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| CMS-PAS-FSQ-17-001 | ||
| Very forward inclusive jet cross sections in p+Pb collisions at $\sqrt{s_{\mathrm{NN}}}= $ 5.02 TeV | ||
| CMS Collaboration | ||
| April 2017 | ||
| Abstract: Measurements of very forward inclusive jet energy spectra with the CMS experiment at the LHC are presented. The data were collected with the CASTOR calorimeter in the pseudorapidity range $-6.6<\eta<-5.2$ in proton lead collisions, with a centre-of-mass energy of $\sqrt{s_{\mathrm{NN}}}= $ 5.02 TeV in 2013. The analysed data samples correspond to integrated luminosities of 3.13 and 6.71 nb$^{-1}$, for beam configurations with the proton (p+Pb) or ion (Pb+p) towards CASTOR, respectively. The results are presented for energy ranges from 600 to 2500 (p+Pb) and 4000 (Pb+p) GeV. The spectra are unfolded to the particle level and compared to predictions of various event generators. In addition, the p+Pb/Pb+p ratio of the spectra is presented, for which the systematic uncertainties in the measurement are significantly reduced. None of the event generators under consideration describe all spectra in their full energy range, and deviations between data and models of more than two orders of magnitude are observed. | ||
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Links:
CDS record (PDF) ;
CADI line (restricted) ;
These preliminary results are superseded in this paper, JHEP 05 (2019) 043. The superseded preliminary plots can be found here. |
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| Figures | |
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Figure 1:
A schematic drawing of one CASTOR half. The diameter of CASTOR is roughly 0.6 m, its length approximately 1.6 m. |
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Figure 2:
The energy spectrum of CASTOR jets in p+Pb collisions, normalised to the cross section. Model predictions are included for EPOS-LHC, HIJING, and QGSJetII-04. |
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Figure 3:
The energy spectrum of CASTOR jets in Pb+p collisions, normalised to the cross section. Model predictions are included for EPOS-LHC, HIJING, and QGSJetII-04. |
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Figure 4:
The energy spectrum of CASTOR jets for the p+Pb/Pb+p ratio, normalised to the cross section. Model predictions are included for EPOS-LHC, HIJING, and QGSJetII-04. |
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Figure 5-a:
The normalised response matrix for p+Pb collisions. For the events that obey the detector and generator level selection criteria, the generator and detector level jets are matched in $\phi $. For the matched jets, the generator jet energy is plotted on the $y$ axis and the detector jet energy on the $x$ axis. |
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Figure 5-b:
The normalised response matrix for Pb+p collisions. For the events that obey the detector and generator level selection criteria, the generator and detector level jets are matched in $\phi $. For the matched jets, the generator jet energy is plotted on the $y$ axis and the detector jet energy on the $x$ axis. |
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Figure 6:
The differential CASTOR jet energy cross section for p+Pb collisions (with the proton towards CASTOR). The CASTOR jets were unfolded to a spectrum of particle level jets in the CASTOR acceptance ($-6.6\leq \eta \leq -5.2$). Model predictions are included for EPOS-LHC, HIJING, and QGSJetII-04. |
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Figure 7:
The differential CASTOR jet energy cross section for Pb+p collisions (with the ion towards CASTOR). The CASTOR jets were unfolded to a spectrum of particle level jets in the CASTOR acceptance ($-6.6\leq \eta \leq -5.2$). Model predictions are included for EPOS-LHC, HIJING, and QGSJetII-04. |
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Figure 8:
The ratio of the differential CASTOR jet energy cross sections for p+Pb/Pb+p. The CASTOR jets were unfolded to a spectrum of particle level jets in the CASTOR acceptance ($-6.6\leq \eta \leq -5.2$). Model predictions are included for EPOS-LHC, HIJING, and QGSJetII-04. |
| Tables | |
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Table 1:
The position of CASTOR during the 2013 p+Pb data taking with its uncertainty. The position is quoted w.r.t. the nominal position of CASTOR, which is defined as (0,0). The NEAR half is located on the inner side of the LHC circle, while the far half is located on the outside. |
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Table 2:
The various contributions to the uncertainty in the energy scale of CASTOR. |
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Table 3:
The contribution of various sources to the systematic uncertainty in the highest and lowest common energy bin for the p+Pb, Pb+p, and (p+Pb)/(Pb+p) spectra. The overall number is also quoted. |
| Summary |
| Forward jet energy spectra have been presented for p+Pb, Pb+p, and p+Pb/Pb+p collisions on particle and detector level. None of the models investigated are capable of describing all the spectra. The p+Pb spectrum is well described by HIJING, while for this spectrum the deviations with data are the largest and more than two orders of magnitude for QGSJet. Further it was shown that the cancellation of systematic uncertainties for the p+Pb/Pb+p spectrum increased the discriminative power of the results. EPOS and QGSJet largely underestimate the p+Pb jet cross sections, but it should be noted these generators were developed to model soft interactions. On the other hand, since the interactions investigated here have a moderate $p_{\mathrm{T}}$, the results could serve as useful input for improvements of their descriptions. |
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