Jessica Leonard Oct. 23, 2006 Physics 835 Search for neutral MSSM Higgs bosons decaying to  pairs in pp collisions at 1.96 TeV (CDF) Jessica Leonard Oct. 23, 2006 Physics 835

MSSM Higgs How do particles have mass? SM Higgs mechanism Problems with SM Higgs may be solved in MSSM Five Higgs in MSSM: 2 charged, 3 neutral This paper deals with neutrals (): 1 CP-odd: A 2 CP-even: h (lighter), H (heavier) MSSM parameters: mA tan  = vu/vd, where vu, vd are vev’s of neutral Higgs that couple to up- and down-type fermions 10/23/06 Jessica Leonard

MSSM Higgs For large tan b, one CP-even Higgs has similar mass, couplings to A Dominant  production mechanisms: Gluon fusion bb fusion Dominant decay modes for A, mass-degenerate CP-even state:  -> bb (~90%)  ->  (~10%) 10/23/06 Jessica Leonard

The search at CDF Tevatron: CM energy 1.96 TeV Data collected at CDF II between 2002-04 Integrated luminosity 310 pb-1  ->  for 90 < mA < 250 GeV/c2 One  -> lepton + neutrinos (e, ) Other  -> hadrons + neutrino (had) 10/23/06 Jessica Leonard

CDF detector =-ln(tan(/2)) 10/23/06 Jessica Leonard

Event selection For the  ->  search, each event must contain a lepton candidate (e or ) and hadrons consistent with a  decay. Pre-select with a “lepton plus track” condition Lepton and track must both point into central cal. Must have azimuthal separation of > 10o e/ determination: Electrons only deposit energy in EM calorimeter Muons seen in muon chambers outside cal. Momentum of neutrinos: missing transverse energy 10/23/06 Jessica Leonard

Event selection Hadron reconstruction Energy from  decays are deposited in a small, contiguous region Four-momentum of this jet determined from tracks of charged particles and energies of 0’s within “signal cone” Particles in a ring outside the signal cone must have very low transverse energy (< 1 GeV total). This isolation cuts out quark and gluon jets. 10/23/06 Jessica Leonard

Event selection Hadron reconstruction The jets must have 1 or 3 tracks (charged particles), and sum of charges 1 Invariant mass must be < 1.8 GeV/c2 ( = m) Require (Ecl/Psigtrk)(0.95-f)>0.1 to reject electrons Ecl: value of energy deposit in the calorimeter f: ratio of electromagnetic to hadronic energy Psigtrk: scalar sum of track momenta in signal cone Require ETcl > 15 GeV to reject muons 10/23/06 Jessica Leonard

Event selection Hadron reconstruction efficiency: 38% at pThad = 15 GeV/c 46% at pThad > 25 GeV/c Probability of misidentifying quark or gluon jet 1.5% at ETjet = 20 GeV 0.1% at ETjet = 100 GeV 10/23/06 Jessica Leonard

Monte Carlo Simulation Event generation: PYTHIA, with CTEQ5L PDFs Tau decays: TAUOLA package Detector response: GEANT-based model 10/23/06 Jessica Leonard

Backgrounds Dominant background: Z/* ->  Second-highest: “fake” ’s (misidentified quark or gluon jets) from processes like di-jet, multi-jet, W+jets, +jets Third: Z/* -> ll, WW, WZ, ZZ, tt Background contributions determined by Monte Carlo 10/23/06 Jessica Leonard

Eliminating backgrounds Cut out low-energy multi-jet backgrounds Each e/ candidate must pass pT threshold of 10 GeV/c Each had candidate must pass pT threshold of 15 GeV/c, must also have opposite charge Require |pTl|+|pThad|+|ETmiss| > 50 GeV 10/23/06 Jessica Leonard

Eliminating backgrounds Cut out W+jets backgrounds Define: pvis = (pl + phad)   pETmiss = ETmiss   Require pETmiss > 0.6pvis - 10 GeV/c Removes ~85% W+jets events, keeps ~95% of signal Cut out Z -> ll decays with misidentified lepton: reject events with lepton + 1-prong had invariant mass within 10 GeV/c2 of Z mass 10/23/06 Jessica Leonard

Signal Acceptance For mA = 90 GeV/c2, combined acceptance for ehad and had channels is 0.8% For mA = 250 GeV/c2, combined acceptance is 2.0% 10/23/06 Jessica Leonard

Uncertainties Systematic uncertainties for particle ID efficiency: had 3.5%, e 1.3%,  4.6% Uncertainties in trigger efficiency: ehad 2.1%, had 1.4% Jet ->  misidentification 20% (3% bg. overall) Uncertainty in signal acceptance Due to event-level cuts < 2% Due to PDFs: 5.7% 10/23/06 Jessica Leonard

Expected events from SM Number of expected standard model events passing all cuts: 4965(stat)28(sys)25(lumi) for a range of 438 to 554 events Breakdown: 405 from Z/* ->  75 from jet ->  misidentification 16 from all remaining background sources 10/23/06 Jessica Leonard

Data 487 observed events Reconstructed the mass (mvis) for each event: invariant mass of visible tau decay products and ETmiss NOTE: This is incorrect! Binned the data to compare with background and hypothetical Higgs data No signal evidence observed for mA = 90 through 250 GeV/c2 10/23/06 Jessica Leonard

Example plot: mA = 140 GeV/c2 10/23/06 Jessica Leonard

Exclusion limits 10/23/06 Jessica Leonard

Excluded regions Plotted excluded regions in parameter space for four situations mhmax vs. no-mixing  > 0 and  < 0 10/23/06 Jessica Leonard

Excluded regions 10/23/06 Jessica Leonard

Conclusions LEP excluded mA < 93 GeV/c2, higher mA for small tan  This search also excluded regions of higher tan  Results similar to those of D0 10/23/06 Jessica Leonard