ukhep forum, april 2004 dan tovey 1 prospects for susy at atlas and cms dan tovey university of...

11 UKHEP Forum, April 2004UKHEP Forum, April 2004Dan ToveyDan Tovey

Prospects for SUSY at ATLAS and CMS

Prospects for SUSY at ATLAS and CMS

Dan Tovey

University of Sheffield


IntroductionIntroduction• SUSY particularly well-motivated solution to gauge hierarchy

problem, unification of couplings etc. etc. (see Weiglein talk).• Also often provides natural solution to Dark Matter problem of

astrophysics/cosmology.• One of main motivations for building LHC and GPDs.• Much work carried out historically by LHC experiments esp:

– ATLAS Detector and Physics Performance TDR (http://atlasinfo.cern.ch/Atlas/GROUPS/PHYSICS/TDR/access.html).

– CMS SUSY mega-note (J. Phys. G28 (2002) 469).

• Will concentrate in this talk on more recent studies and areas where new groups/people could get involved.

• DISCLAIMER: Will try to cover both CMS and ATLAS activities where relevant, however in places will focus more on ATLAS (personal bias due to familiarity).

• Will not cover non-SUSY exotica (ED, BH production etc.)• PS: Spot a missing tilde and win a prize!


Model FrameworkModel Framework• Minimal Supersymmetric Extension of the Standard Model (MSSM)

contains > 105 free parameters, NMSSM etc. has more 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 mSUGRA/CMSSM framework : unified masses and couplings at the GUT scale 5 free parameters(m0, m1/2, A0, tan(), sgn()).

• 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…

LHCC mSUGRA Points

1 2

3

45


SUSY SignaturesSUSY Signatures• Q: What do we expect SUSY events @ LHC to look like?• A: Look at typical decay chain:

• Strongly interacting sparticles (squarks, gluinos) dominate production.

• Heavier than sleptons, gauginos etc. 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 ET

miss signature (c.f. Wl).

• Closest equivalent SM signature tWb.

lqq

l

g~ q~ l~

~

~

p p


Inclusive SearchesInclusive Searches

• One of first tasks of LHC experiments (SUSY cross-section large).• Is LHC sensitive to all phenomenologically favoured models?• Especially important given current interest in focus-point models

with large mass scales.

• Use 'golden' Jets + n leptons + ETmiss discovery channel.

– Heavy strongly interacting sparticles produced in initial interaction

– Cascade decay via jets and leptons

– R-Parity conservation gives stable LSP (neutralino) at end of chain

• Map statistical discovery reach in mSUGRA m0-m1/2 parameter space.

• Sensitivity only weakly dependent on A0, tan() and sign().

– Choose 'reasonable' values e.g.A0=0, tan() = 10, 35, sign()=+/-1

• Systematic + statistical discovery reach harder to assess– Focus of current and future work.


mSUGRA ReachmSUGRA Reach

ATLAS

5 5


SUSY Mass ScaleSUSY Mass Scale• First measured SUSY parameter

likely to 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 ET

miss:

Meff=pTi| + ET

miss.

• Distribution peaked at ~ twice SUSY mass scale for signal events.

• Pseudo 'model-independent' measurement.

• Typical measurement error (syst+stat) ~10% for mSUGRA models for 10 fb-1.

Jets + ETmiss + 0 leptons

ATLAS

ATLAS

10 fb-1

10 fb-1


Exclusive StudiesExclusive 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) 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 ( mass from decay spectrum, W (transverse) mass in Wl).

• Difference here is we don't know mass of neutral final state particles.

lqql

g~ q~ lR

~

~

~p p


Dilepton Edge MeasurementsDilepton Edge Measurements• When kinematically

accessible canundergo

sequential two-body decay to

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

e+e- + +- - e+- - +e-

• Position of edge measured with precision ~ 0.5%

(30 fb-1).

~~02

~01

l ll

e+e- + +-

~

~

30 fb-1

atlfast

Physics TDR

Point 5

e+e- + +- - e+- - +e- 5 fb-1

FULL SIM

Modified Point 5 (tan() = 6)

ATLAS ATLAS

Preliminary


Measurements With SquarksMeasurements 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.

~~

~

l ll

qL

q

~

~

~

bh

qL

q

~

b

llq edge1% error(100 fb-1)

lq edge1% error(100 fb-1)

llq threshold2% error(100 fb-1)

bbq edge

TDR,Point 5

TDR,Point 5

TDR,Point 5

TDR,Point 5

ATLAS ATLAS ATLAS ATLAS

1% error(100 fb-1)


‘Model-Independent’ Masses‘Model-Independent’ Masses

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

01 lR

02 qL

Mass (GeV)Mass (GeV)

Mass (GeV)Mass (GeV)

~

~

~

~

ATLAS ATLAS

ATLAS ATLAS

Sparticle Expected precision (100 fb-1)

qL 3%

02 6%

lR 9%

01 12%

~

~

~

~


Sbottom MassSbottom 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 (but actually two peaks).

lbb

l

g~ b~ lR

~

~

~p p

GeV 7500b)χ~M( 02 GeV 503.9

)b~

BR(σ)b~

BR(σ

)b~

BR(σ)b~

M()b~

BR(σ)b~

M()b

~(M

21

2211

Post-LEP Point B: m0=100 GeV, m1/2 = 250 GeV, tan() = 10, A0=0, >0

10 fb-1CMS


Gluino MassGluino Mass• Can also move further up the decay chain to

gain sensitivity to gluino mass.• Can use either light squark decay or sbottom

(as here).

• Problem with large error on input 01 mass

remains solve by reconstructing difference of gluino and squark/sbottom masses.

• Allows separation of b1 and b2 with 300 fb-1.

300 fb-1

Sbottom Chain Squark Chain

10 fb-1 60 fb-1 300 fb-1 10 fb-1 60 fb-1 300 fb-1

M(sbottom) 500±7 502±4 497±2 M(squark) 536±10 532±2 536±1

(sbottom) 42±5 41±4 36±3 (squark) 60±9 36±1 31±1

M(gluino) 594±7 592±4 591±3 M(gluino) 592±7 595±2 590±2

(gluino) 42±7 46±3 39±3 (gluino) 75±5 59±2 59±2

M(gl)-M(sb) 92±3 88±2 90±2 M(gl)-M(sq) 57±3 47±2 44±2

(gl-sb) 17±4 20±2 23±2 (gl-sq) 9±3 16±5 11±2

GeV 3195bb)~M( 02

Post-LEP Point B CMS

CMS

Post-LEP Point B

300 fb-1

~

~ ~


Higgs SignaturesHiggs Signatures

• Lightest Higgs particle produced copiously in 0

2 decays if kinematically allowed.

• Prominent peak in bb invariant mass distribution.

• Possible discovery channel.

~

CMS

CMS

100 fb-1

m0=500 GeV, m1/2 = 500 GeV, tan() = 2, A0=0, <0


RH Squark MassRH Squark Mass• Right handed squarks difficult as rarely decay via ‘standard’ 0

2 chain

– Typically BR (qR 01q) > 99%.

• Instead search for events with 2 hard jets and lots of ETmiss.

• Reconstruct mass using ‘stransverse mass’ (Allanach et al.):mT2

2 = min [max{mT2(pT

j(1),qT(1);m),mT

2(pTj(2),qT

(2);m)}]

• Needs 01 mass measurement as input.

• Also works for sleptons.

qT(1)+qT

(2)=ETmiss

~ ~

~qR

q~

ATLAS

ATLAS

ATLAS

30 fb-130 fb-1 30 fb-1

Preliminary Preliminary

Preliminary

Left sleptonRight

squark

Right squark

~

~

SPS1a

SPS1aSPS1a

Precision ~ 3%


Heavy Gaugino MeasurementsHeavy Gaugino Measurements

• Also 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).

ATLAS100 fb-1

Preliminary

ATLAS100 fb-1

Preliminary Preliminary

ATLAS100 fb-1

ATLASPreliminary

SPS1a

SPS1a


Mass Relation MethodMass Relation Method• Hot off the press: new idea for reconstructing SUSY masses!• ‘Impossible to measure mass of each sparticle using one channel

alone’ (Page 8).– Should have added caveat: Only if done event-by-event!

• Remove ambiguities by combining different events analytically ‘mass relation method’ (Nojiri et al.).

• Also allows all events to be used, not just those passing hard cuts (useful if background small, buts stats limited – e.g. high scale SUSY).

Preliminary

ATLAS

AT

LA

S

SPS1a


Chargino Mass MeasurementChargino Mass Measurement• Mass of lightest chargino very

difficult to measure as does not participate in standard dilepton SUSY decay chain.

• Decay process via +slepton gives too many extra degrees of freedom - concentrate instead on decay +

1 W 01.

• Require dilepton 02 decay

chain on other ‘leg’ of event and use kinematics to calculate chargino mass analytically.

• Using sideband subtraction technique obtain clear peak at true chargino mass (218 GeV).

• ~ 3 significance for 100 fb-1.

PRELIMINARY

lqql

g~q~

lR

~02

~ 01

~p

p

+1

~~q

qq q

q01

~

Wg~

Modified LHCC Point 5: m0=100 GeV; m1/2=300 GeV; A0=300 GeV; tanß=6 ; μ>0

100 fb-1

~

~ ~


Measuring Model ParametersMeasuring 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.

Point m0 m1/2 A0 tan() sign() LHC Point 5 100 300 300 2 +1 SPS1a 100 250 -100 10 +1

Parameter Expected precision (300 fb-1) m0 2% m1/2 0.6% tan() 9% A0 16%


SUSY Dark MatterSUSY Dark Matter

Baer et al. hep-ph/0305191

LEP 2 No REWSB

LHC Point 5: >5 error (300 fb-1)

p=10-11 pb

p=10-10 pb

p=10-9 pb

• Can use parameter measurements for many purposes, e.g. estimate LSP Dark Matter properties (e.g. for 300 fb-1, SPS1a)– h2 = 0.1921 0.0053– log10(p/pb) = -8.17 0.04 SPS1a: >5

error (300 fb-1)

Micromegas 1.1 (Belanger et al.)+ ISASUGRA 7.69

ATLAS

300 fb-1

Preliminary

p

ATLAS

300 fb-1

Preliminary

DarkSUSY 3.14.02 (Gondolo et al.)+ ISASUGRA 7.69

h2


SUSY Dark MatterSUSY Dark Matter• SUSY (e.g. mSUGRA) parameter space strongly constrained by

cosmology (e.g. WMAP satellite) data.

mSUGRA A0=0, tan() = 10, >0

'Bulk' region: t-channel slepton exchange - LSP mostly Bino. 'Bread and Butter' region for LHC Expts.

'Focus point' region: significant h component to LSP enhances annihilation to gauge bosons

~

Ellis et al. hep-ph/0303043

01

01

l

llR

~

~~

01

1

/Z/h1

~

~~

Disfavoured by BR (b s) = (3.2 0.5) 10-4 (CLEO, BELLE)

Favoured by g-2 (E821) Assuming = (26 10) 10 -10 from SUSY ( 2 )

0.094 h2 0.129 (WMAP)

Slepton Co-annihilation region: LSP ~ pure Bino. Small slepton-LSP mass difference makes measurements difficult.

Also 'rapid annihilation funnel' at Higgs pole at high tan(


Coannihilation ModelsCoannihilation Models• Small slepton-neutralino mass difference gives soft leptons from

decay– Low electron/muon/tau energy thresholds crucial.

• At high tan() stau decay channel dominates. – Need to be able to ID soft taus (good jet rejection).

• Study just started within ATLAS examining signatures of these models.

• Study point chosen within coannihilation region :– m0=70 GeV; m1/2=350 GeV; A0=0; tanß=10 ; μ>0

• Same model to be used for ATLAS DC2 SUSY study (see later).

lqql

g~ q~ lR

~

~

~p p


Coannihilation SignaturesCoannihilation Signatures

• ETmiss>300 GeV

• 2 OSSF leptons PT>10 GeV• >1 jet with PT>150 GeV• OSSF-OSOF subtraction applied

• ETmiss>300 GeV

• 1 tau PT>40 GeV;1 tau PT<25 GeV• >1 jet with PT>100 GeV• SS tau subtraction

• Chosen model point has very rich phenomenology.

• Decays of 02 to both lL and lR

kinematically allowed.– Double dilepton invariant

mass edge structure;– Edges expected at 57 GeV and

101 GeV

• Stau decay channels enhanced– Soft tau signatures;– Edge expected at 79 GeV;– Less clear due to poor tau

visible energy resolution.

ATLAS

ATLAS

Preliminary

Preliminary

100 fb-1

100 fb-1

~~~


Super-LHCSuper-LHC

• Proposal to increase sqrt(s) to 28 TeV, luminosity to 1035

cm-2 s-1 after initial running (14 TeV, Lmax= 1034 cm-2 s-1).

• Significant impact on detector performance, esp. tracking, electronics etc.

• Increased luminosity improves discovery reach by ~ 300 GeV.

• Increased sqrt(s) (less easy technologically) more useful: 800 GeV improvement.

• Needs further study.

CMSA0 = 0; tan=10; >0


ATLAS: DC1 SUSY ChallengeATLAS: DC1 SUSY Challenge• First attempt at large-scale simulation of

SUSY signals in ATLAS (100 000 events: ~5 fb-1) in early 2003.

• Tested Geant3 simulation and ATHENA (C++) reconstruction software framework thoroughly.

• UK sites contributed 40% of initial 50 000 event sample.

No b-tagWith b-tag

llj endpoint

ATLAS

ATLAS

ATLAS

ATLAS

SUSY Mass Scale

Dijet mT2 distribution

ll endpoint

Modified LHCC Point 5: m0=100 GeV; m1/2=300 GeV; A0=300 GeV; tanß=6 ; μ>0

Preliminary

Preliminary

Preliminary

Preliminary


• ATLAS has just embarked on DC2 (main production over summer).• SUSY Working Group goals:

– To validate complete ATLAS simulation and reconstruction software chain using physics objects in SUSY events (jets, taus, leptons etc.);

– To carry out sample physics analyses for well-motivated SUSY models using fully simulated data.

• Models to be studied include: – DC1 point (for validation of Geant4 sim. + new reconstruction tools);

– New coannihilation point (rich in signatures).

• Activity just started (open call for volunteers + phone meeting so far).• UK interest so far from Cambridge, RHUL and Sheffield. • More volunteers very welcome! (please see me for details)• Similar activity within CMS (DC04, PRS SUSY/BSM WG) – aim to scan

parameter space and perform detailed studies with specific models in preparation for Physics TDR (late 2005). Contact Luc Pape <[email protected]> if interested.

Data Challenge ActivitiesData Challenge Activities


SupersummarySupersummary

• The LHC will be THE PLACE to search for, and hopefully study, SUSY from 2007 onwards.

• SUSY searches will commence on Day 1 of LHC operation.• Big challenge for discovery will be understanding systematics.• Many studies of exclusive channels already performed.• Massive scope for further work!• ATLAS and CMS currently focusing on Data Challenges.• Significant UK involvement already.• Please get involved – this is a great opportunity for the UK to

exploit its hardware investment.

ukhep forum, april 2004 dan tovey 1 prospects for susy at atlas and cms dan tovey university of...

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