Minutes of the 37th meeting,
2 June 1994
1. Start-up and performance of LEP 1
S. Myers reported on the rapid LEP start-up. LEP has reached a peak luminosity of 1.5 x 1031 cm-2s-1 and an integrated luminosity of 500 nb-1 per day. The target for 1994 is 60 pb-1 to be compared with last yearís total of 40 pb-1).
2. Progress report on the LEP 2 superconducting rf system
D. Boussard presented a progress report on the work of the SL-RF group in preparing the LEP 2 sc rf cavities. The areas of particular concern are cavity production, power couplers, higher-order-mode couplers, and in-situ recovery of cavity performance. A sc rf module 4 cavities) will be installed in the floating 2-week technical stop, which is foreseen for September. During the October technical stop, a second sc rf module will be installed, with improved couplers of perhaps the final design. If machine tests on the latter module prove successful, production retro-fitting could then proceed on the full set of sc rf cavities for LEP 2.
3. Status report on the bunch-trains working group
T. Camporesi presented a status report on the bunch-trains working group. After considering the constraints of the machine and the detectors, the plan is to develop LEP operation with 4 x n bunches per beam where the number of bunches per train, n = 2, 3 or 4) and with a maximum bunch-train width of about 750 ns. This scheme would involve head-on crossings and vertical beam separation near the interaction regions to avoid parasitic beam collisions. Recent tests have confirmed that large bumps do not create aperture or injection problems for the machine nor do they produce serious backgrounds in the detectors. If the bunch-trains scheme proves successful, LEP could potentially produce 120 pb-1 in 1995 by operating with 4 x 4 bunches per beam to be compared with a total since LEP started of about 90 pb-1 per detector, up to the end of 1993). A final document from the working group is expected in August.
4. Reports on the LEP experiments
Present: J. Allaby, W. Bartel, L.L. Camilleri,
T. Camporesi, P. Darriulat, J.D. Dowell Chairman), R. Eichler, J. Feltesse,
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, D.O. Williams and C. Wyss.
Part time: A. Blondel, D. Boussard and C.H. Llewellyn Smith.
Apologies: G. Coignet, G. Kantardjian, H.
Wenninger, P.M. Zerwas and F. Zwirner.
1. Approval of the minutes of the 36th meeting
The minutes of the 36th meeting LEPC 94-6, LEPC
36) were approved without modifications.
2. Chairman's report
The Chairman joined with the committee in congratulating the LEP team for the rapid machine start-up this year.
It was reported that the Research Board had approved
all the recommendations made at the last LEPC meeting.
3. Discussion on LEP 2 progress
C. Wyss presented an update on aspects of the LEP
2 programme not covered by the talk of D. Boussard in the open session.
Preparations for all of the systems-cryogenics, RF power supplies, controls,
vacuum chambers, superconducting quadrupoles, vertical separators and collimators-are
proceeding smoothly. The working plan is to install at least 8 sc rf modules
during the 94/95 shutdown, with the aim of running at 45 GeV in 1995 with
sc cavities only.
4. Discussion of bunch-train operation in LEP
Assuming the bunch train scheme is successful, the
present peak luminosity of about 1.6 x 1031
could be raised by up to a factor of three, to 5 x 1031
with 4 x 4 bunches per beam). In the case of LEP 2, the peak luminosity
could reach 7 x 1031 cm-2s-1
with 4 x 2 bunches per beam), which is five times the design luminosity.
The committee noted that all four LEP detectors have indicated they can
operate up to a maximum train width of about 750 ns corresponding to 4
x 4 bunches) - and that the upgrade costs are reasonable 200-300 kCHF
per detector). However, ALEPH has indicated that their data suffer some
deterioration beyond 600 ns train width and, although accepting 4 x 4 bunches
at LEP 1, they would oppose trains longer than 600 ns at LEP 2. Also noted
were the positive results from the bunch-train tests that have been made
so far, although definitive tests cannot take place until after the October
technical stop. The committee therefore expressed strong support for
LEP to operate with bunch trains, commencing at the beginning of 1995,
the LEP detectors to make the necessary preparations.
5. Discussion of the L3 request to extend the 94/95 shutdown
The LEPC indicated a strong reluctance towards an extension of the 94/95 shutdown until the end of May, which was requested by L3 in the open session. The next year is seen both as an important year for physics high-luminosity LEP 1 operation with bunch trains) and as a crucial year for LEP 2 preparations. L3 is therefore encouraged to adjust its plans for the 94/95 shutdown to fit within the presently-foreseen schedule. If the L3 collaboration wishes to make a formal request for this extension, a detailed paper would be required for the next meeting of the LEPC.
6. Discussion of the Proposal LEPC 94-8/P8: A Test of Longitudinal Spin Polarization at LEP
Since there was no open presentation of this proposal,
A. Blondel was invited to present a summary in the closed session. This
was preceded by a brief presentation from W. Bartel of the impressive new
results obtained with the spin rotator at HERA. A transverse polarization
of 65% has been measured for the electron beam at 27.5 GeV, and it is not
affected by turning on the spin rotator or by beam collisions. Successful
longitudinal spin polarization has therefore been achieved. After a discussion
of the LEP proposal and the severe constraints on the LEP programme, the
proponents were invited to make an open presentation at the next meeting,
and three referees W. Bartel, W. Hollik and G. Matthiae) were appointed.
7. Discussion of the Proposal LEPC 94-9/P3: Proposal to Install Scintillating Tiles in the OPAL Endcap
In view of the late receipt of this paper, the committee
was unable to reach a conclusion at the present meeting. The proponents
are invited to present the upgrade proposal at the next open session. In
addition, a referee B. Foster) was appointed and asked to make a report
at the same meeting.
8. Discussion of the Memorandum LEPC 94-10/M109: Search for Cosmic Ray Coincidences with Detectors in the LEP tunnel
The committee took note of this memorandum, which
is ultimately aimed at a search for cosmic ray coincidences in several
detectors around the LEP ring. The present proposal involves only the ALEPH
detector and scintillator arrays placed nearby in the LEP tunnel. The committee
requested a presentation be made at the next open session.
9. LEP schedule for 1994
The likely dates for the ëfloatingí 2-week technical
stop for installation of a superconducting rf module are in September 1994.
The precise dates will be fixed shortly by the LEP co-ordinator, in consultation
with the LEP accelerator team, and communicated to the LEP detectors.
10. Any other business
The committee requested that G. Von Holtey present a progress report at the next open session on the LEP 2 detector masks. Of particular interest are the results from the prototype LEP 2 masks in DELPHI, their compatibility with bunch-trains operation, and the plans for equipping all detectors.
The Chairman reported that the dates for the Cogne meeting to review LEP physics and plans are 25-30 September 1995.
Finally, the Chairman thanked the outgoing LEPC members
-L.L. Camilleri, R. Eichler, J. Feltesse, A. Menzione and P. Zerwas- for
their excellent work on the committee, and warmly expressed his gratitude
to the outgoing Research Director, Pierre Darriulat, for his continuous
advice and support.
11. LEPC meetings in 1994
The date of the next meeting of the LEPC will be
16 September. In order to better match the expected progress of LEP,
the final LEPC meeting of 1994 has been postponed from the original dates
of 7-8 November to Friday 9 December.
 Proposal: A Test of Longitudinal Spin Polarization at LEP G. Alexander et al.), LEPC 94-8/P8.
 Proposal to Install Scintillating Tiles in the OPAL Endcap OPAL Collaboration), LEPC 94-9/P3.
 Search for Cosmic Ray Coincidences with Detectors
in the LEP tunnel A. Ball et al.), LEPC 94-10/M109.