Measurement of the Upsilon(1S) Production Cross-Section in pp Collisions at sqrt(s) = 7 TeV in ATLAS

TL;DR

This paper reports a measurement of the Upsilon(1S) production cross-section in proton-proton collisions at 7 TeV, comparing results with theoretical models and highlighting discrepancies with certain predictions.

Contribution

First measurement of Upsilon(1S) cross-section at 7 TeV in specific kinematic bins, with detailed comparison to NRQCD and color-singlet model predictions.

Findings

Results agree within a factor of two with NRQCD-based predictions.

Results differ by up to a factor of ten from color-singlet NLO predictions.

Measurement reduces uncertainties by requiring muons with pT > 4 GeV and |eta| < 2.5.

Abstract

A measurement of the cross-section for Upsilon(1S) -> mu+mu- production in proton-proton collisions at centre of mass energy of 7 TeV is presented. The cross-section is measured as a function of the Upsilon(1S) transverse momentum in two bins of rapidity, |y(Upsilon1S)| < 1.2 and 1.2 < |y(Upsilon1S)| < 2.4. The measurement requires that both muons have transverse momentum pT(mu) > 4 GeV and pseudorapidity |eta(mu)| < 2.5 in order to reduce theoretical uncertainties on the acceptance, which depend on the poorly known polarization. The results are based on an integrated luminosity of 1.13 pb-1, collected with the ATLAS detector at the Large Hadron Collider. The cross-section measurement is compared to theoretical predictions: it agrees to within a factor of two with a prediction based on the NRQCD model including colour-singlet and colour-octet matrix elements as implemented in PYTHIA while it disagrees by up to a factor of ten with the next-to-leading order prediction based on the colour-singlet-model.