single boson production at lep
DESCRIPTION
Single boson production at LEP. Guillaum e Leibenguth On behalf of the LEP experiments Institut de physique nucl éaire Universit é catholique de Louvain DIS’04, Štrbské Pleso. Two Channels. W exchange: Test of the Standard Model: IR Study of the trilinear gauge coupling - PowerPoint PPT PresentationTRANSCRIPT
Single boson production at LEPSingle boson production at LEP
Guillaume Leibenguth
On behalf of the LEP experiments
Institut de physique nucléaire
Université catholique de Louvain
DIS’04, Štrbské Pleso
G. Leibenguth Single Boson Production at LEP 2
Two ChannelsTwo Channels
• W exchange:– Test of the Standard Model: IR – Study of the trilinear gauge coupling– Measurement of W mass at the next linear collider
• Z/ exchange:– Electroweak Compton scattering process– Cross section refers to 48 Feynman Diagrams Diagrams involving Higgs boson are neglected
G. Leibenguth Single Boson Production at LEP 3
Single W Production: ContextSingle W Production: Context
W pair production
Single W production:fermion-antifermioncomes from the W Boson,t-channel diagram
96 Charged or NeutralCurrents
G. Leibenguth Single Boson Production at LEP 4
And Difficulties…And Difficulties…
Single W production is in Yellow!
Data taken between 161 and 209 GeV
• qq+isr: photon emitted along the beam pipe
• qq: little missing energy
• W pair: 4q: no missing energy, lqq: high energetic lepton visible
fully leptonic: 2 leptons alone!
• Z pair: irreducible bkg ee• single W boson (signal We!)
• Zee (second part of the talk)
G. Leibenguth Single Boson Production at LEP 5
Signal Definition L3 (single W)Signal Definition L3 (single W)Generated phase space = SIGNAL:
• |cos e+ | > 0.997
• Min (Ef, Ef’) > 15 GeV
• for ee only: |cos e- | < 0.75
for Z ()ee rejection
Analysis relies on:
• Two fermions and Pmiss
e+ in the beam pipe
MC: e+qq’
Angular acceptance of LEP detectors
G. Leibenguth Single Boson Production at LEP 6
L3 Single W AnalysisL3 Single W Analysis
Hadronic channel
• Two acoplanar jets
• Ee.m > 15 GeV
• 0.3 < Evis/s < 0.65
• ET > 0.2 Evis
• |cos miss | < 0.92
• Acoplanarity > 11º• No high Elepton
• Anti ZZ cut
• Neural Network (NN)
Leptonic channel
• High energetic lepton
• No other activity in the detector
G. Leibenguth Single Boson Production at LEP 7
Signal Definition AlephSignal Definition Aleph
Generated phase space requirement:• |cos e | > 0.9994• Mqq’ > 60 GeV/c² for eqq’OR• |cos l | < 0.95 and El > 20 GeV for el
Monte Carlo signal : Grc4f
A candidate:
G. Leibenguth Single Boson Production at LEP 8
ALEPH Single W AnalysisALEPH Single W Analysis
Hadronic channel
• |cos miss | < 0.90
• Acollinearity between the two hemisphere momentum < 165º
• Energy of a wedge of 30º centered on missing momentum direction
• Energy in a cone of 12º (E12) around the beam pipe < 0.025 s
• Invariant hadronic mass < 60 GeV/c²
• Neural Network
• High energetic isolated lepton• No E12 energy, missing
momentum unbalance
Leptonic channel
G. Leibenguth Single Boson Production at LEP 9
Signal Definition Opal-DelphiSignal Definition Opal-Delphi
Graph content (and not generated phase space):
• t-channel diagram only
• Mqq > 45 GeV/c2
• |cos e- | < 0.95, El+ > 20 GeV and |cos e+ | > 0.95 for ee
Monte Carlo Signal: Wphact (Delphi), KoralW, Grc4f, Excalibur (Opal)
MC Background: 2 fermions: KK2f (Delphi) KoralZ (Opal), e+e- : TEEGG & BHWIDE, PYTHIA 6.143 & BDK (Delphi), Pythia, Herwig, Phojet, twogen, Phot02 (Opal)
The LEP experiments have agreed to use this definition as LEP wide.
G. Leibenguth Single Boson Production at LEP 10
DELPHI single W analysisDELPHI single W analysis
Hadronic selection• Ee.m/s < 50 %• Evis/s > 20 %• ET > 0.2 Evis • |cos miss | < 0.98• Acoplanarity > 10 deg• No E.M Cluster > 45 GeV• Multiplicity < 50• 30 <Mvis < 110 GeV/c2 • E(e,) < 7.5 (10) s % • Neural Network
Leptonic channel• One Lepton, El (Et) /s< 45 (12)%• | IPR | < 0.2 cm for muon
G. Leibenguth Single Boson Production at LEP 11
OPAL Single W AnalysisOPAL Single W Analysis
Hadronic channel• Two non collinear jets
recoiling against the neutrino in the transverse plane
• 120 > Mqq > 40 GeV/c²• 15 % < Ee.m/s < 50 %• WW eqq removed• No lepton isolated• |cos miss | < 0.96• Acoplanarity > 7.5 º• Likelihood selection
Leptonic selection very sophisticated
ee
e
G. Leibenguth Single Boson Production at LEP 12
Combining …Combining …
• Take the Delphi-Opal definition (rescale the phase space cut L3, Aleph to it)
• Correlation between uncertainties are taken into account
• Only a preliminary analysis of 189 GeV data from OPAL
Systematic errors are treated in 4 different ways!
Several sources, but a few really contribute:
• Limited amount of MC stat
• Background estimate• Luminosity• For the muon channel,
triggering issue (ALEPH and L3)
• 5 % accuracy of signal modelling
G. Leibenguth Single Boson Production at LEP 13
Accuracy of SM predictionAccuracy of SM prediction
Good agreement in all experiment between the expected and the observed number of events.
Luminosity used by Aleph : 683.4 pb-1
Delphi : 619.3 pb-1
L3 : 675.5 pb-1
Opal : 174.7 pb-1
G. Leibenguth Single Boson Production at LEP 14
Comparison Grc4f-WphactComparison Grc4f-Wphact
G. Leibenguth Single Boson Production at LEP 15
Sensitivity to Sensitivity to
Assuming SU(2)xU(1) symmetry
-> 3 couplings
0.90 < < 1.32 (L3)
The sensitivity to z is weaker.
For a more complete discussion on TGC, see U. Parzelfall’s talk
G. Leibenguth Single Boson Production at LEP 16
Z/Z/ exchange exchange
Main diagrams contributing to the “ single Z ” production
G. Leibenguth Single Boson Production at LEP 17
DELPHI Zee AnalysisDELPHI Zee Analysis
Requirement on the phase space
(COMMON LEP Definition!) un < 12 º, 12 º < sc<120º
and Esc > 3 GeV
• Mqq or M > 60 GeV/c2
Analysis based on:• A loose preselection• Identification of an isolated electron• Cut on Mqq or M
G. Leibenguth Single Boson Production at LEP 18
ALEPH Zee AnalysisALEPH Zee Analysis
Hadronic channel
• A loose preselection
• Identification of an isolated electron with
E> 3GeV
• cos e < 0.8
• Qe cos z > -0.85
• Qz cos miss > 0.9
• Mhad > 50 GeV/c²
• Emiss / s > 25 %Leptonic channel
• Three Leptons
• Charge = +/- 1
G. Leibenguth Single Boson Production at LEP 19
L3 Zee AnalysisL3 Zee Analysis
Hadronic channel
• An electron identified in the BGO with an energy of 3 GeV
• 50<Mhad < 130 GeV
• Qe cos z > -0.5
• Qz cos miss > 0.94
• Two jets (Durham)
• Opening angle of
the two jets > 150• 55 < M < 145 GeV/c²• -0.5 < q cos < 0.93, q cos miss > 0.5• Q cos z < 0.40
:
G. Leibenguth Single Boson Production at LEP 20
OPAL Zee AnalysisOPAL Zee Analysis
Hadronic channel• Two jets• EM. Cluster larger than 1 GeV• dE/dx consistent with electron• Qe cos miss 0• Mqq’ > 25 GeV/c² +Kin. Fit.• Eem/ s < 0.93• |Pmiss| > 35 GeV/c• Isolation of the electron: nothing in 0.6 rad cone• Qe cos miss 0.95, Emax in forward detector < 30 GeV• - Qe cos e 0.65 or Ee 0.35 E
Eqq
Ee
Mqq
G. Leibenguth Single Boson Production at LEP 21
Comparison Grc4f -WphactComparison Grc4f -Wphact
G. Leibenguth Single Boson Production at LEP 22
ConclusionsConclusions
• Standard model is in a very good shape• Even when these difficult corner of phase space are
studied and tested to a 5% accuracySo• L3 has already published its final results• ALEPH and DELPHI are really close to finalizing their
publications• OPAL has only analyzed 189 GeV data set• Final LEP word on this issue hopefully in summer 2004And• The single W cross section is rising! These channels are of
importance in view of the next linear collider