# ATLAS Results M. Cobal, INFN & University Udine PART II XXIV SEMINARIO NAZIONALE

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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

1Why Mtop and MW are interesting?2Mtop , MW and EW precision measurements = cross check of SM and constrain MH

EW fit dominating uncertainties: Mtop and MW

For MW not to be the dominant error in the EW fit:

MW 0.007Mtop

2EWK fit3

Private communication M. Grunewald:

adding mH=125 2 GeV to the EWK fit:gives 2 / Ndf = 17.95 / 14, Prob = 20.9%Extending the concept to a BSM framework,On the left, comparison of the Standard Model prediction of the W boson mass for varying values of theHiggs boson mass compared to the direct measurement. The previous world average, prior to the measurementspresented in this note, is marked by the dashed ellipse. The green band is a purely experimental exclusion anddoes not include limits from perturbative unitarity.3Key SM background processes4

The typical analysis 5Design 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.The typical plot6Analyses 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 ().

Expected sensitivity: measures how performing is the analysis

The colored bands give the expected statisticalsystematic variation of the result wrt to the expectedNearby points are correlated depending on the mass resolution

The observed (full line) and expected (dashed line) 95% CL combined upper limits on the SM Higgs boson production cross section divided by the Standard Model expectation as a function of mH in the full mass range considered in this analysis. The dashed curves show the median expected limit in the absence of a signal and the green and yellow bands indicate the corresponding 68% and 95% intervals. 6H gg7

Composition of gg sample:

75-80% QCD gg production 20-25% g-jet or jet-jet, jet mis-ID eg due to hard p0Separation of g-po in Lar Calog pointing to locate primary vertexEvent display of a diphoton event candidate where both photon candidates are unconverted. The event number is 56662314 and it was recorded during run 203779 at sqrt(s) = 8 TeV. The leading photon has eT = 62.2 GeV and eta = 0.39. The subleading photon has eT = 55.5 GeV and eta = 1.18. The measured diphoton mass is 126.9 GeV. The pT and pTt of the diphoton are 9.3 GeV and 6.5 GeV, respectively. Only reconstructed tracks with pT > 1 GeV, hits in the pixel and SCT layers and TRT hits with a high threshold are shown. 7H gg8

1) The distributions of the invariant mass of diphoton candidates after all selections for the combined 7 TeV and 8 TeV data sample. The inclusive sample is shown in a) and a weighted version of the same sample in c); the weights are explained in the publication. The result of a fit to the data of the sum of a signal component fixed to mH = 126.5GeV and a background component described by a fourth-order Bernstein polynomial is superimposed. The residuals of the data and weighted data with respect to the respective fitted background component are displayed in b) and d).

2) Expected and observed local p0 values for a SM Higgs boson as a function of the hypothesized Higgs boson mass mH for the combined analysis and for the sqrt(s)=7 TeV and sqrt(s)=8 TeV data samples separately. The observed p0 including the effect of the photon energy scale uncertainty on the mass position is included via pseudo-experiments and shown as open circles.

The local probability p0 for a background-only experiment to be more signal-like than the observation in the full mass range of this analysis as a function of mH. The 8H ZZ* 4 leptons (e,m) 9

Golden channel: few events but small background. Good mass resolution

1) The distribution of the four-lepton invariant mass, m_4l, for the selected candidates compared to the background expectation for the 80-250 GeV mass range for the (a) sqrt{s}=8 TeV, (b) sqrt{s}=7 TeV and (c) combined datasets. Error bars represent 68.3% central confidence intervals. The signal expectation for several m_H hypotheses is also shown

2) The observed local p0 for the combination of the 2011 and 2012 datasets (solid black line); the sqrt{s}=7 Tev and sqrt{s}=8 Tev data results are shown in solid lines (blue and red, respectively). The dashed curves show the expected median local p0 for the signal hypothesis when tested at the corresponding m_H. The horizontal dashed lines indicate the p0 values corresponding to local significances of 1sigma, 2sigma, 3sigma and 4sigma. 9H WW* enmn10

Transverse mass (mT) distribution in the H + 0 jet (a, b) and H + 1 jet (c, d) channels, for events satisfying all criteria. The plots on the left (a, c) show the events with a subleading muon, and the plots on the right (b, d) show the events with a subleading electron. The expected signal for a SM Higgs boson with mH = 125 GeV is added on top of the estimated total background. The W+jets background is estimated directly from data and WW and top backgrounds are scaled to use the normalisation derived from the corresponding control regions described in the text. The hashed area indicates the total uncertainty on the background prediction.

2) Observed (solid line) probability for the background-only scenario, p0, as a function of mH, for the combined 7 TeV and 8 TeV data. The dashed line shows the corresponding expectation for the mH = 125 GeV hypothesis. (b) Observed (solid) and expected (dashed) 95% CL upper limits on the cross section, normalised to the SM Higgs boson production cross section and as a function of mH, over the full mass range considered in the 7 and 8 TeV combined data. Due to the excess of events observed in the low mass signal region, the corresponding mass points cannot be excluded as expected. The results at neighbouring mass points are highly correlated due to the limited mass resolution in this final state. The green and yellow regions indicate the 1 sigma and 2 sigma uncertainty bands on the expected p0/limit, respectively. 10Combined Significance11

1) Combined search results: The observed (solid) 95% CL upper limit on the signal strength as a function of mH and the expectation (dashed) under the background-only hypothesis. The dark and light shaded bands show the plus/minus one sigma and plus/minus two sigma uncertainties on the background-only expectation. Combined search results: The observed (solid) local p0 as a function of mH and the expectation (dashed) for a SM Higgs boson signal hypothesis (mu = 1) at the given mass. Combined search results: The best-fit signal strength muhat as a function of mH. The band indicates the approximate 68% CL interval around the fitted value.

2) The observed (solid) local p0 as a function of mH in the low mass range. The dashed curve shows the expected local p0 under the hypothesis of a SM Higgs boson signal at that mass with its plus/minus one sigma band. The horizontal dashed lines indicate the p-values corresponding to significances of 1 to 6 sigma.

11P-value evolution adding modes12

gg and ZZ combo only5 s excess (expect 4.7 s)Is it a boson: yes, significance from di-photon channelAdding WW5.1 s excess (expect 5.2 s)All channels together4.9 s excess (expect 5.9 s)Significance of the p-value13 5.9 (ATLAS) and 4.9 (CMS) excess

Impressive consistency between 7TeV and 8TeV data

The LHC discovery14

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 fromThe LHC discovery15ATLAS and CMS: significance driven by the , ZZ and WW channels

Besides the excess at 125-126 GeV: 95% CL exclusion of a SM-like Higgs up to ~600 GeV

Characterisation of the excess in the H ZZ() 4, H and HWW() channels and the combination of all channelslisted in Table 6. The mass value mmax for which the local significance is maximum, the maximum observed local significance Zl and the expectedlocal significance E(Zl) in the presence of a SM Higgs boson signal at mmax are given. The best fit value of the signal strength parameter atmH = 126 GeV is shown with the total uncertainty. The expected and observed mass ranges excluded at 95% CL (99% CL, indicated by a *) arealso given, for the combined s = 7 TeV and s = 8 TeV data.15Properties of the new boson16Mass

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-interactionSignal strenght

3) Measurements of the signal strength parameter mu for mH=126 GeV for the individual channels and their combination. 17Mass vs Signal strenght18Mass compatibility between different channels estimated with 2D likelihood, fitting simultaneously and mH in each channel

Probability that a single boson produces mass peaks in H and H4l separated by more than the amount observed is 20%

Mass measurement: performed using profile likelihood ratio with mH floating (channels used: H and H4l with separate parameters)

Main systematics from energy scale

expected precision at the LHC: ~100 MeVexpected precision at a linear collider: 40-50 MeVConfidence intervals in the (mu, mH ) plane for the H to ZZ(*) to 4l, H to gamma gamma, and H to WW(*) to l nu l nu channels, including all systematic uncertainties. The markers indicate the maximum likelihood estimates (muhat, mHhat ) in the corresponding channels (the maximum likelihood estimates for H to ZZ(*) to 4l and H to WW(*) to l nu l nu coincide).

shows the 1-sigma contours for the different final states: the WW measurement is the one which extends the most in the horizontal axis, because of the large indetermination in the mass due to the escaping neutrino pair. 18JP 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 JP: by end of 8 TeV run, assuming 35/fb per exp: ~4 separation of 0+ vs 0- and 0+ vs 2+

CP: more tricky, basic question of possible mixture of CP-even and CP-oddIf focus at LHC stays on WW*, ZZ* and VBF: limited sensitivity to distinguish pure CP-even state from admixture CP-even / CP-oddLinear collider: threshold behaviour of e+e-ttH gives precision measurement of CP mixing.

arXiv:1208.4018v1 [hep-phJP: LHC 2012 prospects

for 35/fb per exp.Expected hypotheses separation significance versus signal observation significance for the SM Higgs boson versus 0(left) and 2+m (right) hypotheses. Points show two luminosity scenarios tested with generated experiments and expectationsare extrapolated linearly to other significance scenarios. Dashed lines indicate what might be expected with 35 fb1 of data atone LHC experiment.19Projections 20coupling 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 accessible at the 20% level, with a HL-LHC

Higgs self-coupling(double-Higgs production): currently under study.3/exp possible at HL-LHC, and 30% prec. on HHH possible if more channels added and exps. combined

Expected hypotheses separation significance versus signal observation significance for the SM Higgs boson versus 0(left) and 2+m (right) hypotheses. Points show two luminosity scenarios tested with generated experiments and expectationsare extrapolated linearly to other significance scenarios. Dashed lines indicate what might be expected with 35 fb1 of data atone LHC experiment.20I 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.

Astrophysics observations: - Neutrino oscillations - Dark matter - Dark Energy

The standard model problems: - Higgs NO unitarity violation New interactions to cancel this amplitude; - Higgs YES hierarchy problem for the higgs mass

Beyond the SM21

Pf < L

Supersymmetry22

Minimal MSSM23

Minimal Supersymmetric Standard Model24

ATLAS SUSY strategySearch in every corners of the SUSY phase space

Status of SUSY searches1. Inclusive searches2. Natural SUSY3. Long lived particles4. RPVMinimal Supersymmetric Standard Model

SUSY theory phase spaceMSSM: 29 sparticles+5 Higgs undiscovered

Goal: find hints of (N)MSSM particles in the 100 GeV 1 TeV rangeStatus of exotic searches

ConclusionsProbed 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-1Direct sbottom & stopGluino mediated stop/sbottomDirect 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.