CMS-PAS-FTR-18-025

CMS-PAS-FTR-18-025
Performance of jet quenching measurements in pp and PbPb collisions with CMS at the HL-LHC
CMS Collaboration
December 2018

Abstract: The projected performance of different jet measurements to be carried out with the large data samples expected in PbPb and pp collisions during the high-luminosity phase of the LHC (HL-LHC) is presented. The analyses are based on Monte Carlo simulations and extrapolations from data collected in pp and PbPb collisions between 2010 and 2016. The extrapolated performance for PbPb collisions, corresponding to an integrated luminosity of 10 nb $^{-1}$ at $\sqrt{s_{_\textrm{NN}}}=$ 5.02 TeV and an upgraded CMS detector, shows significant reductions in the uncertainties of the measurements of photon-tagged jet shapes and D $^0$ -jet correlations. The large proton-proton data sample at $\sqrt{s}=$ 14 TeV, to be collected under low-pileup conditions in Run 3 and beyond, will also provide new opportunities for the study of jet quenching phenomena in small systems, as shown through $\gamma$ , Z-jet transverse momentum imbalance distributions in high-multiplicity pp events.
Links: CDS record (PDF) ; inSPIRE record ; CADI line (restricted) ;

Figures	Summary	References	CMS Publications

Figures
png pdf	Figure 1: Ratio of the density of particles produced at a radius $r$ in photon-tagged jets in PbPb (0-10% most central) and pp collisions. The left panel shows the expected distribution at the HL-LHC with the error bars (bands) indicating statistical (systematic) uncertainties. The right panel shows a comparison of the current total uncertainty in the 2015 data (grey bands) [17] to the projected HL-LHC total uncertainty (violet bands).
png pdf	Figure 1-a: Ratio of the density of particles produced at a radius $r$ in photon-tagged jets in PbPb (0-10% most central) and pp collisions. The panel shows the expected distribution at the HL-LHC with the error bars (bands) indicating statistical (systematic) uncertainties.
png pdf	Figure 1-b: Ratio of the density of particles produced at a radius $r$ in photon-tagged jets in PbPb (0-10% most central) and pp collisions. The panel shows a comparison of the current total uncertainty in the 2015 data (grey bands) [17] to the projected HL-LHC total uncertainty (violet bands).
png pdf	Figure 2: Left: Projected distributions of ${\mathrm {D}^{0}}$ mesons with ${{p_{\mathrm {T}}} ^\mathrm {D}} =$ 4-20 GeV/ $c$ (top) and ${{p_{\mathrm {T}}} ^\mathrm {D}} >$ 20 GeV/ $c$ (bottom), as a function of their distance $r$ from the jet axis (for jets of ${{p_{\mathrm {T}}} ^\mathrm {jet}} >$ 60 GeV/ $c$ and $\|\eta ^{\mathrm {jet}}\| <$ 1.6) in pp and PbPb collisions at $\sqrt {s_{NN}}=$ 5.02 TeV at the HL-LHC. The error bands (error bars, barely seen) indicate systematic (statistical) uncertainties. The horizontal bars indicate the size of the bin width. Right: Same distributions as on the left, comparing the current total uncertainty (wide bands) [36] and the projected total uncertainty (thin bands).
png pdf	Figure 2-a: Left: Projected distributions of ${\mathrm {D}^{0}}$ mesons with ${{p_{\mathrm {T}}} ^\mathrm {D}} =$ 4-20 GeV/ $c$ , as a function of their distance $r$ from the jet axis (for jets of ${{p_{\mathrm {T}}} ^\mathrm {jet}} >$ 60 GeV/ $c$ and $\|\eta ^{\mathrm {jet}}\| <$ 1.6) in pp and PbPb collisions at $\sqrt {s_{NN}}=$ 5.02 TeV at the HL-LHC. The error bands (error bars, barely seen) indicate systematic (statistical) uncertainties. The horizontal bars indicate the size of the bin width. Right: Same distribution as on the left, comparing the current total uncertainty (wide bands) [36] and the projected total uncertainty (thin bands).
png pdf	Figure 2-b: Left: Projected distributions of ${\mathrm {D}^{0}}$ mesons with ${{p_{\mathrm {T}}} ^\mathrm {D}} >$ 20 GeV/ $c$ , as a function of their distance $r$ from the jet axis (for jets of ${{p_{\mathrm {T}}} ^\mathrm {jet}} >$ 60 GeV/ $c$ and $\|\eta ^{\mathrm {jet}}\| <$ 1.6) in pp and PbPb collisions at $\sqrt {s_{NN}}=$ 5.02 TeV at the HL-LHC. The error bands (error bars, barely seen) indicate systematic (statistical) uncertainties. The horizontal bars indicate the size of the bin width. Right: Same distribution as on the left, comparing the current total uncertainty (wide bands) [36] and the projected total uncertainty (thin bands).
png pdf	Figure 3: Left: Projected ratios at the HL-LHC of the radial distributions of ${\mathrm {D}^{0}}$ mesons produced in PbPb over pp collisions at $\sqrt {s_{NN}} =$ 5.02 TeV, for ${{p_{\mathrm {T}}} ^\mathrm {D}} =$ 4-20 GeV/ $c$ (top) and ${{p_{\mathrm {T}}} ^\mathrm {D}} >$ 20 GeV/ $c$ (bottom). The error bars (bands) indicate statistical (systematic) uncertainties. The horizontal bars indicate the size of the bin width. Rigth: Same distributions as on the left, comparing the current total uncertainty (grey bands) [36] and the projected total uncertainty at the HL-LHC (yellow bands).
png pdf	Figure 3-a: Left: Projected ratios at the HL-LHC of the radial distributions of ${\mathrm {D}^{0}}$ mesons produced in PbPb over pp collisions at $\sqrt {s_{NN}} =$ 5.02 TeV, for ${{p_{\mathrm {T}}} ^\mathrm {D}} =$ 4-20 GeV/ $c$ . The error bars (bands) indicate statistical (systematic) uncertainties. The horizontal bars indicate the size of the bin width. Rigth: Same distribution as on the left, comparing the current total uncertainty (grey bands) [36] and the projected total uncertainty at the HL-LHC (yellow bands).
png pdf	Figure 3-b: Left: Projected ratios at the HL-LHC of the radial distributions of ${\mathrm {D}^{0}}$ mesons produced in PbPb over pp collisions at $\sqrt {s_{NN}} =$ 5.02 TeV, for ${{p_{\mathrm {T}}} ^\mathrm {D}} >$ 20 GeV/ $c$ . The error bars (bands) indicate statistical (systematic) uncertainties. The horizontal bars indicate the size of the bin width. Rigth: Same distribution as on the left, comparing the current total uncertainty (grey bands) [36] and the projected total uncertainty at the HL-LHC (yellow bands).
png pdf	Figure 4: Distributions of transverse momentum imbalance, $x_{j\gamma}$ , in three different centrality classes of pp isolated-photon+jet events ( ${p_{\mathrm {T}}} ^{\gamma} >$ 60 GeV/ $c$ and $\|\eta _{\gamma}\| <$ 1.44, ${{p_{\mathrm {T}}} ^\mathrm {jet}} >$ 30 GeV/ $c$ and $\|\eta _{\rm jet}\| <$ 1.6) with 200 (dashed line) and 2000 (solid line) pb $^{-1}$ integrated luminosities expected to be taken under low-pileup conditions at HL-LHC. The central values of the distributions are derived from existing measurements [43] combined with PYTHIA 8 MC simulations. The error bars (bands) indicate statistical (systematic) uncertainties.
png pdf	Figure 5: Distributions of transverse momentum imbalance, $x_{jZ}$ , in two different centrality classes of pp Z+jet events ( ${p_{\mathrm {T}}} ^{Z} >$ 60 GeV/ $c$ , ${{p_{\mathrm {T}}} ^\mathrm {jet}} >$ 30 GeV/ $c$ and $\|\eta _{\rm jet}\| <$ 1.6) with 200 (dashed line) and 2000 (solid line) pb $^{-1}$ integrated luminosities expected to be taken under low-pileup conditions at HL-LHC. The central values of the distributions are derived from existing measurements [38] combined with PYTHIA 8 MC. The error bars (bands) indicate statistical (systematic) uncertainties.

Summary

The projected performance of different jet measurements expected to be carried out with large data samples of PbPb and low-pileup pp collisions at HL-LHC are presented. The HL-LHC performance, extrapolated from existing PbPb data and Monte Carlo simulations, corresponding to a total integrated luminosity of 10 nb

$^{-1}$ at

${\sqrt{s_{_{\text{NN}}}}} =$ 5.02 TeV, shows significantly improved precision in the measurements of photon-tagged jet shapes and

$\mathrm{D}^{0}$ -jet correlations. These measurements will provide new constraints on models of jet quenching in the QGP, heavy quark production and diffusion inside the medium, and improved understanding of the medium response and medium excitation to hard probes. The large pp data samples at

${\sqrt{s}} =$ 14 TeV with low pileup, expected to be collected in Run 3 and beyond, will also provide precise measurements of boson-jet transverse momentum imbalance distributions in (high-multiplicity) small systems, and thereby study the system-size dependence of jet quenching phenomena.

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