4f Final States and Photoproduction at LEP2

1
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

2
4f production at LEP2

• ee-?4f large set of processes (everything not
  ee-? ff or ee-???(?) ). 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, TGCs
• 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
Z
e
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
• ?? ? ll- 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 lt 0.95 l e,?
• m(qq) gt 5 GeV (to avoid resonance region)
• m(ee) gt 2 GeV m(??) any
• diagram selection
• all but multipheripheral

NC08 graphs
(m.p.)
background
eeqq only
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 lt 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)
Final state Signature ?
??qqeeqq Z? dominating at low m(ll) 42 (24 )
??qq monojet topology 39
Qqqq qq ?(???) 2
llll ee??mainly 15

• DELPHI (ME) Signal definition
• cos?f? lt 0.98
• Conversion graphs only

DELPHI analyses qq??, qqee qq?? (monojet),
llll qqqq (low mass)
8
Z? production (DELPHI)

• Common LEP signal definition
• to combine results ... (new)
• eeqq,??qq
• cos ?llt0.95
• Mllgt5 GeV
• Mqqgt10 GeV
• ??qq
• Mqqgt10 GeV
• ??ll
• Mllgt10 GeV
• ml?ltgt70,90 GeV
• llLL
• cos ?l,Llt0.95
• Mllgt5 GeV
• mLLgt5 GeV
• only one m(ff) in mZ-2?Z , mZ2?Z) for all
  final states

9
Single Boson Production
Zee (DELPHI)
We? (ALEPH)
10
Single boson production We-?e
Check of SM cross sections TGCs couplings (?? )
s-channel
Lep common definition t-channel graphs
s-channel
multiperipheral
t-channel
t-chanel
11

• 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
More results on We?

• Hadronic We? cross section

We? cross section as a function of
15
Single boson production Zee
multiperipheral
Common LEP signal definition all graphs (NC48)
phase space cuts Mff? 60 GeV 600lt ? e- lt
1680 (visible electron) ? egt1680 12 (lost
positron) E e- gt 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
  (Qecos?e, Qecos?pmiss)

Qecos?e
Qecos?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 0.037lta?lt0.006 d?lt2.9 10-16 e cm at 95
  CL
• L3
• a? lt 0.107 d?lt1.14 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