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LHC Phenomenology LHC Phenomenology Heather Logan Carleton University 31st Symposium on Physics in Collision Vancouver, Canada, 28 Aug{1 Sep, 2011 1 Outline Introduction: why we expect new discoveries at the LHC Higgs constraints and phenomenology Frameworks for physics beyond the Standard Model I: Supersymmetry Frameworks for physics beyond the Standard Model II: Composite models Summary and outlook Heather Logan (Carleton U.) LHC Phenomenology Physics In Collision 2011 2 The Standard Model is extremely successful so far. Can't we get by with just the degrees of freedom that we've observed? - 3 generations of quarks; CKM matrix for flavor physics - 3 generations of charged leptons - Neutrinos with mass (might need something new there) - gluons from SU(3) strong interaction - photon plus massive W and Z from SU(2) U(1) ± × (Electroweak symmetry is broken, but do we really have to worry about how?) - (Dark matter?) - (How to bring gravity into the quantum theory?) Heather Logan (Carleton U.) LHC Phenomenology Physics In Collision 2011 3 The Standard Model is extremely successful so far. Can't we get by with just the degrees of freedom that we've observed? - 3 generations of quarks; CKM matrix for flavor physics - 3 generations of charged leptons - Neutrinos with mass (might need something new there) - gluons from SU(3) strong interaction - photon plus massive W and Z from SU(2) U(1) ± × (Electroweak symmetry is broken, but do we really have to worry about how?) - (Dark matter?) - (How to bring gravity into the quantum theory?) The answer is no: the SM without a Higgs is intrinsically incomplete. Heather Logan (Carleton U.) LHC Phenomenology Physics In Collision 2011 4 Scattering of longitudinally-polarized W s exposes need for a Higgs∗ 4 SU(2) x U(1) @ E Sum 0 Graphics from R.S. Chivukula, LHC4ILC 2007 ∗or something to play its role 5 Scattering of longitudinally-polarizedWhy a Higgs?W s exposes need for a Higgs∗ 2 SU(2) x U(1) @ E E < √8πv 1.2 TeV " including (d+e) Graphics from R.S. Chivukula, LHC4ILC 2007 ∗or something to play its role 6 Standard Model Higgs mechanism: Electroweak symmetry broken by an SU(2)-doublet scalar field: G+ H = 0 (h + v)=p2 + iG =p2 ! G+ and G0 are the Goldstone bosons (eaten by W + and Z). • v is the SM Higgs vacuum expectation value (vev), • v = 2m =g 246 GeV. W ' h is the SM Higgs field, a physical particle. • Electroweak symmetry breaking comes from the Higgs potential: 2 2 V = µ HyH + λ(HyH) where λ (1) ∼ O and µ2 (M2 ). ∼ −O EW v2 = µ2/λ = (246 GeV)2, ) − M2 = 2λv2 = 2µ2. ) h − Heather Logan (Carleton U.) LHC Phenomenology Physics In Collision 2011 7 Direct SM Higgs searches { LEP expts final combination 2 ! 1 e+e Z ZH LEP − ! ∗ ! (a) !s = 91-210 GeV SM Higgs decay BRs assumed Observed Expected for background -1 10 ξ = scaling factor 95% CL limit on on ZZH relative to SM -2 10 SM limit: 20 40 60 80 100 120 2 MH 114:4 GeV mH(GeV/c ) ≥ Final LEP combination, Phys. Lett. B565, 61 (2003) ) ) - – Heather Logan (Carleton U.) LHC Phenomenology Physics In Collision 2011 1 " 1 + bb LEP LEP (b) " (c) 8 " s = 91-210 GeV s = 91-210 GeV ! – ! + - H"bb " H"" " B(H 2 B(H 2 ! ! -1 -1 10 10 95% CL limit on -2 -2 10 95% CL limit on 10 20 40 60 80 100 120 20 40 60 80 100 120 2 2 mH(GeV/c ) mH(GeV/c ) 2 SM 2 Figure 10: The 95% confidence level upper bound on the ratio ξ =(gHZZ/gHZZ) (see text). The dark and light shaded bands around the median expected line correspond to the 68% and 95% probability bands. The horizontal lines correspond to the Standard Model coupling. (a): For Higgs boson decays predicted by the Standard Model; (b): for the Higgs boson decaying exclusively into bband(c):into¯ + τ τ − pairs. 22 Latest SM Higgs results from Tevatron (EPS-HEP 2011) Tevatron combined, arXiv:1107.5518 [hep-ex], shown at EPS-HEP 2011 Heather Logan (Carleton U.) LHC Phenomenology Physics In Collision 2011 9 Latest SM Higgs results from LHC (Lepton-Photon 2011) SM Higgs Search Combination CMS PRELIM ATLAS-CONF-2011-135Expected exclusion CMS PAS mass HIG-11-022 range: 130 (LP2011) – 440 GeV Observed exclusion mass range: 145-216, 226-288, 310-400 GeV 26 CMS + ATLAS exclude (at 95% CL) all mass regions except: below 145 GeV, 288{296 GeV, and above 464 GeV. Higgs with suppressed gluon-fusion production coupling and/or suppressed W W; ZZ decay BRs still allowed in the SM-excluded mass regions. Heather Logan (Carleton U.) LHC Phenomenology Physics In Collision 2011 10 Precision electroweakSM Higgs mass fit (summer 2011) LEP Electroweak Working Group (2011) Precision EW favors low-mass allowed window, 114.4{145 GeV. (Fit valid only in SM context; new physics can change preferred mass range.) Heather Logan (Carleton U.) LHC Phenomenology Physics In Collision 2011 11 LHC Higgs channels: focus on SM, low-mass range W=ZH; H b¯b ! H ττ H b¯b ! ! H ZZ H ττ !4` ! ! H ZZ H γγ !4` ! ! H WW H γγ !`ν`ν ! ! H WW ! combined ATLAS-CONF-2011-135 CMS PAS HIG-11-022 (LP2011) Not yet done: VBF H ττ;WW;ZZ;γγ; ttH; H bb; γγ; W W ; W H; H γγ ! ! ! ! Heather Logan (Carleton U.) LHC Phenomenology Physics In Collision 2011 12 Low-mass range most interesting for extracting Higgs couplings. - Ratios of rates give ratios of partial widths. - Add theory assumption: hW W; hZZ SM fit Higgs coups. ≤ ) 1 g2(H,Z) (H,X) 2 2 (H,X) 2 g (H,W) g g 0.9 ∆ g2(H,τ) g2(H,b) 0.8 g2(H,t) 0.7 ΓH without Syst. uncertainty 0.6 2 Experiments -1 L dt=2*300 fb 0.5 ∫ WBF: 2*100 fb -1 0.4 0.3 0.2 0.1 0 110 120 130 140 150 160 170 180 190 mH [GeV] 1 1 [L] 200 fb− (except 300 fb− for ttH( bb), WH( bb)). Zeppenfeld, hep-ph/0203123 [R] D¨uhrssen,Heinemeyer, H.L., Rainwater,! Weiglein! & Zeppenfeld, hep-ph/0406323 Plus input from Tevatron at low end of mass range? Heather Logan (Carleton U.) LHC Phenomenology Physics In Collision 2011 13 Measure tensor structureTensor stru ofctHVVure ofcouplingthe HVV incou VBF:pling µν Most general HVV vertex T (q1, q2) g Physical interpretation of terms: µ µ q q q q q µ q1 V 1 H H SM Higgs I HVµV a1 q L ∼ −→ q2 V 2 Q QQ Q ν ν (a) (b) loop induced couplings for neutral scalar µν CP even HVµν V a Le f f ∼ −→ 2 Tµν = a gµν + 1 ˜ µν µ CP odd e f f HVµν V a3 a q q gµν qνq + L ∼ −→ 2 1 · 2 − 1 2 εµνρσ a3 ! q1ρq2σ " Must distinguish a1, a2, a3 experimentally The ai = ai(q1, q2) are scalar form factors Slide from D. Zeppenfeld, plenary talk at SUSY'06 conference Dieter Zeppenfeld Higgs Bosons at the LHC 27 Heather Logan (Carleton U.) LHC Phenomenology Physics In Collision 2011 14 HVV vertex structureSignals fo givesr CP v differentiolation in distributionsthe Higgs Se inctojjr azimuthal angle ∆φ: 0.009 CP-even, CP-odd 0.008 CP-even mixed CP case: 0.007 CP-odd a = a , a = 0 jj 2 3 1 0.006 SM Δφ 0.005 / d pure CP-even case: σ d 0.004 σ a2 only 1/ 0.003 0.002 pure CP odd case: 0.001 a3 only 0 -160 -120 -80 -40 0 40 80 120 160 Δφjj Figy, Hankele, Kl¨amke, & Zeppenfeld, hep-ph/0609075; plot for MH = 120 GeV Position of minimum of ∆φjj distribution measures relative size of CP-even and CP-odd couplings. For µ HV Vµ structure is \smoking gun" for Higgs mechanism EWSB. a1 = 0, a2 = d cosα, a3 = d µνsinα, Check for CP violation and/or loop-induced HV Vµν structure. = CanMaxim alsoa at α useand αH π ZZ; W W lepton distributions. ⇒ ±! Heather Logan (Carleton U.) LHC Phenomenology Physics In Collision 2011 15 Why expect more than just SM Higgs: The Hierarchy Problem The Higgs mass-squared parameter µ2 gets quantum corrections that depend quadratically on the high-scale cutoff of the theory. × M t t T Calculate radiative corrections T T from, e.g., a top quark loop. ! ! ! ! H t t H H T T H 2 = 2 + ∆ 2 H H µ µ0 µ !"T a) t b) T c) -------- MT For internal momentum p, large compared to mt and external h momentum: d4p i i Diagram = ( )N Tr iλ iλ (2 )4 c t t Z π − " p= p=# d4p 1 = N λ2 Tr Tr [1] = 4 c t (2 )4 2 − Z π "p # 4N λ2 d4p = c t (2 )4 2 − π Z p Momentum cutoffΛ: Integral diverges likeΛ 2. Heather Logan (Carleton U.) LHC Phenomenology Physics In Collision 2011 16 Full 1-loop calculation gives 2 2 Ncλt 2 2 ∆µ = 2Λ + 6m ln(Λ=mt) + 16π2 − t ··· h i 2 2 2 4 2 We measure µ (MEW) (100 GeV) = 10 GeV . ∼ −O ∼ − 2 − Nature sets the bare parameter µ0 at the cutoff scale Λ. 1 18 2 35 2 If Λ = MPl = 10 GeV, then∆ µ 10 GeV ! p8πGN ∼ ∼ − - Not an inconsistency in the theory. 2 Renormalizable: absorb the divergence into the bare parameter µ0. 2 - But it is an implausibly huge top-down coincidence that µ0 and ∆µ2 cancel to 31 decimal places! Looks horribly fine-tuned.
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