Hunting for the Intermediate-Mass Higgs Boson in a Hadron Collider

Abstract

We examine the feasibility of identifying in a hadron machine the standard, neutral Higgs boson, produced in association with a W, when the mass of the Higgs is between approximately 100 GeV and 2m w -The production cross section is calculated with quasirealistic cuts imposed under the assumption that the Higgs decays into 11 Possible backgrounds arising from the continuum production of / U ib, or lb accompanied by a Ware computed as well.PACS numbers: 14.80.Gt, 13.85.QkThe search for the standard model Higgs boson is one of the most important efforts of present and future accelerators. A Higgs boson with mass m n < 100 GeV/c 2 will be identifiable at SLC, LEP I, or LEP II through production in association with a virtual or onshell Z° or in the radiative decays of toponium. 1 (The 100-GeV/c 2 mass limit is determined solely by the center-of-mass energy that will be available at these machines.) Heavier Higgs bosons will be produced at detectable rates first at planned hadron facilities such as the superconducting super collider (SSC). 1 Unfortunately, direct production in hadron collisions of the Higgs (via gluon 2 or W pair 3 fusion) followed by its decay is identifiable only when m H > 2m w \ in this case its primary decay modes are into W + W~ and Z°Z° intermediate vector boson pairs. Continuum W+ W~ and Z°Z° pair production is sufficiently small that a modest pair resolution will suppress this background adequately. 4 Below m H = 2m w but above m H = 2m t the Higgs boson decays almost exclusively into 11 pairs. In this intermediate mass range the QCD continuum prqduction cross section is so large that any feasible 11-pair mass resolution is not sufficient to make possible the identification of the Higgs. For ra, = 40 GeV/c 2 , one findswhere AM 2~0 .1/«H. Mis the 11 pair mass. Thus, it is of considerable importance to find a production mode for a Higgs boson with mass in the range 100 GeV/c 2 < m H < 2m w for which continuum backgrounds are manageable and event rates are adequate. In this Letter we show that hadronic production of an intermediate-mass Higgs in association with a trigger W + or W , followed by Higgs decay to a 11 pair, 5 pp~* H°W ± X,(1) L,7provides a potentially viable detection mode for this otherwise problematic mass range. We demonstrate that the background reactionsand pp-+ (W+7b)X or (W-tb)X,where the b (b) in the latter reaction is misidentified as a t (t), are sufficiently small that 10% to 20% resolution in M, 2 yand 1/100 b/t)et discrimination will provide a clear Higgs signal. We have not considered in detail the production of H° in association with a Z° be-_ cause the irreducible continuum background of Z° 11 arising from gluon-gluon scattering will certainly be overwhelming. The basic cross section for reaction (1), including appropriate cuts, is of order 1 pb, equivalent to 10 4 events for a standard L = 10 40 /cm 2 y. Triggering on the Wv'm leptonic decay modes into e, /x, or r yields over 10 3 events, with the assumption of leptonic detection efficiencies over 50%. If any of th...

Semileptonic decays of the standard Higgs boson

“…For the tt background it is at least plausible that a veto on extra hard jets, perhaps combined with a b-jet veto, will give the required rejection without sacrificing much of the signal [5,12]. For the diboson and W + 2j backgrounds, the most-cited strategy is to restrict the analysis to Higgs production via vector boson fusion [8][9][10]16]; the requirement of forward jet tagging then gives a factor of ∼ 100 reduction in these backgrounds. However the reduction in the Higgs signal, versus inclusive Higgs production, is also severe: a factor of ∼ 10 at the Tevatron, and also at the LHC for M h 500 GeV.…”

“…This process was first discussed as a potential Higgs discovery channel for the SSC [8][9][10][11], emphasizing the case of a very heavy Higgs boson, where the golden mode starts to become rate-limited. Like the golden mode, the semileptonic h 0 → W W modes have the advantage of being fully-reconstructible: when the leptonic W is close to on shell, the W mass constraint determines the longitudinal momentum of the neutrino, up to a two-fold ambiguity [11].…”

The anatomy of electroweak symmetry breaking

“…The separation of the signal and backgrounds was optimized using neutral network techniques which lead to an appreciable increase of the signal significance [412,413]. The W H → ℓνbb channel has been also discussed for the LHC [315,318] but due to the much larger QCD background, it is not considered alone as a clear discovery channel [228,235,[414][415][416]. The significance of the signal is at the level of ∼ 3σ for M H = 120 GeV with L = 30 fb −1 [415] when the W bb and tt backgrounds have been sufficiently suppressed.…”

“…The various detection channels at the LHC [315][316][317][318][319] and at the Tevatron [320][321][322][323] and [319] will be discussed in §3.7.…”

Old physics, new physics and colliders

“…46 The rates for Higgs production via these mechanisms are smaller than those discussed above and will be useful only if the additional particles can be used as a tag in order to improve the signal-to-noise ratio. 47 The signals for Higgs bosons at the SSC are discussed extensively elsewhere. 48 • 49 At the Tevatron the rates are reasonable only for Higgs masses less than 150 Ge V or so.…”