Minutes of the 38th meeting,
16 September 1994
R. Bailey reported on LEP operations so far this
year. Peak luminosities are routinely above 1.5 x 1031
and a new record of 2.2 x 1031 cm-2s-1
has been achieved. The machine is currently operating at an integrated
luminosity of 600 nb-1 per day, and 48
pb-1 has been accumulated in 1994 up to
12 September. Although some incremental improvements could be envisaged,
this performance essentially represents maturity for the 8-bunch pretzel
optics (typical tune shifts are 0.035, with a best of 0.043). Each of the
LEP detectors has encountered some background problems but they have been
solved with the exception of L3, which still suffers from frequent background
spikes and Time Expension Chambertrips.
2. Report from the bunch-trains working group
T. Camporesi presented the report from the bunch
train working group (LEPC 94-13/M110). The design train lengths are 425
ns (4 x 2 bunches per beam), 670 ns (4 x 3) and 741 ns (4 x 4). The four
LEP detectors have indicated they will be prepared to handle all of these
trains by the beginning of the 1995 run, with the exception of ALEPH which
cannot accommodate at present a train length greater than 680 ns (i.e.
the 4th bunch in the 4 x 4 scheme would not contribute). Active work is
going on in the collaboration to try to find a solution to this problem.
So far, all machine tests of bunch-train operation have been positive -in
particular an improved asymmetric beam separation near the interaction
region has provided a strong reduction of detector backgrounds. The definitive
machine tests with a train of 1 x n (n = 2,
3 or 4) bunches providing collisions in ALEPH and DELPHI will take place
after the October technical stop.
3. Synchrotron radiation masks for LEP 2
G. Von Holtey presented a status report on the preparations
for the additional radiation masks required for LEP 2 operation. Highly
successful tests have been made in DELPHI of the new synchrotron radiation
masks and shielding at z = 2.3 m. Photon background rates in DELPHI have
been reduced by up to an order of magnitude, without any increase in the
off-momentum particle background. The masks produce no deterioration in
LEP machine performance. The designs of synchrotron radiation masks for
the other three LEP detectors are well advanced; the masks for OPAL will
be installed in the 94/95 shutdown and for ALEPH and L3 in the 95/96 shutdown.
4. LEP 2 physics workshop update
F. Zwirner outlined the plans for the workshop on
physics at LEP 2. The organising committee (chaired by G. Altarelli) is
planning three, or perhaps four, general meetings from January to October
1995 leading to the publication of a CERN yellow report by the end of the
year. The individual working groups are organised into four main groups:
standard physics, new physics, event generators and physics-machine interface.
Convenors and contact persons for each of these groups are being finalised
over the next few weeks.
5. Presentations of experimental proposals
A. Blondel presented a proposal to test longitudinal spin polarization at LEP (LEPC 94-8/ P8).
A. Ball presented a proposal to install scintillating tiles in the OPAL endcap (LEPC 94-9/P3).
H. Wachsmuth presented a proposal to search for cosmic
ray coincidences with detectors in LEP; CosmoLEP (LEPC 94-10/M109).
Present: J. Allaby, W. Bartel, M. Calvetti, T. Camporesi, G. Coignet, J.D. Dowell (Chairman), L. Foà, B. Foster, P. Hansen, W. Hollik, K. Hübner, P.G. Innocenti, J. Kirkby (Secretary), K.H. Kissler, M. Klein, B. Mansoulié, G. Matthiae, D.J. Miller, S. Myers, J. Panman, D. Schlatter, A. Weidberg, H. Wenninger, D.O. Williams and F. Zwirner.
Apologies: G. Kantardjian.
1. Approval of the minutes of the 37th meeting
The minutes of the 37th meeting (LEPC 94-11, LEPC
37) were approved without modifications.
2. Chairman's report
The Chairman welcomed the new members of the committee: M. Calvetti, P. Hansen, M. Klein, B. Mansoulié and J. Panman.
The Chairman thanked the RF group for the committeeís visit of the LEP 2 superconducting cavities test and assembly area on 15 September. The visit had provided the committee with a deeper understanding and appreciation of the work underway to prepare the LEP 2 superconducting cavities.
The Chairman joined with the committee in congratulating the LEP team for the record performance of the machine. It appears very likely that the target for 1994 of 60 pb-1 will be exceeded.
He also reported that the Research Board had approved
the recommendation concerning bunch trains made at the last LEPC meeting.
3. Discussion on bunch-trains
The committee took note of the encouraging machine
tests related to the operation of LEP with bunch trains, and looks forward
to hearing the results of the definitive tests of up to 1 x 4 bunches at
the next meeting in December.
4. Discussion of the LEP 2 detector masks
The committee was impressed by the excellent results
obtained with the new LEP 2 synchrotron radiation masks in DELPHI and congratulated
the machine and experimental teams responsible. Sufficient information
now exists that the committee encouraged all LEP detectors to proceed
with their plans to install synchrotron radiation masks and shielding near
z = 2.3 m.
5. Discussion of the Proposal LEPC 94-8/P8: A Test of Longitudinal Spin Polarization at LEP
The three referees (W. Bartel, W. Hollik and G. Matthiae)
presented their report on this proposal and thanked J. Jowett for providing
expert advice on the machine-related aspects. Recent measurements have
shown a substantial reduction of transverse polarization at the Z0
peak due to collisions (beam-beam interaction): with the present optics,
the polarization is reduced from 20%, before colliding, to an asymptotic
value of 5% after colliding. In view of the importance of first observing
high (~50%) transverse beam polarization at the Z0
with high luminosity, the committee recommended a two-day machine
test be taken in 1994 (from physics running time) at an energy of peak-2
GeV, where high single-beam polarization has previously been observed.
Further decisions regarding the proposal were deferred to the December
6. Discussion of the Proposal LEPC 94-9/P3 add.3: Proposal to Install Scintillating Tiles in the OPAL Endcap
The referee (B. Foster) presented his report on this
proposal which aims to install a redundant forward trigger system in the
OPAL endcap during the 95/96 shutdown. The committee recommended approval
the proposal subject to the availability of the necessary funds.
7. Discussion of the Memorandum LEPC 94-10/M109: Search for Cosmic Ray Coincidences with Detectors in the LEP tunnel
The committee recommended approval of the
test experiment described in the present memorandum, which involves only
the ALEPH detector and scintillator arrays placed nearby in the LEP tunnel.
8. Report from the LEP Co-ordinator
T. Camporesi reported on the LEP schedule for the remainder of 1994 and the 94/95 shutdown, and presented the proposed schedule for 1995. The second floating LEP technical stop is scheduled for 24 October - 4 November 1994. The dates of the 94/95 LEP shutdown are 5 December 1994 - 14 April 1995. Following cold check-out, LEP will start up on 24 April 1995.
Two long technical stops -each lasting about 3 weeks-
are foreseen during 1995 for the installation of superconducting cavities
for LEP 2. This would allow the possibility of high energy running by the
end of the 1995 run. The proposed date for LEP shutdown is 20 November
1995. This shutdown starts about two weeks earlier than normal in order
to accommodate the extensive repairs and installation required by L3 in
preparation for LEP 2 operation. The totals are 118 days of physics in
1995 and 34 days of MD; the corresponding numbers for 1994 are 128 days
and 37 days, respectively.
9. LEPC meetings in 1994 and 1995
The date of the next meeting of the LEPC will be Friday 9 December. The tentative dates of LEPC meetings at CERN in 1995 are:
 Report from the Bunch Train Working Group (T. Camporesi et al.), LEPC 94-13/M110.