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1. chinaXiv:201609.00748 [pdf]

Scaling properties of fractional momentum loss of high-$p_T$ hadrons in nucleus-nucleus collisions at $\sqrt{s}__NN$ from 62.4 GeV to 2.76 TeV

Adare, A. and others
Subjects: Physics >> Nuclear Physics

Measurements of the fractional momentum loss (Sloss≡δpT/pT) of high-transverse-momentum-identified hadrons in heavy ion collisions are presented. Using?π0?in Au+Au and Cu+Cu collisions at?sNN???√=62.4?and 200 GeV measured by the PHENIX experiment at the Relativistic Heavy Ion Collider and and charged hadrons in Pb+Pb collisions measured by the ALICE experiment at the Large Hadron Collider, we studied the scaling properties of?Sloss?as a function of a number of variables: the number of participants,?Npart, the number of quark participants,?Nqp, the charged-particle density,?dNch/dη, and the Bjorken energy density times the equilibration time,?εBjτ0. We find that the?pT?where?Sloss?has its maximum, varies both with centrality and collision energy. Above the maximum,?Sloss?tends to follow a power-law function with all four scaling variables. The data at?sNN???√=200 GeV and 2.76 TeV, for sufficiently high particle densities, have a common scaling of?Sloss?with?dNch/dη?and?εBjτ0, lending insight on the physics of parton energy loss.

submitted time 2016-09-12 Hits879Downloads544 Comment 0

2. chinaXiv:201609.00747 [pdf]

Transverse energy production and charged-particle multiplicity at midrapidity in various systems from $\sqrt{s}_NN=7.7$ to 200 GeV

Adare, A. and others
Subjects: Physics >> Nuclear Physics

Measurements of midrapidity charged particle multiplicity distributions,?dNch/dη, and midrapidity transverse-energy distributions,?dET/dη, are presented for a variety of collision systems and energies. Included are distributions for Au+Au collisions at?sNN???√=200, 130, 62.4, 39, 27, 19.6, 14.5, and 7.7 GeV, Cu+Cu collisions at?sNN???√=200?and 62.4 GeV, Cu+Au collisions at?sNN???√=200?GeV, U+U collisions at?sNN???√=193?GeV,?d+Au collisions at?sNN???√=200?GeV,?3He+Au collisions at?sNN???√=200?GeV, and?p+p?collisions at?sNN???√=200?GeV. Centrality-dependent distributions at midrapidity are presented in terms of the number of nucleon participants,?Npart, and the number of constituent quark participants,?Nqp. For all?A+Acollisions down to?sNN???√=7.7?GeV, it is observed that the midrapidity data are better described by scaling with?Nqp?than scaling with?Npart. Also presented are estimates of the Bjorken energy density,?εBJ, and the ratio of?dET/dη?to?dNch/dη, the latter of which is seen to be constant as a function of centrality for all systems.

submitted time 2016-09-12 Hits951Downloads546 Comment 0

3. chinaXiv:201609.00746 [pdf]

$\phi$ meson production in the forward/backward rapidity region in Cu$+$Au collisions at $\sqrt{s}_NN=200$ GeV

Adare, A. and others
Subjects: Physics >> Nuclear Physics

The PHENIX experiment at the Relativistic Heavy Ion Collider (RHIC) has measured???meson production and its nuclear modification in asymmetric Cu+Au heavy-ion collisions at?sNN????√=200?GeV at both forward Cu-going direction (1.2

submitted time 2016-09-12 Hits910Downloads555 Comment 0

4. chinaXiv:201609.00741 [pdf]

Forward $J/\psi$ production in U$+$U collisions at $\sqrt{s}_NN$=193 GeV

Adare, A. and others
Subjects: Physics >> Nuclear Physics

The invariant yields for?J/ψ?production at forward rapidity?(1.2<|y|<2.2)?in U+U collisions at?sNN???√=193 GeV have been measured as a function of collision centrality. The invariant yields and nuclear-modification factor?RAA?are presented and compared with those from Au+Au collisions in the same rapidity range. Additionally, the direct ratio of the invariant yields from U+U and Au+Au collisions within the same centrality class is presented, and used to investigate the role of?cc??coalescence. Two different parameterizations of the deformed Woods-Saxon distribution were used in Glauber calculations to determine the values of the number of nucleon-nucleon collisions in each centrality class,?Ncoll, and these were found to give significantly different?Ncoll?values. Results using?Ncoll?values from both deformed Woods-Saxon distributions are presented. The measured ratios show that the?J/ψ?suppression, relative to binary collision scaling, is similar in U+U and Au+Au for peripheral and midcentral collisions, but that?J/ψ?show less suppression for the most central U+U collisions. The results are consistent with a picture in which, for central collisions, increase in the?J/ψ?yield due to?cc??coalescence becomes more important than the decrease in yield due to increased energy density. For midcentral collisions, the conclusions about the balance between?cc??coalescence and suppression depend on which deformed Woods-Saxon distribution is used to determine?Ncoll.

submitted time 2016-09-12 Hits977Downloads593 Comment 0

5. chinaXiv:201609.00733 [pdf]

Dielectron production in Au$+$Au collisions at $\sqrt{s}_NN$=200 GeV

Adare, A. and others
Subjects: Physics >> Nuclear Physics

We present measurements of?e+e??production at midrapidity in Au+Au collisions at?sNN???√?= 200 GeV. The invariant yield is studied within the PHENIX detector acceptance over a wide range of mass (mee

submitted time 2016-09-12 Hits898Downloads564 Comment 0

6. chinaXiv:201609.00073 [pdf]

Measurements of double-helicity asymmetries in inclusive $J/\psi$ production in longitudinally polarized $p+p$ collisions at $\sqrts=510$ GeV

PHENIX Collaboration
Subjects: Physics >> Nuclear Physics

We report the double helicity asymmetry,?AJ/ψLL, in inclusive?J/ψ?production at forward rapidity as a function of transverse momentum?pT?and rapidity?|y|. The data analyzed were taken during?s√=510GeV longitudinally polarized?p+p?collisions at the Relativistic Heavy Ion Collider (RHIC) in the 2013 run using the PHENIX detector. At this collision energy,?J/ψ?particles are predominantly produced through gluon-gluon scatterings, thus?AJ/ψLL?is sensitive to the gluon polarization inside the proton. We measured?AJ/ψLL?by detecting the decay daughter muon pairs?μ+μ??within the PHENIX muon spectrometers in the rapidity range?1.2<|y|<2.2. In this kinematic range, we measured the?AJ/ψLL?to be?0.012±0.010~(stat)~±~0.003(syst). The?AJ/ψLL?can be expressed to be proportional to the product of the gluon polarization distributions at two distinct ranges of Bjorken?x: one at moderate range?x≈0.05?where recent RHIC data of jet and?π0?double helicity spin asymmetries have shown evidence for significant gluon polarization, and the other one covering the poorly known small-x?region?x≈2×10?3. Thus our new results could be used to further constrain the gluon polarization for?x<0.05.

submitted time 2016-09-06 Hits745Downloads418 Comment 0

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