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Large Transverse Momentum Jet Production and the Gluon Distribution Inside the Proton

J. Huston, E. Kovacs, S. Kuhlmann, H. L. Lai, J. F. Owens, D. Soper, W. K. Tung

TL;DR

The paper addresses an apparent excess in high-p_t jet production at the Tevatron and tests whether it can be explained within the Standard Model by modifying the gluon distribution inside the proton within a global NLO QCD framework. It performs a global fit including the CDF jet data and finds two viable gluon distributions that raise high-p_t jet cross sections by about 25–35% while preserving consistency with DIS, Drell-Yan, and direct-photon data. The analysis shows that jet data can constrain the gluon shape in 0.08 < x < 0.45, but UA2 data and systematic effects complicate a single, universal interpretation. The study underscores the need for further experimental and theoretical work, including cross-checks with additional observables and resummation effects, before asserting new physics.

Abstract

The CDF experiment has reported an excess of high-$p_t$ jets compared to previous next-to-leading order QCD expectations. Before attributing this to new physics effects, we investigate whether these high-$p_t$ jets can be explained by a modified gluon distribution inside the proton. We find enough flexibility in a global QCD analysis including the CDF inclusive jet data to provide a 25-35\% increase in the jet cross sections at the highest $p_t$ of the experiment. Two possible sets of parton distributions are presented, and the effects of these on other existing data sets are presented. Further theoretical and experimental work needed to clarify unresolved issues is outlined.

Large Transverse Momentum Jet Production and the Gluon Distribution Inside the Proton

TL;DR

The paper addresses an apparent excess in high-p_t jet production at the Tevatron and tests whether it can be explained within the Standard Model by modifying the gluon distribution inside the proton within a global NLO QCD framework. It performs a global fit including the CDF jet data and finds two viable gluon distributions that raise high-p_t jet cross sections by about 25–35% while preserving consistency with DIS, Drell-Yan, and direct-photon data. The analysis shows that jet data can constrain the gluon shape in 0.08 < x < 0.45, but UA2 data and systematic effects complicate a single, universal interpretation. The study underscores the need for further experimental and theoretical work, including cross-checks with additional observables and resummation effects, before asserting new physics.

Abstract

The CDF experiment has reported an excess of high- jets compared to previous next-to-leading order QCD expectations. Before attributing this to new physics effects, we investigate whether these high- jets can be explained by a modified gluon distribution inside the proton. We find enough flexibility in a global QCD analysis including the CDF inclusive jet data to provide a 25-35\% increase in the jet cross sections at the highest of the experiment. Two possible sets of parton distributions are presented, and the effects of these on other existing data sets are presented. Further theoretical and experimental work needed to clarify unresolved issues is outlined.

Paper Structure

This paper contains 4 sections, 4 figures.

Table of Contents

  1. Global QCD Analysis Incorporating CDF Jet Data
  2. Comparisons to Deep-Inelastic Scattering and Direct Photon Data
  3. UA2 Inclusive Jet Data
  4. Conclusions

Figures (4)

  • Figure 1: The preliminary CDF jet data is compared to a NLO QCD calculation using the conventional CTEQ3M parton distributions (points), and the new parton distributions fit to the jet data (solid and dashed lines that lie on top of each other).
  • Figure 2: (a) The gluon distributions at $\mu=150$ GeV from the norm=1.0 and the norm=0.93 jet-fits are compared to that of CTEQ3M: (b) the ratio of the two jet-fit gluons to CTEQ3M (see text).
  • Figure 3: The WA70 direct photon data is compared to NLO QCD calculations using conventional, ABFOW parton distributions in a). Different choices of scale are shown as well as the effect of adding additional $k_t$ broadening to the theory. In b) the WA70 direct photon data is compared to NLO QCD calculations using the two sets of jet-fit gluons. (see text)
  • Figure 4: The CDF and UA2 jet production measurements are compared to NLO QCD calculations (see text).