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Register a new userForward $J/psi$ production in U$+$U collisions at $sqrt{s_{NN}}$=193 GeV
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The invariant yields for $J/psi$ production at forward rapidity $(1.2<|y|<2.2)$ in U$+$U collisions at $sqrt{s_{_{NN}}}$=193 GeV have been measured as a function of collision centrality. The invariant yields and nuclear-modification factor $R_{AA}$ 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 $cbar{c}$ 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, $N_{rm coll}$, and these were found to give significantly different $N_{rm coll}$ values. Results using $N_{rm coll}$ values from both deformed Woods-Saxon distributions are presented. The measured ratios show that the $J/psi$ suppression, relative to binary collision scaling, is similar in U$+$U and Au$+$Au for peripheral and midcentral collisions, but that $J/psi$ 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 $J/psi$ yield due to $cbar{c}$ coalescence becomes more important than the decrease in yield due to increased energy density. For midcentral collisions, the conclusions about the balance between $cbar{c}$ coalescence and suppression depend on which deformed Woods-Saxon distribution is used to determine $N_{rm coll}$.
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We report first measurements of $e^{+}e^{-}$ pair production in the mass region 0.4 $<M_{ee}<$ 2.6 GeV/$c^{2}$ at low transverse momentum ($p_T<$ 0.15 GeV/$c$) in non-central Au$+$Au collisions at $sqrt{s_{NN}}$ = 200 GeV and U$+$U collisions at $sqrt{s_{NN}}$ = 193 GeV. Significant enhancement factors, expressed as ratios of data over known hadronic contributions, are observed in the 40-80% centrality of these collisions. The excess yields peak distinctly at low-$p_T$ with a width ($sqrt{langle p^2_Trangle}$) between 40 to 60 MeV/$c$. The absolute cross section of the excess depends weakly on centrality while those from a theoretical model calculation incorporating an in-medium broadened $rho$ spectral function and radiation from a Quark Gluon Plasma or hadronic cocktail contributions increase dramatically with increasing number of participant nucleons. Model calculations of photon-photon interactions generated by the initial projectile and target nuclei describe the observed excess yields but fail to reproduce the $p^{2}_{T}$ distributions.
The PHENIX experiment at the Relativistic Heavy Ion Collider measured $pi^0$ and $eta$ mesons at midrapidity in U$+$U collisions at $sqrt{s_{_{NN}}}=192$ GeV in a wide transverse momentum range. Measurements were performed in the $pi^0(eta)rightarrowgammagamma$ decay modes. A strong suppression of $pi^0$ and $eta$ meson production at high transverse momentum was observed in central U$+$U collisions relative to binary scaled $p$$+$$p$ results. Yields of $pi^0$ and $eta$ mesons measured in U$+$U collisions show similar suppression pattern to the ones measured in Au$+$Au collisions at $sqrt{s_{_{NN}}}=200$ GeV for similar numbers of participant nucleons. The $eta$/$pi^0$ ratios do not show dependence on centrality or transverse momentum, and are consistent with previously measured values in hadron-hadron, hadron-nucleus, nucleus-nucleus, and $e^+e^-$ collisions.
We present systematic measurements of azimuthal anisotropy for strange and multistrange hadrons ($K^{0}_{s}$, $Lambda$, $Xi$, and $Omega$) and $phi$ mesons at midrapidity ($|y| <$ 1.0) in collisions of U + U nuclei at $sqrt{s_{NN}} = 193$ GeV, recorded by the STAR detector at the Relativistic Heavy Ion Collider. Transverse momentum ($p_{text{T}}$) dependence of flow coefficients ($v_{2}$, $v_{3}$, and $v_{4}$) is presented for minimum bias collisions and three different centrality intervals. Number of constituent quark scaling of the measured flow coefficients in U + U collisions is discussed. We also present the ratio of $v_{n}$ scaled by the participant eccentricity ($varepsilon_{n}leftlbrace 2 rightrbrace$) to explore system size dependence and collectivity in U + U collisions. The magnitude of $v_{2}/varepsilon_{2}$ is found to be smaller in U + U collisions than that in central Au + Au collisions contradicting naive eccentricity scaling. Furthermore, the ratios between various flow harmonics ($v_{3}/v_{2}^{3/2}$, $v_{4}/v_{2}^{4/2}$) are studied and compared with hydrodynamic and transport model calculations.
We present a measurement of the inclusive production of Upsilon mesons in U+U collisions at 193 GeV at mid-rapidity (|y| < 1). Previous studies in central Au+Au collisions at 200 GeV show a suppression of Upsilon(1S+2S+3S) production relative to expectations from the Upsilon yield in p+p collisions scaled by the number of binary nucleon-nucleon collisions (Ncoll), with an indication that the Upsilon(1S) state is also suppressed. The present measurement extends the number of participant nucleons in the collision (Npart) by 20% compared to Au+Au collisions, and allows us to study a system with higher energy density. We observe a suppression in both the Upsilon(1S+2S+3S) and Upsilon(1S) yields in central U+U data, which consolidates and extends the previously observed suppression trend in Au+Au collisions.
We have implemented spherical harmonics in default Wood Saxon distribution of the HIJING model and calculated various physical observables such as transverse momentum, charged particle multiplicity, nuclear modification factor and particle ratios for charged particles at top RHIC energy with collisions of Uranium (U) nuclei. Results have been compared with available experimental data. We observe that, a particular type of collision configuration can produce significant magnitude change in observables. We have noticed that the tip-tip configuration shows higher magnitude of particle yield in central collisions, while the body-body configuration shows higher value in the cases of peripheral collisions, with the flip in the trend occurring for the mid-central U+U collisions. We observe that particle ratios are independent of configuration type.
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