Transcript Prospects for SUSY at ATLAS and CMS

Supersymmetry
at ATLAS
Dan Tovey
University of Sheffield
Dan Tovey
1
Kyoto, January 2005
Supersymmetry
• Supersymmetry (SUSY) fundamental
continuous symmetry connecting
fermions and bosons
Qa|F> = |B>,
Qa|B> = |F>
• {Qa,Qb}=-2gmabpm: generators of SUSY ~
‘square-root’ of translations
– 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.
Dan Tovey
2
Kyoto, January 2005
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
Dan Tovey
3
Kyoto, January 2005
SUSY & Dark Matter
• R-Parity Rp = (-1)3B+2S+L
• Conservation of Rp
(motivated e.g. by string
models) attractive
m1/2 (GeV)
– e.g. protects proton from
rapid decay via SUSY states
Universe Over-Closed
• 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 of
astrophysics / cosmology
• R-Parity violating models still
possible  not covered here.
Dan Tovey
Baer et al.
4
m0 (GeV)
Kyoto, January 2005
SUSY @ ATLAS
• LHC will be a 14 TeV proton-proton
collider located inside the LEP
tunnel at CERN.
• Luminosity goals:
– 10 fb-1 / year (first 3 years)
– 100 fb-1/year (subsequently).
• First data in 2007.
• Higgs & SUSY main goals.
• Much preparatory work carried out
historically by ATLAS
– Summarised in Detector and
Physics Performance TDR (1998/9).
• Work continuing to ensure ready to
test new ideas in 2007.
• Concentrate here on more recent
work.
Dan Tovey
5
Kyoto, January 2005
Model Framework
• Minimal Supersymmetric Extension of the Standard Model (MSSM)
contains > 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
LHCC
(m0, m1/2, A0, tan(b), sgn(m)).
mSUGRA
• R-Parity assumed to be conserved.
Points
• Exclusive studies use benchmark
3
points in mSUGRA parameter space:
•
•
•
•
LHCC Points 1-6;
Post-LEP benchmarks (Battaglia et al.);
Snowmass Points and Slopes (SPS);
etc…
Dan Tovey
6
5
1
2
4
Kyoto, January 2005
SUSY Signatures
• Q: What do we expect SUSY events @ LHC to look like?
• A: Look at typical decay chain:
p
p
~
g
q
~
q
~
c0 2
q
~
c0 1
~
l
l
l
• 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.
Dan Tovey
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Kyoto, January 2005
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
Dan Tovey
ATLAS
8
Kyoto, January 2005
SUSY Mass Scale
• First measured SUSY parameter
likely to be mass scale:
Jets + ETmiss + 0 leptons
– Defined as weighted mean of
masses of initial sparticles.
ATLAS
• Calculate distribution of 'effective
mass' variable defined as scalar
sum of masses of all jets (or four
hardest) and ETmiss:
Meff=S|pTi| + ETmiss.
• 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.
Dan Tovey
9
10 fb-1
ATLAS
10 fb-1
Kyoto, January 2005
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.
p
p
~
q
~g
q
~
c0 2
q
~
lR
l
~
c0 1
l
• 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.
Dan Tovey
10
Kyoto, January 2005
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
c~02
l
c~01
l
e+e- + m+m- e+m- - m+e-
e+e- + m+mPoint 5
ATLAS
~
l
30 fb-1
atlfast
Physics
TDR
5 fb-1
FULL SIM
ATLAS
Modified
Point 5
(tan(b) = 6)
e+e- + m+m- - e+m- - m+e-
• Position of edge measured
with precision ~ 0.5%
(30 fb-1).
Dan Tovey
11
Kyoto, January 2005
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.
~
qL
~
q c0 2
l
~
l
l
~
qL
~
c0 1
~
q c0 2
llq threshold
lq edge
1% error
(100 fb-1)
1% error
(100 fb-1)
ATLAS
Dan Tovey
TDR,
Point 5
ATLAS
h
b
llq edge
TDR,
Point 5
2% error
(100 fb-1)
TDR,
Point 5
ATLAS
12
~
c0 1
b
bbq edge
1% error
(100 fb-1) TDR,
Point 5
ATLAS
Kyoto, January 2005
‘Model-Independent’ Masses
• Combine measurements from edges
from different jet/lepton
combinations to obtain ‘modelindependent’ mass measurements.
~
c0
ATLAS
Mass (GeV)
~c0
2
ATLAS
LHCC
Point 5
~
lR
1
Mass (GeV)
ATLAS
Mass (GeV)
~
q
L
ATLAS
Mass (GeV)
Sparticle Expected precision (100 fb-1)
~
qL
 3%
~
c02
 6%
~
lR
 9%
~
c01
 12%
Dan Tovey
13
Kyoto, January 2005
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.
~0 mass
• Problem with large error on input c
1
remains g reconstruct difference of gluino
and sbottom masses.
~
~
• Allows separation of b1 and b2 with 300 fb-1.
p
p
~g ~
b
b
Dan Tovey
~0
c2
b
~
lR
l
~
~0 )
m(g)-0.99m(c
1
= (500.0 ± 6.4) GeV
300 fb-1
ATLAS
SPS1a
~)
~
m(g)-m(b
1
= (103.3 ± 1.8) GeV
~
~
m(g)-m(b
2)
= (70.6 ± 2.6) GeV
ATLAS
300 fb-1
~0
c1
SPS1a
l
14
Kyoto, January 2005
Stop Mass
• Look at edge in tb mass distribution.
• Contains contributions from
–
–
–
~ ~ tbc
~+
gtt
1
1
~
~+
~
gbb
1btc 1
SUSY backgrounds
120 fb-1
ATLAS
• Measures weighted mean of end-points
• Require m(jj) ~ m(W), m(jjb) ~ m(t)
mtbmax = (510.6 ± 5.4stat)
GeV
Expected = 543 GeV
120 fb-1
ATLAS
LHCC Pt 5
(tan(b)=10)
mtbmax = (443.2 ± 7.4stat)
GeV
Expected = 459 GeV
LHCC Pt 5
(tan(b)=10)
• Subtract sidebands from m(jj)
distribution
• Can use similar approach with
~
~
gtt1ttc~0i
– Di-top selection with sideband
subtraction
• Also use ‘standard’ bbll analyses
(previous slide)
Dan Tovey
15
Kyoto, January 2005
RH Squark Mass
• Right handed squarks difficult as rarely decay via ‘standard’ ~
c02 chain
~ gc
~0 q) > 99%.
– Typically BR (q
R
1
• Instead search for events with 2 hard jets and lots of ETmiss.
• Reconstruct mass using ‘stransverse mass’ (Allanach et al.):
mT22 =
min
c(1)
c(2)
miss
[max{mT2(pTj(1),qTc(1);mc),mT2(pTj(2),qTc(2);mc)}]
q
+q
=E
~
0
• Needs c 1 mass measurement as input.
• Also works for sleptons.
T
T
T
~
c0 1
q
ATLAS
ATLAS
30 fb-1
30 fb-1
Right
squark
SPS1a
~
qR
ATLAS
100 fb-1
SPS1a
SPS1a
Right
squark
Left slepton
Precision ~ 3%
Dan Tovey
16
Kyoto, January 2005
Heavy 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).
ATLAS
SPS1a
ATLAS
100 fb-1
Dan Tovey
ATLAS
100 fb-1
17
ATLAS
100 fb-1
SPS1a
Kyoto, January 2005
Mass Relation Method
• New idea for reconstructing SUSY masses!
• ‘Impossible to measure mass of each sparticle using one channel
alone’ (Slide 10).
– Should have added caveat: Only if done event-by-event!
• Assume in each decay chain 5 inv. mass constraints for 6 unknowns (4
~0 momenta + gluino mass + sbottom mass).
c
1
• Remove ambiguities by combining different events analytically g
‘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).
ATLAS
Preliminary
Dan Tovey
ATLAS
SPS1a
18
Kyoto, January 2005
Chargino Mass Measurement
• Mass of lightest chargino very
difficult to measure as does not
participate in standard dilepton
SUSY decay chain.
• Decay process via n+slepton
gives too many extra degrees
of freedom - concentrate
~+ g W c~0 .
instead on decay c
1
1
• Require dilepton ~
c02 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 s significance for 100 fb-1.
Dan Tovey
~0
c
1
~
c+1
W
q q q
~
q q~
g
p
p
~
g
~ c~01
lR
~
c 02
~
q
q
q
l
PRELIMINARY
Modified
LHCC Point 5:
m0=100 GeV;
m1/2=300 GeV;
A0=300 GeV;
tanß=6 ; μ>0
100 fb-1
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Kyoto, January 2005
l
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.
Point
LHC Point 5
SPS1a
Parameter
m0
m1/2
tan(b)
A0
Dan Tovey
m0 m1/2 A0
100 300 300
100 250 -100
tan(b) sign(m)
2
+1
10
+1
Expected precision (300 fb-1)
 2%
 0.6%
 9%
 16%
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Kyoto, January 2005
SUSY Dark Matter
• 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
Micromegas 1.1
(Belanger et al.)
+ ISASUGRA 7.69
Wc
Dan Tovey
h2
Baer et al. hep-ph/0305191
LHC Point 5: >5s error (300 fb-1)
SPS1a: >5s
error (300 fb-1)
scp=10-11 pb
DarkSUSY 3.14.02
(Gondolo et al.)
+ ISASUGRA 7.69
scp=10-10 pb
scp
scp=10-9 pb
300 fb-1
300 fb-1
ATLAS
ATLAS
21
LEP 2
No REWSB
Kyoto, January 2005
SUSY Dark Matter
• SUSY (e.g. mSUGRA) parameter space strongly constrained by
cosmology (e.g. WMAP satellite) data. mSUGRA A0=0,
tan(b) = 10, m>0
Ellis et al. hep-ph/0303043
'Focus point'
region:
~
significant h
component to
LSP enhances
annihilation to
gauge bosons
Disfavoured by BR (b  sg) =
(3.2  0.5)  10-4 (CLEO, BELLE)
c~01
'Bulk' region: tchannel slepton
exchange - LSP
mostly Bino.
'Bread and
Butter' region for
LHC Expts.
Dan Tovey
DC1/2
Rome
c~01
~0
c
1
l
~
lR
t~1
t
t~1
g/Z/h
Slepton Coannihilation
region: LSP ~
pure Bino. Small
slepton-LSP
mass difference
makes
measurements
difficult.
l
Also 'rapid
annihilation funnel'
at Higgs pole at
0.094  W c h2  0.129
(WMAP)
high tan(b), stop
co-annihilation
region at large A0
22
Kyoto, January 2005
Coannihilation Signatures
• Small slepton-neutralino mass
difference gives soft leptons
100 fb-1
– Low electron/muon/tau energy
thresholds crucial.
ATLAS
• Study point chosen within region:
– m0=70 GeV; m1/2=350 GeV; A0=0;
tanß=10 ; μ>0;
– Same model used for DC2 study.
• ETmiss>300 GeV
• 2 OSSF leptons
PT>10 GeV
• >1 jet with PT>150
GeV
• OSSF-OSOF
subtraction applied
Preliminary
~
~
• Decays of ~c02 to both lL and lR
kinematically allowed.
– Double dilepton invariant mass
edge structure;
– Edges expected at 57 / 101 GeV
100 fb-1
• Stau channels enhanced (tanb)
– Soft tau signatures;
– Edge expected at 79 GeV;
– Less clear due to poor tau visible
energy resolution.
Dan Tovey
Preliminary
23
ATLAS
• ETmiss>300 GeV
• 1 tau PT>40
GeV;1 tau PT<25
GeV
• >1 jet with
PT>100 GeV
• SS tau
subtraction
Kyoto, January 2005
Focus Point Models
• Large m0  sfermions are heavy
• Most useful signatures from heavy neutralino decay
• Study point chosen within focus point region :
– m0=3000 GeV; m1/2=215 GeV; A0=0; tanß=10 ; μ>0
~0 → c
~0 ll
• Direct three-body decays c
n
1
~0 )-m(c
~0 )
~
• Edges give m(c
c 02 → ~
c01 ll
n
1
~0 → ~
c
c01 ll
3
ATLAS
Z0 → ll
ATLAS
30 fb-1
Preliminary
Preliminary
Dan Tovey
24
Kyoto, January 2005
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 proposal – 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
Spin-0
Measure
Angle
A
Spin-½

l l
  
l l
Point 5
Point 5
ATLAS
150 fb -1
mlq
spin-0=flat
Polarise
Spin-½,
Spin-0
mostly wino
Dan Tovey
150 fb -1
ATLAS
Straight
line distn
(phase-space)
Spin-½,
mostly bino
25
Kyoto, January 2005
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.
ll endpoint
ATLAS
Preliminary
No b-tag
With b-tag
llj endpoint
Modified
LHCC Point 5:
ATLAS
Preliminary m0=100 GeV;
m1/2=300 GeV;
A0=300 GeV;
tanß=6 ; μ>0
SUSY
Mass
Scale
Dijet mT2
distribution
ATLAS
Preliminary
ATLAS
Preliminary
Dan Tovey
26
Kyoto, January 2005
DC2 SUSY Challenge
• DC2 testing new G4 simulation and
reconstruction.
• Points studied:
m+m- endpoint
– DC1 bulk region point (test G4)
– Stau coannihilation point (rich in signatures test reconstruction)
ATLAS
Preliminary
DC1 Point
• Further studies planned in run up to Rome
Physics Workshop (Focus Point model etc.)
Work in Progress!
m+m-
endpoint
ll endpoint
DC1 Point
ATLAS
Coannihilation
Point
Preliminary
ATLAS
Coannihilation
Point
Preliminary
ll endpoint
Dan Tovey
27
Kyoto, January 2005
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.
• Different situation to Run II (no previous s measurements at same s)
• 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.
• Aim to study with full-sim (DC2) data
Dan Tovey
28
Kyoto, January 2005
Background Estimation
• Main backgrounds:
–
–
–
–
• Also:
– Single top
– WW/WZ/ZZ
Z + n jets
W + n jets
ttbar
QCD
Jets + ETmiss + 0 leptons
ATLAS
10 fb-1
• Generic approach :
– Select low ETmiss background calibration
samples;
– Extrapolate into high ETmiss signal region.
QCD
W+jet
Z+jet
ttbar
ATLAS
Dan Tovey
• Used by CDF / D0
• Extrapolation non-trivial.
– Must find variables uncorrelated with ETmiss
• Several approaches developed.
• Most promising: Use Z ( ll) + jets to
estimate Z ( nn) / W ( ln) + jets
29
Kyoto, January 2005
Top Background
• Estimation using simulation possible
(normalised to data ttbar selection) –
cross-check with data
• Isolate clean sample of top events
using mass constraint(s).
• Then plot ETmiss distribution (large
statistical errors), compare with same
technique applied to SUSY events
(SPS1a benchmark model).
• Reconstruct leptonic W momentum
from ETmiss vector and W mass
constraint (analytical approach –
quadratic ambiguity).
• Select solution with greatest W pT.
• Select b-jet with greatest pT.
• Plot invariant mass of combination.
Dan Tovey
30
ATLAS
ttbar
Preliminary
SUSY
ATLAS
Preliminary
Kyoto, January 2005
Top Background
• Select events in peak and examine
ETmiss distribution.
• Subtract combinatorial background with
appropriately weighted (from MC)
sideband subtraction.
• Good agreement with top background
distribution in SUSY selection.
ttbar
ATLAS
Preliminary
SUSY
ATLAS
Preliminary
• With this tuning does not select
SUSY events (as required)
• Promising approach but more work
needed (no btag etc.)
Histogram – 1 lepton SUSY selection (no b-tag)
Data points – background estimate
Dan Tovey
31
Kyoto, January 2005
Supersummary
• The LHC will be THE PLACE to search for, and hopefully study, SUSY
from 2007 onwards (at least until ILC).
• SUSY searches will commence on Day 1 of LHC operation.
• Many studies of exclusive channels already performed.
• Lots of input from both theorists (new ideas) and experimentalists
(new techniques).
• Renewed emphasis on use of full simulation tools.
• Big challenge for discovery will be understanding systematics.
• Big effort ramping up now to understand how to exploit first data in
timely fashion
–
–
–
–
Calibrations
Background rejection
Background estimation
Tools
• Massive scope for further work!
Dan Tovey
32
Kyoto, January 2005
BACK-UP SLIDES
Dan Tovey
33
Kyoto, January 2005
llq Edge
• Dilepton edges provide starting point for other measurements.
• Use dilepton signature to tag presence of ~
c02 in event, then work back
up decay chain constructing invariant mass distributions of
combinations of leptons and jets.
~
qL
e.g. LHC Point 5
q
~0
c2
l
~
l
~0
c1
l
• Hardest jets in each event produced
by RH or LH squark decays.
• Select smaller of two llq invariant
masses from two hardest jets
ATLAS
1% error
(100 fb-1)
Physics
TDR
Point 5
– Mass must be < edge position.
• Edge sensitive to LH squark mass.
Dan Tovey
34
Kyoto, January 2005
lq Edge
• Complex decay chain at LHC Point 5 gives
additional constraints on masses.
• Use lepton-jet combinations in addition to
lepton-lepton combinations.
• Select events with only one dilepton-jet
pairing consistent with slepton hypothesis
g Require one llq mass above edge and one
below (reduces combinatorics).
Point 5
Physics
TDR
• Construct distribution of
invariant masses of 'slepton'
jet with each lepton.
• 'Right' edge sensitive to
slepton, squark and ~
c 02
masses ('wrong' edge not
visible).
ATLAS
1% error
(100 fb-1)
Physics
TDR
Point 5
Dan Tovey
ATLAS
35
Kyoto, January 2005
hq edge
• If tan(b) not too large can also observe two body decay of ~c02 to
~0 .
higgs and c
1
• Reconstruct higgs mass (2 b-jets) and combine with hard jet.
• Gives additional mass constraint.
~
qL
ATLAS
q
~
c0 2
~
c0 1
h
b
b
Point 5
1% error
(100 fb-1)
Physics
TDR
Dan Tovey
36
Kyoto, January 2005
llq Threshold
• Two body kinematics of sleptonmediated decay chain also provides
still further information (Point 5).
• Consider case where ~
c01 produced
~0 frame.
near rest in c
2


ATLAS
Physics
TDR
Point 5
Dilepton mass near maximal.
~ 0 ).
p(ll) determined by p(c
2
ATLAS
Physics
TDR
Point 5
2% error
(100 fb-1)
Dan Tovey
• Distribution of llq invariant
masses distribution has
maximum and minimum (when
quark and dilepton parallel).
• llq threshold important as
contains new dependence on
mass of lightest neutralino.
37
Kyoto, January 2005
Mass Reconstruction
• Combine measurements from
edges from different
jet/lepton combinations.
• Gives sensitivity to masses
(rather than combinations).
Dan Tovey
38
Kyoto, January 2005
High Mass mSUGRA
• ATLAS study of sensitivity to models
with high mass scales
• E.g. CLIC Point K  Potentially
observable … but hard!
ATLAS
1000 fb -1
• Characteristic double peak in signal
Meff distribution (Point K).
• Squark and gluino production crosssection reduced due to high mass.
• Gaugino production significant
Dan Tovey
39
Kyoto, January 2005
AMSB
• Examined RPC model with
tan(b) = 10, m3/2=36 TeV, m0=500
GeV, sign(m) = +1.
~
~
• c+/-1 near degenerate with c01.
~
~
• Search for c+/-1 g p+/-c01
(Dm = 631 MeV g soft pions).
• Also displaced vertex due to phase
space (ct=360 microns).
• Measure mass difference between
chargino and neutralino using mT2
variable (from mSUGRA analysis).
Dan Tovey
40
Kyoto, January 2005
GMSB
• Kinematic edges also useful for GMSB models when neutral
LSP or very long-lived NLSP escapes detector.
• Kinematic techniques using invariant masses of
combinations of leptons, jets and photons similar.
• Interpretation different though.
• E.g. LHC Point G1a (neutralino NLSP with prompt decay to
gravitino) with decay chain:
~0
c2
l
Dan Tovey
~
l
~0
c1
l
41
g
~
G
Kyoto, January 2005
GMSB
• Use dilepton edge as before (but different position in chain).
• Use also lg, llg edges (c.f. lq and llq edges in mSUGRA).
• Get two edges (bonus!) in lg as can now see edge from 'wrong' lepton
(from c02 decay). Not possible at LHCC Pt5 due to masses.
• Interpretation easier as can assume gravitino massless:
Dan Tovey
42
Kyoto, January 2005
R-Parity Violation
•
•
Missing ET for events at
SUGRA point 5 with and
without R-parity violation
RPV removes the classic
SUSY missing ET signature
• Use modified effective mass
variable taking into account pT of
leptons and jets in event
mT ,ce nt   pTje t,le pton
 2
Dan Tovey
43
Kyoto, January 2005
R-Parity Violation
• Baryon-Parity violating case
hardest to identify (no leptons).
Phase space
sample 8j +2l
– Worst case: "212 - no heavy-quark jets
• Test model studied with decay
chain:
q˜ L  c˜ 20q  l˜Rlq  c˜ 10llq
• Lightest neutralino decays via BPV
coupling:
c˜ 10  cds
• Reconstruct neutralino mass from
3-jet combinations (but large
combinatorics : require > 8 jets!)
Dan Tovey
44
Kyoto, January 2005
R-Parity Violation
• Use extra information from
leptons to decrease background.
0
• Sequential decay of q~L to c˜ 1
~
0
through c˜ 2 and lR producing
Opposite Sign, Same Family
(OSSF) leptons
c˜ 20
q~L
q
Dan Tovey
Test point
~
lR
l
Decay via ~lR allowed where
0
~
m( c˜ 2 ) > m( lR )
c˜ 10
l
q
q
q
45
Kyoto, January 2005
R-Parity Violation
• Perform simultaneous (2D) fit to 3jet and 3jet + 2lepton combination
(measures mass of c~02).
No peak in
phase space
sample
Gaussian fit:
m( c˜ 10 ) = 118.9  3 GeV, (116.7 GeV)
m( c˜ 20 ) = 218.5  3 GeV (211.9 GeV)
• Jet energy scale
uncertainty  3%
 3 GeV systematic
• Can also measure squark and slepton masses.
Dan Tovey
46
Kyoto, January 2005
R-Parity Violation
Distinguishing
 " ijk from  " lmn
uds
udb
usb
cds
cdb
csb
udb
usb
cds
cdb
csb
usb
cds
cdb
csb
cds
cdb
csb
cdb
csb
• Different ”ijk RPV couplings
cause LSP decays to different
quarks:
0
1
1 2 3
c˜  q q q
• Identifying the dominant ”
gives insight into flavour
structure of model.
• Use vertexing and non-isolated
muons to statistically separate
c- and b- from light quark jets.
• Remaining ambiguity from d s
• Dominant coupling could be
identified at > 3.5 s
Dan Tovey
47
Vertexing
c2 / df P / %
59.1/1 73.0/1 30.5/1 106.9/1 113.4/1 1.6/2 44
10.3/2 1
18.3/2 16.3/2 17.5/2 12.1/2 9.9/2
1
56.1/2 55.8/2 0.6/2 72
Muons
Combined
c2 / df P / %
s
28.7/1
9.4
31.7/1
10.2
4.0/1
4
5.9
47.2/1
12.4
49.2/1
12.8
0.4/1
54
1.4
13.0/1
4.8
6.8/2
3
5
5.1/2
8
4.6
17.2/1
5.9
5.1/1
2
4.2
3.1/1
8
3.6
37.4/1
9.7
35.3/1
9.5
1.3/2
51
1.4
Kyoto, January 2005