Two searches for the production of Higgs bosons decaying into tau and mu leptons, using data collected with the DZero detector at the Fermilab Tevatron p-bar(p)collider, are presented. A search for the pair production of doubly charged Higgs bosons in the processq-bar(q) to H {++}H {--}, where H {++} decays to tau-tau, mu-mu or tau-mu lepton pairs, with an integrated luminosity of up to L= 7.0 fb {-1}, is presented. No significant excess of data over the expected SM background is observed and the results are used to set 95\% C.L. limits on the pair production cross section of doubly charged Higgs bosons in the range 90
Two searches for the production of Higgs bosons decaying into [tau] and [mu] leptons, using data collected with the DØ detector at the Fermilab Tevatron p$\bar{p}$ collider, are presented. A search for the pair production of doubly charged Higgs bosons in the process q$\bar{q}$ 2!H++H--, where H ±± decays to [tau][tau], [mu][mu] or [tau][mu] lepton pairs, with an integrated luminosity of up to L = 7:0 fb-1, is presented. No signi cant excess of data over the expected SM background is observed and the results are used to set 95% C.L. limits on the pair production cross section of doubly charged Higgs bosons in the range 90
The gauge symmetry is the heart of our understanding of the electroweak interaction and describes all the current experimental results. However, the intrinsic incompatibility between the gauge invariance and the mass of particles leads to the introduction of a new particle, the Higgs boson, for which we have no experimental evidence as of today. This thesis describes the Higgs boson search in the [mu] + [tau] final state in 7.3 fb-1 of pp collisions at √s = 1.96 TeV collected by the DØ detector at the Tevatron. This analysis completes the golden channels (dimuons, electron-muon, dielectrons) exploiting the decay chain H → WW → lvlv , which is the main Higgs boson decay mode in the mass window accessible to the Tevatron. Since the final state includes a lepton, work was done to improve their identification among jets. An increase of 15% was achieved thanks to the the following : changing tuning parameters for the identification neural network, use of the kinematical dependence of the algorithm performances, incorporation of the [tau] lepton life time information and full study of the additionnal information coming from the central preshower measurements. Then, since the dominant background of the [mu] + [tau] Higgs boson search is W+jets (where one jet fakes a [tau] ), a method was developed to obtain good modeling of this background, not provided by the default simulation. This method is based, among other things, on the charge correlation between the muon and the [tau] candidate which allows for calibration of this background in the data excluding the signal region. Finally, all the kinematic and/or topological differences between the signal and the background were exploited to optimize this search, reaching an (observed) expected sensitivity of 7.8 (6.6) times the Standard Model for mH = 165 GeV=c2. In addition, this result was also interpreted in a fourth fermion generation scenario. For the first time, this analysis is included in the D and Tevatron combinations, both presented at Moriond EW and EPS 2011.
We present a search for the standard model Higgs boson in final states with an electron or muon and a hadronically decaying tau lepton in association with two or more jets using 9.7 fb-1 of Run II Fermilab Tevatron Collider data collected with the D0 detector. The analysis is sensitive to Higgs boson production via gluon fusion, associated vector boson production, and vector boson fusion, followed by the Higgs boson decay to tau lepton pairs or to W boson pairs. The ratios of 95% C.L. upper limits on the cross section times branching ratio to those predicted by the standard model are obtained for orthogonal subsamples that are enriched in either H → [tau] [tau] decays or H → WW decays, and for the combination of these subsample limits. The observed and expected limit ratios for the combined subsamples at a Higgs boson mass of 125 GeV are 11.3 and 9.0 respectively.
We search for the pair production of doubly charged Higgs particles followed by the lepton-flavor violating decay of each Higgs into electron-and-tau and muon-and-tau pairs using 350 pb{sup -1} of data collected by the CDF II experiment at the Fermilab Tevatron. Separate searches investigate cases where three or four final state leptons are detected, and the limits for each exclusive decay mode reflect the combined results of both searches. Assuming the H{sup {+-}{+-}}{sub L} decays exclusively into like sign electron-and-tau pairs, we set a lower limit on its mass of 114 GeV/c2 at the 95 % confidence level. In the case of exclusive muon-and-tau decays, we set a lower mass limit of 112 GeV/c2 also at the 95% confidence level.
The cross-section times branching ratio of the Higgs boson decaying to [tau]+[tau]- final state in the Standard Model (SM) is too small to play any role in the SM Higgs boson searches. This, however, is different in the Minimal Supersymmetric Standard Model (MSSM), which predicts two Higgs doublets leading to five Higgs bosons: a pair of charged Higgs boson (H±); two neutral CP-even Higgs bosons (h,H) and a CP-odd Higgs boson (A). A search for the production of neutral Higgs bosons decaying into [tau]+[tau]- final states in p{bar p} collisions at a centre-of-mass energy of √s = 1.96 TeV is presented in this thesis. One of the two [tau] leptons is required to decay into a muon while the other decays hadronically. The integrated luminosity is L = 1.0-5.36 fb -1, collected by the D0 experiment at the Fermilab Tevatron Collider from 2002 to 2009 in the Run II.
A search for the decay to a pair of new particles of either the 125 GeV Higgs boson (h) or a second charge parity (CP)-even Higgs boson (H) is presented. The data set corresponds to an integrated luminosity of 20.3 fb-1 of pp collisions at [arrow]" = 8 TeV recorded by the ATLAS experiment at the LHC in 2012. The search was done in the context of the next-to-minimal supersymmetric standard model, in which the new particles are the lightest neutral pseudoscalar Higgs bosons (a). One of the two a bosons is required to decay to two muons while the other is required to decay to two [tau] leptons. No significant excess is observed above the expected backgrounds in the dimuon invariant mass range from 3.7 to 50 GeV. The upper limits are placed on the production of h 2!aa relative to the standard model gg 2!h production, assuming no coupling of the a boson to quarks. The most stringent limit is placed at 3.5% for ma = 3.75 GeV. Upper limits are also placed on the production cross section of H 2!aa from 2.33 to 0.72 pb, for fixed ma = 5 GeV with mH ranging from 100 to 500 GeV.
The authors search for pair production of doubly charged Higgs particles (H{sup ±±}) followed by decays into electron-tau (e[tau]) and muon-tau ([mu][tau]) pairs using a data set corresponding to an integrated luminosity of 350 pb−1 collected from {bar p}p collisions at √s = 1.96 TeV by the CDF II experiment. They search separately for cases where three or four final-state leptons are detected, and then combine the results into limits for each exclusive flavor decay mode of the H{sup ±±}. Assuming 100% branching ratios of the H{sup {+-}{+-}} to left-handed e[tau] ([mu][tau]) pairs, they set an H{sup {+-}{+-}} lower mass limit of 114 (112) GeV/c2 at the 95% confidence level (C.L.).
In this dissertation, I present a search for non-standard decays of a Standard Model-like Higgs boson to pairs of light bosons, as predicted in models with extended Higgs sectors. In two Higgs doublet models, including the next-to-minimal supersymmetric standard model, the Higgs boson can decay into a pair of light pseudoscalars a. In this search, the gluon fusion, W and Z associated Higgs, and vector boson fusion production channels for the Higgs are all considered, and the decay H->aa with a->[tau][tau] is reconstructed from the tau decay products. The final state is characterized by one isolated high p[subscript]T muon plus at least one highly boosted pair of taus, of which one of the taus is required to decay to a muon.Using 19.7 fb−1 of 8 TeV center of mass pp collision data recorded by the Compact Muon Solenoid experiment at the Large Hadron Collider, a counting experiment is performed in a region of high di-tau invariant mass. We have found no excess of events above the Standard Model backgrounds, and the observed data is used to set upper limits on the branching ratio Br(H->aa)Br2(a->[tau][tau]). These results are equally applicable to decays of the SM-like Higgs boson to a pair of light scalars h.
