Measurement of W(->lv)+charm Production Cross-Section

with SLTmu c-tagging


Alice Bridgeman, Lucio Cerrito+, Ulysses Grundler,

Tony Liss,  Xiaojian Zhang

*University of Illinois Urbana-Champaign

                                                                                +University College London



This page is for the measurement of the W(->lv)+charm cross section using SLT_mu tagger to identify c-jets.
The preblessing was given on 07/26/2007 blessing talk was given on 08/09/2007. The acceptance is  recalculated from MC samples with increased charm pT cut (8 -> 20GeV/c) and smaller pseudorapidity cut (3.0 -> 1.5) -- thanks to the GP committees for the suggestions. This change minimizes  the otherwise large systematic uncertainty due to the dependence on the charm pT  distribution, given that the signal has charm pT mostly above 20 GeV/c. The new results was reblessed on 11/01/2007.

The public note

The previous results with the old kinematic cuts on the charm quark

The Analysis:


In this analysis we measure the W(->lv)+charm production cross section using lepton + 1 & 2jets events. In the lepton plus jets events resulting from the W+charm production, we look for events that the W boson decays semileptonically to an electron/muon plus neutrino (taus are not included) and the charm decays semileptonically to muons, resulting in a topology of one high-Pt electron or muon (referred as Tight Lepton, TL), missing transverse energy and one charm jet, where the lepton from the W decay and the muon from the charm semileptonic decay have opposite signs. The charm jet is tagged by the Soft Muon Tagger (SLT).  We require 0 or 1 generic jet other than the charm jet to maximize the statistic power. The charge anti-correlation in the W(->lv)+charm events gives a large charge asymmetry in the Wc sample. The charge asymmetry is defined as [N(OS)-N(SS)]/[N(OS)+N(SS)], where N(OS) is the number of the opposite sign events and N(SS) is the number of the same sign events. We found the charge asymmetry is 0.720+/-0.011 from Alpgen Monte Carlo W(->lv)+charm samples. The MC sample has requirements of charm pT>20GeV and pseudorapidity of charm within [-1.5,1.5]. The backgrouonds of this analysis include QCD production of W+jets, Non-W events and DY events. They have smaller charge asymmetries except DY events. This analysis first counts in data sample the difference between the number of opposite sign events and the number of same sign events, i.e. N(OS)-N(SS). The background events are then properly deducted. The acceptance of the signal events (opposite sign minus same sign events) is determined from MC sample to be (0.833+/- 0.010)x10-2, including the charge asymmetry implicitly The measurement is based on 1.8 fb-1 of proton-antiproton collision data, the measured Wc cross section is 

sigma_{Wc}(ptc>20 GeV , |eta|<1.5)*BR(W->e nu)

                                      = 9.8+/-2.8(stat)+1.4-1.6(sys)+/-0.6(lum)pb

where the first uncertainty is statistical, the second is systematic and the last is uncertainty from the luminosity uncertainty.






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SLTm tagger & c-tagging

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Systematic Uncertainty Table. 



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Delta Phi between missing Et and SLT tagged muon.


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The pT distribution  of  SLT tagged muon.

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Delta_R between the tight lepton and the SLT tagged muon.


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Misiing Et.

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The SLT pT relative to the SLT tagged jet axis.



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Signed impact  parameter.



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Track multiplicity of the SLT tagged jet. 

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Uncorrected  jet energy of the SLT tagged jet.


SLTm efficiency for the central  muon detector (CMUP) as a function of pT measure from JPsi & Z0


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SLTm efficiency for the extended muon detector (CMX) as a function of pT measure from JPsi & Z0


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Last Updated : Wednesday, 11/02/2007, 11:21pm by Xiaojian