Yldrm D Mutaf SUNY at Stony Brook on

Yıldırım D. Mutaf SUNY at Stony Brook (on behalf of DØ Collaboration) Abstract Data Sample & Event Selection 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 Z+bjet to Z+jet inclusive production. The analysis is performed in two channels as characterized by the decays of the Z boson: Dielectron Channel ( Z ee ) DØ Detector & Run II Multi-purpose Collider Detector at FNAL 1. 96 Te. V proton/anti-proton collisions ü New Tracking System (including a silicon vertex and central fiber tracking detector) & 2 T magnet ü New Central/Forward Pre. Shower Detectors ü Upgrade Calorimeter Electronics & Muon System Improvements ü New Trigger System p Taggable Jet p. T (Ge. V/c) Zc Zq Z μμ Z+taggable jet sis aly Zb Zc Zq R≡ Zc Zq Zc • 2 isolated muons with both having matching central tracks • |ημ| < 2. 0 and p. T> 15 Ge. V • 65. 0 < Mμ 1μ 2< 115. 0 Ge. V Z μμ DØ Run-II Preliminary Bckg (μμ+ee) (μμ) B Zb Zb • 2 isolated electrons with at least 1 track match • |ηe| < 2. 5 and p. T> 15 Ge. V • 80. 0 < Me 1 e 2< 100. 0 Ge. V Z μμ SV Tagging Z+btagged jet Zb Dilepton Mass (≥ 1 btagged jets) Bckg Taggability • Luminosity ~180 pb-1 (recorded) • Calorimeter cone jets, R=0. 5 • |ηj| < 2. 5 and p. T> 20 Ge. V • Taggability requirement • Calorimeter jets are required to have matching tracks for taggability • B-tag the jets with reconstructed Secondary Vertices, δR < 0. 5 Z + taggable jet & btagged jet events Zb • Luminosity ~184 pb-1 Jet Selection & B-tagging p Z+jet Dimuon Channel ( Z μμ ) Z ee Methodology & Selected Events An Measurement of the Ratio of Inclusive Cross Sections σ(pp→Z+b)/σ(pp→Z+j) Measurement of the Ratio of Inclusive Cross Sections σ(pp Z+b)/σ(pp Z+j) at DØ Run. II Z ee Zq 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 (Z+btagged jet). Z ee 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 Z+j MC (open histogram) and overlayed with expected background contribution (dark fill histogram. ) The dielectron & dimuon channels are combined statistically to obtain the final result: RIGHT : Dimuon mass distribution for b-tagged jet events. Shown for data events alone without the invariant mass cut. Systematic Uncertainties Calculating the Background Contributions • 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, SV’s don’t 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 †. R = 0. 024 0. 005(stat) + 0. 005 - 0. 004 (syst) Consistent with theoretical calculation of ~0. 020†. † J. M. Campbell, R. K. Ellis, F. Maltoni and S. Willenbrock, Phys. Rev. D 69 (2004) 074021