Dimuon Decay Channel Research Articles

Quark flavor dependence of particle flow in nucleus-nucleus collisions measured by PHENIX

We present measurements of the nuclear modification factor RAA and azimuthal anisotropy v2 for electrons from charm and bottom hadron decays at mid-rapidity (|y|<0.35) and for inclusive J/ψ via the di-muon decay channel at forward-rapidity (1.2<|y|<2.2) in Au+Au collisions at sNN=200GeV. Charm and bottom decay electron RAA can be described by a T-Matrix model based on a strongly coupling QGP scenario (2πTD=4) as well as SUBATECH and DGLV models based on quark mass dependent energy loss. Finite charm and bottom decay electron v2 are observed with significances of 3.5 and 1.1 σ. The charm decay electron v2 is better described by the Langevin + viscous hydro calculation with coalescence than that without coalescence. The charm decay electron v2 is larger than inclusive J/ψv2 with a significance of 0.7 σ. These observations hint that charm quarks are dragged by the medium and hadronize via coalescence with light-flavor quarks. Complete analyses of 36 billion Au+Au collision events from RHIC 2014 and 2016 runs increase the integrated luminosity by a factor of 8 for the charm and bottom decay electron RAA measurements, by a factor of 2 for the charm and bottom decay electron v2 measurements, and by a factor of 5 for the inclusive J/ψv2 measurements.

J/\u03c8 production as a function of charged-particle multiplicity in p-Pb collisions at sqrt{s_{mathrm{NN}}} = 8.16 TeV

Inclusive J/ψ yields and average transverse momenta in p-Pb collisions at a center-of-mass energy per nucleon pair sqrt{s_{mathrm{NN}}} = 8.16 TeV are measured as a function of the charged-particle pseudorapidity density with ALICE. The J/ψ mesons are reconstructed at forward (2.03 < ycms< 3.53) and backward (−4.46 < ycms< −2.96) center-of-mass rapidity in their dimuon decay channel while the charged-particle pseudorapidity density is measured around midrapidity. The J/ψ yields at forward and backward rapidity normalized to their respective average values increase with the normalized charged-particle pseudorapidity density, the former showing a weaker increase than the latter. The normalized average transverse momenta at forward and backward rapidity manifest a steady increase from low to high charged-particle pseudorapidity density with a saturation beyond the average value.

Z-boson production in p-Pb collisions at sqrt{s_{mathrm{NN}}} = 8.16 TeV and Pb-Pb collisions at sqrt{s_{mathrm{NN}}} = 5.02 TeV

Measurement of Z-boson production in p-Pb collisions at sqrt{s_{mathrm{NN}}} = 8.16 TeV and Pb-Pb collisions at sqrt{s_{mathrm{NN}}} = 5.02 TeV is reported. It is performed in the dimuon decay channel, through the detection of muons with pseudorapidity −4 < ημ< −2.5 and transverse momentum {p}_{mathrm{T}}^{mu } > 20 GeV/c in the laboratory frame. The invariant yield and nuclear modification factor are measured for opposite-sign dimuons with invariant mass 60 < mμμ< 120 GeV/c2 and rapidity 2.5 < {y}_{mathrm{cms}}^{mu mu} < 4. They are presented as a function of rapidity and, for the Pb-Pb collisions, of centrality as well. The results are compared with theoretical calculations, both with and without nuclear modifications to the Parton Distribution Functions (PDFs). In p-Pb collisions the center-of-mass frame is boosted with respect to the laboratory frame, and the measurements cover the backward (−4.46 < {y}_{mathrm{cms}}^{mu mu} < −2.96) and forward (2.03 < {y}_{mathrm{cms}}^{mu mu} < 3.53) rapidity regions. For the p-Pb collisions, the results are consistent within experimental and theoretical uncertainties with calculations that include both free-nucleon and nuclear-modified PDFs. For the Pb-Pb collisions, a 3.4σ deviation is seen in the integrated yield between the data and calculations based on the free-nucleon PDFs, while good agreement is found once nuclear modifications are considered.

ϒ production in p–Pb collisions at [formula omitted

ϒ production in p–Pb interactions is studied at the centre-of-mass energy per nucleon–nucleon collision sNN=8.16 TeV with the ALICE detector at the CERN LHC. The measurement is performed reconstructing bottomonium resonances via their dimuon decay channel, in the centre-of-mass rapidity intervals 2.03<ycms<3.53 and −4.46<ycms<−2.96, down to zero transverse momentum. In this work, results on the ϒ(1S) production cross section as a function of rapidity and transverse momentum are presented. The corresponding nuclear modification factor shows a suppression of the ϒ(1S) yields with respect to pp collisions, both at forward and backward rapidity. This suppression is stronger in the low transverse momentum region and shows no significant dependence on the centrality of the interactions. Furthermore, the ϒ(2S) nuclear modification factor is evaluated, suggesting a suppression similar to that of the ϒ(1S). A first measurement of the ϒ(3S) has also been performed. Finally, results are compared with previous ALICE measurements in p–Pb collisions at sNN=5.02 TeV and with theoretical calculations.

J/ψ and ψ(2S) production at forward rapidity in p+p collisions at s=510 GeV

The PHENIX experiment at the Relativistic Heavy Ion Collider has measured the differential cross section, mean transverse momentum, mean transverse momentum squared of inclusive J/ψ, and cross section ratio of ψ(2S) to J/ψ at forward rapidity in p+p collisions at s=510 GeV via the dimuon decay channel. Comparison is made to inclusive J/ψ cross sections measured at s=200 GeV and 2.76–13 TeV. The result is also compared to leading-order nonrelativistic QCD calculations coupled to a color-glass-condensate description of the low-x gluons in the proton at low transverse momentum (pT) and to next-to-leading order nonrelativistic QCD calculations for the rest of the pT range. These calculations overestimate the data at low pT. While consistent with the data within uncertainties above ≈3 GeV/c, the calculations are systematically below the data. The total cross section times the branching ratio is BR dσppJ/ψ/dy(1.2<|y|<2.2,0<pT<10 GeV/c)=54.3±0.5(stat)±5.5(syst) nb.4 MoreReceived 1 January 2020Accepted 19 February 2020DOI:https://doi.org/10.1103/PhysRevD.101.052006Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI. Funded by SCOAP3.Published by the American Physical SocietyPhysics Subject Headings (PhySH)Research AreasLeptonic, semileptonic & radiative decaysParticle productionRelativistic heavy-ion collisionsPhysical SystemsCharmed mesonsMuonsTechniquesHadron collidersParticles & Fields

Studies of J/\u03c8 production at forward rapidity in Pb\u2013Pb collisions at sqrt{s_{mathrm{NN}}} = 5.02 TeV

The inclusive J/ψ production in Pb–Pb collisions at the center-of-mass energy per nucleon pair sqrt{s_{mathrm{NN}}} = 5.02 TeV, measured with the ALICE detector at the CERN LHC, is reported. The J/ψ meson is reconstructed via the dimuon decay channel at forward rapidity (2.5 < y < 4) down to zero transverse momentum. The suppression of the J/ψ yield in Pb–Pb collisions with respect to binary-scaled pp collisions is quantified by the nuclear modification factor (RAA). The RAA at sqrt{s_{mathrm{NN}}} = 5.02 TeV is presented and compared with previous measurements at sqrt{s_{mathrm{NN}}} = 2.76 TeV as a function of the centrality of the collision, and of the J/ψ transverse momentum and rapidity. The inclusive J/ψ RAA shows a suppression increasing toward higher transverse momentum, with a steeper dependence for central collisions. The modification of the J/ψ average transverse momentum and average squared transverse momentum is also studied. Comparisons with the results of models based on a transport equation and on statistical hadronization are carried out.

Charmonium production in pp, p+Pb and Pb+Pb collisions with CMS experiment

We report the measurements of the prompt and non-prompt J/ψ and ψ(2S) nuclear modification factors (RAA) using pp and PbPb data and the RpPb using pPb data collected by CMS at the LHC. All measurements were performed via the dimuon decay channel. The RAA analysis is based on PbPb and pp data samples collected at √sNN = 5.02 TeV in 2015, corresponding to integrated luminosities of 464 μb−1 and 28 pb−1. These measurements are performed in the dimuon rapidity range of |y| < 2.4 as a function of centrality, rapidity, and transverse momentum (pT) from pT = 3GeV/c in the most forward region and up to 50 GeV/c. The RpPb analysis based on pPb data, is performed for prompt J/ψ and ψ(2S) in different kinematic bins of pT and rapidity.

Quarkonium Production Measurements with the ALICE Detector at the LHC

In (ultra-)relativistic heavy-ion collisions, the strongly interactingmatter is predicted to undergo a phase transition into a plasma of deconfinedquarks and gluons (QGP) and quarkonia probe different aspects of this medium.However, the medium modification of quarkonium production includes also the contribution of cold nuclear matter effects (CNM), such as shadowing or nuclear break-up in addition to QGP effects. Proton--nucleus collisions, where no QGP is expected, are used to measure cold nuclear matter effects on quarkonium production. Vacuum production of quarkonia is modelled in proton--proton (pp) collisions, which are used as reference for both heavy-ion and proton--nucleus collisions. Besides serving as reference, results in pp collisions represent a benchmark test of QCD based models in both perturbative and non-perturbative regimes. The ALICE detector has unique capabilities at the LHC for measuring quarkonia down to zero transverse momentum. Measurements are carried out at both central and forward rapidity, in the dielectron and dimuon decay channel, respectively. In this contribution the latest quarkonium measurements for various energies and colliding systems, performed by the ALICE Collaboration during the LHC Run-2 period, will be discussed.

Measurement of inclusive J/ψ suppression in Au+Au collisions at [formula omitted] GeV through the dimuon channel at STAR

J/ψ suppression has long been considered a sensitive signature of the formation of the Quark-Gluon Plasma (QGP) in relativistic heavy-ion collisions. In this letter, we present the first measurement of inclusive J/ψ production at mid-rapidity through the dimuon decay channel in Au+Au collisions at sNN=200 GeV with the STAR experiment. These measurements became possible after the installation of the Muon Telescope Detector was completed in 2014. The J/ψ yields are measured in a wide transverse momentum (pT) range of 0.15 GeV/c to 12 GeV/c from central to peripheral collisions. They extend the kinematic reach of previous measurements at RHIC with improved precision. In the 0-10% most central collisions, the J/ψ yield is suppressed by a factor of approximately 3 for pT>5 GeV/c relative to that in p+p collisions scaled by the number of binary nucleon-nucleon collisions. The J/ψ nuclear modification factor displays little dependence on pT in all centrality bins. Model calculations can qualitatively describe the data, providing further evidence for the color-screening effect experienced by J/ψ mesons in the QGP.

Recent progress of quarkonium measurements in heavy-ion collisions at RHIC energies from STAR

One of the primary goals of relativistic heavy-ion collisions is searching for quark-gluon plasma and studying its properties. Among the probes of QGP, the suppression of heavy quarkonium, due to color screening, in heavy-ion collisions has been proposed as a direct signature of QGP formation. However, other effects, such as regeneration and cold nuclear matter effect, would also significantly modify the production of heavy quarkonium in heavy-ion collisions. Recently, the STAR collaboration has installed a new detector, the Muon Telescope Detector. It enables the STAR collaboration to measure quarkonium precisely via di-muon decay channel to constrain the motion of heavy quarkonium in QGP. In this article, the recent progress of quarkonium measurements in p+Au and Au+Au collisions at 200 GeV will be reviewed. Moreover, the measurement of very-low- p T J/ψ, which is likely from coherent photoproduction in heavy-ion collisions, and its physics implication will be discussed.

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 ϕ -meson production at forward rapidity in p+p collisions at s=510 GeV and its energy dependence from s=200 GeV to 7 TeV

The PHENIX experiment at the Relativistic Heavy Ion Collider has measured the differential cross section of $\phi$(1020)-meson production at forward rapidity in $p$$+$$p$ collisions at $\sqrt{s}=$510 GeV via the dimuon decay channel. The partial cross section in the rapidity and $p_T$ ranges $1.2<|y|<2.2$ and $2<p_T<7$ GeV/$c$ is $\sigma_\phi=[2.28 \pm 0.09\,{\rm (stat)} \pm 0.14\,{\rm (syst)} \pm 0.27\, {\rm (norm)}] \times 10^{-2}$~mb. The energy dependence of $\sigma_\phi$ ($1.2<|y|<2.2, \; 2<p_T<5$ GeV/$c$) is studied using the PHENIX measurements at $\sqrt{s}=$200 and 510 GeV and the Large-Hadron-Collider measurements at $\sqrt{s}=$2.76 and 7 TeV. The experimental results are compared to various event generator predictions ({\sc pythia6, pythia8, phojet, ampt, epos3,} and {\sc epos-lhc}).

Prompt and non-prompt J/psi elliptic flow in Pb+Pb collisions at sqrt{s_{_text {NN}}} = 5.02 Tev with the ATLAS detector\xa0

The elliptic flow of prompt and non-prompt J/psi was measured in the dimuon decay channel in Pb+Pb collisions at sqrt{s_{_text {NN}}}=5.02 text {TeV} with an integrated luminosity of 0.42~mathrm {nb}^{-1} with the ATLAS detector at the LHC. The prompt and non-prompt signals are separated using a two-dimensional simultaneous fit of the invariant mass and pseudo-proper decay time of the dimuon system from the J/psi decay. The measurement is performed in the kinematic range of dimuon transverse momentum and rapidity 9<p_mathrm {T}<30 text {GeV}, |y|<2, and 0–60% collision centrality. The elliptic flow coefficient, v_2, is evaluated relative to the event plane and the results are presented as a function of transverse momentum, rapidity and centrality. It is found that prompt and non-prompt J/psi mesons have non-zero elliptic flow. Prompt J/psi v_2 decreases as a function of p_mathrm {T}, while for non-prompt J/psi it is, with limited statistical significance, consistent with a flat behaviour over the studied kinematic region. There is no observed dependence on rapidity or centrality.

Prompt and non-prompt J/psi and psi (2mathrm {S}) suppression at high transverse momentum in 5.02~mathrm {TeV} Pb+Pb collisions with the ATLAS experiment

A measurement of J/psi and psi (2mathrm {S}) production is presented. It is based on a data sample from Pb+Pb collisions at sqrt{s_{mathrm {NN}}} = 5.02~mathrm {TeV} and pp collisions at sqrt{s} = 5.02~mathrm {TeV} recorded by the ATLAS detector at the LHC in 2015, corresponding to an integrated luminosity of 0.42~mathrm {nb}^{-1} and 25~mathrm {pb}^{-1} in Pb+Pb and pp, respectively. The measurements of per-event yields, nuclear modification factors, and non-prompt fractions are performed in the dimuon decay channel for 9< p_{T}^{mu mu } < 40 GeV in dimuon transverse momentum, and -2< y_{mu mu } < 2 in rapidity. Strong suppression is found in Pb+Pb collisions for both prompt and non-prompt J/psi , increasing with event centrality. The suppression of prompt psi (2mathrm {S}) is observed to be stronger than that of J/psi , while the suppression of non-prompt psi (2mathrm {S}) is equal to that of the non-prompt J/psi within uncertainties, consistent with the expectation that both arise from b-quarks propagating through the medium. Despite prompt and non-prompt J/psi arising from different mechanisms, the dependence of their nuclear modification factors on centrality is found to be quite similar.

Observation of the χ_{b1}(3P) and χ_{b2}(3P) and Measurement of their Masses.

The χ_{b1}(3P) and χ_{b2}(3P) states are observed through their ϒ(3S)γ decays, using an event sample of proton-proton collisions collected by the CMS experiment at the CERN LHC. The data were collected at a center-of-mass energy of 13TeV and correspond to an integrated luminosity of 80.0 fb^{-1}. The ϒ(3S) mesons are identified through their dimuon decay channel, while the low-energy photons are detected after converting to e^{+}e^{-} pairs in the silicon tracker, leading to a χ_{b}(3P) mass resolution of 2.2MeV. This is the first time that the J=1 and 2 states are well resolved and their masses individually measured: 10513.42±0.41(stat)±0.18(syst) MeV and 10524.02±0.57(stat)±0.18(syst) MeV; they are determined with respect to the world-average value of the ϒ(3S) mass, which has an uncertainty of 0.5MeV. The mass splitting is measured to be 10.60±0.64(stat)±0.17(syst) MeV.

Measurement of the inclusive J/psi polarization at forward rapidity in pp collisions at mathbf {sqrt{s} = 8}\xa0TeV

We report on the measurement of the inclusive J/psi polarization parameters in pp collisions at a center of mass energy sqrt{s} = 8 TeV with the ALICE detector at the LHC. The analysis is based on a data sample corresponding to an integrated luminosity of 1.23 pb^{-1}. J/psi resonances are reconstructed in their di-muon decay channel in the rapidity interval 2.5< y < 4.0 and over the transverse-momentum interval 2< p_mathrm{T} < 15 mathrm {GeV}/c. The three polarization parameters (lambda _theta , lambda _varphi , lambda _{theta varphi }) are measured as a function of p_mathrm{T} both in the helicity and Collins-Soper reference frames. The measured J/psi polarization parameters are found to be compatible with zero within uncertainties, contrary to expectations from all available predictions. The results are compared with the measurement in pp collisions at sqrt{s} = 7 TeV.

Suppression of Excited ϒ States Relative to the Ground State in Pb-Pb Collisions at sNN=5.02 TeV

The relative yields of $\Upsilon$ mesons produced in pp and PbPb collisions at $\sqrt{s_\mathrm{NN}}$ = 5.02 TeV and reconstructed via the dimuon decay channel are measured using data collected by the CMS experiment. Double ratios are formed by comparing the yields of the excited states, $\Upsilon$(2S) and $\Upsilon$(3S), to the ground state, $\Upsilon$(1S), in both PbPb and pp collisions at the same center-of-mass energy. The double ratios, [$\Upsilon$(nS)/$\Upsilon$(1S)]$_\mathrm{PbPb}$ / [$\Upsilon$(nS)/$\Upsilon$(1S)]$_\mathrm{pp}$, are measured to be 0.308 $\pm$ 0.055 (stat) $\pm$ 0.019 (syst) for the $\Upsilon$(2S) and less than 0.26 at 95% confidence level for the $\Upsilon$(3S). No significant $\Upsilon$(3S) signal is found in the PbPb data. The double ratios are studied as a function of collision centrality, as well as dimuon transverse momentum and rapidity. No significant dependencies are observed.

Measurement of Z0-boson production at large rapidities in Pb–Pb collisions at [formula omitted

The production of Z0 bosons at large rapidities in Pb–Pb collisions at sNN=5.02TeV is reported. Z0 candidates are reconstructed in the dimuon decay channel (Z0→μ+μ−), based on muons selected with pseudo-rapidity −4.0<η<−2.5 and pT>20GeV/c. The invariant yield and the nuclear modification factor, RAA, are presented as a function of rapidity and collision centrality. The value of RAA for the 0–20% central Pb–Pb collisions is 0.67±0.11(stat.)±0.03(syst.)±0.06(corr. syst.), exhibiting a deviation of 2.6σ from unity. The results are well-described by calculations that include nuclear modifications of the parton distribution functions, while the predictions using vacuum PDFs deviate from data by 2.3σ in the 0–90% centrality class and by 3σ in the 0–20% central collisions.

Measurement of quarkonium production cross sections in pp collisions at [formula omitted

Differential production cross sections of prompt J/ψ and ψ(2S) charmonium and ϒ(nS) (n=1,2,3) bottomonium states are measured in proton–proton collisions at s=13TeV, with data collected by the CMS detector at the LHC, corresponding to an integrated luminosity of 2.3 fb−1 for the J/ψ and 2.7 fb−1 for the other mesons. The five quarkonium states are reconstructed in the dimuon decay channel, for dimuon rapidity |y|<1.2. The double-differential cross sections for each state are measured as a function of y and transverse momentum, and compared to theoretical expectations. In addition, ratios are presented of cross sections for prompt ψ(2S) to J/ψ, ϒ(2S) to ϒ(1S), and ϒ(3S) to ϒ(1S) production.

Measurement of quarkonium production in proton\u2013lead and proton\u2013proton collisions at 5.02~mathrm {TeV} with the ATLAS detector

The modification of the production of J/psi , psi (2mathrm {S}), and varUpsilon (nmathrm {S}) (n = 1, 2, 3) in p+Pb collisions with respect to their production in pp collisions has been studied. The p+Pb and pp datasets used in this paper correspond to integrated luminosities of 28~mathrm {nb}^{-1} and 25~mathrm {pb}^{-1} respectively, collected in 2013 and 2015 by the ATLAS detector at the LHC, both at a centre-of-mass energy per nucleon pair of 5.02 TeV. The quarkonium states are reconstructed in the dimuon decay channel. The yields of J/psi and psi (mathrm {2S}) are separated into prompt and non-prompt sources. The measured quarkonium differential cross sections are presented as a function of rapidity and transverse momentum, as is the nuclear modification factor, R_{pmathrm {Pb}} for J/psi and varUpsilon (nmathrm {S}). No significant modification of the J/psi production is observed while varUpsilon (nmathrm {S}) production is found to be suppressed at low transverse momentum in p+Pb collisions relative to pp collisions. The production of excited charmonium and bottomonium states is found to be suppressed relative to that of the ground states in central p+Pb collisions.