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(htt)
BR(hWW)
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.