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(Forward Look at) Physics at the LHC

(Forward Look at) Physics at the LHC. Outline The LHC – quick introduction/reminder The detectors Higgs physics – in the SM and the MSSM Supersymmetry: Sparticles (squarks/gluinos/gauginos) Precision measurements Other (possible) new physics TeV-scale gravity Current status Summary.

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(Forward Look at) Physics at the LHC

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  1. (Forward Look at) Physics at the LHC Outline • The LHC – quick introduction/reminder • The detectors • Higgs physics – in the SM and the MSSM • Supersymmetry: • Sparticles (squarks/gluinos/gauginos) • Precision measurements • Other (possible) new physics • TeV-scale gravity • Current status • Summary Paris Sphicas CERN and Univ. of Athens International School on High Energy Physics Crete, October 2003 LHC Physics

  2. Standard Model Higgs

  3. V(f) f Limits on MH (I): EWK vaccum stability • Central to the Higgs mechanism: that point with vev0 is stable (genuine minimum) • Radiative corrections can change this V(f) • For large top masses, potential can curve back down; two terms fighting: • lf4 vs ~ - (mt/v)4 • And since MH2~lv2, get a lower bound on MH (~ 130 GeV) f LHC Physics

  4. Limits on MH (II): triviality bound • From previous discussion: need a high value of l (i.e. self-coupling) to protect the vacuum • However, the running of the coupling results in an increase with Q2: • So, as Q2, l  • Alternative: if l is normalized to a finite value at the pole then it must vanish at low Q2. Theory is non-interacting  “trivial” • Way out: assume that analysis breaks down at some scale L (clearly, when gravity gets added, things will change) LHC Physics

  5. Information (limits) on MH: summary • Triviality bound <f0>0 • Precision EWK measurements LEP direct search: MH>114 GeV/c2 LHC Physics

  6. Expected Fermilab Reach • Reach has been updated. Also Tevatron luminosity profiles; expect 5-10fb-1 by LHC start (+ a bit) LHC Physics

  7. SM Higgs at the LHC • Production mechanisms & cross section LHC Physics

  8. SM Higgs • Decays & discovery channels • Higgs couples to mf2 • Heaviest available fermion (b quark) always dominates • Until WW, ZZ thresholds open • Low mass: b quarks jets; resolution ~ 15% • Only chance is EM energy (use gg decay mode) • Once MH>2MZ, use this • W decays to jets or lepton+neutrino (ETmiss) LHC Physics

  9. Low mass Higgs (MH<140 GeV/c2) • Hgg: decay is rare (B~10-3) • But with good resolution, one gets a mass peak • Motivation for LAr/PbWO4 calorimeters • Resolution at 100 GeV, s1GeV • S/B  1:20 LHC Physics

  10. Intermediate mass Higgs • HZZl+l– l+l– (l=e,m) • Very clean • Resolution: better than 1 GeV (around 100 GeV mass) • Valid for the mass range 130<MH<500 GeV/c2 LHC Physics

  11. High mass Higgs • HZZ l+l–jet jet • Need higher Branching fraction (also nn for the highest masses ~ 800 GeV/c2) • At the limit of statistics LHC Physics

  12. Higgs discovery prospects @ LHC • The LHC can probe the entire set of “allowed” Higgs mass values • in most cases a few months at low luminosity are adequate for a 5s observation CMS LHC Physics

  13. Significance for 30 fb-1 No K factors Luminosity (in fb-1) for 5s discovery of MH<160 NLO K factors for ggH A closer look at the discovery lumi LHC Physics

  14. HWW(*); also a prime discovery mode • Large backgrounds from top production, WW SM production LHC Physics

  15. Status of H bb̅ (I) • Low mass Higgs; useful for coupling measurement • H bb̅ in t t ̅H production • s.Br=300 fb • Backgrounds: • Wjjjj, Wjjbb̅ • t t ̅jj • Signal (combinatorics) • Tagging the t quarks helps a lot • Trigger: t b(e/m)n • Reconstruct both t quarks • In mass region 90GeV<M(bb̅)<130GeV, S/B =0.3 LHC Physics

  16. Status of H bb̅ (II) • H bb̅ in WH production • Big background subtraction • Mainly: Wjj, t t ̅ (smaller: tX,WZ) • Example (below) at 105: • in mass region 88GeV<M(bb̅)<121GeV, S/B =0.03 After bkg subtraction LHC Physics

  17. Weak Boson Fusion (I) • WW interaction -> Higgs • Main characteristic: the two forward “tag” jets LHC Physics

  18. Weak Boson Fusion (II) • Observation of qqH, HWW(*)22n • WBF cuts • Angle between leptons (against top and WW backgrounds) • B-jet VETO (against top) • Tau-jet veto (against ttjj) • Cuts on: • M() • ETmiss • MT(ETmiss) (against DY) • Top background extractible from the data (using semileptonic top events: tt n+jets ) LHC Physics

  19. In addition to WBF cuts: Tau-id (for +h mode) Tau reco (xtl,xth>0) MT(n)<30 GeV ETmiss, mass window Systematics: Z+tt background; 10% on shape WBF + Htt ATLAS; ++ETmiss CMS; +h+ETmiss LHC Physics

  20. SM Higgs properties (I): mass • Mass measurement • Limited by absolute energy scale • leptons & photons: 0.1% (with Z calibration) • Jets: 1% • Resolutions: • For gg & 4l ≈ 1.5 GeV/c2 • For bb ≈ 15 GeV/c2 • At large masses: decreasing precision due to large GH • CMS ≈ ATLAS LHC Physics

  21. SM Higgs properties (II): width • Width; limitation: • Possible for MH>200 • Using golden mode (4l) CMS LHC Physics

  22. SM Higgs; (indirect) width for MH<2MZ • Basic idea: use qqqqH production (two forward jets+veto on central jets) • Can measure the following: Xj = GWGj/G from qqqqH qqjj • Here: j = g, t, W(W*); precision~10-30% • One can also measure Yj= GgGj/G from ggHjj • Here: j = g, W(W*), Z(Z*); precision~10-30% • Clearly, ratios of Xj and Yj (~10-20%)  couplings • But also interesting, if GW is known: • G = (GW)2/XW • Need to measure H  WW* • e=1-(Bb+Bt+BW+BZ+Bg+Bg)<<1 • (1-e)GW= Xt(1+y)+XW(1+z)+Xg+Xg • z= GW/GZ; y= Gb/Gt=3hQCD(mb/mt)2 Zeppenfeld, Kinnunen, Nikitenko, Richter-Was LHC Physics

  23. SM Higgs properties (III) • Biggest uncertainty(5-10%): Luminosity • Relative couplings statistically limited • Small overlap regions LHC Physics

  24. SM Higgs: properties (IV) • Self-coupling • From HH production • Cross sections are low • Relevant for MH<200 GeV/c2 Need higher statistics, i.e. luminosities; for example, WW(*) with ln+jetjet channel visible (with 10x the statistics) Measures l to 20-25% LHC Physics

  25. MSSM Higgs(es)

  26. Remark on SUSY studies (I) LHC Physics

  27. Remark on SUSY studies (II) LHC Physics

  28. MSSM Higgs(es) • Complex analysis; 5 Higgses (FH±;H0,h0,A0) • At tree-level, all masses & couplings depend on only two parameters; tradition says take MA & tanb • Modifications to tree-level mainly from top loops • Important ones; e.g. at tree-level, Mh<Mzcosb, MA<MH; MW<MH+; radiative corrections push this to 135 GeV. • Important branch 1: SUSY (s)particle masses (a) M>1 TeV (i.e. no F decays to them); well-studied (b) M<1 TeV (i.e. allows F decays to them); “on-going” • Important branch 2: stop mixing; value of tanb (a) Maximal–No mixing (b) Low (≈2-3) and high (≈30) values of tanb LHC Physics

  29. MSSM Higgses: masses • Mass spectra for MSUSY>1TeV • The good news: Mh<135 GeV/c2 LHC Physics

  30. MSSM: h/A decay • h is light • Decays to bb (90%) & tt (8%) • cc, gg decays suppressed • H/A “heavy” • Decays to top open (low tanb) • Otherwise still to bb & tt • But: WW/ZZ channels suppres-sed; lose golden modes for H – No mixing – LHC Physics

  31. MSSM Higgs production • Cross section prop to tan2b • Third-generation fermions • e.g., bbA production LHC Physics

  32. Higgs channels considered • Channels currently being investigated: • H, hgg, bb̅ (Hbb̅ in WH, t t ̅H) • hgg in WH, t t ̅h  ℓ g g • h, H  ZZ*, ZZ  4 ℓ • h, H, A t+t- (e/m)+ + h-+ ETmiss e+ + m- + ETmiss inclusively and in bb̅HSUSY h+ + h- + ETmiss • H+  t+n from t t ̅ • H+  t+n and H+  t b̅ for MH>Mtop • A  Zh with h bb̅; A gg • H, A  c̃02c̃̃02, c̃0ic̃0j, c̃+ic̃-j • H+  c̃+2c̃02 • qq qqH with H t+t- • H tt, in WH, t t ̅H (very) important and hopeful fairly new and promising LHC Physics

  33. The tau: the LHC-SUSY lepton • Taus are the new element of the LHC • Most SUSY models have e/m universality • but t-leptons are special • Usually: t1 is the lightest slepton • implies that t’s may be the only leptons produced in gaugino decays • What the b-quark (and the associated tagging) was to the Tevatron experiments LHC Physics

  34. H,Att; 3rd-generation lepton the LHC • Most promising modes for H,A • t’s identified either in hadronic or leptonic decays • Mass reconstruction: take lepton/jet direction to be the t direction LHC Physics

  35. H, A reach via t decays • Contours are 5s; MSUSY=1 TeV LHC Physics

  36. H+ detection • Associated top-H+ production: • Use all-hadronic decays of the top (leave one “neutrino”) • H decay looks like W decay  Jacobian peak for t-missing ET • In the process of creating full trigger path + ORCA analysis ET(jet)>40 |h|<2.4 Veto on extra jet, and on second top Bkg: t t ̅H LHC Physics

  37. Other modes: Hmm in bbA production • Pros: clean signature, good mass resolution (1-2%) • Cons: Br(A/Hmm)~410-3 • BUT: cross section enhanced by tanb • Backgrounds: • Z/g* : suppressed with b-tagging: vertex+ip; no cut on PT(b) • ttmm+X: suppressed with jet-veto + ETmiss LHC Physics

  38. Can one separate A & H? LHC Physics

  39. SUSY reach on tanb-MA plane • Adding bb̅ on the t modes can “close” the plane Wh (e/m)n bb̅ No stop mixing maximal stop mixing with 30 fb-1 maximal stop mixing with 300 fb-1 LHC Physics

  40. h,A,H,H h,A,H h,H MSSM Higgs bosons 4 Higgs observable 5s contours 3 Higgs observable h 2 Higgs observable H,H 1 Higgs observable Assuming decays to SM particles only h,H h,H h,,H,H h,A,H,H Observability of MSSM Higgses LHC Physics

  41. If SUSY charg(neutral)inos < 1 TeV (I) • Decays H0 c̃02c̃̃02, c̃+ic̃-j become important • Recall that c̃02c̃̃01ℓ+ℓ_ has spectacular edge on the dilepton mass distribution • Example: c̃02c̃02. Four (!) leptons (isolated); plus two edges 100 fb-1 Four-lepton mass LHC Physics

  42. If SUSY charg(neutral)inos < 1 TeV (II) • Helps fill up the “hole” Wh Area covered by H0 c̃02c̃̃02, 4ℓeptons 100 fb-1 (e/m)n bb̅ No stop mixing maximal stop mixing with 30 fb-1 maximal stop mixing with 300 fb-1 LHC Physics

  43. Measurement of tanb: bbA with Att LHC Physics

  44. Only h found; is it SM or MSSM? LHC Physics

  45. MSSM: Higgs summary • At least one f will be found in the entire MA-tanb plane • latter (almost) entirely covered by the various signatures • Full exploration requires 100 fb–1 • Difficult region: 3<tanb<10 and 120<MA<220; will need: • > 100 fb–1 or hbb decays • Further improvements on t identification? • Intermediate tanb region: difficult to disentangle SM and MSSM Higgses (only h is detectable) • Potential caveats (not favored) • Sterile (or “invisible”) Higgs • Still doable – but invisible… LHC Physics

  46. Strong “EWK” interactions

  47. Strong boson-boson scattering • Example: WLZL scattering • W, Z polarization vector emsatisfies: empm=0; • for pm=(E,0,0,p), em=1/MV(p,0,0,E)  Pm/MV+O(MV/E) • Scattering amplitude ~ (p1/MW) (p2/MZ) (p3/MW) (p4/MZ), i.e. s~s2/MW2MZ2 • Taking MH the H diagram goes to zero (~ 1/MH2) • Technicalities: diagrams are gauge invariant, can take out one factor of s • but the second always remains (non-abelian group) • Conclusion: to preserve unitarity, one must switch on the H at some mass • Currently: MH700 GeV LHC Physics

  48. The no Higgs case: VLVL scattering • Biggest background is Standard Model VV scattering • Analyses are difficult and limited by statistics Resonant WZ scattering at 1.2 & 1.5 TeV Non-resonant W+W+ scattering MH=1 TeV L=300 fb-1 WTWT LHC Physics

  49. Other resonances/signatures • Technicolor; many possibilities • Example: rT±W±Z0 l±nl+l– (cleanest channel…) • Many other signals (bb, tt resonances, etc…) • Wide range of observability ATLAS; 30 fb–1 – – LHC Physics

  50. Summary

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