Version 2
Constraining gluon distributions in nuclei using dijets in proton-proton and proton-lead collisions at $\sqrt{s_{_\mathrm{NN}}} =$ 5.02 TeV

The CMS collaboration Sirunyan, Albert M ; Tumasyan, Armen ; Adam, Wolfgang ; et al.
Phys.Rev.Lett. 121 (2018) 062002, 2018.
Inspire Record 1672941 DOI 10.17182/hepdata.83198

The pseudorapidity distributions of dijets as a function of their average transverse momentum ($p_\mathrm{T}^\text{ave}$) are measured in proton-lead (pPb) and proton-proton (pp) collisions. The data samples were collected by the CMS experiment at the CERN LHC, at a nucleon-nucleon center-of-mass energy of 5.02 TeV. A significant modification of the pPb spectra with respect to the pp spectra is observed in all $p_\mathrm{T}^\text{ave}$ intervals investigated. The ratios of the pPb and pp distributions are compared to next-to-leading order perturbative quantum chromodynamics calculations with unbound nucleon and nuclear parton distribution functions (PDFs). These results give the first evidence that the gluon PDF at large Bjorken $x$ in lead ions is strongly suppressed with respect to the PDF in unbound nucleons.

42 data tables

The ratio of pPb to pp $\eta_{\mathrm{dijet}}$ spectra for dijets in the range $55 < p_{\mathrm{T}}^{\mathrm{ave}} < 75$ GeV.

The ratio of pPb to pp $\eta_{\mathrm{dijet}}$ spectra for dijets in the range $55 < p_{\mathrm{T}}^{\mathrm{ave}} < 75$ GeV.

The ratio of pPb to pp $\eta_{\mathrm{dijet}}$ spectra for dijets in the range $75 < p_{\mathrm{T}}^{\mathrm{ave}} < 95$ GeV.

More…

Study of jet quenching with isolated-photon+jet correlations in PbPb and pp collisions at $\sqrt{s_{_{\mathrm{NN}}}} =$ 5.02 TeV

The CMS collaboration Sirunyan, Albert M ; Tumasyan, Armen ; Adam, Wolfgang ; et al.
Phys.Lett.B 785 (2018) 14-39, 2018.
Inspire Record 1638996 DOI 10.17182/hepdata.80815

Measurements of azimuthal angle and transverse momentum ($p_\mathrm{T}$) correlations of isolated photons and associated jets are reported for pp and PbPb collisions at $\sqrt{s_{_{\mathrm{NN}}}} =$ 5.02 TeV. The data were recorded with the CMS detector at the CERN LHC. For events containing a leading isolated photon with $p_\mathrm{T}^\gamma >$ 40 GeV$/c$ and an associated jet with $p_\mathrm{T}^\text{jet} >$ 30 GeV$/c$, the photon+jet azimuthal correlation and $p_\mathrm{T}$ imbalance in PbPb collisions are studied as functions of collision centrality and $p_\mathrm{T}^\gamma$. The results are compared to pp reference data collected at the same collision energy and to predictions from several theoretical models for parton energy loss. No evidence of broadening of the photon+jet azimuthal correlations is observed, while the ratio $p_\mathrm{T}^\text{jet}/p_\mathrm{T}^\gamma$ decreases significantly for PbPb data relative to the pp reference. All models considered agree within uncertainties with the data. The number of associated jets per photon with $p_\mathrm{T}^\gamma >$ 80 GeV$/c$ is observed to be shifted towards lower $p_\mathrm{T}^\text{jet}$ values in central PbPb collisions compared to pp collisions.

7 data tables

Jet resolution parameters for pp and PbPb collisions in various centrality bins.

The azimuthal correlation of photons and jets in five $p_{\mathrm{T}}^{\gamma}$ intervals for 0-30% and 30-100% centrality PbPb collisions. The smeared pp data are included for comparison.

Distribution of $x_{\mathrm{j}\gamma} = p_{\mathrm{T}}^{\mathrm{jet}} / p_{\mathrm{T}}^{\gamma}$ in five $p_{\mathrm{T}}^{\gamma}$ intervals for 0-30% and 30-100% centrality PbPb collisions. The smeared pp data are included for comparison. Empty bins are denoted as 'empty' in the table.

More…