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4f Final States and Photoproduction at LEP2

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. 4f production at LEP2.

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4f Final States and Photoproduction at LEP2

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  1. 4fFinal States and Photoproduction at LEP2 Maurizio Bonesini Sezione INFN Milano ( Dipartimento di Fisica G Occhialini, Universita’ di Milano-Bicocca) on behalf of LEP collaborations

  2. 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

  3. 4f cross sections at LEP2 e e e W f  f e W e e e W e e e W Z e e e Z e e e Z W e  e Z  e W e * e e

  4. 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

  5. Z* Production • OPAL : Z(Z/*)qq Z(Z /*)qqee • 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 NC08 graphs (m.p.) eeqq only background

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

  7. Z* production (DELPHI) • DELPHI (ME) Signal definition: • |cosf| < 0.98 • Conversion graphs only DELPHI analyses : qq, qqee qq (monojet), llll qqqq (low mass)

  8. Common LEP signal definition to combine results ... (new) eeqq,qq: |cos l|<0.95 Mll>5 GeV Mqq>10 GeV qq: Mqq>10 GeV ll: Mll>10 GeV ml<>[70,90] GeV llLL |cos l,L|<0.95 Mll>5 GeV mLL>5 GeV + only one m(ff) in [mZ-2Z , mZ+2Z) for all final states Z* production (DELPHI)

  9. Single Boson Production Zee (DELPHI) We (ALEPH)

  10. W e  e  Single boson production :W+e-e Check of SM cross sections TGC’s couplings ( ) s-channel Lep common definition: t-channel graphs + s-channel multiperipheral t-channel t-chanel

  11. W W  • 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% at tree level in SM k=1 =0

  12. Data selection (We) signal input Hadronic channel Pair of acoplanar jet + undetected  (arge pmiss )  use FF neural nets Leptonic channels (e,,) High energy lepton + large Emiss output

  13. LEP average (ADLO): still 2002 LEP combination (W had, W ff’) taking into account correlations between systematics Rff’= meas/ SM (WPHACT) =0.978  0.080

  14. Hadronic We cross section More results on We We cross section as a function of

  15. e Z  e e Single boson production: Zee multiperipheral Common LEP signal definition: all graphs (NC48)+ phase space cuts: Mff 60 GeV 600<  e- < 1680 (visible electron)  e+>1680 12 (lost positron) E e- > 3 GeV (also e - e +) s-channel t-channel SM500 fb eeqq; 50 fb ee

  16. Experimental selection: • jet pair (muon pair) from */Z decay • isolated electron • missing momentum along the beamline • e+/e- symmetric cuts using “signed” variables (Qe*cose, Qe*cospmiss) Qe*cose Qe*cospmiss

  17. Lep average (ADL): new 2003 = 0.9320.068 • Limited by data statistics • Accuracy of prediction 5.0 %

  18.  • New results from DELPHI (183-208 GeV) + L3 (161- 208 GeV) at LEP2 Test of QED at O(4) level

  19. Anomalous  dipole moments  sensitive to anomalous  dipole moments (in SM at tree level a=0,d=0) • DELPHI 0.037<a<0.006 |d|<2.9 •10-16 e cm at 95% CL • L3 |a| < 0.107 |d|<1.14 •10-15 e cm at 95% CL

  20. 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

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