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Page 1: ATLAS  Results M. Cobal, INFN & University  Udine  PART II XXIV  SEMINARIO NAZIONALE

ATLAS ResultsM. Cobal, INFN & University Udine

PART IIXXIV SEMINARIO NAZIONALE

di FISICA NUCLEARE E SUBNUCLEARE

OTRANTO, Serra degli Alimini,

21-27 Settembre 2012

Page 2: ATLAS  Results M. Cobal, INFN & University  Udine  PART II XXIV  SEMINARIO NAZIONALE

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

Page 3: ATLAS  Results M. Cobal, INFN & University  Udine  PART II XXIV  SEMINARIO NAZIONALE

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,

Page 4: ATLAS  Results M. Cobal, INFN & University  Udine  PART II XXIV  SEMINARIO NAZIONALE

Key SM background processes

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Page 5: ATLAS  Results M. Cobal, INFN & University  Udine  PART II XXIV  SEMINARIO NAZIONALE

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.

Page 6: ATLAS  Results M. Cobal, INFN & University  Udine  PART II XXIV  SEMINARIO NAZIONALE

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

Page 7: ATLAS  Results M. Cobal, INFN & University  Udine  PART II XXIV  SEMINARIO NAZIONALE

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

Page 8: ATLAS  Results M. Cobal, INFN & University  Udine  PART II XXIV  SEMINARIO NAZIONALE

H → gg

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Page 9: ATLAS  Results M. Cobal, INFN & University  Udine  PART II XXIV  SEMINARIO NAZIONALE

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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Page 12: ATLAS  Results M. Cobal, INFN & University  Udine  PART II XXIV  SEMINARIO NAZIONALE

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

Page 13: ATLAS  Results M. Cobal, INFN & University  Udine  PART II XXIV  SEMINARIO NAZIONALE

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

Page 14: ATLAS  Results M. Cobal, INFN & University  Udine  PART II XXIV  SEMINARIO NAZIONALE

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

Page 15: ATLAS  Results M. Cobal, INFN & University  Udine  PART II XXIV  SEMINARIO NAZIONALE

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

Page 16: ATLAS  Results M. Cobal, INFN & University  Udine  PART II XXIV  SEMINARIO NAZIONALE

Signal strenght

Page 17: ATLAS  Results M. Cobal, INFN & University  Udine  PART II XXIV  SEMINARIO NAZIONALE

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≾

Page 18: ATLAS  Results M. Cobal, INFN & University  Udine  PART II XXIV  SEMINARIO NAZIONALE

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.

Page 19: ATLAS  Results M. Cobal, INFN & University  Udine  PART II XXIV  SEMINARIO NAZIONALE

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

Page 20: ATLAS  Results M. Cobal, INFN & University  Udine  PART II XXIV  SEMINARIO NAZIONALE

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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Page 24: ATLAS  Results M. Cobal, INFN & University  Udine  PART II XXIV  SEMINARIO NAZIONALE

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

Page 26: ATLAS  Results M. Cobal, INFN & University  Udine  PART II XXIV  SEMINARIO NAZIONALE

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

Page 27: ATLAS  Results M. Cobal, INFN & University  Udine  PART II XXIV  SEMINARIO NAZIONALE

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.