Transcript Electroweak Physics and Searches for New Physics at CDF Beate Heinemann

Electroweak Physics and
Searches
for New Physics at CDF
Beate Heinemann
University of Liverpool
Mini-Symposium on CDF @University of Chicago
5th of March 2004
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, γ
-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
Particle
Mass
(GeV/c2)
Force
Photon (γ)
0
Electroweak
W±
80.450
Electroweak
Z0
91.187
Electroweak
Gluons (g)
0
Strong
Higgs Boson
-Vacuum quantum numbers (0++)
-Couples to mass
-Mh = ?
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Why not the Standard Model?
• 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/ antimatter asymmetry in universe
• No accounting for dark matter in
universe
• Many free parameters, e.g. masses of
all particles: unsatisfactory
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Coupling constants
U(1)
SU(2)
WMAP satellite
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What could be Beyond the SM?
• Supersymmetry (SUSY):
– Each SM particle has a
“super”-partner with same
quantum numbers apart from
spin (top <-> stop, photon <->
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
~10
• 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.v’s tanβ, Higgs mixing parameter μ
• LSP is neutralino χ0 or sneutrino ~
ν
– Gauge-mediated models (GMSB): SUSY broken at lower energies
– breaking scale F an important parameter.
~
~
• Gravitino G is the LSP (NLSP χ0 →Gγ )
– If “R-Parity” conserved:
• SUSY particles can only be pair-produced
•
Lightest SUSY Particle (LSP) stable and escapes detection
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Liverpool
If conserved: Beate
LSPHeinemann
stable,- University
carriesofaway
missing
ET
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Searches for New Physics: Strategy
1.
2.
3.
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
•
•
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
Cross Sections (fb)
Search for as many signatures as
possible, involving:
•
•
•
WW, Wγ, Zγ,
?
Higgs
Interpret:
•
•
Provide cross section limits and
acceptances (try to be as generic/modelindependent as possible) applicable to
future models!
In context of specific models of physics
beyond the SM
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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 by>5 compared to Run 1
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The CDF 2 Detector
Retained from Run 1
New for Run 2
• Solenoidal magnet (1.4 Tesla) • Tracking System
• Central Calorimeters
• Central Muon Detectors • Scintillating tile forward
calorimeter
• Intermediate
muon
detectors
• Time-Of-Flight system
• Front-end
electronics (132
ns)
• Trigger System (pipelined)
• DAQ system
 Silicon Vertex detector (SVX II)
 Intermediate silicon layers (ISL)
 Central Outer tracker (COT)
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Outline
• W and Z production
– Establish understanding of detector
– Alternative luminosity measurement
– Test NNLO QCD calculations
• Wγ, Zγ and γγ 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→μν and W→eν signal:
• Backgrounds from QCD, Z→ℓ+ℓ−,
W→τν and cosmic μ’s
• Excellent description by MC
simulation
Candidate events
in 72pb-1
Estimated
background
Acceptance x
efficiency
W → μν
31,722
(10.6 ± 0.4)%
(17.94+0.36−0.33)%
W → eν
37,574
( 4.4 ± 0.8)%
(14.39+0.32−0.31)%
M T  ET ()  ET ( )  p x ()  p x ( )  p y ()  p y ( )
σ(pp→W →lν ) = 2777 ±10(stat) ± 52 (syst) ±167 (lum) pb
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J. Stirling: SM (NNLO)=2770 pb
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Z Production Cross Section
• Z → e+ e− signal and Z →μ+ μ−
signals
• 66 < m(ℓℓ)/GeVc-2 < 116
• Small backgrounds from QCD,
Z/W→τ, cosmics μ’s: less
than 1.5%
Number of events
in 72pb-1
acceptance x
efficiency
Z → e+ e−
4242
(22.74
Z → μ+ μ−
1785
(10.18+0.24−0.28)%
+0.47
−0.48)%
SM: 250.2 pb
For 66<m(l+l-)<116 GeV/c2 :
σ(pp→Z/γ* →l+l-) = 254.3
±3.3(stat)
± of4.3
(syst) ±15.3 (lum) pb
Beate Heinemann
- University
Liverpool
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W and Z Cross Sections: Summary
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Wγ Production
•pp → Wγ → ℓνγ:
•probes ewk boson selfcoupling: 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: ET>7GeV,
ΔR(γ,ℓ)>0.7
•1 neutrino: large missingET>25 GeV
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Separate WWγ vertex from (boring)
Lepton Bremsstrahlung
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Di-boson production: Wγ
• Data agree with SM expectation:
Nexp (L=198.3/pb)
W+ MC
W+jet BG
180.51+-2.08+-11.2
49.52+-0.10+-14.95
Z+
22.37+-0.38+-1.20
W+ (tau)
3.23+-0.24+-0.17
Total SM
255.63+-2.13+-26.43
data
259
MT (lγ,ν)
/GeV
ET(γ)/GeV
  BR ( pp  W   )  19.7  1.7( stat )  2.0( sys )  1.2(lum ) pb
NLO prediction (U. Baur):
  BR ( pp  W   )  19.3  1.3 pb
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Next: extract WWγ coupling from
Photon Et spectrum
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Zγ Production
• pp → Zγ → ℓ+ℓ-γ
•2 leptons with Et>25 GeV
• 1 photon with Et>7 GeV,
ΔR(lγ)>0.7
•New physics at Zγ vertex?
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Di-boson production: Zγ
• Data agree with SM expectation:
Combined e and μ
Z+ MC
65.76+-3.76
Z+jet BG
4.44+-1.33
Fake Z+
0.26+-0.20
Total SM
70.46+-4.00
data
69
sigma*BR=5.3+-0.6(stat)+-0.3(sys)+-0.3(lumi) pb
NLO prediction (U. Bahr)
(LO + ET(γ) dependent k –factors):
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  BR ( pp  Z   )  5.4  0.4 pb
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W/Z+gamma+X: 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!
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SUSY?
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Search for
+ E/ T
e.g.
~~
• Gravitino is the LSP
~
~~
• NLSP: Neutralino 1 G
~~
Run 1: eeEt
pp → XX + Y → GG + Y
• Experimental Signature: +ET
SUSY would show up as an excess
of events with large Missing Energy
For Missing Et>25GeV
• Search Selection:
2 central photons w/ Et>13(25)
Cosmic/beam halo removal
Expected background: 22
Observed:
2
 Set cross section limit
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GMSB Search in
+ E/ T
Acceptance
Set the lower mass limit on the lightest
chargino in GMSB:
Mc>113 GeV @ 95% C.L.
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Di-lepton Production @ High Mass
• Select 2 opposite sign
leptons: ee or μμ (ττ
soon)
• Here ee channel:
– 2 central e (CC)
– 1 central and 1 forward e
(CP)
– NEW: 2 forward e’s (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 σxBR for
particles with spins 0, 1 and 2
• applicable to any new possible future
theory
•Observed limit consistent with
expectation
spin-2
•New Plug-Plug result not yet included
•Muon analysis also ongoing
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Limits on Several Models
• Z’ occurs naturally in extensions
of SM towards GUT scale, e.g.
“E6” models
– M(Z’)>570 GeV for E6 models
(depends on exact model:
couplings to quarks and leptons)
– M(Z’)>750 GeV for SM coupling
G
Z’
• Sneutrino in R-Parity violating
SUSY may decay to 2 leptons:
– M>600 GeV for couplingxBR=0.01
• Randall-Sundrum gravitons
– Mass> 600 GeV for k/MPl >0.01
• Techni- pion’s, -omega’s
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~
ν
Beate Heinemann - University of Liverpool
~
ν
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Z→e+e− Forward-Backward Asymmetry
e+
P
angle between
p and e−
θ
P
e−
 (cos   0)   (cos   0)
Afb 
 (cos   0) +  (cos   0)
• Tevatron uniquely sensitive to
Z-γ* interference at high
invariant masses.
• Shape of the Afb spectrum can
be used to extract values for
sin2(θW) 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 β unknown, convention:
•β=1 means 100% BR LQ→l±q
•β=0 means 100% BR LQ→νq
•Also sensitive to e.g. squarks in RPV
(exactly the same!)
ee
Nice competition between world’s accelerators:
•HERA, LEP and Tevatron
•At Tevatron: independent of coupling λ
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Leptoquarks: 1st generation
• New analysis in run 2:
– Search for LQ’s decaying LQ→νq
(β=1)
• 2 jets (Et>) and Et>60 GeV:
– Experimentally challenging
• Result:
– 124 events observed
– 118.3±14.5 events expected
–  exclude LQ masses with
78<M<118 GeV
• eejj channel:
– M(LQ)>230 GeV for β=1 (72 pb-1 )
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Leptoquarks: 2nd generation
• Signature:
– 2 high Pt muons
– 2 high Et jets
• Suppress Z→μμ
background
Expect 3.15±1.17 events, observe 2
 Exclude LQ’s at M(LQ)<240 GeV
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The Higgs Boson: the missing piece?
– MW =80.450 +- 0.034 GeV/c2
– Mtop=174.3 +- 5.1 GeV/c2
• Prediction of higgs boson
mass within SM due to loop
corrections, e.g.
MW (GeV)
• Precision measurements of
TeVatron
Run 2
Mtop (GeV)
Indirect constraints versus direct
searches! Will they agree?
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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 WWγ and WWZ vertex
•Higgs discovery channel
•Anything new/unexpected?
•2 leptons +missing Et +no jet with Et>15 GeV:
•Observed: 5 events
•Expected:
•WW: 6.89±1.53
•BG:
2.34±0.83
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Doubly Charged Higgs: H++/H-• H++ (double charged higgs)
predicted in some extensions of
SM and SUSY: M=100…1000 GeV
• Striking signature: decay into 2
like-sign leptons
background
– ee channel:
• M(ee)>100 GeV to suppress large
BG from Z’s (conversions:
e±→e±γ→e±e+e- )
– eμ and μμ channels
• Sensitive to single and pair
production of H++/H—
• Blind analysis
– search region: M>100 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++)>130 GeV
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Rare Decays: Bs->μ+μ• 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
(~tan6β ?)
SM vs e.g. SUSY
• Blind analysis with a priori
optimisation:
– 1 event observed, ~1+-0.3 expected
90% CL limits:
– BR(Bs→μμ)<5.8 X 10-7
– BR(Bd→μμ)<1.5 X 10-7
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SUSY Sensitivity: Bs->μμ
90% CL limit: BR(Bs→μμ)<5.8 x 10-7
• SO(10) GUT model (R. Dermisek et al.: hep/ph0304101) :
•accounts for dark matter and massive
neutrinos
•largely ruled out by new result
•mSugra at high tanβ (A. Dedes et al.: hep/ph0108037):
•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!
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