constraints on the scale of new physics phenomena from the combined lep ii f f and γγ...

Constraints on the Scale of New Constraints on the Scale of New Physics Phenomena from the Combined Physics Phenomena from the Combined

LEP IILEP IIf ff f and and γγγγ Measurements Measurements

Dimitri BourilkovUniversity of Florida

for the LEP Electroweak WG

APS April Meeting 2004, Denver, CO, USA

May 1, 2004

D.Bourilkov APS 2004 Denver 2

LEP2 Constraints on New PhysicsLEP2 Constraints on New Physics

Anything coupling to ff / γγ can be probed

New Physics at much higher scale can give observable effects through interference with the SM amplitudes

LEP2 provides a window (in many cases still the best) to TeV scale physics: extra dimensions, contact interactions, heavy Z’ bosons, leptoquarks …


Fermion-pair production @ LEP2Fermion-pair production @ LEP2

Falling signal, rising backgrounds (2, W+W-, ZZ …)

Initial state radiation: select non-radiative samples highest energy / sensitivity to new physics – probe higher scales than direct searches at same s

Anything coupling to ff can be probed

LEP2 Monte Carlo Workshop,

hep-ph/0007180, CERN-YR-2000-009


Photon-pair ProductionPhoton-pair Production


LEP2LEP2f f and f f and γγ Groupsγγ Groups

Combine the measurements of LEP2 data to a common signal definition:

720 pb-1/exp @ 130-208 GeV (> 190 GeV final/preliminary)

• Total and differential cross sections (f f and γγ )

• Forward-backward asymmetries (μ+μ- and τ+τ-)

• Heavy flavors: Rb and Rc, , Afb

• Test the SM at % level and constrain tightly current / future extensions

• Correlations obtain full error matrices after averaging

• Latest results: hep-ex/0312023, CERN-EP/2003-091

Web page: http://lepewwg.web.cern.ch/LEPEWWG/lep2


Contact Interactions etc.Contact Interactions etc. general framework for new int.:• scale s• coupling g (convention g2 = 4)• we constrain g / • operators with canonical

dimension N > 4 coupling 1/MN-4

• |ij| < 1 helicity amplitudes


Fermion Pairs Fermion Pairs

Averaged over s: h/ h < 1 % (theory 0.3 %); Afb ~ 0.01 (th. 0.004)

Good agreement with SM – hadron xsec 1.7 s.d. excess averaged over all s


dd/dcos/dcos e e++ee--

Averaged over s: (/ )forward ~ 1 % (th ~ 0.5%) (/ )central ~ 1.5 % (theory ~ 1.5%)

Contact interactions scale > 16 (18) TeV (VV) re < 1.4 10-19 m

Extra dimensions scale > 1.2 (1.1) TeV (=1) (1999: scale Ms > 1.1 TeV from combined analysis of 183-189 GeV data: JHEP 08(1999)006 )


dd/dcos/dcosμμ++μμ-- and τ and τ++ττ--


Heavy FlavorsHeavy Flavors

Averaged over s: Rb/Rb ~ 2.5 % ; Afbbb ~ 0.06


Contact InteractionsContact Interactions

95% CL limits for

μ+μ- and τ+τ- :

> 8.6 – 21.7 TeV

Assume only 1 flavor active

> 2.2 – 15.3 TeV bb

> 1.5 – 10.3 TeV cc

95% CL limits for hadrons:

> 3.7 – 9.3 TeV


Z’ BosonsZ’ Bosons

• New neutral, heavy boson Z’ (arises in many models)• Couplings of Z’ tof f model dependent• Z and Z’ can mix mixing angle ZZ’ (from LEP1 mixing is

very small; assume 0)

Model MZ’ (GeV)

Limits @ 95 % CL

673

481

434

LR 804

SSM 1787


γγγγ

(/ ) ~ 1.2 % (theory ~ 1 %) + > 392 GeV - > 364 GeV Ms > 0.97 TeV


Scales for New PhysicsScales for New Physics

• Extra dimensions from e+e- and γγ combined (DB):

MHewett > 1.4 (1.2) TeV (=1) (D0 2001 -1.1(1.0) TeV)

• Contact interactions: scales up to 21.7 TeV• Z’ : m > 0.434 – 1.787 TeV (diff. models)

• Size of the electron: re < 1.4 10-19 m

(quark: r < ~10-18 m HERA, r < 5.6 10-19 m CDF 1997)

• QED cutoff: + > 392 GeV - > 364 GeV

• LHC – contact interactions up to 30 – 50 TeV LC – up to ~ 90 TeV (r < 3 10-20 m ; e.g. hep-ph/0305125)

Extra dimension up to ~ 4 TeV


ConclusionsConclusions

• SM describes the full set of precise LEP2 measurements @ 130-208 GeV (results above 190 GeV final/preliminary)

• No hint for new phenomena … in spite of sensitive searches!

• Many new limits @ TeV scale (Extra dimensions, CI, Z’, leptoquarks …) – already “eating” in the LHC / LC

direct discovery range• Combine final measurements, provide a reference point

in the era after LEP & constrain tightly physics beyond the SM

constraints on the scale of new physics phenomena from the combined lep ii f f and γγ...

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