Charmonium spectroscopy from inclusive ψ’ and J/ψ radiative decays

Abstract:We have studied the transverse-momentum (p T ) dependence of the inclusive J/ψ production in p-Pb collisions at √ s NN = 5.02 TeV, in three center-of-mass rapidity (y cms ) regions, down to zero p T . Results in the forward and backward rapidity ranges (2.03 < y cms < 3.53 and −4.46 < y cms < −2.96) are obtained by studying the J/ψ decay to µ + µ − , while the mid-rapidity region (−1.37 < y cms < 0.43) is investigated by measuring the e + e − decay channel. The p T dependence of the J/ψ production cross section and nuclear modification factor are presented for each of the rapidity intervals, as well as the J/ψ mean p T values. Forward and mid-rapidity results show a suppression of the J/ψ yield, with respect to pp collisions, which decreases with increasing p T . At backward rapidity no significant J/ψ suppression is observed. Theoretical models including a combination of cold nuclear matter effects such as shadowing and partonic energy loss, are in fair agreement with the data, except at forward rapidity and low transverse momentum. The implications of the p-Pb results for the evaluation of cold nuclear matter effects on J/ψ production in Pb-Pb collisions are also discussed. JHEP06(2015)055The suppression of charmonia, bound states of c andc quarks, and in particular of the J/ψ state, has long been proposed as a signature for the formation of a plasma of quarks and gluons (QGP) [1] in ultrarelativistic nucleus-nucleus collisions. However, it was soon realized that charmonium production can also be modified by nuclear effects not necessarily related to QGP formation [2]. These so-called cold nuclear matter (CNM) effects can be investigated by studying charmonium production in proton-nucleus (p-A) collisions as confirmed by the analysis of results obtained by several fixed-target (SPS [3, 4], HERA [5] and Tevatron [6]) and collider (RHIC [7] and LHC [8, 9]) experiments.Theoretical models have studied the production of charmonium in p-A collisions and the effects of the surrounding cold nuclear medium by introducing various mechanisms which include nuclear shadowing, gluon saturation, energy loss and nuclear absorption. Models [10][11][12] inspired by Quantum ChromoDynamics (QCD) describe charmonium production as a two-step process, with the cc pair created in a hard parton scattering, followed by its evolution into a bound state with specific quantum numbers. The pair creation is sensitive to the Parton Distribution Functions (PDFs) in both colliding partners and, at high energy, occurs mainly via gluon fusion. Although PDFs are known to be modified in a nuclear environment, information on the dependence of such modifications on the fraction x (Bjorken-x) of the nucleon momentum carried by the gluons and on the four-momentum squared Q 2 transferred in the scattering is still limited [13][14][15]. Charmonium production measurements can therefore provide insight into the so-called nuclear shadowing, i.e., on how the nucleon gluon PDFs are modified in a nucleus.Modifications of the initial state of the ...

Section: Jhep06(2015)055mentioning

confidence: 99%

Rapidity and transverse-momentum dependence of the inclusive J/ψ nuclear modification factor in p-Pb collisions at s N N $$ \sqrt{s_{N\ N}} $$ = 5.02 TeV

Adam¹,

Adamová²,

Aggarwal³

et al. 2015

“…The χ c1 and χ c2 signal pdfs M 1,2 (∆m) are each described by a Crystal Ball (CB) function [29][30][31]. The CB function is characterised by a Gaussian core with a width σ i (associated with the pdf M i (∆m)) and a power law low-mass tail described by the parameter n. The transition between the core and tail is described by the threshold parameter α.…”

Section: Jhep07(2014)154mentioning

confidence: 99%

Measurement of χ c1 and χ c2 production with s $$ \sqrt{s} $$ = 7 TeV pp collisions at ATLAS

Agustoni¹,

Beck²,

Albert³

et al. 2014

Self Cite

Abstract:The prompt and non-prompt production cross-sections for the χ c1 and χ c2 charmonium states are measured in pp collisions at √ s = 7 TeV with the ATLAS detector at the LHC using 4.5 fb −1 of integrated luminosity. The χ c states are reconstructed through the radiative decay χ c → J/ψγ (with J/ψ → µ + µ − ) where photons are reconstructed from γ → e + e − conversions. The production rate of the χ c2 state relative to the χ c1 state is measured for prompt and non-prompt χ c as a function of J/ψ transverse momentum. The prompt χ c cross-sections are combined with existing measurements of prompt J/ψ production to derive the fraction of prompt J/ψ produced in feed-down from χ c decays. The fractions of χ c1 and χ c2 produced in b-hadron decays are also measured. The ATLAS collaboration 36 Keywords: Hadron-Hadron Scattering IntroductionThe study of heavy quarkonium production in hadronic collisions offers a unique insight into the dynamics of the strong interaction. Understanding the hadronic production of quarkonium states within quantum chromodynamics (QCD) has been a long-standing challenge, complicated by the presence of several important energy scales [1]. While the production -1 - JHEP07(2014)154of a heavy quark pair is generally a high-energy process that can be well described perturbatively, the energy scale associated with the evolution of a heavy quark pair into a physical bound state introduces large uncertainties to theoretical predictions. Understanding the hadronic production of the charmonium states is particularly challenging as the mass of the charm quark is such that the modelling of the bound state as a simple non-relativistic system is less well motivated than for the heavier bottomonium system. Several theoretical approaches have been developed to describe hadronic charmonium production, though the wealth of production and polarisation measurements that now exist are not comprehensively described by any single theoretical approach [2]. However, progress is being made in the calculation of colour-singlet (CS) and colour-octet (CO) production processes at higher perturbative orders and recent calculations provide a good description of the world data on prompt J/ψ production cross-sections [3].The χ cJ (1P ) states (with J = 0, 1, 2) are the only triplet of P -wave states below the open-charm threshold. The spectroscopy of these states is characterised by small hyperfine mass splittings and the branching fractions for the decays χ cJ → J/ψ γ are large for the J = 1, 2 states (34.4% and 19.5%, respectively), while the corresponding branching fraction for the J = 0 state is significantly lower (1.3%) [4]. The χ cJ states may be produced directly in hadronic collisions or through the decay of higher-mass quarkonium states; these production modes are referred to as prompt. In addition to prompt production, the decay chains of b-hadrons can also produce χ cJ states; these production modes are referred to as non-prompt.The large cross-section for inclusive charmonium production and extensive data ...

“…In both types of fits, the sum of a Gaussian and a Crystal Ball [23] function is used for the description of the signals, simultaneously taking into account FSR and rapiditydependent resolution variations. In the J/ψ-only fits, an exponential function is used to describe the background.…”

Section: Inclusive Yield Determinationmentioning

confidence: 99%

J/ψ and ψ(2S) production in pp collisions at $ \sqrt {s} = 7{\text{Tev}} $

Chatrchyan¹,

Khachatryan²,

Sirunyan³

et al. 2012

Self Cite

100

A measurement of the J/ψ and ψ(2S) production cross sections in pp collisions at $ \sqrt {s} = 7{\text{TeV}} $ with the CMS experiment at the LHC is presented. The data sample corresponds to an integrated luminosity of 37 pb−1. Using a fit to the invariant mass and decay length distributions, production cross sections have been measured separately for prompt and non-prompt charmonium states, as a function of the meson transverse momentum in several rapidity ranges and integrated in the kinematical regions considered in this study. In addition, cross sections restricted to the acceptance of the CMS detector are given, which are not affected by the polarization of the charmonium states. The ratio of the differential production cross sections of the two states, where systematic uncertainties largely cancel, is also determined. The branching fraction of the inclusive B → ψ(2S)X decay is extracted from the ratio of the non-prompt cross sections to be: $ \mathcal{B}\left( {{\text{B}} \to \psi \left( {\text{2S}} \right)X} \right) = \left( {{3}.0{8}\pm 0.{12}\left( {{\text{stat}}. + {\text{syst}}.} \right)\pm 0.{13}\left( {{\text{theor}}.} \right)\pm 0.{42}\left( {{\mathcal{B}_{\text{PDG}}}} \right)} \right) \times {1}{0^{{ - {3}}}}. $