Prospects for SUSY at ATLAS and CMS

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Dark Matter Searchesat ATLAS
Dan Tovey University of Sheffield
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ATLAS
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(No Transcript)
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First Astroparticle Data
First cosmic muons observed by ATLAS in the
underground cavern on June 20th 2005 (recorded by
hadron Tilecal calorimeter)
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Event Rates

• Main asset of LHC huge event statistics thanks
  to high ?s and L
• Allows precision measurements/tests of SM
• Searches for new particles with unprecedented
  precision.

Process Events/s
Events per year Total statistics
collected

at previous machines by 2008
W? e? 15
108
104 LEP / 107 Tevatron
Z? ee 1.5
107
107 LEP
tt 1
107
104 Tevatron
bb 106
1012 1013
109 Belle/BaBar?
H m130 GeV 0.02
105 ?
m 1 TeV 0.001
104 ---
Black holes 0.0001
103
--- m gt 3 TeV (MD3 TeV, n4)
L 1033 cm-2 s-1
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Dark Matter _at_ ATLAS

• Characteristic signature for Dark Matter
  production at ATLAS Missing Transverse Energy
  (MET)
• Valid for any DM candidate (not just SUSY)
• Observation of MET signal necessary but not
  sufficient to prove DM signal (DM particle could
  decay outside detector)

c01
MET
Conclusive proof of both existence and identity
of DM by combining LHC data with astroparticle
data

c01
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Complementarity
Polesello et al JHEP 0405 (2004) 071

• Measurements at ATLAS complementary to direct and
  indirect astroparticle searches / measurements
• Uncorrelated systematics
• Measures different parameters

No. MC Experiments
scpsi
Wch2
EDELWEISS
Wch2
log10 (scpsi / 1pb)
CDMS
scpsi (cm2)
DAMA

• Aim to test compatibility of e.g. SUSY signal
  with DM hypothesis (data from astroparticle
  experiments)
• Fit SUSY model parameters to ATLAS measurements
• Use to calculate DM parameters Wch2, mc, scpsi
  etc.

CDMS-II
ZEPLIN-I
CRESST-II
scpsi
ZEPLIN-2
ZEPLIN-4
EDELWEISS 2
GENIUS
XENON
ZEPLIN-MAX
mc
Provides strongest possible test of Dark Matter
model
DM particle mass mc (GeV)
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SUSY DM Strategy

• SUSY Dark Matter studies at ATLAS will proceed in
  four stages

• SUSY Discovery phase
• Inclusive Studies (measurement of SUSY Mass
  Scale, comparison of significance in inclusive
  channels).
• Exclusive studies and interpretation within
  specific model framework (e.g. Constrained MSSM /
  mSUGRA)
• Specific model needed to calculate e.g. relic
  density g general SUSY studies will be less model
  dependent.
• Less model-dependent interpretation
• Relax model-dependent assumptions

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• Stage 1
• SUSY Discovery

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SUSY Signatures

• Q What do we expect SUSY events _at_ LHC to look
  like?
• A Look at typical decay chain

• Strongly interacting sparticles (squarks,
  gluinos) dominate production.
• Heavier than sleptons, gauginos etc. g cascade
  decays to LSP.
• Long decay chains and large mass differences
  between SUSY states
• Many high pT objects observed (leptons, jets,
  b-jets).
• If R-Parity conserved LSP (lightest neutralino in
  mSUGRA) stable and sparticles pair produced.
• Large ETmiss signature (c.f. Wgln).
• Closest equivalent SM signature tgWb.

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Inclusive Searches

• Use 'golden' Jets n leptons ETmiss discovery
  channel.
• Map statistical discovery reach in mSUGRA m0-m1/2
  parameter space.
• Sensitivity only weakly dependent on A0, tan(b)
  and sign(m).
• Syst. stat. reach harder to assess focus of
  current future work.

5s
5s
ATLAS
ATLAS
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Background Systematics

• Z g nn n jets, W g ln n jets, W g tn (n-1)
  jets (t fakes jet)
• Estimate from Z g ll- n jets (e or m)
• Tag leptonic Z and use to validate MC / estimate
  ETmiss from pT(Z) pT(l)
• Alternatively tag W g ln n jets and replace
  lepton with n (0l)
• higher stats
• biased by presence of SUSY

(Z?ll)
ATLAS
Preliminary
(W?ln)
ATLAS
Preliminary
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• Stage 2
• Inclusive Studies

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Inclusive Studies

• Following any discovery of SUSY next task will be
  to test broad features of potential Dark Matter
  candidate.
• Question 1 Is R-Parity Conserved?
• If YES possible DM candidate
• LHC experiments sensitive only to LSP lifetimes lt
  1 ms (ltlt tU 13.7 Gyr)

LHC Point 5 (Physics TDR)
R-Parity Conserved
R-Parity Violated
ATLAS

Non-pointing photons from c01gGg

• Question 2 Is the LSP the lightest neutralino?
• Natural in many MSSM models
• If YES then test for consistency with
  astrophysics
• If NO then what is it?
• e.g. Light Gravitino DM from GMSB models (not
  considered here)

GMSB Point 1b (Physics TDR)
ATLAS
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Measuring Parameters

• First indication of mSUGRA parameters from
  inclusive channels
• Compare significance in jets ETmiss n leptons
  channels
• Detailed measurements from exclusive channels
  when accessible.
• Consider here two specific example points studied
  previously

ATLAS
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• Stage 3
• Exclusive studies and interpretation within
  specific model framework

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Exclusive Studies

• With more data will attempt to measure weak scale
  SUSY parameters (masses etc.) using exclusive
  channels.
• Different philosophy to TeV Run II (better S/B,
  longer decay chains) g aim to use
  model-independent measures.
• Two neutral LSPs escape from each event
• Impossible to measure mass of each sparticle
  using one channel alone
• Use kinematic end-points to measure combinations
  of masses.
• Old technique used many times before (n mass from
  b decay spectrum, W (transverse) mass in Wgln).
• Difference here is we don't know mass of neutral
  final state particles.

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Dilepton Edge Measurements

• When kinematically accessible c02 can undergo
  sequential two-body decay to c01 via a
  right-slepton (e.g. LHC Point 5).
• Results in sharp OS SF dilepton invariant mass
  edge sensitive to combination of masses of
  sparticles.
• Can perform SM SUSY background subtraction
  using OF distribution
• ee- mm- - em- - me-
• Position of edge measured with precision 0.5
• (30 fb-1).

• m0 100 GeV
• m1/2 300 GeV
• A0 -300 GeV
• tan(b) 6
• sgn(m) 1

ee- mm- - em- - me-
ee- mm-
Point 5
ATLAS
ATLAS
30 fb-1 atlfast
5 fb-1 SU3
Physics TDR
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Measurements With Squarks

• Dilepton edge starting point for reconstruction
  of decay chain.
• Make invariant mass combinations of leptons and
  jets.
• Gives multiple constraints on combinations of
  four masses.
• Sensitivity to individual sparticle masses.

bbq edge
llq threshold
1 error (100 fb-1)
2 error (100 fb-1)
TDR, Point 5
TDR, Point 5
TDR, Point 5
TDR, Point 5
ATLAS
ATLAS
ATLAS
ATLAS
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Model-Independent Masses

• Combine measurements from edges from different
  jet/lepton combinations to obtain
  model-independent mass measurements.

c01
lR
ATLAS
ATLAS
Mass (GeV)
Mass (GeV)


c02
qL
ATLAS
ATLAS
LHCC Point 5
Mass (GeV)
Mass (GeV)
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Measuring Model Parameters

• Alternative use for SUSY observables (invariant
  mass end-points, thresholds etc.).
• Here assume mSUGRA/CMSSM model and perform global
  fit of model parameters to observables
• So far mostly private codes but e.g. SFITTER,
  FITTINO now on the market
• c.f. global EW fits at LEP, ZFITTER, TOPAZ0 etc.

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Dark Matter Parameters

• Can use parameter measurements for many purposes,
  e.g. estimate LSP Dark Matter properties (e.g.
  for 300 fb-1, SPS1a)
• Wch2 0.1921 ? 0.0053
• log10(scp/pb) -8.17 ? 0.04

Baer et al. hep-ph/0305191
LHC Point 5 gt5s error (300 fb-1)
SPS1a gt5s error (300 fb-1)
Micromegas 1.1 (Belanger et al.) ISASUGRA 7.69
DarkSUSY 3.14.02 (Gondolo et al.) ISASUGRA 7.69
scp10-11 pb
scp10-10 pb
Wch2
scp
scp10-9 pb
300 fb-1
300 fb-1
No REWSB
LEP 2
ATLAS
ATLAS
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Target Models

• SUSY (e.g. mSUGRA) parameter space strongly
  constrained by cosmology (e.g. WMAP satellite)
  data.

mSUGRA A00, tan(b) 10, mgt0
Slepton Co-annihilation region LSP pure Bino.
Small slepton-LSP mass difference makes
measurements difficult.
Ellis et al. hep-ph/0303043
Disfavoured by BR (b ? s?) (3.2 ? 0.5) ?
10-4 (CLEO, BELLE)
'Bulk' region t-channel slepton exchange - LSP
mostly Bino. 'Bread and Butter' region for LHC
Expts.
Also 'rapid annihilation funnel' at Higgs pole at
high tan(b), stop co-annihilation region at large
A0
0.094 ? ? ? h2 ? 0.129 (WMAP)
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Coannihilation Signatures

• Small slepton-neutralino mass difference gives
  soft leptons
• Low electron/muon/tau energy thresholds crucial.
• Study point chosen within region
• m070 GeV m1/2350 GeV A00 tanß10 µgt0
• Decays of c02 to both lL and lR kinematically
  allowed.
• Double dilepton invariant mass edge structure
• Edges expected at 57 / 101 GeV
• Stau channels enhanced (tanb)
• Soft tau signatures
• Edge expected at 79 GeV
• Less clear due to poor tau visible energy
  resolution.

• ETmissgt300 GeV
• 2 OSSF leptons PTgt10 GeV
• gt1 jet with PTgt150 GeV
• OSSF-OSOF subtraction applied

100 fb-1
ATLAS
Preliminary

• ETmissgt300 GeV
• 1 tau PTgt40 GeV1 tau PTlt25 GeV
• gt1 jet with PTgt100 GeV
• SS tau subtraction

100 fb-1
ATLAS
Preliminary
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Focus Point Signatures

• Large m0 ? sfermions are heavy
• Most useful signatures from heavy neutralino
  decay
• Study point chosen within focus point region
• m03550 GeV m1/2300 GeV A00 tanß10 µgt0
• Direct three-body decays c0n ? c01 ll
• Edges give m(c0n)-m(c01) flavour subtraction
  applied

M mAmB m mA-mB
Parameter Without cuts Exp. value
M1 6892 103.35
M2-M1 57.71.0 57.03
M3-M1 77.61.0 76.41
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• Stage 4
• Less model-dependent interpretation

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Dark Matter in the MSSM

• Can relax mSUGRA constraints to obtain more
  model-independent relic density estimate.
• Much harder needs more measurements
• Not sufficient to measure relevant (co-)
  annihilation channels must exclude all
  irrelevant ones also
• Stau, higgs, stop masses/mixings important as
  well as gaugino/higgsino parameters

Nojiri, Polesello Tovey, JHEP 0603 (2006) 063
s(Wch2) vs s(mtt)
Wch2
Wch2
s(mtt)5 GeV
s(mtt)0.5 GeV
300 fb-1
300 fb-1
SPA point
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Heavy Gaugino Measurements

• Potentially possible to identify dilepton edges
  from decays of heavy gauginos.
• Requires high stats.
• Crucial input to reconstruction of MSSM
  neutralino mass matrix (independent of SUSY
  breaking scenario).

ATLAS
SPS1a
ATLAS
ATLAS
ATLAS
100 fb-1
100 fb-1
100 fb-1
SPS1a
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Summary

• Following a (SUSY) discovery ATLAS will aim to
  test the (SUSY) Dark Matter hypothesis.
• Conclusive result only possible in conjunction
  with astroparticle experiments (constraints on
  LSP life-time).
• Estimation of relic density and direct / indirect
  DM detection cross-sections in model-dependent
  scenario will be first goal.
• Less model-dependent measurements will follow.
• Ultimate goal observation of neutralinos at LHC
  confirmed by observation of e.g. signal in
  (in)direct detection Dark Matter experiment at
  predicted mass and cross-section.

• This would be major triumph for both
• Particle Physics and Cosmology!

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• BACK-UP SLIDES

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Supersymmetry

• Supersymmetry (SUSY) fundamental continuous
  symmetry connecting fermions and bosons
• QaFgt Bgt, QaBgt Fgt
• Qa,Qb-2gmabpm generators obey
  anti-commutation relations with 4-mom
• Connection to space-time symmetry
• SUSY stabilises Higgs mass against loop
  corrections (gauge hierarchy/fine-tuning problem)
• Leads to Higgs mass 135 GeV
• Good agreement with LEP constraints from EW
  global fits
• SUSY modifies running of SM gauge couplings just
  enough to give Grand Unification at single scale.

LEPEWWG Winter 2006
mHlt207 GeV (95CL)
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SUSY Spectrum

• SUSY gives rise to partners of SM states with
  opposite spin-statistics but otherwise same
  Quantum Numbers.

• Expect SUSY partners to have same masses as SM
  states
• Not observed (despite best efforts!)
• SUSY must be a broken symmetry at low energy
• Higgs sector also expanded

h
ne
e
d
u
nm
m
s
c
nt
t
b
t
G
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Model Framework

• Minimal Supersymmetric Extension of the Standard
  Model (MSSM) contains gt 105 free parameters,
  NMSSM etc. has more g difficult to map complete
  parameter space!
• Assume specific well-motivated model framework in
  which generic signatures can be studied.
• Often assume SUSY broken by gravitational
  interactions g mSUGRA/CMSSM framework unified
  masses and couplings at the GUT scale g 5 free
  parameters

• (m0, m1/2, A0, tan(b), sgn(m)).
• R-Parity assumed to be conserved.
• Exclusive studies use benchmark points in mSUGRA
  parameter space
• LHCC Points 1-6
• Post-LEP benchmarks (Battaglia et al.)
• Snowmass Points and Slopes (SPS)
• etc

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SUSY Dark Matter

• R-Parity Rp (-1)3B2SL
• Conservation of Rp (motivated e.g. by string
  models) attractive
• e.g. protects proton from rapid decay via SUSY
  states
• Causes Lightest SUSY Particle (LSP) to be
  absolutely stable
• LSP neutral/weakly interacting to escape
  astroparticle bounds on anomalous heavy elements.
• Naturally provides solution to dark matter
  problem
• R-Parity violating models still possible ? not
  covered here.

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Stop Mass
mtbmax (443.2 7.4stat) GeV Expected 459 GeV

• Look at edge in tb mass distribution.
• Contains contributions from
• g?tt1?tbc1
• g?bb1?btc1
• SUSY backgrounds
• Measures weighted mean of end-points
• Require m(jj) m(W), m(jjb) m(t)

120 fb-1
ATLAS
LHCC Pt 5 (tan(b)10)
mtbmax (510.6 5.4stat) GeV Expected 543 GeV

• Subtract sidebands from m(jj) distribution
• Can use similar approach with g?tt1?ttc0i
• Di-top selection with sideband subtraction
• Also use standard bbll analyses (previous slide)

120 fb-1



ATLAS
LHCC Pt 5 (tan(b)10)
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Preparations for 1st Physics

• Preparations needed to ensure efficient/reliable
  searches for/measurements of SUSY particles in
  timely manner
• Initial calibrations (energy scales, resolutions,
  efficiencies etc.)
• Minimisation of poorly estimated SM backgrounds
• Estimation of remaining SM backgrounds
• Development of useful tools.
• Definition of prescale (calibration) trigger
  strategy
• Different situation to Run II (no previous s
  measurements at same Ös)
• Will need convincing bckgrnd. estimate with
  little data as possible.
• Background estimation techniques will change
  depending on integrated lumi.
• Ditto optimum search channels cuts.
• Aim to use combination of
• Fast-sim
• Full-sim
• Estimations from data.
• Use comparison between different techniques to
  validate estimates and build confidence in
  (blind) analysis.

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Black Hole Signatures
Mp1TeV, n2, MBH 6.1TeV

• In large ED (ADD) scenario, when impact parameter
  smaller than Schwartzschild radius Black Hole
  produced with potentially large x-sec (100 pb).
• Decays democratically through Black Body
  radiation of SM states Boltzmann energy
  distribution.

ATLAS
w/o pile-up
ATLAS
w/o pile-up

• Discovery potential (preliminary)
• Mp lt 4 TeV ? lt 1 day
• Mp lt 6 TeV ? lt 1 year
• Studies continue

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Sbottom/Gluino Mass

• Following measurement of squark, slepton and
  neutralino masses move up decay chain and study
  alternative chains.
• One possibility require b-tagged jet in addition
  to dileptons.
• Give sensitivity to sbottom mass (actually two
  peaks) and gluino mass.
• Problem with large error on input c01 mass
  remains g reconstruct difference of gluino and
  sbottom masses.
• Allows separation of b1 and b2 with 300 fb-1.

m(g)-0.99m(c01) (500.0 6.4) GeV
300 fb-1
ATLAS
SPS1a



m(g)-m(b1) (103.3 1.8) GeV
ATLAS




m(g)-m(b2) (70.6 2.6) GeV
300 fb-1
SPS1a
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RH Squark Mass

• Right handed squarks difficult as rarely decay
  via standard c02 chain
• Typically BR (qR g c01q) gt 99.
• Instead search for events with 2 hard jets and
  lots of ETmiss.
• Reconstruct mass using stransverse mass
  (Allanach et al.)
• mT22 min maxmT2(pTj(1),qTc(1)mc),
  mT2(pTj(2),qTc(2)mc)
• Needs c01 mass measurement as input.
• Also works for sleptons.

qTc(1)qTc(2)ETmiss
ATLAS
ATLAS
30 fb-1
100 fb-1
30 fb-1
Right squark
SPS1a
ATLAS
SPS1a
Right squark
SPS1a
Left slepton
Precision 3
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Physics Strategy

• December 2007(?) 900 GeV calibration run
• commence tuning trigger menus / in situ
  calibration
• Summer 2008 first 14 TeV physics run (L lt 1032
  cm-2 s-1, Lint 1 fb-1)
• commence tuning trigger menus / in situ
  calibration
• First SM measurements min bias, PDF constraints,
  Z / W / top / QCD
• 2008/9 physics run (L 2x1033 cm-2 s-1, Lint
  10 fb-1)
• First B-physics measurements rare decay
  searches (e.g. Bs?J/yf)
• First searches high mass dilepton / Z,
  inclusive SUSY, Black Hole production, Higgs in
  easier channels e.g. H?4l
• 2009/10 physics run (L 2x1033 cm-2 s-1, Lint
  10 fb-1/year)
• First precision SM B-physics measurements
  (systematics under control)
• Improved searches sensitivity
• Light Higgs searches (ttH, H?gg, VBF qqH(H?tt)
  etc.)
• 2010/11 High luminosity running (L 1034, Lint
  100 fb-1/year)
• High precision measurements of New Physics (e.g.
  Higgs/SUSY/ED properties)

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Inclusive SUSY

• First SUSY parameter to be measured may be mass
  scale
• Defined as weighted mean of masses of initial
  sparticles.
• Calculate distribution of 'effective mass'
  variable defined as scalar sum of masses of all
  jets (or four hardest) and ETmiss
• MeffSpTi ETmiss.
• Distribution peaked at twice SUSY mass scale
  for signal events.
• Pseudo 'model-independent' measurement.
• With PS typical measurement error (syststat)
  10 for mSUGRA models for 10 fb-1 , errors much
  greater with ME calculation ? an important lesson
  

Jets ETmiss 0 leptons
ATLAS
10 fb-1
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SUSY Spin Measurement

• Q How do we know that a SUSY signal is really
  due to SUSY?
• Other models (e.g. UED) can mimic SUSY mass
  spectrum
• A Measure spin of new particles.
• One possibility use standard two-body slepton
  decay chain
• charge asymmetry of lq pairs measures spin of c02
• relies on valence quark contribution to pdf of
  proton (C asymmetry)
• shape of dilepton invariant mass spectrum
  measures slepton spin

Point 5
ATLAS
150 fb -1
mlq
spin-0flat
150 fb -1
ATLAS
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Processing the Data

• Many events
• 109 events/experiment/year
• 3 MB/event raw data
• several passes required
• Worldwide LHC computing requirement (2007)
• 100 Million SPECint2000 (20,000 of todays
  fastest processors)
• 12-14 PetaBytes of data per year (100,000 of
  todays highest capacity HDD).

• Understand/interpret data via numerically
  intensive simulations
• e.g. 1 event (ATLAS Monte Carlo Simulation) 20
  mins/3 MB
• Use worldwide computing Grid to solve problem

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25 ns

• Event rate in ATLAS
• N L x ? (pp) ? 109 interactions/s
• Mostly soft ( low pT ) events

• Interesting hard (high-pT ) events are rare
• Each accompanied by 20 soft events
• ?Also additional soft interactions (UE)

47
Background Estimation

• Inclusive signature jets n leptons ETmiss
• Main backgrounds
• Z n jets
• W n jets
• QCD
• ttbar
• Greatest discrimination power from ETmiss
  (R-Parity conserving models)
• Generic approach to background estimation
• Select low ETmiss background calibration samples
• Extrapolate into high ETmiss signal region.
• Used by CDF / D0
• Extrapolation is non-trivial.
• Must find variables uncorrelated with ETmiss
• Several approaches being developed.

Jets ETmiss 0 leptons
ATLAS
10 fb-1