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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>
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.94 No.3
<P>We present measurements of second-order azimuthal anisotropy (v(2)) at midrapidity (vertical bar y vertical bar < 1.0) for light nuclei d, t, He-3 (for root s(NN) = 200, 62.4, 39, 27, 19.6, 11.5, and 7.7 GeV) and antinuclei <(d)over bar> (root s(NN) = 200, 62.4, 39, 27, and 19.6 GeV) and (3)(He) over bar (root s(NN) = 200 GeV) in the STAR (Solenoidal Tracker at RHIC) experiment. The v(2) for these light nuclei produced in heavy-ion collisions is compared with those for p and (p) over bar. We observe mass ordering in nuclei v(2)(p(T)) at low transverse momenta (p(T) < 2.0 GeV/c). We also find a centrality dependence of v(2) for d and <(d)over bar>. The magnitude of v(2) for t and He-3 agree within statistical errors. Light-nuclei v(2) are compared with predictions from a blast-wave model. Atomic mass number (A) scaling of light-nuclei v(2)(p(T)) seems to hold for p(T)/A < 1.5 GeV/c. Results on light-nuclei v(2) from a transport-plus-coalescence model are consistent with the experimental measurements.</P>
Charged-to-neutral correlation at forward rapidity in Au + Au collisions at<sub>sNN</sub>=200GeV
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.,Banerjee, A.,Beavis, D. R.,Bellwi American Physical Society 2015 PHYSICAL REVIEW C - Vol.91 No.3
Azimuthal Anisotropy inU+UandAu+AuCollisions at RHIC
Adamczyk, L.,Adkins, J. K.,Agakishiev, G.,Aggarwal, M. M.,Ahammed, Z.,Alekseev, I.,Alford, J.,Aparin, A.,Arkhipkin, D.,Aschenauer, E. C.,Averichev, G. S.,Banerjee, A.,Bellwied, R.,Bhasin, A.,Bhati, A. American Physical Society 2015 Physical review letters Vol.115 No.22
Adamczyk, L.,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.,Attri, A.,Averic American Physical Society 2017 Physical Review D Vol.95 No.7
<P>We report the first measurement of the longitudinal double-spin asymmetry A(LL) for midrapidity dijet production in polarized pp collisions at a center-of-mass energy of root s = 200 GeV. The dijet cross section was measured and is shown to be consistent with next-to-leading order (NLO) perturbative QCD predictions. A(LL) results are presented for two distinct topologies, defined by the jet pseudorapidities, and are compared to predictions from several recent NLO global analyses. The measured asymmetries, the first such correlation measurements, support those analyses that find positive gluon polarization at the level of roughly 0.2 over the region of Bjorken-x > 0.05.</P>
Single spin asymmetry A<sub>N</sub> in polarized proton-proton elastic scattering at s=200 GeV
STAR Collaboration,Adamczyk, L.,Agakishiev, G.,Aggarwal, M.M.,Ahammed, Z.,Alakhverdyants, A.V.,Alekseev, I.,Alford, J.,Anson, C.D.,Arkhipkin, D.,Aschenauer, E.,Averichev, G.S.,Balewski, J.,Banerjee, A North-Holland Pub. Co 2013 Physics letters: B Vol.719 No.1
We report a high precision measurement of the transverse single spin asymmetry A<SUB>N</SUB> at the center of mass energy s=200 GeV in elastic proton-proton scattering by the STAR experiment at RHIC. The A<SUB>N</SUB> was measured in the four-momentum transfer squared t range 0.003≤|t|≤0.035 (GeV/c)<SUP>2</SUP>, the region of a significant interference between the electromagnetic and hadronic scattering amplitudes. The measured values of A<SUB>N</SUB> and its t-dependence are consistent with a vanishing hadronic spin-flip amplitude, thus providing strong constraints on the ratio of the single spin-flip to the non-flip amplitudes. Since the hadronic amplitude is dominated by the Pomeron amplitude at this s, we conclude that this measurement addresses the question about the presence of a hadronic spin flip due to the Pomeron exchange in polarized proton-proton elastic scattering.
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>