Forward physics at the LHC: QCD, electro weak & Higgs

Transcription

1 Forward physics at the LHC: QCD, electro weak & Higgs QCD School Les Houches March 25th Apr. 4th, 2008 CERN 1/35

2 LHC forward physics: why? Many interesting (mostly color singlet exchange) scatt. processes at the LHC are characterized by forward particle production: elastic/diffractive interactions: QCD: low x: cosmic rays MCs EWK: two photon, photon proton colls. Higgs: VBF, central exclusive, h,h,a MSSM Higgs,... 2/35

3 LHC forward detectors: where? Near beam detectors (CMS/ATLAS): = ln tan( /2) 3 cavern tunnel ~O(mm) or on beam ~O(10cm)from beam Zero degree Proton taggers calorimeter s > 8. ~420, 220 m ~140 m (calorimeters) ~7 ~14 m ~1 1m 0m 1) p,n tagging devices 2) Direct particle measurements: fwd. jets,... 3) Hadron vetoing devices: rapidity gaps 3/35 (gap)

4 Lectures Programme 0. Introduction 1. Forward detectors at the LHC 1st 2. QCD physics with forward detectors: Diffractive/Elastic scattering. UHE cosmic rays MCs. 2nd Low x QCD 3. EW physics with forward detectors: 3 th photon photon, photon proton collisions 4. Higgs physics with forward detectors VBF Higgs, central exclusive Higgs,... 4/35

5 EWK (γ γ,γ p) physics 5/35

6 The LHC as a photon collider Electromagnetic field of a relativistic charged particle: An observer at a perpendicular distance b from the trajectory sees: (i) E B Fermi (ii) (E B) (iii) t ~ b/ [1924, hep-th/ ]: The effect of the fields is equivalent to a flux of of photons with a continuous energy spectrum. pulse width b/ the spectrum contains photons with < /b Weizsäcker, Williams [1935]: Quantum-mechanical derivation Equivalent photon spectrum n( ) calculable through Fourier transform. 6/35

7 Equivalent spectrum & luminosities Spectrum of photons with fractional energy x = E /Ebeam & virtuality Q2 : Q2min constrained by x, projectile mass. Q2max given by form factor for hadron beams: Q2max = (1/R)2. Equivalent photon luminosity: - integrating over all virtualities - accounting for collider luminosity (energy in rest frame of the target) 7/35

8 proton interactions at the LHC [UC Louvain CMS group] (gap) (p tag) Significant Cleaner, cross sections up to few TeV! better S/B (than parton parton) measurements of: Top physics (e.g. Vtb via Wt channel) Associated W H production: O(20fb) (Anomalous) single top production: O(100fb) (Anomalous) triple gauge boson couplings 8/ & 420 m proton detectors essential for processes tagging.

9 γ p W : triple gauge couplings [U.Dreyer, ECT* UPC'07] W photoproduction allows one to probe triple (anomalous?) gauge coupling vertex WW : ~50 evts./100 pb 1 in p p 14 TeV Leading neutron,proton tagging in ZDC / RPs [Also quartic couplings: γγ WW,ZZ (see later)] 9/35

10 interactions at the LHC [UC Louvain CMS group] (p tag) (p tag) Photon photon physics up to 1 TeV! Very clean processes: central X, fwd. p's Accessible measurements: Luminosity via QED: ℓ+ℓ (large!) (Anomal.) quartic gauge couplings: WW ~~ ~+ℓ~ SUSY pair production: ℓ 10/35

11 γ γ dileptons: LHC luminosity Exclusive ℓ+ℓ (e+e,µ+µ ) production (fwd. proton in RPs) γ l+ γ l (µ+µ in muon chambers) (e+e in T2/CASTOR) (fwd. proton in RPs) QED process: x section known precisely (p T>2.5 GeV/c) = 75 pb (LPAIR) Interests: ~700 evts./100 pb 1 in CMS (plus photoproduction) absolute p p luminosity within ~3% (stat.) Cross calibration of fwd. proton taggers (FP420,TOTEM). 11/35

12 γ γ WW: quartic gauge couplings [UC Louvain CMS group] Probe quartic (anomalous?) gauge coupling vertex WW 12/35 :

13 Higgs (VBF tagging) 13/35

14 SM Higgs: production modes at the LHC Gluon fusion: gg fusion VBF gg H dominant, large QCD backgrounds Vector Boson Fusion: qq qq H ~20% of σh distinct final state (fwd. jets) LEP excl. Associated: tth, WH, ZH small cross sections associated 14/35

15 SM Higgs: decay modes GeV: BR MH<135 Dominant BR: bbar Huge QCD bckgd! Very difficult at the LHC Discovery channels: MH>135 GeV: LEP Dominant BR: WW(*),ZZ(*) excl. (relatively easy discovery via leptonic W,Z decays) 15/35

16 SM Higgs: signal significance (30 fb 1) With K factors 5 with K factors 5 LHC: ~1 fb 1 in 2009(?), increasing to 100 fb 1/year at design luminosity. 16/35

17 Vector Boson Fusion Higgs (I) qq qqh distinct signature: fwd jet forward jets φ 2 jets (pt~20 60 GeV) w/ large η~5 separation fwd jet Fwd. jets allow for good rejection of QCD backgrounds: H WW( l±jj ν) vs. ttbar, WW Higgs decay η H ττ vs. Z+nj, W+nj, ttbar bckgd. jets at central rapidities 17/35

18 Vector Boson Fusion Higgs (II) VBF (qq qqh) with Higgs decay in ττ,ww channels shows good discovery potential: fwd jet fwd jet [Note: All this also applies for VBF MSSM Higgs & for VB scatt.: WW WW,...] 18/35

19 Pseudo rapidity of VBF quarks VBF quarks peaked at η~4.7 (mh=120 GeV) η ~3, η1 η2<0 C A Average rapidity separation: η~5.1 (mh=200 GeV) H H F F S T O R (more fwd jets for increasing mh) CMS: CASTOR+HF fwd. jet acceptance to 3.< η < 6. (+15% extra VBF tagging efficiency) 19/35

20 Higgs (central exclusive) 20/35

21 Central exclusive Higgs: motivation [FP420 R&D report] Central exclusive Higgs production: pp p H p (leading proton) H decay in central det. σh = 3 10 fb (SM), x10(0) in MSSM (leading proton) Excellent physics motivations! Quantum numbers: central system is approx. JPC = 0++ (selection rule) Excellent mass resolution: from protons, indep. of central decay products. Enhanced S/B: Reduced QCD background. H bbar channel accessible! CP violation in Higgs sector: directly measurable from protons asymmetry Discovery channel (bbar, ) in certain regions in MSSM 21/35

22 Central exclusive Higgs: SM x section Central exclusive Higgs calculable via pqcd: KMR = Khoze Martin Ryskin σh = 3 10 fb (SM) pp php = updf gg H S2gap-survival LEP (updfs: standard PDFs taken) excl. Two extra ingredients: (i) gap survival S2 : probability to fill rap gap with hadrons (rescattering corrs.) S2 (ii) Sudakov form factor: large, S~log2(Mgg2), virtual corrs. Sudakov form factor 22/35

23 Central exclusive Higgs: x section validation Exclusive dijets (CDF) have same type of diagrams as for Higgs: validation of KMR model & npqcd ingredients (ExHuME MC): In particular: S2 ~0.03 Note Mjj~130 GeV! 23/35

24 MSSM Higgs' MSSM: Minimal Supersymmetric SM extension 2 Higgs doublets 8 degrees of freedom (5 physical states): CP even : h,h CP odd: A Charged: H+,H MSSM parameter space: MA, tan vev2/vev1 At high MA, heavy H's degenerate in mass & h saturates at Mh~130 GeV Couplings to SM particles modified: Decay into 3d generation fermions (b, ) enhanced at high tan : challenging discovery in normal bosonic modes! 24/35

25 MSSM Higgs': Central exclusive [FP420 R&D report] MSSM Higgs(es): tagged proton channel is discovery channel (bbar and decays!) in wide ma tan range: Higgs line shape in bbar channel! 60 fb 1, 3.5 [Cox/Loebinger/Pilkington JHEP 0710:090,2007] [Heinemann et al.arxiv: ] 25/35

26 Central exclusive Higgs: FP 420 project [FP420 R&D report] For mh< 200 GeV, proton tagging acceptance needed at ±420 m FP420 Novel R&D project (ATLAS/CMS): technologies: (i) Moving beampipe in cold LHC area (ii) Very fast (τ ~10 ps) Cerenkov detectors: GASTOF (gas), Quartic (Quartz) Precise leading protons time difference to isolate pp p H p vertex in high luminosity (~25 p p colls.) conditions 26/35

27 Central exclusive Higgs: LHC optics Scattered protons survive interaction & lose only a small fraction ξ of their initial longitudinal momentum (a few 100 rads): ξ1 ξ2 s = M2 dipole beam dipole For s=14tev, MX=120 GeV: p proton tagger p proton tagger proton fractional momentum loss: ξ % With nominal LHC optics: LHC beam magnets deflect leading protons by a few mm after ~420 m: Detection needed inside beam pipe. 27/35

28 FP420(+220m): central exclusive acceptance Scattered proton inside beam trajectory: transverse distance at 220m & 420m Acceptance of FP m versus CEP Higgs mass: ξ=0.015 ξ=0.002 ξ=0 (beam) Nominal LHC beam optics: Low b* (0.5m): Lumi = cm 2s 1 (0.02 < ξ < 0.2): acceptance for mh>150 GeV, but ξ resolution inferior (0.002 < ξ < 0.02): superior ξ (i.e. in Higgs mass) resolution, but cannot be used in L1 trigger (too far away) 28/35

29 FP420: new connection cryostat [FP420 R&D report] scattered protons emerge here 420m from the IP in the cold section of the LHC. New connection cryostat needed: Modify LHC Arc Termination Modules for cold to warm transition such that detectors can be operated at ~ room temperature 29/35

30 FP420: new Hamburg beam pipe Beam position monitor Silicon detector box Gastof or Quartic fast timing dets. Moveable beam pipe with detector stations attached Move detectors toward beam envelope once beam is stable 30/35

31 FP 420: proton Si detectors 3D edgeless Silicon detectors: Edgeless, i.e. distance to beam envelope can be minimized. Radiation hard, can withstand 5 years at 1035 cm 2 s 1 Use ATLAS pixel chip (rad hard) for readout Active edges: the edge is itself an electrode, so dead volume at the edge < 5 Electrodes are processed inside the detector bulk instead of being implanted on the wafer s surface. 31/35

32 FP 420: proton Si detectors 3 A complete tracking station (+lid) detector stations with 8 layers each Tracking performances: Detection efficiency: ~80 86% Angular resolution: 0.9 rad 32/35

33 FP 420: fast timing detectors Fast timing detectors needed to identify CEP vertex out of other pile up events. Micro channel plate photo multiplier tubes (MCP PMT) employed in Cherenkov light based TOF detector with resolution of ~10ps. Expected z vertex resolution of better than 3mm. Two technologies: Quartz or gas based Cherenkov. GASTOF (UC Louvain) QUARTIC (U Texas Arlington): Cherenkov medium is a gas Cherenkov medium is fused Silica 33/35

34 Summary: forward LHC ATLAS CMS CASTOR TOTEM T1 LUCID TOTEM T2 ATLAS ZDCs ATLAS ALFA CMS ZDCs TOTEM RPs ALICE ZDCs LHCf FP420 34/35

35 Summary: forward LHC p p σtot, elastic scatt. hard diffraction VM photoprod. (B)SM Higgs H,h,A Fdjj dijets gluon saturation, CGC MB/UE/MPI UHE cosmic rays low x PDFs BFKL E W (γ γ,γ W,...) 35/35

36 Backup slides 36/35

37 Summary: forward LHC possible upgrade RP220 with Si detectors 37/35 possible addition

38 VBF tagging in CMS (HF+CASTOR) CASTOR+HF extends effective jet acceptance to 3.< η < 6.: C A H H F F C A S S T T O O R R Sharp drop of jet effic. beyond η ~4.4 38/35

39 Vector Boson Fusion Higgs tagging qq qqh [DdE/LeMenedeu, BWS'07] accompanied by forward jets: ~20% of σh 2 jets (pt~20 60 GeV) w/ large η~5 separation Good QCD background rejection : H WW( l±jj ν) H ττ vs. Combined HF+CASTOR extends vs. ttbar,ww Z+nj, W+nj, ttbar (~15%) VBF jet tagging efficiency: Jet C H H A F F S T Jet C A S m ~120 GeV RPs@150m ZDC RPs@220m H T O O R R mh~200 GeV background jets at central rapidities 39/35

40 SUSY pairs [Cf. Séverine Ovyn & UCL CMS group] Production x sections defined only by mass, charge & spin! Very clean signature: 2 (and only 2) opposite charged leptons & MET Three post WMAP msugra benchmark points checked: LM1: light LSP, light sleptons & charginos, tan( )=10 LM2: medium LSP, heavy sleptons&charginos, tan( )=30 LM6: heavy LSP, medium right sleptons, tan( )=10 40/35

41 Central exclusive MSSM Higgs S.Heinemeyeretal M A = 130 GeV tanβ = 50 H bb toappear No mixingscenario Contoursofratioofsignaleventsin them SSM overthesm 41/35

42 Central exclusive MSSM Higgs Intense coupling regime of the MSSM: CEP as discovery channel Mh~MA ~ MH ~ O(100GeV): coupling to γγ, WW*, ZZ* strongly suppressed 8 discovery very challenging at the LHC 100 fb Cross section of two scalar (0+) Higgs bosons enhanced compared to SM Higgs Production of pseudo scalar (O ) Higgs suppressed because of JZ selection rule Kaidalov et al, hep ph/ , hep ph/ fb Superior missing mass resolution from tagged protons allows to separate h, H Spin partity of Higgs can be determined from the azimuthal angles between the two taggedprotons (JZ rule only approx) 42/35

43 Higgs spin parity Azimuthal angle between outgoing protons sensitive to Higgs spin parity: JP=0+ vs JP=0 (recall JZ selection rule only approximate) 100 fb 0 1 fb 0+ Kaidalov et al., hep ph/ /35

44 Central exclusive SM Higgs Central exclusive Higgs production: pp p H p Generator studies with detector cuts b jets : H MH = 120 GeV; = 2 fb (uncertainty factor ~ 2.5) MH = 140 GeV; = 0.7 fb MH = 120 GeV: S/B=11 signal/o(10) in 30 fb 1 w/ detector cuts 100 fb Note: This H decay channel is impossible in see Kaidalov et al, hep-ph/ , hep-ph/ WW* : 1 fb non CEP production! MH = 120 GeV; = 0.4 fb MH = 140 GeV; = 1 fb MH = 140 GeV : S/B=8 signal / O(3) in 30 fb 1 with detector cuts Note: Use semi leptonic decays for measurement 44/35

45 Central exclusive MSSM Higgs'es Intense coupling regime: similar masses of the 3 neutral Higgs bosons and tan is large suppressed enhanced 0++ selection rule suppresses A production: CEDP filters out pseudo scalar production, leaving pure H sample for study ma = 130 GeV, tan β = 50 mh = 124 GeV : S/B = 70 / (3 10) in 30 fb 1 mh = 135 GeV : S/B = 125 / (2 5) in 30 fb 1 ma = 130 GeV : S/B =3 / (2 5) in 30 fb 1 Tagged proton channel may well be the discovery channel, and is certainly a powerful spin/parity filter 45/35

46 other BSM signals... Transplanckian effects Once you pass the Planck scale s >> MD Processes with small momentum transfer e.g. : Elastic transplanckian colls.: Study gravity propagation in ED s Signal: dijets with large y, Mjj Large rapidity separation of 2 jets 46/35 Giudice, Rattazzi, Wells, NPB 630 (2002)293

47 CMS+TOTEM forward detectors CMS (central, CASTOR, ZDC)+TOTEM: largest acceptance ever at a collider CMS ZDC (neutral) TAS? 47/35

48 EW & Higgs forward measurements 1. EW: Two photon interactions: Absolute luminosity via: pp γγ p `+` p Triple/Quartic gauge boson couplings via: pp γp pnw, γγ WW,ZZ SUSY pair production: γγ kk, 3. EW: γ proton interactions: AbsA 5. Higgs Vector Boson Fusion SM Higgs tagging Central exclusive (SM, MSSM) Higgs 48/35