electroweak precision measurements: today
TRANSCRIPT
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Boost 2014
Particle Physics after LHC Run I
Electroweak Precision Measurements: Today
J. Hewett
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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
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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
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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!
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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
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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
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Measurements at Z-pole § Peak hadronic cross section
§ Total and partial widths
§ Decay ratios
§ Asymmetries
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Top-quark Mass Determination
mt loop predictions since 1990!
EW fits have been proven to be very accurate
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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
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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
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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
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What’s New Since 2005: Theory
R. Kogler
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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
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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
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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
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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
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Fit to W-Boson Mass
1407.3792
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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
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Oblique Precision EW Parameters: 2014
STU fit is now very precise
1407.3792
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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!
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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!
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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!
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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
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The Future: Higgs Coupling Fits
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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
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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
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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