Post on 21-Jan-2021
20 November 2012 E. Richter-Was 1
Living in incredibly exciting time for fundamental partcile physics!
Najnowsze wyniki eksperymentu ATLAS(CERN, LHC) dla 15 fb-1
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The sucess story so far
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Higgs-like particle: 4-th July
We are living a privileged moment in the history of HEP.
OUR FIRST FUNDAMENTAL SCALAR (?) The discovery came at half of the design energy,
much more several pile-up and one-third of integrated luminosity than was originally judged as necessary.
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Definitions: Global signal strength factor Scale factor on the total number of events predicted by the SM
for the Higgs boson signal: =0 - bgd only hypothesis =1 - SM signal in addition to the bgd Hypothesised values of tested with statistics based on profile
likelihood ratio.
Local p0:
Probability that the background can produce a fluctuation greater than or equal to the excess observed in data. Equivalent in terms of number of standard deviations is called local significance.
95% CLs exclusion: Value of is regarded as excluded at 95%CL when CLs is less
than 5%. A SM Higgs boson with mass mH is conisdered excluded at 95%CL when =1 is exluded at that mass.
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Standard Model Higgs
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Hadron Collider Physics: 12-16 November
Great collections of new results from LHC and Tevatron exp. ->Updates on direct New Phys. searches. ->Precision measurements QCD, W/Z bosons, top physics-indirect New Phys. searches
For the SM Higgs we are entering measurement-based phase.
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ATLAS: update on sensitivity with 13fb-1
The H-> and H->bb channels approaching SM sensitivity, but still compatible with either bgd-only or SM hypothesis.For H->WW channel sensitivity confirmed, significance ~2.6
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H->bb: Diboson production
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ATLAS: update on combination
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Channels entering HCP combination
Couplings measurement not updated for HCP: uncertainies of 20-30%
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Higgs couplings workshop
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Higgs production and decay at LHC
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Higgs production and decay at LHC
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Higgs production and decay at LHC
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Higgs production and decay at LHC
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Higgs production and decay at LHC
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HIGGS landscape
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SUSY
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SUSY
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SUSY
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SUSY
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SUSY
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SUSY
1 TeV
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Rare decays
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Constraints in CMSSM model
At lower tan the relative importance of direct searches increases.
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Exotics
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Exotics
1 TeV
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Parton luminosity
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Parton luminosity
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Global fit to the Standard Model
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W and Z boson physics
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Drell-Yan production at high masses
Starting to challenge NNLO predictions Measurement of
absolute differential cross-section in range [116-1500] GeV
Compared to pQCD at NNLO from FEWZ 3.1 which includes NLO EWK corrections such as photon induced background ->ee process (of the same size as syst. from PDFs and s uncertainties)
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Z/* transverse momenta
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EW physics: Dibosons Measurements crucial
to check the gauge structure of the Standard Model
Cross-section measurements performed in WW, WZ, W, Z and ZZ channels. Results in agreement with SM predictions. Typical precision comparable with size of NLO corrections.
Sensitivity to new physics in most channels: imposing contraints by setting limits on aTGC (anomalous couplings)
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QCD : jet physics
Rates span 10 orders of magnitude
Absolute NLO theory prediction for both shape and normalisation, agreement to within 20% Residual discrepancy consistent with PDF's and perturbative NLO uncertainties Jet properties: fragmentation function, jet shapes, <Nch>, angular
decorelations,... data more precise than theory predictions.
Starting to explore also ratios of 8 TeV/7 TeV which reduces syst. errors.
Should be able to probe Njet ~ 11-12 (pT>60 GeV) by end of 2012
New ideas: subjets within jets
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QCD: V+jets (b-jets)
W+b-jet: exactly 1 b-jet required (+ light jet)
Theory (NLO) consistent within 1.5
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Top physics: mass
Top mass
measurements from different experiments and different techniques agree well within each other.
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Top physics: cross-section
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Top physics: properties
Statistics available at LHC allowed for new and more precise measurements
Spin correlations in to pair production observed
First measurements of top quark polarisation
Precise measurements of W helicity allowed to set stringent limits on the anomalous Wtb couplings
Exotic top-quark charge excluded
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Electroweak production of top quark
For the first time evidence at Tevatron in 2010 ( s+t channel)
It is challenging even for LHC, in particular s-channel observation is a long shot (background)
All diagrams have Vtb vertex
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Electroweak production of top quark
Vtb might stay at 10% precision for some time
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Luminosity colected up to date
Almost 4 x more data with 8 TeV pp available for analysis today: about 20fb-1 recorded
Some channels updated with 12-13fb-1, presented at HCP conference
Next major updates planned for Moriond 2013 …
However still not excluded that new intermediate results will be released for December CERN Counsil week.
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Standard Model: global fitSince then:→ New mW
measurement→ Higgs-like
particle discovery
Moriond 2012
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SM Higgs production at the LHC
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SM Higgs decays
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ATLAS results of 4-th July
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ATLAS results of 4-th July
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ATLAS results of 4-th July
Excess consistent with H-> and H->ZZ*->4l decays
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SM predictions for H->
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H-> event signature
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Shower shapes and vertex reconstr.
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Event categorization
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Energy calibration and resolution
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Invariant mass distribution
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Quantifying the excess
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Signal strenght
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Properties of new resonance
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Since then....... (4-th July)
ATLASThe WW channel completed with 5.8fb-1 and released
end of July, included in the SM Higgs published paper. Low mass channels with decay to WW, bb, updated
with ~13fb-1 (2012) and released for HCP conference.Update on combination for signal strength.
CMSUpdated ZZ, WW, bb, with ~12 fb-1 (2012).Updated combination, couplings and spin.
TevatronUpdate on H->bb analysis with 10fb-1.
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The TEVATRON update
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The TEVATRON update
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ATLAS H->bb: analysis strategy
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H->bb: backgrounds
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H->bb: example flavour fit
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H->bb: systematic uncertainties
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H->bb: mbb distribution (1 lepton)
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H->bb: Diboson production
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H->bb: Expected and observed events
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H->bb: Expected and observed events
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H->: sensitivity not yet reached
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ATLAS: update on combination
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Channels entering HCP combination
Coupling measurement not updated for HCP: uncertainies of 20-30%
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Final comments:
For SM Higgs physics we are shifting from a search-based to a measurement based program. It presents a challenge.
In particular final fitting and fit models undergo much deeper scrutinity and optimisation
→ Enormous numbers of nuisance parameters in the likelihoods require deep understanding of their uncertainties and petential correlations
→ Fitting process itself is very complicated and time consuming
→ Mixture of fitered Monte Carlo and data-driven techniques makes understanding of uncertainties particularly challenging.