Fourth Tropical Workshop on Particle Physics and Cosmology

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CP Violation, Dark Matter and Extra Dimensions in
the D-Zero experiment at the Tevatron ?
Peter Ratoff Lancaster University
Fourth Tropical Workshop on Particle Physics and
Cosmology FLAVOUR PHYSICS AND PRECISION
COSMOLOGY 9-13 June 2003, Cairns,
Queensland, Australia
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The Tevatron
_
p-p collisions at ?s 1.96 TeV
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The DØ Detector in Run 2
New Software (OO C)
STT displaced track trigger, Summer03
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Tevatron operating parameters
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Run 2 Luminosity Performance
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Physics in Run 2
events in 1 fb-1
1014
1011
107
104
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Detector Performance electrons and muons
Electrons
D0 10 Lumi error
Muons
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Detector Performance Jets
Dominant systematic error Jet energy scale (will
improve with statistics)
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Detector Performance bs and Bs
Jet
Signed IP
Golden mode for CP violn (Sin2?)
Track
Interaction vertex
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Detector Performance Taus
Isolated electron opposite to narrow, single
track jet. Signal enhanced using NN
Evidence for Z ? ??- ?eth (similar study in Z
??????h)
(New at DØ)
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Putting everything together the top !
3? observation
X-section
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B Physics at the Tevatron?

• Large Cross Section!
• Produce bottom mesons with all flavor
  combinations as well as bottom baryons
• Bd, Bu, Bc, Bs, Lb, ?b, ...
• DØ is a multipurpose detector capable of
  reconstructing many B final states
• Rich B physics program
• Cross-sections
• Bs mixing
• B lifetime
• CP violation in Bd and Bs
• Rare decays

Bd
Lb
Bs
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B Physics Triggers

• Have to go down from 2.5 MHz crossing rate to 50
  Hz writing to disk (0.25 MB/event)
• Sophisticated 3-level trigger system
• Most useful triggers for B physics so far dimuon
  triggers (simple and unprescaled)
• Central (?lt1) pTgt3.5 GeV
• Forward (1lt?lt2) pTgt2-2.5 GeV
• But can also do physics with single muon trigger
  ...
• Coming soon (this summer)
• L2 track trigger (track match to m/e)
• L2 (STT) silicon track trigger (displaced
  vertices)

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Inclusive b cross-section

• Begin with m in jet cross section
• Extract b content via fit to pTrel distribution

• Unfold jet energy resolution (unsmearing)
• Dominant error jet energy scale corrections

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J/? data sample

• Exploit J/? ? mm mode
• Results based on 40 pb-1 collected data (75k J/?)
• Calibration not finalized, mass not in good
  agreement with PDG

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Charged B lifetime
Full reconstruction (B ? J/? K ) no
hadronization or momentum uncertainties
ctB Lxy M B / pT B
lttBgt 1.76 ? 0.24(stat) ps (PDG 1.674 ?
0.018)
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Semi-leptonic B meson decay
2 of current Run II data !

• single muon trigger works!
• abundance of SL B decays
• other decay channels to follow
• B ? ?DX
• B ? ?DX
• B ? ?Ds X
• excellent opportunities for various
• B measurements (mixing, CP viol)
• good source of B hadrons for
• technical studies (trigger, b-tagging)

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B mixing - flavour tagging status
Tagging power eD2 Significance of a mixing

measurement is proportional to eD2
e efficiency for a tag D Dilution
Tagging performance measured in B ?J/?K - close
to simulation expectations
Jet tag
Muon tag
Signal region
Sidebands

eD2 for signal
Muon tag Charge of highest pT muon in the event
(excluding those from reconstructed B) gives
(opposite-side) b-tag
Jet tag QS qi pTi / S pTi, count events with
Qgt0.2
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CP violation in B hadron decays

• Able to reconstruct golden channels for CP
  violation measurements
• High statistics measurements with BS only
  possible at hadron colliders

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B physics prospects(with 2fb-1)
Both competitive and complementary to B
-factories

• Bs mixing Bs ? Ds?(Ds???) (xs up to 60, with
  xd meas. one side of U.T.)
• Angle ? B0 ? J/? Ks (refine CDF Run1 meas.
  up to ?(sin2?) ? 0.05)
• CP violation, angle ? B0 ? ??(?K), Bs ?
  KK(K?)
• Angle ?s and ??s/ ?s Bs ? J/? ? (probe for
  New Physics)
• Precise Lifetimes, Masses, BR for all B-hadrons
  Bs, Bc, ?b
• (CDF observed Bc ? J/? e(?)?. Now hadronic
  channels Bc ? Bs X can be explored)
• Cross sections

• Stringent tests of SM or evidence for new
  physics !!

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SUSY models

• SUSY is the best motivated scenario today for
  physics beyond the Standard Model
• doesnt contradict precise Electroweak data
• predicts light Higgs
• unification of gauge couplings at GUT scale
• essential element of String Theories
• provides explanation of Cold Dark Matter in the
  Universe!
• SUSY must be broken symmetry (otherwise MSUSY
  MSM)
• variety of models proposed - differ mainly in the
  nature of the messenger interactions
• most experimental results obtained in the context
  of the SUGRA and GMSB models

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SUSY production

• Neutralinos/charginos
• - trilepton channel
• - dilepton channel
• squarks/gluinos (dominant)
• jets mET
• stop and sbottom

squarks and gluinos are quite heavy ? decay via
multi-step cascades ? many high Pt jets and
leptons plus large missing transverse energy
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SUGRA models

• SUSY breaking is communicated to the physical
  sector by gravitational interactions
• GUT scale parameters RGEs ? low-scale
  phenomenology

M0 common scalar mass M1/2 common gaugino
mass A0 common trilinear coupling value tanb
ratio of the V.E.V. of the two Higgs
doublets sign of m Higgsino mass parameter
Highly constrained minimal SUGRA
? LSP is lightest neutralino - a neutral WIMP ?
excellent CDM candidate
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GMSB models

• Messenger sector couples to source of
  SUSY-breaking and physical sector of MSSM
  (through gauge interactions)
• The identity of the NLSP and its lifetime
  determine the phenomenology

c?
neutralino ???G
slepton l?lG
NLSP
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Current DØ searches for new phenomena

• Model Independent
• e? X
• Supersymmetry
• SUGRA-inspired
• Jets Missing ET (Squarks)
• Trileptons (Gauginos)
• GMSB
• Diphotons Missing ET

• Leptoquarks
• 1st and 2nd generations
• New Gauge Bosons
• Dielectrons
• Large Extra Dimensions
• Dielectrons Diphotons
• Dimuons

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Jets missing ET
Generic signature for squarks and gluinos which,
in SUGRA inspired models, cascade decay to
(quarks and gluons ? jets) (two LSPs ? missing
ET)

• Select events with
• at least one jet with pT gt 100 GeV
• Apply topological cuts
• (e.g., on jet- missing ET angles)
• Simulate physics backgrounds
• (with real missing ET)
• Estimate the large instrumental
• QCD background from the data
• (empirical fit)

Proof of existence with 4 pb-1
No surprise For missing ET gt 100 GeV 3 events
observed vs. (2.7 ? 1.8) expected
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eel X
Similar analysis in the e?l channel
Signal
Start from dielectron sample (40 pb-1)
allows for ??h
Typical mSUGRA selection efficiency 3 to 4 at
the edge of the excluded region
Sensitivity still about a factor 7 away from
extending the excluded domain
Golden channel very low backgrounds, but large
statistics will be needed
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GMSB - diphotons
In GMSB, the LSP is a light gravitino With a
bino NLSP, the signature is therefore two
photons with missing ET Require two
isolated photons with pT gt 20 GeV Apply
topological cuts Determine the instrumental
QCD background from the data (inversion of
photon quality cuts)
Theory "Snowmass slope M 2?, N5 1, tan
? 15, ?gt 0
With 50 pb-1, the Run I limit is approached
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Large Extra Dimensions
Search for the effects of KK graviton exchange in
the ee, ?? and ?? final states
Ms is the fundamental Planck scale. To solve the
hierarchy problem, one can have Ms in the TeV
scale for n gt 2 extra dimensions (n1 is ruled
out and n2 is tightly constrained).

• Two discriminating variables are used
• the dilepton/diphoton mass
• the scattering angle in the rest frame

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LED in the ee/?? channels

• Determine
• Physics backgrounds from simulation
• Instrumental backgrounds from data

• Require
• 2 EM objects with pT gt 25 GeV
• and missing ET lt 25 GeV

Fit ?G gt MS gt 1.12 TeV in GRW formalism
MEM-EM 394 GeV cos ? 0.49
(with 50 pb-1 close to Run I, similar to LEP)
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LED in the ?? channel

• Determine
• Drell-Yan background from simulation
• QCD background from data

• Require
• 2 opposite sign muons with pT gt 15 GeV
• and M?? gt 40 GeV

With 30 pb-1 MS gt 0.79 TeV in GRW formalism
M?? 347 GeV
(New channel at the Tevatron, similar to LEP)
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Large Extra Dimensions Search Results

• Fit the distributions in the Mll - cos? plane
  to determine the value of hG ( hG 0 in
  SM)Di-EM analysis hG 0.0 0.27
  TeV-4Di-Muon analysis hG 0.02 1.35
  TeV-4
• Extract 95 CL upper limits on hG
• Translate to 95 CL lower limits on Planck scale
  MS , in TeV, using different formalisms for F

Di-EM limit close to Run I Di-Muon (new)
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Summary and Conclusions

• DØ is almost fully operational following major
  upgrades
• for Run II (some trigger improvements to come
  e.g STT)
• The Run I data sample has now been exceeded and
  physics
• results are emerging from the first 40-50 pb-1
• The B physics potential of DØ has been
  established
• Good lepton, photon, jet and missing ET
  detection enables
• DØ to perform many new physics searches
• Measurements of cosmological significance can be
  expected
• in the coming few years with data samples gt 5
  fb-1
• CP violation (unitary triangle angles, beyond
  the SM?)
• dark matter candidates/limits (e.g. neutralino
  LSP)
• large extra dimensions/limits

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SUSY Particle Zoo

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Where we are standing Run I vs Run II

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Where we are standing Run I vs Run II

A lot of another analyses are going on gauge
interactions search, SUGRA particles search with
the different jets leptons mET signatures
etc