Measurements of charged particle spectra and nuclear modification factor in p+Pb collisions with the ATLAS detector

Abstract

The ATLAS detector at the LHC obtained the sample of p+Pb data at √ s NN = 5.02 TeV with integrated luminosity of 25 nb −1 , which can be compared to the pp data obtained by interpolating pp measurements at √ s = 2.76 TeV and 7 TeV. Due to the excellent capabilities of the ATLAS detector, and its stable operation in heavy ion as well as proton-proton physics runs, the data allow measurements of the nuclear modification factor, ratio of heavy ion charged particle spectra divided by pp reference, in different centrality classes over a wide range of rapidity. The charged particle nuclear modification factor is found to vary significantly as a function of transverse momentum with a stronger dependence in more peripheral collisions.

Predictions for p+Pb Collisions at sNN = 5TeV: Comparison with Data

“…Similar indications of a large p T enhancement are also present in the preliminary ATLAS data, 59 but since these data have been centrality selected, no direct comparison is made due to the biases that the centrality classification in p+Pb collisions is known to pose. 60 On the contrary, the ALICE data 51 for the same observable shows no sign of such an increase.…”

Predictions for p +Pb Collisions atsNN=5 TeV: Comparison With Data

“…Similar indications of a large p T enhancement are also present in the preliminary ATLAS data, 59 but since these data have been centrality-selected, no direct comparison is made due to the biases that the centrality classification in p+Pb Fig. 9.…”

The Muon Puzzle in cosmic-ray induced air showers and its connection to the Large Hadron Collider

“…If a parton has to traverse a QGP medium, it looses energy compared to free propagation. This effect was first discovered at RHIC in Au-Au collisions and has been extensively studied in Pb-Pb and Xe-Xe at the LHC (Adcox et al 2002;Arsene 2013;Balek 2014;Jung 2014;Sirunyan et al 2018dSirunyan et al , 2017bAaboud et al 2019b;Sirunyan et al 2018aSirunyan et al , 2019bKhachatryan et al 2017a;Acharya et al 2019dAcharya et al , 2018Adam et al 2016b,a;Festanti 2014;Grelli 2013). It is measured with the nuclear modification factor R AA , which compares the p T -dependent yields for particle production in A-A collisions with the corresponding p-p collision.…”

“…It is measured with the nuclear modification factor R AA , which compares the p T -dependent yields for particle production in A-A collisions with the corresponding p-p collision. This effect is absent in p-Pb (Abelev et al 2013c;Balek 2014;Aad et al 2015;Jung 2014;Li 2014;Adam et al 2015e,b;Khachatryan et al 2017a;Sirunyan et al 2017d;Balek 2017;Sun 2019;Acharya et al 2021aAcharya et al , 2018, which implies it is also absent in p-air and therefore irrelevant for the Muon Puzzle. Some modification is observed at low p T in p-Pb collisions, but that is attributed to the initial state, such as modifications of the parton density functions of the nucleon inside a nucleus compared to free protons.…”