atlas results m. cobal, infn & university udine part ii xxiv seminario nazionale
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ATLAS Results M. Cobal, INFN & University Udine PART II XXIV SEMINARIO NAZIONALE di FISICA NUCLEARE E SUBNUCLEARE OTRANTO, Serra degli Alimini, 21 -27 Settembre 2012. Why M top and M W are interesting?. - PowerPoint PPT PresentationTRANSCRIPT
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ATLAS ResultsM. Cobal, INFN & University Udine
PART IIXXIV SEMINARIO NAZIONALE
di FISICA NUCLEARE E SUBNUCLEARE
OTRANTO, Serra degli Alimini,
21-27 Settembre 2012
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Why Mtop and MW are interesting?
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Mtop , MW and EW precision measurements = cross check of SM and constrain MH
EW fit dominating uncertainties: ΔMtop and ΔMW
For ΔMW not to be the dominant error in the EW fit:
ΔMW 0.007∼ ΔMtop
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EWK fit
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Private communication M. Grunewald:
adding mH=125 ± 2 GeV to the EWK fit:- gives χ2 / Ndf = 17.95 / 14, Prob = 20.9%
Extending the concept to a BSM framework,
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Key SM background processes
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The typical analysis
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• Design a selection at a given mass maximizing an estimator (eg s/√bkg). Often cutting the phase-space in many regions
• Compute the expected SM background from control samples, side bands, etc.. also with the help from MC simulation (shapes). Assess the systematic error.
• Evaluate the signal efficiency using SM Higgs MC simulation
• Compute with statistical methods the largest signal cross section one can accommodate in the data.
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The typical plot
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• Analyses optimized for exclusion.The result is expressed at a given mass as exclusion at 95% of a cross section
• The excluded cross section is computed in unit of SM cross section (μ).
• Expected sensitivity: measures how performing is the analysis
• The colored bands give the expected statistical⊕systematic variation of the result wrt to the “expected”
• Nearby points are correlated depending on the mass resolution
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H → gg
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Composition of gg sample:
• 75-80% QCD gg production• 20-25% g-jet or jet-jet, jet mis-ID eg due to hard p0
Separation of g-po in Lar Calo• g pointing to locate primary vertex
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H → gg
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H → ZZ*→ 4 leptons (e,m)
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Golden channel: few events but small background. Good mass resolution
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H → WW*→ enmn
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Combined Significance
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Significance of the p-value
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• 5.9 (ATLAS) and 4.9 (CMS) σ excess
• Impressive consistency between 7TeV and 8TeV data
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The LHC discovery
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Heinemeyer et al,Implications of LHC results for TeV-scale physics: signals of electroweak symmetry breaking,Submitted to the Open Symposium of the European Strategy Preparatory Group.
A=ATLASC=CMS√ = channel analyzed
most of the LHC sensitivity comes from
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The LHC discovery
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ATLAS and CMS: significance driven by the γγ, ZZ and WW channels
Besides the excess at 125-126 GeV: 95% CL exclusion of a SM-like Higgs up to ~600 GeV
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Properties of the new boson
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• Mass
• spin and parity ( JP )
• CP (even, odd, or admixture?)
• couplings to vector bosons: is this boson related to EWSB, and how much does it contribute to restoring unitarity in WLWL scattering
• couplings to fermions- is Yukawa interaction at work?- contribution to restoring unitarity?
• couplings proportional to mass ?
• is there only one such state, or more?
• elementary or composite?
• self-interaction
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Signal strenght
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Mass vs Signal strenght
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• Mass compatibility between different channels estimated with 2D likelihood, fitting simultaneously μ and mH in each channel
• Probability that a single boson produces mass peaks in H→γγ and H→4l separated by more than the amount observed is 20%
• Mass measurement: performed using profile likelihood ratio with mH floating (channels used: H→γγ and H→4l with separate μ parameters)
• Main systematics from energy scale
expected precision at the LHC: ~100 MeVexpected precision at a linear collider: 40-50 MeV≾
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JP and CPSTATUS AND QUESTIONS:
• decay to two photons: cannot be spin 1 (Landau-Yang theorem)
• JP: currently tested at the LHC, using angular correlations in ZZ*, WW* and γγ
• JP: by end of 8 TeV run, assuming 35/fb per exp: ~4 σ separation of 0+ vs 0- and 0+ vs 2+
• CP: more tricky, basic question of possible mixture of CP-even and CP-odd
• If focus at LHC stays on WW*, ZZ* and VBF: limited sensitivity to distinguish pure CP-even state from admixture CP-even / CP-odd
• Linear collider: threshold behaviour of e+e-→ttH gives precision measurement of CP mixing.
arXiv:1208.4018v1 [hep-ph
JP: LHC 2012 prospects
for 35/fb per exp.
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Projections
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coupling scale factors:5-10% with 300/fb at 14 TeV
ratios of partial widths: 5-30%, for luminosities up to 3/ab
very rare channels H→μμ accessible at the 20% level, with a HL-LHC
Higgs self-coupling(double-Higgs production): currently under study.3σ/exp possible at HL-LHC, and 30% prec. on λHHH possible if more channels added and exps. combined
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1. I The fundamental symmetries:
Are there more general symmetries than SU(3)C SU(2)L U(1)Y ?
Of course we will be happy to include the gravity in the extend theory.
2. Astrophysics observations:
- Neutrino oscillations
- Dark matter
- Dark Energy
3. The standard model problems:
- Higgs NO unitarity violation
New interactions to cancel this amplitude;
- Higgs YES hierarchy problem for the higgs mass
Beyond the SM
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Pf < L
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Supersymmetry
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Minimal MSSM
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Minimal Supersymmetric Standard Model
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ATLAS SUSY strategy
Search in every corners of the SUSY phase space
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Status of SUSY searches
1. Inclusive searches
2. Natural SUSY
3. Long lived particles
4. RPV
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Minimal Supersymmetric Standard Model
SUSY theory phase space MSSM: 29 sparticles+5 Higgs undiscovered
Goal: find hints of (N)MSSM particles in the 100 GeV – 1 TeV range
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Status of exotic searches
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Conclusions
• Probed a wide variety of SUSY – motivated final states
• Nothing found so far, but developed detailed understanding of BG, prerequisite for a discovery
• Transinioning to targeted searches, optimized for specific well-motivated models (eg: natural SUSY)
• Strong push on naturalness dedicated searches for L=2-4.7 fb-1• Direct sbottom & stop• Gluino mediated stop/sbottom• Direct Gauginos [Also sensitive to direct slepton !]
• Analyses of 8 TeV data are in progress. Expect 20 fb-1 of data by the end of the year.