Minutes of the 36th meeting,
1 - 2 February 1994


1. LEP machine report

S. Myers summarized the outcome of the Fourth LEP Performance Workshop at Chamonix, 17-21 January 1994. Part of the machine development planned for 1994 is on multi-bunch schemes for increased luminosity, compatible with both LEP I and LEP II. The schemes will include further development of the 8 x 1 pretzel and also bunch trains with zero crossing angle 4 x n; n=2,3,4,..). A decision will be made as soon as possible mid 1994) on the multi-bunch scheme in order to allow time for the necessary preparations by the experiments.

C. Wyss summarized the status of the preparations for LEP II, especially regarding the superconducting cavities and power couplers. A regrouping of all RF activities for LEP within a single group SL-RF) has taken place in order to apply the maximum expertise and resources towards solving the technical challenges and handling the increased workload. Present plans foresee several superconducting cavities with improved main couplers to be installed in LEP during technical stops this year. The working hypothesis is that beam energies of up to 65 or 70 GeV will be reached by the end of 1995, with the aim to reach W pair threshold during 1996.

2. Review of LEP physics

W. Hollik reviewed the status of LEP I physics and the prospects for further improvements. LEP I has already achieved far higher precisions than originally foreseen e.g. dMZ is now 7 MeV, whereas it was originally expected to be 50 MeV) and there are rich physics prospects ahead.

F. Zwirner reviewed the status of LEP II physics. With regard to New Physics Higgs, SUSY, Zí, etc.), the importance of reaching the highest possible energy was stressed, even with modest luminosities. An update was also provided on the LEP II Workshop which is being organized under the chairmanship of G. Altarelli. Around 3 or 4 General Meetings are foreseen between October 1994 and June 1995, leading up to the preparation of a CERN yellow report on LEP II physics.

3. Reports on the LEP experiments

DELPHI:     J. E. Augustin
ALEPH:      L. Foà
L3:               S.C.C. Ting
OPAL:        R. Heuer
The spokesmen of the LEP detectors presented the technical status of their detectors and preparations for LEP II. Each of the four experiments requested that all physics running in 1994 be at the Z0 peak.

L. Foà described the status of a leak that has appeared in the cryogenic system of the ALEPH superconducting solenoid. The fault has been located and a difficult in situ repair is in progress. It is hoped that this will be successful; if not, it would be necessary to move ALEPH off-line, with consequent impact on the LEP schedule.


Present: J. Allaby, W. Bartel, T. Camporesi, G. Coignet, P. Darriulat, J.D. Dowell Chairman), L. Foà, B. Foster,
W. Hollik, K. Hübner, P.G. Innocenti, J. Kirkby Secretary), K.H. Kissler, G. Matthiae, A. Menzione, D.J. Miller,
S. Myers, L. Rolandi, D. Schlatter, A. Weidberg, H. Wenninger, D.O. Williams, C. Wyss, P.M. Zerwas, and F. Zwirner.

Part time: A. Blondel, L.L. Camilleri, R. Eichler, J. Feltesse, G. Kantardjian, M. Placidi

Apologies: None

1. Approval of the minutes of the 35th meeting

The Minutes of the 35th meeting LEPC 93-16, LEPC 35) were approved without modifications.

2. Discussion of the document LEPC 94-1/P7 Add. 1: Addendum to the Proposal for an Internal Jet-Target Experiment at LEP

The Committee discussed the Addendum to the Proposal for an Internal Jet-Target Experiment at LEP LEPC 93-14/P7, LEPC 94-1/P7 Add.1), which responded to questions raised at the previous LEPC meeting on 11 November 1993. The opinion of the Committee was that the achievement of the physics objectives could not be reasonably assured, given the insufficient knowledge of the magnitude of the analyzing power. Therefore an experiment on the proposed large scale could not be justified, and the Committee unanimously recommended rejection of the proposal.

3. Discussion of the Letter of Intent LEPC/94-3/I 12: A Test of Longitudinal Spin Polarization at LEP

The Committee discussed the letter-of-intent to perform a test of longitudinal spin polarization at LEP LEPC/94-3/I 12). The importance of the measurement of the left-right polarization asymmetry ALR, which could eventually lead to a determination of sin2qW to a precision of 1 x 10-4, was strongly endorsed by the Committee. However, manpower and other concerns were raised regarding the proposed timescale for the polarization work during 1994 and 1995, which coincides with the preparations for the highest-priority programme, LEP II. The Committee noted that the proposed first step - namely a study of the effect of beam-beam collisions on transverse polarization - is already planned for 1994 in connection with energy calibration during Z0 physics runs. In addition, there should be new information from HERA on polarization rotation by the summer of 1994. The Committee nevertheless encouraged further studies towards the preparation of a more complete proposal, which should make use of existing detectors and preferably be compatible with full-energy LEP II operation. The Committee requested that a range of options be studied, including the possibility of the physics measurement taking place after the completion of LEP II running.

4. Discussion of the document LEPC/94-5/P4 Add.2: Some Improvements to the L3 Detector for LEP 200

The Committee discussed the paper from the L3 Collaboration LEPC/94-5/P4 Add.2) outlining a number of modest upgrades to the detector in preparation for LEP II, which were presented in the Open Session. The Committee noted that the increase in the central magnetic field and the toroidal magnetization of the iron doors are both subject to a satisfactory outcome of machine tests, which have yet to be performed. The Committee understood that the necessary resources were available and considered the gains in performance to be worthwhile. The Committee therefore recommended approval of the upgrades to L3.

5. Discussion of the L3 Request to Extend the Present LEP Shutdown

The Committee discussed the request by the L3 Collaboration to extend the present shutdown by 5 days until 29 April. The L3 Collaboration are asked to revise their schedule in order to maximize the readiness of L3 on the present LEP schedule. The situation will be reviewed closely by the LEP Co-ordinator, in consultation with the LEPC Chairman and the Research Director.

6. LEP schedule for 1994

L. Rolandi presented the LEP schedule for 1994 appended). According to the unanimous request of the four experiments, the entire 1994 period will be at the Zo peak, interspersed with an adequate number of beam-energy calibration runs. The Committee confirmed the `floatingí 2-week technical stop requested for installation of superconducting cavities in 1994. This is expected to take place during the summer; the precise dates will be decided closer to the time and transmitted to the experiments at least 4 weeks beforehand. The appended schedule indicates 140 days for physics which, after subtracting up to 14 days for the floating technical stop not indicated), will provide essentially the same physics period as in 1993 128 days).

7. Any other business

Following the Chamonix discussions on new multi-bunch operation of LEP, a Working Group on LEP Bunch Configuration is being set up under the chairmanship of T. Camporesi. The purpose of the group is to ensure good communications and compatibility between the machine and the detectors regarding new bunch configurations for higher luminosity and higher energy. The working group will have representatives from the machine and a representative from each of the four LEP detectors.

The Chairman reported that a Cogne meeting to review LEP physics and plans is foreseen in September 1995.

Finally, the Chairman and Research Director thanked the outgoing LEP Co-ordinator, L. Rolandi, for his excellent work and for a very enjoyable collaboration, and they welcomed T. Camporesi, who will be the new LEPCo-ordinator from 1 April 1994 sic).

The dates of the next LEPC meeting are Thursday-Friday, 2-3 June 1994.

                                                                                                                    J. Kirkby


[1] Addendum to the Proposal for an Internal Jet-Target Experiment at LEP The HELP Collaboration; Brno, CERN, Ferrara, Geneva, Genova, Iowa, JINR, Lyon, Milano, Moscow, Legarno, Praha, Trieste, Yerevan, Zilina),
LEPC 94-1/P7 Add. 1.

[2] Letter of Intent; A Test of Longitudinal Spin Polarization at LEP A. Blondel et al.), LEPC 94-3/I12.

[3] Some Improvements to the L3 Detector L3 Collaboration), LEPC 94-5/P4 Add.2.