Formation of dense partonic matter in relativistic nucleus–nucleus collisions at RHIC: Experimental evaluation by the PHENIX Collaboration

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.…”

“…The relative change in low momentum jets ( p T, jet < 100 GeV/c) between the interquartile range provided by the two Monte Carlo event generators is around [4][5][6][7][8][9][10]% for any clustering algorithm and subjets reconstructed with R subjet ≤ 0.15. For R subjet = 0.2, this change increases to 17%, independently of the clustering algorithm.…”

“…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.…”

CMS Physics Technical Design Report: Addendum on High Density QCD with Heavy Ions

“…The measured single hadron p T spectra at RHIC and SPS have an inverse slope parameter T eff larger than that measured in pp collisions, increasing with reaction centrality and with hadron mass, as expected if collective expansion blue-shifts the hadron spectra. Phenomenological fits of the spectra to "blast wave" models (T eff ≈ T + β T 2 m) yield transverse flow velocities β T ≈ 0.6 [68].…”

“…Measurements at RHIC suggest that the initial state described by the concept of parton saturation is directly reflected in the multiplicity of produced hadrons and their phase-space distribution. These global features of multiparticle production, measured by PHOBOS and others [64,68,147,159], exhibit great simplicity, such as factorisation into separate dependencies on energy and collision geometry as well as the general feature of extended longitudinal scaling over a large fraction of the rapidity range [141,142]. In CMS, the high tracking efficiency and low rate of fake tracks, together with a large calorimetric coverage, provide a precise measurement of global event characteristics, event by event.…”