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Single boson production at LEP Guillaume Leibenguth On behalf of the LEP experiments Institut de physique nucléaire Université catholique de Louvain DIS’04,

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Presentation on theme: "Single boson production at LEP Guillaume Leibenguth On behalf of the LEP experiments Institut de physique nucléaire Université catholique de Louvain DIS’04,"— Presentation transcript:

1 Single boson production at LEP Guillaume Leibenguth On behalf of the LEP experiments Institut de physique nucléaire Université catholique de Louvain DIS’04, Štrbské Pleso

2 G. LeibenguthSingle Boson Production at LEP2 Two 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

3 G. LeibenguthSingle Boson Production at LEP3 Single W Production: Context W pair production Single W production: fermion-antifermion comes from the W Boson, t-channel diagram 96 Charged or Neutral Currents

4 G. LeibenguthSingle Boson Production at LEP4 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, l qq: 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)

5 G. LeibenguthSingle Boson Production at LEP5 Signal Definition L3 (single W) Generated phase space = SIGNAL: |cos  e+ | > 0.997 Min (Ef, Ef’) > 15 GeV for e e only: |cos  e- | < 0.75 for Z (  )ee rejection Analysis relies on: Two fermions and P miss e + in the beam pipe MC: e+ qq’ Angular acceptance of LEP detectors

6 G. LeibenguthSingle Boson Production at LEP6 L3 Single W Analysis Hadronic channel Two acoplanar jets E e.m > 15 GeV 0.3 < E vis /  s < 0.65 E T > 0.2 E vis |cos  miss | < 0.92 Acoplanarity > 11º No high E lepton Anti ZZ cut Neural Network (NN) Leptonic channel High energetic lepton No other activity in the detector

7 G. LeibenguthSingle Boson Production at LEP7 Signal Definition Aleph Generated phase space requirement: |cos  e | > 0.9994 Mqq’ > 60 GeV/c² for e qq’ OR |cos  l | < 0.95 and E l > 20 GeV for e l Monte Carlo signal : Grc4f A candidate:

8 G. LeibenguthSingle Boson Production at LEP8 ALEPH 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

9 G. LeibenguthSingle Boson Production at LEP9 Signal Definition Opal-Delphi Graph content (and not generated phase space): t-channel diagram only Mqq > 45 GeV/c2 |cos  e- | 20 GeV and |cos  e+ | > 0.95 for e e 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.

10 G. LeibenguthSingle Boson Production at LEP10 DELPHI single W analysis Hadronic selection E e.m /  s < 50 % E vis /  s > 20 % E T > 0.2 E vis |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, E l (E t ) /  s< 45 (12)% | IP R  | < 0.2 cm for muon

11 G. LeibenguthSingle Boson Production at LEP11 OPAL Single W Analysis Hadronic channel Two non collinear jets recoiling against the neutrino in the transverse plane 120 > Mqq > 40 GeV/c² 15 % < E e.m /  s < 50 % WW  e qq removed No lepton isolated |cos  miss | < 0.96 Acoplanarity > 7.5 º Likelihood selection Leptonic selection very sophisticated e ee

12 G. LeibenguthSingle Boson Production at LEP12 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

13 G. LeibenguthSingle Boson Production at LEP13 Accuracy 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

14 G. LeibenguthSingle Boson Production at LEP14 Comparison Grc4f-Wphact

15 G. LeibenguthSingle Boson Production at LEP15 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

16 G. LeibenguthSingle Boson Production at LEP16 Z/  exchange Main diagrams contributing to the “ single Z ” production

17 G. LeibenguthSingle Boson Production at LEP17 DELPHI Zee Analysis DELPHI Zee Analysis Requirement on the phase space (COMMON LEP Definition!)  un < 12 º, 12 º <  sc <120º and E sc > 3 GeV Mqq or M  > 60 GeV/c2 Analysis based on: A loose preselection Identification of an isolated electron Cut on Mqq or M 

18 G. LeibenguthSingle Boson Production at LEP18 ALEPH 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 M had > 50 GeV/c² E miss /  s > 25 % Leptonic channel Three Leptons Charge = +/- 1

19 G. LeibenguthSingle Boson Production at LEP19 L3 Zee Analysis Hadronic channel An electron identified in the BGO with an energy of 3 GeV 50<Mhad < 130 GeV Q e cos  z > -0.5 Q z cos  miss > 0.94 Two jets (Durham) Opening angle of the two jets > 150  55 < M  < 145 GeV/c² -0.5 0.5 Q cos  z < 0.40  :

20 G. LeibenguthSingle Boson Production at LEP20 OPAL Zee Analysis Hadronic channel Two jets EM. Cluster larger than 1 GeV dE/dx consistent with electron Q e cos  miss  0 Mqq’ > 25 GeV/c² +Kin. Fit. E em /  s < 0.93 |P miss | > 35 GeV/c Isolation of the electron: nothing in 0.6 rad cone Q e cos  miss  0.95, Emax in forward detector < 30 GeV - Qe cos  e  0.65 or E e  0.35 E Eqq Ee Mqq

21 G. LeibenguthSingle Boson Production at LEP21 Comparison Grc4f -Wphact

22 G. LeibenguthSingle Boson Production at LEP22 Conclusions Standard model is in a very good shape Even when these difficult corner of phase space are studied and tested to a 5% accuracy So 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 2004 And The single W cross section is rising! These channels are of importance in view of the next linear collider


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