Minutes of 18th FFIR meeting on 11/15/2000

The meeting was held in a room of 3-425 at KEK, 13:30-15:30, 11/15/2000. We have (1)a brief report of LCWS00 and discussed on (2) update of dump line, (3) ACFA report and (4) others.

(1) Report of LCWS00 (transparencies, 33 pages of pdf ,1.85MB) Tauchi briefly reported the LCWS00. The LCWS00, the 5th international workshop on physics and detector at linear colliders was held in October 24-28,2000, at Fermilab. The first workshop has been held in 1990. Number of registered participants was 278. On the first day, the workshop was begun by a welcome speech by FNAL director Mike Withrell, and there were plenary talks on Physics perspective, LC status reports (TESLA, NLC, JLC and CLIC), Accelerator options ( Giga-Z, gamma-gamma collisions,FEL etc. ) and etc.. Parallel sessions, which were actually 6 at the same time, were held for following two days, discussing on physics (Higgs, SUSY, Top/QCD, Other New Particles and Alternative Theories, Two photon/QCD, Precision Electroweak and Strong Gauge Interactions), detectors( Vertex & tracking, Particle ID & muons, Calorimetry, Data Acquisition and triggering) and Interaction region,backgrounds,e-e-,e-gamma, gamma-gamma. The last two days were summary talks.The detailed informations can be found at a web page of http://www-lc.fnal.gov/lcws2000/ .

Here some topics related to machines were mentioned. O.Napoly(CEA/Saclay) represented the TESLA group. Construction phase of superconducting cavity has been moved from R&D to production. Scenario of the cost-down has been achieved, i.e. 200k/mࣵMV/m=40k/MV in 1991 shall be 50k-euro/m25MV/m=2k-euro/MV in 2000, although there was no direct proof nor the written cost estimation. Therefore, the total cost of superconducting modules (cavities and cryostats) must be one billion dollars. One justification was that 40% yield of the cavities with more than 25MV/m at the first production has been improved to 80% at the third one. So, he was confident on this achievement.
For the NLC, T.Raubenheimer (SLAC) reported emphasizing on design changes since the Lehman review committee in last May. One of major changes was a Hi/Lo IR layout. In the new layout, two linacs are not on a line but they are horizontally crossed by 20mrad for future multi-TeV operation. From CLIC-3TeV studies, this large crossing angle must be needed to avoid multi-bunch kink instabilities and disrupted coherent e+e- pairs. Since a big bend generates unacceptably large emittance growth, two beams must be collided with no such bend. For lower energy collisions at Ecm=92 - 350GeV, a second beam-delivery line shall be constructed with a big bend. Thus, as a world LC, the NLC can be operated at wide energy region from 92GeV to 5TeV in CM-frame. The luminosity at Ecm=500GeV becomes the similar value of the TESLA with 190bunch/train at 180Hz, which is very close to the JLC-Y. Overall, they could achieve 30% cost-reduction.
I.Wilson (CERN) presented the CLIC status focussed on a design of Ecm=3TeV and L=10^{35}/cm^2/sec. He also commented on a recent serious problem of break-down observed in high gradient accelerating structures as follows. "In 1994 before we had 30 GHz power source we built a 26 cm 11.4 GHz low-group- velocity structure and tested it at SLAC to peak gradient of 154 MV/m (125 MV/m average) with 150 ns pulse length. So here is a proof of existence of the very high gradients we are aiming for. So what about the breakdown and damage observed in the CTF2 ? Damage has been observed at relatively low gradients (60 MV/m) so there is clearly a problem BUT we do not consider these results to be representative of what we can finally achieve. Why ? (i) Damage confined to the input coupler which has a 40% over-voltage enhancement - can be taken out by modifying the design this is foreseen. (ii) Structures were exposed to air (and dust) for about 6-7 years and were operated under unusually poor vacuum (perhaps as bad as 10 -3 torr). (iii) Structures were conditioned using aggressive conditioning procedures and with a limited number of pulses (CTF2 only runs at 5 Hz !). Have to wait for new round of high gradient tests on structures with an improved coupler design and better vacuum conditions before we can really say if we have a serious problem or not."
Y.H.Chin (KEK) reported the JLC status. He concentrated on the status of X-band RF system, c-band RF system and the ATF.

In afternoon of the fourth day, there was a panel discussion among directors of KEK, DESY, SLAC, Novosibirsk and FNAL while CERN director L.Maiani was absent. They discussed on international collaboration toward the realization of a linear collider. Among the discussion, a committee was proposed in order to review and compare various technologies of linear colliders which have been developed in the world. This committee may be re-organization of previous TRC (Technical Review Committee, so called Greg Loew committee). There was no consensus on its purpose (design of a single LC in the world?) and schedule ( as soon as possible or at least a few years necessary for fair comparison etc. ).

Finally, P.Grannis (spokesman of D0 group at Tevatron) concluded the workshop. His talk was well-prepared and his transparencies were clearly written. So, please read directly his transparencies for details. He began his talk from the schedules of TESLA, JLC and NLC for the proposals. TESLA will complete the TDR until next March, 2001 to be reviewed by German science council, and it is expected German government decision in 2002 for the construction start in 2003. JLC proposal will be made within 2 or 3 years. NLC needs 2-3 years for R&D to be ready for the proposal. Then, he concluded that "The cost will be high. Unless we internationalize so as to satisfy the needs of all regions and allow productive collaboration, we jeopardize the prospect of the LC, or any other new frontier facility anywhere."

S.Komamiya (representative in Asian region) announced that the next LCWS will be in Korea , May, 2002, and see you there again.

(2) Update of dump line (transparencies, 8pages, update, pdf , 64kB and 8pages, a trial for less backgrounds, pdf , 64kB ) Kubo updated the dump-line design. Major change was an optimization of apertures for magnets as seen in page-6 in order to make slits for disrupted particles. The total energy loss is 0.96%. He also corrected an estimation of neutron-generation, that is, the previous estimation was wrongly set to be 1n/100MeV, but the correct one is 1 n/10GeV, so it was 100 times overestimation ! The neutron background at the VTX was estimated to be 3.6 x 10^{11}/cm^2/year, which is still 10 times more than the tolerable level.
To reduce the background, the first quadrupole QD1 was slightly moved away. In this design the energy resolution measured downstream was degraded since the resolution depends strongly on the distance and the shorter distance is better. However, the energy loss was only reduced by half. So, further optimization of the apertures and shielding masks must be necessary.

(3) ACFA report (transparencies, 6 pages, pdf , 133kB ) As you know from the ACFA-email, the ACFA-JLC report shall be completed at 31th March, 2001 ( see http://acfahep.kek.jp/acfareport/index.html ). The first draft is due to 31th December, 2000. The report should be very close to the technical design report.
There must be three chapters which are directly related to our sub-group or the members. They are (a)Interaction Region, (b) Detector Magnet (H.Yamaoka et.al.) and (c) Detector Integration (H.Yamaoka et. al.).
(a)Interaction Region There should be sections of Backgrounds, Layout, Pair monitor, Active mask, Luminosity monitor, Support system and Dump line. Luminosity measurement must be discussed in a section of Forward tracker which actually determines accolinearity angles of Bhabha events for luminosities as a function of Ecm, especially within "the energy spread (<1%)". All the designs and performance studies shall be made with parameters of B=3Tesla, L*=4m and the new mask system and even with the JLC-Y option. We would like to use superconducting QC1 as the nearest focussing magnet.
(b)Detector Magnet Superconducting coil and iron structure shall be explained at B=3Tesla. They have been investigated by H.Yamaoka since last year, summer, who has presented the design at the 2nd ACFA workshop, Seoul, 11/4-9,1999 . This report expects more detailed engineering designs and a possible cost estimation.
(c)Detector Integration This topics has never been studied systematically. However, for a completeness of the report, it shall be implemented in it. For this purpose, detailed designs of all the detectors and cablings will be requested. H.Yamaoka is going to take a major role in the engineering study.

(4) Others At next meeting, we will discuss on superconducting QC1, a report of GM2000 and progress reports.

The next meeting will be on 29 November (Wednesday), 2000 13:30 - 15:30 at 3 gokan, 425.