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| CMS-PAS-HIN-16-021 | ||
| Pseudorapidity distributions of charged hadrons in proton-lead collisions at $\sqrt{s_{\mathrm{NN}}} = $ 5.02 and 8.16 TeV | ||
| CMS Collaboration | ||
| July 2017 | ||
| Abstract: The pseudorapidity distributions of charged hadrons in proton-lead (pPb) collisions at $\sqrt{s_{\mathrm{NN}}}=$ 5.02 and 8.16 TeV are measured using a data sample obtained with the CMS detector at the CERN LHC. The yield of primary charged long-lived hadrons produced in non-single-diffractive pPb collisions is determined in the central region of the CMS pixel detector ($ | \eta | < $ 2.4) using hit pairs. The result is compared to predictions from calculations with gluon saturation models, Monte Carlo event generators, and to similar measurements made at lower collision energies. | ||
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Links:
CDS record (PDF) ;
inSPIRE record ;
CADI line (restricted) ;
These preliminary results are superseded in this paper, JHEP 01 (2018) 045. The superseded preliminary plots can be found here. |
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| Figures | |
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Figure 1:
The $\Delta \eta $ (left) and $\Delta \phi $ (right) distributions of hit pairs for tracklets in 8.16 TeV data (squares) and from MC simulations with the EPOS generator (histogram). |
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Figure 1-a:
The $\Delta \eta $ distribution of hit pairs for tracklets in 8.16 TeV data (squares) and from MC simulations with the EPOS generator (histogram). |
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Figure 1-b:
The $\Delta \phi $ distribution of hit pairs for tracklets in 8.16 TeV data (squares) and from MC simulations with the EPOS generator (histogram). |
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Figure 2:
Distributions of the pseudorapidity density of charged hadrons in the region $ {| \eta | } < $ 2.4 in NSD pPb collisions at 5.02 (blue) and 8.16 TeV (orange) as measured in data. The measurement at 5.02 TeV from the ALICE collaboration is shown in green. The shaded boxes encompassing the data points indicates their correlated systematic uncertainties. |
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Figure 3:
Distributions of the pseudorapidity density of charged hadrons in the region $ {| \eta | } < $ 2.4 in NSD pPb collisions at 8.16 TeV (right, orange) as measured in data, compared to predictions from various Monte-Carlo event generators and models. |
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Figure 4:
Comparison of the measured $ { {\mathrm {d}}{}N_{\mathrm {ch}}/ {\mathrm {d}}\eta } $ at midrapidity, scaled by the number of partipating nucleons ($N_{part}$) in pPb [25,26], pAu [27], dAu [28] and central heavy-ion collisions [29,30,31,32,33,34,35,36,37,38,39,19] as well as pp NSD [40,41,42,43,44,15,16] and inelastic [45,42,46,29,18]. The curves which are superimposed on the data are from [46,38]. |
| Summary |
| The pseudorapidity distribution of charged hadrons has been measured by the CMS experiment at the LHC in proton-lead collisions at $\sqrt{s} = $ 5.02 and 8.16 TeV. Based on hit pairs in the barrel region of the CMS pixel detector, the distributions have been obtained for NSD pPb events at both collision energies. The measured ${\mathrm {d}}{}N_{\mathrm {ch}}/ {\mathrm {d}}\eta$ distributions at 5.02 TeV are consistent with published results from the ALICE collaboration and with the predictions from the EPOS (LHC tune) event generator, while the measured ${\mathrm {d}}{}N_{\mathrm {ch}}/ {\mathrm {d}}\eta$ distributions at 8.16 TeV are higher than the predictions of EPOS \ (LHC tune) event generator and significantly lower than the prediction from the HIJING 1.3 event generator. At midrapidity, the charged particle density at 8.16 TeV is in good agreement with KLN model calculations and predictions from the HIJING 2.1 event generator with gluon shadowing. These results constitute the first measurement of hadron production at the new center-of-mass energy frontier in heavy-ion collisions, and provide new constraints for the improvement of perturbative and nonperturbative QCD aspects implemented in event generators for the description of high-energy nuclear collisions. |
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