Abstract
The differential yields of charged particles having pseudorapidity within |η| < 1 are measured using xenon-xenon (XeXe) collisions at sqrt{s_{mathrm{NN}}} = 5.44 TeV. The data, corresponding to an integrated luminosity of 3.42 μb−1, were collected in 2017 by the CMS experiment at the LHC. The yields are reported as functions of collision centrality and transverse momentum, pT, from 0.5 to 100 GeV. A previously reported pT spectrum from proton-proton collisions at sqrt{s}=5.02 TeV is used for comparison after correcting for the difference in center-of-mass energy. The nuclear modification factors using this reference, RAA*, are constructed and compared to previous measurements and theoretical predictions. In head-on collisions, the RAA* has a value of 0.17 in the pT range of 6–8 GeV, but increases to approximately 0.7 at 100 GeV. Above ≈6 GeV, the XeXe data show a notably smaller suppression than previous results for lead-lead (PbPb) collisions at sqrt{s_{mathrm{NN}}}=5.02 TeV when compared at the same centrality (i.e., the same fraction of total cross section). However, the XeXe suppression is slightly greater than that for PbPb in events having a similar number of participating nucleons.
Highlights
The CMS detectorThe central feature of the CMS apparatus is a superconducting solenoid of 6 m internal diameter, providing a magnetic field of 3.8 T
A previously reported pT spectrum from proton-proton collisions at s = 5.02 TeV is used for comparison after correcting for the difference in center-of-mass energy
Complemen√tary measurements of the nuclear modification factor in proton-lead collisions at sNN = 5.02 TeV indicate that high-pT charged-particle yields are not strongly modified in this smaller colliding system, ruling out effects related to the initial-state conditions of the lead nucleus as a cause of the high-pT suppression seen in PbPb collisions [14, 17, 18]
Summary
The central feature of the CMS apparatus is a superconducting solenoid of 6 m internal diameter, providing a magnetic field of 3.8 T. Within the solenoid volume are a silicon pixel and strip tracker, a lead tungstate crystal electromagnetic calorimeter, and a brass and scintillator hadron calorimeter, each composed of a barrel and two endcap sections. Forward calorimeters extend the η coverage provided by the barrel and endcap detectors. The silicon tracker measures charged particles within the range |η| < 2.5. It consists of 1856 silicon pixel and 15 148 silicon strip detector modules. The hadron forward (HF) calorimeter uses steel as an absorber and quartz fibers as the sensitive material. During XeXe operation the first level trigger (L1), composed of custom hardware processors, uses information from the calorimeters to select events at a rate of around 4 kHz within a time interval of less than 4 μs. A more detailed description of the CMS detector, together with a definition of the coordinate system used and the relevant kinematic variables, can be found in ref. [27]
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