DIS 2004, Štrbské Pleso 16 April 2004Ulrich Parzefall 1 Triple Gauge Couplings at LEP Ulrich Parzefall Universität Freiburg

DIS 2004, Štrbské Pleso 16 April 2004Ulrich Parzefall 2 Charged Gauge Boson Couplings Non-Abelian nature of EW sector means couplings between gauge bosons One of the major LEP2 tasks Accessible at LEP2: Trilinear Gauge Couplings (TGC) –Charged TGC from WWV vertex (V=Z or γ) –Neutral TGC Quartic Gauge Boson Couplings (QGC) –ZZγγ (not in SM) –WWVγ (σ ~3fb in SM) –See Paul Bell’s talk

DIS 2004, Štrbské Pleso 16 April 2004Ulrich Parzefall 3 Charged Trilinear Gauge Couplings Couplings associated with WWγ/WWZ vertex Most general description with 14 independent couplings Assume C, P conservation and gauge invariance -> 3 Parameters: g 1 z, λ γ, κ γ g 1 z gives weak charge of W W magnetic dipole moment μ W ~(1+λ γ +κ γ ) W electric quadrupole moment q W ~(λ γ -κ γ ) Contributions from WW, single W, single γ single- and multi-parameter fits done by ADLO

DIS 2004, Štrbské Pleso 16 April 2004Ulrich Parzefall 4 Charged TGC Measurements TGC sensitivity comes from –Total cross-section –Differential distributions W-production angle most important (cos θ W ) Fermion angles have also significant contribution –WW-channel contributions differ in sensitivity qqlv most sensitive qqqq also important (limited W charge tagging and jet pairing efficiency reduce sensitivity) lvlv also used (ambiguities due to two neutrinos) Analysis methods: –Angular variables –Optimal observable techniques

DIS 2004, Štrbské Pleso 16 April 2004Ulrich Parzefall 5 Charged TGC Results Single LEP experiments combine energies and WW decay channels –Dominated by qqlv –Also sensitivity from qqqq and lvlv channels, and as cross-check –Single W important for k γ ALEPH, DELPHI, L3 and OPAL have similar measurements LEP cTGC combination –full likelihood based (no straight averaging) CERN-EP

DIS 2004, Štrbské Pleso 16 April 2004Ulrich Parzefall 6 LEP-Combined TGC Results Single-parameter fit combination –Precision of 0.02 – 0.05 –Consistent with SM –Sensitive to radiative corrections Long-standing issue: agree on treatment of LEP correlated systematics –what to study –how to quantify –non-Gaussian problems –how to include in LEP-combined fit –combination more complex than cross-section measurements, eg R WW

DIS 2004, Štrbské Pleso 16 April 2004Ulrich Parzefall 7 LEP-Combined TGC Results Systematics inclusion now based on joint minimization of stat & syst errors Dominant systematic: theory uncertainty in radiative corrections –Doube Pole Approximation (DPA) –progress in 2003: replaced conservative ‘full difference’ estimate with fullsim results –Reduction of σ DPA by ~50% Now: g 1 z, λ γ, κ γ statistics limited –stat & systematic errors similar

DIS 2004, Štrbské Pleso 16 April 2004Ulrich Parzefall 8 Charged Trilinear Gauge Couplings LEP WG performs also 2D and 3D cTGC fits results agree with SM ADLO Status –Final papers out by L3, OPAL –ALEPH, DELPHI publications expected this summer –LEP combination to follow

DIS 2004, Štrbské Pleso 16 April 2004Ulrich Parzefall 9 Neutral Gauge Boson Couplings Couplings: Z γγ, ZZ γ, ZZZ Neutral TGCs vanish in SM Final States: ZZ, Z γ –Populated by other SM processes –Place limits on anomalous couplings Coupling parameters It is possible to express the nTGCs as only two independent parameters – CP-violating & CP-conserving e + e -  Z γ e + e -  ZZ CP-viol.h 1 γ, Z,h 2 γ, Z f 4 γ, Z CP-cons.h 3 γ, Z,h 4 γ, Z f 5 γ, Z SM: Anomalous Couplings:

DIS 2004, Štrbské Pleso 16 April 2004Ulrich Parzefall 10 Z γ -Couplings Measurement Z γ -couplings are sensitive to –Total cross-section –Diff. distributions: |cos θ γ |, E γ, angle( γ,jet) LEP combination for e + e -  Z γ

DIS 2004, Štrbské Pleso 16 April 2004Ulrich Parzefall 11 ZZ-Couplings Measurement ZZ-Couplings are sensitive to –Total cross-section –|cos θ Z | LEP combination for e + e -  ZZ

DIS 2004, Štrbské Pleso 16 April 2004Ulrich Parzefall 12 Conclusions All four LEP experiments have measured charged and neutral Triple Gauge Couplings –Results agree with SM predictions –Non-Abelian nature of electroweak sector proven by cTGCs –Neutral TGC vertices were not observed Final LEP combinations expected this year – Place limits on W magnetic & electric moments from cTGCs –Express nTGC results as two parameters LEP cTGC limits will be setting the standard for some time LEP2TevatronLHCTESLA κγκγ ~ λγλγ ~ g1zg1z 0.025~ (FERMILAB-PUB , CMS NOTE 2001/056, ATLAS IN 060, LC-PHSM )

DIS 2004, Štrbské Pleso 16 April 2004Ulrich Parzefall 13 How Did We Do? The LEP EWWG has combined ADLO results and deals with systematics to achieve maximal precision LEP2 has done its homework: –Couplings (cTGCs to 2-5%) –Cross-sections (R WW to 1%) – m W = ± GeV

DIS 2004, Štrbské Pleso 16 April 2004Ulrich Parzefall 14 THE END

DIS 2004, Štrbské Pleso 16 April 2004Ulrich Parzefall 15 DIS2004 Spares DELPHI

DIS 2004, Štrbské Pleso 16 April 2004Ulrich Parzefall 16 Radiative Corrections Success of LEP σ WW (R WW ) and cTGC combinations showed precision would reach theory error in MC (2% at start of LEP2) Challenge for theorists to do better and include radiative corrections –Double Pole Approximation (DPA) calculations were performed –YFSWW & RacoonWW emerged, reducing theory error from 2% to 0.5% Cross-section prediction reduced by ~2% This shifts the TGCs by 0.02 to 0.05 –Comparable to stat. precision G.Passarino, summary of LEP MC workshop

DIS 2004, Štrbské Pleso 16 April 2004Ulrich Parzefall 17 TGC Sensitivity