Results Of Recent SUSY Studies At ATLAS Ignacio Aracena University of Bern On behalf of the ATLAS collaboration SUSY 2005 July 18 – 23, 2005, IPPP Durham,

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

2

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.


3

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


4

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


5

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


6

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


7

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


8

• 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


9

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.


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


10

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


11

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


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.


12

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.


13

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


14

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.


15


full sim. 20 fb-1


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.


16

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

)


17

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!

BACKUP SLIDES


19

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


20

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


21

Focus point – mass spectrum

• m0 = 3550; m1/2 = 300; A0 = 0; tanβ=10; μ>0

m(g) = 857 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


σLO = 4.9pb


22

Funnel region – mass spectrum

• m0 = 320; m1/2 = 375; A0 = 0; tanβ=50; μ>0

m(g) = 895 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


σLO = 4.5pb


23

Bulk region – mass spectrum

• m0 = 100; m1/2 = 300; A0 = -300; tanβ=6; μ>0

m(g) = 717 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


σLO = 6.8pb


24

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


25

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


26

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~(


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


27

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


28

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


29

Lepton+jets distributions - coannihilation

mqll (GeV)


)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


30

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


31


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


32

The ATLAS detector


33

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

Documents

Results Of Recent SUSY Studies At ATLAS Ignacio Aracena University of Bern On behalf of the ATLAS collaboration SUSY 2005 July 18 – 23, 2005, IPPP Durham,