EPS03 Aachen 4f at LEP2 Maurizio Bonesini 4f Final States and Photoproduction at LEP2 Maurizio Bonesini Sezione INFN Milano ( Dipartimento di Fisica G Occhialini, Universita’ di Milano-Bicocca) on behalf of LEP collaborations

EPS03 Aachen 4f at LEP2 Maurizio Bonesini 4f production at LEP2 e + e -  4f large set of processes (everything not e + e -  ff or e + e -  (  ) ). Can proceed via two, one or no resonant bosons exchange Number of contributing diagrams depends on final state; measurements may require the choice of a subset of “interesting” diagrams (e.g. Single W: t-channels diagrams only)  Test of SM: cross sections, TGC’s  background to Higgs searches and physics beyond the SM

EPS03 Aachen 4f at LEP2 Maurizio Bonesini 4f cross sections at LEP2 e e e e e e e e e e e e e e e e f f W W Z Z e W e e W W Z W e  e e Z **

EPS03 Aachen 4f at LEP2 Maurizio Bonesini 4f (non resonant) physics interest  Z  * : test of SM, ZZ  and Z  anomalous couplings  Single W production: test of SM, WW  vertex  Zee : test of SM    l + l - : test of QED mainly statistics limited  WW,ZZ see next talk by Sonia Natale

EPS03 Aachen 4f at LEP2 Maurizio Bonesini Z  * Production OPAL : Z(Z/  *)  qq  Z(Z /  *)  qqee background OPAL signal definition: –topology: |cos  ℓ | < 0.95 ℓ =e,  m(qq) > 5 GeV (to avoid resonance region) m(ee) > 2 GeV; m(  ) any – diagram selection: all but multipheripheral eeqq only (m.p.) NC08 graphs

EPS03 Aachen 4f at LEP2 Maurizio Bonesini Experimental Selection 1.hadronic presel + ℓ candidates 2.4C fit 3.ℓ-ID 4.p(ℓ) cut 5.ℓ-isolation 6.m(qq) and m(ℓℓ) 7.Anti-multipheripheral for eeqq: |cos  e | < 0.7 Syst uncertainties: 1.Choice of  ( 3 %) 2.Signal  Grc4f vs Excalibur/KoralW (8-10 %) 3.Background MC (1%) eeqq: 199 ± 27 ± 30 fb (SM*: 180 fb)  qq: 160 ± 26 ± 13 fb(SM*: 165 fb) *grc4f with 1/  =128

EPS03 Aachen 4f at LEP2 Maurizio Bonesini DELPHI analyses : qq , qqee qq (monojet), llll qqqq (low mass) Z  * production (DELPHI) Final state Signature   qq eeqq Z  * dominating at low m(ll) 42 % (24 %) qq monojet topology 39%39% Qqqq qq  (  ) 2% llll ee  mainly 15% DELPHI (ME) Signal definition: |cos  f  | < 0.98 Conversion graphs only

EPS03 Aachen 4f at LEP2 Maurizio Bonesini Z  * production (DELPHI) Common LEP signal definition to combine results... (new)  eeqq,  qq:  |cos l |<0.95  M ll >5 GeV  M qq >10 GeV  qq:  M qq >10 GeV  ll:  M ll >10 GeV  m l <>[70,90] GeV  llLL  |cos l,L |<0.95  M ll >5 GeV  m LL >5 GeV + only one m(ff) in [m Z -2  Z, m Z +2  Z ) for all final states

EPS03 Aachen 4f at LEP2 Maurizio Bonesini Single Boson Production Zee (DELPHI) We (ALEPH)

EPS03 Aachen 4f at LEP2 Maurizio Bonesini Single boson production :W + e - e Check of SM cross sections TGC’s couplings (   ) s-channel t-channel multiperipheral Lep common definition: t-channel graphs + e  e W s-channel t-chanel

EPS03 Aachen 4f at LEP2 Maurizio Bonesini Anomalous TGC (WW  ) (see talk of R.Bruneliere) But also… test of SM calculations (forthcoming LC) –Technical: process fwd peaked collinear singularity  full massive calculation needed –Physics: different energy scales involved (couplings + ISR)  benchmark for 4f codes at LEP2 (GRC4F, WPHACT,...)  /   5%  W W at tree level in SM k  =1  =0

EPS03 Aachen 4f at LEP2 Maurizio Bonesini Data selection (We ) signal Hadronic channel Pair of acoplanar jet + undetected (arge p miss )  use FF neural nets Leptonic channels (e, ,  ) High energy lepton + large E miss input output

EPS03 Aachen 4f at LEP2 Maurizio Bonesini R ff’ =  meas /  SM (WPHACT) =0.978  LEP combination (W  had, W  ff’) taking into account correlations between systematics LEP average (ADLO): still 2002

EPS03 Aachen 4f at LEP2 Maurizio Bonesini Hadronic We cross section More results on We We cross section as a function of

EPS03 Aachen 4f at LEP2 Maurizio Bonesini Single boson production: Zee e  ee Z Common LEP signal definition : all graphs (NC48)+ phase space cuts: M ff  60 GeV 60 0 <  e- < (visible electron)  e+ > (lost positron) E e- > 3 GeV (also e -  e + )  SM  500 fb eeqq; 50 fb ee  s-channel t-channel multiperipheral

EPS03 Aachen 4f at LEP2 Maurizio Bonesini Experimental selection: –jet pair (muon pair) from  * /Z decay –isolated electron –missing momentum along the beamline –e+/e- symmetric cuts using “signed” variables (Q e *cos  e, Q e *cos  pmiss ) Q e *cos  pmiss Q e *cos  e

EPS03 Aachen 4f at LEP2 Maurizio Bonesini =   Limited by data statistics  Accuracy of prediction  5.0 % Lep average (ADL): new 2003

EPS03 Aachen 4f at LEP2 Maurizio Bonesini  New results from DELPHI ( GeV) + L3 ( GeV) at LEP2 Test of QED at O(  4 ) level

EPS03 Aachen 4f at LEP2 Maurizio Bonesini Anomalous  dipole moments  sensitive to anomalous  dipole moments (in SM at tree level a  =0,d  =0) oDELPHI 0.037<a  <0.006 |d  |< e cm at 95% CL oL3 |a  | < |d  |< e cm at 95% CL

EPS03 Aachen 4f at LEP2 Maurizio Bonesini Summary Measurement of non resonant 4f production is a good test of SM and theoretical calculations (  /   5 %) in difficult regions of phase space First measurement of processes that will be dominant at LC for precise SM physics Precise measurement of background processes relevant to searches  Final LEP2 accuracy: We, Zee   7 % Acknowledgements: many thanks to E. Migliore, P. Bambade, R. Chierici, E. Graziani,... for the generous help in preparing this talk