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Constraints on New Physics Scales from LEP II Measurements

Explore limits on new physics scales from LEP II data, probing couplings to fermion pairs and photons, with a focus on extra dimensions, contact interactions, heavy Z' bosons, and leptoquarks. The combined measurements offer insights into TeV scale physics. The study also highlights constraints on coupling strengths and operators, providing a comprehensive framework for understanding new interactions beyond the Standard Model. Results indicate good agreement with the Standard Model, but also unveil limits and potential hints of new phenomena at higher scales. The findings serve as a crucial reference point for post-LEP era investigations.

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Constraints on New Physics Scales from LEP II Measurements

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  1. Constraints on the Scale of New Physics Phenomena from the Combined LEP IIf f and γγ Measurements Dimitri Bourilkov University of Florida for the LEP Electroweak WG APS April Meeting 2004, Denver, CO, USA May 1, 2004

  2. 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 … LEP2 Constraints on New Physics APS 2004 Denver

  3. 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 Fermion-pair production @ LEP2 APS 2004 Denver

  4. Photon-pair Production APS 2004 Denver

  5. LEP2f f and γγ 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 APS 2004 Denver

  6. 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 Contact Interactions etc. APS 2004 Denver

  7. Fermion Pairs Averaged over s: h/ h < 1 % (theory 0.3 %);  Afb ~ 0.01 (th. 0.004) Good agreement with SM – hadronxsec 1.7 s.d. excess averaged over all s APS 2004 Denver

  8. 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 ) d/dcos e+e- APS 2004 Denver

  9. d/dcosμ+μ- and τ+τ- APS 2004 Denver

  10. Heavy Flavors Averaged over s: Rb/Rb ~ 2.5 % ;  Afbbb ~ 0.06 APS 2004 Denver

  11. 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 Contact Interactions 95% CL limits for hadrons:  > 3.7 – 9.3 TeV APS 2004 Denver

  12. Z’ Bosons • New neutral, heavy boson Z’ (arises in many models) • Couplings of Z’ tof f model dependent • Z and Z’ can mix  mixing angle ZZ’(from LEP1 mixing is very small; assume 0) APS 2004 Denver

  13. γγ (/ )~ 1.2 % (theory ~ 1 %) + > 392 GeV - > 364 GeV Ms > 0.97 TeV APS 2004 Denver

  14. Scales 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 APS 2004 Denver

  15. Conclusions • 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 APS 2004 Denver

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