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Prospects for New Physics at the LHCAyana T ArceAPS/AAPT MeetingFebruary 13, 2010
atlas
New Physics @ LHC
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+Outline
New physics at the LHC
Looking for new physics with ATLAS and CMS
The art of the search
Possible discoveries using leptons, jets and lifetimes
Outlook
13 February 2010
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New Physics @ LHC
3New physics (to us)
Abell
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TSci
Bulle
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hand
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TeV-scale: age less than 1 picosecond
(very old physics!)
us
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New Physics @ LHC
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+new physics with the
Large Hadron Collider
gaps up to 3 μs even in 2808x2808 mode
ATLAS
CMS
cosmics,beam halo
3.5 TeV
3.5 TeV
bunches can cross every 25 ns(small fraction filled in early 2010 )
<1 inelastic interaction per crossingexpected in early 2010
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New Physics @ LHC
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+new physics with the
Large Hadron ColliderHow will the reduced energy for proton beams affect sensitivity?
Quig
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unfavorable BG scaling
Studies in this talk: 10 and 14 TeV simulation
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New Physics @ LHC
6seeing new physics with
ATLAS and CMS
?
e
Mostly looking for ~stable SM particles from exotic decays
but we might also “see” a dark matter candidate
neutral, invisible, stable missing
transverse momentum (MET)
and we can’t rule out new nearly-stable interacting (or late-
decaying) particles
new = heavy, so slow to arrive at a sensor
ubiquitous: jets (quarks/gluons made
anonymous)
rare: isolated leptons
rare in SM collisions: missing energy
optimize efficiency, ‘fake’ rate, energy resolution for e, Υ, μ, jets
13 February 2010
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New Physics @ LHC
7seeing new physics with
ATLAS and CMS
ATLAS (pixel/strip sensors + straw transition radiation tracker) TRT sensitive toβ(e/π separation)
toroidal µ spectrometer combined ID+ µ: σ(pT )≈5%
(prompt µ from 1-TeV resonance)
CMS: (pixel/strip sensors) solenoidal µ spectrometer
combined tracker+muon pT resolution ≈5% @1 TeV
B=4TR=7.5m
B=2TR=11m
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New Physics @ LHC
8seeing new physics with
ATLAS and CMS
LAr + Cu accordion EM calorimeter: σ(E)/E≈1% for 100 GeV e
fine strip granularity (.003 in η) 3 samplings: 4.3,16, 2 X0 in barrel
Fe + scintillating tile hadronic calorimeter: resolution at 1 TeV: 3%
PbWO4 crystal EM calorimeter: σ(E)/E≈0.5% for 120 GeV e
(0.0175)2 η×ϕ granularity
Cu +scintillator hadronic calorimeter: resolution at 1 TeV: 6%
muons
e,γ,jets
Q≠0
3 longitudinal segments
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New Physics @ LHC
9The art of the search Tevatron m(squark, gluino) limits: ~300-400 GeV
m( )> 149 GeV if short-lived Z’-like resonances not seen below ~1 TeV Large extra dimensions scale > 1 TeV (N>4)
SM is “unknown” in p+p @7 TeV choose between model+luminosity or
‘sideband extrapolation’ uncertainty
absolute jet calibration: statistics+time (ϒ,Z+jets): uncertainties affect efficiency (degrade
limits) , and background rejection (reduce
significance)
& li
mit
ati
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know
your lim
its…
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New Physics @ LHC
10The art of discovery
Data-driven background methods (cf. sideband subtraction)
inclusive searches: greater challenge to prove backgrounds are understood
Beware bias from presence of signal (blunted sensitivity)
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New Physics @ LHC
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Searchesdilepton resonances
tt resonances
extra dimensions
supersymmetry
lifetime signatures
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New Physics @ LHC
12early probes of new physics:
searching for dilepton pairs
dilepton resonances are generic to many models: GUTs, little Higgs, technicolor, Randall-Sundrum gravitons…
Background : predominantly Drell-Yan top, diboson: ~10% at higher mass
Sensitivity depends strongly on mass resolution
e, μ
e,μ
μe technique
Drell-Yan parameterization
ee: 14 TeV
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New Physics @ LHC
13early probes of new physics:
searching for dilepton pairs
Model width @ 1 TeV
Signal evts
Drell-Yan evts
SSM 30 GeV 16.9 0.11
Phi 6 GeV 4.33 0.60
GRS (c=0.1) 14 GeV 20.7 0.91
GRS (c=0.3) 3.5 GeV 4.87 .0036CMS100pb-1 @ 10 TeV
μμ14 TeV
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New Physics @ LHC
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2&3 TeV
Tags:jet masssecondary vertex tag
kT-like splitting scale
non-isolated muon
understanding the large top mass:
looking for tt resonances
can we explain mT ~ 175 GeV by enhanced couplings (Topcolor Z’; R-S with bulk fermions)?
Challenges: top identification; mass reconstruction with top quarks
escaping neutrinos
jets (heavy flavor)
angular separation decreases with energy
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New Physics @ LHC
15understanding the large top mass:
looking for tt resonances
10TeV
CMS semileptonic:~4% signal efficiency @ 1 TeV
CMS all-hadronic ‘double tags’ signal
efficiency 0.34% @ 1 TeV
100pb-1
1 fb-1
ATLAS: strong rejectionfor 2 TeV Z’ search
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New Physics @ LHC
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effects of strong gravity at distances ≤ 1/TeV:
black holes or stringballs (democratic decay to a large number of objects per event)
some searches for hidden dimensions:
BH events
Black holes
14 TeV
Cuts: 4 high-pt objects and a lepton
High pT objects (>200 GeV):
pass single jet triggers without prescale
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effects of strong gravity at distances ≤ 1/TeV:
black holes or stringballs (democratic decay to a large number of objects per event)
some searches for hidden dimensions:
BH events
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stringballs
10 TeV
High pT objects (>200 GeV):
pass single jet triggers without prescale
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New Physics @ LHC
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graviton+jet signature: “monojet” collision backgrounds:
invisible Z+jet top/single top: reducible “invisible W,” Wtau
also contaminated by cosmic rays, beam halo
14 TeV
Z/Winvisible background: normalize to Wmuon
some searches for hidden dimensions:
gG events
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New Physics @ LHC
19sparticles and dark matter: inclusive SUSY searches
ttbar-like events
Typically heavy squarks/gluinos
cascade to LSP:
energetic SM particles emitted at each decay
large missing energy from dark matter candidate
600-700 GeV squark/gluino masses accessible with 200 pb-1
Lead jet: 100-180 GeV
~40-50 GeV jets20 GeV leptons
missing E(T):~ 0.3*M(Eff)
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New Physics @ LHC
20sparticles and dark matter:
GMSB signature: nLSP
Photon “tracking” without conversions measure lifetime via displacement + TOF
few cm displacement
~50 GeV photon trigger (or multi- jets)
# photons
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New Physics @ LHC
21other long-lived signatures:
charged massive particle ID charge allows velocity measurement
by time of flight and ionization
signalBG
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TRT high-threshold hits
10 TeV
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New Physics @ LHC
22working overtime:
searching for split SUSY R-hadrons can stop in the detector material
Note axis units! Uncertainties: gluino production model
exotic stopping power of CMS LHC operations
Selection BG rate Efficiency
Trigger 5Hz 31%
50 GeV jet 0.02 Hz 20%
Muon veto 0.005 Hz 19%
Cleaning cuts
0.4 mHz 16%
collisions
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New Physics @ LHC
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+ New (timely!) theory ideas, bigger backgrounds, new
experimental challenges: analyses are maturing before high-energy data arrives
This was a truncated overview: the first discovery may not be in these slides… it may show
up as something entirely unexpected!
Outlook
13 February 2010