Dielectron Decay Channel Research Articles

Overview of quarkonium production with ALICE at the LHC

ALICE is a general purpose experiment designed to investigate nucleus-nucleus collisions at the Large Hadron Collider (LHC), located at CERN. The ALICE detector is optimized for the reconstruction of quarkonia through the dimuon decay channel at foward rapidity as well as the dielectron decay channel at midrapidity. In this contribution, quarkonium measurements performed by the ALICE collaboration at both midrapidity and forward rapidity for various energies and colliding systems (pp, p-Pb and Pb-Pb), will be discussed and compared to theory.

J/ψ production at midrapidity in p-Pb collisions at sqrt{s_{textrm{NN}}} = 8.16 TeV

The production of inclusive, prompt and non-prompt J/ψ was studied for the first time at midrapidity (−1.37 < ycms< 0.43) in p-Pb collisions at sqrt{s_{textrm{NN}}} = 8.16 TeV with the ALICE detector at the LHC. The inclusive J/ψ mesons were reconstructed in the dielectron decay channel in the transverse momentum (pT) interval 0 < pT< 14 GeV/c and the prompt and non-prompt contributions were separated on a statistical basis for pT> 2 GeV/c. The study of the J/ψ mesons in the dielectron channel used for the first time in ALICE online single-electron triggers from the Transition Radiation Detector, providing a data sample corresponding to an integrated luminosity of 689 ± 13 μb−1. The proton-proton reference cross section for inclusive J/ψ was obtained based on interpolations of measured data at different centre-of-mass energies and a universal function describing the pT-differential J/ψ production cross sections. The pT-differential nuclear modification factors RpPb of inclusive, prompt, and non-prompt J/ψ are consistent with unity and described by theoretical models implementing only nuclear shadowing.

Inclusive, prompt and non-prompt J/ψ production at midrapidity in p-Pb collisions at sqrt{s_{mathrm{NN}}} = 5.02 TeV

A measurement of inclusive, prompt, and non-prompt J/ψ production in p-Pb collisions at a nucleon-nucleon centre-of-mass energy sqrt{s_{mathrm{NN}}} = 5.02 TeV is presented. The inclusive J/ψ mesons are reconstructed in the dielectron decay channel at midrapidity down to a transverse momentum pT = 0. The inclusive J/ψ nuclear modification factor RpPb is calculated by comparing the new results in p-Pb collisions to a recently measured proton-proton reference at the same centre-of-mass energy. Non-prompt J/ψ mesons, which originate from the decay of beauty hadrons, are separated from promptly produced J/ψ on a statistical basis for pT larger than 1.0 GeV/c. These results are based on the data sample collected by the ALICE detector during the 2016 LHC p-Pb run, corresponding to an integrated luminosity mathcal{L} int = 292 ± 11 μb−1, which is six times larger than the previous publications. The total uncertainty on the pT-integrated inclusive J/ψ and non-prompt J/ψ cross section are reduced by a factor 1.7 and 2.2, respectively. The measured cross sections and RpPb are compared with theoretical models that include various combinations of cold nuclear matter effects. From the non-prompt J/ψ production cross section, the mathrm{b}overline{mathrm{b}} production cross section at midrapidity, {mathrm{d}sigma}_{mathrm{b}overline{mathrm{b}}} /dy, and the total cross section extrapolated over full phase space, {sigma}_{mathrm{b}overline{mathrm{b}}} , are derived.

Prompt and non-prompt J/ψ production cross sections at midrapidity in proton-proton collisions at sqrt{mathrm{s}} = 5.02 and 13 TeV

The production of J/ψ is measured at midrapidity (|y| < 0.9) in proton-proton collisions at sqrt{s} = 5.02 and 13 TeV, through the dielectron decay channel, using the ALICE detector at the Large Hadron Collider. The data sets used for the analyses correspond to integrated luminosities of mathcal{L} int = 19.4 ± 0.4 nb−1 and mathcal{L} int = 32.2 ± 0.5 nb−1 at sqrt{s} = 5.02 and 13 TeV, respectively. The fraction of non-prompt J/ψ mesons, i.e. those originating from the decay of beauty hadrons, is measured down to a transverse momentum pT = 2 GeV/c (1 GeV/c) at sqrt{s} = 5.02 TeV (13 TeV). The pT and rapidity (y) differential cross sections, as well as the corresponding values integrated over pT and y, are carried out separately for prompt and non-prompt J/ψ mesons. The results are compared with measurements from other experiments and theoretical calculations based on quantum chromodynamics (QCD). The shapes of the pT and y distributions of beauty quarks predicted by state-of-the-art perturbative QCD models are used to extrapolate an estimate of the mathrm{b}overline{mathrm{b}} pair cross section at midrapidity and in the total phase space. The total mathrm{b}overline{mathrm{b}} cross sections are found to be {sigma}_{mathrm{b}overline{mathrm{b}}} = 541 ± 45 (stat.) ± 69 {left(mathrm{syst}.right)}_{-12}^{+10} (extr.) μb and {sigma}_{mathrm{b}overline{mathrm{b}}} = 218±37 (stat.)±31 {left(mathrm{syst}.right)}_{-9.1}^{+8.2} (extr.) μb at sqrt{s} = 13 and 5.02 TeV, respectively. The value obtained from the combination of ALICE and LHCb measurements in pp collisions at sqrt{s} = 13 TeV is also provided.

Centrality and transverse momentum dependence of inclusive J/ψ production at midrapidity in Pb–Pb collisions at [formula omitted] TeV

The inclusive J/ψ meson production in Pb–Pb collisions at a center-of-mass energy per nucleon–nucleon collision of sNN=5.02 TeV at midrapidity (|y|<0.9) is reported by the ALICE Collaboration. The measurements are performed in the dielectron decay channel, as a function of event centrality and J/ψ transverse momentum pT, down to pT=0. The J/ψ mean transverse momentum 〈pT〉 and rAA ratio, defined as 〈pT2〉PbPb/〈pT2〉pp, are evaluated. Both observables show a centrality dependence decreasing towards central (head-on) collisions. The J/ψ nuclear modification factor RAA exhibits a strong pT dependence with a large suppression at high pT and an increase to unity for decreasing pT. When integrating over the measured momentum range pT<10GeV/c, the J/ψRAA shows a weak centrality dependence. Each measurement is compared with results at lower center-of-mass energies and with ALICE measurements at forward rapidity, as well as to theory calculations. All reported features of the J/ψ production at low pT are consistent with a dominant contribution to the J/ψ yield originating from charm quark (re)combination.

Inclusive J/\u03c8 production at mid-rapidity in pp collisions at sqrt{s} = 5.02 TeV

Inclusive J/ψ production is studied in minimum-bias proton-proton collisions at a centre-of-mass energy of sqrt{s} = 5.02 TeV by ALICE at the CERN LHC. The measurement is performed at mid-rapidity (|y| < 0.9) in the dielectron decay channel down to zero transverse momentum pT, using a data sample corresponding to an integrated luminosity of Lint = 19.4 ± 0.4 nb−1. The measured pT-integrated inclusive J/ψ production cross sec- tion is dσ/dy = 5.64 ± 0.22(stat.) ± 0.33(syst.) ± 0.12(lumi.) μb. The pT-differential cross section d2σ/dpTdy is measured in the pT range 0–10 GeV/c and compared with state-of- the-art QCD calculations. The J/ψ 〈pT〉 and leftlangle {p}_{mathrm{T}}^2rightrangle are extracted and compared with results obtained at other collision energies.

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.

Quarkonium in A—A collisions with the ALICE experiment

Quarkonia, i.e. bound states of heavy quarks (charm/bottom), provide remarkable probes of the hot and strongly-interacting medium, the quark gluon plasma (QGP), which is created during heavy-ion collisions. Heavy quarks are produced during initial hard-scattering processes prior to the QGP formation and their number is conserved throughout the partonic and hadronic phases of the collision. At LHC, experimental observations of quarkonium states in A-A collisions are reproduced through two antagonist mechanisms: the sequential suppression and quarkonium production by (re)combination of deconfined quarks. Recent measurements of a significant J/ψ elliptic flow (v2) in Pb-Pb collisions at TeV suggest a participation of the charm quarks to the collectivity of the medium. However, quarkonium interactions in the medium are not yet fully understood and several points should still be clarified. The ALICE experiment at the LHC measures quarkonia at mid-rapidity in the dielectron decay channel and at forward rapidity in the dimuon one, both down to zero transverse momentum. Latest measurements of quarkonium nuclear modification factor and elliptic flow in Pb-Pb collisions will be presented and compared to lower energy results and theoretical predictions.

Prompt and non-prompt hbox {J}/psi production and nuclear modification at mid-rapidity in p\u2013Pb collisions at mathbf{sqrt{{ s}_{text {NN}}}= 5.02}\xa0TeV

A measurement of beauty hadron production at mid-rapidity in proton-lead collisions at a nucleon–nucleon centre-of-mass energy sqrt{s_text {NN}}=5.02 TeV is presented. The semi-inclusive decay channel of beauty hadrons into hbox {J}/psi is considered, where the hbox {J}/psi mesons are reconstructed in the dielectron decay channel at mid-rapidity down to transverse momenta of 1.3 GeV/c. The hbox {b}bar{hbox {b}} production cross section at mid-rapidity, hbox {d}sigma _{hbox {b}bar{hbox {b}}}/hbox {d}y, and the total cross section extrapolated over full phase space, sigma _{text {b}bar{text {b}}}, are obtained. This measurement is combined with results on inclusive hbox {J}/psi production to determine the prompt hbox {J}/psi cross sections. The results in p–Pb collisions are then scaled to expectations from pp collisions at the same centre-of-mass energy to derive the nuclear modification factor R_{text {pPb}}, and compared to models to study possible nuclear modifications of the production induced by cold nuclear matter effects. R_{text {pPb}} is found to be smaller than unity at low p_{mathrm{T}} for both hbox {J}/psi coming from beauty hadron decays and prompt hbox {J}/psi .

Centrality and transverse momentum dependence of J/ψ production in Pb-Pb collisions at √SNN = 5.02 TeV at mid-rapidity with ALICE

We present new results for the nuclear modification factor RAA of J/ψ mesons as a function of centrality and transverse momentum at mid-rapidity. The measurement is carried out with the ALICE central barrel detectors in the acceptance range |y| &lt; 0.9 and pT &gt; 0 in the dielectron decay channel.

J/ψ Elliptic Flow in Pb-Pb Collisions at sqrt[s_{NN}]=5.02 TeV.

We report a precise measurement of the J/ψ elliptic flow in Pb-Pb collisions at sqrt[s_{NN}]=5.02 TeV with the ALICE detector at the LHC. The J/ψ mesons are reconstructed at midrapidity (|y|<0.9) in the dielectron decay channel and at forward rapidity (2.5<y<4.0) in the dimuon channel, both down to zero transverse momentum. At forward rapidity, the elliptic flow v_{2} of the J/ψ is studied as a function of the transverse momentum and centrality. A positive v_{2} is observed in the transverse momentum range 2<p_{T}<8 GeV/c in the three centrality classes studied and confirms with higher statistics our earlier results at sqrt[s_{NN}]=2.76 TeV in semicentral collisions. At midrapidity, the J/ψ v_{2} is investigated as a function of the transverse momentum in semicentral collisions and found to be in agreement with the measurements at forward rapidity. These results are compared to transport model calculations. The comparison supports the idea that at low p_{T} the elliptic flow of the J/ψ originates from the thermalization of charm quarks in the deconfined medium but suggests that additional mechanisms might be missing in the models.

J/ψproduction at the STAR experiment

The suppression of J/ψ production in heavy-ion collisions compared to p+p collisions, caused by the color screening in the deconfined medium, has been proposed as a signature of the formation of the Quark-Gluon Plasma. However, J/ψ production rates are also sensitive to other effects such as the cold nuclear matter effects and recombination. To understand the interplay of these mechanisms, it is important to study J/ψ production for different collision geometries.In these proceedings, we present recent result on J/ψ production via the di-electron decay channel from the STAR experiment at RHIC in p+p collisions at √sNN = 200, 500 GeV, in d+Au collisions at √sNN = 200 GeV and in heavy-ion collisions, specifically Au+Au collisions at √sNN = 200 GeV and U+U collisions at √sNN = 193 GeV. We also show measurements on J/ψ production via the di-muon decay channel in p+p collisions at √sNN = 500 GeV and in Au+Au collisions at √sNN = 200 GeV using the newly installed Muon Telescope Detector.

Measurements of Quarkonium Polarization and Production versus Charged-Particle Multiplicity in p + p Collisions at [formula omitted] in the STAR Experiment: The XXVth International Conference on Ultrarelativistic Nucleus-Nucleus Collisions

We report on the J/ψ production and polarization as a function of pT and xT, measured via the dielectron decay channel at mid-rapidity in p+p collisions at s=500 GeV in the STAR experiment. The measured J/ψpT spectrum is in agreement with NRQCD and CGC+NRQCD predictions, while the J/ψ polarization shows a trend towards longitudinal polarization with increasing pT. In addition, first measurements of the J/ψ production as a function of charged-particle multiplicity are presented at s=500 GeV. A strong correlation between the J/ψ yield and charged-particle multiplicity is observed with a hint of J/ψpT dependence.

Inclusive J/ψ and ψ(2S) production in p–Pb collisions with ALICE at the LHC

The ALICE Collaboration studied the inclusive J/ψ and ψ(2S) production in p-Pb collisions at the nucleon-nucleon centre of mass energy sNN=5.02 TeV. The J/ψ and the ψ(2S) are detected through their decays into muon pairs and the J/ψ is also studied in the dielectron decay channel. The J/ψ and ψ(2S) nuclear modification factors and the double ratio [σψ(2S)/σJ/ψ]pPb/[σψ(2S)/σJ/ψ]pp are presented as a function of the collision centrality. Our measurements are compared to theoretical calculations.

J/ψ and ψ(2S) measurement in p+p collisions √S = 200 and 500 GeV with the STAR experiment

In this paper, results on the J/ψ cross section and polarization measured via the dielectron decay channel at mid-rapidity in p + p collisions at √s = 200 and 500 GeV in the STAR experiment are discussed. Also, first measurements of the J/ψ production as a function of the charged-particle multiplicity density and of ψ(2S) to J/ψ ratio at √s = 500 GeV are reported.

Centrality dependence of inclusive J/ψ production in p-Pb collisions at s N N = 5.02 $$ \sqrt{s_{\mathrm{NN}}}=5.02 $$ TeV

We present a measurement of inclusive J/$\psi$ production in p-Pb collisions at $\sqrt{s_{\rm NN}}$ = 5.02 TeV as a function of the centrality of the collision, as estimated from the energy deposited in the Zero Degree Calorimeters. The measurement is performed with the ALICE detector down to zero transverse momentum, $p_{\rm T}$, in the backward ($-4.46 < y_{\rm cms} < -2.96$) and forward ($2.03 < y_{\rm cms} < 3.53$) rapidity intervals in the dimuon decay channel and in the mid-rapidity region ($-1.37 < y_{\rm cms} < 0.43$) in the dielectron decay channel. The backward and forward rapidity intervals correspond to the Pb-going and p-going direction, respectively. The $p_{\rm T}$-differential J/$\psi$ production cross section at backward and forward rapidity is measured for several centrality classes, together with the corresponding average $p_{\rm T}$ and $p^2_{\rm T}$ values. The nuclear modification factor, $Q_{\rm pPb}$, is presented as a function of centrality for the three rapidity intervals, and, additionally, at backward and forward rapidity, as a function of $p_{\rm T}$ for several centrality classes. At mid- and forward rapidity, the J/$\psi$ yield is suppressed up to 40% compared to that in pp interactions scaled by the number of binary collisions. The degree of suppression increases towards central p-Pb collisions at forward rapidity, and with decreasing $p_{\rm T}$ of the J/$\psi$. At backward rapidity, the $Q_{\rm pPb}$ is compatible with unity within the total uncertainties, with an increasing trend from peripheral to central p-Pb collisions.

ϕmeson production ind+Aucollisions atsNN=200GeV

The PHENIX experiment has measured $\phi$ meson production in $d$$+$Au collisions at $\sqrt{s_{_{NN}}}=200$ GeV using the dimuon and dielectron decay channels. The $\phi$ meson is measured in the forward (backward) $d$-going (Au-going) direction, $1.2<y<2.2$ ($-2.2<y<-1.2$) in the transverse-momentum ($p_T$) range from 1--7 GeV/$c$, and at midrapidity $|y|<0.35$ in the $p_T$ range below 7 GeV/$c$. The $\phi$ meson invariant yields and nuclear-modification factors as a function of $p_T$, rapidity, and centrality are reported. An enhancement of $\phi$ meson production is observed in the Au-going direction, while suppression is seen in the $d$-going direction, and no modification is observed at midrapidity relative to the yield in $p$$+$$p$ collisions scaled by the number of binary collisions. Similar behavior was previously observed for inclusive charged hadrons and open heavy flavor indicating similar cold-nuclear-matter effects.

Measurement of charm and beauty production at central rapidity versus charged-particle multiplicity in proton-proton collisions at s = 7 $$ \sqrt{s}=7 $$ TeV

Prompt D meson and non-prompt J/$\psi$ yields are studied as a function of the multiplicity of charged particles produced in inelastic proton-proton collisions at a centre-of-mass energy of $\sqrt{s}=7$ TeV. The results are reported as a ratio between yields in a given multiplicity interval normalised to the multiplicity-integrated ones (relative yields). They are shown as a function of the multiplicity of charged particles normalised to the average value for inelastic collisions (relative charged-particle multiplicity). D$^0$, D$^+$ and D$^{*+}$ mesons are measured in five $p_{\rm T}$ intervals from 1 to 20 GeV/$c$ and for $|y|<0.5$ via their hadronic decays. The D-meson relative yield is found to increase with increasing charged-particle multiplicity. For events with multiplicity six times higher than the average multiplicity of inelastic collisions, a yield enhancement of a factor about 15 relative to the multiplicity-integrated yield in inelastic collisions is observed. The yield enhancement is independent of transverse momentum within the uncertainties of the measurement. The D$^0$-meson relative yield is also measured as a function of the relative multiplicity at forward pseudorapidity. The non-prompt J/$\psi$, i.e. the B hadron, contribution to the inclusive J/$\psi$ production is measured in the di-electron decay channel at central rapidity. It is evaluated for $p_{\rm T}>1.3$ GeV/$c$ and $|y|<0.9$, and extrapolated to $p_{\rm T}>0$. The fraction of non-prompt J/$\psi$ in the inclusive J/$\psi$ yields shows no dependence on the charged-particle multiplicity at central rapidity. Charm and beauty hadron relative yields exhibit a similar increase with increasing charged-particle multiplicity. The measurements are compared to PYTHIA 8, EPOS 3 and percolation calculations.

J/ψ and ψ(2S) measurement in p+p collisions at = 200 and 500 GeV in the STAR experiment

In this paper, results on the J/ψ cross section and polarization measured via the dielectron decay channel at mid-rapidity in p + p collisions at = 200 and 500 GeV in the STAR experiment are discussed. The first measurement of ψ(2S) to J/ψ ratio at = 500 GeV is also reported.

Study of Z production in PbPb and pp collisions at s N N = 2.76 $$ \sqrt{s_{\mathrm{NN}}}=2.76 $$ TeV in the dimuon and dielectron decay channels

The production of Z bosons is studied in the dimuon and dielectron decay channels in PbPb and pp collisions at sqrt(s[NN]) = 2.76 TeV, using data collected by the CMS experiment at the LHC. The PbPb data sample corresponds to an integrated luminosity of about 150 inverse microbarns, while the pp data sample collected in 2013 at the same nucleon-nucleon centre-of-mass energy has an integrated luminosity of 5.4 inverse picobarns. The Z boson yield is measured as a function of rapidity, transverse momentum, and collision centrality. The ratio of PbPb to pp yields, scaled by the number of inelastic nucleon-nucleon collisions, is found to be 1.06 +/- 0.05 (stat) +/- 0.08 (syst) in the dimuon channel and 1.02 +/- 0.08 (stat) +/- 0.15 (syst) in the dielectron channel, for centrality-integrated Z boson production. This binary collision scaling is seen to hold in the entire kinematic region studied, as expected for a colourless probe that is unaffected by the hot and dense QCD medium produced in heavy ion collisions.