Function Of Transverse Momentum Research Articles

Measurement of prompt D0, D+, D*+, and {mathrm{D}}_{mathrm{S}}^{+} production in p\u2013Pb collisions at sqrt{{mathrm{s}}_{mathrm{NN}}} = 5.02 TeV

The measurement of the production of prompt D0, D+, D*+, and {mathrm{D}}_{mathrm{S}}^{+} mesons in proton–lead (p–Pb) collisions at the centre-of-mass energy per nucleon pair of sqrt{s_{mathrm{NN}}} = 5.02 TeV, with an integrated luminosity of 292 ± 11 μb−1, are reported. Differential production cross sections are measured at mid-rapidity (−0.96 < ycms< 0.04) as a function of transverse momentum (pT) in the intervals 0 < pT< 36 GeV/c for D0, 1 < pT< 36 GeV/c for D+ and D*+, and 2 < pT< 24 GeV/c for D+ mesons. For each species, the nuclear modification factor RpPb is calculated as a function of pT using a proton-proton (pp) ref- erence measured at the same collision energy. The results are compatible with unity in the whole pT range. The average of the non-strange D mesons RpPb is compared with theoretical model predictions that include initial-state effects and parton transport model predictions. The pT dependence of the D0, D+, and D*+ nuclear modification factors is also reported in the interval 1 < pT< 36 GeV/c as a function of the collision centrality, and the central-to-peripheral ratios are computed from the D-meson yields measured in different centrality classes. The results are further compared with charged-particle measurements and a similar trend is observed in all the centrality classes. The ratios of the pT-differential cross sections of D0, D+, D*+, and {mathrm{D}}_{mathrm{S}}^{+} mesons are also reported. The {mathrm{D}}_{mathrm{S}}^{+} and D+ yields are compared as a function of the charged-particle multiplicity for several pT intervals. No modification in the relative abundances of the four species is observed with respect to pp collisions within the statistical and systematic uncertainties.

Measurement of ϒ(1S) Elliptic Flow at Forward Rapidity in Pb-Pb Collisions at sqrt[s_{NN}]=5.02 TeV.

The first measurement of the ϒ(1S) elliptic flow coefficient (v_{2}) is performed at forward rapidity (2.5<y<4) in Pb-Pb collisions at sqrt[s_{NN}]=5.02 TeV with the ALICE detector at the LHC. The results are obtained with the scalar product method and are reported as a function of transverse momentum (p_{T}) up to 15 GeV/c in the 5%-60% centrality interval. The measured ϒ(1S)v_{2} is consistent with 0 and with the small positive values predicted by transport models within uncertainties. The v_{2} coefficient in 2<p_{T}<15 GeV/c is lower than that of inclusive J/ψ mesons in the same p_{T} interval by 2.6 standard deviations. These results, combined with earlier suppression measurements, are in agreement with a scenario in which the ϒ(1S) production in Pb-Pb collisions at LHC energies is dominated by dissociation limited to the early stage of the collision, whereas in the J/ψ case there is substantial experimental evidence of an additional regeneration component.

Anisotropic flow of charged and identified hadrons at FAIR energies and its dependence on the nuclear equation of state

In this article, we examine the equation of state (EoS) dependence of the anisotropic flow parameters ($v_{1}$, $v_{2}$ and $v_{4}$) of charged and identified hadrons, as a function of transverse momentum ($p_{\rm T}$), rapidity ($y_{c.m.}$) and the incident beam energy ($\rm E_{\rm Lab}$) in mid-central Au + Au collisions in the energy range $\rm E_{\rm Lab} = 6 -25$ A GeV. Simulations are carried out by employing different variants of the Ultra-relativistic Quantum Molecular Dynamics (UrQMD) model, namely the pure transport (cascade) mode and the hybrid mode. In the hybrid mode, transport calculations are coupled with the ideal hydrodynamical evolution. Within the hydrodynamic scenario, two different equations of state (EoS) viz. Hadron gas and Chiral + deconfinement EoS have been employed separately to possibly mimic the hadronic and partonic scenarios, respectively. It is observed that the flow parameters are sensitive to the onset of hydrodynamic expansion of the fireball in comparison to the pure transport approach. The results would be useful as predictions for the upcoming low energy experiments at Facility for Antiproton and Ion Research (FAIR) and Nuclotron-based Ion Collider fAcility (NICA).

Multiplicity dependence of light (anti-)nuclei production in p–Pb collisions at [formula omitted] TeV

The measurement of the deuteron and anti-deuteron production in the rapidity range −1<y<0 as a function of transverse momentum and event multiplicity in p–Pb collisions at sNN = 5.02 TeV is presented. (Anti-)deuterons are identified via their specific energy loss dE/dx and via their time-of-flight. Their production in p–Pb collisions is compared to pp and Pb–Pb collisions and is discussed within the context of thermal and coalescence models. The ratio of integrated yields of deuterons to protons (d/p) shows a significant increase as a function of the charged-particle multiplicity of the event starting from values similar to those observed in pp collisions at low multiplicities and approaching those observed in Pb–Pb collisions at high multiplicities. The mean transverse particle momenta are extracted from the deuteron spectra and the values are similar to those obtained for p and Λ particles. Thus, deuteron spectra do not follow mass ordering. This behaviour is in contrast to the trend observed for non-composite particles in p–Pb collisions. In addition, the production of the rare He3 and He‾3 nuclei has been studied. The spectrum corresponding to all non-single diffractive p-Pb collisions is obtained in the rapidity window −1<y<0 and the pT-integrated yield dN/dy is extracted. It is found that the yields of protons, deuterons, and He3, normalised by the spin degeneracy factor, follow an exponential decrease with mass number.

Distribution of strange particles transverse momentum and rapidity in high energy proton–proton collisions at s = 0.9 TeV at LHC

In this paper, we have studied the spectra of strange particles in pp collision at [Formula: see text] = 0.9 TeV by using different simulation models, EPOS-1.99, SIBYLL-2.3c, QGSJETII-04 and EPOS-LHC. The transverse momentum and rapidity distribution in the [Formula: see text] range of [Formula: see text] GeV/c and [Formula: see text] GeV/c, respectively, are investigated for the strange particles, [Formula: see text], [Formula: see text], [Formula: see text]. Similarly, a comparative study is done for the ratio of [Formula: see text] and [Formula: see text] as a function of transverse momentum and rapidity. The validity of simulation models is tested by comparing simulation results to the CMS experimental data at [Formula: see text] = 0.9 TeV. For [Formula: see text] distributions, the EPOS-LHC model in the [Formula: see text] range [Formula: see text] GeV/c, [Formula: see text] GeV/c and in [Formula: see text] GeV/c while EPOS-1.99 model in the [Formula: see text] range [Formula: see text] GeV/c and QGSJETII-04 model in the [Formula: see text] range [Formula: see text] GeV/c as well as, [Formula: see text] GeV/c explain the experimental data well. For the, [Formula: see text] and [Formula: see text] versus transverse momentum distributions, EPOS-LHC model in the [Formula: see text] range of, [Formula: see text] GeV/c and [Formula: see text] GeV/c, EPOS-1.99 model in the [Formula: see text] range, [Formula: see text] GeV/c, SIBYLL-2.3c model in the [Formula: see text] range, [Formula: see text] GeV/c and QGSJETII-04 model in the [Formula: see text] range [Formula: see text] GeV/c explain the experimental data very well. Similarly, for [Formula: see text] and [Formula: see text] versus rapidity distribution QGSJETII-04 predictions in the rapidity region, [Formula: see text], [Formula: see text], and [Formula: see text], while EPOS-LHC model in the region, [Formula: see text], very well explained the experimental data. Although good comparison of the models predictions with the experimental data is observed, none of them completely describe the experimental data the spectra of strange particles over the entire [Formula: see text] and [Formula: see text] range.

Measurements of the transverse-momentum-dependent cross sections of J/ψ production at mid-rapidity in proton+proton collisions at s=510 and 500 GeV with the STAR detector

We present measurements of the differential cross sections of inclusive $J/\psi$ meson production as a function of transverse momentum ($p_{T}^{J/\psi}$) using the $\mu^{+}\mu^{-}$ and $e^{+}e^{-}$ decay channels in proton+proton collisions at center-of-mass energies of 510 and 500 GeV, respectively, recorded by the STAR detector at the Relativistic Heavy Ion Collider. The measurement from the $\mu^{+}\mu^{-}$ channel is for 0 $< p_{T}^{J/\psi} <$ 9 GeV/$c$ and rapidity range $|y^{J/\psi}| < $ 0.4, and that from the $e^{+}e^{-}$ channel is for 4 $< p_{T}^{J/\psi} <$ 20 GeV/$c$ and $|y^{J/\psi}| < $ 1.0. The $\psi(2S)$ to $J/\psi$ ratio is also measured for 4 $< p_{T}^{\rm meson} <$ 12 GeV/$c$ through the $e^{+}e^{-}$ decay channel. Model calculations, which incorporate different approaches toward the $J/\psi$ production mechanism, are compared with experimental results and show reasonable agreement within uncertainties.

Measurement of [formula omitted] meson production in pp and PbPb collisions at [formula omitted] TeV

The production cross sections of Bs0 mesons and charge conjugates are measured in proton-proton (pp) and PbPb collisions via the exclusive decay channel Bs0→J/ψϕ→μ+μ−K+K− at a center-of-mass energy of 5.02 TeV per nucleon pair and within the rapidity range |y|<2.4 using the CMS detector at the LHC. The pp measurement is performed as a function of transverse momentum (pT) of the Bs0 mesons in the range of 7 to 50 GeV/c and is compared to the predictions of perturbative QCD calculations. The Bs0 production yield in PbPb collisions is measured in two pT intervals, 7 to 15 and 15 to 50 GeV/c, and compared to the yield in pp collisions in the same kinematic region. The nuclear modification factor (RAA) is found to be 1.5±0.6(stat)±0.5(syst) for 7–15 GeV/c, and 0.87±0.30(stat)±0.17(syst) for 15–50 GeV/c, respectively. Within current uncertainties, the Bs0 results are consistent with models of strangeness enhancement, and suppression by parton energy loss, as observed for the B+ mesons.

Identical pion intensity interferometry in central Au + Au collisions at 1.23A GeV

We investigate identical pion HBT intensity interferometry in central Au+Au collisions at 1.23A GeV. High-statistics π−π− and π+π+ data are measured with HADES at SIS18/GSI. The radius parameters, derived from the correlation function depending on relative momenta in the longitudinally comoving system and parametrized as three-dimensional Gaussian distribution, are studied as function of transverse momentum. A substantial charge-sign difference of the source radii is found, particularly pronounced at low transverse momentum. The extracted source parameters agree well with a smooth extrapolation of the center-of-mass energy dependence established at higher energies, extending the corresponding excitation functions down towards a very low energy.

Anisotropic hydrodynamic modeling of 200 GeV Au-Au collisions

We compare phenomenological results from 3+1d quasiparticle anisotropic hydrodynamics (aHydroQP) with experimental data collected in RHIC 200 GeV Au-Au collisions. We present comparisons of identified particle spectra in different centrality clases, charged particle multiplicity versus pseudorapidity, identified particle multiplicity versus centrality across a wide range of particle species, identified particle elliptic flow versus transverse momentum, and charged particle elliptic flow as a function of transverse momentum and rapidity. We use the same aHydroQP and hadronic production/feed down codes that were used previously to describe LHC 2.76 TeV data. The aHydroQP hydrodynamic model includes the effects of both shear and bulk viscosities in addition to an infinite number of transport coefficients computed self-consistently in the relaxation time approximation. To convert to the final state hadrons, we use anisotropic Cooper-Frye freeze-out performed on a fixed-energy-density hypersurface and compute the production/feed down using a customized version of Therminator 2. We find good agreement with many heavy-ion collision observables using only smooth Glauber initial conditions parameterized by an initial central temperature of T_0 = 455 MeV, a constant shear viscosity to entropy density ratio eta/s= 0.179, and a switching (freeze-out) temperature of T_FO=130 MeV.

Production and polarization of prompt ϒ(nS) in the improved color evaporation model using the kT -factorization approach

We calculate the polarization of prompt $\varUpsilon$($n$S) production in the improved color evaporation model at leading order employing the $k_T$-factorization approach. We present the polarization parameter $\lambda_\vartheta$ of prompt $\varUpsilon$($n$S) as a function of transverse momentum in $p+p$ and $p+\bar{p}$ collisions to compare with data in the helicity, Collins-Soper and Gottfried-Jackson frames. We also present calculations of the bottomonium production cross sections as a function of transverse momentum and rapidity. This is the first $p_T$-dependent calculation of bottomonium production and polarization in the improved color evaporation model. We find agreement with both bottomonium cross sections and polarization measurements.

Study of J/\u03c8 azimuthal anisotropy at forward rapidity in Pb-Pb collisions at sqrt{s_{mathrm{NN}}}=5.02 TeV

The second (v2) and third (v3) flow harmonic coefficients of J/ψ mesons are measured at forward rapidity (2.5 < y < 4.0) in Pb-Pb collisions at sqrt{s_{mathrm{NN}}}=5.02 TeV with the ALICE detector at the LHC. Results are obtained with the scalar product method and reported as a function of transverse momentum, pT, for various collision centralities. A positive value of J/ψ v3 is observed with 3.7σ significance. The measurements, compared to those of prompt D0 mesons and charged particles at mid-rapidity, indicate an ordering with vn(J/ψ) < vn(D0) < vn(h±) (n = 2, 3) at low and intermediate pT up to 6 GeV/c and a convergence with v2(J/ψ) ≈ v2(D0) ≈ v2(h±) at high pT above 6–8 GeV/c. In semi-central collisions (5–40% and 10–50% centrality intervals) at intermediate pT between 2 and 6 GeV/c, the ratio v3/v2 of J/ψ mesons is found to be significantly lower (4.6σ) with respect to that of charged particles. In addition, the comparison to the prompt D0-meson ratio in the same pT interval suggests an ordering similar to that of the v2 and v3 coefficients. The J/ψ v2 coefficient is further studied using the Event Shape Engineering technique. The obtained results are found to be compatible with the expected variations of the eccentricity of the initial-state geometry.

Non-linear flow modes of identified particles in Pb–Pb collisions at [formula omitted] with the ALICE detector

The non-linear flow modes, v4,22, v5,32 and v6,33 as a function of transverse momentum (pT) have been measured for the first time in Pb–Pb collisions at sNN=5.02TeV for identified particles, i.e. charged pions, kaons and (anti-)protons. These observables probe the contribution of the second and third initial anisotropy coefficients to the higher order flow harmonics. Interestingly, all the characteristic features observed in previous pT-differential as well as pT-integrated measurements (e.g. v2 and v3) for various particle species are present in these measurements, i.e. increase of magnitude with increasing centrality percentile, a mass ordering in the low pT region and a particle type grouping in the intermediate pT region. The results cover 0–1% (ultra-central collisions), 10–20% (mid-central collisions) and 40–50% (mid-peripheral collisions) centrality intervals and allow to test models that attempt to describe initial conditions and the mode-coupling of different harmonics.

ϒ measurements in Au+Au collisions at [formula omitted] with the STAR experiment

We present the latest measurements of ϒ production in Au+Au collisions at sNN=200GeV via both di-muon and di-electron decay channels by the STAR experiment at RHIC. With the addition of the 2016 data set to those taken in 2011 and 2014, the precision of ϒ measurements is significantly improved compared to previous preliminary results, especially for the excited ϒ states. The nuclear modification factors for the ground and excited ϒ states are shown as a functions of transverse momentum or centrality, and are compared to results from the LHC as well as to theoretical calculations.

Measurement of anisotropic flow in XeXe collisions at 5.44 TeV with the CMS experiment

New measurements of anisotropic flow in XeXe collisions at a center-of-mass energy of 5.44 TeV per nucleon pair, collected by the CMS experiment at the LHC, are presented. The ν2, ν3 and ν4 Fourier coefficients of the anisotropic azimuthal distribution are obtained employing three different analysis techniques: two-particle correlations, the scalar product method, and multiparticle cumulants, which have different sensitivities to non-flow and flow fluctuation effects. The results are shown as a function of transverse momentum (pT) for various centrality selections, and compared with corresponding results from PbPb collisions. These new measurements in a smaller nucleus-nucleus system than PbPb provide additional insights into the system-size dependence of the collective flow induced by the dominant collision geometry and its fluctuations. In particular, these results, compared to theoretical predictions and Monte Carlo generators, will provide important details on the system size dependence of the medium response in heavy ion collisions. They also offer a unique opportunity to study the onset of flow from small to large systems.

Measurements of directed and elliptic flow for D0 and [formula omitted] mesons using the STAR detector at RHIC

We report on the first evidence for a non-zero rapidity-odd directed flow (νv1) for D0 and D0‾ mesons in 10-80% centrality Au+Au collisions at sNN=200GeV measured with the STAR detector at RHIC. The slope of the ν1 rapidity dependence (dν1/dy) averaged over D0 and D0‾ mesons is -0.081 ± 0.021 ± 0.017, while that of charged kaons is -0.0030 ± 0.0001 ± 0.0002, suggesting significantly larger slope for the D0 mesons. Models indicate that the large dν1/dy of D0 mesons is sensitive to the initially tilted source. We also present a new measurement of the D0 meson elliptic flow (ν2) as a function of transverse momentum (pT) in Au+Au collisions at sNN=200GeV with an improved precision with respect to the previously published results.The D0ν2 results are compared to those of light-flavor hadrons to test the number-of-constituent-quark (NCQ) scaling. Both the ν1 and ν2 results are compared to recent hydrodynamic and transport model calculations.

NA61/SHINE measurements of anisotropic flow relative to the spectator plane in Pb+Pb collisions at 30A GeV/c

We present an analysis of the anisotropic flow harmonics in Pb+Pb collisions at beam momenta of 30A GeV/c collected by the NA61/SHINE experiment in the year 2016. Directed and elliptic flow coefficients are measured relative to the spectator plane estimated with the Projectile Spectators Detector (PSD). The flow coefficients are reported as a function of transverse momentum in different classes of collision centrality. The results are compared with a new analysis of the NA49 data for Pb+Pb collisions at 40A GeV using forward calorimeters (VCal and RCal) for event plane estimation.

Energy and system dependence of nuclear modification factors of inclusive charged particles and identified light hadrons measured in p–Pb, Xe–Xe and Pb–Pb collisions with ALICE

We report recent ALICE results on primary charged particle and neutral meson production in pp, p–Pb, Pb–Pb and Xe–Xe collisions at LHC energies. In this article, measurements of the nuclear modification factors RAA of primary charged particles and of light neutral mesons in Pb–Pb, in Xe–Xe and in p–Pb collisions in a wide pT range and different centrality classes are discussed. We compare the nuclear modification factors obtained for different collision systems as a function of transverse momentum, collision centrality as well as charged particle multiplicity (dNch/dη). We also present comparison of experimental results to model calculations.

ϕ Meson and K*0 Global Spin Alignment at STAR

The spin alignment of ϕ and K*0 vector mesons is sensitive to different hadronization scenarios and the vorticity of the colliding system. We present STAR's measurement of global spin alignment of ϕ and K*0 for Au + Au collisions at sNN=7.7 (ϕ meson only), 11.5, 14.5 (K*0 meson only) 19.6, 27, 39 and 200 (ϕ meson only) GeV. The alignment is quantified by the diagonal spin density matrix element, ρ00, with respect to the normal of the event plane. The ρ00 measurement based on the 1st- and 2nd-order event planes are presented. The results are shown as a function of transverse momentum, collision centrality and beam energy The implications of our results on the vorticity and the hadronization scenarios are discussed.

ϒ suppression at forward rapidity in Pb–Pb collisions at [formula omitted

Inclusive ϒ(1S) and ϒ(2S) production have been measured in Pb–Pb collisions at the centre-of-mass energy per nucleon–nucleon pair sNN=5.02 TeV, using the ALICE detector at the CERN LHC. The ϒ mesons are reconstructed in the centre-of-mass rapidity interval 2.5<y<4 and in the transverse-momentum range pT<15 GeV/c, via their decays to muon pairs. In this Letter, we present results on the inclusive ϒ(1S) nuclear modification factor RAA as a function of collision centrality, transverse momentum and rapidity. The ϒ(1S) and ϒ(2S) RAA, integrated over the centrality range 0–90%, are 0.37±0.02(stat)±0.03(syst) and 0.10±0.04(stat)±0.02(syst), respectively, leading to a ratio RAAϒ(2S)/RAAϒ(1S) of 0.28±0.12(stat)±0.06(syst). The observed ϒ(1S) suppression increases with the centrality of the collision and no significant variation is observed as a function of transverse momentum and rapidity.

Production and polarization of prompt J/ψ in the improved color evaporation model using the kT -factorization approach

We calculate the polarization of prompt $J/\psi$ production in the improved color evaporation model at leading order employing the $k_T$-factorization approach. In this paper, we present the polarization parameter $\lambda_\vartheta$ of prompt $J/\psi$ as a function of transverse momentum in $p+p$ and $p$ + A collisions to compare with data in the helicity, Collins-Soper and Gottfried-Jackson frames. We also present calculations of the charmonium production cross sections as a function of rapidity and transverse momentum. This is the first $p_T$-dependent calculation of charmonium polarization in the improved color evaporation model. We find agreement with both charmonium cross sections and polarization measurements.