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

03-05-2004 U. of Chicago Beate Heinemann - University of Liverpool 2

-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


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


• 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?


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

~

~~


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)


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


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


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?


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


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


W and Z Cross Sections: Summary


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


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:


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?


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


• 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?


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.

~ ~

~


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


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


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


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~


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


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


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

)


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


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


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


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


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


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


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


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!

Electroweak Physics and Searches for New Physics at CDF

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