searches for higgs and bsm physics with atlas
DESCRIPTION
Searches for Higgs and BSM physics with ATLAS. Osamu Jinnouchi (Tokyo Institute of Technology) KIAS Pheno Workshop 2011/11/16-19 . contents. (1) The ATLAS experiment at LHC quick overview of the 2010/2011 data. (2) Search for the Standard Model Higgs boson Analysis strategy - PowerPoint PPT PresentationTRANSCRIPT
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Searches for Higgs and BSM physics with ATLAS
Osamu Jinnouchi(Tokyo Institute of Technology)
KIAS Pheno Workshop2011/11/16-19
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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
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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
2011/11/17-19 ATLAS / JINNOUCHI 3
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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
2011/11/17-19 ATLAS / JINNOUCHI 4
LHC will run in 2012then long shutdown / willrestart at higher energy
2010
Log
scal
e
2011 Line
ar s
cale
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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
2011/11/17-19 ATLAS / JINNOUCHI 5
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
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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%
2011/11/17-19 ATLAS / JINNOUCHI 6
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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
2011/11/17-19 ATLAS / JINNOUCHI 7
Z with 20 reconstructed vertices 𝜇𝜇 mean # collisions6.3 11.6 (after reducing beam size)
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2011/11/17-19 ATLAS / JINNOUCHI 8
Mass and EW symmetry breaking
HIGGS
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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
2011/11/17-19 ATLAS / JINNOUCHI 9
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
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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(*)
2011/11/17-19 ATLAS / JINNOUCHI 10
Dependence of the branching fractions on MH drives search strategy
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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
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(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
2011/11/17-19 ATLAS / JINNOUCHI 12
S2 (“middle”)
S1 (“strip”)pre-sampler
S3 (“back”)
PP
𝜸PP
𝝅0
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(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
2011/11/17-19 ATLAS / JINNOUCHI 13
No signal found set upper limits on for 𝜇range 110<MH<150GeV
signal x 5
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(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
2011/11/17-19 ATLAS / JINNOUCHI 14
∂
∂
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(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
2011/11/17-19 ATLAS / JINNOUCHI 15
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
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(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)
2011/11/17-19 ATLAS / JINNOUCHI 16
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
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2011/11/17-19 ATLAS / JINNOUCHI 17
4 candidate event with M𝜇 4l =143.5GeV (M12=90.6GeV, M34=47.4GeV)
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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)
2011/11/17-19 ATLAS / JINNOUCHI 18
Observed Limit > Expected Limit more data than SM prediction (vice versa)
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Limits on ATLAS Higgs boson searches (combined)
2011/11/17-19 ATLAS / JINNOUCHI 19
• 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
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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
2011/11/17-19 ATLAS / JINNOUCHI 20
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2011/11/17-19 ATLAS / JINNOUCHI 21
Hierarchy puzzles at TeV scale
Beyond the Standard Model
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Let’s start with .... summary of BSM searches
2011/11/17-19 ATLAS / JINNOUCHI 22
• 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?
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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
2011/11/17-19 ATLAS / JINNOUCHI 23
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2011/11/17-19 ATLAS / JINNOUCHI 24
(1)search for new particles
model independent approach
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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
2011/11/17-19 ATLAS / JINNOUCHI 25
σxBR(ZZ4l)~40fb
Measuring cross-sections down to a few pb (~40fb including BR)
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Search for Z’ boson in di-leptons (ee or )𝜇𝜇• simple/robust analysis : search a peak in a di-lepton invariant mass spectrum
2011/11/17-19 ATLAS / JINNOUCHI 26
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
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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
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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
2011/11/17-19 ATLAS / JINNOUCHI 28
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)
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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
2011/11/17-19 ATLAS / JINNOUCHI 29
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
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2011/11/17-19 ATLAS / JINNOUCHI 30
(2)searching model specific signature
SUSY
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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
2011/11/17-19 ATLAS / JINNOUCHI 31
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
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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
2011/11/17-19 ATLAS / JINNOUCHI 32
• 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
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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
2011/11/17-19 ATLAS / JINNOUCHI 33
W+jets tt+jets
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Meff search with no-lepton (1.04 fb-1)
• Leading jet pT>130GeV, ETMiss>130GeV)
• ∆𝜙(jet, ETMiss)min > 0.4
2011/11/17-19 ATLAS / JINNOUCHI 34
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
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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
2011/11/17-19 ATLAS / JINNOUCHI 35
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
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Interpretation
2011/11/17-19 ATLAS / JINNOUCHI 36
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
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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
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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
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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
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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)
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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
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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 !!
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EXTRA SLIDES
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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
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Pixel dE/dx Bethe-Bloch 𝛽Tile HadCal timing 𝛽
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ATLAS Data Quality
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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)
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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
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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
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electrons
MuonsJets
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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
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Full number of ATLAS jobs per day
2011.03 2011.07
analysis
simulation
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kT and anti-kT Jet algorithms
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advanced b-taggings •
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for QCD jet events: fraction of light jets incorrectly tagged as b-jetsis substantially reduced with the advanced taggers
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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%)
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Rate (2010/ design)Bunch crossing: 1MHz/40MHzLevel-1: 20kHz / 75kHzLevel-2: 3.5kHz / 2kHzEF: 300Hz / 200HzGRID: 1-4GB/s / 2GB/s
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ATLAS calorimeter and inner detectors
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