1. P. Sphicas/ISHEP2003LHC Physics1 (Forward Look at) Physics at the LHC Outline n The LHC – quick introduction/reminder n The detectors n Higgs physics – in the SM and the MSSM n Supersymmetry: u Sparticles (squarks/gluinos/gauginos) u Precision measurements n Other (possible) new physics n TeV-scale gravity n Current status n Summary Paris Sphicas CERN and Univ. of Athens International School on High Energy Physics Crete, October 2003

2. P. Sphicas/ISHEP2003 Standard Model Higgs

3. P. Sphicas/ISHEP2003LHC Physics3 Limits on M H (I): EWK vaccum stability n Central to the Higgs mechanism: that point with vev  0 is stable (genuine minimum) u Radiative corrections can change this  V  u For large top masses, potential can curve back down; two terms fighting:   4 vs ~ - (m t /v) 4  And since M H 2 ~ v 2, get a lower bound on M H (~ 130 GeV)  V 

4. P. Sphicas/ISHEP2003LHC Physics4 Limits on M H (II): triviality bound From previous discussion: need a high value of (i.e. self-coupling) to protect the vacuum u However, the running of the coupling results in an increase with Q 2 :  So, as Q 2  ,    Alternative: if is normalized to a finite value at the pole then it must vanish at low Q 2. Theory is non-interacting  “trivial”  Way out: assume that analysis breaks down at some scale  (clearly, when gravity gets added, things will change)

5. P. Sphicas/ISHEP2003LHC Physics5 Information (limits) on M H : summary Triviality bound  0 n Precision EWK measurements LEP direct search: M H >114 GeV/c 2

6. P. Sphicas/ISHEP2003LHC Physics6 Expected Fermilab Reach n Reach has been updated. Also Tevatron luminosity profiles; expect 5-10fb -1 by LHC start (+ a bit)

7. P. Sphicas/ISHEP2003LHC Physics7 SM Higgs at the LHC n Production mechanisms & cross section

8. P. Sphicas/ISHEP2003LHC Physics8 SM Higgs n Decays & discovery channels u Higgs couples to m f 2 l Heaviest available fermion (b quark) always dominates l Until WW, ZZ thresholds open u Low mass: b quarks  jets; resolution ~ 15% Only chance is EM energy (use  decay mode) u Once M H >2M Z, use this l W decays to jets or lepton+neutrino (E T miss )

9. P. Sphicas/ISHEP2003LHC Physics9 Low mass Higgs (M H <140 GeV/c 2 ) H  : decay is rare (B~10 -3 ) u But with good resolution, one gets a mass peak u Motivation for LAr/PbWO 4 calorimeters  Resolution at 100 GeV,  1GeV l S/B  1:20

10. P. Sphicas/ISHEP2003LHC Physics10 Intermediate mass Higgs H  ZZ  + –  + – ( =e,  ) u Very clean l Resolution: better than 1 GeV (around 100 GeV mass) u Valid for the mass range 130<M H <500 GeV/c 2

11. P. Sphicas/ISHEP2003LHC Physics11 High mass Higgs H  ZZ  + –  jet jet  Need higher Branching fraction (also  for the highest masses ~ 800 GeV/c 2 ) u At the limit of statistics

12. P. Sphicas/ISHEP2003LHC Physics12 Higgs discovery prospects @ LHC n 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 5  observation CMS

13. P. Sphicas/ISHEP2003LHC Physics13 A closer look at the discovery lumi n Significance for 30 fb -1 u No K factors Luminosity (in fb -1 ) for 5  discovery of M H <160 u NLO K factors for gg  H

14. P. Sphicas/ISHEP2003LHC Physics14 H  WW (*) ; also a prime discovery mode n Large backgrounds from top production, WW SM production

15. P. Sphicas/ISHEP2003LHC Physics15 Status of H  bb ̅ (I) n Low mass Higgs; useful for coupling measurement  H  bb ̅ in t t ̅ H production .Br=300 fb l Backgrounds: –Wjjjj, Wjjbb ̅ –t t ̅ jj –Signal (combinatorics) l Tagging the t quarks helps a lot –Trigger: t  b(e/  ) –Reconstruct both t quarks l In mass region 90GeV<M(bb ̅ )<130GeV, S/B =0.3

16. P. Sphicas/ISHEP2003LHC Physics16 Status of H  bb ̅ (II) H  bb ̅ in WH production u Big background subtraction Mainly: Wjj, t t ̅ (smaller: tX,WZ) l Example (below) at 105: –in mass region 88GeV<M(bb ̅ )<121GeV, S/B =0.03 After bkg subtraction

17. P. Sphicas/ISHEP2003LHC Physics17 Weak Boson Fusion (I) n WW interaction -> Higgs u Main characteristic: the two forward “tag” jets

18. P. Sphicas/ISHEP2003LHC Physics18 Weak Boson Fusion (II) Observation of qqH, H  WW (*)  2 2 u WBF cuts u Angle between leptons (against top and WW backgrounds) u B-jet VETO (against top)  Tau-jet veto (against  jj) u Cuts on: l M( ) l E T miss l M T ( E T miss ) (against DY) u Top background extractible from the data (using semileptonic top events: tt   jets )

19. P. Sphicas/ISHEP2003LHC Physics19 WBF + H  n In addition to WBF cuts: u Tau-id (for +h mode) u Tau reco (x tl,x th >0)  M T ( )<30 GeV u E T miss, mass window n Systematics: u Z+tt background; 10% on shape ATLAS; + +E T miss CMS; +h+E T miss

20. P. Sphicas/ISHEP2003LHC Physics20 SM Higgs properties (I): mass n Mass measurement u Limited by absolute energy scale l leptons & photons: 0.1% (with Z calibration) l Jets: 1% u Resolutions: For  & 4 ≈ 1.5 GeV/c 2 l For bb ≈ 15 GeV/c 2  At large masses: decreasing precision due to large  H u CMS ≈ ATLAS

21. P. Sphicas/ISHEP2003LHC Physics21 SM Higgs properties (II): width n Width; limitation: u Possible for M H >200 Using golden mode (4 ) CMS

22. P. Sphicas/ISHEP2003LHC Physics22 SM Higgs; (indirect) width for M H <2M Z n Basic idea: use qq  qqH production (two forward jets+veto on central jets)  Can measure the following: X j =  W  j /  from qq  qqH  qqjj Here: j = , , W(W*); precision~10-30%  One can also measure Y j =  g  j /  from gg  H  jj Here: j = , W(W*), Z(Z*); precision~10-30% u Clearly, ratios of X j and Y j (~10-20%)  couplings  But also interesting, if  W is known:  = (  W ) 2 /X W l Need to measure H  WW*  =1-(B b +B  +B W +B Z +B g +B  )<<1 (1-  )  W = X  (1+y)+X W (1+z)+X  +X g z=  W /  Z ; y=  b /    3  QCD (m b /m  ) 2 Zeppenfeld, Kinnunen, Nikitenko, Richter-Was

23. P. Sphicas/ISHEP2003LHC Physics23 SM Higgs properties (III) n Biggest uncertainty(5-10%): Luminosity u Relative couplings statistically limited l Small overlap regions

24. P. Sphicas/ISHEP2003LHC Physics24 SM Higgs: properties (IV) n Self-coupling u From HH production u Cross sections are low l Relevant for M H <200 GeV/c 2 Need higher statistics, i.e. luminosities; for example, WW (*) with +jetjet channel visible (with 10x the statistics) Measures to 20-25%

25. P. Sphicas/ISHEP2003 MSSM Higgs(es)

26. P. Sphicas/ISHEP2003LHC Physics26 Remark on SUSY studies (I)

27. P. Sphicas/ISHEP2003LHC Physics27 Remark on SUSY studies (II)

28. P. Sphicas/ISHEP2003LHC Physics28 MSSM Higgs(es) Complex analysis; 5 Higgses (  H ± ;H 0,h 0,A 0 )  At tree-level, all masses & couplings depend on only two parameters; tradition says take M A & tan  u Modifications to tree-level mainly from top loops Important ones; e.g. at tree-level, M h <M z cos , M A <M H ; M W <M H + ; radiative corrections push this to 135 GeV. u Important branch 1: SUSY (s)particle masses (a) M>1 TeV (i.e. no  decays to them); well-studied (b) M<1 TeV (i.e. allows  decays to them); “on-going”  Important branch 2: stop mixing; value of tan  (a) Maximal–No mixing (b) Low (≈2-3) and high (≈30) values of tan 

29. P. Sphicas/ISHEP2003LHC Physics29 MSSM Higgses: masses n Mass spectra for M SUSY >1TeV u The good news: M h <135 GeV/c 2

30. P. Sphicas/ISHEP2003LHC Physics30 MSSM: h/A decay n h is light  Decays to bb (90%) &  (8%) l cc, gg decays suppressed n H/A “heavy”  Decays to top open (low tan  )  Otherwise still to bb &  u But: WW/ZZ channels suppres- sed; lose golden modes for H – No mixing –  g(  uu)g(  dd)g(  VV) h cos  /sin   1 -sin  /cos   1 sin(  )  1 H sin  /sin   1/tan  cos  /cos   tan  cos(  )  1 A 1/tan  tan  0

31. P. Sphicas/ISHEP2003LHC Physics31 MSSM Higgs production Cross section prop to tan 2  u Third-generation fermions u e.g., bbA production

32. P. Sphicas/ISHEP2003LHC Physics32 Higgs channels considered n Channels currently being investigated:  H, h , bb ̅ (H  bb ̅ in WH, t t ̅ H)  h  in WH, t t ̅ h  ℓ  u h, H  ZZ*, ZZ  4 ℓ  h, H, A       e/  ) + + h  + E T miss  e + +   + E T miss inclusively and in bb ̅ H SUSY  h + + h  + E T miss  H +  +  from t t ̅  H +  + and H +  t b ̅ for M H >M top  A  Zh with h  bb ̅ ; A   H, A  ̃    ̃ ̃    ̃  i  ̃  j   ̃  i  ̃  j  H +  ̃    ̃    qq  qqH with H      H , in WH, t t ̅ H fairly new and promising (very) important and hopeful

33. P. Sphicas/ISHEP2003LHC Physics33 The tau: the LHC-SUSY lepton n Taus are the new element of the LHC  Most SUSY models have e/  universality but  -leptons are special  Usually:  1 is the lightest slepton  implies that  ’s may be the only leptons produced in gaugino decays n What the b-quark (and the associated tagging) was to the Tevatron experiments

34. P. Sphicas/ISHEP2003LHC Physics34 H,A  ; 3 rd -generation lepton the LHC n Most promising modes for H,A   ’s identified either in hadronic or leptonic decays u Mass reconstruction: take lepton/jet direction to be the  direction

35. P. Sphicas/ISHEP2003LHC Physics35 H, A reach via  decays Contours are 5  ; M SUSY =1 TeV

36. P. Sphicas/ISHEP2003LHC Physics36 H + detection H + detection n Associated top-H + production: u Use all-hadronic decays of the top (leave one “neutrino”)  H decay looks like W decay  Jacobian peak for  -missing E T u In the process of creating full trigger path + ORCA analysis E T (jet)>40 |  |<2.4 Veto on extra jet, and on second top Bkg: t t ̅ H

37. P. Sphicas/ISHEP2003LHC Physics37 Other modes: H  in bbA production n Pros: clean signature, good mass resolution (1-2%) Cons: Br(A/H  )~4  10 -3  BUT: cross section enhanced by tan  n Backgrounds:  Z/  * : suppressed with b-tagging: vertex+ip; no cut on PT(b)  tt  X: suppressed with jet-veto + E T miss

38. P. Sphicas/ISHEP2003LHC Physics38 Can one separate A & H?

39. P. Sphicas/ISHEP2003LHC Physics39 SUSY reach on tan  -M A plane Adding bb ̅ on the  modes can “close” the plane Wh bb ̅ (e/  ) No stop mixing maximal stop mixing with 30 fb -1 maximal stop mixing with 300 fb -1

40. P. Sphicas/ISHEP2003LHC Physics40 Observability of MSSM Higgses 4 Higgs observable 3 Higgs observable 2 Higgs observable 1 Higgs observable MSSM Higgs bosons h,A,H,H  Assuming decays to SM particles only h,H  h h,A,H H,H  h,,H,H  h,H 5  contours

41. P. Sphicas/ISHEP2003LHC Physics41 If SUSY charg(neutral)inos < 1 TeV (I) Decays H 0   ̃ 0 2  ̃̃ 0 2,  ̃ + i  ̃ - j become important  Recall that  ̃ 0 2  ̃̃ 0 1 ℓ + ℓ _ has spectacular edge on the dilepton mass distribution  Example:  ̃ 0 2  ̃ 0 2. Four (!) leptons (isolated); plus two edges Four-lepton mass 100 fb  1

42. P. Sphicas/ISHEP2003LHC Physics42 If SUSY charg(neutral)inos < 1 TeV (II) n Helps fill up the “hole” Wh bb ̅ (e/  ) No stop mixing maximal stop mixing with 30 fb -1 maximal stop mixing with 300 fb -1 Area covered by H 0   ̃ 0 2  ̃̃ 0 2,  4ℓeptons 100 fb -1

43. P. Sphicas/ISHEP2003LHC Physics43 Measurement of tan  : bbA with A 

44. P. Sphicas/ISHEP2003LHC Physics44 Only h found; is it SM or MSSM?

45. P. Sphicas/ISHEP2003LHC Physics45 MSSM: Higgs summary At least one  will be found in the entire M A -tan  plane u latter (almost) entirely covered by the various signatures u Full exploration requires 100 fb –1  Difficult region: 3<tan  <10 and 120<M A <220; will need: l > 100 fb –1 or h  bb decays Further improvements on  identification?  Intermediate tan  region: difficult to disentangle SM and MSSM Higgses (only h is detectable) n Potential caveats (not favored) u Sterile (or “invisible”) Higgs l Still doable – but invisible…

46. P. Sphicas/ISHEP2003 Strong “EWK” interactions

47. P. Sphicas/ISHEP2003LHC Physics47 Strong boson-boson scattering n Example: W L Z L scattering  W, Z polarization vector   satisfies:   p  =0; for p  =(E,0,0,p),   =1/M V (p,0,0,E)  P  /M V +O(M V /E)  Scattering amplitude ~ (p 1 /M W ) (p 2 /M Z ) (p 3 /M W ) (p 4 /M Z ), i.e.  ~s 2 /M W 2 M Z 2 u Taking M H  the H diagram goes to zero (~ 1/M H 2 ) u Technicalities: diagrams are gauge invariant, can take out one factor of s l but the second always remains (non-abelian group) u Conclusion: to preserve unitarity, one must switch on the H at some mass l Currently: M H  700 GeV

48. P. Sphicas/ISHEP2003LHC Physics48 The no Higgs case: V L V L scattering n Biggest background is Standard Model VV scattering u Analyses are difficult and limited by statistics L=300 fb -1 Resonant WZ scattering at 1.2 & 1.5 TeV Non-resonant W + W + scattering M H =1 TeV WTWTWTWT

49. P. Sphicas/ISHEP2003LHC Physics49 Other resonances/signatures n Technicolor; many possibilities  Example:  T ±  W ± Z 0  ± + – (cleanest channel…) u Many other signals (bb, t t resonances, etc…) u Wide range of observability ATLAS; 30 fb –1 – –

50. P. Sphicas/ISHEP2003 Summary

51. LHC Physics51 Higgs Summary