Measurements of the Upsilon(1S), Upsilon(2S), and Upsilon(3S) differential cross sections in pp collisions at sqrt(s) = 7 TeV

TL;DR

This paper reports measurements of the differential cross sections of Upsilon(1S), (2S), and (3S) states in proton-proton collisions at 7 TeV, revealing a transition in behavior around 20 GeV and differences in spectrum hardness.

Contribution

First detailed measurement of Upsilon states' differential cross sections at 7 TeV, showing transition from exponential to power-law behavior in the spectrum.

Findings

Transition from exponential to power-law at ~20 GeV

Upsilon(3S) and (2S) spectra are harder than (1S) at high pt

Cross section ratios increase then plateau with pt

Abstract

Differential cross sections as a function of transverse momentum pt are presented for the production of Y(nS) (n = 1, 2, 3) states decaying into a pair of muons. Data corresponding to an integrated luminosity of 4.9 inverse femtobarns in pp collisions at sqrt(s) = 7 TeV were collected with the CMS detector at the LHC. The analysis selects events with dimuon rapidity abs(y) < 1.2 and dimuon transverse momentum in the range 10 < pt < 100 GeV. The measurements show a transition from an exponential to a power-law behavior at pt ~ 20 GeV for the three Y states. Above that transition, the Y spectrum is significantly harder than that of the Y(1S) and Y(2S). The ratios of the Y(3S) and Y(2S) differential cross sections to the Y(1S) cross section show a rise as pt increases at low pt, then become flatter at higher pt.