CMS-HIN-18-020

CMS-HIN-18-020 ; CERN-EP-2020-060
Measurement of b jet shapes in proton-proton collisions at $\sqrt{s} = $ 5.02 TeV
CMS Collaboration
28 May 2020
JHEP 05 (2021) 054
Abstract: We present the first study of charged-hadron production associated with jets originating from b quarks in proton-proton collisions at a center-of-mass energy of 5.02 TeV. The data sample used in this study was collected with the CMS detector at the CERN LHC and corresponds to an integrated luminosity of 27.4 pb$^{-1}$. To characterize the jet substructure, the differential jet shapes, defined as the normalized transverse momentum distribution of charged hadrons as a function of angular distance from the jet axis, are measured for b jets. In addition to the jet shapes, the per-jet yields of charged particles associated with b jets are also quantified, again as a function of the angular distance with respect to the jet axis. Extracted jet shape and particle yield distributions for b jets are compared with results for inclusive jets, as well as with the predictions from the PYTHIA event generator.
Links: e-print arXiv:2005.14219 [hep-ex] (PDF) ; CDS record ; inSPIRE record ; HepData record ; CADI line (restricted) ;

Figures & Tables	Summary	References	CMS Publications

Figures
png pdf	Figure 1: Charged particle yield distributions $Y({\Delta r})$ of inclusive (left) and b (right) jets with $ {p_{\mathrm {T}}} > $ 120 GeV as functions of $ {\Delta r} $ are presented differentially for $ {{p_{\mathrm {T}}} ^{\text {trk}}} $ bins. The shadowed boxes represent the systematic uncertainties, although they are generally too small to be visible.
png pdf	Figure 2: Charged particle yield distributions $Y({\Delta r})$ of inclusive jets (left) and b jets (middle) with 1 $ < {{p_{\mathrm {T}}} ^{\text {trk}}} < $ 12 GeV are presented as functions of $ {\Delta r} $. Both types of jets with $ {p_{\mathrm {T}}} > $ 120 GeV and charged particles with 1 $ < {{p_{\mathrm {T}}} ^{\text {trk}}} < $ 12 GeV are used to construct the distributions as functions of $ {\Delta r} $ for data (red), PYTHIA 6.426 (blue line) and PYTHIA 8.230 (green dashed line) simulations, respectively. The right plot shows the particle yield difference of b jets and inclusive jets as functions of $ {\Delta r} $ for pp data and PYTHIA 6.426 (blue line) and PYTHIA 8.230 (green dashed line) simulations. The shadowed boxes represent the systematic uncertainties.
png pdf	Figure 3: The jet shape distribution $ {\rho ({\Delta r})} $ of inclusive jets (left) and b jets (right) with $ {p_{\mathrm {T}}} > $ 120 GeV as functions of $ {\Delta r} $ are presented differentially for all $ {{p_{\mathrm {T}}} ^{\text {trk}}} $ bins for data. The shadowed boxes represent the systematic uncertainties, although they are generally too small to be visible.
png pdf	Figure 4: The jet shape distribution $ {\rho ({\Delta r})} $ of inclusive jets (left) and b jets (middle), both with $ {p_{\mathrm {T}}} > $ 120 GeV and $ {{p_{\mathrm {T}}} ^{\text {trk}}} > $ 1 GeV are presented as functions of $ {\Delta r} $ for data(red markers), the PYTHIA 6.426 (blue line) and the PYTHIA 8.230 (green dashed line) simulations. The right plot shows the b-to-inclusive jet shape ratio as functions of $ {\Delta r} $ for data, PYTHIA 6 (blue line) and PYTHIA 8.230 (green dashed line) simulations. The shadowed boxes represent the systematic uncertainty.

Tables
png pdf	Table 1: Systematic uncertainties in percentage for the measurements of the jet-track correlations. Where an uncertainty range is given, the upper edge of the range corresponds to the bin with the smallest ${{p_{\mathrm {T}}} ^{\text {trk}}}$ values. The sources from the decontamination and tagging bias are exclusive for b jets.

Summary

The first measurements of charged-particle yields and jet shapes for b jets in proton-proton collisions are presented, using data collected with the CMS detector at the LHC at a center-of-mass energy of $\sqrt{s} = $ 5.02 TeV. The correlations of charged particles with jets are studied, using the particles with transverse momentum $p_{\mathrm{T}}^{\text{trk}} > $ 1 GeV and pseudorapidity $|\eta| < $ 2.4, and the jets with ${p_{\mathrm{T}}} > $ 120 GeV and $|\eta| < $ 1.6. Charged-particle yields associated with jets are presented as functions of the relative angular distance ${\Delta r} = \sqrt{\smash[b]{(\Delta\eta)^{2}+(\Delta\phi)^{2}}}$ from the jet axis. In these studies, a large number of associated charged particles at low ${\Delta r} $ are found for b jets compared to those for inclusive jets, which are produced predominantly by gluons and light flavor quarks. The trends observed in pp data for particle yield distributions associated with both types of jets are reproduced by PYTHIA calculations (in versions 6.426 and 8.230).

In addition to the charged-particle yields, we examine the jet transverse momentum profile variable ${\rho({\Delta r} )} $, defined using the distribution of charged particles in annular rings around the jet axis, with each particle weighted by its $p_{\mathrm{T}}^{\text{trk}}$ value. The measured shapes of b jets are broader than those of inclusive jets. The shapes for both types of jets are reproduced by PYTHIA calculation in the small ${\Delta r} $ region, with PYTHIA 6.426 giving a better agreement. However, measured transverse momenta distributions at larger ${\Delta r} $ are underestimated in PYTHIA simulations for b and inclusive jets, with larger data-to-simulation differences observed for b jets.

This result provides new constraints on perturbative quantum chromodynamics calculations for flavor dependence in parton fragmentation and gluon radiation, as well as the relative contributions of different processes to b quark production. These measurements are also expected to offer an important reference for future studies of flavor dependence for parton interactions with the quark-gluon plasma formed in relativistic heavy ion collisions.

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