Dimuon%20Channel%20(%20Z?

1
Measurement of the Ratio of Inclusive Cross
Sections s(pp ? Zb)/s(pp ? Zj) at DØ RunII
Yildirim D. Mutaf SUNY at Stony Brook (on behalf
of DØ Collaboration)
Abstract We study the b-jet production in
association with the Z boson at DØ, using Run II
data collected between August'02 and September'03
corresponding to about 180 pb-1 of recorded
luminosity. In this study, we also present a
measurement of the ratio of cross sections of
Zbjet to Zjet inclusive production.
Data Sample Event Selection
The analysis is performed in two channels as
characterized by the decays of the Z boson

• Dimuon Channel ( Z?µµ )
• Luminosity 180 pb-1 (recorded)
• 2 isolated muons with both having matching
  central tracks
• ?µ lt 2.0 and pTgt 15 GeV
• 65.0 lt Mµ1µ2lt 115.0 GeV

• Dielectron Channel ( Z?ee )
• Luminosity 184 pb-1
• 2 isolated electrons with at least 1 track match
• ?e lt 2.5 and pTgt 15 GeV
• 80.0 lt Me1e2lt 100.0 GeV

DØ Detector Run II

• Multi-purpose Collider Detector at FNAL
• 1.96 TeV proton/anti-proton collisions
• New Tracking System (including a silicon vertex
  and central fiber tracking detector) 2T magnet
• New Central/Forward PreShower Detectors
• Upgrade Calorimeter Electronics Muon System
  Improvements
• New Trigger System

Z? µµ
Z?ee
Jet Selection B-tagging
Methodology Selected Events

• Calorimeter cone jets, R0.5
• ?j lt 2.5 and pTgt 20 GeV
• Taggability requirement
• Calorimeter jets are required to have matching
  tracks for taggability
• B-tag the jets with reconstructed Secondary
  Vertices, dR lt 0.5

Measurement of the Ratio of Inclusive Cross
Sections s(pp?Zb)/s(pp?Zj)
p
Z taggable jet btagged jet events
DØ Run-II Preliminary
Zjet
Dilepton Mass (1 btagged jets)
Taggable Jet pT (GeV/c)
Zc
Zq
Bckg
Zb
Taggability
Z? µµ
Z? µµ
Ztaggable jet
Zb
Zc
Zq
Bckg
Analysis
SV Tagging
Zbtagged jet
Zb
Zc
Zq
B
Zb
R
The secondary vertex (SV) decay length
significance plot along with track multiplicity
and b-tagged jet momentum plots shows the heavy
quark domination in the tagged sample (Zbtagged
jet).
Z?ee
Z?ee
Zb
Zc
Zq
Selected Z Event Counts
Systematics Results
LEFT Taggable jet transverse momentum
spectrum.The data (points) with jet-energy-scale
errors (shades over points) are compared to
ALPGEN Zj MC (open histogram) and overlayed with
expected background contribution (dark fill
histogram.) RIGHT Dimuon mass distribution for
b-tagged jet events. Shown for data events alone
without the invariant mass cut.
The dielectron dimuon channels are combined
statistically to obtain the final result R
0.024?0.005(stat) (syst)
Calculating the Background Contributions
0.005 - 0.004

• The multijet (mostly bbbar) background is
  calculated from data using the inefficiency of
  the isolation requirement as the major
  characteristic for this type of background.
• The mistag(light jet tagging) rate is extracted
  from jet triggered data
• For the charm contribution, SVs dont provide a
  distinction between b c type of quarks so we
  used
• MC charm tagging efficiency and scale this
  efficiency to what we expect in data
• The b/c data composition ratio is obtained from
  theoretical calculations .

Consistent with theoretical calculation of
0.020. J. M. Campbell, R. K. Ellis,
F.Maltoni and S.Willenbrock, Phys. Rev. D69
(2004) 074021