Photon fusion production of the Higgs boson in proton nucleus collisions at the LHC

Transcription

1 Photon fusion production of the Higgs boson in proton nucleus collisions at the LHC Forward Physics at the LHC Manchester, Dec. 13th 2009 David d'enterria ICREA, ICC Univ. Barcelona [DdE & Jean Philippe Lansberg, arxiv: , PRD to appear] 1/20

2 Overview Intro: Conventional Higgs searches at the LHC Exclusive electromagnetic SM Higgs production: pp,ppb,pbpb p(pb) H p(pb) at s = TeV Photon (p,a) fluxes. (elastic & semielastic), MadGraph, HEFT: _ ( H)~0.1 fb,0.3 pb,10 pb (also ( bb), x30 higher) Luminosity & pileup considerations. Rates: 0.1,30,80 H/year _ ppb H bb measurement in ATLAS/CMS. Acceptance, efficiency, backgd. subtraction cuts Significance: 3 signal in 3 years 2/20

3 Higgs production modes (p p, LHC) Gluon fusion: gg fusion VBF gg H dominant, large QCD backgrounds Vector Boson Fusion: LEP qq qq H excl. ~20% of H distinct final state (fwd. jets) Associated: tth, WH, ZH associated extra hard activity, low x sections 3/20

4 Higgs decay channels mh<135 GeV/c2: mh>135 GeV/c2: Dominant decay: b bar Dominant decay: WW(*),ZZ(*) But huge QCD bckgd! Easy discovery via Discovery channels: leptonic W,Z e, decays 4/20

5 Higgs discovery potential (LHC, 30 fb 1) mh<135 GeV/c2: Dominant decay: b bar Huge QCD bckgd! Inaccessible at the LHC. H b coupling not measurable! Discovery channels: mh>135 GeV/c2: Dominant decay: WW(*),ZZ(*) Easy discovery via leptonic W,Z e, decays No possibility to test Higgs Yukawa coupling to quarks at the LHC!? 5/20

6 Exclusive Higgs production (p p, LHC) Two additional (colour singlet) Higgs production channels: Diffractive production: pp (gg)(gg) php Photon fusion production: pp php Low x sections (x10 4, 5 less) but very clean events (~zero bckgd). Require forward proton tagging in LHC tunnel. 6/20

7 Photon photon collisions with heavy ions High energy heavy ions produce strong EM fields due to coherent action of Z = 82 protons: Huge photon fluxes: ( ) ~ Z4 (~5 107) times larger than e± beams! Quasi real photons (coherence): Q ~ 1/R ~ 0.06 GeV (Pb), 0.28 GeV (p) Max. LHC energies: Max. LHC c.m. energies: ~ 80 GeV (Pb beam), ~ 2.5 TeV (p beam) PbPb: s 160 GeV s (LEP) ppb: s 260 GeV 2 mh 7/20

8 Higgs production in p A collisions Elastic gamma gamma colls: Semielastic gamma gamma colls: (rap gap) (rap gap) (rap gap) Photons emitted coherently by p & A. Proton & nucleus survive interaction. Two rapidity gaps (p & A sides). (nucleus) emitted coherently, (proton) emitted by quark. Proton breaks up. Nucleus survives. One rapidity gap (nucleus side). [We require: Qmax (p)<5 GeV, & no p fragment within y <2.5] 8/20

9 x sections p p, p A, A A Higgs MadGraph v4.0 LO evt generator. Equivalent photon approx: Photon fluxes: PbPb A: p: pa Budnev et al. [74]. q: Ohnemus el a.[94] ( H) in the HEFT approx: pp Extra contrib.: (semiel.)~ (elastic) pp, pa, AA Higgs x sections: 9/20

10 Luminosity considerations (I) PbPb H x section largest but PbPb lumis limited to 1027cm 2s 1 due to: (i) Bound free pair prod.: ( =280 b!) (ii) Coulomb dissociation: ( =215 b!) Beam losses p A lumis not limited by EM interactions (Z2~7000 less than Pb Pb). Effective luminosity: pp pa PbPb 10/20

11 Luminosity considerations (II) Default p Pb lumis still improvable by factor x60 up to 1031 cm 2s 1: x10 increasing to nominal p intensity x6 via expected (slhc) * & kpb upgrades 11/20

12 Expected Higgs counts/year Higgs event rates: Negligible for nominal heavy ion lumis (1029) & runtimes (1 month). But, for 1031 cm 2s 1 & t=107 s: 25 H bbar/year 8.8 TeV: highest Higgs rates with lowest event pileup. 12/20

13 Potential backgrounds Experimental Hadronic signal signature: 2 high pt b jets & rap gaps. (peripheral) heavy Q pair production. Removal cuts: (1) Jet multiplicity: N(jets) = 2 (2) Exclusivity: No hadronic activity outside jets in tracker ( <2.5)& calos ( <5) (3) Coherence: Low pt(jet pair): pt(jet pair)<5 GeV/c Diffractive & Photoprod. heavy Q pair production. Removal cuts: (1) Exclusivity: x sect ~103 larger but gap survival: S2( P, P P)~10 2,10 3 << S2( )~1 (2) Forward neutrons: Nucleus = fragile object (8 MeV/nucleon): Require no ZDC activity (Note: no GDR excitation in EM p nucleus interactions) (3) Coherence: d /dt~e bt, b( )<<b( P P). Low pt(jet pair): pt(jet pair)<5 GeV/c 13/20

14 Irreducible backgrounds Heavy Q pair continuum:,c,q,c,q x sections ( GeV/c2): (1) bbar continuum: ~25 times Higgs (2) ccbar continuum: ~600 times Higgs ~1.5 after double mistag probab. (3) qqbar continuum: ~1600 times Higgs ~1/3 after double mistag probab. 14/20

15 Experimental cuts L1 trigger: 2.5 units rap gap in Pb direction, 2 jets above 40 GeV/c trigg ~ 100%] b jet acceptance: 2 b jets within y <2.5 (note rapidity shift: ycm=1.4) [Acc ~ 60%] b tagging efficiency: Efficiency: 70% for a single b jet, i.e. 49% for a bbar system. tagg ~ 50%] Mistagging prob.: 5% for c jets, i.e. 1/400 for a dijet system. Mistagging prob.: 1.5% for light q jets, i.e for a dijet system. 15/20

16 [ b jet (mis)tagging efficiency ] How realistic is our b jet tagging working point (70% 5% 1.5%)? State of the art (preliminary) Combined Multi Variate Analysis algorithm C.Saout [CMS Collab.] 16/20

17 Background suppression (I) b jet transverse momentum cut: At least 1 jet within pt = GeV/c ~ mh/2 [Acc ~ 28%] 96% of background removed. 49% of signal loss 17/20

18 Background suppression (II) b jet acoplanarity cut: cos( ) <0.45 in helicity frame [Acc ~ 28%] 88% of background removed. 55% of signal loss 18/20

19 Final result: mass plot & significance Combined cuts: 80% signal loss, x50,x5 103,4 105 bckgd. removal Log likelihood fit of 500 pseudo datasets mass distrib. with 2 curves: 1) Null hypothesis: Background continuum (exponential) 2) Higgs signal (Gaussian, M=7 GeV/c2) + background Significance = diff. between 2 of fits: S = ( 2)1/2 p 8.8 TeV 3 years at 1031 cm 2s 1 H bbar 3 observation with 300 pb 1! 19/20

20 Conclusion Exclusive electromagnetic SM Higgs production: pp,ppb,pbpb p(pb) H p(pb) at s = TeV Cross sections (EPA,MadGraph,HEFT): ( H)~0.1 fb,0.3 pb,10 pb. Rates: 0.1, 30, 80 H/year p Pb preferred: Maximum rates with minimum pileup (Npileup~1) (rap gap) (rap gap) 3 _ signal in 3 p Pb years. Only chance to see SM H bb at LHC!? 20/20

21 Back up slides 21/20

22 Signal cross sections 22/20

23 Equivalent spectrum Electromagnetic Spectrum ultra peripheral collisions (UPCs): bmin~2ra~20 fm of photons with fractional energy x = E /Ebeam & virtuality Q2 : Q2max given by form factor for hadron beams: Q2max = (1/R)2. Q2min constrained by x, projectile mass. Equivalent photon spectrum: 23/20

24 Higgs boson characterization? undetected? LHC experiments observe a Higgs like resonance. Properties? (1) b quark coupling? very challenging b bbar decay: (H bb) 20 pb (bb) 500 b (2) Quantum numbers? spin parity JPC = 0++ very difficult to determine (3) Additional (e.g. MSSM) nearly degenerate states? not easy to separate... (4) Mass & width in (BSM) invisible decays? No. (Only counting in VBF channels) The LHC experiments do not observe any SM Higgs like resonance... (1) MSSM Higgs' w/ enhanced b, decay in difficult ma tan LHC wedge region? (2) MSSM Higgs' w/ CP violating mixings? (3) NMSSM Higgs' w/ dominant (complicated) decay h aa 4? Can LHC do anything about all this before a (next?) e+e linear collider? 24/20