1. Physics at LHC: Selected results from EW sector and news on Run II
E. Richter-Was, Institute of Physics UJ
Results from EW sector:
Higgs Boson couplings (ATLAS & CMS combination)
Standard Model precision measurements
News on Run II
E. Richter-Was, seminarium IFT UW

2. E. Richter-Was, seminarium IFT UW
LHC physics
E. Richter-Was, seminarium IFT UW

3. Higgs boson in Standard Model
Run I of LHC was the run of the Higgs Boson
Rapid transition from searches over discovery to measurement
E. Richter-Was, seminarium IFT UW

4. Higgs boson measurements
Typically divided into
Coupling measurements: measure event counts in various phase-space regions, naturally emerges from searches
Properties measurements: measure quantum numbers and other properties using dedicated analyses
E. Richter-Was, seminarium IFT UW

5. E. Richter-Was, seminarium IFT UW
Mass of Higgs boson
Measured with < 0.2% precision (ATLAS+CMS)
E. Richter-Was, seminarium IFT UW

6. Higgs boson: spin-0 particle, compatible with CP-even
Angular analysis of CMS and ATLAS Run I data rules out spin 2 at 99.9% C. L.
E. Richter-Was, seminarium IFT UW

7. Higgs boson couplings (ATLAS-CONF-2015-044, CMS-PAS-HIG-15-002)
Reach experimental area of Higgs properties: the Higgs couplings strength to other SM particles, e.g.
All coupling strengths predicted by SM, given known
Higgs boson mass
Accessible in various combinations and admixtures, large variety of ATLAS & CMS observed Higgs boson decay rates.
Powerful test of nature of Higgs boson: SM or subtly different?
E. Richter-Was, seminarium IFT UW

8. Higgs bosons – alternatives to the SM Higgs boson
What else could the 125 GeV state be? Many alternative theories exist, for example
Light CP-even h(125) of a Two Higgs double Model (h, H, H+-, A)
Pseudo NG boson from high energy theory (Composite Higgs)
In either case, couplings of BSM h(125) candidate (slightly) different from SM Higgs boson
Goal here is not to pick a specific model – but to develop a generic framework to quantify possible deviations in Higgs couplings from SM
E. Richter-Was, seminarium IFT UW

9. Standard Model Higgs boson decays
The natural width of the Higgs boson is expected to be very small (<< resolution)
E. Richter-Was, seminarium IFT UW

10. Higgs boson production in the SM
E. Richter-Was, seminarium IFT UW

11. Higgs boson production in the SM
E. Richter-Was, seminarium IFT UW

12. Higgs boson production in the SM
Very small SM cross-section due to almost completely destructive interference. For opposite sign W/t Higgs couplings , s(tHqb) increases by factor 13 and s(WtH) by factor 6.
E. Richter-Was, seminarium IFT UW

13. Higgs boson production in the SM
Diagram similar to ttH, but experimentally not really distinguishable from ggF and 100x smaller in SM
E. Richter-Was, seminarium IFT UW

14. Higgs production and decay – input measurements
E. Richter-Was, seminarium IFT UW

15. Signal strength measurements by ATLAS and CMS
Each experiment has O(15) signal strength measurements focusing on the variety of production and decay models.
E. Richter-Was, seminarium IFT UW

16. Signal strength fits of individual measurements
E. Richter-Was, seminarium IFT UW

17. Understanding signal strength
Signal strength m is observed rates normalised to SM predictions
Disentangling production (mi) and decay (uf) always requires assumption of narrow Higgs width
Additional assumptions required when combining measurements
E. Richter-Was, seminarium IFT UW

18. Beyond signal strength – the k framework
Alternatively one can disentangle deviations in production and decay with explicit modeling of Higgs width
Introduce functions ki to describe deviations from SM
E. Richter-Was, seminarium IFT UW

19. Beyond signal strength – the k framework
Parameters kj correspond to LO degrees of freedom
E. Richter-Was, seminarium IFT UW

20. The k framework - the total width
Note that total H width scales all observed cross-sections
Since GH is not yet directly measured with a meaningful precision, must make assumption on GH to interpret cross-sections in terms of Higgs couplings. Eg. in absence of BSM H decays (invisible, undetected, etc.) can assume SM width, adjusted by effect of k-rescaled couplings.
E. Richter-Was, seminarium IFT UW

21. The k framework - the dictionary
E. Richter-Was, seminarium IFT UW

22. The k framework - the dictionary
E. Richter-Was, seminarium IFT UW

23. E. Richter-Was, seminarium IFT UW
Single measurement
Every measurement consists of one or more signal regions designed to select target Higgs production/decay
Distribution of a (multivariate) discriminant is interpreted in terms of sum of signal and background contributions.
E. Richter-Was, seminarium IFT UW

24. Profile likelihood formalism for (systematic) uncertainties
Build likelihood function for each signal, control region of the data.
E. Richter-Was, seminarium IFT UW

25. Profile likelihood formalism for (systematic) uncertainties
Build likelihood function for each signal, control region of the data.
E. Richter-Was, seminarium IFT UW

26. Decomposition of signal contributions in channel
Channels selections hardly ever 100% pure in production process (especially ‚untagged’) -> separately model distributions from all contributing Higgs production processes.
Channels selections hardly ever 100% pure in decay mode (eg. H->WW selection has contribution of H->tt decays) -> Interpret such contributions as Higgs signal (of appropriate type) in coupling analysis.
E. Richter-Was, seminarium IFT UW

27. Measurements of backgrounds often data-driven using control regions
E. Richter-Was, seminarium IFT UW

28. Distributions: subject to systematic uncertainties
Expected distributions mostly derived from simulation chain.
E. Richter-Was, seminarium IFT UW

29. Profiled likelihood formalism for (systematic) uncertainties
Extended description of each signal/background distribution so that it can describe distribution under a wide range of parameters for which the true values are unknown (energy scales, QCD scales…)
E. Richter-Was, seminarium IFT UW

30. Profiled likelihood formalism for (systematic) uncertainties
Correlate parameters as needed between channels, experiments
E. Richter-Was, seminarium IFT UW

31. Correlated uncertainties in ATLAS/CMS combination
Full combination describes ~580 signal regions & control regions from both experiments. Grand total of ~4200 nuisance parameters, related to (systematic) uncertainties.
Correlation strategy of nuisance parameters a delicate and complicated task:
Detector systematic uncertainties: generally correlated within, not between experiments
Signal theory uncertainties (QCD scales, PDF, UEPS) on inclusive cross-sections: generally correlated between experiments
Signal theory uncertainties on acceptance and selection efficiency: uncorrelated between experiments
PDF uncertainties on signal cross-sections: uncorrelated between experiments
E. Richter-Was, seminarium IFT UW

32. Signal strength fits of individual measurements
E. Richter-Was, seminarium IFT UW

33. The global signal strength
Assuming SM ratios of production cross-sections and decay rates
E. Richter-Was, seminarium IFT UW

34. Higgs signal strength by production and decay mode
E. Richter-Was, seminarium IFT UW

35. Signal strength in V, F – mediated production by decay
Measure ggF+ttH production „fermion mediated” and VBF+VH production „boson mediated” for each decay mode
E. Richter-Was, seminarium IFT UW

36. Constraints for Higgs couplings to fermions, bosons
Assume universal scaling parameters for Higgs couplings to fermions (kF), bosons (kV), resolved loops, only SM physics in loops, no invisible Higgs decays, kF,V ≥ 0)
E. Richter-Was, seminarium IFT UW

37. Constraints for Higgs couplings to fermions, bosons
Expanding parameter range to include negative couplings
E. Richter-Was, seminarium IFT UW

38. Constraints on tree-level Higgs couplings
Assume only SM physics in loops, no visible Higgs decays
Fit for scaling parameters for Higgs couplings to W, Z, b, t, t, m
NB: low measured value of kb reduces total width GH => all ki measured low [w.r.t m=1.09]
E. Richter-Was, seminarium IFT UW

39. Constraints on tree-level Higgs couplings
E. Richter-Was, seminarium IFT UW

40. Allowing for BSM contributions in Higgs coupling interpretations
Results shown so far assumed no invisible (BSM) Higgs decays nor BSM contributions to loops. Now drop these assumptions.
Represent loop processes (ggF, H->Z/gg) with effective parameters (kg,kg), rather than assuming SM content
2. Allowing BSM Higgs decays (invisible, undetected etc…) to increase the total width
E. Richter-Was, seminarium IFT UW

41. Limit on invisible Higgs decays from Higgs couplings
Concept: set limit on BR to (invisible, undetected) Higgs decays
Scenario 1: - Assume 6 tree-level couplings at SM (k=1) but 2 effective loop couplings floating
Scenario 2: - Keep all 6+2 coupling parameters floating, but bound vector boson couplings kW,kZ ≤ 1
E. Richter-Was, seminarium IFT UW

42. Focus on effective couplings for loop processes
Fix all tree-level Higgs couplings to SM (kW,kZ,kb,kt,km,kt=1) and BRinv = 0
E. Richter-Was, seminarium IFT UW

43. Constraints on Higgs couplings allowing BSM physics in loops & decays
E. Richter-Was, seminarium IFT UW

44. Generic parametrizations
Goal of (most) generic parametrizations is to provide summary of Higgs coupling while make minimal number of assumptions and with minimal exposure to theory uncertainties
Most generic model is signal strength model with ratios.
Choose ggF H->ZZ as reference channel since it is the cleanest channel and has the smallest systematic uncertainty.
Ratios of cross-sections and BRs reduce exposure to dominant theoretical uncertainties on inclusive cross-sections
E. Richter-Was, seminarium IFT UW

45. Signal strength models with ratios
E. Richter-Was, seminarium IFT UW

46. Alternatively, measure ratio of couplings strengths
No assumption on Higgs total width needed, as GH cancels in all expressions.
E. Richter-Was, seminarium IFT UW

47. E. Richter-Was, seminarium IFT UW
Summary
ATLAS and CMS Higgs boson coupling results have been combined, sensitivity on signal strength improved by almost sqrt(2)
Higgs to tt and VBF production established at more than 5s level
The most precise results on Higgs production and decay and constraints on its couplings have been obtained at O(10%) precision.
Different parametrisations have been studied, all consistent with the SM predictions within uncertainties
SM p-value of all combined fits in range of 10%-88%
E. Richter-Was, seminarium IFT UW

48. Run I electro-weak measurements
E. Richter-Was, seminarium IFT UW

49. Electroweak measurements at LHC
EWK production
Three-boson
VVV
Di-boson VV
E. Richter-Was, seminarium IFT UW

50. E. Richter-Was, seminarium IFT UW
VBS ssWW production
First evidence for Vector-Boson-Scattering based on use of same-sign WW final state
Essential to experimentally probe the nature of the EWSB, flagship analysis for Run 2 and beyond!
In Run 1 both ATLAS and CMS has sensitivity for first evidence
Observed (Expected) significance: ATLAS 3.6s (2.8s) , CMS 1.9s (2.9s)
Experimental signatures:
Dilepton +MET + 2 jets
Combination of „EWK” and „QCD” (O(as2aEW4))
E. Richter-Was, seminarium IFT UW

51. E. Richter-Was, seminarium IFT UW
VBS ssWW production
E. Richter-Was, seminarium IFT UW

52. E. Richter-Was, seminarium IFT UW
VBS ssWW: aQGC limits
E. Richter-Was, seminarium IFT UW

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54. E. Richter-Was, seminarium IFT UW
Data with Run II
E. Richter-Was, seminarium IFT UW

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59. E. Richter-Was, seminarium IFT UW
BACKUP
E. Richter-Was, seminarium IFT UW

60. Focus on up/down-type fermion and lepton/quark asymmetries
Several BSM physics models (notably 2HDM), predicts asymmetries in couplings between up-type and down-type fermion couplings, and between lepton and quarks couplings
Since goal is to measure asymmetry, directly parametrize model in terms of rations and coupling strength modifiers.
Assume no BSM physics in loop processes. No assumption on invisible decays needed, since no assumption on GH needed (total width cancels in ratio of couplings)
E. Richter-Was, seminarium IFT UW

61. Focus on up/down-type fermion and lepton/quark asymmetries
Several BSM physics models (notably 2HDM), predicts asymmetries in couplings between up-type and down-type fermion couplings, and between lepton and quarks couplings
E. Richter-Was, seminarium IFT UW

62. Higgs coupling model with ratios
E. Richter-Was, seminarium IFT UW

63. Higgs coupling model with ratios
E. Richter-Was, seminarium IFT UW

64. Statistical treatment - profile likelihood
From L(ATLAS+CMS) construct the profile likelihood for a statement on the parameter(s) of interest a
68% confidence interval defined by z rise of 1 unit in L(a) (asymptotic limit)
E. Richter-Was, seminarium IFT UW

65. Specific model II: resolved loops, no BSM
E. Richter-Was, seminarium IFT UW

66. Electroweak measurements at LHC
Electroweak sector of the SM based on SU(2)xU(1) gauge group, that is non-Abelian
-> Triple and quartic gauge couplings
Measurements:
VBF/VBS: observation and evidence
Di-boson and three-boson measurements
Measurements require complex analyses (syst. limited)
Run 1 more to offer before Run 2 takes over
Challenges also for theorists, clearly need for precise predictions
E. Richter-Was, seminarium IFT UW