We present, the measurements of the $ϕ$-meson production and elliptic flow ($v_{2}$) at mid-rapidity in Au + Au collisions at $\sqrt{s_{NN}}$ = 7.7 - 200 GeV using the STAR detector in the years 2010 and 2011. The energy dependence of nuclear modification factors ($R_{\rm{CP}}$) is presented. At the intermediate transverse momentum ($p_{T}$) the $Ω/ϕ$ ratio shows a different trend for $\sqrt{s_{NN}}$ = 11.5 GeV compared to higher beam energies. This may suggest change of particle production mechanism at $\sqrt{s_{NN}}$ = 11.5 GeV. The number-of-constituent quark (NCQ) scaling of $v_{2}$ has been studied at various beam energies. The NCQ scaling holds for all identified particles for $\sqrt{s_{NN}}$ $\geq$ 19.6 GeV, which can be considered as an evidence of partonic collectivity. We observe at $\sqrt{s_{NN}}$ = 7.7 and 11.5 GeV, the $ϕ$-meson $v_{2}$ falls off the trend from the other hadrons at highest measured $p_{T}$ values by 1.8$σ$ and 2.3$σ$, respectively. This may indicate that the hadronic interaction plays an important role at lower beam energies.
We present the measurement of elliptic flow ($v_{2}$) as a function of transverse momentum ($p_{T}$) for the $ϕ$-meson in Au+Au collisions at $\sqrt{s_{NN}}$ = 7.7, 11.5 and 39 GeV. At low $p_{T}$ $ϕ$-meson $v_{2}$ decreases with decrease in beam energy. The number of constituent quark ($n_{\rm{cq}}$) scaled $v_{2}$ for $ϕ$-meson vs ($m_{T} - m_{0}$)/$n_{\rm{cq}}$ follows similar trend as other hadrons for $\sqrt{s_{NN}}$= 39 GeV whereas the $n_{\rm{cq}}$ scaled $v_{2}$ for $ϕ$-mesons follows a different trend compared to the other hadrons at $\sqrt{s_{NN}}$= 11.5 GeV.
The measurement of D-meson production in heavy-ion collisions at LHC energy provides insights into the mechanisms of interaction of charm quarks in the hot and dense medium formed in these collisions. ALICE results on the D-meson nuclear modification factor and azimuthal anisotropy in Pb-Pb collisions at $\sqrt{s_{\rm NN}}=2.76$ TeV are presented.
Azimuthally anisotropic distributions of D$^0$, D$^+$ and D$^{*+}$ mesons were studied in the central rapidity region ($|y|<0.8$) in Pb-Pb collisions at a centre-of-mass energy $\sqrt{s_{\rm NN}} = 2.76$ TeV per nucleon-nucleon collision, with the ALICE detector at the LHC. The second Fourier coefficient $v_2$ (commonly denoted elliptic flow) was measured in the centrality class 30-50% as a function of the D meson transverse momentum $p_{\rm T}$, in the range 2-16 GeV/$c$. The measured $v_2$ of D mesons is comparable in magnitude to that of light-flavour hadrons. It is positive in the range $2…
In these proceedings, we present the measurements of elliptic ($v_2$) and triangular ($v_3$) flow of (multi-)strange hadrons and $ϕ$ mesons in 19.6 and 14.6 GeV Au+Au collisions from STAR. The number of constituent quark (NCQ) scaling of $v_2$ and $v_3$ holds well at $\sqrt{ s_{\mathrm{ NN }} } $ = 19.6 GeV, which indicates the collective flow is built up in the partonic stage. At these energies, the anti-particles show better NCQ scaling than the particles for both $v_2$ and $v_3$, which may be caused by the different contributions from the produced and transported quarks.
We present here recent open heavy-flavour results from the ALICE experiment, including measurements of D-meson, $\mathrm{Λ_{c}^{+}}$ baryon and $\mathrm{Ξ_c^0}$ baryon production in pp collisions at $\sqrt{s} = 7~\mathrm{TeV}$ and p-Pb collisions at $\sqrt{s_{\mathrm{NN}}} = 5.02~\mathrm{TeV}$.
The first measurement of the $ρ^{0}$ - vector meson elliptic flow $v_{2}$ at mid-rapidity ($|y |$ $<$ 0.5) in $40 - 80$ $%$ centrality in $Au+Au$ collisions at $\sqrt{s_{NN}} = 200$ GeV from the STAR experiment at RHIC is presented. The study is through the $π^{+} π^{-}$ hadronic decay channel of $ρ^{0}$ which has a branching ratio of $\sim$ 100 %. The analysis is being carried out in two different methods. The $v_{2}$ results obtained in these methods are consistent. Number of Constituent Quark (NCQ) scaling of $v_{2}$ of $ρ^{0}$ meson with respect to other hadrons at intermediate $p_{T}$ is …
We present the recent results for D-meson production measured by the ALICE collaboration in pp collisions at $\sqrt{s}=7$ TeV, Pb-Pb collisions at $\sqrt{s_\mathrm{NN}}=2.76$ TeV and p-Pb collisions at $\sqrt{s_\mathrm{NN}}=5.02$ TeV.
A measurement of the elliptic flow ($v_2$) of prompt J/$ψ$ mesons in high-multiplicity pPb collisions is reported using data collected by the CMS experiment at a nucleon-nucleon center-of-mass energy $\sqrt{s_\mathrm{NN}} =$ 8.16 TeV. Prompt J/$ψ$ mesons decaying into two muons are reconstructed in the rapidity region in the nucleon-nucleon center-of-mass frame ($y_\mathrm{cm}$), corresponding to either $-$2.86 $\lt y_{\mathrm{cm}} <$ $-$1.86 or 0.94 $\lt y_{\mathrm{cm}} <$ 1.94. The average $v_2$ result from the two rapidity ranges is reported over the transverse momentum (p$_\mathrm{T}$) ran…
We present the measurements of strange hadron elliptic flow at mid-rapidity in Au + Au collisions at $\sqrt{s_{NN}}$ = 7.7 - 200 GeV using the STAR detector in the years 2010 and 2011. The transverse momentum and collision centrality dependence of elliptic flow is presented. At the intermediate transverse momentum $Ω$ baryon and $ϕ$-meson show baryon-meson separation effect similar to proton and pion for minimum-bias Au+Au collision at $\sqrt{s_{NN}}$ =200 GeV. This indicates formation of collective flow at the early partonic phase. The separation between baryons and mesons at intermediate tra…
The production yield of prompt D mesons and their elliptic flow coefficient $v_2$ were measured with the Event-Shape Engineering (ESE) technique applied to mid-central (10-30% and 30-50% centrality classes) Pb-Pb collisions at the centre-of-mass energy per nucleon pair $\sqrt{s_{\rm NN}} =5.02$ TeV, with the ALICE detector at the LHC. The ESE technique allows the classification of events, belonging to the same centrality, according to the azimuthal anisotropy of soft particle production in the collision. The reported measurements give the opportunity to investigate the dynamics of charm quarks…
We present the measurement of the $p_{\rm T}$-differential production cross section of $ω$ mesons in pp and p$-$Pb collisions at $\sqrt{s_{\rm NN}} = 5.02$ TeV at midrapidity by ALICE. In addition, the first measurement of the nuclear modification factor $R_{\text{pPb}}$ for $ω$ mesons at LHC energies is presented, complementing the existing measurements of lighter neutral mesons such as the $π^0$ and $η$. Within the measured $p_{\rm T}$-range, the $R_{\text{pPb}}$ of $ω$ mesons is compatible with no cold nuclear matter effects within the uncertainties, consistent with previous measurements at…
The azimuthal correlations of D mesons and charged particles were measured with the ALICE detector in pp collisions at $\sqrt{s}=7$ TeV and p-Pb collisions at $\sqrt{s_{\rm NN}}=5.02$ TeV at the Large Hadron Collider. D$^0$, D$^+$, and D$^{*+}$ mesons and their charge conjugates with transverse momentum $3<p_{\rm T}<16$ GeV/$c$ and rapidity in the nucleon-nucleon centre-of-mass system $|y_{\rm cms}|<0.5$ (pp collisions) and $-0.96<y_{\rm cms}<0.04$ (p-Pb collisions) were correlated to charged particles with $p_{\rm T}>0.3$ Gev/$c$. The properties of the correlation peak induced by the jet cont…
We present the measurements of D0, D+, D*+ meson v_2 as well as D0 R_{AA} in different directions with respect to the estimated reaction plane in Pb-Pb collisions at sqrt(s_{NN)) = 2.76 TeV with the ALICE detector at the LHC.
The $p_{\rm T}$-differential production cross sections of the prompt charmed mesons $D^0$, $D^+$, $D^{*+}$ and $D_{\rm s}^{+}$ and their charge conjugate in the rapidity interval $-0.96 < y_{\rm cms} < 0.04$ were measured in p-Pb collisions at a centre-of-mass energy $\sqrt{s_{\rm NN}} = 5.02$ TeV with the ALICE detector at the LHC. The nuclear modification factor $R_{\rm pPb}$, quantifying the D-meson yield in p-Pb collisions relative to the yield in pp collisions scaled by the number of binary nucleon-nucleon collisions, is compatible within the 15-20% uncertainties with unity in the transve…
We present the measurement of light neutral mesons, $π^{0}$ and $η$, in pp collisions at different center-of-mass energies obtained with the ALICE experiment at the LHC. The $π^{0}$ and $η$ mesons are measured via photons reconstructed by the electromagnetic calorimeters and the central tracking system. The invariant cross-section of $π^{0}$ and $η$ mesons are measured in a broad $p_{\rm T}$ range at $\sqrt{s} = 0.9, 2.76, 7, 5.02$ and 8 TeV. The spectra of $π^{0}$ and $η$ mesons measured in pp collisions at different collision energies show $x_{\rm T}$-scaling at high $p_{\rm T}$ and violatio…
Differential elliptic flow (v_2) for phi mesons and (anti)deuterons (d^bar)d is measured for Au+Au collisions at sqrt(s_NN) = 200 GeV. The v_2 for phi mesons follows the trend of lighter pi^+/- and K^+/- mesons, suggesting that ordinary hadrons interacting with standard hadronic cross sections are not the primary driver for elliptic flow development. The v_2 values for (d^bar)d suggest that elliptic flow is additive for composite particles. This further validation of the universal scaling of v_2 per constituent quark for baryons and mesons suggests that partonic collectivity dominates the tran…
The properties of the hot and dense QCD medium formed in ultra-relativistic heavy ion collisions, as well as the mechanism of in-medium partonic energy loss, can be accessed via the study of the D mesons nuclear modification factor. The ALICE experiment has measured D meson production in pp and Pb-Pb collisions at the LHC at $\sqrt{s}$ =7 and 2.76 TeV and at $\sqrt{s_{NN}}$ = 2.76 TeV, respectively, via the exclusive reconstruction of hadronic decay channels. D mesons are selected by exploiting the high-resolution tracking performance and the hadron identification capabilities of the ALICE det…
Heavy quarks are effective probes of the properties of the QGP created in ultra-relativistic heavy-ion collisions. The ALICE Collaboration measured the non-strange D-meson production in Pb--Pb collisions at $\sqrt{s_{\rm NN\,}}=5.02$ TeV. The in-medium energy loss can be studied via the nuclear modification factor measurement. The measurement of the D-meson elliptic flow, $v_2$, allows us to investigate the participation of the heavy quarks in the collective expansion of the system at low momentum and their possible thermalization in the medium. Furthermore, the Event-Shape Engineering techniq…
Vector mesons are copiously produced in ultra-peripheral nucleus-nucleus collisions. In these collisions, the nuclei are separated by impact parameters larger than the sum of the nuclear radii, and the interaction is mediated by the electromagnetic field. The interaction effectively corresponds to a photonuclear interaction between a photon, generated from the electromagnetic field of one of the nuclei, and the target nucleus. The ALICE Collaboration has previously published results on exclusive J/psi photoproduction at mid and forward rapidities in Pb-Pb collisions. The cross section for this…
Differential invariant cross sections of light neutral mesons in p-Pb collisions at $\sqrt{s_{\text{NN}}}$ = 8.16 TeV and in pp collisions at $\sqrt{s}$ = 8 TeV have been measured up to very high transverse momentum ($p_{\text{T}}$). By combining independent reconstruction techniques available in ALICE using the EMCal and PHOS calorimeters as well as the central barrel tracking detectors, the combined spectra cover almost two orders of magnitude in $p_{\rm T}$ for the $π^{0}$ meson. The nuclear modification factor $R_{\text{pPb}}$ has been measured for the $π^{0}$ and $η$ mesons and is found t…
Elliptic flow (v_2) of ϕ-meson is shown to be a sensitive probe of the partonic collectivity using A Multi Phase Transport (AMPT) model. Within the ambit of the AMPT model with partonic interactions (string melting version), the ϕ-meson v_2 at midrapidity is found to have negligible contribution from hadronic interactions for Au+Au collisions at 200 GeV per nucleon. Changing the hadron cascade time in the model calculations does not change the ϕ-meson v_2, while it reduces the v_2 of proton at low transverse momentum (pT). These observations indicate that a substantial reduction in ϕ-mesons v_…
We present the measurements of the $ϕ$-meson production and elliptic flow ($v_{2}$) at mid-rapidity in Au + Au collisions at $\sqrt{s_{NN}}$ = 7.7 - 200 GeV. The data are collected using the STAR detector in the years 2010 and 2011. The energy dependence of nuclear modification factor ($R_{\rm{CP}}$) of $ϕ$ meson is presented. The $ϕ$-meson $R_{\rm{CP}}$ has a value $\geq$ 1.0 for $\sqrt{s_{NN}}$ $\leq$ 39 GeV. The $Ω/ϕ$ ratios are also presented and show a different trend at the intermediate transverse momentum ($p_{T}$) for $\sqrt{s_{NN}}$ = 11.5 GeV compared to higher beam energies. The num…
We present the first measurement of the nuclear modification factor $R_{AA}$ and elliptic flow $v_{2}$ of $D_{s}$ in Au+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV with the STAR detector. These results have been compared with those of other open charm mesons and strange mesons to determine how the (possibly) strangeness equilibrated partonic matter affects the $D_{s}$ meson production. We find that the nuclear modification factor of $D_{S}$ are systematically higher than unity and $D^{0}$ $R_{\rm{AA}}$. The ratio $D_{s}/D^{0}$ is shown as a function of transverse momentum for the 10-40$\%$ most…
We present spectra of $π^0$, $η$ and $ω$ mesons in pp collisions and $π^{0}$ mesons in Pb-Pb collisions measured with ALICE at LHC energies. The $π^0$ and $η$ mesons are reconstructed via their two-photon decays by two complementary methods, using the electromagnetic calorimeters and photon conversion technique; both measurements show perfect agreement. We measure the nuclear modification factor ($R_{AA}$) of $π^0$ production in Pb-Pb collisions at different collision centralities and compare with lower energy results and theoretical predictions.
Azimuthal distributions of $η$ and $π^{0}$ mesons emitted at midrapidity in collisions of 1.9 AGeV $^{58}$Ni+$^{58}$Ni and 2 AGeV $^{40}$Ca+$^{nat}$Ca are studied as a function of the number of projectile-like spectator nucleons. The observed anisotropy corresponds to a negative elliptic flow signal for $η$ mesons, indicating a preferred emission perpendicular to the reaction plane. In contrast, only small azimuthal anisotropies are observed for $π^{0}$ mesons. This may indicate that $η$ mesons freeze out earlier from the fire ball than pions.
Heavy-flavour hadrons are effective probes to study the Quark-Gluon Plasma (QGP) formed in ultra-relativistic heavy-ion collisions. The ALICE Collaboration measured the D-mesons (D$^{0}$, D$^{+}$, D*$^{+}$ and D$^{+}_{\text s}$) production in Pb-Pb collisions at $\sqrt{s_{\text{NN}}}$ = 5.02 TeV. The in-medium energy loss can be studied by means of the nuclear modification factor ($R_{\text{AA}}$). The comparison between the D$^{+}_{\text s}$ and the non-strange D-meson $R_{\text{AA}}$ can help to study the hadronisation mechanism of the charm quark in the QGP. In semi-central collisions the m…
A Large Ion Collider Experiment (ALICE) is one of the four large experiments at the Large Hadron Collider (LHC), and it is dedicated to the study of ultra-relativistic heavy-ion collisions, with the goal of investigating the properties of the high-density state of QCD matter produced in these collisions. The study of D meson production azimuthal anisotropy and the measurement of their elliptic flow (v2) can provide insight on the degree of thermalisation of charm quarks in the medium and on the charm hadronization mechanism. We present the measurement of the D+ and D0 meson v2 in Pb-Pb collisi…
The study of charm production in heavy-ion collisions is considered an excellent probe for the properties of the hot and dense medium created in heavy-ion collisions. Measurements of D-meson nuclear modification can provide strong constraints into the mechanisms of in-medium energy loss and charm flow in the medium. The measurement of $D^0$ elliptic flow in pPb collisions helps us understand the strength of charm quarks coupling to significantly reduced systems which demonstrate hydrodynamic properties. In this paper, the measurements of the $D^0$ nuclear modification factor in PbPb collisions…
A study of elliptic flow of open charm mesons, $D^0$ and $D_S ^\pm$ using quark coalescence as a mechanism of hadronization of heavy quarks implemented in conjunction with A Multi Phase Transport (AMPT) model has been presented. We have studied the transverse momentum dependence of the elliptic flow parameter at mid-rapidity ($|y|$ $<$ 1.0) for Au+Au collisions at $\sqrt{s_{NN}} = 200$ GeV (RHIC) and Pb+Pb collisions at $\sqrt{s_{NN}} = 2.76$ TeV (LHC) for different values of partonic interaction cross-section and QCD coupling constant. We have compared our calculations with the experimentally…
Heavy quarks are a powerful probe for investigating the properties of the Quark-Gluon Plasma created in heavy-ion collisions, since they are produced in initial hard scattering processes and experience all the stages of the medium evolution. ALICE has measured the production of $\mathrm{D}^0$, $\mathrm{D}^+$, $\mathrm{D}^{*+}$, and $\mathrm{D}_{\mathrm{s}}^+$ mesons at central rapidity in their hadronic decay channels in various collision systems and energies. We present recent results for D-meson production measured by the ALICE Collaboration in pp collisions at $\sqrt{s}=7$ and 2.76 TeV, Pb-…
The observation of meson and baryon grouping in the $R_{CP}$ and $v_2$ measurements at intermediate $p_T$ has been interpreted as a manifestation of bulk partonic matter hadronization through multi-parton dynamics such as recombination of partons. $ϕ$ mesons provide unique sensitivity to test these theoretical scenarios, since the $ϕ$ has a mass heavier than the proton and close to the hyperons. The $R_{CP}$ and $v_2$ measurements of $ϕ$ mesons from Run IV Au+Au collisions at $\sqrt{s_{NN}}=200$ GeV at STAR are presented. Energy and colliding system dependence of the $ϕ$ yields at mid-rapidity…
In this work we analyse the theoretical uncertainties on the predictions for the photoproduction of light vector mesons in coherent pp, pA and AA collisions at the LHC energies using the color dipole approach. In particular, we present our predictions for the rapidity distribution for rh0 and phi photoproduction and perform an analysis on the uncertainties associated to the choice of vector meson wavefunctionand the phenomenological models for the dipole cross section. Comparison is done with the recent ALICE analysis on coherent production of rho at 2.76 TeV in PbPb collisions.
We discuss coherent and incoherent photoproduction of $J/Ψ$ vector mesons in high energy heavy ion collisions. In a dipole picture for the photon both can be naturally related to the dipole cross section that is also probed in inclusive DIS. We compare results of a particular calculation to ALICE data.
Ultra-peripheral heavy ion collisions involve long range electromagnetic interactions at impact parameters larger than twice the nuclear radius, where no nucleon-nucleon collisions occur. We report on the first observation of rho meson production in dAu->d Au rho^0 and dAu-> n p Au rho^0.
We report the preliminary results of the azimuthal correlations between $D^{*\pm}$ mesons and charged hadrons ($D^{*}$-h) measured by the STAR experiment in proton+proton collisions at $\sqrt{s}$ = 500 GeV. Results at mid-rapidity in the transverse-momentum range 8 $\le$ $p^{D^{*}}_{T}$ $\le$ 20 GeV/$c$ are compared with light hadron triggered correlations (h-h) and PYTHIA predictions. We also present an exploratory study of azimuthal correlations between $D^{*+}$ and $D^{*-}$ mesons in p+p collisions. The prospects of measuring heavy-flavor triggered correlations in heavy-ion collisions at RH…
This review covers the recent experimental development on spin alignment measurements of $K^{*0}$ and $ϕ$ vector mesons in heavy-ion and pp collisions at RHIC and LHC energies. Measurements in $e^+e^-$ collisions at LEP energies are also discussed. Spin alignment of vector mesons are studied by measuring the second diagonal element $ρ_{00}$ of spin density matrix. The $ρ_{00}$ is obtained by measuring the angular distribution of vector meson decay daughter with respect to the quantization axis in vector meson rest frame. Measured $ρ_{00}$ values for vector mesons are found to be larger than 1/…
We report on the first evidence for a non-zero rapidity-odd directed flow ($v_{1}$) for $D^{0}$ and $\overline{D^{0}}$ mesons in 10-80\% centrality Au+Au collisions at $\sqrt{s_{\rm NN}}$ = 200~GeV measured with the STAR detector at RHIC. The slope of the $v_1$ rapidity dependence ($dv_{1}/dy$) averaged over $D^{0}$ and $\overline{D^{0}}$ mesons is -0.081 $\pm$ 0.021 $\pm$ 0.017, while that of charged kaons is -0.0030 $\pm$ 0.0001 $\pm$ 0.0002, suggesting significantly larger slope for the $D^{0}$ mesons. Models indicate that the large $dv_{1}/dy$ of $D^{0}$ mesons is sensitive to the initiall…
We present the results for the measurement of $ϕ$ meson production in $\sqrt{s_{NN}}$ = 200 GeV Au+Au and pp collisions at the Relativistic Heavy Ion Collider (RHIC). Using the event mixing technique, spectra and yields are obtained from the $ϕ\to K^{+}K^{-}$ decay channel for five centrality bins in Au+Au collisions and in pp collisions. We observe that the spectrum shape in Au+Au collisions depends weakly on the centrality and the shape of the spectrum in pp collisions is significantly different from that in Au+Au collisions.
The ALICE detector at the LHC studies $π^0$ and $η$ meson production by two complementary methods, using electromagnetic calorimeters and the central tracking system for converted photons. Production spectra of $π^0$ and $η$ mesons were measured with ALICE in pp collisions at LHC energies at mid-rapidity in a wide transverse momentum range. The spectrum and the nuclear modification factor $R_{AA}$ of $π^0$ measured in Pb-Pb collisions at different centralities, show a clear pattern of strong suppression in a hot QCD medium with respect to pp collisions.
We present recent result on strange and non-strange D-meson production measured with ALICE in Pb--Pb collisions at the LHC. In addition, the measurements of the $Λ_{\rm c}^+$-baryon production and of the $Λ_{\rm c}^+/{\rm D^0}$ ratio in pp, p--Pb, and, for the first time ever, Pb--Pb collisions are reported.
We argue that the NICA fixed target experiment will be able to provide very important new experimental data on dilepton and $ϕ$ meson production in the basically undiscovered energy domain between the SIS and SPS energies. Experimental information about elementary cross sections in this energy region is an essential ingredient of models of nuclear collisions in the same energy range.
We present first measurements of the $ϕ$-meson elliptic flow ($v_{2}(p_{T})$) and high statistics $p_{T}$ distributions for different centralities from $\sqrt{s_{NN}}$ = 200 GeV Au+Au collisions at RHIC. In minimum bias collisions the $v_{2}$ of the $ϕ$ meson is consistent with the trend observed for mesons. The ratio of the yields of the $Ω$ to those of the $ϕ$ as a function of transverse momentum is consistent with a model based on the recombination of thermal $s$ quarks up to $p_{T}\sim 4$ GeV/$c$, but disagrees at higher momenta. The nuclear modification factor ($R_{CP}$) of $ϕ$ follows th…
Heavy-flavour hadrons are recognised as a powerful probe for the characterisation of the deconfined medium created in heavy-ion collisions, the Quark-Gluon Plasma (QGP). The ALICE Collaboration measured the production of ${\rm D}^{0}$, ${\rm D}^{+}$, ${\rm D}^*$ and ${\rm D_s}^{+}$ mesons in Pb-Pb collisions at $\sqrt{s_{\rm NN}}=5.02~{\rm TeV}$. The measurement of the nuclear modification factor ($R_{\rm AA}$) provides a strong evidence of the in-medium parton energy loss. The comparison between the ${\rm D_s}^{+}$ and the non-strange D-meson $R_{\rm AA}$ can help to study the hadronisation m…
We present measurements of elliptic flow and event-by-event fluctuations established by the PHOBOS experiment. Elliptic flow scaled by participant eccentricity is found to be similar for both systems when collisions with the same number of participants or the same particle area density are compared. The agreement of elliptic flow between Au+Au and Cu+Cu collisions provides evidence that the matter is created in the initial stage of relativistic heavy ion collisions with transverse granularity similar to that of the participant nucleons. The event-by-event fluctuation results reveal that the in…
Polarized $p+p$ collisions provide insight into the structure of the nucleon. $A_N$ of eta mesons at forward rapidities are of particular interest, as asymmetries of other mesons observed both by PHENIX and other experiments show significant deviation from zero in the forward region. Several mechanisms have been proposed that attempt to explain these non-zero asymmetries, and a comparison of different probes may further constrain these models. Therefore, measurements of $A_N$ with inclusive eta mesons at forward rapidities are an important tool toward understanding the underlying mechanism. Us…
We present the results for the measurement of $ϕ$ meson production in $\sqrt{s_{NN}}$ = 200 GeV Au+Au and pp collisions at the Relativistic Heavy Ion Collider (RHIC). Using the event mixing technique, spectra and yields are obtained from the $ϕ\to K^{+}K^{-}$ decay channel for different centrality bins in Au+Au collisions and in pp collisions. We observe that the spectrum shape in Au+Au collisions depends weakly on the centrality and the shape of the spectrum in pp collisions is significantly different from that in Au+Au collisions. In Au+Au collisions, the extracted yield of $ϕ$ meson is flat…
Elliptic flow from nuclear collisions is a hadronic observable sensitive to the early stages of system evolution. We report first results on elliptic flow of charged particles at midrapidity in Au+Au collisions at sqrt(s_NN)=130 GeV using the STAR TPC at RHIC. The elliptic flow signal, v_2, averaged over transverse momentum, reaches values of about 6% for relatively peripheral collisions and decreases for the more central collisions. This can be interpreted as the observation of a higher degree of thermalization than at lower collision energies. Pseudorapidity and transverse momentum dependenc…
Experimental searches for modifications of vector mesons in the nuclear medium are reviewed. Data on $ρ,ω$ and $Φ$ mesons are presented. The results have been obtained in elementary reactions with proton and photon beams as well as in heavy-ion collisions. Compared to the free particle properties, the $ω$ and $Φ$ meson are found to drop in mass at normal nuclear matter density by 9-14% and 3.5% whereas their widths are reported to increase by factors of about 16 and 3.6, respectively. For the $ρ$ meson, conflicting results on in-medium mass shifts and broadening have been published. The experi…
The PHENIX experiment at RHIC measured $ω$, $η$ and $K_{S}^{0}$-meson production at high $p_{T}$ in $p+p$, $d+Au$ and $Au+Au$ collisions at $\sqrt{s_{NN}}=200$ $GeV$. Measurements performed in different hadronic decay channels give consistent results. The measured ratios of all three mesons to $π^{0}$ are found to be flat as a function of $p_{T}$ in $p+p$ collisions and equal to $ω/π^{0}=0.81\pm0.02\pm0.07$, $η/π^{0}=0.48\pm0.02\pm0.02$ and $K_{S}^{0}/π^{0}=0.45\pm0.01\pm0.05$. Nuclear modification factor measured for $ω$-mesons in central Au+Au collisions is $R_{AA}=0.4\pm0.15$.
In this proceedings, we present our first measurements of $ϕ$ meson and $Ξ^-$ hyperon production in Au+Au collisions at $\sqrt{s_{NN}}$ = 3 GeV. Various models including thermal and transport model calculations are compared to data, these results imply that the matter produced in the 3 GeV Au+Au collisions is considerably different from that at higher energies.
A compilation of recently measured STAR data for elliptic flow ($v_{2}$) of $ϕ$ mesons in RHIC Beam Energy Scan program and comparison with a multiphase transport model (AMPT) has been presented. The experimental data at $\sqrt{s_{NN}}$ $\geq$ 19.6 GeV agrees well with string melting version of the AMPT model. The model includes partonic interactions and quark coalescence as a mechanism of hadronization. This indicates that there is a substantial contribution to collectivity from partonic interactions at $\sqrt{s_{NN}}$ $\geq$ 19.6 GeV. The measured $ϕ$-meson $v_{2}$ at $\sqrt{s_{NN}}$ = 7.7 a…
The azimuthal angular distribution of K+ mesons has been measured in Au + Au collisions at 1 AGeV. In peripheral and semi-central collisions, K+ mesons preferentially are emitted perpendicular to the reaction plane. The strength of the azimuthal anisotropy of K+ emission is comparable to the one of pions. No in-plane flow was found for K+ mesons near projectile and target rapidity.
Heavy quarks are sensitive probes of the colour-deconfined medium formed in ultra-relativistic heavy-ion collisions, the Quark-Gluon Plasma (QGP). The ALICE Collaboration measured the production of $\rm D^0$, $\rm D^+$, and $\rm D^{*+}$ mesons in Pb-Pb collisions at $\sqrt{s_{\rm NN}}=5.02$ TeV. The properties of the in-medium energy loss are investigated via the measurement of the nuclear modification factor ($R_{\rm AA}$) of non-strange D mesons. The modification of the D-meson transverse momentum ($p_{\rm T}$) distributions inside the jet is studied via the measurement of the D-meson tagged…
Azimuthal distributions of pi+, K+ and K- mesons have been measured in Au+Au reactions at 1.5 AGeV and Ni+Ni reactions at 1.93 AGeV. In semi-central collisions at midrapidity, pi+ and K+ mesons are emitted preferentially perpendicular to the reaction plane in both collision systems. In contrast for K- mesons in Ni+Ni reactions an in-plane elliptic flow was observed for the first time at these incident energies.
We investigate the elliptic and the triangular flow of heavy mesons in ultrarelativistic heavy-ion collisions at RHIC and the LHC. The dynamics of heavy quarks is coupled to the locally thermalized and fluid dynamically evolving quark-gluon plasma. The elliptic flow of $D$ mesons and the centrality dependence measured at the LHC is well reproduced for purely collisional and bremsstrahlung interactions. Due to the event-by-event fluctuating initial conditions from the EPOS2 model, the $D$ meson triangular flow is predicted to be nonzero at $\sqrt{s}=200$ GeV and $\sqrt{s}=2.76$ TeV. We study th…
The elliptic flows in both Cu+Cu and Au+Au collisions at the Relativistic Heavy Ion Collider are studied in a multi-phase transport model. For both collisions at same reduced impact parameter and minimum bias collisions, the elliptic flow of partons in Cu+Cu collisions is about a factor of three smaller than that in Au+Au collisions at same energy. The reduction factor is similar to the ratio of the sizes of the two colliding systems and is also related to the combined effects of initial energy density and spatial elliptic deformation in the two reactions. A similar system size dependence is a…
The ALICE Collaboration has measured the production of prompt D mesons in pPb collisions at sqrt(s_NN) = 5.02 TeV in the rapidity range -0.04 < y_{cms} < 0.96 via the exclusive reconstruction of their hadronic decays D0->K-pi+, D+->K- pi+ pi+, D*+->D0 pi+ and Ds->phi pi+. The pT-differential production cross sections and the pT-dependent nuclear modification factors with respect to a proton-proton reference, RpPb, are presented.
This paper presents results of elliptic flow measurements at moderate high transverse momentum in Au+Au collisions using the STAR detector at RHIC. Sizable $v_{2}$ is found up to 7 GeV/c in transverse momentum. Non-flow effects are discussed comparing correlations in p+p collisions and Au+Au collisions. $v_{2}$ from two-, four- and six-particle cumulant are shown and discussed.
Collective flow reflects dynamical evolution in high-energy heavy ion collisions. In particular, the strange hadron elliptic flow reflects early collision dynamics. We present results from a systematic analysis of the centrality dependence of strange hadron elliptic flow ($v_2$) measurement of $K_{S}^{0}$, $Λ$ and $Ξ$ for Cu + Cu collisions at 200 GeV. Results for Cu + Cu collisions are compared with results previously reported for Au + Au collisions. We will also compare our data with results from ideal hydrodynamic calculations.
