Higgs physics at the LHC

Transcription

1 Higgs physics at the LHC Kati Lassila-Perini CMS Collaboration Helsinki Institute of Physics Acknowledgements: Atlas colleagues and ATLAS Physics TDR CMS colleagues especially Sasha Nikitenko and Daniel Denegri Michael Spira, PSI, Villigen LHC2, 26..

2 Higgs physics at the LHC Outline What are we looking for? The Higgs sector in the Standard Model and its Minimal Supersymmetric extension What are we going to see? The discovery potential of the LHC experiments What do we learn from it? Determination of the SM and MSSM parameters Visions for fb.

3 Higgs physics at the LHC:What are we looking for? The Standard Model:the missing piece(s) Extremely good agreement with experimental measurements. The SM requires a Higgs boson: ISO9 masses of fermions and gauge bosons remedy for the unitarity violation in gauge boson scattering at s WW TeV. The only unknown parameter of the SM Higgs sector is m H. precision measure- indirect theoretical constrains, e.w. ment, LEP: m H > 4. GeV The SM Higgs would be the first fundamental scalar particle allows for the spontaneous symmetry breaking giving gauge bosons their masses provides fermions their masses through Yukawa couplings however, its mass diverges in the perturbation theory.!

4 Higgs physics at the LHC:What are we looking for? Minimal Supersymmetric Standard Model ISO9 ISO9 The introduction of supersymmetric partners cancels the quadratic divergence in the Higgs boson mass. The MSSM is minimal in sense that a minimum number of Higgs doublets is introduced. Observable Higgs particles in the MSSM: neutral CP-even h and H, a CP-odd A, and charged H + and H. In the MSSM, at the tree level, the Higgs sector is defined by two parameters: m A and tan β The mixing between heavy squarks, the top mass and mass scales of SUSY particles enter in the radiative corrections.

5 Higgs physics at the LHC:What are we looking for? The MSSM Higgs masses hep-ph/338 tan β m h m A m H m h,max mh =mh,max m H m A m H± Excluded by LEP LEP limits: m h > 9 GeV, m A > 9.9 GeV, m ± H > 78.6 GeV m A tan β: maximal mixing.5 < tan β<2.4 excluded minimal mixing.7 < tan β<.5 excluded

6 The SM Higgs production at the LHC σ (pb) gg H σ(pp H+X) s = 4 TeV m t = 75 GeV CTEQ4M qq Hqq - qq' HW gg,qq Htt -3 M. Spira et al. gg,qq Hbb 2-4 NLO QCD qq HZ M H events for 5 pb - g g g fusion : g g t t fusion : g q WW, ZZ fusion : q q t W,Z t t W,Z W,Z t t q t t H o W,Z H o H o q W, Z bremsstrahlung H o

7 The SM Higgs discovery channels bb BR (H) A. Djouadi, J. Kalinowski, M. Spira WW ZZ σbr (fb) 4 3 H ZZ 2l2ν H WW+2j lν2j+2j H ZZ+2j 2l2j+2j - ττ BR (H) cc gg tt γγ Zγ 2 3 M H D_D_9.c 2 H γ γ H ZZ (*) 4l H WW 2l2ν m H To complete: H b b for 9 m H 2 GeV qq qqh withh ττ

8 The two precision channels H γγ m H = 2 GeV in fb in CMS H 4l m H = 3 GeV in fb in ATLAS Events/5 MeV 8 Signal + background fb - Events/5 MeV 4 2 Background subtracted Events/7.5 GeV 5 L dt = fb - (no K-factors) m γγ m γγ 2 4 m 4l

9 H b b t th SM l± νq qb bb b m H = 5 GeV /c 2 events / GeV/c CMS L int = 3 fb - k =.5 gen. m H : 5 GeV/c 2 const. : 3.63 ± 3.76 mean :.3 ± 4.4 sigma : 4.32 ± m inv (j,j) [GeV/c 2 ] 9 <m<3 GeV/c 2 : N H5 = 38 N t tz = 3 N t tb b = 23 N t tjj = 26 N BG = 52 results (stat.): S/B = 73% S/ B =5.3 y t /y t = 3% m/m =3.8%

10 The vector boson fusion channels Profit from the two forward tagging jets and clean central area of the VBF channel. Example, qq Hqq, H ττ in ATLAS: evts / 5 GeV m H =2 GeV Z jj t t, WW EW significance all e µ significance m m ττ H m H

11 The SM Higgs discovery potential Discovery reach for fb Minimum luminosity for 5 σ Signal Significance 2 H γγ + WH, tth (H γγ) tth (H bb) H ZZ (*) 4 H WW (*) IνIν H ZZ IIνν H WW Iνjj Total significance fb 5σ ATLAS fb no K-factors 2 3 M H Discovery Luminosity [ fb - ] 2 5 σ Higgs Signals (statistical errors only) LHC 4 TeV (SM, Signal with σ NLO ) pp H γ γ pp H ZZ llll pp H WW lνlν pp H ZZ llνν qq qqh γ γ qq qqh WW lνlν qq qqh WW lνjj qq qqh ZZ llνν M Higgs [ GeV ]

12 The MSSM Higgs production at the LHC:h/H Cross-section (pb) h H Hbb Htt M. Spira: programs for Higgs production tan β = 3 Maximal mixing gg H (SM) gg H Hqq Cross-section (pb) h H Hbb Hqq Htt M. Spira: programs for Higgs production tan β = 3 Maximal mixing gg H (SM) gg H -3 2 HZ HW m h/h -3 2 HZ HW m h/h The total rate suppressed/enhanced with low/high tan β Vector boson fusion generally suppressed Hb b enhanced.

13 The MSSM Higgs production at the LHC:A M. Spira: programs for Higgs production M. Spira: programs for Higgs production Cross-section (pb) Abb Att gg A tan β = 3 Maximal mixing gg H (SM) Cross-section (pb) Att Abb gg A tan β = 3 Maximal mixing gg H (SM) -3 2 m A -3 2 m A The total rate suppressed/enhanced with low/high tan β Vector boson fusion suppressed Ab b enhanced.

14 The MSSM branching ratios:h/h Branching ratio HDECAY (M 2 =2 GeV, µ=-2 GeV, M SUSY =TeV, A T = 6M SUSY ) bb WW hh tt χ + χ - ττ gg ττ cc ZZ ZA WW γγ ss γγ µµ Wh Zγ bb gg cc Zγ ss µµ ZZ χ χ tan β = 3 Maximal mixing 2 3 m h/h Branching ratio HDECAY (M 2 =2 GeV, µ=-2 GeV, M SUSY =TeV, A T = 6M SUSY ) bb bb - χ χ WW χ + χ - ττ ττ gg WW tan β = 3 ZZ cc gg Maximal mixing -2 cczz -3-4 γγ Zγ gg gg ss ss γγ Zγ µµ µµ WW hh 2 3 m h/h tt m h = m h,max :couplings as in the SM b b dominant for h with m h <m h,max and for H with high tan β WW and ZZ suppressed with rising tan β ττ enhanced very rich decay structure at low tan β.

15 The MSSM branching ratios:a Branching ratio - -2 HDECAY (M 2 =2 GeV, µ=-2 GeV, M SUSY =TeV, A T = 6M SUSY ) bb tt ττ χ χ Zh χ + χ - tan β = 3 Maximal mixing Branching ratio - -2 HDECAY (M 2 =2 GeV, µ=-2 GeV, M SUSY =TeV, A T = 6M SUSY ) bb ττ χ χ χ + χ - tan β = 3 Maximal mixing -3 gg ss cc -3 gg ss tt -4 µµ γγ 2 3 m A -4 µµ 2 3 m A b b dominant ττ important

16 The MSSM branching ratios:h ± Branching ratio bc cs µν HDECAY (M 2 =2 GeV, µ=-2 GeV, M SUSY =TeV, A T = 6M SUSY ) τν tb AW Wh χ +/- χ tan β = 3 Maximal mixing Branching ratio bc cs µν HDECAY (M 2 =2 GeV, µ=-2 GeV, M SUSY =TeV, A T = 6M SUSY ) τν tb χ +/- χ tan β = 3 Maximal mixing -4 su 2 3 m A -4 su Wh 2 3 m A tb dominant where possible τν dominant <m top

17 The MSSM Higgs discovery channels Channels of major importance: h γγ h b b H/A ττ H ± τν The best SM channel H ZZ 4l strongly suppressed Several possible channels to complete in different regions of the parameter space: H hh A Zh H/A µµ H ± tb SUSY scale allowing: H/A χ 2χ 2 χ 2 hχ

18 h γγ h SM-like at m h = m h,max SM production and decays h γγ suppressed below m h = m h,max gg h is affected by large mixing and a light stop quark However, the Wh and tth are enhanced in that case.

19 h b b Same features as in the SM Large BR over the whole parameter space the reach of the channel extends to the lower values of m A where m h <m h,max.

20 H/A ττ H/A ττ lτ-jet + X H/A ττ 2τ-jets + X H/A ττ 2l + X Events for 3* 4 pb / 4 GeV Events for 3* 4 pb / 4 GeV > 4 GeV, p l T > 5 GeV, φ(jl) < 75, ET miss > 2 GeV p jet T (a) (b) A, H, h ττ I ± +τ jet + E t miss signal m A = 2 GeV tan β = M ττ A, H, h ττ I ± +τ jet + E t signal m A = 2 GeV tan β = 3 with b tagging One tagged b-jet miss M ττ D_D_ 229 c > 6 GeV, p h T > 4 GeV, φ(jj) < 75, ET miss > 4 GeV p jet T Events for 3 * 4 pb / 4 GeV Events for 3 * 4 pb / 4 GeV (a) A, H ττ h + + h + X m A = 5 GeV tan β = 2 signal M ττ 3 (a) A, H ττ h + + h + X with b tagging m A = 5 GeV tan β = 2 One tagged b-jet signal M ττ D_D_ 23 c p l T > 2 GeV, cut on imp. param., φ(eµ) < 75,jetp jet T > 2 GeV

21 H/A parameter space coverage H/A separation Width A tan β = H m H -m A m H/A

22 H ± τν Production: m ± H <m top : t t events with t H ± b m ± H >m top : gb th ± and qq H ± Example:2 and 4 GeV H ± τν integrated luminosity fb exploit the τ polarisation Events for 5 pb - / 2 GeV pp th ±, H ± τν, t qqb m H = 4 GeV, tanβ = 3 Signal ~ 55 events miss m T (τ jet, E t ) [GeV] veto on a central jet Et jet > 4 GeV, η jet < 2.5 vetoonasecondtop m τνj m top > 3 GeV Events for 5 pb - / 2 GeV pp th ±, H ± τν, t qqb m H = 2 GeV, tanβ = 2 jet and top veto Total background Signal ~ 6 events DD_ miss m T (τ jet, E t ) [GeV]

23 5 σ reach for MSSM Higgses

24 Effect of light SUSY particles SUSY particle loops may suppress or enhance the production or decay (e.g. gg H γγ). Light sparticles compete with the SM decay modes of A, H and H ± (e.g. H/A χ 2χ 2 2lχ 2lχ ). h in cascade decays of SUSY particle (e.g. χ 2 hχ ). H/A χ 2 χ 2 4l, CMS m A-tan β ( fb ), ATLAS Events / 5 GeV Events / 5 GeV tanβ 5 2 sign(µ) = lepton effective mass lepton effective mass m A

25 Higgs physics at the LHC:What do we learn from it? Determination of the SM Higgs parameters ATLAS Physics TDR Higgs mass Higgs width Higgs rate m H /m H - -2 Γ H /Γ H - Error on σx BR (%) m H m H 2 3 m H <% accuracy in m H 6% above 3 GeV 2% for 2 <m H < 6 GeV Sensitivity to Higgs spin (H ZZ) and CP state (HWW coupling in VBF)

26 Higgs physics at the LHC:What do we learn from it? Determination of the SM Higgs couplings and branching ratios Assume 3 fb The luminosity uncertainty largely cancels in ratios. The error is often dominated by lack of statistics. σ B (WH γγ) σ B (WH bb) σ B (H γγ) σ B (H ZZ*) BR (H γγ) BR (H bb) BR (H γγ) BR (H ZZ*) known to ~ 3% stat. limited only for: 8 < m H < 2 GeV ~ ~ known to ~ 5% stat. limited only for: 25 < m H < 55 GeV ~ ~ σ B (tth γγ/bb) σ B (WH γγ/bb) g2 H tt g 2 H WW known to ~ 25% stat. limited only for: 8 < m H < 3 GeV ~ ~ σ B (H WW*/W) σ B (H ZZ*/Z) DD_25c g2 H WW g2 H ZZ known to ~ 3% stat. (ZZ*) limited only for: 6 < m H < 8 GeV ~ ~

27 Higgs physics at the LHC:What do we learn from it? Determination of the MSSM parameters Fabiola Gianotti In large area of the parameter space more than one Higgs boson available compensate with sparticle searches.

28 Higgs physics at the LHC:What do we learn from it? Determination of the MSSM parameters Masses (< % forγγ and µµ, -3%forb b, -2% for ττ): relation between the MSSM masses Width:SM/MSSM disentangling Rates:SM/MSSM disentangling, couplings (-2%) tan β:example (ATLAS Physics TDR): tan β, m A = 5 GeV tan β, m A = 3 GeV tanβ/tanβ (%) Ldt = 3 fb - m A = 5 GeV tanβ/tanβ (%) Ldt = 3 fb - m A = 3 GeV tanβ tanβ

29 Higgs physics at the LHC Visions: γγ bump at 2 GeV after fb Events/5 MeV 5 CMS.3.27 (LO) Events/5 MeV 5 m H = 2 GeV ( fb - ) S/ B = m γγ 2 3 m γγ What about the SM if this is the SM Higgs? MSSM h: m h = m h,max (γγ is visible only there) minimal mixing excluded (m h too large) wait for A/H ττ to appear

30 Higgs physics at the LHC Visions:excess in WW lνlν at 7 GeV after fb SM H: Dittmar, Dreiner Wait for H ZZ 4l to appear (4 fb ) Cannot be h in the MSSM MSSM H: if H WW visible, tan β low BR(WW) tan β =3 at low tan β H production rate suppressed m H = 7±5 GeV m A = 5± GeV Fall in the m A -tan β plane hole Could H WW fill the hole? m h GeV Wait for h b b to appear (6 fb )

31 Higgs physics at the LHC Visions:excess in WW lνlν at 7 GeV after fb

32 Higgs physics at the LHC Conclusions The SM Higgs searches cover the entire mass range and with more than one decay mode for each mass. The low mass range the most demanding with H γγ and H b b. Precision measurement possible for SM Higgs properties. In the MSSM, the entire Higgs sector parameter space can be covered with 3 fb /experiment. Several decay modes and several Higgses available apart from small regions. Significant part can be covered with fb /experiment. Precision measurements of the Higgs sector can constrain the the other parameters of the SUSY model. As elusive as it is know, the Higgs sector will be well known/constrained in 7 years from now.