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J/psi production at sqrt(s)=1.96 and 7 TeV: Color-Singlet Model, NNLO* and polarisation

J. P. Lansberg

TL;DR

The paper analyzes J/psi production in pp collisions at sqrt(s)=1.96 and 7 TeV within the Colour-Singlet mechanism, including NLO corrections and dominant NNLO* contributions. It evaluates the $P_T$-dependent cross section and polarisation in the helicity frame, using a data-driven treatment of χ_c feed-down to the prompt yield. Results indicate that CS predictions can approximate the data if the NNLO* upper range tracks the true NNLO, though NNLO* is not a complete NNLO calculation and may carry IR-cut uncertainties. For polarisation, the direct J/psi polarisation becomes more longitudinal with increasing $P_T$, and the prompt polarisation can be compatible with measurements depending on χ_c feed-down, suggesting color-octet contributions may not be required pending a full NNLO calculation.

Abstract

We study J/psi production in pp collisions at sqrt(s)=1.96 and 7 TeV using the Colour-Singlet Model (CSM), including next-to-leading order (NLO) corrections and dominant alphaS^5 contributions (NNLO*). We find that the CSM reproduces the existing data if the upper range of the NNLO* is near the actual --but presently unknown-- NNLO. The direct yield polarisation for the NLO and NNLO* is increasingly longitudinal in the helicity frame when P_T gets larger. Contrary to what is sometimes claimed in the literature, the prompt J/psi yield polarisation in the CSM is compatible with the experimental data from the CDF collaboration, when one combines the direct yield with a data-driven range for the polarisation of J/psi from chi(c).

J/psi production at sqrt(s)=1.96 and 7 TeV: Color-Singlet Model, NNLO* and polarisation

TL;DR

The paper analyzes J/psi production in pp collisions at sqrt(s)=1.96 and 7 TeV within the Colour-Singlet mechanism, including NLO corrections and dominant NNLO* contributions. It evaluates the -dependent cross section and polarisation in the helicity frame, using a data-driven treatment of χ_c feed-down to the prompt yield. Results indicate that CS predictions can approximate the data if the NNLO* upper range tracks the true NNLO, though NNLO* is not a complete NNLO calculation and may carry IR-cut uncertainties. For polarisation, the direct J/psi polarisation becomes more longitudinal with increasing , and the prompt polarisation can be compatible with measurements depending on χ_c feed-down, suggesting color-octet contributions may not be required pending a full NNLO calculation.

Abstract

We study J/psi production in pp collisions at sqrt(s)=1.96 and 7 TeV using the Colour-Singlet Model (CSM), including next-to-leading order (NLO) corrections and dominant alphaS^5 contributions (NNLO*). We find that the CSM reproduces the existing data if the upper range of the NNLO* is near the actual --but presently unknown-- NNLO. The direct yield polarisation for the NLO and NNLO* is increasingly longitudinal in the helicity frame when P_T gets larger. Contrary to what is sometimes claimed in the literature, the prompt J/psi yield polarisation in the CSM is compatible with the experimental data from the CDF collaboration, when one combines the direct yield with a data-driven range for the polarisation of J/psi from chi(c).

Paper Structure

This paper contains 4 sections, 2 figures.

Table of Contents

  1. Introduction
  2. Cross-section
  3. Polarisation
  4. Conclusion

Figures (2)

  • Figure 1: $d\sigma/dP_T \times {\rm Br}$ for direct $J/\psi$ production from NLO and NNLO$^\star$ CS contributions at $\sqrt{s}=1.96\mathrm{~TeV}$ (left) and at $\sqrt{s}=7\mathrm{~TeV}$ for central (middle) and forward (right) rapidities. These are compared to the CDF Acosta:2004yw, ATLAS, CMS and LHCb data Khachatryan:2010yrATLAS:2011spAaij:2011jh multiplied by a constant direct fraction from CDF Abe:1997yz. See text for details on theoretical-error bands.
  • Figure 2: Comparison between the extrapolation of $\alpha$ for prompt $J/\psi$ in $pp$ at $\sqrt{s}=1.96\mathrm{~TeV}$ (red band), the direct NLO $\alpha$ (gray line), the direct NNLO$^\star$$\alpha$ (thinner dark-red band) and the CDF data Abulencia:2007us for prompt $J/\psi$.