/ hep-ex CERN-EP-2017-004

Femtoscopy with identified charged pions in proton-lead collisions at $\sqrt{s_{\mathrm{NN}}}=5.02$ TeV with ATLAS

Published in: J.Phys.Conf.Ser.
Year: 2017
Vol.: 832    Num./Issue: 1
Page No: 012014
Pages: 4
Year: 2017-04-25 published

Abstract: Bose-Einstein correlations between identified charged pions are measured for $p$+Pb collisions at $\sqrt{s_{\mathrm{NN}}}=5.02$ TeV using data recorded by the ATLAS detector at the LHC corresponding to a total integrated luminosity of $28$ $\mathrm{nb}^{-1}$. Pions are identified using ionization energy loss measured in the pixel detector. Two-particle correlation functions and the extracted source radii are presented as a function of collision centrality as well as the average transverse momentum ($k_{\mathrm{T}}$) and rapidity ($y^{\star}_{\pi\pi}$) of the pair. Pairs are selected with a rapidity $-2 < y^{\star}_{\pi\pi} < 1$ and with an average transverse momentum $0.1 < k_{\mathrm{T}} < 0.8$ GeV. The effect of jet fragmentation on the two-particle correlation function is studied, and a method using opposite-charge pair data to constrain its contributions to the measured correlations is described. The measured source sizes are substantially larger in more central collisions and are observed to decrease with increasing pair $k_{\mathrm{T}}$. A correlation of the radii with the local charged-particle density is demonstrated. The scaling of the extracted radii with the mean number of participating nucleons is also used to compare a selection of initial-geometry models. The cross-term $R_\mathrm{ol}$ is measured as a function of rapidity, and a nonzero value is observed with $5.1\sigma$ combined significance for $-1 < y^{\star}_{\pi\pi} < 1$ in the most central events.
Bose-Einstein correlations between identified charged pions are measured for p+Pb collisions at $\sqrt{{s}_{{\rm{NN}}}}$ = 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 (${y}_{\pi \pi }^{* }$) as well as collision centrality. Pairs are selected with a rapidity −2 < ${y}_{\pi \pi }^{* }$ < 1 and with an average transverse momentum 0.1 < k(T) < 0.8 GeV. The effect on the two-particle correlation function from jet fragmentation is studied, and a new method for constraining its contributions to the measured correlations is described. The measured source sizes are substantially larger in more central collisions and are observed to decrease with increasing pair k(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(ol), 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 ${y}_{\pi \pi }^{* }$ > −1 in the most central events.

Note: 56 pages in total, author list starting page 40, 35 figures, 1 table, submitted to Phys. Rev. C., all figures including auxiliary figures are available at https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/HION-2015-11/

Total numbers of views: 13656
Numbers of unique views: 8042
DOI: 10.1088/1742-6596/832/1/012014