Transcript Slide 1
ATLAS
Higgs and SUSY at the LHC
Alan Barr
on behalf of the ATLAS and
CMS collaborations
ICHEP-17 Aug 2004, Beijing
Outline
• Discovery and measurement of:
– Higgs sector of MSSM
– SUSY partners of SM particles
• SUSY and Higgs discovery reviewed
– Reach, channels
• Focus on some recent work:
– Determination of higgs v.e.v. ratio (tan b)
– SUSY spin measurement
– Mixed Higgs + SUSY cascade decays
(S)particle reminder
SM+ MSSM Higgs
Spin-1/2
Spin-1
Spin-0
quarks (L&R)
leptons (L&R)
neutrinos (L&?)
Z0
W±
gluon
h0
H0
A0
H±
B
W0
SUSY
squarks (L&R)
sleptons (L&R)
sneutrinos (L&?)
Bino
Wino0
Wino±
gluino
~
H0
~
H±
Extended higgs sector
(2 doublets)
Spin-0
After
Mixing
4 x neutralino
Spin-1/2
gluino
2 x chargino
Neutral Higgs
production
Mass of H or h
SM-like higgs discovery
h → tt requires
excellent low-pT lepton
+ tau jet trigger
fb-1
1 year
@1034
time
1 year
@1033
1 month
@1033
ATLAS
Values for single experiment
h: Number of observable final states
Conservative in tan b
1 channel
2 channels
3 channels
4 channels
Excluded by LEP
5 channels
300 fb-1
several channels
observable
allows parameter
determination ?
Suppressed g coupling
Suppressed b, t
Heavy neutral higgs (H,A)
Measuring tan b (1)
• Ratio of v.e.v.s of the 2 MSSM Higgs
doublets
• Important for understanding EWSB
gg A0 , H 0bb
~
• For large (>5)
tan b
–
–
–
–
b Yukawa dominates s
s tan2 b
Measure s
Compare to NLO
Measuring tan b (2)
• Errors
dominated by
theoretical
uncertainty
on NLO
cross-section
• With signal
discovery at
5σ, tan b
measurable to
35%.
N.B. m, M2 kept fixed here
Charged higgs production/decay
• Associated
production with t
and b quarks
• Decay H± →
– Very complicated
final state!
– Combinatorial BG
• Also H± → t nt
– BR decreases as mA
increases
~6 jet + lepton + missing energy
SM background uncertain?
Charged higgs
ATLAS
• When H+ is
close to top
mass:
– H+ -> tb
or
– t -> H+b
• Revised
analyses in
progress
Overall Discovery Potential: 300 fb-1
ATLAS
• Whole plane
covered for at
least one Higgs
• Large wedge area
(intermediate tan
b) where only h is
observed
• No direct
evidence for higgs
beyond SM
Can we distinguish between SM and extended Higgs
sectors by parameter measurements?
SM or Extended Higgs
Sectors?
ATLAS
First look using rate
measurements from VBF
channels (30fb-1)
R=
BR(htt)
BR(hWW)
Deviation from SM expectation
D=|RMSSM-RSM|/sexp
potential for discrimination
seems promising!
only statistical errors considered
assumes Higgs mass exactly known
Searching for SUSY
• If SUSY was exact we’d have seen it
already
• Variety of ways to induce SUSY masses:
– Minimal super-gravity (mSUGRA)
– Anomaly mediated SUSY breaking (AMSB)
– Gauge mediated SUSY breaking (GMSB)
• Experimental emphasis is on building
general toolkit of techniques based on
types of signatures of above
• Generally search reach ~2 TeV.
SUSY Discovery - mSUGRA
Gaugino mass term
• Finial discovery
limit ~ 2.5 TeV
squark or gluino
• Initially will be
limited by
detector
uncertainties,
not SUSY
stats!
Scalar mass term
• Also need to
understand SM
backgrounds
Slepton, squark, neutralino
masses
~
qL
~
0
q c2
l
Apply corrections for
electron and muon
energy scale and
efficiency
Flavor Subtracted
mass to remove the
contribution from
uncorrelated SUSY
decays:
e+e- + m+m- - e+m- - e-m+
~
l
~
c0 1
l
M(c2)-M(c1) ≈ 105 GeV
5 fb-1
SUSY measurements - mass
• Mass measurements
from exclusive
cascade decays
• Mass differences well
measured
– Typically limited by
detector performance
• Of order 1%
• Error in overall mass
scale
– Unknown missing energy
• Of order 10%
q
~
qR
p
p
~
qR
q
c0 1
c0 1
ATLAS
Squark – neutralino1
mass difference
5 fb-1
SUSY SPIN @ LHC
• SUSY particles
have spin
differing by ½
from SM
• “Discovering
SUSY” means
measuring spins of
new particles
• Possible at LHC?
• Investigation of
mSUGRA “Point 5”
Chiral coupling
l {e, m}
Measure
Angle (or inv mass)
Spin-0
Spin-½
Polarise
Spin-½,
mostly wino
Spin-0
Spin-½,
mostly bino
Final state = jet + l+ + l- + ET
( + decay of other sparticle)
Similar technique allows measurement of tanb from muon/electron asymmetry
l-
A
ATLAS
parton-level
l+
Charge asymmetry,
Events
SUSY spin – observable distributions
l l
l l
spin-0
detector-level
ATLAS
Lepton+jet invariant mass
* 0
-> Measure spin-1/2 nature of neutralino-2
-> Also can measure scalar nature of slepton
-> Success at several distinct points in parameter space
* 1
SUSY produces Higgs
q~
(720 GeV)
g~ (600 GeV)
Strongly interacting,
g~ (1200 GeV)
so high rate
~c
~c (1000 GeV)
~c
0
4
2
0
3
~c
~c
0
4
~c
(340 GeV)
2
q~
(800 GeV)
0
Other points &
combinations also
investigated
3
~c
~c
0
h0, H0, A0, H±
~c
~c
0
2
(170 GeV)
2
(400 GeV)
1
h0, H 0, A0, H±
1
~c
0
1
(95 GeV)
~c
0
1
(200 GeV)
• Provided Heavy higgs are ~<150 GeV -> produced
• Missing energy + jet/lepton + higgs decay->bb
• Apply very simple (general) analysis
SUSY -> h,H,A -> bb
h
H,A
30 fb-1
h
H,A
: susy signal
: susy bkg
: SM tt bkg
H0, A0 -> SUSY -> leptons
hep-ph/0303095
SUSY -> light higgs
• Region of
parameter
space where h
is discoverable
• ~ cosmological
“bulk region”
CMS note 2003-033 for summary
±
H
-> SUSY
• Harder!
• Works in
restricted area
of m, M2 space
• Complements
tau, tb analysis.
H c2,30 c1,2 3l + ETmiss
hep-ph/0303093
Conclusions (1)
• LHC SUSY and Higgs search strategies
well developed
– Constantly being reviewed / developed
• New techniques in Higgs sector
– Production via Vector Boson Fusion
• Improves reach for MSSM benchmarks
– Couplings if only lightest higgs accessible
• Infer non-SM Higgs sector
– Measurement of tan b
Conclusions (2)
• New SUSY techniques
– Lepton asymmetry
• Charge -> spin determination
• Flavour -> tan b
– Full likelihood event reconstruction
• 3rd generation squarks + heavy gauginos
– (not covered in this talk)
• Combined SUSY + Higgs
– Complimentary to standard Higgs searches
– Could help dis-entangle complex SUSY chains
• Much work going on for trigger,
calibration, systematics.
Backup slides
SM-like higgs discovery
ATLAS
h → tt requires multi-object t-jet, lepton trigger
Charged higgs
SUSY spin – lepton asymmetry
Probability
quark
θ*
q~L
lepton
qL
0
~
c
2
Back to back
in c20 frame
Invariant mass
l
~
lR
R
Phase space -> factor of sin ½θ*
Spin projection factor in |M|2:
l+q -> sin2 ½θ*
l-q -> cos2 ½θ*
l+
Phase space
l-
m/mmax = sin ½θ*
In presence of spincorrelations, lq invariant mass
is different for l+ and l-
mSUGRA Dilepton edge reach
SM-like higgs rate measurement
Overall Summary
Two experiments,
30 fb-1, charged
and neutral higgs.