Search for the SM Higgs in τ l τ h jj Final States: Production Modes and Background Modeling

Transcription

1 Search for the SM Higgs in τ l τ h jj Final States: Production Modes and Background Modeling Ian Howley on behalf of the DØ Collaboration APS April Meeting, Atlanta GA March 30, 2012 I. Howley (UT Arlington) ττjj at DØ March 30, / 12

2 Production and Decay Modes Trigger Backgrounds Conclusion Overview In the following companion presentation (W. Ye) we discuss the multivariate techniques and final combination limits 3 channels are combined: - µτ 0, µτ 2, and eτ 2. Our primary focus will be on the 2 jet channels I. Howley (UT Arlington) τ τ jj at DØ March 30, / 12

3 Higgs Signals H ττjj has 3 production channels, that give 1 e/µ, 1 hadronic τ, 2 jets, and missing energy. Associated Production Gluon-Gluon Fusion (GGF) Vector-Boson Fusion (VBF) Our final state is sensitive to both H ττ and H WW. I. Howley (UT Arlington) ττjj at DØ March 30, / 12

4 Higgs Signals II There are 9 physical processes, in two large mass ranges It is important to know the dominant process in the low and high mass ranges. Name Decay low mass HZ H(bb) + Z(ττ) ZH Z(qq) + H(ττ) WH W (qq ) + H(ττ) VBF qq qq + H(ττ) GGF gg H(ττ) + 2jets high mass ZH WW Z(qq) + H(WW ) WH WW W + H(WW ) VBF WW qq qq + H(WW ) GGF WW gg H(WW ) + 2jets Fractional signal yield Signal HZ Signal ZH Signal WH Signal GGF Signal VBF (b) m H [GeV] I. Howley (UT Arlington) ττjj at DØ March 30, / 12

5 Hadronic τ Decays Hadronic τ decays are reconstructed as narrow jets dr = ( φ) 2 + ( η) 2 = 0.4 It is useful to classify the main hadronic decays based on their detector signature We employ a neural network (NN τ ) to distinguish τ s from fakes DØ Work in Progress τ type Physical Process BR 1 τ ± π ± ν τ.9% 2 τ ± ρ ± ( π 0 π ± )ν τ 36.5% τ ± ( 2π 0 )π ± ν τ 3 τ ± a ± 1 ( π± π π ± )ν τ 13.9% I. Howley (UT Arlington) ττjj at DØ March 30, / 12

6 Inclusive Triggering The inclusive approach gives an increase in data of 40% The µτ channels employ an inclusive trigger approach, whereby we accept events that fire any trigger, not just a single muon trigger To measure the efficiency we calculate ratio of inclusively triggered data to single-muon triggered data, ξ µτ0: ξ is a function of p τ T µτ2: ξ has no observed dependence Apply product of ratio and single muon efficiency to MC The eτ channel uses a single EM object trigger, and will use an inclusive trigger approach when analyzing the full dataset I. Howley (UT Arlington) ττjj at DØ March 30, / 12

7 Background There are 5 backgrounds considered: Z ee/µµ and Z ττ (irreducible) Z ee dominant in the eτ channel W +jets is the primary background for the µτ0 channel t t contributes 15% Di-boson contribution is quite small Multi-jet (MJ) arise from QCD heavy flavor events, where jets fake either the τ or the electron It is instrumentally induced and hard to simulate, and thus estimated from data We use standard definitions of p T η, and other variables to ensure we use good quality electrons, muons, taus, jets and missing energy MET I. Howley (UT Arlington) ττjj at DØ March 30, / 12 Entries 40 data MJ 35 tt w+jets lν+jets 30 z+jets τ τ +jets 25 z+jets ll+jets DiBoson DØ Work in Progress

8 MJ Definition We define a set of multi-jet enriched events MJ Control by reversing the τ and lepton quality Subtract all other SM backgrounds to acquire the MJ shape (M) The number of MJ events in the signal sample, NOS MJ, are scaled by the ratio ρ i NOS MJ = ρ i (NSS DATA NSS SM ) ρ i = M OS M SS i = 1, 2, 3 (τ type) MJ systematics are estimated from the MJ Test sample TAu Quality MJ Test MJ Control Signal (Z+Jets) W+Jets (MJ-Alt) Lepton Quality W+Jets I. Howley (UT Arlington) ττjj at DØ March 30, / 12

9 Z ee Supression The eτ channel is overwhelmed by Z ee background We employ a series of cuts to reduce the background contribution We remove events in the following regions: Type 1: 1.5 < η τ d < KS test = DØ Work in Progress TauDetEta Type 2: TauNNel < DØ KS Work test = in Progress TauNNel Type 2: 0.9 < φ PS < 0.1 Events/ KS test = DØ Work in Progress TauphiPS I. Howley (UT Arlington) ττjj at DØ March 30, / 12

10 Data and MC Agreement The background contributions to each channel are quite different. It is very important to check the MC modeling before moving to a multivariate analysis Events/ GeV D0 L=7.3 fb data (a) Z+jets W+jets other multijets signal(x 0) M(μ μ, τ, MET) [GeV] Events/ GeV Events/ GeV D0 L=6.2 fb data (b) 80 Z+jets W+jets 70 other 60 multijets 50 signal(x 0) [GeV] M jj 1 D0 L=4.3 fb data Z+jets W+jets other (c) multijets signal (x 0) M(e, τ, MET) [GeV] I. Howley (UT Arlington) ττjj at DØ March 30, 2012 / 12

11 Conclusions Accurate and precise modeling of the major backgrounds is essential before any multivariate analysis can be performed Our recent publication (arxiv: v1 [hep-ex]) uses up to 7.3fb 1 of data, and is included in the most recent SM Higgs Tevatron combination result (FERMILAB-CONF E) This is the first publication to included the eτ channel at DØ Multivariate Techniques and combination limits are discussed in the following talk I. Howley (UT Arlington) ττjj at DØ March 30, / 12

12 Search for the SM Higgs in τ l τ h jj Final States: Production Modes and Background Modeling Ian Howley on behalf of the DØ Collaboration APS April Meeting, Atlanta GA March 30, 2012 Thank you I. Howley (UT Arlington) ττjj at DØ March 30, / 12