Searches for Higgs and BSM physics with ATLAS

Searches for Higgs and BSM physics with ATLAS

Osamu Jinnouchi(Tokyo Institute of Technology)

KIAS Pheno Workshop2011/11/16-19

contents

(1) The ATLAS experiment at LHCquick overview of the 2010/2011 data

2011/11/17-19 ATLAS / JINNOUCHI 2

(2) Search for the Standard Model Higgs boson Analysis strategy Search channels ATLAS Combined results

(3) Search for physics beyond the Standard Model Look for new particle resonances Look for specific signatures based on supersymmetry Look for exotic signatures

(4) Conclusion

in This Talk

• Look into two major topics in the LHC physics i.e. • Mass and EW symmetry breaking (Higgs)• Hierarchy puzzles at TeV scale (BSM)

• These are “Searches”, therefore they have to be based on the good control over the BG• heavily rely on

• the trigger and detector performance • the large number of ATLAS SM measurements • MCs finely tuned with data

• many analysis use the data-driven estimates of BG • measurement in the data control region, transfer it to

the signal region with the help of MC


LHC (pp) runs in 2010 and 2011

• In 2010• First 7TeV pp collisions started • 48 pb-1 pp collisions delivered (45pb-1 recorded by ATLAS)

• In 2011 (pp run finished at Oct 30.)• Peak luminosity 3.65 x 1033cm-2s-1 • ATLAS : 5.2(5.6) fb-1 data recorded(delivered)• ATLAS data taking efficiency : ~ 93.5% (over the year)• 1380 bunches, 50nsec spacing, 1.5E11 p/ bunch


LHC will run in 2012then long shutdown / willrestart at higher energy

2010

Log

scal

e

2011 Line

ar s

cale

ATLAS detector• Gigantic general purpose detector with well balanced

performance on resolutions and high hermetic acceptance • Emphasis on lepton measurements with excellent magnets

• 2T central solenoid for inner tracker• Air core Toroid magnet (less MS + forward acceptance)

for outer muon system• Accordion shape LAr EM calorimeters for

fine lateral + longitudinal EM shower shape


Tracking 2 Silicon systems + Transition radiation trackerEM Calo sampling LAr caloHAD Calo plasti scintilator (barrel) + LAr (endcap)Muon trigger chambers (RPC, TGC) + precision chambers (MDT, CSC)

• Hadron Calorimeter is fully hermetic and thickness is ~ 30 X0

good jet/missing ET resolution

Trigger and data taking performance

• Flexible trigger menu:• definition continuously updated

along the luminosity evolvement through the year

• primary unprescaled triggers in 2011 for 3x1033cm-2s-1 menu • electrons: pT>22GeV

• muons: pT>20GeV

• jets: pT>240GeV

• etmiss: pT>60GeV

• combinatory menu for low pT

• Data taking and quality • efficiency ~ 93.5% • single detector operational

fraction > 97%


High luminosity = Pile up: the new challenge in 2011

• most of 2011 data, 50nsec bunch trains running at LHC• in-bunch & out-of-bunch pile-up effects need to be taken into account • MC superimposes reweighted MB events to reproduce data


Z with 20 reconstructed vertices 𝜇𝜇 mean # collisions6.3 11.6 (after reducing beam size)


Mass and EW symmetry breaking

HIGGS

Theoretical and indirect exp. Higgs constraints

• in the Standard Model, Higgs must be light • However in the BSM, Higgs can be heavy must also search for a heavy Higgs boson


Perturbativity and (meta) stability bounds versus the SM cut-off scale L EW fit not including direct Higgs searches

J. Ellis et al., arXiv:0906.0954

http://cern.ch/gfitter

theory narrow venue if it is to survive up to Planck scale

indirect meas. prefer low mass95% CL upper limit : 170GeV

Higgs search strategy at LHC

• multi-channel combined analysis is required

• expected cross sections are in any case below “a few pb”

• integrated luminosity and BG rej. are the two important factors

• light Higgs• 𝛾𝛾 final state• 𝜏𝜏 final state• lepton final states via WW*,ZZ*

•heavy Higgs• lepton final states via WW(*),ZZ(*)


Dependence of the branching fractions on MH drives search strategy

General search strategy Cut & Count based analysis

• trigger • (changing along the luminosity evolution)

• event Selection • Object definition (leptons, jets, missing ET, ...)

• Specific event selection and acceptance definition• Collision event selection (common method)

• background evaluation• Mostly data driven methods

• count events in background enhanced control regions (CR)• extrapolation to signal region (SR) based on MC or data

• for each value of MH, likelihood fit of data with one or more variablesConfidence Interval based on CLS method on = /𝜇 𝜎 𝜎SM

• finally, channel combination Confidence Intervals for vs. M𝜇 H2011/11/17-19 ATLAS / JINNOUCHI 11

(1) H : the low mass “golden channel”𝛾𝛾• low cross-section (<0.1pb) but very

clean signature with limited BG

• photon identification based on calorimeter segmentation• narrow energy cluster | |𝜂• small leakage into HCal• cut on shower shape,

discriminating from jets, , 𝛾 𝜋 𝜂• photon isolation energy criterion to

reduce jet background • reduce fragmentation component• sum of transverse energy in ∆R

cone (=0.4) around 𝛾• corrections event by event

• remove leakage from into cone𝛾• remove energy from pileup & UE


S2 (“middle”)

S1 (“strip”)pre-sampler

S3 (“back”)

PP

𝜸PP

𝝅0

(1) H : the low mass “golden channel”𝛾𝛾• trigger :

• 2 photons with ET>20GeV

• selection: • two isolated “photons”

ET1>40GeV, ET

2>25GeV

• di-photon inv. mass 100-160GeV• backgrounds:

• di-photon (irreducible) 72%• photon + jet (rej.needed ~ 104)• di-jets (rej.needed ~ 107)

• discriminant variable • m𝛾𝛾 (resolution ~ 1.7GeV)

• fit with• BG: exponential• signal : CrystalBall function


No signal found set upper limits on for 𝜇range 110<MH<150GeV

signal x 5

(2) HWW(*)2 (e, )+2 𝓁 𝜇 𝜈• Not clean but with large x Br 𝜎 : the best channel at intermediate mass

• highest sensitivity for 130< MH<200GeV

• signatures : • two leptons

• W polarization : correlated lepton emission opening angle is a discriminant

• missing Et : Higgs mass not reconstructed • count events in signal region heavily rely on the BG estimation

• “limited“ jet activityLook into 0 and 1 jet channels

• Backgrounds: • WW production (irreducible)• top pair production• single top • Z + jets


∂

∂

(2) HWW(*)2 (e, )+2 𝓁 𝜇 𝜈• Selection:

• 2 opposite sign isolated high-pT leptons (20,15)GeV• missing ET > 30 GeV• topological cuts on lepton system (mll, pT

ll, ∆𝜙ll)• transverse mass : 0.75xMH < mT < MH

• different background composition in 0 and 1 jet channels


jet : anti-kT R=0.4 pT>25GeV | |<4.5, b-tag veto𝜂

1-jet0-jet

data

/mc

entri

es /

10G

eV

no signal found set upper limits on for range 𝜇150<MH<300GeV

trigger : single leptonpT(e)> 20-22GeV or pT( )>18GeV𝜇

(3) H ZZ(*)4 : the “golden” channel𝓁• very clean signature (4 , 4e, 2 2e) 𝜇 𝜇 with good sensitivity in the full mass range• trigger : single lepton pT(e)>20-22GeV or pT( )>18GeV𝜇• selection :

• 4 isolated leptons : 2 with pT > 20Gev, 2 with pT>7GeV

• two pairs of same flavour opposite sign leptons• M12 within MZ±15GeV, 115GeV>M34> 15-60GeV (depends on M4l)

• backgrounds : • ZZ (dominant irreducible) • Z + jets (electron channel), Zbb (muon channel)


count the events after the selectionand compare with the BG estimate

no signal found set upper limits on 𝜇for range 110<MH<600GeV

PLB705(2011)435


4 candidate event with M𝜇 4l =143.5GeV (M12=90.6GeV, M34=47.4GeV)

Limits on ATLAS Higgs boson searches

• Upper limits on the cross section divided by the SM Higgs boson production cross section (i.e. ) as a function of m𝜇 H

• 95% C.L. limit on for all channels (frequentist CL𝜇 S method)

• solid lines : observed limit (data)• dashed lines : expected limit (based on MC pseudo-experiments)


Observed Limit > Expected Limit more data than SM prediction (vice versa)

Limits on ATLAS Higgs boson searches (combined)


• Upper limits on the cross section divided by the SM Higgs boson production cross section (i.e. ) as a function of m𝜇 H

• 95% C.L. limit on for all channels (frequentist CL𝜇 S method)

• solid lines : observed limit (data)• dashed lines : expected limit (based on MC pseudo-experiments)

2010 data (35pb-1)

EPS results(July, 1-1.2 fb-1)

Most recent results(August, 1-2.3 fb-1)

ATLAS excludes SM higgs boson @ 95% C.L. in three mass region : 146<MH<232GeV, 256<MH<282GeV,296<MH<466GeV

LEP

Teva

tron

SM Higgs searches : conclusions

• ATLAS has performed a Higgs search with 1~2.3 fb-1 pp data using various channels

• Shown here only part of major search channels• No significant excess found so far in the mass range 110-600GeV• Exclusion limit at 95% C.L. set in the range

• 146 < MH < 232 GeV

• 256 < MH < 282 GeV

• 296 < MH < 466 GeV

• There will be an update of ATLAS-CMS combined results today presented at HCP (during this afternoon)

• BSM Higgs not covered : Fermiophobic H , MSSM H𝜸𝜸 , 𝞃𝞃charged H+, H++

• Significant updates expected for winter conference with 5 fb-1 then definitive answer should be obtained by the end of 2012 with O(10fb-1) data



Hierarchy puzzles at TeV scale

Beyond the Standard Model

Let’s start with .... summary of BSM searches


• O(3000) authors a huge number of interesting channels covered• limits go up to 0.5 ~ 1.5 TeV, progressing with larger data stats• exceeding Tevatron results in many places• the published data (up to summer 2011) found no “significant excess” yet so far

Were our search strategies optimal?

Two experimental approaches for “unknown”

(1) Search for new particles / phenomena via model independent approach

• Cross section (and many other observables) measurements of Standard Model processes, compared to theory prediction

• Search the “peaks” or “excess” in mass distributions, or in many other kinetic observables

(2) Search for specific signatures corresponding to well defined BSM physics models

• Supersymmetry, Extra Dimensions, etc • search strategy should be model-independent as

much as possible within the framework



(1)search for new particles

model independent approach

Cross section measurements compared to SM predictions • compared to the predictions evaluated at NLO or more• good agreements over 4 orders of magnitude, indicating followings

• No surprise observed ... • SM prediction is still applicable at 7TeV era • Detector performance extrapolated to high energy regime works fine


σxBR(ZZ4l)~40fb

Measuring cross-sections down to a few pb (~40fb including BR)

Search for Z’ boson in di-leptons (ee or )𝜇𝜇• simple/robust analysis : search a peak in a di-lepton invariant mass spectrum


e+e- channel

𝜇+𝜇- channel

model independent upper limits on x Br𝜎as a function of the mass of the new vector boson

model dependent lower limits on the Z’ mass:• SSM: m(Z’)> 1.83TeV @ 95% C.L.• RS graviton: m(G*)>1.64TeV @ 95% C.L.

arXiv: 1108.1582

Search for W’ boson in lepton + neutrino (e or )𝜈 𝜇𝜈• search for a “Jacobian” peak in a transverse mass spectrum

2011/11/17-19 ATLAS / JINNOUCHI 27ν

model independent upper limits on x Br𝜎as a function of the mass of the new vector boson

model dependent lower limits on the W’ mass:• SSM: m(W’)> 2.15TeV @ 95% C.L.

e+ channel𝜈

𝜇+ channel𝜈

Di-jet mass and angular distributions

• motivated by many models : excited quarks, contact interactions, axigluons, ...• search for jet-jet resonances in di-jet events, look for a peak in the Mjj spectrum


new way to express the difference to MCsignificance in Z instead of rel. difference

1.0fb-1 36fb-1

36fb-1

with this variable , one expects peak 𝛘around 1 for heavy resonant particle (back to back jets)

Di-jet mass and angular distributions

• motivated by many models : excited quarks, contact interactions, axigluons, ...• search for jet-jet resonances in di-jet events, look for a peak in the Mjj spectrum


model dependent mass lower limit (1fb-1): excited quarks : M(q*) > 2.99TeV axigluons: M(A) > 3.32TeV color octet scalar : M(S) > 1.92TeV

new way to express the difference to MCsignificance in Z instead of rel. difference

1.0fb-1 36fb-1


(2)searching model specific signature

SUSY

Search for new physics in the context of SUSY

• Typical event topology : cascade decay + stable LSP from R-parity large ET

miss and multi-jet/leptons


examples of strong ( ) productions

incomplete event reconstruction

no peak & evidence will be at tail of distribution

understanding of backgrounds (top, W/Z+jets, QCD) is the highest priority from experiment

is used MC(Z/W/top)/Data(QCD) normalizedto data in the region sensitive to each BG

believe MC shape to transferfrom CR to SR

BG prediction

Control Region

Signal Region

Background estimate [1]: QCD multi-jets, Z+jets

• QCD : huge cross section x high rejection at event selection + large theoretical uncertainty data driven estimate necessary

• CR is obtained by requiring ∆ (jet, E𝜙 T

Miss)min < 0.4

• Pythia6 (+MRST2007LO*) is used


• Z( )+jets : 𝜈𝜈• CR is Z (ee/ ) + jets 𝜇𝜇• P(ee/ ) is added to E𝜇𝜇 T

Miss toreproduce Meff

• ALPGEN (+CTEQ6L1) is used

QCD Z+jets

Background estimate [2]: W+jets, tt+jets

W/tt control region (MT = 30 ~100GeV, ETMiss >130GeV)

separate two components via b-tagging • b-tag veto : enhancing W+jets • with b-tag : enhancing tt + jets• ALPGEN (+CTEQ6L1) is used for W+jets• MC@NLO(+CTEQ6.6) is used for tt + jets• extremely important to understand the shape of large Meff


W+jets tt+jets

Meff search with no-lepton (1.04 fb-1)

• Leading jet pT>130GeV, ETMiss>130GeV)

• ∆𝜙(jet, ETMiss)min > 0.4 　


arXiv:1109.6572

4jet channel • 2-4 jets pT > 40GeV• ET

Miss/Meff > 0.25• Meff > 1000GeV

• data = 40 • SM = 33.9±2.9±6.2 (Z=16.2/W=13.0/tt=4.0/QCD=0.7)

4jet high-mass channel • 2-4 jets pT > 80GeV• ET

Miss/Meff > 0.20• Meff > 1100GeV

• data = 18• SM = 13.1±1.9±2.5 (Z=3.3/W=2.1/tt=5.7/QCD=2.1)

Jet energy scale (~4%)Theoretical error (depends onchannel) dominates

consistent with SM, thoughthere are some candidates events. hope to keep watching for high stats

Meff search with 1-lepton (1.04 fb-1)

Selections:

• Electron (pT>25GeV) or Muon (pT>20GeV)

• jet pT(1) > 60GeV, jet pT(2-4) >40GeV

• ETMiss/Meff > 0.15, ET

Miss>200GeV

• Meff > 500GeV


Matrix method for QCD: 1) define “loose” and “tight” leptons 2) assess efficiency for real and fake leptons 3) use data with “loose leptons” to estimate data with “tight”

Non QCD: use MT to separate signal from background

Muon Channel• data = 7• SM = 6.0±2.7 (tt=4.7/W/Z=1.4/QCD=0.0)

Electron Channel• data = 9• SM = 8.0±3.7 (tt=4.5/W/Z=3.5/QCD=0.0)

electron

muon

consistent with SM

Interpretation


0-lepton (4jet 1.04fb-1, 6jet 1.34fb-1) :

1-lepton case (1.04fb-1):

4-jet

6-jet

95% C.L. exclusion range in MSUGRA/CMSSM param. plane

800 GeV

700 GeV

800 GeV

900 GeV800 GeV

600 GeV

1400 GeV1000 GeV

as a result of several different assumptions/topologies studied we learnt that squarks and gluinos are not light ... or cannot be found with the simple model

𝛾𝛾 + missing ET channel

• Sensitive to GMSB (or UED) models• Bino is NLSP, two high-pT photons in the

final state, gravitinos create high Missing ET

• Minimal Gauge Mediation (MGM) model, where one mass scale for the symmetry breaking and messenger mass determine the mass hierarchy (bench mark point : SPS8)

• General Gauge Mediation (GGM) Recent analysis relaxes the constraint on mass hierarchy between gluinos and neutralinos

• No excess observed yet (1.07fb-1), set the limit on gluino mass• GGM: Mgluino > 776GeV

• MGM (SPS8): >145TeV 𝛬2011/11/17-19 ATLAS / JINNOUCHI 37

2011/11/17-19 38

(2’)even more specific signatures

SUSY

• EW gaugino production • 2 leptons + missing • multi-leptons + missing

• 3rd generation light squarks • direct prodcution• from gluino decays

• RPV • resonant sneutrino• displaced vertex

• special final status• disappearing (or kink) track• stable massive particle• .... etc, etc

resonant sneutrino

disappearing (or kink) track

ATLAS looks for many directions other than ordinary strong production

RPV search

• exactly 1 electron and 1 muon (opposite sign)• BG are SM processes with emu final state • Z/ *𝛾 , ttbar, single top, WW, WZ, ZZ𝞃𝞃• also from instrumental backgrounds with fake

leptons


look for

experiments usually assume only and

No significant deviation from SM expectations

arXiv:1109.3089

D0 is competitive in low mass region

scalar tau neutrino search at 1 fb-1

excluded m𝜈<1.32 TeV ( ’𝝀 311=0.10,λ312=0.05)

Search for disappearing (kinked) tracks

• AMSB: almost degenerate and • chargino long lived, decays inside tracking volume • pion is soft, looks like disappearing of the tracks• BG: interaction with TRT, mismeasured low pT tracks


Concluding remarks

• ATLAS has recorded/analyzed good amount of data(no excuse for “we just started...” phrase anymore)

• keep updating the exclusion limits in many area

• Search for the SM Higgs boson• large area unveiled, can expect for significant updates by

winter conferences• Search for the beyond-SM phenomena

• large number of analysis performed• exclusion reach updated in many channels• establishing analysis frameworks, better understanding

on systematics faster production on results(paper factory mode)

• No big surprise yet Let’s hope they are just around the corner !

2011/11/17-19 ATLAS / JINNOUCHI 41!! good luck with 2011 & 2012 data !!

EXTRA SLIDES


　


Search for stable long lived and

• new meta-stable particles features in many BSM scenarios• Sleptons would interact with detector as slow moving muons• or e-charged/neutral, color singlet bound state R-hadrons


Pixel dE/dx Bethe-Bloch 𝛽Tile HadCal timing 𝛽

ATLAS Data Quality


luminosity weighted fraction of good quality dataduring LHC stable beam runs, L=2.33fb-1 (3/13-8/13)

as of 2011/10/05

Operational fractions very high(> 97%)

high good quality data (>98% except LAr)

Upgrade & long shutdown (LS) plan (as of today)

• LS1: 2013 – 2014 shutdown 24month physics-to-physics• Machine : mainly splices consolidation and repairs• ATLAS : IBL, Pixel new SQP, new LVPS for tile/lar, FTK, etc....

• RUN : 2015-2017 • √s ~ 13-14TeV, β*=0.55m, L~1x1034 ~50fb-1

• LS2: 2018 shutdown (Phase-I): ~1 year• Machine : injectors (LINAC4) and collimators • ATLAS : L1 trigger (topological, more granular), Muon Small Wheels, etc

• RUN : 2018-2021• L~2x1034 300fb-1

• LS3: 2022-2023 shutdown (Phase-II): ~2years • Machine : new inner triplets, crab cavities• ATLAS : new tracker, new calorimeter electronics,

new FCAL, etc• RUN : 2024 -

• L~5x1034 up to 3000fb-1


ATLAS Trigger performance

• High level trigger menu : software based, continuous update with luminosity

• 3x1033cm-2s-1 menu • Prescaled triggers

• Electrons pT>22GeV• Muons pT>20GeV• Jets pT>240GeV• EtMiss > 60GeV• (Di)photons pT> 80(20)GeV

• 5x1033cm-2s-1 menu • Even tighter menus planned


electrons

MuonsJets

Data preparation and computing

• Raw data are reconstructed at Tier-0 site (CERN) within 2days• Calibration and data quality performed for physics analysis • Data are ready for analysis on the grid within a week• Up to 800k jobs/day are processed on Tier-1 and Tier-2 sites

• Analysis, Simulation, Reprocessing, various productions


Full number of ATLAS jobs per day

2011.03 2011.07

analysis

simulation

kT and anti-kT Jet algorithms


advanced b-taggings •


for QCD jet events: fraction of light jets incorrectly tagged as b-jetsis substantially reduced with the advanced taggers

ATLAS detector performance in 2010• Inner detector

• momentum scale known to 1% level (<100GeV) • reconstruction eff > 99% (muons > 20GeV)• material distribution known better than 10% (goal is 5%)

• EM Calorimeter• scale uniformity ~2% in eta, <0.7% in phi (goal is < 1%)• energy scale known to < 1% (goal is 0.1%)• electron ID efficiency known with ~1% precision

• HAD Calorimeter• Jet energy scale uncertainty 4~5% (goal is 1%)• missing Et : good MC/data agreement

no tail from instrumental origin after calibration with 15M minbias• MUONS

• momentum scale known to 1%• momentum resolution known to rel. 10%• reconstruction eff known to 1-2% (goal is 1%)

• Trigger / Data GRID transfer• Luminosity 2010 (Van der Meer scan)

• final uncertainty 3.2% (most of the papers used the previous estimation 11%)


Rate (2010/ design)Bunch crossing: 1MHz/40MHzLevel-1: 20kHz / 75kHzLevel-2: 3.5kHz / 2kHzEF: 300Hz / 200HzGRID: 1-4GB/s / 2GB/s

ATLAS calorimeter and inner detectors


Documents

Searches for Higgs and BSM physics with ATLAS