Searches at the Run II Tevatron Collider

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Searches at the Run II Tevatron Collider

• Leslie Groeron behalf of the DØ and CDF
  Collaborations
• Columbia University, New York
• Conference on the Intersections of Particle and
  Nuclear Physics
• New York City, NY
  May 22, 2003

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Searching for New Phenomena at the Tevatron

• Many different forms
• Observation of the last unseen particle predicted
  by SM
• Higgs
• Discovery of particles not in the SM
• SUSY, Leptoquarks
• Identification of new gauge interactions
• W/Z, Technicolor
• Unexpected complexities beyond the SM
• Compositeness
• Fundamental changes to modern physics
• Extra dimensions
• Common theme - look for experimental signatures
  that could exhibit deviations from expectations
• Prefer to set model independent limits

• Outline
• Tevatron Run II
• CDFDØ Detectors
• Preliminary Results
• Higgs
• New Physics
• Run II future prospects
• Conclusions

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Tevatron Run II pp Collider
-

• 92-96 Run I 125 pb-1
• top quark discovery
• 96-00 Accelerator and Detector upgrades
• Main Injector and Recycler rings
• Increased luminosity and energy
• 2001-2005 Run IIa 2 fb-1
• Upgrade Silicon and Trigger
• 2006? Run IIb 9-15 fb-1

Run II Delivered Luminosity Total 240 pb-1
Best week 7 pb-1 L 4.5 x 1031 cm-2s-1

• 1.8 TeV ? 1.96 TeV
• e.g. ?tt increase 30
• 6 p x 6 pbar ? 36 p x 36 pbar
• Bunch spacing 3.5?s ? 0.396?s

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CDF DØ Run II Detectors
CDF

• Major upgrades to both detectors
• New inner tracking chambers and silicon detectors
• Extensions and improvements to muon systems and
  triggering
• Complete replacement of trigger and DAQ elements
  for higher rate

DØ

• DØ SMT, CFT, 2T superconducting solenoid,
  preshowers, forward muon

• CDF SVX, ISL, COT, TOF, plug calorimeters,
  intermediate muon

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Hunting for the Higgs at the Tevatron
Gluon fusion

• Decay channels
• For MH lt 135 GeV, H ? bb
• For MH gt 135 GeV, H?WW

LEP 95 CL MHgt114.4 GeV/c2
H ??bb
H ? WW
H ? bb
H ? WW

• Production cross section and decays are all
  calculable within the SM
• Inclusive Higgs cross section 1pb
• gg fusion 0.7 pb (MH 120 GeV) (very large
  background)
• Associated production with W/ZWH 0.16 pb ZH
  0.1 pb
• leptonic decays of W/Z help give the needed
  background rejection
• At higher masses, can use inclusiveproduction
  plus WW decays

b-tagging and Mbb resolution scale are
critical for a light Higgs !
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W/Z Jets in Leptonic Channels

• Zjets
• 2 high pT lepton (ee or ??) with mass consistent
  with Z
• Jets pT gt 20 GeV in ? lt 2.5

• First step towards W(?lv )/Z(?ll) H(?bb)
  measurement
• Major background W/Z di-jets
• Wjets
• Isolated high pT lepton (e or ?) with large
  missing ET
• Jets pT gt 20 GeV in ? lt 2.5

Dominated by Jet energy scale systematic
uncertainty

• Improvements
• b-tags
• Jet and mET resolutions
• Optimize analyses

36 events
340 events
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Higgs?WW/?? final states

• H?WW?ll-?? (search for dilepton mET)
• h??? (search for high pT isolated diphotons)
• A lot of interest in these channels as could be
  greatly enhanced by new couplings
• 4th generation
• Fermiophobic or Topcolor Higgs
• Physics backgrounds Z/?, WW, tt, W/Zjets, QCD
• Use spin correlations to suppress background
  contributions in leptonic mode(??)
• Derive ?.Br limits assuming BR 1

H?WW?ll-??

h???
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CDF Searches for H

• LR Symmetry breaking SU(2)L x SU(2)L x
  U(1)B-L ? SU(2)L x U(1)L
• Higgs fields are a left-right doublet ?(½,½,0)
  and 2 triplets
• SUSY models suggest low mass doubly-charged Higgs
• H Properties and Selection
• Pair (?/Z exchange) or singly (WW fusion)
  produced in pp collisions
• Same sign leptons decay mode provide strong
  experimental signature
• Inclusive electron trigger used (91?5.3 pb-1)
• Two central same-sign electrons required
• MH ?10 dielectron mass windows explored
• Acceptance 20-35
• 0 events observed
• Bckd 0.6?0.5

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Limits on new Neutral Gauge Bosons Z

• Neutral Gauge Bosons Z
• Assume SM couplings
• Searches in both ee and ?? channels
• No excess observed in e or ? channels
• Bckds DY, QCD misid electrons, WW, WZ, tt

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Searches for Large Extra Dimension

• Assume SM particles are confined to a 3D-brane
• Gravity propagates in the extra dimensions
• Signature is an excess of high mass dilepton and
  diphoton events from virtual KK graviton diagrams
• Angular distribution asymmetries arise from
  inteference terms
• DØ searches in diEM and dimuon
• Invariant mass
• Cos ? (? scattering angle in rest frame)

di-EM
DØ Run II Preliminary
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R-S Extra Dimension Searches

• Excited graviton in 5 dimensions
• Kaluza-Klein Modes lead to observable spin-2
  resonances?G
• Free parameters mass MG and coupling k/MPL

em combined

• Look for high mass excess in Drell-Yan dilepton
  events
• CDF searches in ee and ?? channels

Dielecton MG gt 535 GeV/c2 Dimuon MG gt 370
GeV/c2
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New Physics Searches in Diphoton Channels

• Gravity Mediated SUSY
• LSP is a light (ltlt 1 keV) gravitino,
  phenomenology driven by nature of the NLSP (?0)
• Signatures include 2? and missing ET
• DØ search
• Require two photons with pT gt 20 GeV, apply
  quality and topological cuts
• 0 events observed
• QCD fake background determined from data (1.6 ?
  0.4)
• Derive limits in Snowmass model
• 95 CL on ? 51 TeV gives equivalent limit on
  Snowmass model gives M(?0) gt 66 GeV
• Run I limit gt 75 GeV

DØ Run II Preliminary
ET
L 50.0 pb-1
DØ Run II Preliminary
M?0 gt 66 GeV/c2
Theory "Snowmass slope M 2L, N5 1, tan b
15, m gt 0
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Limits on New Physics in the emX channel

• Very low backgrounds ? pursue analysis in a
  model-independent way
• Require e, m pT gt 15 GeV, estimate fake rates
  from data, physics backgrounds from simulation
• 13 events, 9.6 ? 2.7 exp. background(Z???,
  QCDWjets, WW?e?, tt)

Cross-section Limit as a function of missing ET
A snew physics (e.g. acceptance for WW?e? 17)
L 33.0 pb-1

• At low MET physics backgrounds dominate, at high
  MET instrumental effects
• Complementary search in jets MET
• Sensitivity at the 0.1 pb level already

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Search in Trileptons eel X

• Start from dielectron sample understand trigger,
  reconstruction, simulation
• Also verify determination of QCD fake background
  (from data)
• Main backgrounds Z?ee,?? and W?e?)
• ?.Br(3 leptons) lt 3.5 pb (95 C.L.)

L 42.0 pb-1

• Typical selection efficiency for SUGRA 2-4
• Sensitivity still about factor 7 away from
  extending excluded area in parameter space
• working on improving efficiency, adding channels

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New CDF Search for Excited Electrons e

• pp ? e e ? e? e (U. Baur PRD42, 3,
  1990)
• Compositeness scale ?
• Reconstruct M(e?) in ee? events
• Bckds Z?, Zjet, Multijet, Wjets
• No events observed in 72 pb-1
• New Limit on e mass is 785 GeV (?Me)
• Previous limit from H1 was 223 GeV

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Searches in heavy flavor tau leptons

• Measurements of tau leptons important for tests
  of the SM and in the Higgs and SUSY sectors
• Large backgrounds from jets
• Multivariate techniques useful
• Both experiments have established a Z ? ?? ? eh
  signal
• CDF has measured ?.B(W? ?h?)

CDF Z??
?.BR(W???) 2.62 ? 0.07stat ? 0.21sys ? 0.16lum
nb ?.BR(W?l?) 2.69 ? 0.1 nb (NNLO)
DØ Z????eh
OS-SScollinear approximation
CDF Run II Preliminary
L 70 pb-1
L 50 pb-1
14 ? 9 data, 13 ? 4 expected
Ntracks

• DØ also seen Z ? ?? ? ?h using NN techniques

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Search for LeptoQuarks

• Extended gauge sectors and composite models?LQ
• Directly couple leptons and quarks
• LQ ? l?q or ?q, ?BR(LQ?lq)

• Search for dilepton jets and reconstruct LQ
  mass- or -
• Search for mET and dijets
• Limits depend on coupling
• Assume ?1 or 0 for limits

L 40.0 pb-1
MLQ2 gt 157 GeV/c2
Run I gt200 GeV
DØ LQ2
MLQ1 gt 230 GeV/c2 Run I gt 220 GeV/c2
60 lt MLQ gt 107 GeV/c2
CDF LQ??q
0 events, bckd 3.4?3
42 events, bckd 43?11
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Search for Resonances in Dijets

• Test QCD and sensitive to high mass resonances
• Both experiments have measured dijet
  cross-section in Run II
• Agreement so far with SM expectations
• No significant excess beyond the Standard Model

• Fit mass spectrum with simple background
  parameterization
• Search for bumps comparable with the mass
  resolution

• Derive mass limits on the ??BR for various exotic
  particles

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CHArged Massive stable Particles

To set limits usestable stopmodel
TOF

• Long lived particles escape without decaying
• Look like isolated slow-moving high-pT muon
• Use TOF and look for t(TOF) t (interaction)
• Derive limit on production
• Interpret 95 CL limits in stable stop model
• M(isolated stop) gt 107 GeV/c2
• M(non-isolated stop) gt 96 GeV/c2
• Limits independent of details of SUSY
• Previous limits from ALEPH M gt 95 GeV

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Conclusions

• Run II is well underway
• We have commissioned all the detectors and have
  initial physics results
• Cross-sections W/Z, b-quarks, jets, B-lifetimes,
  rediscovered top
• New phenomena and Higgs searches are underway!
• Many results already competitive with Run I
• Excellent performance of new tracking systems
• CDF L2 Silicon displaced Vertex Trigger a great
  success
• DØ Silicon Track Trigger online by this summer
• Fully exploiting the luminosity delivered by the
  Tevatron
• New Physics results this summer (LP03, etc)
  publications
• Sensitive at the 0.1 pb and 1 TeV scale in many
  channels
• Joint working group re-evaluating the Tevatron
  Higgs reach
• CoM Energy ( x1.3-2), luminosity ( x20-50),
  better detectors and analysis techniques ( x2?)
  ? x100 increase in sensitivity for some channels

The Tevatron will be the place for high-pT for
the next few years
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Backups
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CDFII Detector
Retained from Run I Solenoid (1.4 Tesla) Central
calorimeters Central muon detectors
New in Run II Tracking system Silicon vertex
detector (SVXII) Intermediate silicon
layers Central outer tracker (COT) End plug
calorimeter Intermediate muon detectors Time of
flight system Front-end electronics Trigger
system DAQ system
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DØ Inner Tracking Volume
(2T)
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Tevatron Higgs Working Group

• The Higgs discovery potential for Run II was
  evaluated(hep-ph/0010338) using a parameterized
  fast detector simulation
• Discovery at 3-5? can be made
• Combine all channels, data from both D0 and CDF
• Improve understanding of signal and background
  processes
• b-tagging, resolution of Mbb
• Advanced analysis techniques are vital
• Largest luminosity required to discover Higgs
• Reevaluation of the expectations with real
  detector simulations and Run II experience
  underway at the moment

Fermilab Run II Higgs Workshop
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Searching for the Higgs

• Focus has been on experiments at the LEP ee
  collider at CERN (European Laboratory for
  Particle Physics)
• Fits of electroweak data from precision
  measurements of parameters of the W and Z
  bosons, combined with Fermilabs top quark mass
  measurements, set an upper limit of mH 200 GeV
  
• direct searches for Higgs production exclude mH
  lt 114.4 GeV/c2
• Much of the favored region already excluded
• Fermilab Tevatron Run II has an exciting window
  of opportunity before LHC turn on

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Tevatron Luminosity Goals 2003

• Base
• 200 pb-1 for FY03
• 10 pb-1/week by year end
• Stretch
• 320 pb-1 for FY03
• 15 pb-1/week by year end
• FY02
• 80 pb-1 for the year
• 6.7 pb-1 best week

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Tevatron Luminosity Scenarios
Earliest date for LHC physics
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Expected?bb mass resolutions

• Directly influences signal significance
• Requires b-jet specific energy corrections
  (semi-leptonic, fragmentation)
• Z ? bb will be a calibration signal for b-jet
  energy corrections
• To improve mass resolution, combine tracks with
  calorimeter cells for jet energy measurement

CDF observation in Run I Z ? bb
Jet energy corrections
Higgs simulation for 2 x 15fb-1 (2 expts)
Z
Higgs
mH 120 GeV
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SUSY Higgs Production at the Tevatron

• bb(h/H/A) couplings are enhanced at large tan ?
  ( ratio of v.e.vs)
• ? 1 pb for tan ? 30 and mh 130 GeV

bb(h/A) ? 4b
one expt
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b-tagging

• b-tagging explores IP significance method
• Lepton from semileptonic decay of b is very useful

• Impact Parameter gt 0
• ? track crosses jet axis after primary vertex

m jet sample
Jet
Positive IP
Resolution
track
Interaction point
b enhanced

• Impact Parameter lt 0
• track crosses jet axis before primary
• vertex

Jet
Interaction point
Significance IP/sIP
track
Negative IP
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B-tagging

• B-tagging is crucial for light Higgs search to
  reject light-quark content
• Estimated efficiency and fake rates from impact
  parameter resolution
• b-tag efficiency 60
• c-quark mistag rate 15-20
• Light quarks (u,d,s) mistag rate few
• Ongoing improvement in alignment and
  track-finding efficiency

High-pTrel muon sample
MC
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DØ Search Scorecard
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Run IIa Prospects

• Towards the next few years

Event yields per experiment (2 fb-1)
DØ / CDF Run 2a Prediction
Sample Wln Zll WV (Wln, VW,g,Z) ZV (Zll,
VW,g,Z) tt (mass sample, ?1 b-tag)
Run I 77k 10k 90 30 20
Run IIa 2300k 202k 1800 500 800
?MW40 MeV ?Mt 3 GeV
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Run IIB Upgrades

• Both detectors were designed to withstand 2-4
  fb-1 with an average of 2-3 interactions per
  crossing
• Integrated luminosity limited by radiation damage
  to silicon tracker
• Instantaneous luminosity limited by trigger
  rejection
• Tevatron goals for Run IIb are to accumulate5-15
  fb-1 with an average of 5 interactions per
  crossing, necessitating
• Replacement of silicon trackers
• Similar design for both and common SVX4 chip
• Replacement and upgrades to few key trigger and
  DAQ components for high-pT physics program
• Run 2 to continue in 2006 following 7 month
  shutdown
• All critical elements have been prototyped,
  sensor procurement has begun

DØ
CDF
CDF
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The Luminosity Lift

• New physics panoramas open up each time we take
  the Luminosity Lift