During Run II of the Tevatron collider, D0 collaboration has made extensive searches for the neutral MSSM Higgs bosons ({phi}), produced in p{bar p} collisions at {radical}s = 1.96 TeV. Two such analyses, addressing inclusive {phi} production with {phi} {yields} {tau}{sup +}{tau}{sup -}, and associated {phi}b(b) production with {phi} {yields} b{bar b} are reported here. No excess of events above the background expectation has been observed in any of these analyses. The results are combined to set constraints on the MSSM parameter space

Mal, Prolay Kumar

U., /Notre Dame

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Fermilab FERMILAB-CONF-06-398-ESUSY Higgs Searches at DØ , TevatronProlay Kumar Mal(for DØ Collaboration)University of Notre Dame,Notre Dame, Indiana 46556, USAAbstract. During Run II of the Tevatron collider, DØ collaboration has made extensive searchesfor the neutral MSSM Higgs bosons (φ ), produced in pp¯ collisions at   s  1  96 TeV. Two suchanalyses, addressing inclusive φ production with φ  τ  τ  , and associated φb  ¯b  production withφ  b¯b are reported here. No excess of events above the background expectation has been observedin any of these analyses. The results are combined to set constraints on the MSSM parameter space.Keywords: MSSM, Higgs, DØ, TevatronPACS: 11.30.Pb, 12.60.Fr, 13.85.Rm, 14.80.CpINTRODUCTIONThe Standard Model (SM) of particle physics has been observed to be a consistenttheory of fundamental particles and their interactions up to the energies they havebeen studied although one remaining essential ingredient the Higgs boson is yet to bediscovered. Theoretical considerations teach us that SM can not be the ultimate theory ofelementary particles and their interactions. Amongst many other compelling theories, theMinimal Supersymmetric extension of the SM (MSSM) is one of the viable theoreticalframeworks which has the potential to overcome some of the short comings of the SMby incorporating minimal supersymmetric particle spectrum.Because of its supersymmetric structure, the MSSM[1][2] requires at least two Higgsdoublets to generate masses to both “up”-type and “down”-type quarks (and the re-spective charged leptons). Such a two-Higgs-doublet model predicts five physical Higgsbosons: two CP-even Higgs bosons, h and H, one CP-odd Higgs bosons, A and a pairof charged Higgs bosons, H  . The MSSM Higgs sector at the lowest order can fullybe described in terms of one Higgs boson mass (MA is chosen in CP-conserving sce-nario and MH	 in CP-violating scenario) and tanβ  v2  v1, where v2  v1  refers to theHiggs field that couples to the “up”(“down”)-type quarks. However, additional param-eters viz., MSUSY  M2  µ and mg˜ enter at the level of radiative corrections. It is to benoted that the coupling of the Higgs boson A to “down”-type quark such as bottom quarkis proportional to tanβ . So with respect to the SM, the production cross section for Ain association with bottom quark(s) gets enhanced by a factor of tan2β . Furthermore, atlarge tanβ (  50), there is mass degeneracy between the Higgs bosons A and h or Hdepending on the value of mA. Therefore, the total production cross section for MSSMneutral Higgs bosons i.e., hHA  φ is twice that of the Higgs boson A. Previously,LEP experiments have set the mass of light Higgs boson mh to be greater than 92.8GeV[3] at 95% CL.The MSSM neutral Higgs bosons (φ ) mostly decay into b¯b pairs (90%) or intoτ  τ  pairs (  8%). So, at the Tevatron pp¯  φ b¯bb¯bX and pp¯  φ τ  τ Xprocesses are considered to be the most promising channels to look for the signature ofMSSM neutral Higgs bosons. Here we report on the searches for MSSM neutral Higgsbosons in the above channels performed by the DØ experiment [4]. The combined resultsare interpreted in different MSSM benchmark scenarios[5]: “mmaxh ” and “no-mixing”.SEARCH FOR pp¯ φ  b¯b  b  ¯b  XThe analysis focuses on MSSM neutral Higgs boson production in association with oneor two bottom quark(s) resulting in three or four bottom quarks in the final state while,CP-conservation in the Higgs sector is assumed. 260 pb  1 of DØ data collected betweenNovember 2002 and June 2004 have been utilized for this analysis. The data are firstfiltered using a dedicated on line trigger designed to maximize the signal acceptance.The Secondary Vertex (SV) tagging algorithm has been used to select the b-jets. TheDØ SV b-tagging algorithm selects central b-jets (pT  35 GeV) with an efficiency of 55% while the mis-tag rate for similar light quark jets is about 1%.For Higgs masses between 90 and 150 GeV, the hb  b¯bb signal events have beengenerated using the Pythia [6] event generator followed by the full DØ detector sim-ulation and reconstruction. The Pythia generated pT and rapidity spectra of the Higgsbosons have been adjusted to those from NLO calculations [7]. The largest backgroundcontribution from QCD multijet processes have been determined directly from datawhile contributions from other background processes such as t¯t, Z0 b¯b+jets havebeen determined from Monte Carlo.The selected events are required to have at least three b-tagged jets (within η 2 ﬀ 5) with pT  35, 20 and 15 GeV respectively for the leading pT jets. The invariantmass distribution of the two leading pT jets in data is then compared with that of thebackground expectation and no excess has been observed. Fig. 1(a) shows the limiton the production cross section at 95% CL, as a function of mA for tanβ  80 in “nomixing” scenarios. The results are also interpreted in the “maximal mixing” case and thelimits in tanβ ﬁ mA plane for both scenarios are shown in Fig. 1(b).  (GeV)                     Aﬂm80 100 120 140 160Cross section  (pb)   10210310DØExpectedMeasured = 80βtan   (GeV)                   Aﬃm80100 120 140                 βtan20406080100 DØMSSM Higgs bosons = h, H, Aφ),  b b→(φbbExcluded at LEPNo mixingMax. mixingﬃ                 βtan(a) (b)FIGURE 1. (a) The upper limits on the production cross section as a function of Higgs mass and (b)the limits on tanβ ! mA plane at 95% CL.SEARCH FOR pp¯ φ  τ " τ #$ XThe analysis is based on 325 pb  1 of data collected by the DØ experiment during theperiod September 2002 to August 2004. The signal consists of a pair of tau leptons.One of the tau leptons is required to decay leptonically into electron or muon, leading tothree final state signature: eτh, µτh and eµ , where τh represents a hadronically decayedtau lepton. The three types of hadronically decayed τ leptons,• τ-type 1: a single track with a calorimeter cluster without any electromagnetic subclusters (1-prong, pi-like)• τ-type 2: a single track associated with a calorimeter cluster and electromagneticsub clusters (1-prong, ρ-like)• τ-type 3: two or at least three tracks with invariant mass below 1.1 or 1.7 GeVrespectively (3-prong)have been utilized in this analysis. A set of neural networks†, one for each type havebeen used for further discrimination over the backgrounds.The signal as well as various background processes have been generated using Pythia.Events are then passed through the full chain of DØ detector simulation and reconstruc-tion software. Apart from the QCD multijet background where a jet mimics an elec-tron/muon from tau lepton, all other background processes are normalized to NLO andNNLO (Z0 boson, W  boson, Drell-Yan and di-boson) cross sections.The reconstructed visible mass defined as Mvis   Pτ1 % Pτ2 % P/T  2, where Pτ1 & 2 isthe four vector of the visible tau decay products and P/T   E/T  E/x  E/y  0  , is used to dis-criminate between signal and background processes. No excess over the background ex-pectation has been observed. The Figs. 2(a)-(b) show the distributions of Mvis (denotedas “Inv ﬀ Masseµtauhad  E/T  " and “Inv ﬀ Mass  e  µ  E/T  " respectively in the figure) fordifferent final states, while Fig. 2(c) displays the upper limits on production cross sectionas a function of Higgs mass.(a) (b) (c)FIGURE 2. The distribution of reconstructed visible mass Mvis (see text) for (a) eτh+µτh channel, and(b) eµ channel. (c) The upper limits on the production cross section as a function of Higgs mass at 95%CL.† Identical to the ones used for Z0 ' γ () τ  τ  cross section measurements[8]COMBINED LIMITSThe DØ results obtained from the above two analyses [9][10] are combined togetherand are re-interpreted in “mmaxh ” and “no-mixing” scenarios. Fig. 3 shows the currentDØ limits on MSSM parameter space. The similar limits obtained by the CDF [11] arealso displayed for the purpose of comparison.(a) (b)FIGURE 3. The excluded region in the (MA * tanβ ) plane for the mmaxh and no-mixing scenario withµ ,+ 200 GeV.CONCLUSIONSDØ has performed searches for the MSSM neutral Higgs bosons and the current DØlimit on MSSM parameter space is the most sensitive to date. Additional search channelslike pp¯  φ τ  τ b¯bX , advanced analysis techniques and larger dataset willprovide further scope to improve the sensitivity in future.REFERENCES1. H. P. Nilles, Phys. Rep., 110, 1 (1984).2. H. P. Nilles and H. E. Haber and G. L. Kane, Phys. Rep., 117, 75 (1985).3. The LEP Working Group for Higgs Boson Searches, CERN-PH-EP/2006-001 (2006).4. V. M. Abazov et al. (DØ Collaboration), Nucl. Instrum. and Methods A 565, 463 (2006).5. M. Carena et al, Eur.Phys.J. C, 45, 797 (2006).6. T. Sjöstrand et al, Comp. Phys. Comm., 135, 238 (2001).7. J. Campbell et al, Phys Rev D, 67, 095002 (2003).8. V. M. Abazov et al. (DØ Collaboration), Phys Rev D, 71, 072004 (2005).9. V. M. Abazov et al. (DØ Collaboration), Phys. Rev. Lett., 95, 151801 (2005).10. V. M. Abazov et al. (DØ Collaboration), Phys. Rev. Lett., 97, 121802 (2006).11. A. Abulencia et al. (CDF Collaboration), Phys. Rev. Lett., 96, 011802 (2006).

SUSY Higgs Searches at D0, Tevatron

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SUSY Higgs Searches at D0, Tevatron

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