Search for vector bosons produced in association with Upsilons|
using the full CDF dataset
The production of the Upsilon (1S) meson in association with a vector boson is a rare process
with a standard model cross section predicted to be outside the range of sensitivity at the Tevatron.
Observation of this process could signify problems with the current non-relativistic QCD models
used for the cross section calculation, or it might signify a contribution from new physics models.
We perform a first search for this process using the full 9.7 fb-1 of Run 2 data collected by CDF,
using the Υ → μμ decay together with the charged lepton decay modes of the W and Z bosons.
In these purely leptonic decay channels, we observe one Υ + W candidate over an expected background of 1.2 ± 0.5
events, and one Υ + Z candidate over an expected background of 0.1 ± 0.1 events. Having not seen evidence
for Υ + W/Z production we calculate cross section limits at 1.96 TeV. These are the best cross section limits
for this process, and also provide a guide to limits on new physics processes producing an Υ + W/Z.
Data and signal MC samples
We use the high-pT electron triggered dataset and high-pT muon triggered dataset for the main analysis. We also use the upsilon trigger dataset for the estimation of the fake W/Z background. The signal MC is generated using MadGraph + Pythia.
Events are required to have an upsilon candidate: two opposite-charged low-pT (< 15 GeV) muons, 7 GeV/c² < dimuon mass < 13 GeV/c². The dimuon mass spectra of the upsilon trigger dataset are shown below.
The selection cuts of Υ + W are
The missing ET and transverse mass distributions for Υ + W, W → lν are shown below.
- An upsilon 1S candidate (9.25 GeV/c² < dimuon mass < 9.65 GeV/c²)
- Exactly one additional high-pT (> 20 GeV) isolated electron or muon
- The high-pT lepton is triggerable
- Missing ET > 20 GeV
- Transverse mass of W candidate in the range 50 - 90 GeV/c²
The selection cuts of Υ + Z are
The dilepton mass distributions for Υ + Z, Z → ll are shown below.
- An upsilon 1S candidate
- Exactly two additional high-pT (> 15 GeV) isolated electrons or muons
- One of the high-pT leptons is triggerable with pT > 20 GeV
- Opposite charge
- Dilepton mass in the range 76 - 106 GeV/c²
The fake Υ + real W/Z background is estimated using the sideband regions of the dimuon mass spectra. The real Υ + fake W/Z is estimated using jet candidates that satisfy relaxed lepton identification criteria.
The systematic uncertainties of the signal acceptance are shown in the table below.
Expected and observed events
We observe one Υ + W candidate over an expected background of 1.2 ± 0.5
events, and one Υ + Z candidate over an expected background of 0.1 ± 0.1 events.
The event display of the Υ + Z candidate is shown below.
We set 95% C.L. cross section limits.
More details are provided in the public note
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Updated by Chen Zhou
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Last updated: Dec 4 2013.