We present an overview of searches for MSSM Higgs at the Tevatron,
concentrating on searches probing the high tan(beta) region. We discuss the
search for A/H -> tau tau which is soon to be completed in the Run I data and
review the new tau triggers implemented by CDF and D0 in Run II, which will
greatly impact this analysis. We also present the results of a Run I search for
A/H bb -> bbbb performed by CDF and highlight expected improvements in this
channel by both experiments in Run II.Comment: 3 pages with 1 figure, to be published in "Proceedings of the 31st
  International Conference on High Energy Physics ICHEP 2002

A. Connolly

Carena

Haber

Hagiwara

Nilles

Spira

English

arXiv

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Search for MSSM Higgses at the Tevatron

We present an overview of searches for MSSM Higgs at the Tevatron, concentrating on searches probing the high tan {beta} region. We discuss the search for A/H {yields} {tau}{tau} which is soon to be completed in the Run I data and review the new tau triggers implemented by CDF and D0 in Run II, which will greatly impact this analysis. We also present the results of a Run I search for A/Hbb {yields} bbbb performed by CDF and highlight expected improvements in this channel by both experiments in Run II

Connolly, A.

UNT (University of North Texas) Digital Library

Fermilab FERMILAB-Conf-02/265-E  October 20021Search for MSSM Higgses at the TevatronA. Connolly aFor the CDF and D0 CollaborationsaLawerence Berkeley National Laboratory, 50B-5239, One Cyclotron Rd., Berkeley, CA 94720 U.S.A.We present an overview of searches for MSSM Higgs at the Tevatron, concentrating on searches probing the hightan region. We discuss the search for A=H !  which is soon to be completed in the Run I data and reviewthe new tau triggers implemented by CDF and D0 in Run II, which will greatly impact this analysis. We alsopresent the results of a Run I search for A=Hbb! bbbb performed by CDF and highlight expected improvementsin this channel by both experiments in Run II.1. MOTIVATIONThe Higgs mechanism breaks electroweak sym-metry in the Standard Model, giving mass to par-ticles through its couplings. Current data fromelectroweak precision measurements points to alight Higgs (MHiggs < 199 GeV @ 95% CL [1]).However, the Higgs has never been denitivelyobserved (MHiggs > 114 GeV at 95% CL [2]).A Standard Model Higgs suers from the so-called hierarchy problem. The theory needs ne-tuned parameters to accomodate a light Higgsmass. Supersymmetry oers a solution to thisproblem, through a symmetry between fermionsand bosons.The Minimal Supersymmetric Standard Model(MSSM) contains two Higgs doublets, leading tove physical Higgs bosons: Two neutral CP-evenstates (h and H), one neutral CP-odd (A), andtwo charged states (H+ and H ). At tree-level,the masses are governed by two parameters, oftentaken to be mA and tan [3]. When tan >>1 , A is nearly degenerate with one of the CP-even states (denoted ). Where mA  130 GeV(mA  130), mA = mh (mA = mH).In this same large tan region, the cross sec-tions for some production mechanisms such aspp! A() and pp! A()bb are enhanced by fac-tors of tan2(sec2). For example, withps = 2TeV, tan = 30 and mA = 100 GeV, the crossCurrent address is Fermi National Accelerator Labora-tory, P.O. Box 500, M.S. 318, Batavia, IL 60510 U.S.A.sections for pp ! A and pp !  are each of or-der 10 pb[4]. The cross section for pp ! A=bbis smaller, but within the same order of magni-tude. In the same region, the branching ratios toA=! bb and  dominate, at  90% and  10%respectively, independent of mass.Due to their similar masses, cross-sections andbranching ratios in the high tan region, wesearch for both A and  simultaneously. At theTevatron, we search for pp ! A= !  (the bbnal state is expected to be overwhelmed by dijetbackground) and pp! A=bb! bbbb.2. SEARCH FOR pp! A=! + This search is underway at CDF. The dominantissues for this analysis are: tau identication, di-tau mass reconstruction, irreducible backgroundfrom Z !  , and event loss at the trigger level.Wherever not specied, we use the benchmarkcase of mA = 95 GeV and tan = 40 to quoteeciencies and cross-sections.2.1. Tau IdenticationCompared to QCD jets, taus are highly col-limated, leaving narrow jets with low track andphoton multiplicity, and low mass.In CDF, when selecting taus, one typically re-quires a jet with high visible ET containing a highpT track. The jet is required to be isolated in a10o  30o annulus around the high pT track. Thevisible energy in a 10o cone is required to satisfylow track and photon multiplicity requirements2and to reconstruct a mass m < 1:8 GeV. Addi-tionally, a requirement is made on the charge ofthe tracks in the 10o cone when appropriate. InRun I, CDF acheived fake rates in the range 1.2- 0.7 % for jet ET between 20 and 200 GeV[5].2.2. Ditau Mass ReconstructionThe full mass of a ditau system may be recon-structed [6] if the neutrinos are assumed to travelin the same direction as their parent taus, by solv-ing the following system of equations:Emeasx= = E1x= +E2x= (1)Emeasy= = E1y= +E2y= (2)where Emeasx;y= are the x and y components of themeasured event missing energy, and E1x;y= andE2x;y= denote the missing energy from each tau.Equations 1 and 2 do not give a meaning-ful solution when the taus are back-to-back inthe transverse plane. Therefore, we require thatj sinj > 0:3, where  is the azimuthal anglebetween the tau candidates.When the solution to Equations 1 and 2 givesE1= < 0 or E2= < 0, the event is thrown out,causing about 50% of the Higgs signal to be lost.However, 97% of W+jets events are rejected inthis way, which would otherwise be a formidablebackground.We generate A=!  events in Pythia 6.203with mA = 95 GeV and tan = 40. After sim-ulation of the Run I CDF detector, a ditau massdistribution is reconstructed with a mean valueof 93.7 GeV with an RMS of 24.1 GeV.2.3. Irreducible BackgroundThe dominant reducible backgrounds to thisanalysis are QCD, Z ! ee, and W+jets. Z ! is an irreducible background, but Higgs events aremore ecient for this search than Z's for a coupleof reasons.First, in the high tan region, A='s have ahigh branching ratio to taus (9%) compared toZ's (3.7%). Second, an A= is typically producedwith a stier pT than a Z. This means that the re-quirement j sinj > 0:3, which is nearly equiva-lent to pA==ZT > 15 GeV, is  30% more ecientfor Higgs events than Z events.2.4. TriggersSince there was no  trigger in Run I at CDF,the analysis uses a lepton trigger requiring pT >18 GeV, seeking events with one leptonic andone hadronic decay. Since only half of the sig-nal events decay in this way, and of these, only20% contain a lepton which satises the pT re-quirement within the acceptance, the signal rateis greatly diminished at the trigger level.This major loss at the trigger level is problem-atic, since the cross section drops by a factor of4 from mA = 95 GeV to mA = 120 GeV, beforethe mass reconstruction, with an RMS of 24 GeV,can discriminate from Z !  . Therefore, in RunII, CDF and D0 are both implementing triggersdesigned for tau physics. Lowered pT thresholdsand new decay modes available will greatly in-crease the acceptance for this search.In Run II, CDF and D0 both have lepton +track triggers and  + ET= triggers. In addition,both experiments are triggering on events withtwo hadronic taus. CDF's trigger is calorimeter-based, while D0's is track-based.The Run I search for A= !  is still workin progress, and the Run II analysis is also in theworks.3. SEARCH FOR pp! A=bb! bbbbCDF performed this search in Run I. Both ex-periments expect to improve on the analysis inRun II.3.1. Run I searchThe Run I search at CDF [7]utilized a 4-jettrigger requiring ET > 125 GeV. Three b-tagswere required based on displaced vertices, and theb jets were required to be separated in azimuthalangle,  > 1:9. To optimize sensitivity, the ETcuts on the jets varied with mass hypothesis. Formass hypothesis below 120 GeV (above 120 GeV),the second and third b-tagged jets (rst and sec-ond jets) ordered in ET were chosen for the massreconstruction. The search is performed in masswindows dependedent on mass hypothesis.The product of branching ratio and acceptanceranged from 0.2 to 0.6% in the mass range 70and 300 GeV. For a mass hypothesis of 70 GeV,35 events were observed with 4.6  1.4 expected.Only these 5 events appear in the higher masswindows. No excess above predicted is observed.Figure 1 shows the mA   tan region excluded.Figure 1. Region of themA tan region exludedby the CDF search.3.2. Run II ImprovementsAt CDF, studies of Z ! bb events show animproved dijet mass resolution after correctingfor muons, ET= , and nonlinearities in the hadroniccalorimeter. Separate studies of QCD jets usingsimilar techniques show a 30% improvement in jetresolution.B-tagging in Run II at CDF will be im-proved with the new ability to reconstruct three-dimensional tracks. Extended coverage fromjj < 1 (Run I) to jj < 2 means improve b-jetand lepton acceptance. Additionally, new triggerswill also recover acceptance, including a displacedtrack trigger, and an improved multijet trigger.With a new silicon detector, D0 will also beperforming this search in Run II, expecting a12% dijet mass resolution. Both experimentsperform a study of their expected sensitivity topp! A=bb! bbbb in Run II, and obtain similarresults[8]. We present the D0 study here.D0 also uses a multijet trigger, requiring fourjets, each with ET > 15 GeV. To maximize sensi-tivity, mass dependent ET cuts are made on thejets. At least 3 b tags are required. All masscombinations are plotted, and a 2.5 bbmass win-dow is used. With 2fb 1, D0 concludes that theTevatron is expected to exclude mA < 160 GeVfor tan = 40 at 95% CL, and a 5 discovery formA < 115 GeV for the same tan.4. CONCLUSIONSRun I results of the search for A= !  atCDF are to be completed soon, and a rst glimpseof Run II data is on the way.The Run I search for pp ! A=bb ! bbbb de-rives lower mass limits for tan in excess of 35. InRun II with both experiments searching for thisdecay mode, the Tevatron is expected to exclude(or make a discovery in) a signicant region ofMSSM parameter space. Both experiments areoptimistic about improvements from triggers, jetresolution, and b-tagging to make this search evenstronger than the current projections.REFERENCES1. K. Hagiwara et al., Physical Review D66,010001 (2002).2. ALEPH Collaboration, DELPHI Collabora-tion, L3 Collaboration, OPAL Collabora-tion and LEP Higgs Working Group, LHWGNote/2001-03,hep-ex/0107029.3. For a review of the MSSM, see H.P. Nilles,Phys. Rept. 110:1,1984, H. Haber, G. Kane,Phys. Rept. 117:75,1985.4. M. Spira, Nucl.Instrum.Meth.A389:357-360,19975. CDF Collaboration, Phys.Rev.Lett.79:357-362, 19976. CMS Technical Proposal, CERN/LHCC 94-38, December 1994, pp. 191-192.7. CDF Collaboration, Phys.Rev.Lett.86(2001)4472-4478.8. M.Carena, J.S.Conway, H.E.Haber,J.D.Hobbs, et al, Fermilab-Conf-00/279-T and SCIPP-00/37,hep-ph/0010338.

Search for MSSM Higgses at the Tevatron

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