Minutes of the meeting of the LDC concept group
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24/8/2006
People/ groups present:
Chris Damerell, Lee Sawyer, Henri Videau, Peter Wienemann, Ron Settles, Klaus Moenig, Jan TImmermanns, Winfried Mitaroff, Dave Bailey, Mark Thompson, David Ward, Norman Graf, DESY Hamburg, DESY Zeuthen
1) Status of LDC DOD
A new version of the LDC DOD has been put on the WEB. It includes the comments received so far. People are asked to check in partiuclar numbers, to make sure that the document is self consistent. Please send errors and problems to Ties.Behnke@desy.de
We aim to prepare a hardcopy of the DOD by mid-September.
2) Crossing angle discussion
Karsten Buesser presented the state of discussion on the crossing angle. A change request has been put forward by the ILC machine to change the machine baseline from 2/20 mrad to 14/14 mrad. This does imply changes to the forward region of the LDC detector.
Going to a larger crossing angle does reduce somewhat the physics reach for searches which include missing energy signatures and forward directions. Examples are some SUSY searches in specific scenarios. It was felt that the loss of efficiency was not very large. On the other hand there are some indications that the backgrounds, assuming a Anti DID field, are somewhat reduced. These things need to be studied seriously until hard and reliable numbers are available. Nevertheless the consensus was that LDC will not object to this change, as long as the 2mrad option is continued to be studied from the machine side.
3) Surface assembly vs underground assembly of the detector
Norbert Meyners presented some first studies of how a surface assembly and a smaller underground cavern would impact the LDC. There seem to be no show stoppers in principle. The main change to LDC would be that the Barrel Yoke has to be split into three rings, to limit to weight of the heaviest object to something below 2000 t (a 2000 t crane seems to be close to the optimum for such heavy lifting assemblies).
The concept then uses a somewhat reduced hass size of 30x45 m^2 area, which will allow the assembly of the detector and service to the detector at a later stage. Many details still need to be worked out, but again no major show stopper was found.
One of the motivations of surface assembly was the statement that this might save overall time since the underground hall could become available later. The feeling was that this is only a real effect for a deep site, and may not be applicable for a shallow site. Again though real studies are needed. A question which is unclear at the moment is how machine commissioning will be handled. If machine commissiong should go on while the detectors are assembled (as was assumed in the TESLA scheme) this has major repercussions on the hall size and the availability of a complete assembly position underground.
At the moment 3 month are foreseen for detector commisioning after lowering the detector into the cavern. This seemed very short and very ambitious to peope here. CMS plans something closer to 3/4 of a year as far as people are aware. No detailed plan exists for LDC though, so we have to rely on guesses.
The question was raised whether one could live in a surface assembly scenario with one large access shaft serving both IP's. The initial reaction of people was not very much in favour of this, but again this need to be looked at and studied in more detail.
4) AOB: We aim for the next LDC meeting in about one month, in September, to follow up on these items.