Femtoscopy in √SNN= 5.02 TeVp-Pb collisions withATLAS

Michael Clark

doi:10.1051/epjconf/201714101013

Abstract

Bose-Einstein correlations between identified charged pions are measured for p +Pb collisions at √S NN = 5.02 TeV with the ATLAS detector using a total integrated luminosity of 28 nb−1 . Pions are identified using ionisation energy loss measured in the pixel detector. Two-particle correlation functions and the extracted source radii are presented as a function of average transverse pair momentum (k T ) and rapidity (y ππ *) as well as collision centrality. Pairs are selected with a rapidity −2 ππ * T T . A correlation with the local single-particle multiplicity dN ch /dy * is demonstrated. The scaling of the extracted radii with the mean number of participants is also used to compare a selection of initial-geometry models. The cross term R o1 , which couples radial and longitudinal expansion, is measured as a function of rapidity, and a departure from zero is observed with 4.8 σ combined significance for y ππ * > −1 in the most central events.

Highlights

Multi-particle correlations in proton-lead (p+Pb) [1,2,3,4,5] and proton-proton (p + p) [6] collisions exhibit long-range azimuthal correlations similar to those observed in lead-lead (Pb+Pb) collisions, in which they are attributed to collective expansion of the quark-gluon plasma
The measured Hanbury Brown and Twiss (HBT) radii, which are interpreted as the size of the particle-emitting region at freezeout, are expected to decrease with rising transverse momentum if the source expands [11]
While femtoscopic methods have already been applied to p+Pb systems at the Large Hadron Collider (LHC) [12, 13], these results are obtained using a new data-driven technique to constrain the significant background contribution from jet fragmentation, and they provide the first measurements of the dependence of these source radii on the rapidity yππ

Summary

Femtoscopy in

Michael Clark1,a on behalf of the ATLAS Collaboration 1Columbia University, 116th St & Broadway, New York, NY 10027, USA. Ap+bPstbraccotl.liBsioosnes-Eatin√stesiNnN correlations between identified charged = 5.02 TeV with the ATLAS detector pions using are measured for a total integrated luminosity of 28 nb−1. Two-particle correlation functions and the extracted source radii are presented as a function of average transverse pair momentum (kT) and rapidity (yππ) as well as collision centrality. Pairs are selected with a rapidity −2 < yππ < 1 and with an average transverse momentum 0.1 < kT < 0.8 GeV. The measured source sizes are substantially larger in more central collisions and are observed to decrease with increasing pair kT. The cross term Rol, which couples radial and longitudinal expansion, is measured as a function of rapidity, and a departure from zero is observed with 4.8 σ combined significance for yππ > −1 in the most central events

Introduction

Experimental Analysis

Results