Inclusive jet production, parton distributions, and the search for new physics

Abstract

Jet production at the Tevatron probes some of the smallest distance scales currently accessible.A gluon distribution that is enhanced at large x compared to previous determinations provides a better description of the Run 1b jet data from both CDF and DØ. However, considerable uncertainty still remains regarding the gluon distribution at high x. In this paper, we examine the effects of this uncertainty, and of the remaining uncertainties in the NLO QCD theory, on jet cross section comparisons to Run 1b data. We also calculate the range of contributions still possible from any new physics. Predictions are also made for the expanded kinematic range expected for the ongoing Run 2 at the Tevatron and for the LHC. I. INTRODUCTION: JET CROSS SECTIONS AT THE TEVATRONJet production at the Tevatron probes the highest momentum transfer region currently accessible. As this region is potentially sensitive to a wide variety of new physics, there was great interest when the inclusive jet cross section measured by the CDF collaboration in Run 1b exhibited an excess in the highest E T range, when compared to NLO predictions using then-current parton distribution functions [1]. In an attempt to determine if conventional physics could explain the deviation, the CTEQ PDF fitting group carried out a global analysis using information from deep-inelastic scattering and Drell-Yan data, as well as from jet data from the Tevatron, but giving a higher statistical emphasis to the high E T jet data from CDF [2]. NLO predictions using the resulting fit (CTEQ4HJ) reduced the size of the excess observed by CDF. The jet data from both CDF and DØ were also used in a more conventional fit (CTEQ4M) where no special emphasis was given to the high E T data [3].The dominant subprocess that contributes to jet production at high E T is quark-(anti)quark scattering. However, the quark distributions in the corresponding x range are very well constrained by the precise DIS and DY data used in the global fits. Only the gluon distribution has the flexibility to change significantly in the high x region, and indeed the gluon distribution increases by roughly a factor of 2 for x values of about 0.5 in the CTEQ4HJ fit. The gluon-quark scattering subprocesses increase from approximately 20% of the total jet cross section at high E T using CTEQ4M to 40% using CTEQ4HJ [2]. The next group of PDF's from CTEQ (CTEQ5) [4] also contained two sets: CTEQ5M, the standard lowest χ 2 solution, and CTEQ5HJ, defined by a similar statistical enhancement applied to the high E T data from CDF [5] and DØ [6].More recently, DØ has measured the inclusive jet cross section as a function of rapidity y over the range 0 ≤ |y| ≤ 3 [7]. This data set, comprised of 90 data points, has a greater statistical power in the global fits than the CDF and DØ jet cross section measurements in the central region alone. The CTEQ6M fit [8] utilizes these DØ jet cross section measurements, along with the CDF measurements in the central rapidity region, as well as the most recent DIS data from HERA an...

Nuclear PDFs at NLO – status report and review of the EPS09 results

“…[1]. We define the bound proton PDFs relative to the free proton ones, taking the set CTEQ6.1M [19] as our baseline:…”

Search for Heavy Resonances in the Dimuon Channel with the DØ Detector

“…For each sample, the hard scatter interaction subprocess cross section was calculated to leading order (LO) in the coupling constants and convoluted with the CTEQ6L1 parton distribution functions (also calculated to LO) which are compiled by the CTEQ collaboration [72,73]. 51 52 CHAPTER 4.…”

“…A linear interpolation is used to obtain a K-factor with errors for continuous values of the Drell-Yan mass. Errors on the (normalized) Drell-Yan production cross sections due to uncertainties in the parton distribution functions were calculated in [78] by adding in quadrature the variations of the (differential) cross-sections calculated with each of 40 CTEQ6.1M (normalized) error functions, following the prescription of [72]. The same prescription was followed to calculate the error on the signal acceptance; see section 6.…”

“…The uncertainty on the signal efficiency due to the PDF uncertainties was calculated following the prescription of [72]. The CTEQ collaboration provides a collection of 2 × 20 error sets with the CTEQ6.1M PDF.…”

“…These represent a basis of "barely tolerable" fits, which have a χ 2 = χ 2 0 + T 2 , where χ 2 0 is of the optimal fit (i.e., the CTEQ6.1M PDF) and T is the "tolerance" which is chosen to be T ∼ 10. For more details see [72].…”