The LEP collaborations ALEPH, DELPHI, L3 and OPAL have searched for the
neutral Higgs bosons which are predicted within the framework of the Minimal
Supersymmetric Standard Model (MSSM). The data of the four collaborations are
statistically combined and show no signicant excess of events which would
indicate the production of Higgs bosons. The search results are thus used to
set upper bounds on the cross sections of various Higgs-like event topologies
and limits on MSSM benchmark models, including CP-conserving and CP-violating
scenarios. Here, the limits on the model parameters of the CP-violating
benchmark scenario CPX and derivates of this scenario are shown.Comment: 5 pages, 4 figures, contribution to the proceedings of the
  International Europhysics Conference on High Energy Physics, Lisbon, 200

/SLAC

Bechtle, Philip

English

arXiv

The LEP collaborations ALEPH, DELPHI, L3 and OPAL have searched for the neutral Higgs bosons which are predicted within the framework of the Minimal Supersymmetric Standard Model (MSSM). The data of the four collaborations are statistically combined and show no signicant excess of events which would indicate the production of Higgs bosons. The search results are thus used to set upper bounds on the cross sections of various Higgs-like event topologies and limits on MSSM benchmark models, including CP-conserving and CP-violating scenarios. Here, the limits on the model parameters of the CP-violating benchmark scenario CPX and derivates of this scenario are shown.The LEP collaborations ALEPH, DELPHI, L3 and OPAL have searched for the neutral Higgs bosons which are predicted within the framework of the Minimal Supersymmetric Standard Model (MSSM). The data of the four collaborations are statistically combined and show no signicant excess of events which would indicate the production of Higgs bosons. The search results are thus used to set upper bounds on the cross sections of various Higgs-like event topologies and limits on MSSM benchmark models, including CP-conserving and CP-violating scenarios. Here, the limits on the model parameters of the CP-violating benchmark scenario CPX and derivates of this scenario are shown

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Search for CP Violating neutral Higgs bosons in the MSSM at LEP

Philip Bechtle

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Search for a CP Violating neutral Higgs boson in MSSM at LEP

The LEP collaborations ALEPH, DELPHI, L3 and OPAL have searched for the neutral Higgs bosons which are predicted within the framework of the Minimal Supersymmetric Standard Model (MSSM). The data of the four collaborations are statistically combined and show no significant excess of events which would indicate the production of Higgs bosons. The search results are thus used to set upper bounds on the cross sections of various Higgs-like event topologies and limits on MSSM benchmark models, including CP-conserving and CP-violating scenarios. Here, the limits on the model parameters of the CP-violating benchmark scenario CPX and derivates of this scenario are shown

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Work supported in part by Department of Energy contract DE-AC02-76SF00515Search for CP Violating neutral Higgs bosons in theMSSM at LEPPhilip Bechtle∗†Stanford Linear Accelerator Center, 2575 Sand Hill Road, Menlo Park, CA 94025, USAE-mail: bechtle@slac.stanford.eduThe LEP collaborations ALEPH, DELPHI, L3 and OPAL have searched for the neutral Higgsbosons which are predicted within the framework of the Minimal Supersymmetric StandardModel (MSSM). The data of the four collaborations are statistically combined and show no sig-nicant excess of events which would indicate the productionof Higgs bosons. The search resultsare thus used to set upper bounds on the cross sections of varius Higgs-like event topologies andlimits on MSSM benchmark models, including CP-conserving ad CP-violating scenarios. Here,the limits on the model parameters of the CP-violating benchmark scenario CPX and derivates ofthis scenario are shown.International Europhysics Conference on High Energy PhysicsJuly 21st - 27th 2005Lisboa, Portugal∗Speaker.†For the LEP collaborationshep-ex/0602046SLAC-PUB-117481. IntroductionIt is generally assumed that the Higgs mechanism [1] is responsible for the breaking of elec-troweak symmetry and for the generation of elementary particle masses, both in the Standard Modeland in one of its most popular extensions, Supersymmetry (SUSY) [2]. In the implementationof SUSY with minimal additional particle content, the Minimal Supersymmetric Standard Model(MSSM), two Higgs doublets are needed. Hence, three neutralHiggs bosons and a pair of chargedHiggs bosons can be searched for.Most of the experimental investigations carried out in the past at LEP and elsewhere wereinterpreted in MSSM scenarios which assume CP conservationin the Higgs sector. However, CPviolation in the Higgs sector cannot be a priori excluded [3]. Scenarios with CP violation aretheoretically appealing since they provide one of the ingredients needed to explain the observedcosmic matter-antimatter asymmetry. In the MSSM, however,substantial CP-violating effects canbe induced by radiative corrections, especially from thirdgeneration scalar-quarks. In the CP-violating scenario the three neutral Higgs mass eigenstates, H1, H2 and H3, are mixtures of CP-even and CP-odd fields. The Higgs boson production and decay properties may therefore be widelydifferent and, consequently, the experimental exclusionspublished so far for the CP-conservingMSSM scenario may be invalidated by CP-violating effects.In this paper, the results from the combination of the Higgs bo on searches of the four LEPcollaborations [4] at√s = 91− 209GeV in model-independent cross-section limits on variousMSSM-Higgs-like topologies and in exclusion of CP-violating MSSM benchmark scenarios arepresented.2. Higgs Boson Searches at LEPIn the CP-conserving MSSM, the two dominant production mechanisms Higgsstrahlung(e+e−→hZ, σhZ ∝ sin2(β − α )) and pair production (e+e−→hA, σhA ∝ cos2(β −α )) are com-plementary and ensure the coverage of the whole kinematically accessible plane of Higgs bosonmasses, because for large cos2(β −α ) the two Higgs bosons h (CP-even) and A are close to eachother in mass.In the CP-violating MSSM, the experimental coverage of the mass plane is lost, since first allthree Higgs bosons can be produced in Higgsstrahlung (and hence the direct complementary of twomodes is lost), and second, because there can be large mass differences betweenmH1 andmH2 overthe whole parameter space. Additionally, the cascade decayH2→H1H1 is dominant in large areasof the parameter space. Hence, the coverage of non-diagonalpair production mechanisms and thecoverage of cascade decays is crucial for the experimental access to the CP-violating models. Thisis shown in Fig. 1. In (a), the 95 % confidence level (CL) exclusion limits onσ ×BR in the processe+e−→H2Z→H1H1Z→bb̄bb̄Z relative to the nominal SM cross-section is shown. FormH2 up to105 GeV and allmH1, models which predict aσ ×BR value of more than 40 % of the SM cross-section can be excluded. In (b), the coverage for the processe+e−→H2H1→H1H1H1→bb̄bb̄bb̄ isshown, with limits relative to the nominal pair-productioncross-section with cos2(β −α ) = 1.0 20 40 60 80 100 12000.20.40.60.811.20102030405060mH2 (GeV/c2)mH1 (GeV/c2 )LEPexpected S95 limits onH2Z → H1H1Z→ bb bb Z (a)0 20 40 60 80 100 120 140 16000.20.40.60.811.201020304050607080mH2 (GeV/c2)mH1 (GeV/c2 )LEPexpected S95 limits onH2H1 → H1H1H1→ bb bb bb (b)Figure 1: Model independent limits onσ ×BR relative to the nominal 2HDM cross-sections forsin2(β −α ) = 1 in (a) andcos2(β −α ) = 1 in (b).00.010.020.030.040.050.060.070.080.090.12 4 6 8 10 12 14tanβσ (pb-1 ) H1H2→bb bbH1H2→H1H1H1→6bH1Z→2b ZH2Z→H1H1Z→4b Z√s–=202 GeVFigure 2: Model predictions forσ ×BR values of dominant Higgs boson production mechanisms in theCPX scenario for30GeV< mH1 < 40GeV.3. MSSM Models with Additional CP ViolationThe benchmark model used in the combination of the LEP data isthe CPX scenario [5]. Itis characterized by large mixing between CP-even and CP-oddstates in the mass eigenstates. TheCP-even/CP-odd mixingM 2SP is characterized byM2SP ∝m4tv2ℑ (At,bµ)M2SUSY. (3.1)Therefore, large values of the top quark massmt , the Higgsino mixing parameterµ and the imagi-nary part of the trilinear couplings in the stop and sbottom sectorAt,b, coupled with a not too largescale of the squark massesMSUSY is chosen. Effects of the variation of these parameters are stud-ied. Detailed calculations on the two-loop order [6] or on the one-loop renormalization-improvedorder [5] are used to calculate the model predictions.The resulting predictions for selected processes in the CPXscenario are shown in Fig. 2 forlightest Higgs masses of 30GeV< mH1 < 40GeV. For low tanβ = v2/v1, the SM-like production1100 20 40 60 80 100 120 140mH1 (GeV/c2)tanβExcludedby LEPTheoreticallyinaccessible(c)1100 20 40 60 80 100 120 140mH1 (GeV/c2)tanβExcludedby LEPTheoreticallyinaccessible(b)1100 20 40 60 80 100 120 140mH1 (GeV/c2)tanβExcludedby LEPTheoreticallyinaccessible(a)m  = 169.3 GeVt tm  = 179.3 GeVtm  = 174.3 GeV Figure 3: Exclusion areas in the(tanβ ,mH1) plane in the CPX scenario formt = 169.3, 174.3, 179.3GeV.Theoretically inaccessible regions are shown in yellow, experimentally excluded areas in light green (CL =95%) and dark green (CL = 99.7%).mechanism H1Z→(bb̄,τ +τ−)Z is dominant and has a large production cross-section. For interme-diate tanβ , however, all production cross-sections are reduced, since the kinematically accessibleH1 decouples from the Z, hence no Higgsstrahlung occurs, and sincemH2 ≈ 110GeV is close to thekinematic limit. Additionally, the experimentally more difficult cascade decay H2→H1H1 becomesdominant. For large tanβ the production cross-sections increase and finally H1H2→bb̄bb̄ becomesthe dominant mode.4. Interpretation of the LEP Data in the CPV MSSMThe statistical combination of all Higgs boson searches from all four LEP collaborations usesthe modified frequentist approach as implemented in [7]. Theresult of this combination shows nostatistically significant excesses of the data over the expected background. Hence, limits on theparameter space are computed [8]. These limits are shown in Fig. 3 and 4 for the CPX scenario. Ineach case, the full set of MSSM parameters is fixed to the values chosen for the scenario (as givenin [5, 8]), apart from tanβ and the charged Higgs boson massmH±, which are scanned. The resultis then shown in the tanβ ,mH1 projection.In Fig. 3 the results in the CPX scenario are shown for different top quark massesmt . Thepresent experimental value ofmt = 172.7GeV [9] lies between the values used for Fig. 3 (a) and(b). In all cases, the reduction of production cross-sections for intermediate tanβ described inSection 3 causes unexcluded regions for low values of the lightest Higgs boson massmH1. Noabsolute limit onmH1 can be set. For larger values ofmt this effect increases, sincemt stronglyinfluences the mixing of the mass eigenstates (see (3.1)) andincreases the mass splitting betweenmH1 andmH2, hence further decreasing the production cross-sections for intermediate tanβ .The effect of unexcluded regions in the parameter space for low mH1 is clearly connected tothe CP-violating imaginary phase of the trilinear couplings At,b. This is shown in Fig. 4. Only forlarge phases (and hence large mixings in (3.1)) the effect oflarge inaccessible regions is strong.5. ConclusionsThe results from neutral Higgs bosons searches in the context of the MSSM described in this1100 20 40 60 80 100 120 140mH1 (GeV/c2)tanβExcludedby LEPTheoreticallyinaccessible(c)1100 20 40 60 80 100 120 140mH1 (GeV/c2)tanβExcludedby LEPTheoreticallyinaccessible(d)1100 20 40 60 80 100 120 140mH1 (GeV/c2)tanβExcludedby LEPTheoreticallyinaccessible(b)arg(A)=30 arg(A)=60arg(A)=90 Figure 4: Exclusion areas in the(tanβ ,mH1) plane for different values of the phaseargA of the trilinearcoupling parameters in the stop and sbottom sector.paper are based on data collected by the four LEP collaborations, ALEPH, DELPHI, L3 and OPALat√s = 91− 209GeV. No significant excess of data over the expected backgrounds has beenfound. From these results, upper bounds are derived for the cross sections of a number of Higgsevent topologies. These upper bounds cover a wide range of Higgs boson masses and are typicallymuch lower than the largest cross sections predicted withinthe MSSM framework. In the CP-violating benchmark scenario CPX and the variants which have been studied, the combined LEPdata show large unexcluded domains, down to the smallest masses; hence, no absolute limits canbe set for the Higgs boson masses. On the other hand, tanβ c be restricted to values larger than2.9 for mt = 174.3GeV. While the excluded mass domains vary considerably with mt , the boundin tanβ is barely sensitive to the precise choice of the top quark mass.References[1] P. W. Higgs, Phys. Rev. Lett.13(1964) 508; F. Englert and R. Brout, Phys. Rev. Lett.13(1964) 321;G. S. Guralnik, C. R. Hagen, and T. W. B. Kibble, Phys. Rev. Lett. 13(1964) 585.[2] J. Wess and B. Zumino, Nucl. Phys.B70(1974) 39.[3] A. Pilaftsis and C. E. M. Wagner, Nucl. Phys.B553(1999) 3.[4] ALEPH Collab., A. Heisteret al., Phys. Lett.B526 (2002) 191; DELPHI Collab., J. Abdallah et al.,Eur. Phys. J.C32 (2004) 145; L3 Collab., P. Achard et al., Phys. Lett.B545 (2002) 30; OPAL Collab.,G. Abbiendiet al., Eur. Phys. J.C37 (2004) 49.[5] M. Carena, J. R. Ellis, A. Pilaftsis and C. E. Wagner, Phys. Lett. B 495 (2000) 155.[6] S. Heinemeyer, W. Hollik, and G. Weiglein, Comput. Phys.Commun.124(2000) 76;M. Frank, S. Heinemeyer, W. Hollik, and G. Weiglein, arXiv:hep-ph/0212037 (2002).[7] T. Junk, Nucl. Instrum. Meth.A434(1999) 435; P. Bock, arXiv:hep-ex/0405072.[8] ALEPH, DELPHI, L3 and OPAL Collaborations, The LEP Working Group for Higgs BosonSearches,“Search for Neutral MSSM Higgs Bosons at LEP”, CERN-PH-EP/2006-001,arXiv:hep-ex/0602042 (2006).[9] CDF and D0 Collaborations, arXiv:hep-ex/0507091 (2005).

Search for CP Violating neutral Higgs bosons in the MSSM at LEP

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