The CMS potential for the Higgs boson discovery is discussed in the framework of the Standard Model (SM) and its Minimal Supersymmetric extension (MSSM)

Daskalakis, G

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Available on CMS information server CMS CR 2006/021CMS Conference Report10 April 2006Searches for the Higgs Boson in CMSGeorgios Daskalakis AbstractThe CMS potential for the Higgs boson discovery is discussed in the framework of the Standard Model(SM) and its Minimal Supersymmetric extension (MSSM).Imperial College, London, UK1 IntroductionThe Large Hadron Collider (LHC) is designed to collide two counter rotating beams of protons or heavy ions.Proton-proton collisions are foreseen at an energy of 7 TeV per beam with a planned start-up in 2007. The CompactMuon Solenoid (CMS) is one of the two general purpose detectors that will be installed on the collider. One ofits main challenges is the discovery of the Higgs boson. In this report, the CMS potential for the Higgs bosondiscovery is discussed in the framework of the Standard Model (SM) and its Minimal Supersymmetric extension(MSSM). More details can be found in [1].2 Discovery Potential for the Standard Model Higgs BosonThe main production mechanism for the Higgs boson at 14 TeV is the gluon-gluon fusion and the WW/ZZ fusion.For low Higgs boson masses (below 130 GeV/c  ), the most promising channel for discovery is the H 	 . Itssignature is quite clean, mainly based on a well calibrated electromagnetic calorimeter. The H  channel isthe dominant decay but due to the huge QCD background is not useful if the Higgs boson is produced via thegluon-gluon fusion. This decay mode is interesting when the Higgs boson is produced in association with (   ). In that case, the background can be effectively reduced via b-jet tagging. Another interestingdiscovery channel, at the same mass range (around 130 GeV/c  ), is the ﬀﬂﬁﬃ ﬁ"! . It can be searchedfor in the lepton plus ﬁ -jet nal state. The critical factor here is the reconstructed mass resolution due to thedominant QCD and electroweak Zjj background with #$ﬂﬁ%ﬃ&ﬁ"! and the central jet veto.If the Higgs boson has a mass between 130 GeV/c  and 2M ' , the preferred search channels are the (#)#+*and ,.-/-0* , which are abundantly produced and give quite clean signatures especially when the nal stateinvolves muons and/or electrons. For heavier Higgs bosons (M 13254768' ) the golden discovery channels arethe 9#)#:.;=<7;7>&4?<@4?> which will allow a very fast discovery. For very high Higgs boson masses (above500 GeV/c  ) the cross section for the qq  qqH production process is large and the decay channels A#)#:BCBEDDBCB FCFwere found to yield the highest sensitivity even though the large backgrounds and the large Higgs bosonwidth make the discovery much more difcult compared to the lower Higgs boson masses.The statistical signicance expected for 30 fb !HG of integrated luminosity can be seen in Figure 1 when all channelsare combined.)2(GeV/cHmStatistical Significance10100 200 300 400 500 80052040-1 at 30 fbσ5-1 at 10 fbσ5-1 at 2 fbσ5jjlνl→WW→qqH, Hlνlνll→ZZ→qqH, H, NLOlνlνll→WW*/WW→H, NLO-l+l-l+ l→ZZ*/ZZ→H-τ+τ,γγ→qqH, H inclusive, NLOγγ→Hbb→H,WH,HttTotal significance-1CMS, 30 fbFigure 1: Expected sensitivity for the Standard Model Higgs boson observation as a function of its mass with 30fb !)G integrated luminosity.3 Discovery Potential for the MSSM Higgs BosonsIn the MSSM there are ve Higgs bosons: two CP-even Higgs boson mass eigenstates h,H, a charged Higgsboson pair H I and a CP-odd neutral pseudoscalar A. At tree-level the Higgs boson sector is determined by twoparameters. A common choice is the ratio of vacuum expectation values of the two doublets J?KL =u/uGand themass of the pseudoscalar Higgs boson M M . Radiative corrections modify the predictions of the model signicantly:the mass of the lightest higgs boson at tree level is predicted to be below M ' which is already excluded by LEP [2]2but after corrections its mass may rise up to 135 GeV/c  . Several MSSM Higgs boson scenarios have been proposeddepending on different choices of the soft SUSY breaking parameters. For the results presented in this report theSUSY parameters are xed to the values used in the LEP studies [3].In the large M M limit (M MON M ' ), the so-called decoupling region, the heavy Higgs bosons (H, A, H I ) are almostdegenerate in mass. The lighter Higgs boson h is SM-like, so its production cross sections and decay partial widthsare very close to those of the SM Higgs boson. The discovery potential for the lighter scalar Higgs boson h can beseen in Figure 2 for 30 fb !HG of integrated luminosity.)2(GeV/cAm100 150 200 250 300 350 400 450 500βtan1025203040Excluded by LEP-1CMS, 30 fb scenariomaxhmNLO cross sections:,γγ →inclusive h -l+l-l+ l→ ZZ* →h -1, 60 fbb b→h, h tt-1, 60 fbb b→h, h ttγγ →h -1, 60 fbγγ →qqh, h -l+l-l+ l→ ZZ* →h  jetτ l + → -τ+τ →qqh, h 2 = 110 GeV/chm2 = 120 GeV/chm2 = 125 GeV/chm2 = 127 GeV/chmFigure 2: The 5 P discovery contours in the (M M , J7KL ) plane for the light scalar MSSM Higgs boson with 30fb !)G integrated luminosity in the M Q -max scenario.At large J7KL the couplings of the heavy neutral Higgs bosons (H,A) to the electroweak gauge bosons are stronglysuppressed while the couplings to down-type fermions are enhanced allowing a search for H,A in the H,A >)ﬃ > ! and H,A ﬁRﬃ&ﬁ"! decay channels in the associated production gg TSS H/A. In this production process, theassociated b-jets can be used to suppress the Z, U* and QCD multi-jet backgrounds with b-tagging methods. Totake advantage of the hadronic ﬁ decays in the lepton-plus- ﬁ -jet and two- ﬁ -jet nal states from the H/A VﬁHﬃ ﬁ"!decay, an efcient ﬁ -jet (coming from ﬁ hadronic decays) identication method is required to suppress furtherQCD multi-jet and W-plus-jet backgrounds. The Higgs boson mass can be reconstructed also in the H/A TﬁHﬃ ﬁ"!channels from the missing E W and the visible ﬁ momenta exploiting the neutrino collinearity with the parent ﬁdirection. The discovery potential for the H/A Higgs bosons can be seen in Figure 3 for 30 fb !)G of integratedluminosity.)2(GeV/cAm100 200 300 400 500 600 700 800βtan1020304050-1CMS, 30 fb2 = 200 GeV/c2, M2 = 300 GeV/cµ2 = 1 TeV/cSUSY, M2 TeV/c6 = tA-1, 60 fbµµ →H,A  2 leptons+X→ ττ →H,A  l + jet→ ττ →qqH, H Excluded by LEP2 = -200 GeV/cµ 2 = 500 GeV/cµ-1 2 jets + X, 60 fb→ ττ →H,A  lepton + jet + X→ ττ →H,A Figure 3: The 5 P discovery contours in the (M M , J7KL ) plane for the heavy neutral MSSM Higgs bosons H andA with 30 fb !HG integrated luminosity in the M Q -max scenario.3The heavy charged Higgs bosons search proceeds via H IXYﬁD[Z\]S^_a` decay channels, in the associated pro-duction process gg bS\cdI . The W+jet and QCD multi-jet backgrounds can be suppressed with b/ ﬁ -tagging andreconstruction of the associated top quark. The H IeﬂﬁD?Zdecay channel is particularly interesting, when hadronicdecays are required. The light charged Higgs bosons (M1gf0hM iEjlk ) can be searched for in the H Imnﬁ D[Z de-cay channel in the  production, by suppressing the backgrounds with an isolated lepton from the accompanyingW decay. The discovery potential for the H I Higgs bosons can be seen in Figure 4 for 30 fb !HG of integratedluminosity.)2(GeV/cAm100 150 200 250 300 350 400 450 500 550βtan1020304050-1CMS, 30 fb2 = 200 GeV/c2, M2 = -200 GeV/cµ2 = 1 TeV/cSUSY, M2 = 2450 GeV/ctAνντ → ±, H±tHνντ → ± H→’ qqνντ → ±tt, HExcluded by LEPFigure 4: The 5Pdiscovery contours in the (MM,J7KL) plane for the charged Higgs bosons with 30 fb!)Gintegrated luminosity in the MQ-max scenario.4 ConclusionsThe present understanding of the CMS potential for the SM and MSSM Higgs boson discovery has been reviewed.Detailed studies are on going including systematic uncertainties and more sophisticated analysis methods.References[1] S. Abdullin et al., CMS Note 2003/033.[2] LEP Higgs Working Group, Phys. Lett. B565, 61 (2003).[3] LEP Higgs Working Group, LHWG-Note2005-01.4

Searches for the Higgs Boson in CMS

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