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

D.BourilkovAPS 2004 Denver2 LEP2 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 …

D.BourilkovAPS 2004 Denver3 Fermion-pair 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/ , CERN-YR

D.BourilkovAPS 2004 Denver4 Photon-pair Production

D.BourilkovAPS 2004 Denver5 LEP2  f f and γγ Groups Combine the measurements of LEP2 data to a common signal definition: 720 pb GeV (> 190 GeV final/preliminary) Total and differential cross sections (  f f and γγ ) Forward-backward asymmetries (μ + μ - and τ + τ - ) Heavy flavors: R b and R c,, A fb Test the SM at % level and constrain tightly current / future extensions Correlations  obtain full error matrices after averaging Latest results: hep-ex/ , CERN-EP/ Web page:

D.BourilkovAPS 2004 Denver6 Contact Interactions etc. general framework for new int.: scale    s coupling g (convention g 2 = 4  ) we constrain g /  operators with canonical dimension N > 4  coupling 1/M N-4 |  ij | < 1 helicity amplitudes

D.BourilkovAPS 2004 Denver7 Fermion Pairs Averaged over  s :  h /  h < 1 % (theory 0.3 %);  A fb  ~ 0.01 (th ) Good agreement with SM – hadron xsec 1.7 s.d. excess averaged over all  s

D.BourilkovAPS 2004 Denver8 d  /dcos  e + e - Averaged over  s : (  /  ) forward ~ 1 % (th ~ 0.5%) (  /  ) central ~ 1.5 % (theory ~ 1.5%) Contact interactions scale > 16 (18) TeV (VV) r e < 1.4  m Extra dimensions scale > 1.2 (1.1) TeV ( =  1 ) (1999: scale M s > 1.1 TeV from combined analysis of GeV data: JHEP 08(1999)006 )

D.BourilkovAPS 2004 Denver9 d  /dcos  μ + μ - and τ + τ -

D.BourilkovAPS 2004 Denver10 Heavy Flavors Averaged over  s :  R b /R b ~ 2.5 % ;  A fb bb ~ 0.06

D.BourilkovAPS 2004 Denver11 Contact 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

D.BourilkovAPS 2004 Denver12 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) Model M Z’ (GeV) 95 % CL  673  481  434 LR804 SSM1787

D.BourilkovAPS 2004 Denver13 γγ (  /  ) ~ 1.2 % (theory ~ 1 %)  + > 392 GeV  - > 364 GeV M s > 0.97 TeV

D.BourilkovAPS 2004 Denver14 Scales for New Physics Extra dimensions from e + e - and γγ combined (DB): M Hewett > 1.4 (1.2) TeV ( =  1) (D (1.0) TeV) Contact interactions: scales up to 21.7 TeV Z’ : m > – TeV (diff. models) Size of the electron: r e < 1.4  m (quark: r < ~ m HERA, r < 5.6  m CDF 1997) QED cutoff:  + > 392 GeV  - > 364 GeV LHC – contact interactions up to 30 – 50 TeV LC – up to ~ 90 TeV (r < 3  m ; e.g. hep-ph/ ) Extra dimension up to ~ 4 TeV

D.BourilkovAPS 2004 Denver15 Conclusions SM describes the full set of precise LEP GeV ( results above 190 GeV final/preliminary ) No hint for new phenomena … in spite of sensitive searches! Many new 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