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Results Of Recent SUSY Studies At Results Of Recent SUSY Studies At ATLASATLAS
Ignacio AracenaIgnacio Aracena
University of BernUniversity of Bern
On behalf of the ATLAS collaborationOn behalf of the ATLAS collaboration
SUSY 2005SUSY 2005
July 18 – 23, 2005, IPPP Durham, UKJuly 18 – 23, 2005, IPPP Durham, UK
OutlineOutline• Introduction• Inclusive SUSY Signatures• Exclusive Signatures - leptons (electrons, muons) - taus• Conclusions
July 22th 2005 I.AracenaSUSY 2005, Durham, UK
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Introduction
• Preliminary results of recently produced full simulated data with the
initial layout of the ATLAS detector.
• Analyzed SUSY signatures in the mSUGRA (RPC) framework (m0,
m1/2, A0, tanβ, sgn(μ)).
• Selected mSUGRA points chosen according to recent experimental
data (WMAP,LEP limits,CLEO,BELLE).
• The material shown here is the result of a collaboration-wide effort
over the past six months and is a summary of what has been shown
at the ATLAS Physics Workshop in June 2005.
July 22th 2005 I.AracenaSUSY 2005, Durham, UK
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0,0,50tan 0 A
Funnel region s-channel Higgs-exchange.
AH,χ 01
2 mm
The (m0,m1/2) - mSUGRA plane
WMAP: 0.094<Ωχh2<0.129
Excluded by b s(CLEO,BELLE) 0,0,10tan 0 A
Favored by gμ−2 at the 2σ levelMuon g−2 coll.
Stau1=LSP
(Ellis et al., Phys. B565 (2003) 176)
Bulk regiont-channel slepton
exchange.(ATL-PHYS-2004-011)
Stau coannihilationγττ~χ~ 1
01
Focus point
H~
χ~01
July 22th 2005 I.AracenaSUSY 2005, Durham, UK
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mSUGRA points
M0 (GeV) M1/2(GeV) A0 tanβ sgn(μ) mtop (GeV)
Coannihilation 70 350 0 10 + 175
Focus point 3550 300 0 10 + 175
Funnel region 320 375 0 50 + 175
Bulk (ATL-PHYS-2004-011) 100 300 -300 6 + 175
Scan 130-6000 600,1000 0 10 + 175
low mass point 200 160 -400 10 + 175
The following points in the mSUGRA space have been selected for analysis with the full ATLAS detector simulation (GEANT4).
All results shown in this talk are obtained from new All results shown in this talk are obtained from new full simulation datafull simulation data!!
Events generated with HERWIG 6.505 (+JIMMY). SUSY spectra obtained with ISAJET7.71
July 22th 2005 I.AracenaSUSY 2005, Durham, UK
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Inclusive SUSY signatures• A typical SUSY event at LHC will
contain hard jets + n leptons and large missing transverse energy, ET .
• The SUSY mass scale:
• The effective Mass gives a handle on the SUSY mass scale (Hinchliffe et al., Phys. Rev. D55 (1997) 5520):
• Cuts to reject SM background
– 4 jets with PT > 50GeV
– 2 jets with PT > 100GeV
– ET > max(0.2Meff,100GeV)
– no lepton
SUSYmissT
4iTeff MEpM
i
g~
Lq~q 02χ~
l~
l l
01χ~
p
),min( q~g~SUSY mmM
ATLAS 20.6fb−1
SM background(ATL-PHYS-2004-011)
SUSY signal (full sim.)
miss
Preliminary
miss
coannihilation
July 22th 2005 I.AracenaSUSY 2005, Durham, UK
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MSUSY vs. Effective mass
• Plot MSUSY vs. the peak value of
the Meff (from full simulation).
• Repeat this for different mSUGRA
models.
• Correlation line from previous fast
simulation analysis, Hinchliffe et
al., Phys. Rev. D55 ,D. Tovey,
Phys. Lett. B498 (2001) 1.
• Meff can be used over a broad
range of mSUGRA models.
Meff is a good variable for the estimation of the SUSY mass scale
ATLAS Preliminary
July 22th 2005 I.AracenaSUSY 2005, Durham, UK
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Exclusive signatures• After initial discovery of SUSY the measurement of the sparticle masses will
be the next step.
• Two invisible LSP in each event, so no direct mass measurement possible.
• Obtain kinematic edges from invariant mass distributions of involved particles,
e.g. dilepton distribution mll.
• Remove SUSY/SM BG using OppositeFlavor/OppositeSign (OF/OS) pairs,
e.g. .)μe()μμ()e(e mmm
2
l~
2
χ~
2
χ~
2
l~
χ~maxll
R
01
02
R02
11m
m
m
mmm
p
g~
Lq~qq
l~0
2χ~01χ~
l l
p
ATLAS
Bulk region4.20fb−1
Preliminary
• only SUSY signal (full sim.)
• select events with 2 leptons
GeV31.100maxll m
July 22th 2005 I.AracenaSUSY 2005, Durham, UK
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• two edges.
• only signal events with ≥2 leptons.
• Fit results:
- mll,fit (L)=(56.45±1.15)GeV
- mll,fit (R)=(102.0±0.01)GeV
)l~
()χ~( RL,02 mm
max
max
Dilepton distribution - coannihilation
)()() μeμμe(e mmm
MC truth (Herwig)
ATLAS
small BR and at least one lepton has low transverse momentum.
GeV18)χ~()l~
( 01R mmGeV8)l
~()χ~( L
02 mm
%3)ll~
χ~BR( R02 %6)ll
~χ~BR( L
02
MC truth lLMC truth lRfull sim. data
GeV0.56maxLll, m
GeV9.97maxRll, m
20.6fb−1
ATLASPreliminary
pT(lepton) (GeV)
Stau coannihilation region
July 22th 2005 I.AracenaSUSY 2005, Durham, UK
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Dilepton distribution – focus pointFocus point
• heavy scalars, no slepton in decay.
• direct 3-body decay:
• dilepton distribution gives mass diff.
between , , .• only signal events with ≥2 leptons.
01
02,3 χ~llχ~
GeV0.57)χ~()χ~( 01
02 mm
6.9fb−1
ATLAS
χ~
01χ~ 0
2χ~ 03χ~
GeV4.76)χ~()χ~( 01
03 mm
Apply following cuts to reject potential SM BG:
• at least 4 jets with pT>50GeV.
• at least 2 jets with pT>100GeV.
• ETmiss > 100GeV.
)()() μeμμe(e mmm
After SM cuts
Shape not much affected by cuts, but reduced statistics. )χ~()χ~( 0
102 mm )χ~()χ~( 0
103 mm
ATLAS
Preliminary
Preliminary
full sim.
full sim.
6.9fb−1
July 22th 2005 I.AracenaSUSY 2005, Durham, UK
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Combine the two leptons with the twohardest jets in the event:
),,,( 01R
02L χ~l
~χ~q~
minllq
largellq mmmmmm
),,,( 01R
02L χ~l
~χ~q~
maxllq
smallllq mmmmmm
Leptons+jets distributions - mllq
p
g~
Lq~qq
l~0
2χ~01χ~
l l
p
minllqllq
maxllq mmm
Obtain more edges: include the quark coming from the squark decay
ATLAS4.20fb−1
ATLAS4.20fb−1
GeV501maxqll m
PreliminaryPreliminary
0 200 400 600 800 1000
16
12
8
4
0
Ent
ries/
10G
ev
0 200 400 600 800 1000
60
5040302010 0
Ent
ries/
10G
ev
GeV272minqll m
Bulk region: signal evts (full sim.); ≥2 jets and 2 leptons. Apply OF/OS subtraction.
full sim. full sim.
mllq (GeV)small mllq (GeV)large
July 22th 2005 I.AracenaSUSY 2005, Durham, UK
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Take the jet used for and compute mlq
using each of the two leptons (Allanach et al.,
JHEP 0009 (2000) 004):
Leptons+jets distributions - mlq(low), mlq(high)
p
01χ~
g~
Lq~qq
l~0
2χ~nearl
farl
p
ql(near)m ql(far)m
),min( ql(far)ql(near)ql(low) mmm
),max( ql(far)ql(near)ql(high) mmm
Stau coannihilation region
ATLASfull sim.
20.6 fb−1
GeV9.297)(maxlq(low) Rm
GeV3.180)(maxlq(low) Lm
Preliminary
Mlq(low) (GeV)
ATLASfull sim.
GeV7.580)(maxlq(high) Rm
GeV8.603)(maxlq(high) Lm
20.6 fb−1
Preliminary
Mlq(high) (GeV)
)l~
()χ~( RL,02 mm )l
~,l
~(),l
~,l
~( RLlq(high)RLlq(low) mm
≥2 jets/leptons, subtract OF/OS pairs.
July 22th 2005 I.AracenaSUSY 2005, Durham, UK
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Right handed squark mass• In mSUGRA usually large .
• Such events contain two hard jets and missing ET.
• Estimate the mass using the stranverse mass,
(Lester et al., Phys.Lett.B463 (1999) 99):
• Take from dilepton and dilepton+jet measurements.
• If is known, is obtained from the endpoint of the
distribution.
)χ~qq~BR( 01R
Rq~
)]}χ~(;,()),χ~(;,({max[min 01T,2j2T,
01T,1j1T,T
ppp
2T2
TT,2T,1
MppMMppMM
)χ~( 01M
)q~( RM T2M
Rq~
Rq~
jet1
jet2 01χ~
01χ~
)χ~( 01M
Coannihilation region
• Select ≥2 jets PT>200GeV
and ET >400GeV
• Use “true” value
.
• True value .
)χ~( 01M
ATLAS20.6fb−1
GeV136)χ~( 01 M
Preliminary
GeV735)q~( R M
missfull sim.
July 22th 2005 I.AracenaSUSY 2005, Durham, UK
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And they are particularly interesting:
• Non-negligible Yukawa coupling.
• for large tanβ, decays into have large BR.
• Can use tau polarization measurement to further constrain the underlying SUSY model.
Tau signatures
Decay chains involving taus are
challenging, due to:
• Escaping neutrino.
• Only consider hadronic tau decays.
1τ
~
Distorted shape of the ditau mass distribution.
ττχ~ττ~χ~ 011
02
Bulk region MC truth(Herwig)
allhadrons
July 22th 2005 I.AracenaSUSY 2005, Durham, UK
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Ditau mass distribution
Bulk region
• select events with two reconstructed taus.• Uncorrelated pairs accounted for by using same-sign pairs.• True endpoint
• Endpoint structure visible at the expectedvalue.
GeV3.98maxττ m
Shape of can be calculated given knowledge of tau polarizations.
Extracting polarization is challenging.
visττ,m
Reconstruct the dilepton inv. mass in the
decay chain. ττχ~ττ~χ~ 0
1102
)ττ()τ(τ visvis
mm
ATLAS4.2fb−1
full sim.
Preliminary
mττ (vis) (GeV)
mττ (vis)/98.3
Use MC truth as a first approx.and fit obtained function to data.
July 22th 2005 I.AracenaSUSY 2005, Durham, UK
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Ditau mass distribution
full sim. 20 fb-1
Stau coannihilation region
at least one tau has small transverse momentum.
Funnel region
no lepton mass edge:
Select events with ≥2 taus and:
• ≥4 jets with pT>50GeV; ≥1 jet pT>100GeV
• ETmiss ≥ max(100GeV,0.2Meff)
%19)ττ~χ~BR( 102 %2)ττ~χ~BR( 2
02
GeV10)χ~()τ~( 011 mm GeV7)τ~()χ~( 2
02 mm
)χ~()l~
( 02RL, mm
%48)ττ~χ~BR( 102 %100)τχ~τ~BR( 0
11
OS pairs
SS pairs
full sim. 13 fb-1
OS pairs
SS pairs
ATLAS
0 40 80 120 160 200
876543210
ATLASPreliminary
Preliminary
GeV49)2(maxττ m
GeV78)1(maxττ m
GeV125)1(maxττ m
Mττ,vis (GeV)In both scenarios hint for an endpoint, but need more stats for fit.
July 22th 2005 I.AracenaSUSY 2005, Durham, UK
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Reconstruct sparticle masses
Perform a chi-square fit
• Oi
sm observables smeared with exp. resolution, Oi “true” observable values.
M(01) (GeV)
N
mOOm1
2i
2i
smi
2 /))~(()~(
• Assume 1% error on the measured observables:
Can reconstruct mass with ~10% precision, mass diff. with ~1%
(Stau coannihilation region)
ATLAS
Preliminary
M(01) (GeV)
ATLAS
Preliminary
M(
0 2) (
GeV
)
July 22th 2005 I.AracenaSUSY 2005, Durham, UK
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Conclusions
• New studies of mSUGRA signatures using new full simulation data of the ATLAS detector have been shown.
• Various experimentally challenging points in the mSUGRA parameter space in agreement with recent experimental data have been chosen.
• If SUSY exists at the TeV scale, ATLAS should be able to observe clean inclusive signatures above the SM background.
• Lots of techniques exist / are being developed to assess the sparticle masses and the underlying model parameters.
• Many exclusive studies can be carried out with few fb−1 of data, i.e. ~ 1 year at low luminosity.
• There are still many things to be studied more carefully (acceptance, calibration, trigger, SM BG,…).
• Analyses of this new full simulation data have just started. There is still a lot we can learn from this before first collisions in 2007!
July 22th 2005 I.AracenaSUSY 2005, Durham, UK
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SM background
Dominant SM background processes:
• Z+N jets
• W+N jets
• tt+N jets
• multijets (QCD)
• sum of all BG
Previous studies are based on Parton shower.
New SM BG estimation using ME generator(ALPGEN 1.33)
• W/Z + N jets, tt + N jets are generated and processed with the fast ATLAS simulation
• Collinear and soft kinematic regions are assessed with PS (PYTHIA). MLM method used for ME-PS matching.
ATLAS TDR
SM cuts+1lepton
July 22th 2005 I.AracenaSUSY 2005, Durham, UK
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Coannihilation point – mass spectrum
• m0 = 70; m1/2 = 350; A0 = 0; tanβ=10; μ>0
m(g) = 832 GeV
m(dL) = 765 GeV m(dR) = 734 GeV m(χ30) = 466 GeV
m(uL) = 760 GeV m(uR) = 735 GeV m(χ20) = 264 GeV
m(sL) = 765 GeV m(sR) = 734 GeV m(χ10) = 137 GeV
m(cL) = 760 GeV m(cR) = 735 GeV
m(b1) = 698 GeV m(b2) = 723 GeV
m(t1) = 573 GeV m(b2) = 723 GeV
m(eL) = 255 GeV m(eR) = 154 GeV
m(stau1) = 147 GeV m(stau2) = 257 GeV
σLO = 6.8pb
July 22th 2005 I.AracenaSUSY 2005, Durham, UK
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Focus point – mass spectrum
• m0 = 3550; m1/2 = 300; A0 = 0; tanβ=10; μ>0
m(g) = 857 GeV
m(dL) = 3564 GeV m(dR) = 3576 GeV m(χ30) = 180 GeV
m(uL) = 3563 GeV m(uR) = 3574 GeV m(χ20) = 160 GeV
m(sL) = 3564 GeV m(sR) = 3576 GeV m(χ10) = 103 GeV
m(cL) = 3564 GeV m(cR) = 3574 GeV
m(b1) = 2924 GeV m(b2) = 3500 GeV
m(t1) = 2131 GeV m(t2) = 2935 GeV
m(eL) = 3547 GeV m(eR) = 3547 GeV
m(stau1) = 3520 GeV m(stau2) = 3534 GeV
σLO = 4.9pb
July 22th 2005 I.AracenaSUSY 2005, Durham, UK
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Funnel region – mass spectrum
• m0 = 320; m1/2 = 375; A0 = 0; tanβ=50; μ>0
m(g) = 895 GeV
m(dL) = 871 GeV m(dR) = 840 GeV m(χ30) = 477 GeV
m(uL) = 867 GeV m(uR) = 842 GeV m(χ20) = 288 GeV
m(sL) = 871 GeV m(sR) = 840 GeV m(χ10) = 150 GeV
m(cL) = 867 GeV m(cR) = 842 GeV
m(b1) = 717 GeV m(b2) = 779 GeV
m(t1) = 642 GeV m(t2) = 798 GeV
m(eL) = 412 GeV m(eR) = 351 GeV
m(stau1) = 181 GeV m(stau2) = 393 GeV
σLO = 4.5pb
July 22th 2005 I.AracenaSUSY 2005, Durham, UK
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Bulk region – mass spectrum
• m0 = 100; m1/2 = 300; A0 = -300; tanβ=6; μ>0
m(g) = 717 GeV
m(dL) = 636 GeV m(dR) = 611 GeV m(χ30) = 464 GeV
m(uL) = 632 GeV m(uR) = 612 GeV m(χ20) = 219 GeV
m(sL) = 636 GeV m(sR) = 611 GeV m(χ10) = 118 GeV
m(cL) = 631 GeV m(cR) = 612 GeV
m(b1) = 575 GeV m(b2) = 611 GeV
m(t1) = 424 GeV m(t2) = 651 GeV
m(eL) = 230 GeV m(eR) = 155 GeV
m(stau1) = 150 GeV m(stau2) = 232 GeV
σLO = 6.8pb
July 22th 2005 I.AracenaSUSY 2005, Durham, UK
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lepton selection cuts
Cuts applied to all samples:
• Electrons
• pT > 10 GeV, |η| < 2.5
• Isolation: 4 GeV in cone 0.2• eWeight/(eWeight+piWeight) > 0.95• 0.8 < E/p < 1.3 in barrel• 0.7 < E/p < 2.5 in endcap
Muons• pT > 10 GeV, |η| < 2.5• Reco 2 < 20• Isolation: ET < 6 GeV in cone 0.4
July 22th 2005 I.AracenaSUSY 2005, Durham, UK
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Dilepton distribution – Bulk region
• Only SUSY signal events.
• No SM background cuts.
• Fit a triangular shape convoluted with a Gaussian.
Bulk region
ATLAS4.20fb−1
• After SM BG cuts + 2 leptons
• Loose stats but still triangular shape visible.
• Fitted value after cuts:
mll = (99.8±1.2)GeV
GeV31.100maxll m
)()() μeμμe(e mmm Reconstruct the dilepton inv. mass in the
decay chain. llχ~ll~
χ~ 01R
02
ATLAS4.37fb−1
July 22th 2005 I.AracenaSUSY 2005, Durham, UK
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Dilepton distribution – focus pointFocus point
heavy scalars, no slepton in decay.
direct 3-body decay:
Dilepton distribution gives mass diff.between , , .
01
02,3 χ~llχ~
GeV0.57)χ~()χ~( 01
02 mm
6.9fb−1
No SM cuts
ATLAS
χ~
01χ~ 0
2χ~ 03χ~
GeV4.76)χ~()χ~( 01
03 mm
After SM cuts only few events survive:
dominant SUSY production is
but only survive SM cuts.
4.5pb)χ~χ~(
)()() μeμμe(e mmm
0.5pb)g~g~( 6.9fb−1
After SM cuts
Endpoint structure visible, but too little stats available.
)χ~()χ~( 01
02 mm )χ~()χ~( 0
103 mm
ATLAS
Preliminary
Preliminary
July 22th 2005 I.AracenaSUSY 2005, Durham, UK
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Lepton+jets signatures
Combine two leptons with the two hardestjets in the event:
: combination with the larger inv. mass.
: combination with the smaller inv. mass.
largellqm
smallllqm
ATLAS4.20fb−1
bulk region
minllqllq
maxllq mmm Lq~ 0
2χ~Rl
~ 01χ~
q l l
GeV501maxllq
smallllq mm
GeV272minllq
largellq mm
Can use combinations of leptons and jets toconstrain the sparticle mass spectrum.
ATLAS4.20fb−1
bulk region
July 22th 2005 I.AracenaSUSY 2005, Durham, UK
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Take the jet used for and compute mlq
using each of the two leptons (JHEP 0009
(2000) 004):
Apply OF/OS subtraction
Leptons+jets distributions - mlq(near), mlq(far)
p
01χ~
g~q~qq
l~0
2χ~nearl
farl
pql(near)m ql(far)m
),min( ql(far)ql(near)ql(low) mmm ),max( ql(far)ql(near)ql(high) mmm
ATLAS4.20fb−1
bulk region
ATLAS4.20fb−1
bulk region
GeV416maxql(high) mGeV323max
qll m
PreliminaryPreliminary
July 22th 2005 I.AracenaSUSY 2005, Durham, UK
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Lepton+jets distributions - coannihilation
mqll (GeV)
Stau coannihilation region
)l~
()χ~( RL,02 mm )l
~(),l
~( RL,lq(low)RL,lq(high) mm
)l~
( RL,maxllm
mql(low) (R)
mql(low) (L+εR)
mql(low) (L+R)
ATLAS 20.6 fb−1
ATLAS 20.6 fb−1
ATLAS 20.6 fb−1
Use to disentangle the mlq distributions
Divide mllq into mll < 58GeV and 58<mll<101GeV.
Preliminary
Preliminary
Preliminary
July 22th 2005 I.AracenaSUSY 2005, Durham, UK
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Lepton+jets distributions - coannihilation
Move up in the decay chain: Combine the leptons with jets
Lq~ 02χ~
Rl~ 0
1χ~
q l l
ATLAScoannihilation
ATLAScoannihilation
GeV5.611maxqll m GeV5.611min
qll m
GeV5.611)(minqll Lm
20.6 fb−120.6 fb−1
July 22th 2005 I.AracenaSUSY 2005, Durham, UK
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Ditau mass distribution
Funnel region
no lepton mass edge:
Select events with ≥2 taus
)χ~()l~
( 02RL, mm
%48)ττ~χ~BR( 102 %100)τχ~τ~BR( 0
21
full sim. 13 fb-1
OS pairs
SS pairs
ATLAS
Preliminary
GeV125)1(maxττ m
July 22th 2005 I.AracenaSUSY 2005, Durham, UK
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The ATLAS initial layout
Staged components:• One Pixel layer• Transition Radiation Tracker outer end-caps• Cryostat gap scintillator• Part of Muon drift tubes and half cathode strip layers• Part of forward shielding• Part of LAr read-out• Large part of trigger/DAQ CPUs