Fermion-Pair Production

Coordinators: Dimitri Bourilkov and Stephan Wynhoff

The Fermion-Pair Production analysis group is devoted to the measurement of cross-sections and forward-backward asymmetries at LEP2 energies.

Transparencies of Moriond 2000 electroweak sessions

Meetings

Meetings are normally held on every Friday at 14:30 in room 32-SC-14 and are announced in the L3 news. Copies of transparencies should be available in office 32-4B-20.

Protected information (L3 members only)

Results for the 2001 Winter conferences

Notes summarising our preliminary results for measurement of total cross sections and forward-backward asymetries, S-Matrix fits, measurement of Rb, searches for Contact Interactions, Z-prime, Leptoquarks, squarks, extra dimensions, TeV strings, etc. can be found here (section Fermion-Pairs).

Publications

The following cross-section and asymmetry papers have been published by the group:

1. Paper #90 on 130-140 GeV data, published as Phys. Lett. B370 (1996) 195

2. Paper #117 on 161-172 GeV data, published as Phys. Lett. B407 (1997) 361

3. Paper #196 on 183-189 GeV data, CERN-EP/99-181, accepted by Phys. Lett. B.
   This paper also contains the 130-136 GeV data from 1997, combined with the corresponding (re-analyzed) data from 1995

In Paper #131 (Phys. Lett. B414 (1997) 373) the measured cross sections and forward-backward at the various energy points are used. Interpreting the differences w.r.t. the Standard Model values in the context of models involving R-parity breaking sneutrino exchange, limits are set on the corresponding coupling constants.

Similarly, in Paper #143 (Phys. Lett. B433 (1998) 163) the 130-172 GeV data are used to set limits on the scale of four-fermion contact interactions, on leptoquark couplings, and on the couplings for R-parity breaking squark exchange.

In Paper #154 (Phys. Lett. B439 (1998) 183) an alternative analysis of high-energy Bhabha scattering data is used to interprete these data in terms of Bhabha scattering at reduced centre-of-mass energies. A similar analysis also allows to measure quasi-elastic Compton scattering at high energies.

Small angle Bhabha scattering can be used to measure the running of the electromagnetic coupling constant alpha for spacelike momentum transfers. Paper #197 (Phys. Lett. B476 (2000), 101-107) describes this and gives results using data at 189 GeV.

In paper #211 (CERN-EP/2000-061, accepted by Phys. Lett. B) we use the measurements from data up to 189 GeV to search for Manifestations of New Physics.

In paper #214 (CERN-EP/2000-084, accepted by Phys. Lett. B) we determine the Z boson mass and the gamma/Z interference contributions with data up to 189 GeV.

LEP1 analysis

The final publication of cross-section and forward-backward asymmetry measurements at LEP1 energies is submitted. For details please have a look at the Lineshape page.

Miscellanea

Plots related to 1998 data:

• selection plots at 189 GeV for hadrons ( colour, b/w), muons ( colour, b/w), taus ( colour, b/w), and Bhabhas ( colour, b/w)

• sqrt(sprime) distribution at 189 GeV for hadrons ( colour, b/w), muons ( colour, b/w), and taus ( colour, b/w)

• acollinearity angle distribution at 189 GeV for Bhabha events ( colour, b/w)

• hadron cross section ( colour , b/w )

• muon and tau pair cross section ( colour , b/w )

• Bhabha cross section ( colour , b/w )

• muon and tau pair forward-backward asymmetry ( colour , b/w )

• Bhabha forward-backward asymmetry ( colour , b/w )

• muon and tau pair differential cross section at 189 GeV ( colour , b/w )

• Bhabha differential cross section at 189 GeV ( colour , b/w )

Related publications by other experiments:

• DELPHI Collab., A study of the reaction e+e- -> mu+mu- gamma(ISR) at LEP and search for new physics at annihilation energies near 80 GeV

• DELPHI Collab., Measurement and Interpretation of Fermion-Pair Production at LEP energies from 130 to 172 GeV

• DELPHI Collab., Measurement and Interpretation of Fermion-Pair Production at LEP2 Energies of 183 and 189 GeV

• OPAL Collab., Measurement of cross-sections and asymmetries in e+e- collisions at 130-140 GeV centre-of-mass energy

• OPAL Collab., Production of Fermion-pair Events in e+e- Collisions at 161 GeV Centre-of-mass Energy

• OPAL Collab., Tests of the Standard Model and Constraints on New Physics from Measurements of Fermion-pair Production at 130-172 GeV at LEP

• OPAL Collab., Tests of the Standard Model and Constraints on New Physics from Measurements of Fermion-pair Production at 183 GeV at LEP

• OPAL Collab., Tests of the Standard Model and Constraints on New Physics from Measurements of Fermion-pair Production at 189 GeV at LEP

• ALEPH Collab., Measurement of hadron and lepton-pair production from e+e- annihilation at centre-of-mass energies of 130 and 136 GeV

• ALEPH Collab., Study of muon-pair production at centre-of-mass energies from 20 to 136 GeV with the ALEPH detector

• ALEPH Collab., Study of Fermion pair production in e+e- collisions at 130-183 GeV

Combinations of results:

A LEP Working Group has been formed, in charge of performing averages of the results obtained by the individual experiments. The first such average (using only the hadronic, mu+mu-, and tau+tau- channels) has been performed for the 1999 Summer conferences.

LEP2 MC Workshop:

It is expected that, at the end of LEP running, the uncertainty on many quantities (especially upon combining results from the experiments) will be dominated by theory errors. To make progress in this area, a fermion-pair subgroup of the LEP2 MC Workshop has been setup. The aim (for fermion-pair production) is to improve both on the generators and on the theory programs. Contact for L3 is Dimitri Bourilkov.
Comments & suggestions to: Stephan Wynhoff
Last modified: 4 March 2001