Electroweak Physics and Searches for New Physics at CDF

1
Electroweak Physics and Searches for New Physics
at CDF

• Beate Heinemann
• University of Liverpool
• Mini-Symposium on CDF _at_University of Chicago
• 5th of March 2004

2
The Standard Model of Particle Physics

• 3 generations of quarks and leptons interact via
  exchange of gauge bosons
• Electroweak SU(2)xU(1) W, Z, ?
• Strong SU(3) g
• Symmetry breaking caused by Higgs field
• Generates Goldstone bosons
• Longitudinal degrees of freedom for W and Z
• 3 massive and one massless gauge bosons
• -Standard Model survived all experimental
  challenges in past 30 years!
• -electroweak and QCD precision data
• -No New Physics despite many efforts!

Gauge Bosons
Higgs Boson

• Vacuum quantum numbers (0)
• Couples to mass
• Mh ?

3
Why not the Standard Model?
Coupling constants

• Radiative corrections to Higgs mass electroweak
  scale (100 GeV) much much lower than Planck Scale
  (1019 GeV) hierarchy or naturalness problem
• No unification of forces at any scale
• Higgs boson not yet found is it there?
• No explanation for matter/ anti-matter asymmetry
  in universe
• No accounting for dark matter in universe
• Many free parameters, e.g. masses of all
  particles unsatisfactory

U(1)
SU(2)
WMAP satellite
4
What could be Beyond the SM?

• Supersymmetry (SUSY)
• Each SM particle has a super-partner with same
  quantum numbers apart from spin (top lt-gt stop,
  photon lt-gt photino, etc.)
• Masses are O(1 TeV)
• Unification of forces at GUT scale (1016 GeV)
• Hierarchy problem solved
• Extra Dimensions
• String theory links gravity to other forces
• Could be large (0.1mm) probed at TeV scale
• Hierarchy problem solved
• The unexpected

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Supersymmetry Intro

• SM Fermions Boson Superpartners
• SM Bosons Fermion Superpartners
• Physical SUSY sparticles neutralinos (Higgs,
  Photon, Z partners), charginos (Higgs, W
  partners), squarks (quark partners), sleptons
  (lepton partners)
• Different SUSY models
• Supergravity SUSY broken near GUT scale
• GUT scale parameters scalar mass m0 , gaugino
  mass m1/2 , ratio of Higgs v.e.vs tanß, Higgs
  mixing parameter µ
• LSP is neutralino ?0 or sneutrino ?
• Gauge-mediated models (GMSB) SUSY broken at
  lower energies breaking scale F an important
  parameter.
• Gravitino G is the LSP (NLSP ?0 ?G? )
• If R-Parity conserved
• SUSY particles can only be pair-produced
• Lightest SUSY Particle (LSP) stable and escapes
  detection
• If conserved LSP stable, carries away missing ET
  

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Searches for New Physics Strategy

• Establish good understanding of data in EWK/QCD
  physics in Run 2
• Backgrounds to new physics searches
• Indirect sensitivity to New Physics
• Gain understanding of detector
• Search for as many signatures as possible,
  involving
• High Pt leptons
• Large imbalance in transverse momentum (e.g. due
  to neutrino or neutralino)
• High Et jets
• High Et photons
• Rare decays of charm- and bottom-mesons
• Interpret
• Provide cross section limits and acceptances (try
  to be as generic/model-independent as possible)?
  applicable to future models!
• In context of specific models of physics beyond
  the SM

Cross Sections (fb)
?
WW, W?, Z?,
Higgs
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The Tevatron Run 2

• Run 2 started in June 01
• CMS energy 1.96 TeV
• Delivered Lumi 400/pb (run 1 was 110/pb)
• Promising slope in 2004!
• Data taking efficiency about 90!
• Physics Analyses
• Use about 200/pb taken between 03/02 and 09/03

Expect 2 /fb by 2006 and 4.4-8.6 /fb by 2009 ?
sensitivity to New Physics improved bygt5 compared
to Run 1
90 efficiency
Data Recording Efficiency
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The CDF 2 Detector

• New for Run 2
• Tracking System
• Silicon Vertex detector (SVX II)
• Intermediate silicon layers (ISL)
• Central Outer tracker (COT)
• Scintillating tile forward calorimeter
• Intermediate muon detectors
• Time-Of-Flight system
• Front-end electronics (132 ns)
• Trigger System (pipelined)
• DAQ system

• Retained from Run 1
• Solenoidal magnet (1.4 Tesla)
• Central Calorimeters
• Central Muon Detectors

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Outline

• W and Z production
• Establish understanding of detector
• Alternative luminosity measurement
• Test NNLO QCD calculations
• W?, Z? and ?? production
• Anomalous triple gauge couplings
• SUSY?
• High mass di-leptons
• New physics Z, RS gravitons, etc.
• Di-leptons Di-jets
• Leptoquarks, Squarks in RPV SUSY
• Higgs boson
• W mass
• h?WW, double charged higgs
• Bs?µµ
• SUSY?

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Inclusive W cross section

• W?µ? and W?e? signal
• Backgrounds from QCD, Z?ll-, W?t? and cosmic µs
• Excellent description by MC simulation

s(pp?W ?l? ) 2777 10(stat) 52 (syst) 167
(lum) pb
J. Stirling SM (NNLO)2770 pb
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Z Production Cross Section

• Z ? e e- signal and Z ?µ µ- signals
• 66 lt m(ll)/GeVc-2 lt 116
• Small backgrounds from QCD, Z/W?t, cosmics µs
  less than 1.5

SM 250.2 pb
For 66ltm(ll-)lt116 GeV/c2 s(pp?Z/? ?ll-)
254.3 3.3(stat) 4.3 (syst) 15.3 (lum) pb
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W and Z Cross Sections Summary
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W? Production

• pp ? W? ? l??
• probes ewk boson self-coupling direct
  consequence of SU(2)xU(1) gauge theory
• new physics, e.g. composite W modifies coupling
• Selection
• 1 high-PT lepton (e,µ)
• 1 Photon with ETgt7GeV, ?R(?,l)gt0.7
• 1 neutrino large missing-ETgt25 GeV

Separate WW? vertex from (boring) Lepton
Bremsstrahlung
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Di-boson production W?

• Data agree with SM expectation

ET(?)/GeV
NLO prediction (U. Baur)
Next extract WW? coupling from Photon Et spectrum
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Z? Production

• pp ? Z? ? ll-?
• 2 leptons with Etgt25 GeV
• 1 photon with Etgt7 GeV, ?R(l?)gt0.7
• New physics at Z? vertex?

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Di-boson production Z?

• Data agree with SM expectation

sigmaBR5.3-0.6(stat)-0.3(sys)-0.3(lumi) pb
NLO prediction (U. Bahr)
(LO ET(?) dependent k factors)
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W/ZgammaX more exclusive channels

• Run I
• found 1 event with 2 photons, 2 electrons and
  large missing Et
• SM expectation 10-6 (!!!)
• Run II
• Any new such event would be exciting!

SUSY?
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Search for gg
e.g.

• Gravitino is the LSP
• NLSP Neutralino c1? ?G
• Experimental Signature ??ET

Run 1 eeggEt


pp ? XX Y ? ggGG Y
SUSY would show up as an excess of events with
large Missing Energy
For Missing Etgt25GeV Expected background
2?2 Observed 2

• Search Selection
• 2 central photons w/ Etgt13(25)
• Cosmic/beam halo removal

? Set cross section limit
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GMSB Search in gg
Acceptance
Set the lower mass limit on the lightest chargino
in GMSB Mcgt113 GeV _at_ 95 C.L.
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Di-lepton Production _at_ High Mass

• Select 2 opposite sign leptons ee or µµ (tt
  soon)
• Here ee channel
• 2 central e (CC)
• 1 central and 1 forward e (CP)
• NEW 2 forward es (PP)
• Good agreement with SM prediction

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Model Independent Limits spin-0, spin-1 and
spin-2 particles
spin-0
spin-1

• model-independent limits on sxBR for particles
  with spins 0, 1 and 2
• applicable to any new possible future theory
• Observed limit consistent with expectation
• New Plug-Plug result not yet included
• Muon analysis also ongoing

spin-2
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Limits on Several Models

• Z occurs naturally in extensions of SM towards
  GUT scale, e.g. E6 models
• M(Z)gt570 GeV for E6 models (depends on exact
  model couplings to quarks and leptons)
• M(Z)gt750 GeV for SM coupling
• Sneutrino in R-Parity violating SUSY may decay to
  2 leptons
• Mgt600 GeV for couplingxBR0.01
• Randall-Sundrum gravitons
• Massgt 600 GeV for k/MPl gt0.01
• Techni- pions, -omegas

G
Z


?
?
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Z?ee- Forward-Backward Asymmetry
e
angle between p and e-
e-

• Tevatron uniquely sensitive to Z-? interference
  at high invariant masses.
• Shape of the Afb spectrum can be used to extract
  values for sin2(?W) and u, d couplings to Z
• Agreement with SM prediction.

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Lepton Quark Resonances Leptoquarks
Apparent symmetry between the lepton quark
sectors common origin ?

• LQs appear in many extensions of SM
• (compositeness, technicolor)
• Connect lepton quark sectors
• Scalar or Vector color triplet bosons
• Carry both lepton and baryon number
• fractional em. Charge -1/3, -4/3, etc.
• Braching ratio ß unknown, convention
• ß1 means 100 BR LQ?lq
• ß0 means 100 BR LQ??q
• Also sensitive to e.g. squarks in RPV (exactly
  the same!)

e e

• Nice competition between worlds accelerators
• HERA, LEP and Tevatron
• At Tevatron independent of coupling ?

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Leptoquarks 1st generation

• New analysis in run 2
• Search for LQs decaying LQ??q (ß1)
• 2 jets (Etgt) and Etgt60 GeV
• Experimentally challenging
• Result
• 124 events observed
• 118.314.5 events expected
• ? exclude LQ masses with 78ltMlt118 GeV
• eejj channel
• M(LQ)gt230 GeV for ß1 (72 pb-1 )

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Leptoquarks 2nd generation

• Signature
• 2 high Pt muons
• 2 high Et jets
• Suppress Z?µµ background

Expect 3.151.17 events, observe 2 ? Exclude LQs
at M(LQ)lt240 GeV
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The Higgs Boson the missing piece?

• Precision measurements of
• MW 80.450 - 0.034 GeV/c2
• Mtop174.3 - 5.1 GeV/c2
• Prediction of higgs boson mass within SM due to
  loop corrections, e.g.

MW (GeV)
Mtop (GeV)
Indirect constraints versus direct searches! Will
they agree?
193 GeV
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Towards W Mass
Difficult measurement ? Work in progress no
results yet

• Use MC templates to fit to signal background
• CDF Run I mW 80,465
  100(stat) 104(sys) MeV
• CDF Run II for 500/pb estimate X
  40(stat) 55(sys) MeV

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Towards Higgs WW Production

• Motivation
• Sensitive to WW? and WWZ vertex
• Higgs discovery channel
• Anything new/unexpected?
• 2 leptons missing Et no jet with Etgt15 GeV
• Observed 5 events
• Expected
• WW 6.891.53
• BG 2.340.83

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Doubly Charged Higgs H/H--

• H (double charged higgs) predicted in some
  extensions of SM and SUSY M1001000 GeV
• Striking signature decay into 2 like-sign
  leptons
• ee channel
• M(ee)gt100 GeV to suppress large BG from Zs
  (conversions e?e??eee- )
• eµ and µµ channels
• Sensitive to single and pair production of H/H
• Blind analysis
• search region Mgt100 GeV
• 0 events observed
• Result 95 C.L. upper limit on
• cross section x BR for pair production (pp?H
  H--?l l l- l-)
• M(H)gt130 GeV

background
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Rare Decays Bs-gtµµ-

• New Physics can enhance branching ratios of
  B-mesons
• Measure BR in decay modes suppressed in SM
• E.g. Bs?µµ
• Bs bound state of b and s quark
• SM BR(Bs?µµ)10-9
• SUSY BR may be A LOT higher (tan6ß ?)
• Blind analysis with a priori optimisation
• 1 event observed, 1-0.3 expected
• 90 CL limits
• BR(Bs?µµ)lt5.8 X 10-7
• BR(Bd?µµ)lt1.5 X 10-7

SM vs e.g. SUSY
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SUSY Sensitivity Bs-gtµµ
90 CL limit BR(Bs?µµ)lt5.8 x 10-7

• SO(10) GUT model (R. Dermisek et al.
  hep/ph-0304101)
• accounts for dark matter and massive neutrinos
• largely ruled out by new result
• mSugra at high tanß (A. Dedes et al.
  hep/ph-0108037)
• Just about scratching the corner of parameter
  space
• In direct competition with higgs and (g-2)µ

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Conclusion and Outlook

• Physics at CDF is back
• Have twice the Run I luminosity and excellent
  detector
• Electroweak Measurements in good agreement with
  Standard Model
• W and Z cross section, Di-boson production
• W mass in progress
• Searches for New Physics have started
• Expect new physics at the TeV scale (hierarchy
  problem)
• Z, Large extra dimensions, Leptoquarks, SUSY,
  Higgs
• Cover broad range of possible signals
• no signals yet but constraining theoretical
  models
• And many results I could not cover

Many New Exciting Results coming soon!