Study of high-p T charged particle suppression in PbPb compared to pp collisions at $\sqrt{s_{\mathrm{NN}}}=2.76~\mathrm{TeV}$

Abstract

The transverse momentum spectra of charged particles have been measured in pp and PbPb collisions at √ s NN = 2.76 TeV by the CMS experiment at the LHC. In the transverse momentum range p T = 5-10 GeV/c, the charged particle yield in the most central PbPb collisions is suppressed by up to a factor of 7 compared to the pp yield scaled by the number of incoherent nucleon-nucleon collisions. At higher p T , this suppression is significantly reduced, approaching roughly a factor of 2 for particles with p T in the range p T = 40-100 GeV/c.

Measurement of jet fragmentation into charged particles in pp and PbPb collisions at $ \sqrt{{{s_{\mathrm{NN}}}}} = 2.76 $ TeV

“…Results on the suppression of inclusive hadron production at high transverse momenta (p T ), as well as on the modified high-p T dihadron angular correlations obtained from nucleus-nucleus collisions at √ s NN = 200 GeV at the Relativistic Heavy Ion Collider (RHIC) [4][5][6][7] have shown the existence of partonic energy loss in dense strongly interacting matter. Similar observations have been made at the Large Hadron Collider (LHC) [8][9][10][11][12][13][14].…”

“…[9]. The track-finding efficiency in the kinematic range of this study is (60-70)% and the corresponding correction is applied as a function of track p T , jet p T , and event centrality by reweighting the found tracks with the inverse of the reconstruction efficiency.…”

Novel subjet observables for jet quenching in heavy-ion collisions

“…Considerations of the RSD distributions show that the R IQR[ΔS 12 ] carries the largest discrimination power for highp T jets, although there is an associated uncertainty of [10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25]% due to hadronization effects. For low-p T jets ( p T 120 GeV/c) and/or recoil-jets in dijet systems the use of the R Q 1 [ΔS 12 ] and/or the median R Q 2 [ΔS 12 ] may prove more advantageous, with hadronization uncertainties that are smaller than 5% for the chosen subjet parameters.…”

“…Experiments at RHIC and the LHC observed a strong suppression of high transverse momentum particle yields [9][10][11][12][13][14][15], suppression of inclusive and semi-inclusive yields of fully reconstructed jets [16][17][18][19][20], and, more recently, the internal structure of the jets [21][22][23][24][25] for detailed studies of jet quenching. However, in all these measurements the treatment of the background originating from the copiously produced particles not associated to hard scatterings poses an experimental challenge for precise and unbiased measurements.…”

Jet shape and fragmentation function measurements with CMS

“…The objective is to understand how a color charge (carried by quarks and gluons) is transported in the colored medium. It is well established that the parton energy loss is a consequence of the modification of the hard-scattering processes in the final state of the heavy ion collisions at RHIC and LHC [2][3][4]. It is evident in the suppression of high p T charged hadrons and jets, as well as in the associated yield in two-particle correlations measurements [5], which is accompanied by an enhancement of low p T hadrons, suggesting a softening of jet fragmentations.…”