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Internal structure of jets measured in Pb+Pb and pp collisions with the ATLAS detector at the LHC ATLAS-CONF-2015-055 25 September 2015
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| Abstract | ||
| The first measurement of the jet fragmentation done by ATLAS revealed a modest but significant modifications of jet fragmenation functions and distributions of charged particle transverse momenta measured with respect to the jet axis. These observations represent important inputs for constraining the theory of the jet quenching. In this follow-up study, we provide more details needed for a better understanding of the underlying physics meachnisms. This study has been performed using 140 μb−1 of Pb+Pb collision data provided at a nucleon center-of-mass energy of 2.76 GeV by the LHC and collected during 2011 run and with 4.1 pb-1 of pp data at the same center-of-mass energy collected during 2013 run which is used as a reference for the heavy ion measurement. | ||
| Figures | ||
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Figure 1a: The tracking efficiency evaluated for particles in jets with pTjet > 100 GeV as a function of truth charged particle transverse momentum, pTparticle , for jets with |etaa| < 0.3 (left) and 1.2 < |etaa| < 2.1 (right). Efficiency is shown for central and peripheral Pb+Pb collisions as well as for pp collisions. The full line represents the parameterization (for more details see the body of the text). png (107kB), pdf (19kB) |
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Figure 1b: The tracking efficiency evaluated for particles in jets with pTjet > 100 GeV as a function of truth charged particle transverse momentum, pTparticle , for jets with |etaa| < 0.3 (left) and 1.2 < |etaa| < 2.1 (right). Efficiency is shown for central and peripheral Pb+Pb collisions as well as for pp collisions. The full line represents the parameterization (for more details see the body of the text). png (97kB), pdf (19kB) |
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Figure 2: Unfolded charged particle transverse momentum distributions, D(pT), measured in pp collisions and for seven centrality bins measured in Pb+Pb collisions. Four panels show D(pT) distributions with different selection on jet pseudorapidity for jets with pT in the interval of 100-398 GeV. The error bars on the data points indicate statistical uncertainties while the shaded bands indicate systematic uncertainties. png (52kB), pdf (31kB) |
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Figure 3: Unfolded distributions of longitudinal momentum fraction, D(z), measured in pp collisions and for seven centrality bins measured in Pb+Pb collisions. Four panels show D(z) distributions with different selection on jet pseudorapidity for jets with pT in the interval of 100-398 GeV. The error bars on the data points indicate statistical uncertainties while the shaded bands indicate systematic uncertainties. png (51kB), pdf (31kB) |
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Figure 4: The ratio of unfolded D(pT) distributions measured in heavy ion collisions to unfolded D(pT) distributions measured in pp collisions, RD(pT). RD(pT) distributions are evaluated in four different centrality bins (rows) and four different selections on jet pseudorapidity of jets with 100 < pT < 398 GeV (columns). The error bars on the data points indicate statistical uncertainties while the shaded bands indicate systematic uncertainties. png (41kB), pdf (37kB) |
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Figure 5: The ratio of unfolded D(z) distributions measured in heavy ion collisions to unfolded D(z) distributions measured in pp collisions, RD(z). RD(z) distributions are evaluated in four different centrality bins (rows) and four different selections on jet pseudorapidity of jets with 100 < pT < 398 GeV (columns). The error bars on the data points indicate statistical uncertainties while the shaded bands indicate systematic uncertainties. png (39kB), pdf (34kB) |
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Figure 6: The ratio of unfolded D(pT) distributions measured in heavy ion collisions to unfolded D(pT) distributions measured in pp collisions, RD(pT). RD(pT) distributions are evaluated in four different centrality bins (rows) and four different selections on jet pT of jets with |etaa|<2.1 (columns). The error bars on the data points indicate statistical uncertainties while the shaded bands indicate systematic uncertainties. png (44kB), pdf (39kB) |
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Figure 7: The ratio of unfolded D(z) distributions measured in heavy ion collisions to unfolded D(z) distributions measured in pp collisions, RD(z). RD(z) distributions are evaluated in four different centrality bins (rows) and four different selections on jet pT of jets with |etaa|<2.1 (columns). The error bars on the data points indicate statistical uncertainties while the shaded bands indicate systematic uncertainties. png (42kB), pdf (36kB) |
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Figure 8: Upper panels: difference in the total yield of particles in a given pTch interval (indicated in the legend) measured in Pb+Pb and the total yield of particles in the same pTch interval measured in pp collisions, Nch . Lower panels: difference in the total transverse momentum of particles in a given pTch interval measured in Pb+Pb and the total transverse momentum of particles measured in pp , PTch . The differences are evaluated as a function of number of participating nucleons. The error bars on the data points indicate statistical uncertainties while the shaded bands indicate systematic uncertainties. png (26kB), pdf (69kB) |
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