Search for Higgs boson production in proton-antiproton collisions at √s = 1.96 TeV

Abstract

We performed a search for Standard Model Higgs boson production in association with W boson (p$\bar{p}$ → W±H → ℓvb$\bar{b}$) in p$\bar{p}$ collisions at √s = 1.96 TeV. The search uses the data collected between February 2002 and February 2006 at Collider Detector at Fermilab (CDF), which corresponds to an integrated luminosity of about 1 fb-1. The experimental final state of WH → ℓvb$\bar{b}$ process is lepton (e±/μ±), missing transverse energy and two jets. The largest background in lepton+jets events is W+light flavor process, therefore the identification of jets as b-jets reduces this kind of background significantly. We used displaced SECondary VerTeX b-tagging (SECVTX) technique, which utilizes the signature that b-jets have secondary vertex displaced away from primary vertex because of the long life time of B-mesons. However, there is still much contamination in SECVTX b-tagged jets. Finite resolution of secondary vertex tracking measurements results in false tags, and c-jets are also identified as b-jets due to the long life time of D-mesons frequently. For the purpose of increasing the purity of the SECVTX b-tagged jets, we applied Neural Network to SECVTX tagged jets for the first time by using secondary vertex variables and some variables independent of it. Neural Network filter rejects 65% of light flavor jets and 50% of c-jets from the SECVTX tagged jets. We improved the sensitivity of the Higgs boson signal search by 10% with Neural Network b-tagging technique. Events with one high pT electron or muon, large missing transverse energy and either single SECVTX b-tagged jet which passes the Neural Network filter or at least two SECVTX b-tagged jets are selected. The number of selected events and dijet mass distributions are consistent with the Standard Model background expectations. Therefore we set an upper limit on σ(p$\bar{p}$ → WH) • Br(H → b$\bar{b}$) as 3.9 to 1.3 for Higgs boson mass from 110 to 150 GeV/c2 at 95% confidence level (C.L.). The upper limit obtained from WH → ℓvb$\bar{b}$ process with 1 fb-1 is far away from the Standard Model Higgs boson production expectation by a factor of 20 to 100 as a function of Higgs boson mass. To obtain stronger constraint on the Higgs boson production, we combined the upper limits obtained in processes of ZH → {nu}$\bar{v}$b$\bar{b}$, ZH → ℓ$\bar{ℓ}$b$\bar{b}$ and gg → H → W+W- → ℓ$\bar{ℓ}$v$\bar{v}$ at CDF. The combination of different channels gives a constraint on the ratio of 95% confidence level upper limit divided by the Standard Model prediction ((σ • Br)95/(σ • Br)SM), which results in the ratio as 10 to 40 for Higgs boson mass between 110 and 200 GeV/c2. Finally, the combination of Higgs boson searches between CDF and D0 is also performed. The resulting constraint on (σ • Br)95/(σ • Br)SM is about 4 to 10 for Higgs boson mass between 110 and 200 GeV/c2.