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Boost 2014
Particle Physics after LHC Run I
Electroweak Precision Measurements: Today
J. Hewett
The Electroweak Sector of the SM
§ EW sector described by 3 parameters @ tree-level » g,g’ Coupling constants of SU(2)LxU(1)Y » Vacuum expectation value » Weak mixing angle
§ In calculations, trade for the most precisely measured parameters » α: Δα/α = 3x10-10 » GF: ΔGF/GF = 5x10-7 » MZ: ΔMZ/MZ = 2x10-5
Importance of Radiative Corrections § Modify gauge boson propagators and vertices § Parameterize as form factors
ρf, κf, Δr
§ Effective couplings at Z-pole
§ Mass of the W-boson
Importance of Radiative Corrections § Modify gauge boson propagators and vertices § Parameterize as form factors
ρf, κf, Δr
§ Effective couplings at Z-pole
§ Mass of the W-boson Flavor dependent!
Additional Parameters Come Into Play
§ EW form factors ρf, κf, Δr depend on all parameters in the SM
§ EW Sector § GF, MZ, evolution of α to scale µ
§ Fermion masses § mc,b,t
§ Strong sector § αs
§ Higgs sector § mh
Additional Parameters Come Into Play
§ EW form factors ρf, κf, Δr depend on all parameters in the SM
§ EW Sector § GF, MZ, evolution of α to scale µ
§ Fermion masses § mc,b,t
§ Strong sector § αs
§ Higgs sector § mh
Logarithmic dependence
Quadratic dependence
Measurements at Z-pole § Peak hadronic cross section
§ Total and partial widths
§ Decay ratios
§ Asymmetries
Top-quark Mass Determination
mt loop predictions since 1990!
EW fits have been proven to be very accurate
Final Results of Z-pole Measurements
LEPEWWG: Now translated into Haitian Creole and Ukrainian
2005 Physics Reports detailing final results
Global fits now being performed by the Gfitter group
hep-ex/0509008
Final Results of Z-pole Measurements: 2005
0
1
2
3
4
5
6
10030 500mH [GeV]
∆χ
2
Excluded
∆αhad =∆α(5)
0.02758±0.000350.02749±0.00012incl. low Q2 data
Theory uncertainty
Measurement Fit |Omeas−Ofit|/σmeas
0 1 2 3
0 1 2 3
∆αhad(mZ)∆α(5) 0.02758 ± 0.00035 0.02767mZ [GeV]mZ [GeV] 91.1875 ± 0.0021 91.1874ΓZ [GeV]ΓZ [GeV] 2.4952 ± 0.0023 2.4965σhad [nb]σ0 41.540 ± 0.037 41.481RlRl 20.767 ± 0.025 20.739AfbA0,l 0.01714 ± 0.00095 0.01642Al(Pτ)Al(Pτ) 0.1465 ± 0.0032 0.1480RbRb 0.21629 ± 0.00066 0.21562RcRc 0.1721 ± 0.0030 0.1723AfbA0,b 0.0992 ± 0.0016 0.1037AfbA0,c 0.0707 ± 0.0035 0.0742AbAb 0.923 ± 0.020 0.935AcAc 0.670 ± 0.027 0.668Al(SLD)Al(SLD) 0.1513 ± 0.0021 0.1480sin2θeffsin2θlept(Qfb) 0.2324 ± 0.0012 0.2314mW [GeV]mW [GeV] 80.425 ± 0.034 80.389ΓW [GeV]ΓW [GeV] 2.133 ± 0.069 2.093mt [GeV]mt [GeV] 178.0 ± 4.3 178.5
“Blue-band” plot
Final Results of Z-pole Measurements: 2005
10 2
10 3
0.23 0.232 0.234
sin2θlepteff
m H [Ge
V]
χ2/d.o.f.: 11.8 / 5
A0,lfb 0.23099 ± 0.00053
Al(Pτ) 0.23159 ± 0.00041
Al(SLD) 0.23098 ± 0.00026
A0,bfb 0.23221 ± 0.00029
A0,cfb 0.23220 ± 0.00081
Qhadfb 0.2324 ± 0.0012
Average 0.23153 ± 0.00016
∆αhad= 0.02758 ± 0.00035∆α(5)
mt= 178.0 ± 4.3 GeV
Final fit to sin2 ϑeff
This ~3σ discrepancy has haunted us for years
What’s New Since 2005: Theory
R. Kogler
Higgs!! `I Think We Have It’
§ Our shiny new Boson!
[GeV]4lm100 150 200 250
Even
ts/5
GeV
0
5
10
15
20
25
30
35
40
-1Ldt = 4.6 fb∫ = 7 TeV s-1Ldt = 20.7 fb∫ = 8 TeV s
4l→ZZ*→HData 2011+ 2012SM Higgs Boson
=124.3 GeV (fit)H mBackground Z, ZZ*
tBackground Z+jets, tSyst.Unc.
ATLAS
Higgs Boson Mass Determination
1407.3792
Higgs mass predictions since top discovery
Weaker predictions due to log dependence
EW fits have been proven to be very accurate
Global Fit: 2014
1407.3792
• For the first time all observables can be uniquely predicted
• All data agree well with the fit
• Inclusion of mh has modest effects
• Χ2/dof = 18.1/14
The 2014 Electroweak Fit
Fits have been performed with and without the measured Higgs mass
Measured and fitted Higgs mass agree well!
Measured Higgs mass dominates fit
1407.3792
Fit to W-Boson Mass
1407.3792
Oblique Precision EW Parameters
STU parameters designed to “automate” BSM fits to EW data Peskin, Takeuchi ’91
Before Higgs discovery, new physics could hide in mh uncertainties
Oblique Precision EW Parameters: 2014
STU fit is now very precise
1407.3792
The Future: Use Higgs as a Tool for Discovery § Higgs offers unique portal for discovery § Key properties we need to understand » Total width » Couplings to SM particles » Shape of Higgs potential: self-interactions » Is there a CP-odd component? » Do Higgs couplings violate flavor? » How does Higgs interact with neutrinos? » Does the Higgs generate mass for Dark Matter? » How many Higgs Bosons are there? » Is Higgs elementary or composite? » Is the universe in a false vacuum?
Study the Higgs in as much detail as possible!
Higgs Coupling Measurements § Higgs is looking more-or-less SM-like, but
measurements have large errors at present
• tth is 2σ from SM value
• Something to watch!
Fermion/Boson Couplings
• Assume all fermions couple with common strength κF • Assume all bosons couple with common strength κV • No BSM contributions to κγ,g loops
• κF,V ≠ 0 @ > 5σ!
Precision Measurements of Higgs Couplings § Indirect effects of Supersymmetry affects Higgs couplings
§ pMSSM Study: Higgs coupling measurements sensitive to models not accessible to HL-LHC
Cahill-Rowley, JLH, Ismail, Rizzo, 1407.7021
Study Ratio: ΓpMSSM/ΓSM
ττ bb
The Future: Higgs Coupling Fits
Collider Sensitivity to Higgs Self-Coupling
Full ILD detector simulation @ILC with hh to bbbb, bbWW* final states
1310.0763, 1307.5288
bbγγ final state sensitivity/detector More studies needed!
1310.8361 Hadron Colliders
e+e- Colliders
VERY important measurement to determine shape of Higgs potential
Higgs Couplings: Model Independent Approach
§ In a complete analysis all 34 + 25 4-fermion operators need to be considered.
§ Demonstrates the art of choosing a basis
Grzadkowski etal 1008.4884
Summary
§ SM agrees well (too well!) with data § The newly discovered scalar particle agrees with SM
Higgs predictions to the accuracy obtainable so far § No new physics has yet to reveal itself
§ Future prospects » High accuracy Δ(g-2)µ soon underway @FNAL » 13 TeV LHC operations commence next Spring!
• Study Higgs properties to better precision • Improved measurements of MW • Search for new physics
» ILC is on the horizon and will achieve unprecedented precision
• Will write the book on Higgs measurements