Upsilon Production Research Articles

Bottomonia production and polarization in the NRQCD with k_T-factorization. II: Upsilon (2S) and chi _b(2P) mesons

The Upsilon (2S) production and polarization at high energies is studied in the framework of k_T-factorization approach. Our consideration is based on the non-relativistic QCD formalism for bound states formation and off-shell production amplitudes for hard partonic subprocesses. The direct production mechanism, feed-down contributions from radiative chi _b(3P) and chi _b(2P) decays and contributions from Upsilon (3S) decays are taken into account. The transverse momentum dependent gluon densities in a proton were derived from the Ciafaloni–Catani–Fiorani–Marchesini evolution equation, Kimber-Martin-Ryskin prescription and Parton Branching method. Treating the non-perturbative color octet transitions in terms of the mulitpole radiation theory, we extract the corresponding non-perturbative matrix elements for Upsilon (2S) and chi _b(2P) mesons from a combined fit to Upsilon (2S) transverse momenta distributions measured by the CMS and ATLAS Collaborations at the LHC energies sqrt{s} = 7 and 13 TeV and from the relative production rate R^{chi _b(2P)}_{Upsilon (2S)} measured by the LHCb Collaboration at sqrt{s} = 7 and 8 TeV. Then we apply the extracted values to investigate the polarization parameters lambda _theta , lambda _phi and lambda _{theta phi }, which determine the Upsilon (2S) spin density matrix. Our predictions have a good agreement with the currently available data within the theoretical and experimental uncertainties.

Bottomonia production and polarization in the NRQCD with k_T-factorization. I: Upsilon (3S) and chi _b(3P) mesons

The Upsilon (3S) production and polarization at high energies is studied in the framework of k_T-factorization approach. Our consideration is based on the non-relativistic QCD formalism for bound states formation and off-shell production amplitudes for hard partonic subprocesses. The transverse momentum dependent (TMD, or unintegrated) gluon densities in a proton were derived from the Ciafaloni-Catani-Fiorani-Marchesini (CCFM) evolution equation as well as from the Kimber–Martin–Ryskin (KMR) prescription. Treating the non-perturbative color octet transitions in terms of the multipole radiation theory and taking into account feed-down contributions from radiative chi _b(3P) decays, we extract the corresponding non-perturbative matrix elements for Upsilon (3S) and chi _b(3P) mesons from a combined fit to Upsilon (3S) transverse momenta distributions measured by the CMS and ATLAS Collaborations at the LHC energies sqrt{s} = 7 and 13 TeV and central rapidities. Then we apply the extracted values to describe the CDF and LHCb data on Upsilon (3S) production and to investigate the polarization parameters lambda _theta , lambda _phi and lambda _{theta phi }, which determine the Upsilon (3S) spin density matrix. Our predictions have a good agreement with the currently available data within the theoretical and experimental uncertainties.

Coherent and incoherent Upsilon production in ultraperipheral collisions at the Large Hadron Collider

The exclusive photoproduction of $\Upsilon (nS)$ states were calculated in ultra-peripheral collisions for coherent and incoherent process in PbPb at $\sqrt{s_{NN}}$= 5.5 TeV. Different dipole models were compared in the theoretical framework of light-cone color dipole formalism. Moreover, it was calculated the differential cross section for the Upsilon states and their total cross section for two intervals of rapidity: $|y|\leq 4$ 4 and $ 2 \le$ y $\le 4.5$. A systematic study is done on the theoretical uncertainties associated to the production and predictions are presented for the first time for the incoherent cross section of the radially excited states.

Υ production in U + U collisions at sNN=193 GeV measured with the STAR experiment

We present a measurement of the inclusive production of Upsilon mesons in U+U collisions at 193 GeV at mid-rapidity (|y| < 1). Previous studies in central Au+Au collisions at 200 GeV show a suppression of Upsilon(1S+2S+3S) production relative to expectations from the Upsilon yield in p+p collisions scaled by the number of binary nucleon-nucleon collisions (Ncoll), with an indication that the Upsilon(1S) state is also suppressed. The present measurement extends the number of participant nucleons in the collision (Npart) by 20% compared to Au+Au collisions, and allows us to study a system with higher energy density. We observe a suppression in both the Upsilon(1S+2S+3S) and Upsilon(1S) yields in central U+U data, which consolidates and extends the previously observed suppression trend in Au+Au collisions.

Searching for new spin-0 resonances at LHCb

We study the phenomenology of light spin-0 particles and stress that they can be efficiently searched for at the LHCb experiment in the form of dimuon resonances. Given the large production cross sections in the forward rapidity region together with the efficient triggering and excellent mass resolution, it is argued that LHCb can provide unique sensitivity to such states. We illustrate our proposal using the recent measurement of Upsilon production by LHCb, emphasising the importance of mixing effects in the bottomonium resonance region. The implications for dimuon decays of spin-0 bottomonium states are also briefly discussed.

The Latest STAR Results on Quarkonium Production

We report the latest results of J/psi, psi(2S) and Upsilon production in the dielectron decay channel at mid-rapidity, from the STAR experiment. We present J/psi cross section measurements in p+p collisions at 200 and 500 GeV, as well as the first measurement of the psi(2S) to J/psi ratio at 500 GeV. We also show J/psi and Upsilon production in heavy ion collisions: J/psi nuclear modification factors (R_{AA}) in Au+Au collisions at 200, 62.4 and 39 GeV and in U+U collisions at 193 GeV, Upsilon R_{AA} in d+Au, Au+Au and U+U collisions at 200, 200 and 193 GeV, respectively. The results are compared to different model calculations.

Upsilon Production in Pb-Pb and p-Pb Collisions at Forward Rapidity with ALICE at the LHC

The ALICE apparatus at the LHC was designed and built to perform dedicated studies of the Quark-Gluon Plasma (QGP), a strongly interacting phase of QCD matter, expected to be created in heavy-ion collisions, where quarks and gluons are deconfined. In such collisions heavy flavors are produced at the very early stage of the interaction by the initial hard scattering processes and hence can be used to characterize the hot and dense medium. In particular the sequential suppression of quarkonia (charmonia and bottomonia) was proposed as a thermometer of the deconfined medium. The inclusive ϒ(1S) production has been measured down to zero transverse momentum in its dimuon decay channel at forward rapidity (2.5 < ylab < 4.0) using the muon spectrometer. Here results on the ϒ(1S) nuclear modification factor (RAA) in Pb-Pb collisions at = 2.76 TeV are discussed and compared to the measurement at mid-rapidity by the CMS Collaboration and to theoretical predictions. Also recent results on RpPb and forward-to-backward yield ratio (RFB) in p-Pb collisions at = 5.02 TeV are discussed.

Measurement of $${\Upsilon } $$ Υ production in $${{\mathrm {p}}} {{\mathrm {p}}} $$ p p collisions at $${\sqrt{s}} =2.76{\mathrm {\,TeV}} $$ s = 2.76 TeV

The production of Upsilon(1S), Upsilon(2S) and Upsilon(3S) mesons decaying into the dimuon final state is studied with the LHCb detector using a data sample corresponding to an integrated luminosity of 3.3 pb^{-1} collected in proton-proton collisions at a centre-of-mass energy of sqrt{s}=2.76 TeV. The differential production cross-sections times dimuon branching fractions are measured as functions of the Upsilon transverse momentum and rapidity, over the ranges p_T<15 GeV/c and 2.0<y<4.5. The total cross-sections in this kinematic region, assuming unpolarised production, are measured to be sigma(pp -> Upsilon(1S) X) x B(Upsilon(1S) -> mu+mu-) = 1.111 +/- 0.043 +/- 0.044 nb, sigma(pp -> Upsilon(2S) X) x B(Upsilon(2S) -> mu+mu-) = 0.264 +/- 0.023 +/- 0.011 nb, sigma(pp -> Upsilon(3S) X) x B(Upsilon(3S) -> mu+mu-) = 0.159 +/- 0.020 +/- 0.007 nb, where the first uncertainty is statistical and the second systematic.

Search for a low-mass scalar Higgs boson decaying to a tau pair in single-photon decays ofΥ(1S)

We search for a low-mass scalar CP-odd Higgs boson, A0, produced in the radiative decay of the Upsilon resonance and decaying into a tau+tau- pair: Upsilon(1S)->gamma A0. The production of Upsilon(1S) mesons is tagged by Upsilon(2S)->pi+pi-Upsilon(1S) transitions, using a sample of (98.3+/-0.9) million Upsilon(2S) mesons collected by the BaBar detector. We find no evidence for a Higgs boson in the mass range 3.5 GeV<= m(A0)<=9.2 GeV, and combine these results with our previous search for the tau decays of the light Higgs in radiative Upsilon(3S) decays, setting limits on the coupling of A0 to the b/bbar quarks in the range 0.09-1.9. Our measurements improve the constraints on the parameters of the Next-to-Minimal-Supersymmetric Standard Model and similar theories with low-mass scalar degrees of freedom.

ϒ production in pp and pA collisions: from RHIC to the LHC

I discuss Upsilon production in pp collisions at RHIC, Tevatron and LHC energies, in particular the behaviour of the differential cross section in rapidity and the impact of QCD corrections on the P_T differential cross section. I also emphasise the very good agreement between the parameter-free predictions of the Colour-Singlet Model (CSM) and the first LHC data, especially in the region of low transverse momenta, which is the most relevant one for heavy-ion studies. I also show that the CSM predicts Upsilon cross-section ratios in agreement with the most recent LHC data. I then briefly discuss the nuclear-matter effects on Upsilon production at RHIC and the LHC in p(d)A collisions and, by extension, in AA collisions. I argue that a) the Upsilon break-up probability can be neglected, at RHIC and the LHC, b) gluon shadowing --although non-negligible-- is not strong enough to describe forward RHIC data, c) backward RHIC data hints at a gluon EMC effect, possibly stronger than the quark one. Outlooks for the LHC pPb run are also presented.

Measurements of ϒ Production and Nuclear Modification Factor at STAR

Thermal suppression of quarkonium production in heavy-ion collisions, due to Debye screening of the quark–antiquark potential, has been proposed as a clear signature of Quark–Gluon Plasma (QGP) formation. At RHIC energies, the ϒ meson is a clean probe of the early system due to negligible levels of enhancement from b b ¯ recombination and non-thermal suppression from co-mover absorption. We report on our measurement of the ϒ → e + e − cross section in Au+Au collisions at s N N = 200 GeV . We compute the Nuclear Modification Factor by comparing these results to new p+p measurements from 2009 ( 21 pb − 1 in 2009 compared to 7.9 pb − 1 in 2006). In order to have a complete assessment of both hot and cold nuclear matter effects on Upsilon production we also report on results from d+Au collisions.

Measurement of upsilon production in 7 TeVppcollisions at ATLAS

Using 1.8 fb-1 of pp collisions at a center-of-mass energy of 7 TeV recorded by the ATLAS detector at the Large Hadron Collider, we present measurements of the production cross sections of Upsilon(1S,2S,3S) mesons. Upsilon mesons are reconstructed using the di-muon decay mode. Total production cross sections for p_T<70 GeV and in the rapidity interval |Upsilon|<2.25 are measured to be 8.01+-0.02+-0.36+-0.31 nb, 2.05+-0.01+-0.12+-0.08 nb, 0.92+-0.01+-0.07+-0.04 nb respectively, with uncertainties separated into statistical, systematic, and luminosity measurement effects. In addition, differential cross section times di-muon branching fractions for Upsilon(1S), Upsilon(2S), and Upsilon(3S) as a function of Upsilon transverse momentum p_T and rapidity are presented. These cross sections are obtained assuming unpolarized production. If the production polarization is fully transverse or longitudinal with no azimuthal dependence in the helicity frame the cross section may vary by approximately +-20%. If a non-trivial azimuthal dependence is considered, integrated cross sections may be significantly enhanced by a factor of two or more. We compare our results to several theoretical models of Upsilon meson production, finding that none provide an accurate description of our data over the full range of Upsilon transverse momenta accessible with this dataset.

Measurements of Υ Production and Nuclear Modification Factor at STAR

Thermal suppression of quarkonium production in heavy-ion collisions, due to Debye screening of the quark-antiquark potential, has been proposed as a clear signature of quark-gluon plasma (QGP) formation. At RHIC energies, the Υ meson is a clean probe of the early system thanks to negligible levels of enhancement from bb̄ recombination and non-thermal suppression from co-mover absorption. We report on our measurement of the Υ → e+e− cross section in Au+Au collisions at =200 GeV. We compute the Nuclear Modification Factor by comparing these results to p+p collisions. In order to have a complete assessment of both hot and cold nuclear matter effects on Upsilon production we also report on results from d+Au collisions.

Quarkonium Physics at a Fixed-Target Experiment using the LHC Beams

We outline the many quarkonium-physics opportunities offered by a multi-purpose fixed-target experiment using the p and Pb LHC beams extracted by a bent crystal. This provides an integrated luminosity of 0.5 fb-1 per year on a typical 1cm-long target. Such an extraction mode does not alter the performance of the collider experiments at the LHC. With such a high luminosity, one can analyse quarkonium production in great details in pp, pd and pA collisions at sqrt(sNN)~115 GeV and at sqrt(sNN)~72 GeV in PbA collisions. In a typical pp (pA) run, the obtained quarkonium yields per unit of rapidity are 2-3 orders of magnitude larger than those expected at RHIC and about respectively 10 (70) times larger than for ALICE. In PbA, they are comparable. By instrumenting the target-rapidity region, the large negative-xF domain can be accessed for the first time, greatly extending previous measurements by Hera-B and E866. Such analyses should help resolving the quarkonium-production controversies and clear the way for gluon PDF extraction via quarkonium studies. The nuclear target-species versatility provides a unique opportunity to study nuclear matter and the features of the hot and dense matter formed in PbA collisions. A polarised proton target allows the study of transverse-spin asymmetries in J/psi and Upsilon production, providing access to the gluon and charm Sivers functions.

New Measurements of Upsilon Spin Alignment at the Tevatron

We describe a new analysis of Upsilon(nS) to mu+mu- decays collected in proton anti-proton collisions with the CDF II detector at the Fermilab Tevatron. This analysis measures the angular distributions of the final state muons in the Upsilon rest frame, providing new information about Upsilon production polarization. We find the angular distributions to be nearly isotropic up to Upsilon transverse momentum of 40 GeV/c, consistent with previous measurements by CDF, but inconsistent with results obtained by the D0 experiment. The results are compared with recent NLO calculations based on color-singlet matrix elements and non-relativistic QCD with color-octet matrix elements.

Upsilon Production and Upsilon + Hadron Correlations at STAR

The cross-section for the Υ(1S+2S+3S) di-electron decay channel is measured at mid-rapidity in the STAR detector, and the preliminary results for azimuthal correlations between Υ(1S+2S+3S) and hadrons are presented, using p+p and d+Au collisions at the RHIC center-of-mass energy √s = 200 GeV from Runs 6, 8 and 9. The STAR measurements establish a baseline for future Υ measurements in Au+Au collision systems and provide additional opportunities to study the Υ production mechanism.

Heavy-quarkonium production in high energy proton-proton collisions at RHIC

We update the study of the total Psi and Upsilon production cross section in proton-proton collisions at RHIC energies using the QCD-based Color-Singlet (CS) Model, including next-to-leading order partonic matrix elements. We also include charm-quark initiated processes which appear at leading order in alpha_s, but which have so far been overlooked in such studies. Contrary to earlier claims, we show that the CS yield is consistent with measurements over a broad range of J/Psi rapidities. We also find that charm-quark initiated processes, including both intrinsic and sea-like charm components, typically contribute at least 20% of the direct J/Psi yield, improving the agreement with data both for the integrated cross section and its rapidity dependence. The key signature for such processes is the observation of a charm-quark jet opposite in azimuthal angle phi to the detected J/Psi. Our results have impact on the proper interpretation of heavy-quarkonium production in heavy-ion collisions and its use as a probe for the quark-gluon plasma.

Quarkonia measurements with STAR

We report results on quarkonium production from the STAR experiment at the Relativistic Heavy-Ion Collider (RHIC). J/psi spectra in p+p and Cu+Cu collisions at sqrt(s) = 200 GeV with transverse momenta in the range of 0.5-14 GeV/c and 5-8 GeV/c, respectively, are presented. We find that for p_T > 5 GeV/c yields in p+p collisions are consistent with those in minimum-bias Cu+Cu collisions scaled with the respective number of binary nucleon-nucleon collisions. In this range the nuclear modification factor, R_AA, is measured to be 0.9+-0.2(stat). For the first time at RHIC, high-p_T J/psi-hadron correlations were studied in p+p collisions. Implications from our measurements on J/psi production mechanisms, constraints on open bottom yields, and J/psi dissociation mechanisms at high-p_T are discussed. In addition, we give a brief status of measurements of Upsilon production in p+p and Au+Au collisions and present projections of future quarkonia measurements based on an upgrades to the STAR detector and increased luminosity achieved through stochastic cooling of RHIC.

ΥProduction at Fermilab Tevatron and LHC Energies

We update the theoretical predictions for direct Upsilon(nS) hadroproduction in the framework of nonrelativistic QCD. We show that the next-to-leading order corrections in alpha(S) to the color-singlet transition significantly raise the differential cross section at high p(T) and substantially affect the polarization of the Upsilon. Motivated by the remaining gap between the next-to-leading order yield and the cross-section measurements at the Fermilab Tevatron, we evaluate the leading part of the alpha(S)(5) contributions, namely, those coming from Upsilon(nS) associated with three light partons. The differential color-singlet cross section at alpha(S)(5) is in substantial agreement with the data, so that there is no evidence for the need of color-octet contributions. Furthermore, we find that the polarization of the Upsilon(nS) is longitudinal. We also present our predictions for Upsilon(nS) production at the LHC.

Measurement ofΥProduction forp+pandp+dInteractions at800 GeV/c

We report a high statistics measurement of Upsilon production with an 800 GeV/c proton beam on hydrogen and deuterium targets. The dominance of the gluon-gluon fusion process for Upsilon production at this energy implies that the cross section ratio, sigma(p+d-->Upsilon)/2sigma(p+p-->Upsilon), is sensitive to the gluon content in the neutron relative to that in the proton. Over the kinematic region 0<x(F)<0.6, this ratio is found to be consistent with unity, in striking contrast to the behavior of the Drell-Yan cross section ratio sigma(p+d)(DY)/2sigma(p+p)(DY). This result shows that the gluon distributions in the proton and neutron are very similar. The Upsilon production cross sections are also compared with the p+d and p+Cu cross sections from earlier measurements.