Development of a Soft Electron b-tagger for Higgs Searches

1. Muon Detectors Hadronic Cal. EM Cal. Solenoid Si Detectors COT Development of a Soft Electron b-tagger for Higgs Searches Arron Shiffer, Northern Arizona University; Benjamin Kilminster, Fermilab; Shalhout Zaki Shalhout, Wayne State University Abstract The Tevatron experiments, including the Collider Detector at Fermilab (CDF), may soon achieve the sensitivity necessary for finding evidence for or excluding the Higgs boson, the particle that is responsible for imparting mass to the fundamental constituents of matter. For a Higgs boson mass of approximately 120 GeV/c^2, which is favored by fits to precision electroweak data, the Higgs boson is expected to decay to a b quark and anti-b quark, each of which form b hadrons that result in jets of particles in the CDF detector. These can be identified by using special "b-tag" algorithms by reconstructing a displaced vertex from the long lifetime of the b hadron before it decays, or by identifying electrons or muons in the b hadron decay sequence. The Higgs group at CDF currently does not have an option for a soft electron b-tagger. This study uses Pythia Monte Carlo simulations of Higgs decays and jet data to evaluate the best algorithm for identifying the highest fraction of real b hadrons, while maintaining the lowest rate for misidentifying jets from light quark decay. In this analysis, we seek to develop a soft electron b-tagger, which can improve the number of Higgs boson candidate events that we can analyze, and therefore improve the sensitivity of the low-mass Higgs search program at CDF. • Increase Acceptance for Higgs -> bbar • ~70% of Higgs decays at 120 GeV • result in b and bbar quarks. • Higgs decay chain can be tagged • using soft electrons from semileptonic b quark decay. • (* b -> l + v + hadrons) e- The Higgs Mechanism and Higgs Boson The Higgs boson plays a crucial role in the standard model . . . • Scalar Higgs field permeates the universe. • One of the four components that make up the field is the Higgs boson. (The other three components provide the mass for the W and Z bosons.) • Higgs mechanism explains why the photon is massless and why the W and Z bosons are massive. • Higgs boson imparts mass to the quarks and charged leptons (and possibly to neutrinos). • Higgs group uses three b-taggers. • "Secvtx" uses Lxy to find secondary vertices. • "JetProb" uses d0 to find tracks not originating from primary vertex. • "NN tagger" is new and combines vertex information with muon variables. Currently, there is no b-tagger that searches for b-> e + v + hadrons. • CDF has used a soft electron tag algorithm previously for measuring the top cross section, which they measured as sigma_tt = 7.8 +- 2.4 (stat) +- 1.5 (sys) +- 0.5 (lum) pb. The Tevatron at Fermilab 2 TeV Proton – Antiproton Collision at: CDF & DØ The Higgs mass is not specified by theory. So we must rely on experimental constraints to narrow the search region. CES CPR • Silicon Detectors Critical for b-jet ID • Tracking: CDF Drift Chamber (COT) • Calorimeters and Muon Detectors • Central Preshower (CPR) • Shower Max Detector (CES) • (EM Calorimeter) • CDF Data Delivered ~7 fb-1 • CDF Data Acquired ~5.8 fb-1 At lower masses (MH≲ 135 GeV/c2), the dominant Higgs process (gg ➝ H ➝ bb) is overwhelmed by multijet background events, so we rely on WH/ZH modes. Procedure Hepg Results Jet Data Study Resultsb-jets in Higgs MC light jets in jet data "Two b quarks and two anti-b quarks?” • 1. Hepg (High-energy physics generator) Study Using MC generator (truth) information: • Identify Hepg b quarks and electrons (using hepg ID). • Match electrons to b quarks (requiring dR < .4). • Study properties of Hepg electron (Et, Pt, Eta, etc.). • 2. Reconstructed Electron Study Using measured jet and electron collection: • Match jets to b quarks, and electrons to jets. • Study properties of measured electrons. • Electron Et distribution: • b-jets with an electron in them • b-jets have an electron and Et > 1 or Et > 3 GeV. • 3. Jet Data Study Using jet data: • Match jets to b quarks, and match electrons to jet. • Study properties of measured electrons. • (Electron Et , ratio of electron energy to momentum • (E/P), ratio of hadronic energy measured to EM in • calorimeter measurements (Had/EM or Hadem) • Compare signal (Higgs MC) to background (jet data). • 4. Electron Cuts • Remove conversion electrons (photon collisions). • Et and Eta cuts (> 2 GeV Et and < 1 Eta) • Hadem cuts • CES, CPR and other cuts The first b quark 4-momenta is altered by Pythia due to gluon radiation effects. Hepg Results – Jet Matching Reconstructed Electrons Results • We have developed analysis machinery that allows us to test a soft- • electron algorithm both to determine efficiency for real b-jets in Higgs • Monte Carlo and to determine the fake rate of tagging misidentifying a • non-b quark jet in data. • More studies will be conducted in order to reduce the fake rate while  • maintaining a high signal efficiency. • The Tevatron is still collecting data, and improvements to Higgs analyses  • could allow Fermilab to exclude or find evidence for the Higgs boson in • the next few years. 5000 events show electrons have Pt > 1 GeV ~ 72% Pt > 3 GeV ~ 53%.