Searches for Neutral Higgs Boson and Interpretations in the MSSM at LEP

0.09 MB·English

by  P. Bechtle

EurPhysJC(2003)
DigitalObjectIdentifier(DOI)10.1140/epjcd/s2003-03-803-y
Searches for Neutral Higgs Boson and Interpretations in the
MSSM at LEP
PhilipBechtlea
4
0 DESY,Notkestr.85,22607Hamburg,Germany;E-mail:[email protected]
0
2 Received:1Oct2003/Accepted:20Nov2003/
n PublishedOnline:26Nov2003–(cid:13)c Springer-Verlag/Societa`ItalianadiFisica2003
a
J Abstract ThispaperdiscussesrecentpublicationsoftheLEPcollaborationsDELPHI,L3andOPALonsearchesfor

6 HiggsbosonsmotivatedbyMSSMscenariosaswellastheirinterpretationintheMSSM.Withthefinalpublicationof
2 theLEPcollaborationsavailableorawaited,moreandmoreinterpretationsindifferentMSSMmodels,includingboth
CPconservingandCPviolating,becomeavailable.Alsospecializedanalysescloseopenareasintheparameterspace.

2 Inthesametime,bettertheoreticalcalculationswithanincreasedmaximalmassofthehbosonwerepresented.Both
v thenewscenariosaswellasthenewtheoreticallimitonmh hasconsequencesforthelimitsfromLEP.Thesearches,
7 themodelsinwhichtheyareinterpretedandtheimplicationsoftheLEPresultsforfutureSUSYsearches,especially
0
onthetanβlimit,arepresentedhere.
0
1
PACS. 12.60.Fr ExtensionsofelectroweakHiggssector–12.60.Jv Supersymmetricmodels–13.66.Fg Gaugeand
0 Higgsbosonproductionine+e−interactions–14.80.Cp Non-standard-modelHiggsbosons
4
0
/
x 1 Introduction Table1.TheMSSMscenariosusedbytheLEPcollaborations,pro-
e
posedin[2],[3]and[4]
-
p
In the Standard Model (SM) it is generally assumed that the
e
Higgsmechanismisresposibleforthebreakingofelectroweak
h CPconserving
symmetryandforthegenerationofelementaryparticlemasses.
:
v TheMinimalSupersymmetricStandardModel(MSSM)isthe NoMixing Nomixinginthestop-sbottomsector
Xi SUSYextensionoftheSMwithminimalnewparticlecontent. mhmax Maximummhforgiventanβ,mA
Largeµ Alwayskinematicallyaccessible,
It introduces two complex Higgs field doublets. The MSSM
r buth→bb¯suppressed
a predictsfiveHiggsbosons:threeneutralandtwochargedones. m max+ likem max,butfavouredby(g−2) .
AtleastoneoftheneutralHiggsbosonsispredictedtohaveits h h µ
constr.m max likem max,butfavouredby(b→sγ)
mass close to the electroweak energy scale, providing a high h h
gluophobic hggcouplingsuppressed,
motivationtothesearchesatcurrentandfuturecolliders.
reducedLHCproductioncrosssection
In the MSSM theHiggspotentialisassumed tobe invari- smallαeff h→bb¯suppressedbycancellationof
ant under CP transformationat tree level. However, it is pos- b˜−g˜loops
sible to break CP symmetry in the Higgs sector by radiative
CPviolating
corrections,especiallybycontributionsfromcomplextrilinear
couplingsAt,bofthirdgenerationscalar-quarks[1]. CPX MixingofCP-andmass-eigensates
severalderivatesunderstudy
Sincetheinputparameterspaceisgenerallytoolargetobe
scannedcompletely,socalledbenchmarkscenarios(cf.Tab.1)
have been proposed [2,3,4], each emphasising a certain phe-
nomenologicalsituation. The parameters tanβ = v2/v1 and
mAgoverningtheHiggssectorontree-levelarescanned,while
allparametersonlooplevelarekeptfixedforonescenario.CP SincetheendofLEPrunning,theLEPcollaborationshave
conserving(CPC)andCPviolating(CPV)scenariosexist. developednewsearchesclosingsomeoftheseunexcludedar-
DependingontheparametersoftheMSSM,HiggsBosons eas in the parameter space, thereby giving important new in-
can be produced in Higgstrahlung e+e−→hZ, as in the SM, formationaboutthetasksleftoverforfutureexperiments.This
or in pair production e+e−→hA. Flavour independent Higgs publication will focus on new searches dedicated to formerly
decays, Higgs decays into invisible particles or decays of the uncovered final states described in Section 2, on the conse-
typeh→AAadditionallypresentnewtopologies. quencesof new theoreticaldevelopmentsin Section 3 and on
the interpetation of the MSSM Higgs searches in the bench-
a Speaker;onbehalfoftheLEPcollaborations markscenariosinSection4.
2 P.Bechtle:SearchesforNeutralHiggsBosonandInterpretationsintheMSSMatLEP
2 Searches for Higgs bosons in the MSSM
LEP 88-209 GeV Preliminary
The search for Higgs bosons in the MSSM uses a large vari-
β
ety of channels.The SM production channels Higgsstrahlung n
e+e−→hZandBosonfusionarereintrerpretedintheMSSM. ta m -max
h°
Additionally, dedicated searches for Higgsstrahlungschannels
with Higgs decays in the MSSM exist. Also, pair production
1100
e+e−→hA and Yukawa production e+e−→bb¯h/A channels
FeynHiggs 1.3
are used. New searches comprise the search for e+e−→hZ
with h→AA, with mA < 10 GeV below the bb¯ production
Excluded
threshold[5]byOPAL.Thesamefinalstate withheaviermA by LEP
hasbeensought-afterfortheinterpretationinCPVmodels[6].
FeynHiggs 2.0
ThesearchfromDELPHI[7]forinvisiblydecayingHiggs
bosonshas been interpreted in a modified mh−max scenario m +5 GeV
withM2 =µ=150GeV.Itshowsthatthebenchmarkscenar- t
iosfromTab.1donotcoverthefullrangeofpossibleMSSM
11
topologies in the Higgs sector, since the search for invisibly
Theoretically
decayingHiggsbosonsisneededtocoverareasunexcludedby Theoretically
thestandardsearches. inacIcneascsciebssleible
0 20 40 60 80 100 120 140
2
m (GeV/c )
3 New benchmark scenarios and Higgs h°
mass calculations in the MSSM
Figure1.Expectedexclusionareasofthemh−maxscenariointhe
The calculations of the observables of the Higgs sector, the mh,tanβprojectionforincreasedupperboundsonthemassoftheh
masses, branching ratios and cross-sections, depending on boson.TheexperimentalexclusionareasshownarethoseoftheLEP
the choice of SUSY parameters have been performed using combination2001[13].Theexpectedtheoreticalupperboundsformh
two different calculation tools. FEYNHIGGS [8,9] is based given new order α2 loop corrections to the Higgs mass is shown in
t
on the two-loop diagrammatic approach of [10], and SUBH- lightgrey(yellow)andtheadditionaleffectofapossibleshiftinmt
POLE/CPH[4]isbasedontheone-looprenormalization-group by+1σ isoverlaidindarkgrey(red).Thetheoreticallyinaccessible
improvedcalculationof[11,12]. areaisforbiddenbytheory.
ThefirstthreeCPCbenchmarkscenariosofTab.1havetra-
ditionally been considered in the past and have now been ex-
Thisexampleshowsthatnewtheoreticaldevelopmentsand
tendedtoscenarios4and5,motivatedbylimitsonthebranch-
ingratiooftheinclusivedecayofaBmesonintostrangeparti- ahigherprecisiononmt couldwellinfluencetheexclusionof
clestatesandaphotonB→Xsγandmuonanomalousmagnetic lowtanβbyLEP.Ahigherprecisiononmtisthereforehighly
moment(g−2) measurements.ThelasttwoCPCbenchmark desireable.Thiscouldalsohaveimplicationonthesearchchan-
µ
nels that have to be investigated at future accelerator experi-
scansareaimingtosetthestageforfutureHiggssearchesatthe
mentsatLHCsearchingforaMSSMHiggsboson,wherethe
LHC. There,some of the dominantsearchchannelswould be
regionofsmalltanβ cannotberegardedasexcludedbyLEP.
suppressed,resultinginareducedsearchsensitivity.TheCPV
scenario CPX maximises the mixing of CP- and masseigen-
statesandhasbeentestedwithseveraldifferentparameterset-
4 Interpretation of the Higgs searches in the
tings[6].
WithrespecttothecalculationsusedfortheMSSMHiggs MSSM
LEP combination in 2001 [13], new 2-loop calculations of
top loop corrections to the Higgs boson mass have become The combination of all Higgs searches of one experiment is
available [14]. They shift the maximal mh achievable in the used to derive [17,18,6] exclusions in the MSSM parameter
mh−maxscenarioupwardsbyupto5GeV.Themaximalmh space for the scenarios in Tab. 1. No major changes with re-
liesatabout135GeV.Whiletheexpectedexperimentallower specttopreviousinterpretationsarerecievedfortheno-mixing,
limitonmhforlowtanβisnotexpectedtochangemuchwith mh−maxandlarge-µscenarios.Thelatternowcanbealmost
respectto thelatest LEPexclusion(cf.Fig. 1),the theoretical completely exluded by one experiment alone [17], thanks to
upper limit on mh shifted from the border of the black area flavour independentsearches[19]. OPAL has also studied [6]
to the border of the light grey (yellow) area. If the top mass thenewCPCscenarios4to7fromTab.1.
wouldadditionallyshiftupwardsfromitscurrentcentralvalue Insummary,theparameterchoicesofthenewCPCbench-
ofmt =174.3±5.1GeV[15]byonlyonesigma(whichcould markscenariosintroducenoneedfornewsearchesatLEP.Lat-
wellbethecase,givenlatestmeasurementsfromD0inthelep- estinaLEPcombination,alltopologiesarecovereduptothe
tonic decay channel [16]), then the upper limit on mh would kinematiclimitsoftheproductionchannels.Thelimitsonmh
increaseagainbyalmost5GeV,asindicatedbytheborderof andmAarearound85to90GeVforallCPCscenarios[20,17,
thedarkgrey(red)areainFig.1. 18,6].
P.Bechtle:SearchesforNeutralHiggsBosonandInterpretationsintheMSSMatLEP 3
OPAL preliminary cover the rich physics spectrum of the MSSM Higgs sector,
whichonlynowbecomefullyavailable.
β Third, new theoretical developments can influence limits
an MSSM CPX on MSSM parameters. Especially the tanβ exclusion of the
t final LEP combination could be affected. This is also impor-
tantforthepossibleMSSMtopologiesinHiggssearchesatthe
LHC.Theimportanceofexternalmeasurementslikemt from
10 theTevatronbecomesevident.Agreaterprecisiononmtwould
bebenefitial.Fourth,CPVscenariosshowthatthereisstillno
strictlowerlimitontheHiggsmassfromLEP.Especiallyinre-
gionswithlowmH1,buteitherdominante+e−→H2Zordom-
inante+e−→H1H2 productionnotanβ independentlimiton
the Higgs mass exists. Also these regions must probably be
Excluded soughtbyfuturecolliders.
Theoretically References
1
inaccessible
1. A.PilaftsisandC.E.Wagner,Nucl.Phys.B553(1999)3.
2. M. Carena, S. Heinemeyer, C. E. Wagner and G. Weiglein,
0 20 40 60 80 100 120 140 arXiv:hep-ph/9912223.
m (GeV) 3. M. Carena, S. Heinemeyer, C. E. Wagner and G. Weiglein, Eur.
H1 Phys.J.C26(2003)601.
4. M.Carena,J.R.Ellis,A.PilaftsisandC.E.Wagner,Phys.Lett.B
495(2000)155.
Figure2.ExclusionareaoftheCPXscenariointhetanβ,mH1 pro- 5. G.Abbiendietal.[OPALCollaboration],Eur.Phys.J.C27(2003)
jection from OPAL. The theoretically inaccessible area is forbidden
483.
bytheory.
6. OPALCollaboration,SearchforNeutralHiggsBosonsPredicted
by CP Conserving and CP Violating MSSM Scenarios with the
OPALdetectoratLEP,2003,OPALPN524
TheCPXscenariowithmaximalCPviolationintheHiggs
7. [DELPHI Collaboration], Searches for invisibly decaying Higgs
sectorshowsadecouplingofthelightestHiggsbosonsH1from bosons with the DELPHI detector at LEP, DELPHI 2003-
the Z in the intermediate tanβ range from 4 to 10 (H1 and 036CONF656.
H2 being the lightest and next-to-lightest Higgs boson mass 8. S. Heinemeyer, W. Hollik and G. Weiglein,
eigenstates). There anyhow H2 couples to the Z and is heav- Comp. Phys. Comm. 124 (2000) 76; Also see
ierthanaround100GeV.Wherekinematicallyaccessible,the http://www.feynhiggs.de.
decayH2→H1H1 isdominant.Anotherdifferencetothecom- 9. M. Frank, S. Heinemeyer, W. Hollik and G. Weiglein, hep-
monCPCscenariosisthelargemassdifferencemH2−mH1 in ph/0212037.
therangewithdominantpairproduction. Alsoseewww.feynhiggs.de.
Fig. 2 [6] shows the exclusionareas of the CPX scenario. 10. S.Heinemeyer, W.HollikandG.Weiglein,Eur.Phys.Jour.C9
Intheregionwithdominante+e−→H2Z→H1H1Zproduction (1999)343.
11. M. Carena, M. Quiro´s and C.E.M. Wagner, Nucl. Phys. B461
at intermediate tanβ and mh < 50 GeV open areas emerge.
(1996)407.
It is expected that a LEP combination will be able to close
12. M. Carena, S. Mrenna and C. Wagner, Phys. Rev. D60 (1999)
these holes. Also the lower limit on mH1 in the large tanβ 075010.
region,wherepairproductiondominates,isreducedduetothe
13. ALEPH,DELPHI,L3andOPALCollaborations,OPALTN699
largemH2 −mH1. Attanβ > 5 andmH1 < 10GeV, below 14. A.Brignole,G.Degrassi,P.SlavichandF.Zwirner,Nucl.Phys.
thebb¯ productionthresholdandinthepairproductionregion,
B631(2002)195;
hardlyanyexperimentalconstraintsexist,sincenopairproduc-
G.Degrassi,S.Heinemeyer,W.Hollik,P.SlavichandG.Weiglein,
tionsearchesformH2 ≈ 100GeVandmH1 < 10GeVexist. Eur.Phys.J.C28(2003)133.
Onlyatlargetanβ > 20Yukawaproductionsearchescanbe 15. D.E. Groom et al, Eur. Phys. J. C15 (2000) 1, available on the
used. PDGWWWpages(URL:http://pdg.lbl.gov/).
16. M. Coca [CDF & D0 Collaborations], FERMILAB-CONF-03-
238-EPresentedatFlavorPhysicsandCPViolation(FPCP2003),
5 Conclusions Paris,France,3-6Jun2003
17. J. Fernandez [DELPHI Collaboration], DELPHI 2003-045-
CONF-665,contributedpaperno.320
The developmentsin the MSSM Higgs searches at LEP after
18. P.Achardetal.[L3Collaboration],Phys.Lett.B545(2002)30
theendofLEPdatatakinginNovember2000exhibitfourim-
19. M.Boonekamp,FlavourandModelIndependentHiggsSearches,
portantlessons. First, also the increased set of CPC and CPV
theseproceedings
benchmarkscenariosdonotcoverthefullrangeofpossibleex-
20. A. Heister et al. [ALEPH Collaboration], Phys. Lett. B 526
perimentalphenomenain theMSSM Higgssector.Therefore, (2002)191.
secondly,alargevarietyofindividualsearchesisnecessaryto