Upsilon nS Production at CMS

1
Upsilon (nS) Production at CMS
Purdue University D. Bortoletto, A. Garfinkel,
Z. Gecse, M. Jones, N. Leonardo, I. Shipsey, D.
Silvers, Y. Zheng Princeton University N. Adam,
V. Halyo, A. Hunt, A. Petrescu Peking University
S. Guo, S. Qian, Z. Yang, L. Liu
Introduction
Motivations
The narrow resonance of bottomonium, Upsilon
(1S), decaying into a muon pair, certainly plays
an important role in the detector calibration and
alignment.
Alex Petrescu Princeton
Yu Zheng Purdue
Zhen Hu Peking
Adam Hunt Princeton
On the other hand, even though Upsilon (1S) has
been discovered over 30 years ago and has been
studied extensively since then, its production
mechanism at hadron colliders is still not well
understood. It can be produced directly or
indirectly from higher excited states of
bottomonium. The cross section predictions of
the early Color Singlet Model (CSM) were an order
of magnitude lower than that measured by the
Collider Detector at Fermilab (CDF)
collaboration. While the new Color Octet
Mechanism (COM) in the framework of
Non-Relativistic QCD (NRQCD) fits the cross
section measurement well, it is in disagreement
with the polarization measurements. The Large
Hadron Collider (LHC) will produce high pT
Upsilons at a large rate and has the potential to
discriminate between the emerging new models.
Zoltan Gecse Purdue
Nuno Leonardo Purdue
Nadia Adam Princeton
Shuang Guo Peking
Analysis Strategy
Muon Efficiencies
Acceptance
Cross Section

• number of generated Upsilons
• 
  
• number of Upsilons where both daughter muons are
  reconstructed with tracks in the silicon tracker
  with pT gt 3.5 GeV and ? lt 2.1

• - acceptance
• and - identification and
  trigger efficiencies
• - corrected yield of Upsilon
  candidates in a pT bin, extracted from the fit to
  the dimuon mass distribution
• - integrated luminosity
• - Upsilon pT bin size

• Efficiencies are measured with the Tag and Probe
  data driven method. Probe muons are paired with
  well identified Tag muons. Background is
  subtracted by fitting the Upsilon peak of the
  invariant mass distribution.

• Acceptance as a function of pT and rapidity

Event Selection

• Single muon triggered data stream
• Two Tracker Muons of opposite charge
• pT gt 3.5 GeV and ? lt 2.1
• d0 lt 2 cm and z0 lt 25 cm

Cross Section Measurement with ?Ldt 1/pb at 10
TeV
Results
Dimuon Mass Fit
Systematic Uncertainties

• Upsilon candidates are weighted to account for
  acceptance, identification and trigger
  efficiencies
• Unbinned maximum likelihood fit of dimuon mass
• Three double Gaussians and linear background
• Same resolution function for the three Upsilons
• Relative mass difference of Upsilons fixed to
  that of PDG value

• Luminosity measurement (dominant)
• Acceptance and efficiencies measurements
• Tag and Probe bias (due to altered kinematic
  distributions of the probe)
• Unknown polarization
• Choice of probability distribution function

• Normalized differential cross section

References
CMS Analysis Notes 2009/066, 2009/118, 2009/119