Physics @ LHC (Physics @ TeV) Status of LHC/ATLAS/CMS and Physics explored at LHC Fundamentalist of High Energy Physics (U. Tokyo)
[0] Introduction: Most important/urgent topics in Particle Physics are: (1) Understanding of “the origin of mass” (EW symmetry breaking) SSB of Higgs field is most promising scenario, but should be examined directly & determine the potential: (2) Beyond the Standard Model Supersymmetry is most promising, Large Extra Dimension, unexpected scenario… are also exciting. These two topics are main purpose of LHC project:
[1] Status of LHC In 27 km LHC ring, 1232 superconducting dipoles are filled for bending, Magnetic filed is B=8.3 T PP collider √s=14TeV (effective √s is about several TeV: So LHC is a real TeV collider) Design L=10 34 cm -2 s -1 (100fb -1 /year) 10 32 -10 33 for 2008 and 2009 LHC is PP collider, Anti-p is not used. So there is no problem TOTEM due to anpi_proton intensity Two General purpose Detectorｓ ATLAS and CSM
Schedule of LHC Today Feb. 2007 Dipole Magnet Ready Mar. 2007 Machine and Detectors Ready Aug. 2007 √ s=0.9TeV Commissioning Run Nov. 2007 √ s=14TeV Physics Run Jun. 2008 End of 2008 L=2-4 fb -1 (SUSY up to 1.5 TeV , many mass region of Higgs, BH) End of 2009 L = O(10) fb -1 (Higgs completely covered, SUSY up to 2TeV) After 2010 Operated with Design Luminosity (100fb -1 /year) Detail measurements on Higgs/SUSY/LED/ “SM”
[2A] Status of ATLAS Detector Resolution (Pt=100GeV) e, γ 1.3% Muon 2% Jets 8% Very Large Detectors: Well balanced performances are expected. Key of ATLAS •Accordion Shape of L.Ar detectors for Calorimeters detector •Large air-core toroidal magnet for muon system
Tracking System Tracking (|eta|<2.5) is composed with • Si pixels and strips semiconductor • Transition Radiation Tracker Detector (e-ID) • 2T solenoid magnet
Calorimeters Tile Hadron Calorimeter EM+Magnet Calorimeter covers to (|eta|<5 ~ 1degree) : • EM is Pb absorber L. Ar with accordion shape electrode. • HAD is Fe/scintillator (central), • Cu/W-LAr (fwd)
Muon system Endcap muon Toroidal Magnet •Muon Spectrometer (|eta|<2.7) : air-core toroidal with muon chambers (small E loss, benefit in forward region)
Detector will be ready until the end of this summer muon system with Toroidal Endcap Calorimeter Barrel region is already installed behind endcap cal. Tracker calorimeter Detector commissioning has already started using cosmic ray Dead Channel: 0.2% SCT Noise hit ~1 0 -4
[2B] Status of CMS Resolution (Pt=100GeV) e, γ 0.9% Muon 2% Jets 12% H=15m ECAL Magnet L=22m (about half of ATLAS) W=12,500ton (twice of ATLAS) HCAL Tracker There are two key technologies in CMS: • 4T Solenoid Magnet (Strong field & Large Volume D=6m 2.7GJ) Muon chambers • PbWO 4 scintillator is used for EM (good resolution)
4T Magnet is ready and cosmic rays(>14M events) are detected in commissioning run: 2 barrel(PbWO 4 ) modules has installed. Delivery of PbWO 4 crystals is behind. Just Barrel counter is ready before commissioning run. Endcap EM counters will be installed in 2008.
[3] Origin of Mass (Higgs) SSB of Higgs Potential Simulated H → γγ events gives mass to Gauge boson W/Z: (Freedom of ξ ) Higgs boson will be observed Motion in η is corresponding to at LHC like this event (simulation) Higgs boson
[3-1] Production processes of SM Higgs at LHC 4 processes Gluon Fusion Vector Boson Fusion Associate production GF & VBF are important for discovery: with W/Z Cross-section of ttH/bbH is small, but Associate production with t/b give the direct information of Yukawa y t /y b .
Vector Boson Fusion (1998 Zeppenfeld et al.) VBF has an excellent potential because of : Detector Central φ η (1) Scattered “high Pt” jets are observed in the forward regions. Pt ~ Mw Number of jets QCD(color exchange) (2) There is rapidity gap between two VBF jets because there is no color exchange. Only the products from Higgs are observed in the central region. η These are very promising signatures in order to suppress the background.
Precision measurements of [3-2] Decay Branching Fraction the SM at LEP suggests M(H)=115-200GeV (95%CL) In such a light region, there are 5 important decay modes. H → bb,tautau, γγ (M(H)<140GeV) H → ZZ (*) ,WW (*) H → γγ Br is small of about 10 -3, (M(H)>130GeV) But promising mode due to good resolution of γ
[3-3A] H → γγ in GF and VBF (small Br, but excellent M γγ ） H →γγ γγ +0j Xsection (fb/GeV) huge BG. S/N ~1% qq_bar → γγ is dominante BG is High but also signal stat. is high ATLAS preliminary Xsection (fb/GeV) Two leading processes contribute to three different event topologies: S/N and shape of BG are different in 3 class. Discovery potential of them are similar, and we have good redundancy. H →γγ γγ +1j γ -ID and resolution are essential : M γγ (GeV) BG can be estimated with the side band. H →γγ γγ +2j Xsection (fb/GeV) ATLAS preliminary M γγ (GeV) Good S/N and flat BG H→γγ indicates that spin but Stat. limited of Higgs is 0 (or 2). scalar M γγ (GeV)
[3-3B] H → ZZ (*) → ４ leptons Resolution and identifications of leptons are excellent. Invariant mass distributions of 4 leptons are shown with BG contributions. Irreducible BG is qq_bar → ZZ * → 4l (continuous distribution) Reducible BGs are tt & Zbb (lepton comes from semileptonic decay of B B contamination can be suppressed by isolation of track + anti-impact parameter Track quality is essential for this mode ) CMS Full M(H)=200GeV M(H)=140GeV ZZ* → 4l has excellent discovery potential except for M(H)<130GeV and M(H)=170GeV (Branching is small) : We can determine also CP, Spin of Higgs using this channel.
Tau decay includes neutrino, but [3-3C] ＶＢＦ H →ττ Momenta of ν’s can be calculated using mE T information in the collinear limit. Tau can be reconstructed !!!! � + � � � h � � l � � � l � + � � � ll 4 � ATLAS Fast CMS Full This mode is direct evidence of Higgs- fermion coupling (Yukawa) Origin of fermion mass Resolution of mE T is about 10GeV M tautau has sharp peak (sigma ~ 10GeV) Dominant Background process is Z( → tautau)+Njets. Peak appears at 91GeV. Resolution and tail of mE T distribution are essential for this channel
[3-3D] VBF Ｈ→ WW Leptonic decays of W lead to the event topology of W + W � � l � l � Dilepton+mE T Leptons are emitted ATLAS M Ｈ =160GeV in the same direction Higgs Spin0 W- W+ CMS Full e+ e- 2 = 2 / M T P T P .. LL (1 � cos � ) Clear Jacobian Peak is observed: tt → bb l ν l ν is main BG: Leptons are back-to-back in tt. Φ between di-lepton (Rad)
[3-4] Discovery Potential of the SM Higgs LO calculation NLO calculation Similar Discovery potentials are obtained at both ATLAS and CMS (Notice LO calculation vs NLO) VBF γγ + exclusive 1,2 jets analyses will gain significance in low mass regions H-> γγ , tautau covers the region < 130GeV, WW,ZZ > 130GeV 5sigma discovery is possible with L=10fb -1 for both ATLAS and CMS Different technologies are essential for various modes: (Safe and redundant)
Let’s combine ATLAS+CMS performance Needed ∫ Ldt (fb -1 ) ≤ 1 fb -1 for 98% C.L. exclusion per experiment ≤ 5 fb -1 for 5 σ discovery over full allowed mass range 10 --- 98% C.L. exclusion 5 σ discovery is possible within 2008(>130GeV) or early of 2009(<130GeV) 1 measurements of mass, coupling, spin 98%CL exclusion (2008) ATLAS + CMS 10 -1 preliminary No Higgs model? invisible decay? m H (GeV) No resonance? critical test can be performed for “origin of mass”
[3-5] Measurements of Mass & coupling (L=300fb -1 ) Relative coupling (Normalized to g(WH)) •Y ｔ , Y τ 10-15% Mass can be measured •Y b 30-40% with accuracy of 0.1% •G z 、 5-10% if M(H)<400GeV. We can show couplings are proportional to their masses
Accuracy of “absolute measurements” of the couplings. We assume the SM branching fractions except for the leading five processes: Br(H->tautau,tt,bb,ZZ and WW) Within this assumption, Couplings of y t 、 y τ 、 y b, g ZZH and g WWH can be calculated. Accuracy: y t 、 y τ g ZZH and g WWH 20% y b 50%
Higgs Self-couplings In order to determine the shape of Higgs potential, Slope of potential is correspond to Self-coupling σ × Br is small Need very High Luminosity ー＞ SLHC For 6000 fb -1 (SLHC) Δλ ∼ 19% for 170 GeV M H
[4] SuperSymmetry O(TeV) SUSY provides GUT and good candidate of cold dark matter.
( ˜ g ˜ , ˜ g ˜ , ˜ q ˜ g q q ) [4-1] Production cross-section at LHC These couplings are just strong ˜ g :2 TeV interaction ( α s ): large cross-section is expected model independent except for mass ˜ q :2 TeV σ ~100pb m (˜ ) = m (˜ q g ) = 0.5 TeV g ˜ ˜ g ˜ g :1 TeV ˜ q :1 TeV σ ~3pb m (˜ ) = m (˜ q g ) = 1 TeV σ ~20fb m (˜ ) = m (˜ q g ) = 2 TeV u ˜ u ˜ ˜ , ˜ u d
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