Measurement of the sensitivity of two particle correlations in $pp$ collisions at $\sqrt{s}=13$ TeV to the presence of jets with the ATLAS detector

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Measurement of the sensitivity of two particle correlations in $pp$ collisions at $\sqrt{s}=13$ TeV to the presence of jets with the ATLAS detector ATLAS-CONF-2020-018 30 May 2020
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Abstract
Measurements of two-particle correlations in $pp$ collisions show the presence of long-range correlations along $\Delta\eta$ that are strikingly similar to those seen in heavy-ion collisions. In heavy-ion collisions, the long-range correlations are known to arise from the collective dynamics of the produced quark-gluon plasma (QGP). The similarity between the $pp$ and heavy-ion measurements raises the possibility that a tiny droplet of the QGP is produced even in $pp$ collisions. However, models that attribute the correlation in $pp$ collisions to semi-hard processes can qualitatively reproduce the measurements. Thus performing the $pp$ measurements with an active rejection of particles associated with semi-hard processes, such as low-$p_{\mathrm{T}}$ jets, can further elucidate the origin of the long-range correlations. This note presents measurements of two-particle correlations in $pp$ collisions at $\sqrt{s}=13$ TeV, when removing tracks associated with jets from the event. The jets are reconstructed from tracks using the anti-$k_t$ algorithm, and all tracks within one unit of pseudorapidity of the jet are removed from the correlation analysis. It is demonstrated that such removal of particles in the vicinity of jets affects the magnitude of long-range correlations only by a few percent.
Figures
Figure 01: Figures illustrating removal of tracks associated with jets. The circles represent jets that have p_T above 10 GeV. Tracks within Δη = pm1 from the jet axis of any jet are removed from the correlation. The rejection region is indicated by the shaded bands. The unshaded (clear or white) region indicates the η region from which tracks are used in the correlations analysis. png (404kB) pdf (57kB)
Figure 02: The N_ch^rec,corr distribution for AllEvents, NoJet, and WithJet selections. The individual panels show the distributions for different jet p_T thresholds. The discrete jumps in the distributions correspond to the HMT triggers. png (287kB) pdf (67kB)
Figure 03: Comparison of the v₂ obtained with different jet-p_T thresholds. The left panel corresponds to the event set of AllEvents, and the right panel to the WithJet sample. The plots are for the 0.5--5 GeV p_T interval. The error bars correspond to statistical uncertainties only. png (74kB) pdf (35kB)
Figure 04: Comparison of the v₂ as a function of ptb obtained with different jet-pt thresholds for 0.5 GeV<pta<5 GeV. The left panel corresponds to the event set of AllEvents, and the right panel to the WithJet sample. The plots are for the 60--150 multiplicity interval. The error bars correspond to statistical uncertainties only. png (75kB) pdf (37kB)
Figure 05: Template fits to the two-particle correlations in dphi for 0.5 GeV <ptab <5 GeV and 2<\|deta\|<5. The open points correspond to the scaled peripheral reference and the blue dash lines correspond to the cridge. From top to bottom the rows correspond to the Inclusive, AllEvents, NoJet and WithJet samples. From left to right, each panel corresponds to a different multiplicity interval. The error bars correspond to statistical uncertainties. The uncertainties on the fits themselves are not shown for clarity, and are at least as large as the uncertainties on the Fcperi(dphi) term. png (900kB) pdf (141kB)
Figure 06: Template fits to the two-particle correlations in dphi for 0.5 GeV <pta <5 GeV and 2<\|deta\|<5. From left to right, each panel corresponds to a different ptb interval. The open points correspond to the scaled peripheral reference and the blue dash lines correspond to the cridge. From top to bottom the rows correspond to the Inclusive, AllEvents, NoJet and WithJet samples. The error bars correspond to statistical uncertainties. The uncertainties on the fits themselves are not shown for clarity, and are at least as large as the uncertainties on the Fcperi(dphi) term. png (901kB) pdf (140kB)
Figure 07: The left panels show the v_n as a function of the (efficiency corrected) multiplicity. From top to bottom each row shows the results for a different harmonic order. The data-points for the Inclusive sample are drawn at the nominal values while the data-points for the AllEvents and NoJet samples are shifted slightly for clarity. The right panels show the ratio of the v_n for the different samples to the Inclusive sample. The error bars and bands correspond to statistical and systematic uncertainties, respectively. For the ratio plots, the correlated uncertainties between the numerator and denominator are removed. png (177kB) pdf (50kB)
Figure 08: Same as the top panels of Figure 7, but including the results for the WithJet sample. The data-points for the WithJet sample are evaluated over coarser multiplicity intervals to reduce statistical uncertainties. png (73kB) pdf (20kB)
Figure 09: The left panels show the ptb dependence of the v_n obtained for the 60--150 multiplicity interval for 0.5 GeV<pta<5 GeV. From top to bottom each row shows the results for a different harmonic order. In the lower two rows, the data-points for the Inclusive sample are drawn at the nominal values while the data-points for the AllEvents and NoJet samples are shifted slightly for clarity. The right panels show the ratio of the v_n for the different samples to the Inclusive sample. For the top right plot, the ratio is not shown for the 6--8 GeV pt interval where the v₂ values for the Inclusive sample are negative. The error bars and bands correspond to statistical and systematic uncertainties, respectively. For the ratio plots, the correlated uncertainties between the numerator and denominator are removed. png (175kB) pdf (51kB)
Figure 10: Same as the top panels of Figure 9, but including the results for the WithJet sample. The data-points for the WithJet sample are evaluated over coarser p_T intervals to reduce statistical uncertainties. png (68kB) pdf (21kB)
Figure 11: The left panels show the Σ E_T^FCal dependence of the v_n. From top to bottom each panel shows the results for a different harmonic order. The data-points for the Inclusive sample are drawn at the nominal values while the data-points for the AllEvents and NoJet samples are shifted slightly for clarity. The right panels show the ratio of the v_n for the different samples to the Inclusive sample. The error bars and bands correspond to statistical and systematic uncertainties, respectively. For the ratio plots, the correlated uncertainties between the numerator and denominator are removed. png (174kB) pdf (47kB)
Figure 12: Same as the top panels of Figure 11, but including the results for the WithJet sample. The data-points for the WithJet sample are evaluated over coarser Σ E_T^FCal intervals to reduce statistical uncertainties. png (69kB) pdf (18kB)

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2020-12-11 00:37:02