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Total J/Psi and Upsilon production cross section at the LHC: theory vs. experiment

J. P. Lansberg

TL;DR

This paper assesses whether LO color-singlet mechanisms suffuce to describe direct $J/ psi$ and $Upsilon$ production cross sections at LHC energies by computing $P_T$-integrated yields from LO $gg$ fusion across $ ms$ from 200 GeV to 14 TeV and comparing to RHIC and LHC data in central and forward rapidities. The authors find that the LO CS predictions reproduce the observed magnitudes within large theoretical uncertainties and that 7 TeV and 14 TeV results are in the same ballpark as alternative models such as CEM and GTM. They also discuss the potential destabilizing effects of higher-order corrections, including negative yields in some regions, and argue that yield measurements alone cannot definitively discriminate production mechanisms, highlighting the need for additional observables. Overall, the study supports a limited role for colour-octet contributions at low $P_T$ for $J/ psi$ and confirms that LO CS can account for the integrated cross section at $ ms=7$ TeV, while urging further exploration of related production channels.

Abstract

We evaluate the production cross section for direct J/Psi and Upsilon integrated in P_T for various collision energies in the QCD-based Colour-Singlet Model (CSM). We consider the LO contribution from gluon fusion whose P_T-integrated cross section shows a very good agreement with the Tevatron and LHC data, both for J/Psi and Upsilon. The rapidity distribution of this yield is evaluated in the central region relevant for the ATLAS and CMS detectors, as well as in the more forward region relevant for the ALICE and LHCb detectors. The results obtained here are compatible with those of other approaches within the range of the theoretical uncertainties which are admittedly very large. This suggests that the "mere" measurements of the yield at the LHC will not help disentangle between the different possible quarkonium production mechanisms. Yet, the comparison with the first LHC results by ALICE, ATLAS, CMS and LHCb confirms that the CSM correctly accounts for the P_T-integrated yield at sqrt(s)=7 TeV.

Total J/Psi and Upsilon production cross section at the LHC: theory vs. experiment

TL;DR

This paper assesses whether LO color-singlet mechanisms suffuce to describe direct and production cross sections at LHC energies by computing -integrated yields from LO fusion across from 200 GeV to 14 TeV and comparing to RHIC and LHC data in central and forward rapidities. The authors find that the LO CS predictions reproduce the observed magnitudes within large theoretical uncertainties and that 7 TeV and 14 TeV results are in the same ballpark as alternative models such as CEM and GTM. They also discuss the potential destabilizing effects of higher-order corrections, including negative yields in some regions, and argue that yield measurements alone cannot definitively discriminate production mechanisms, highlighting the need for additional observables. Overall, the study supports a limited role for colour-octet contributions at low for and confirms that LO CS can account for the integrated cross section at TeV, while urging further exploration of related production channels.

Abstract

We evaluate the production cross section for direct J/Psi and Upsilon integrated in P_T for various collision energies in the QCD-based Colour-Singlet Model (CSM). We consider the LO contribution from gluon fusion whose P_T-integrated cross section shows a very good agreement with the Tevatron and LHC data, both for J/Psi and Upsilon. The rapidity distribution of this yield is evaluated in the central region relevant for the ATLAS and CMS detectors, as well as in the more forward region relevant for the ALICE and LHCb detectors. The results obtained here are compatible with those of other approaches within the range of the theoretical uncertainties which are admittedly very large. This suggests that the "mere" measurements of the yield at the LHC will not help disentangle between the different possible quarkonium production mechanisms. Yet, the comparison with the first LHC results by ALICE, ATLAS, CMS and LHCb confirms that the CSM correctly accounts for the P_T-integrated yield at sqrt(s)=7 TeV.

Paper Structure

This paper contains 3 sections, 4 figures.

Table of Contents

  1. Introduction
  2. Total $J/\psi$ and $\Upsilon$ cross section at the LHC
  3. Discussion and conclusion

Figures (4)

  • Figure 1: $d\sigma^{direct}_{J/\psi}/dy|_{y=0}\times {\rm Br}$ from $gg$ fusion in $pp$ collisions for $\sqrt{s}$ from 200 GeV up to 14 TeV compared to the PHENIX Adare:2006kf, CDF Acosta:2004yw and ALICE boyer data multiplied by the direct fraction (see text). html:<A name="ref-sigma_vs_s-jpsi">html:</A> LAB: sigma_vs_s-jpsi
  • Figure 2: $d\sigma^{direct}_{\Upsilon}/dy|_{y=0}\times {\rm Br}$ from $gg$ fusion in $pp$ collisions for $\sqrt{s}$ from 200 GeV up to 14 TeV compared to the STAR Abelev:2010am, CDF Acosta:2001gv and CMS CMS-Upsilon data multiplied by the direct fraction (see text).
  • Figure 3: $d\sigma^{direct}_{J/\psi}/dy\times {\rm Br}$ from $gg$ fusion LO contributions in $pp$ collisions at $\sqrt{s}=7$ TeV compared to ALICE boyer, ATLAS ATLAS-JPsi, CMS Collaboration:2010yr and LHCb LHCb-JPsi results multiplied by the direct fraction (and the prompt fraction (10 $\%$) if applicable). html:<A name="ref-7tev-Jpsi">html:</A> LAB: 7tev-Jpsi
  • Figure 4: $d\sigma^{direct}_{\Upsilon}/dy\times {\rm Br}$ from LO CSM via $gg$ fusion in $pp$ collisions at $\sqrt{s}=7$ TeV compared to the preliminary CMS results CMS-Upsilon multiplied by the direct fraction (see text).