ukhep forum, april 2004 dan tovey 1 prospects for susy at atlas and cms dan tovey university of...
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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
22 UKHEP Forum, April 2004UKHEP Forum, April 2004Dan ToveyDan Tovey
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!
33 UKHEP Forum, April 2004UKHEP Forum, April 2004Dan ToveyDan Tovey
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
44 UKHEP Forum, April 2004UKHEP Forum, April 2004Dan ToveyDan Tovey
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
55 UKHEP Forum, April 2004UKHEP Forum, April 2004Dan ToveyDan Tovey
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.
66 UKHEP Forum, April 2004UKHEP Forum, April 2004Dan ToveyDan Tovey
mSUGRA ReachmSUGRA Reach
ATLAS
5 5
77 UKHEP Forum, April 2004UKHEP Forum, April 2004Dan ToveyDan Tovey
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
88 UKHEP Forum, April 2004UKHEP Forum, April 2004Dan ToveyDan Tovey
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
99 UKHEP Forum, April 2004UKHEP Forum, April 2004Dan ToveyDan Tovey
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
1010 UKHEP Forum, April 2004UKHEP Forum, April 2004Dan ToveyDan Tovey
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)
1111 UKHEP Forum, April 2004UKHEP Forum, April 2004Dan ToveyDan Tovey
‘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%
~
~
~
~
1212 UKHEP Forum, April 2004UKHEP Forum, April 2004Dan ToveyDan Tovey
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
1313 UKHEP Forum, April 2004UKHEP Forum, April 2004Dan ToveyDan Tovey
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
~
~ ~
1414 UKHEP Forum, April 2004UKHEP Forum, April 2004Dan ToveyDan Tovey
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
1515 UKHEP Forum, April 2004UKHEP Forum, April 2004Dan ToveyDan Tovey
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%
1616 UKHEP Forum, April 2004UKHEP Forum, April 2004Dan ToveyDan Tovey
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
1717 UKHEP Forum, April 2004UKHEP Forum, April 2004Dan ToveyDan Tovey
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
1818 UKHEP Forum, April 2004UKHEP Forum, April 2004Dan ToveyDan Tovey
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
~
~ ~
1919 UKHEP Forum, April 2004UKHEP Forum, April 2004Dan ToveyDan Tovey
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%
2020 UKHEP Forum, April 2004UKHEP Forum, April 2004Dan ToveyDan Tovey
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
2121 UKHEP Forum, April 2004UKHEP Forum, April 2004Dan ToveyDan Tovey
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(
2222 UKHEP Forum, April 2004UKHEP Forum, April 2004Dan ToveyDan Tovey
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
2323 UKHEP Forum, April 2004UKHEP Forum, April 2004Dan ToveyDan Tovey
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
~~~
2424 UKHEP Forum, April 2004UKHEP Forum, April 2004Dan ToveyDan Tovey
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
2525 UKHEP Forum, April 2004UKHEP Forum, April 2004Dan ToveyDan Tovey
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
2626 UKHEP Forum, April 2004UKHEP Forum, April 2004Dan ToveyDan Tovey
• 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 <luc.pape@cern.ch> if interested.
Data Challenge ActivitiesData Challenge Activities
2727 UKHEP Forum, April 2004UKHEP Forum, April 2004Dan ToveyDan Tovey
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.
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