekseev, I.,Anderson, D.M.,Aoyama, R.,Aparin, A.,Arkhipkin, D.,Aschenauer, E.C.,Ashraf, M.U.,A North-Holland Pub. Co 2018 Physics letters. Section B Vol.783 No.-
<P><B>Abstract</B></P> <P>Flow harmonics ( <SUB> v n </SUB> ) 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, S C ( m , n ) , 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 <SUB> s N N </SUB> = 39 and 200 GeV from data collected by the STAR experiment at RHIC. We observe that <SUB> v 2 </SUB> and <SUB> v 3 </SUB> 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 <SUB> v 2 </SUB> – <SUB> v 4 </SUB> 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 <SUB> v 2 </SUB> and <SUB> v 3 </SUB> . The best description of <SUB> v 2 </SUB> – <SUB> v 4 </SUB> correlations at <SUB> s N N </SUB> = 200 GeV is obtained with inclusion of the system's nonlinear response to initial eccentricities accompanied by the viscous effect with η / s > 0.08 . Theoretical calculations using different initial conditions, equations of state and viscous coefficients need to be further explored to extract η / s of the medium created at RHIC.</P>
Azimuthal Harmonics in Small and Large Collision Systems at RHIC Top Energies
Adam, J.,Adamczyk, L.,Adams, J. R.,Adkins, J. K.,Agakishiev, G.,Aggarwal, M. M.,Ahammed, Z.,Alekseev, I.,Anderson, D. M.,Aoyama, R.,Aparin, A.,Arkhipkin, D.,Aschenauer, E. C.,Ashraf, M. U.,Atetalla, F American Physical Society 2019 Physical review letters Vol.122 No.17