Electroweak Physics and Searches for New Physics at CDF
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Transcript of Electroweak Physics and Searches for New Physics at CDF
Electroweak Physics and Searches
for New Physics at CDF
Beate HeinemannUniversity of Liverpool
Mini-Symposium on CDF @University of Chicago
5th of March 2004
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-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!
Particle Mass (GeV/c2)
Force
Photon (γ) 0 Electroweak
W± 80.450 Electroweak
Z0 91.187 Electroweak
Gluons (g) 0 Strong
Gauge Bosons
Higgs Boson
-Vacuum quantum numbers (0++)
-Couples to mass
-Mh = ?
The Standard Model of Particle Physics
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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/ anti-
matter asymmetry in universe • No accounting for dark matter in
universe• Many free parameters, e.g. masses
of all particles: unsatisfactory
WMAP satellite
U(1)
SU(2)
Coupling constants
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• 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…
What could be Beyond the SM?
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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.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
– If conserved: LSP stable, carries away missing ET
01
~χ
~
~~
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Searches for New Physics: Strategy
1. 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
2. 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-
mesons3. 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
Higgs
?WW, Wγ, Zγ,
Cross Sections (fb)
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The Tevatron: Run 2
Expect 2 /fb by 2006 and 4.4-8.6 /fb by 2009 sensitivity to New Physics improved by>5 compared to Run 1
• 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
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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
• 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
Estimatedbackground
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)
%
)()()()()()( ννν yyxxTTT ppppEEM ⋅−⋅−⋅= lll
σ(pp→W →lν ) = 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 < 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 +0.47−0.48)%
Z → μ+ μ− 1785 (10.18+0.24−0.28)%
For 66<m(l+l-)<116 GeV/c2 :
σ(pp→Z/γ* →l+l-) = 254.3 ±3.3(stat) ± 4.3 (syst) ±15.3 (lum) pb
SM: 250.2 pb
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W and Z Cross Sections: Summary
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Wγ Production
•pp → Wγ → ℓνγ:
•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: ET>7GeV, ΔR(γ,ℓ)>0.7
•1 neutrino: large missing-ET>25 GeV
Separate WWγ vertex from (boring)
Lepton Bremsstrahlung
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Di-boson production: Wγ
pb)(2.1)(0.2)(7.17.19)(BR lumsysstatWpp ±±±=→→⋅ νγγσ l
pb3.13.19)(BR ±=→→⋅ νγγσ lWppNLO prediction (U. Baur):
ET(γ)/GeV
Next: extract WWγ coupling from
Photon Et spectrum
MT (lγ,ν) /GeV
Nexp (L=198.3/pb)
W+γ MC 180.51+-2.08+-11.2
W+jet BG 49.52+-0.10+-14.95
Z+γ 22.37+-0.38+-1.20
W+γ (tau) 3.23+-0.24+-0.17
Total SM 255.63+-2.13+-26.43
data 259
• Data agree with SM expectation:
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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:
pb4.04.5)(BR ±=→→⋅ γγσ llZppNLO prediction (U. Bahr) (LO + ET(γ) dependent k –factors):
Combined e and μ
Z+γ MC 65.76+-3.76
Z+jet BG 4.44+-1.33
Fake Zγ 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
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• 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!
W/Z+gamma+X: more exclusive channels
SUSY?
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Search for γγ+
• Search Selection: 2 central photons w/ Et>13(25)
Cosmic/beam halo removal
For Missing Et>25GeV
Expected background: 22 Observed: 2
• Gravitino is the LSP
• NLSP: Neutralino χ1 γG
• Experimental Signature: γγ+ET
Set cross section limit
/ET
SUSY would show up as an excess of events with large Missing Energy
Run 1: eeγγEtpp →XXY → γγGG + Y
~ ~
~ ~
e.g.
~ ~
~
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GMSB Search in γγ+
Set the lower mass limit on the lightestchargino in GMSB:
Mc>113 GeV @ 95% C.L.
Set the lower mass limit on the lightestchargino in GMSB:
Mc>113 GeV @ 95% C.L.
Acceptance
/ET
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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-2
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
•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
• 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
G
ν
Z’
~ ν~
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Z→e+e− Forward-Backward Asymmetry
• 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.
e+
e−
P P
θangle between p and e−
)0(cos)0(cos
)0(cos)0(cos
<+><−>
=θσθσθσθσ
fbA
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Apparent symmetry between the lepton & quark sectors: common origin ?
e e
Lepton + Quark Resonances : Leptoquarks
• 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!)
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?
• Precision measurements of – 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.
Indirect constraints versus direct searches! Will they agree?
TeVatron Run 2
Mtop (GeV)
MW
(G
eV)
193 GeV
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Towards W Mass
•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
Difficult measurement Work in progress – no results yet
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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– 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
background
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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 ?)
• 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
SM vs e.g. SUSY
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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/ph-0304101) : •accounts for dark matter and massive neutrinos
•largely ruled out by new result
•mSugra at high tanβ (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!