CERN. Geneva. LEP Experiments Committee

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CERN/LEPC 97-4LEPC 455 June 1997LEP EXPERIMENTS COMMITTEEMinutes of the 45th meeting,29 May 1997OPEN SESSION1 . Conclusions of 1997 Chamonix WorkshopS. Myers reported on the conclusions of the Chamonix VII workshop, January 1997.  Themachine will be operated with 90/60 optics in 1997 at a maximum beam energy near 92 GeV.Although 90/60 optics requires a small reduction (0.4 GeV) in beam energy relative to thealternative 108/90 optics, it is expected to result in a higher integrated luminosity.  The integratedluminosity in 1997 cannot be reliably estimated in view of the SPS building fire and subsequentcleaning operation, but a delay in LEP startup of up to about 7 weeks is expected.  In 1998, a peakluminosity of 1032 cm-2s-1 could be reached at Ö s = 192 GeV, which would result in an integratedluminosity of about 200 pb-1, assuming 120 days of physics.During 1999 and 2000, vertical movements of the LEP tunnel by up to 30 mm are expected nearthe experimental pits, due to excavations for the LHC.  These movements will result in the needfor frequent vertical realignment of the affected machine elements during the course of the year.2 . LEP2 physics prospectsSupersymmetry John EllisHigh precision measurements of the Standard Model David CharltonTwo talks were presented on the physics motivation for LEP2 and the interest in reaching a totalenergy close to 200 GeV.  The arguments are based primarily on the Higgs sector andsupersymmetry.  Precision electroweak data favours a light Higgs mass, centred near 150 GeV within a factor ofabout 2.  With a total energy of 200 GeV, LEP2 can cross the difficult mass range between the Zmass and 100 GeV.  With 200 pb-1 per experiment at Ö s = 192 GeV, the combined LEP discoverylimit for the SM Higgs extends to a mass of 96 GeV and the exclusion limit to 99 GeV.  At Ö s =200 GeV and with 150 pb-1 per experiment, the SM Higgs discovery mass extends to100 GeV and the exclusion mass to 106 GeV, providing safe overlap with the Higgs search at theLHC.  Electroweak data is consistent with the supersymmetry prediction of less than 150 GeV for themass of the lightest Higgs.  At Ö s = 200 GeV and assuming a favourable mass, LEP2 can find thelightest Higgs of minimal SUSY for tan b  < 2, even with pessimistic choices for the otherparameters.  Moreover if the fine tuning of parameters is restricted, charginos and neutralinos are expected tohave masses below 100 GeV and 70 GeV, respectively.  At Ö s = 200 GeV, LEP2 will allow athorough exploration of this range of chargino masses, while the lightest neutralino will becompleted explored below a mass of 50 GeV.These considerations underscore the importance of the energy region at the limit of LEP2 and thesignificant potential for discovery.CERN/LEPC 97-4 - 2 -3 . Reports from the LEP experimentsDELPHI Tiziano CamporesiL3 Martin PohlOPAL Rolf-Dieter HeuerALEPH Gigi RolandiAll experiments reported W mass measurements from their total data at 161 and 172 GeV, withstatistical precisions in the range 0.25-0.29 GeV per experiment.  The combined LEP measurementis now m(W) = 80.38 – 0.14 GeV, to be compared with 80.366 – 0.031 GeV from the combinedStandard Model fit to all data [LEP EWWG].  The new data have revealed no clear evidence fornew physics, with, for instance, cross section upper limits of about 0.5 pb for the production ofSUSY particles.  The most significant anomaly is the ALEPH 4-jet signal - a peak containing 19events, with only 4.3 events expected from standard processes.  None of the other three detectorssees this signal even though they have now directly confirmed that their sensitivities to the 4-jetevents are comparable to ALEPH’s.Regarding preferences for high-energy data in 1997, DELPHI, L3 and OPAL requested running at184 GeV for the entire year.  ALEPH also requested a sufficient integrated luminosity be collectedat 184 GeV, but in addition requested the possibility of collecting 12 pb-1 at Ö s = 130-136 GeV atthe end of the run in order to resolve the 4-jet puzzle.Concerning the future operation of LEP, the four collaborations unanimously supported theoperation of LEP in 2000 to fully exploit its physics potential.  The highest emphasis for the finalstage of operation of LEP was placed on reaching the maximum possible energy nearÖ s = 200 GeV and collecting sufficient luminosity to effectively cover the Higgs sector in theexperimentally-difficult mass range up to 100 GeV.CLOSED SESSIONPresent: S. Bethke, J. Drees, L. Foà, G. Goggi, P. Hansen, K. Hübner, J. Kirkby (Secretary),W. Lohmann, T. Lohse, M. Mangano, B. Mansoulié, R. Marshall, J. May, S. Myers, J. Panman,L. Pape, K. Peach, I. Videau, P. Wells and P. Zerwas (Chairman).Apologies: M. Calvetti, J. Dainton, G. Kantardjian, K.-H. Kissler, M. Klein and S. Pokorski.1 . Approval of the minutes of the 44th meetingThe minutes of the 44th meeting (LEPC 96-9/LEPC 44) were approved without modification.2 . Chairman's reportThe chairman welcomed the new members of the committee: Wolfgang Lohmann and Jürgen May.He also expressed his appreciation to Philippa Wells for having accepted to continue as LEPCoordinator for an additional year.The chairman reported on the outcome of a special LEPC meeting that had taken place on25 February to discuss the L3 request for 2.5 pb-1 Z calibration data be taken at the start of LEPrunning each year.  The participants had included the four LEP spokesmen, P. Dornan, S. Myers,M. Pohl, the Directors of Research and Accelerators, the LEP Coordinator, and the Chairman andSecretary of the LEPC.  The conclusion of the meeting was that a clear case exists for therequested calibration data from L3.   Therefore a total of 2.5 pb-1 Z calibration data will be taken atthe beginning of the LEP cycle this year.  Under normal running conditions with 90/60 optics, thisis estimated to take about 6 days; if, for unforeseen reasons, it is found to require a significantly- 3 - CERN/LEPC 97-4longer time then the decision to switch to high-energy running will be taken by the Director ofResearch , in consultation with the LEP spokesmen.3 . Report from the LEP CoordinatorThe LEP Coordinator presented the new draft schedule for 1997.  As a result of the fire in the SPSsurface building and the consequent cleaning operation, the original estimates for 1997 of 108 daysfor physics and 27 days for machine development have been severely reduced.  With an estimatedstartup around the beginning of August, there would be 60-70 days for physics, complemented by20 days for machine development and energy calibration.  After accounting for the Z calibrationrunning, about 50 pb-1 of high energy data could be delivered per experiment.The loss of beam time could be partially compensated by extra running at the end of 1997 and anearly startup in 1998.  Also, one extra week (no. 40) is expected to be available in 1997 due to thecancellation of the Pb ion run.  Early running in 1998 benefits from higher energy (192 GeV),higher luminosity and lower power costs.  After reviewing the schedule of work on the LEPmachine during the 97/98 shutdown, it appears possible to start up one month earlier in 1998.  Regarding the beam energy calibration at LEP2, the expected near-term precisions are s (Ebeam) =30 (40) MeV at Ö s = 172 (184) GeV.  The final goal for LEP2 remains at s (Ebeam) ~15 MeV (to becompared with the expected combined LEP experimental error s (MW) = 30-40 MeV for500 pb-1).  4 . Near-term LEP scheduleAfter discussion, the committee made the following recommendations on the near-term LEPschedule.  Firstly,  following the 2.5 pb-1 of Z calibration data at the start of the cycle, the priority in 1997 isto accumulate 40-50 pb-1 at 184 GeV.  Secondly, concerning the ALEPH request for 12 pb-1 data at 130-136 GeV, the committeerecognises the importance of resolving the 4-jet puzzle experimentally.  ALEPH is invited toprepare a written report for the next meeting in September summarising their request for dedicatedrunning, together with the supporting physics arguments.  The committee indicated that the earliesttimes for any running at 130-136 GeV would be at the end of this year, assuming sufficient highenergy data had been collected, or else during 1998.  Finally, with regard to compensation for the loss of LEP running at the start of this year, thecommittee notes the extra week foreseen in 1997 (no. 40; due to the cancellation of the Pb ion run)and, in addition, recommends starting 4 weeks early in 1998, around 11 May.  Furthermore, iffunds are available and provided it does not compromise the early startup in 1998, the committeerecommends adding a further week in November 1997 (no. 45), at the end of the cycle.  5 . Future operation of LEP in 2000S. Myers presented the prospects for the maximum LEP energy, which depends on the maximumrf accelerating voltage that can be achieved.  Tests will be carried out this year to confirm that thesc rf cavities can be reliably operated at 7 MV/m.  With the extra cooling capacity of the LHCinstallation and additional compressors, the average accelerating gradient of the sc rf system couldbe raised from the present 6 MV/m up to 7 MV/m.  After installing the four spare sc rf modules,this would allow LEP to reach a total energy of about 200 GeV.  This installation could be readyfor March 1999.The committee considers there is a clear and compelling physics motivation for reaching200 GeV.  The SM Higgs discovery region will cross the experimentally difficult range throughthe Z resonance up to 100 GeV, providing safe overlap with the LHC.  The SUSY HiggsCERN/LEPC 97-4 - 4 -discovery region will provide complete coverage for small tan b .  The parameter space for manySUSY particles - charginos, neutralinos, etc. - will be significantly extended in a very interestingmass range.  New forces (contact interactions) between leptons and quarks will be probed up tomass scales near 8 TeV.The committee unanimously and enthusiastically supports the request from the LEP collaborationsto fully exploit the physics potential of LEP by raising the energy to the highest possible value,near 200 GeV.  To exploit the physics potential, in particular the Higgs sector, requires aluminosity of about 200 pb-1 per experiment at an energy near 200 GeV.  In order to meet thisgoal, the committee recommends very strongly that LEP be operated in 2000.  The committee welcomed the decision by CERN management to advance the schedule of the LHCcryogenics installation, which brings 200 GeV operation of LEP within reach.6 . Next LEPC meetingThe dates of the next meeting of the LEPC are Tuesday-Wednesday, 9-10 September1997 .J. Kirkby

LEP Experiments Committee: Minutes of the 45th meeting, 29 May 1997

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