Exploring new physics at the LHC

Transcription

1 Goethe-Universität Frankfurt, January 12th 2011 Exploring new physics at the LHC Michael Krämer (RWTH Aachen) 1 / 46

2 Goethe-Universität Frankfurt, January 12th 2011 Exploring new physics at the LHC Michael Krämer (RWTH Aachen) Entering the Terascale: from electroweak symmetry breaking to new physics The search for supersymmetry at the LHC: from exclusions to (hopefully!) discovery Backup: the quest for the Higgs 1 / 46

3 Summary of new physics searches at the LHC so far but 2011/12 is going to be exciting! 2 / 46

4 Physics at the Terascale Need large energies to resolve small structures: wavelength = hc/energy produce heavy particles: mass = energy/c 2 3 / 46

5 Physics at the Terascale Need large energies to resolve small structures: wavelength = hc/energy produce heavy particles: mass = energy/c 2 Standard unit: 1 electron volt (ev) = kinetic energy gained by electron accelerated through potential difference of 1 volt. A single atom is such a small thing that to talk about its energy in joules would be inconvenient. But instead of taking a definite unit in the same system, like J, [physicists] have unfortunately chosen, arbitrarily, a funny unit called an electronvolt (ev)... I am sorry that we do that, but that s the way it is for the physicists. (Richard Feynman, in a 1961 recorded lecture.) Terascale: tera electron volt = ev resolution m 1/10000 proton radius Note: natural units in particle physics: set = c = 1 [mass] = 1/[length] = 1/[time] = ev 3 / 46

6 Physics at the Terascale The standard model Lagrangian is determined by symmetries L SM = 1 4 F µνf a aµν + i ψdψ gauge sector +ψ i λ ij ψ j H + h.c. flavour sector + DH 2 V (H) EWSB sector +N i M ij N j ν-mass sector 4 / 46

7 Physics at the Terascale The standard model Lagrangian is determined by symmetries L SM = 1 4 F µνf a aµν + i ψdψ gauge sector +ψ i λ ij ψ j H + h.c. flavour sector? + DH 2 V (H) EWSB sector? +N i M ij N j ν-mass sector EWSB in the SM Higgs boson: experimentally not confirmed 5 / 46

8 Physics at the Terascale The standard model Lagrangian is determined by symmetries L SM = 1 4 F a µνf aµν + i ψdψ gauge sector +ψ i λ ij ψ j H + h.c. flavour sector? + DH 2 V (H) EWSB sector? +N i M ij N j ν-mass sector EWSB in the SM Higgs boson: experimentally not confirmed from unitarity: M H < (8π 2/3G F ) 1/2 1 TeV (precision tests & direct searches: 110 GeV < M H < 200 GeV in SM) 5 / 46

9 Physics at the Terascale The standard model Lagrangian is determined by symmetries L SM = 1 4 F a µνf aµν + i ψdψ gauge sector +ψ i λ ij ψ j H + h.c. flavour sector? + DH 2 V (H) EWSB sector? +N i M ij N j ν-mass sector EWSB in the SM Higgs boson: experimentally not confirmed from unitarity: M H < (8π 2/3G F ) 1/2 1 TeV (precision tests & direct searches: 110 GeV < M H < 200 GeV in SM) Higgs boson or alternatives are to be found around 1 TeV 5 / 46

10 Physics at the Terascale The standard model Lagrangian is determined by symmetries L SM = 1 4 F a µνf aµν + i ψdψ gauge sector +ψ i λ ij ψ j H + h.c. flavour sector? + DH 2 V (H) EWSB sector? +N i M ij N j ν-mass sector EWSB in the SM Higgs boson: experimentally not confirmed from unitarity: M H < (8π 2/3G F ) 1/2 1 TeV (precision tests & direct searches: 110 GeV < M H < 200 GeV in SM) Higgs boson or alternatives are to be found around 1 TeV SM Higgs mechanism: not dynamical & Higgs mass instable EWSB & the Higgs physics beyond the standard model 5 / 46

11 Physics at the Terascale The Large Hadron Collider LHC: exciting times have started! 6 / 46

12 The hierarchy problem: why is M Higgs M Planck Masses are affected by quantum fluctuations: m 2 H,phys. = m 2 H,0 + δm 2 H Quantum corrections to the Higgs mass δm 2 H quadratic UV divergencies cutoff Λ represents the scale up to which the SM remains valid need Λ of O(1 TeV) to avoid fine-tuning in mh,phys. 2 = m2 H,0 + α Λ2 < (1 TeV)2 7 / 46

13 The hierarchy problem: why is M Higgs M Planck Masses are affected by quantum fluctuations: m 2 H,phys. = m 2 H,0 + δm 2 H Quantum corrections to the Higgs mass δm 2 H quadratic UV divergencies cutoff Λ represents the scale up to which the SM remains valid need Λ of O(1 TeV) to avoid fine-tuning in mh,phys. 2 = m2 H,0 + α Λ2 < (1 TeV)2 The new physics needs to stabilize the Higgs mass M Higgs < 1 TeV decouple from electroweak precision tests ( discrete R/KK/T-parity) discrete symmetry new stable particles dark matter candidates 7 / 46

14 The hierarchy problem: why is M Higgs M Planck Masses are affected by quantum fluctuations: m 2 H,phys. = m 2 H,0 + δm 2 H Quantum corrections to the Higgs mass δm 2 H quadratic UV divergencies cutoff Λ represents the scale up to which the SM remains valid need Λ of O(1 TeV) to avoid fine-tuning in mh,phys. 2 = m2 H,0 + α Λ2 < (1 TeV)2 Popular new physics models that address the hierarchy problem Supersymmetry Extra dimensions Little Higgs models Technicolour all predict a spectrum of new particles at the TeV-scale and provide DM candidate(s)! 8 / 46

15 Physics beyond the Standard Model at the LHC Many new physics models are addressing two problems: the hierarchy/naturalness problem the origin of dark matter spectrum of new particles at the TeV-scale with weakly interacting & stable particle ( discrete parity) 9 / 46

16 Physics beyond the Standard Model at the LHC Many new physics models are addressing two problems: the hierarchy/naturalness problem the origin of dark matter spectrum of new particles at the TeV-scale with weakly interacting & stable particle ( discrete parity) generic BSM signature at the LHC: cascade decays with E T,miss 9 / 46

17 Supersymmetry Symmetry between fermions and bosons: Q boson = fermion Q fermion = boson with algebra {Q α, Q β } = (σµ ) αβ P µ SUSY is the only possible symmetry between fermions and bosons need to introduce superpartners to standard model particles 10 / 46

18 Supersymmetry Symmetry between fermions and bosons: Q boson = fermion Q fermion = boson with algebra {Q α, Q β } = (σµ ) αβ P µ SUSY is the only possible symmetry between fermions and bosons need to introduce superpartners to standard model particles SUSY protects the Higgs mass from large radiative corrections: δmh 2 α π (m2 F m2 F ) no fine-tuning if m < O(1 TeV) 10 / 46

19 Supersymmetry Symmetry between fermions and bosons: Q boson = fermion Q fermion = boson with algebra {Q α, Q β } = (σµ ) αβ P µ SUSY is the only possible symmetry between fermions and bosons need to introduce superpartners to standard model particles SUSY protects the Higgs mass from large radiative corrections: δmh 2 α π (m2 F m2 F ) no fine-tuning if m < O(1 TeV) SUSY allows for coupling unification, radiative EWSB, dark matter (assuming R-parity), / 46

20 The Minimal Supersymmetric extension of the SM (MSSM) The MSSM particle spectrum 11 / 46

21 SUSY searches Where are we now? indirect searches through quantum fluctuations direct searches at colliders LHC weather forecast: the first phase 2011/12 exclusion: pushing limits discovery: first steps towards parameter determination 12 / 46

22 SUSY searches Where are we now? indirect searches through quantum fluctuations direct searches at colliders LHC weather forecast: the first phase 2011/12 exclusion: pushing limits discovery: first steps towards parameter determination 13 / 46

23 Indirect SUSY searches Current data cannot constrain general SUSY models Consider the cmssm: model with universal scalar and fermion sparticle masses M 0 and M 1/2 at the GUT scale 14 / 46

24 Indirect SUSY searches Current data cannot constrain general SUSY models Consider the cmssm: model with universal scalar and fermion sparticle masses M 0 and M 1/2 at the GUT scale low scale masses RG evolution high scale parameters GeV SPS1a m Ql (µ 2 2 +m Hd ) 1/2 M 3 M 2 M 1 m Er (µ 2 2 +m Hu ) 1/2 SOFTSUSY log 10 (µ/gev) 14 / 46

25 Indirect SUSY searches Wealth of precision measurements from B/K physics, (g 2), astrophysics (DM) and collider limits constraints on certain SUSY masses e.g. through anomalous magnetic moment (g 2) 15 / 46

26 Indirect SUSY searches Wealth of precision measurements from B/K physics, (g 2), astrophysics (DM) and collider limits global fit of constrained SUSY models global fits point to light sparticle spectrum with m < 1 TeV 16 / 46

27 SUSY searches Where are we now? indirect searches through quantum fluctuations direct searches at colliders LHC weather forecast: the first phase 2011/12 exclusion: pushing limits discovery: first steps towards parameter determination 17 / 46

28 SUSY searches at hadron colliders: the players Fermilab s Tevatron: p p collider with 1.96 TeV cms energy ( ) 18 / 46

29 SUSY searches at hadron colliders: the players CERN s LHC: pp collider with 7-14(?) TeV cms energy ( ?) 19 / 46

30 SUSY particle production at hadron colliders SUSY particles would be produced copiously at hadron colliders via QCD processes, eg. 20 / 46

31 SUSY particle production at hadron colliders SUSY particles would be produced copiously at hadron colliders via QCD processes, eg. SUSY signal Tevatron σ( q q + g g + g q) 0.1 pb (M q, g 400 GeV) 20 / 46

32 SUSY particle production at hadron colliders SUSY particles would be produced copiously at hadron colliders via QCD processes, eg. SUSY signal LHC σ( q q + g g + g q) 100 pb (M q, g 500 GeV) 21 / 46

33 Direct SUSY searches: current mass limits CDF Run II Preliminary -1 L=2.0 fb 600 Theoretical uncertainties included observed limit 95% C.L. in the calculation of the limit expected limit mass limits (roughly) (GeV/c M~ q ) UA1 UA2 FNAL Run I LEP A 0 =0, tanβ=5, µ<0 M q ~ = M g ~ no msugra solution M g M q M gluino M t 1 M χ 0 1 M χ ± 1 M sleptons > 250 GeV > 400 GeV > 100 GeV > 50 GeV > 100 GeV > 100 GeV M 2 (GeV/c ) g ~ 22 / 46

34 Direct SUSY searches: current mass limits CDF Run II Preliminary -1 L=2.0 fb 600 Theoretical uncertainties included observed limit 95% C.L. in the calculation of the limit expected limit mass limits (roughly) (GeV/c M~ q ) UA1 UA2 FNAL Run I LEP A 0 =0, tanβ=5, µ<0 M q ~ = M g ~ no msugra solution M g M q M gluino M t 1 M χ 0 1 M χ ± 1 M sleptons > 250 GeV > 400 GeV > 100 GeV > 50 GeV > 100 GeV > 100 GeV M 2 (GeV/c ) g ~ Note: CMSSM searches do not provide generic SUSY mass limits M g < 200 GeV or/and even M χ GeV possible 22 / 46

35 Direct SUSY searches: theory input SUSY mass limits from comparison of experimental cross section limits and theory prediction: CDF Run II Preliminary -1 L=2.0 fb Theoretical uncertainties not included NLO Cross Section [pb] in the calculation of the limit 10 NLO: PROSPINO CTEQ6.1M syst. uncert. (PDF Ren.) observed limit 95% C.L. expected limit 95% C.L M g ~ = M q ~ M 2 [GeV/c ] g ~ need precise cross section prediction 23 / 46

36 Direct SUSY searches: theory input Perturbative cross section predictions involve unphysical scales σ = F non pert. (µ) ( C 0 αs B (µ) + C 1 (µ)αs B+1 (µ) +... ) pert. from the factorization of IR and the renormalization of UV contributions need to include higher-order corrections 24 / 46

37 Direct SUSY searches: theory input Perturbative cross section predictions involve unphysical scales σ = F non pert. (µ) ( C 0 αs B (µ) + C 1 (µ)αs B+1 (µ) +... ) pert. from the factorization of IR and the renormalization of UV contributions need to include higher-order corrections Scale dependence σ (pp g g + X) [fb] s = 14 TeV µ0 = m q = m g = 1 TeV LO NLO NLO+NLL µ/µ0 σ < ±10% at NLO+NLL [Beenakker, Brensing, MK, Kulesza, Laenen, Motyka, Niessen] / 46

38 Direct SUSY searches: first LHC results! first LHC results already exceed Tevatron limits 25 / 46

39 SUSY searches Where are we now? indirect searches through quantum fluctuations direct searches at colliders LHC weather forecast: the first phase 2011/12 exclusion: pushing limits discovery: first steps towards parameter determination 26 / 46

40 Direct SUSY searches at the LHC: expected limits The LHC will probe the preferred region of SUSY parameter space soon 27 / 46

41 Direct SUSY searches at the LHC: expected limits But what if we do not see any SUSY signal at the LHC? 28 / 46

42 Direct SUSY searches at the LHC: expected limits What if we do not see any SUSY signal at the LHC? ( include cross section info into fit by adding χ 2 = ) S S+B [Bechtle, Desch, Dreiner, MK, O Leary, Robens, Sarrazin, Wienemann, preliminary] 29 / 46

43 Direct SUSY searches at the LHC: expected limits What if we do not see any SUSY signal at the LHC? ( include cross section info into fit by adding χ 2 = ) S S+B [Bechtle, Desch, Dreiner, MK, O Leary, Robens, Sarrazin, Wienemann, preliminary] D 95% CL, LO xs, 2fb -1 1D 68% CL, LO xs, 2fb 1400 M 12 (GeV) M 0 (GeV) 29 / 46

44 Direct SUSY searches at the LHC: expected limits What if we do not see any SUSY signal at the LHC? ( include cross section info into fit by adding χ 2 = ) S S+B [Bechtle, Desch, Dreiner, MK, O Leary, Robens, Sarrazin, Wienemann, preliminary] Particle Mass [GeV] Mass Spectrum of SUSY Particles LO xs, 2 fb σ Environment 2σ Environment Best Fit Value h 0 0 A H 0 H + 0 χ χ 0 χ 0 χ 0 χ + + χ ~ l R ~ l L τ 1 τ 2 q ~ q ~ R L 1 b ~ b ~ ~ t 2 1 ~ t 2 g ~ 30 / 46

45 SUSY searches Where are we now? indirect searches through quantum fluctuations direct searches at colliders LHC weather forecast: the first phase 2011/12 exclusion: pushing limits discovery: first steps towards parameter determination 31 / 46

46 Direct SUSY searches at the LHC: parameter determination Mass measurements from cascade decays, e.g. 32 / 46

47 Direct SUSY searches at the LHC: parameter determination Mass measurements from cascade decays, e.g. kinematic endpoints sensitive to masses: (m 2 ll) max = (m 2 χ 0 2 m2 l R )(m 2 l R m 2 χ 0 1 )/m2 l R (m 2 qll) max = (m 2 q L m 2 χ 0 2 )(m2 χ 0 2 m2 χ 0 1 )/m2 χ 0 2 (m 2 ql,min) max = (m 2 q L m 2 χ 0 2 )(m2 χ 0 2 m2 l R )/m 2 χ 0 2 (m 2 ql,max) max = (m 2 q L m 2 χ 0 2 )(m2 lr m 2 χ 0 1 )/m2 lr 32 / 46

48 Direct SUSY searches at the LHC: parameter determination CMSSM fit using Fittino [Bechtle, Desch, Wienemann] 7 TeV & 10 fb 1 : kinematic edges + cross sections 33 / 46

49 Direct SUSY searches at the LHC: parameter determination CMSSM fit using Fittino [Bechtle, Desch, Wienemann] 7 TeV & 10 fb 1 : kinematic edges + cross sections [Dreiner, MK, Lindert, O Leary] (GeV) M m 0 = 99 ± 9 GeV m 1/2 = 250 ± 7 GeV (GeV) M 1/2 2 0 first determination of model parameters possible inclusion of cross sections is crucial 33 / 46

50 Direct SUSY searches at the LHC: parameter determination CMSSM fit using Fittino [Bechtle, Desch, Wienemann] 7 TeV & 10 fb 1 : kinematic edges + cross sections [Dreiner, MK, Lindert, O Leary] (GeV) M m 0 = 99 ± 9 GeV m 1/2 = 250 ± 7 GeV (GeV) M 1/2 2 0 first determination of model parameters possible inclusion of cross sections is crucial work in progress: consider non-minimal SUSY models and non-susy BSM scenarios 33 / 46

51 Conclusions? Too early yet... composite Higgs? SUSY? extra dimensions??? black holes? LHC 2011/12 34 / 46

52 Thanks for your attention! and thanks to... my students/postdocs/collaborators on the work presented: Philip Bechtle, Wim Beenakker, Silja Brensing, Klaus Desch, Herbi Dreiner, Anna Kulesza, Eric Laenen, Jonas Lindert, Irene Niessen, Ben O Leary, Carsten Robens, Björn Sarrazin, Peter Wienemann and my sponsors: SFB/TR 9 Computational Particle Physics, Helmholtz Alliance Physics at the Terascale, BMBF-Theorie-Verbund, Marie Curie Research Training Network Heptools, Graduiertenkolleg Elementarteilchenphysik an der TeV-Skala 35 / 46

53 backup 36 / 46

54 Tevatron SM Higgs searches 37 / 46

55 LHC SM Higgs search projections 95% CL Limit on σ/σ SM 10 1 CMS Preliminary: Oct 2010 Projected 95% CL Limit on σ/σ SM SM TeV TeV TeV TeV TeV Higgs mass, m [GeV/c ] H 38 / 46

56 LHC SM Higgs search projections Significance of Observation (σ) CMS Preliminary: Oct TeV TeV TeV TeV TeV 1 Projected Significance of Observation Higgs mass, m [GeV/c ] H 39 / 46

57 LHC SM Higgs search projections 40 / 46

58 LHC operation / 46

59 BSM parameter determination: spin Use shape of distributions to determine new particle spin (Horsky, MK, Mück, Zerwas, PRD 08) consider charge asymmetry (Barr) A = (dσ/dm ql + dσ/dm ql ) (dσ/dm ql + + dσ/dm ql ) 42 / 46

60 BSM parameter determination: spin Use shape of distributions to determine new particle spin consider charge asymmetry (Barr) A = (dσ/dm ql + dσ/dm ql ) (dσ/dm ql + + dσ/dm ql ) 43 / 46

61 BSM parameter determination: spin Use shape of distributions to determine new particle spin consider charge asymmetry (Barr) A = (dσ/dm ql + dσ/dm ql ) (dσ/dm ql + + dσ/dm ql ) Alternative: consider jet events shapes (MK, Popenda, Spira, Zerwas, PRD 09) spin effects are typically only around 10%, challenging for LHC 44 / 46

62 Indirect searches at the LHC I: virtual effects E.g. MSSM corrections to single W -production (Brensing, Dittmaier, MK, Mück PRD 08) Numerical results: p T,l distribution pp ν l l + (+γ) at s = 14TeV p T,l /GeV SPS1a δ SUSY QCD/% SPS1a δ SUSY EW/% SPS2 δ SUSY QCD/% SPS2 δ SUSY EW/% virtual effects from MSSM corrections are generically small (cf. electroweak precision test) see also virtual SUSY effects in top production (Berge, Hollik, Mösle, Wackeroth) 45 / 46

63 Indirect searches at the LHC II: rare processes E.g. lepton-flavour violating decays τ µµ µ (Giffels, Kallarackal, MK, O Leary, Stahl PRD 08) strongly suppressed in the SM potentially large in many BSM scenarios (SUSY, little Higgs, technicolour,... ) with O(100) events/100 fb 1 discrimate BSM models from differential decay distributions 46 / 46