The expected sensitivity of the LHC experiments to the discovery of the Higgs
boson and the measurement of its properties is presented in the context of both
the standard model and the its minimal supersymmetric extension. Prospects for
a luminosity-upgraded ``Super-LHC'' are also presented.Comment: Invited talk at 2005 International Linear Collider Physics and
  Detector Workshop and Second ILC Accelerator Workshop, Snowmass,
  CO(Snowmass05) 3 pages, 0 figures. PSN ALCPG060

Cranmer, Kyle S.

English

arXiv

The expected sensitivity of the LHC experiments to the discovery of the Higgs boson and the measurement of its properties is presented in the context of both the standard model and the its minimal supersymmetric extension. Prospects for a luminosity-upgraded ''Super-LHC'' are also presented. If it exists, the LHC should discover standard model Higgs boson, measure its mass accurately, and make various measurements of its couplings, spin and CP properties. In the context of the CP-conserving MSSM, the LHC should be able to discover one or more Higgs bosons over the entire m{sub A}-tan {beta} plane, with two or more observable in many cases. The large number of channels available insure a robust discovery and offer many opportunities for additional measurements. Observation of H {yields} {mu}{mu}, measurement of the tri-linear Higgs self-coupling, and various search channels are statistics-limited, and only possible with a luminosity upgrade. A luminosity upgrade would substantially improve some of the coupling measurements and generally extend the sensitivity in the MSSM Higgs plane. Efforts are ongoing to understand the upgrade of the LHC to the Super-LHC

CRANMER, K.S.

UNT Digital Library

      BNL-75328-2006-CP      Potential for Higgs Physics at the LHC and Super-LHC   Kyle S. Cranmer    Presented at the 2005 International Linear Collider Physics and Detector Workshop and Second ILC Accelerator Workshop (Snowmass 05) Snowmass, CO August 1-25, 2005   August 2005    Physics Department   Brookhaven National Laboratory P.O. Box 5000 Upton, NY 11973-5000 www.bnl.gov   Notice: This manuscript has been authored by employees of Brookhaven Science Associates, LLC under Contract No. DE-AC02-98CH10886 with the U.S. Department of Energy. The publisher by accepting the manuscript for publication acknowledges that the United States Government retains a non-exclusive, paid-up, irrevocable, world-wide license to publish or reproduce the published form of this manuscript, or allow others to do so, for United States Government purposes.   This preprint is intended for publication in a journal or proceedings.  Since changes may be made before publication, it may not be cited or reproduced without the author’s permission.      DISCLAIMER  This report was prepared as an account of work sponsored by an agency of the United States Government.  Neither the United States Government nor any agency thereof, nor any of their employees, nor any of their contractors, subcontractors, or their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or any third party’s use or the results of such use of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise, does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof or its contractors or subcontractors.  The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof.                                     arXiv:hep-ph/0512154 v1   12 Dec 20052005 ALCPG & ILC Workshops - Snowmass, U.S.A.Potential for Higgs Physics at the LHC and Super-LHCK. S. CranmerBNL, Upton, NY 11973, USAThe expected sensitivity of the LHC experiments to the discovery of the Higgs boson and the measurement of itsproperties is presented in the context of both the standard model and the its minimal supersymmetric extension.Prospects for a luminosity-upgraded “Super-LHC” are also presented.1. IntroductionThe Large Hadron Collider (LHC) at CERN and the two multipurpose detectors, Atlas and CMS, have beenbuilt in order to discover the Higgs boson, if it exists, and explore the theoretical landscape beyond the standardmodel [1, 2]. The LHC will collide protons with unprecedented center-of-mass energy (√s = 14 TeV) and luminosity(1034 cm−2s−1); the Atlas and CMS detectors will record these interactions with ∼108 individual electronic readoutsper event. The first collisions are expected in 2007, with a possible luminosity upgrade around 2015.Observation of the Higgs boson is key to confirming the description of electroweak symmetry breaking in thestandard model. The standard model Higgs sector has only one free parameter: the mass of the Higgs boson, mH .Masses below 114.4 GeV/c2 have been directly excluded by LEP Higgs searches at the 95% confidence-level [3].Indirect evidence of the Higgs mass, through electroweak precision measurements, indicate a light Higgs (mH <∼ 185GeV/c2), though the theory remains valid until about 1 TeV/c2 [4].For a variety of reasons, it is reasonable to expect that supersymmetry is manifest in nature. The minimalsupersymmetric extension of the standard model (MSSM) requires an extended Higgs sector with two Higgs doublets,corresponding to five physically observable Higgs boson resonances. The MSSM Higgs sector is typically parametrizedby the ratio of the vacuum expectation values of the two doublets, tan β, and the mass of the neutral, CP-odd Higgsboson, mA. Large radiative corrections extend the upper-bound on the mass of the lightest Higgs from its Born-levelvalue mZ to about 133 GeV/c2. Explicit CP-violation in the MSSM complicates matters slightly [5].At the LHC, production cross-section for the standard model Higgs bosons falls from about 30 pb near the LEPlimit to less than 0.1 pb near mH ≈ 1 TeV. The production is dominated by the gluon-fusion process, followed byweak boson fusion, and associated production with weak bosons and heavy quarks. The decay is dominated by heavylepton pairs (bb̄ and τ+τ−), for masses less than 2mW , and pairs of weak bosons once above threshold [6]. Due tothe enormous rate of QCD processes at the LHC, at least one high-pT lepton or photon or very large missing pTis needed to trigger the event.1 Furthermore, due to the high design luminosity of the LHC, an average of 23 softp-p interactions are expected per bunch crossing – a phenomenon referred to as “pile-up” – which makes the LHCenvironment particularly challenging. This pile-up effect will be even more severe at the Super-LHC.2. LHC Discovery and Measurement PotentialThe Higgs discovery potential was detailed several years ago by both Atlas and CMS assuming a total integratedluminosity of 300 fb−1 per experiment [1, 2]. Both experiments concluded that they should discover the standardmodel Higgs with high significance for masses up to 1 TeV and measure the mass of the Higgs boson to within 1%1The trigger requirement rules out the inclusive observation of H → bb̄, i.e. from the dominant gluon-fusion production process.ALCPG0602across the entire mass range (within 0.1% for mH < 400 GeV/c2). For mH > 200 GeV/c2, non-standard spin andCP properties of the Higgs can be highly excluded with 100 fb−1 [7]. Observation of two or more Higgs bosons wouldrule out a standard model Higgs sector, and such observations are expected for many, though not all, regions of theMSSM parameter space.2After the original assessments by Atlas and CMS, phenomenological studies indicated that weak boson fusionHiggs production with decays to W+W−, τ+τ−, and γγ showed great potential for a discovery of the standardmodel Higgs [8, 9, 10]. Within the context of the CP-conserving MSSM, the complementary couplings to the lightand heavy CP-even neutral Higgs bosons allow the τ+τ− channel to cover the entire mA – tan β plane [10]. Theseweak boson fusion analyses have now been studied by the collaborations and provide for a more robust discoverypotential and improved coupling measurements [11, 12].Prior to the addition of weak boson fusion, the two most powerful analyses for low-mass Higgs came from H → γγand ttH → ttbb̄. Since their initial study, great advances have been made in terms of the Monte Carlo used togenerate the particle-level predictions. More detailed study of the ttH → ttbb̄ channel by Atlas incorporating thesystematic uncertainty on the bb̄ invariant mass spectrum indicate that the channel is not as powerful as originallyanticipated3 and is not sufficient for discovery [14]. This loss of sensitivity is found despite the use of multivariatetechniques.By comparing the rates of different Higgs decays, it is possible to measure various properties of the Higgs and howit couples to fermions and bosons. The interpretation of these measurements is tightly coupled to the theoreticalassumptions one makes. Ratios of partial widths and (with mild theoretical assumptions) absolute couplings cantypically be measured to an accuracy of 10-40% [15]. Some improvements to this result are foreseen by reducing theuncertainty on the rate of gg → Hgg by taking advantage of its characteristic φjj shape [16] and arguing that certaintheoretical uncertainties may largely cancel in ratio [17].3. Higgs Prospects at the Super-LHCWhile the prospects for the LHC are quite encouraging, there are many measurements that are statistics-limited.For example, observation of H → µµ (a non-third-generation fermion coupling) is straight forward experimentally,but limited by the small branching ratio [18, 19]. Similarly, additional luminosity would increase the supersymmetricparameter space in which two or more Higgs bosons are visible. Also of great importance is the measurement of theHiggs self-couplings, which is largely limited by the integrated luminosity.For the reasons stated above, a luminosity upgrade to the LHC is being considered. The so-called “Super-LHC”,or SLHC, would have a design luminosity of 1035 cm−2s−1 and would potentially gather 3000 fb−1 of data [20].While details of such an upgrade remain uncertain, it would most likely start around 2015. Significant studiesare already underway to assess the requisite modifications to the accelerator, detector subsystems, and trigger anddata acquisition infrastructure. Studies of the physics potential of the SLHC by the experimental collaborations aresomewhat limited, but they do show the expected gains in coupling measurements and extended discovery potential inthe mA – tanβ plane [21]. Additionally, it has been shown in phenomenological studies that the tri-linear Higgs self-coupling could be measured to 20-30%, and both experiments are working to confirm this result [22]. Unfortunately,small variations in the tri-linear coupling will swamp variations in the quartic-coupling, leaving little hope to measurethe quartic coupling at any foreseeable hadron collider [23].The existing studies show an enticing physics program, but with attention turning to the start-up operations ofthe LHC, additional studies are not likely to be forthcoming. After some experience with pile-up at the LHC designluminosity and potential observations of new physics, the LHC collaborations will undoubtedly embark on morestudies germane to the SLHC physics potential.2CP-violating scenarios have regions of their parameter space in which the current set of search channels are not sensitive.3It is not clear if the Atlas result is in agreement with the one from cms [13].ALCPG06024. ConclusionIf it exists, the LHC should discover standard model Higgs boson, measure its mass accurately, and make variousmeasurements of its couplings, spin and CP properties. In the context of the CP-conserving MSSM, the LHC shouldbe able to discover one or more Higgs bosons over the entire mA – tan β plane, with two or more observable in manycases. The large number of channels available insure a robust discovery and offer many opportunities for additionalmeasurements.Observation of H → µµ, measurement of the tri-linear Higgs self-coupling, and various search channels arestatistics-limited, and only possible with a luminosity upgrade. A luminosity upgrade would substantially improvesome of the coupling measurements and generally extend the sensitivity in the MSSM Higgs plane. Efforts areongoing to understand the upgrade of the LHC to the Super-LHC.AcknowledgmentsI would like to thank David Rainwater and Tilman Plehn for the useful discussions, Wesley Smith and MichaelDührssen for their contributions, and the organizers of Snowmass for their very enjoyable conference.This manuscript has been authored by Brookhaven Science Associates, LLC under Contract No. DE-AC02-98CH1-886 with the U.S. Department of Energy. The U.S. Government retains, and the publisher, by accepting the articlefor publication, acknowledges, a world-wide license to publish or reproduce the published form of this manuscript,or allow others to do so, for the U.S. Government purposes.References[1] ATLAS Collaboration. CERN-LHCC/99-15 (1999).[2] CMS Collaboration. Technical proposal. CERN-LHCC/94-38 (1994).[3] R. Barate et al. Phys. Lett., B565:61–75, 2003.[4] LEP Electroweak Working Group. LEPEWWG/2005-01 and hep-ex/0511027.[5] M. Carena, J. R. Ellis, A. Pilaftsis, and C. E. M. Wagner. Nucl. Phys., B586:92–140, 2000.[6] Les Houches Higgs Working Group. Summary report 2003. 2004.[7] C. P. Buszello, I. Fleck, P. Marquard, and J. J. van der Bij. Eur. Phys. J., C32:209–219, 2004.[8] N. Kauer, T. Plehn, D. Rainwater, and D. Zeppenfeld. Phys. Lett., B503:113–120, 2001.[9] D. Rainwater and D. Zeppenfeld. Phys. Rev., D60:113004, 1999.[10] T. Plehn, D. Rainwater, and D. Zeppenfeld. Phys. Rev., D61:093005, 2000.[11] S. Asai et al. Eur. Phys. J, C32S2:19–54, 2004.[12] S. Abdullin et al. Eur. Phys. J., C39S2:41–61, 2005.[13] V. Drollinger, Th. Müller, and D. Denegri. CMS NOTE-2001/054 (2001).[14] J. Cammin and M. Schumacher. ATLAS Note ATL-PHYS-2003-024 (2003).[15] M. Dührssen et al. Phys. Rev., D70:113009, 2004.[16] V. Del Duca, W. Kilgore, C. Oleari, C. Schmidt, and D. Zeppenfeld. Nucl. Phys., B616:367–399, 2001.[17] C. Anastasiou, K. Melnikov, and F. Petriello. Phys. Rev., D72:097302, 2005.[18] T. Plehn and D. Rainwater. Phys. Lett., B520:108–114, 2001.[19] T. Han and B. McElrath. Phys. Lett., B528:81–85, 2002.[20] O. Bruning et al. CERN-LHC-PROJECT-REPORT-626.[21] F. Gianotti et al. Eur. Phys. J., C39:293–333, 2005.[22] U. Baur, T. Plehn, and D. Rainwater. Phys. Rev. Lett., 89:151801, 2002.[23] T. Plehn and M. Rauch. Phys. Rev., D72:053008, 2005.ALCPG0602

Potential for Higgs Physics at the LHC and Super-LHC

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