Meeting Summary
Not long after the meeting
started on March 9, it started snowing and it did not stop until late evening. Pizza was delivered to the meeting room for dinner,
and the meeting went on. As the snow
was breaking a record (> 1 ft in March) we probably were pretty close to
breaking the record for the longest meeting a day. Miraculously, the airport
was back open next day and all the visitors were able to be back home in time. There
were 20 participants and 16 presenters.
Most comments on the meeting were that the progress we have made was
impressive. There were a lot of active and lively discussions throughout the meeting.
Below is a short summary of what we
have discussed. A copy of all the viewgraphs presented at the meeting is
enclosed for your reference.
I. ACCESS Overall
The CRWG has recommended SEUS to include ACCESS in the NASA strategic plan as a 'New Start' during the period 2003-2007. Betsy Park is about to submit ACCESS to NASA HQ as part of the Program Operating Plan (POP) for GSFC. According to Betsy, the current estimate of ACCESS cost is $180M, which is about a factor of two too high. She said her team was looking into ways of reducing the estimated cost, including as a last resort descoping, possibly by removing one of the three instruments. She discussed the ACCESS mass limit (presently set at 13500 lbs). This includes non-detector components (e.g. AMB) which will reduce mass available for the detectors. She also reported on the possibility of breaking ACCESS into two segments to fly on two ULC’s. Each has a 2500 kg limit, but the carrier mass is not counted in the mass budget.
Vernon Jones said that ACCESS is at a crossroads, with Alan Bunner’s clear indication that he can not support it for at new start at more than $100M. Vernon supports finding ways to do all the ACCESS science, but he was very doubtful that all three instruments can be included for less than $100M. He suggested considering the JEM for one of the instruments. He said that the ACCESS cost had to be < $100M, with at least 25% reserve, based on both GSFC and TMCO estimates, regardless of what the instrument teams estimate. He also emphasized NASA’s concern about too many co-I’s and the need to focus on one compelling science objective.
Bob Streitmatter suggested to have an ACCESS Working Group meeting during the week of 7/12.
Baseline study: According to Eun-Suk Seo (UMD)’s report, the baseline calorimeter gives mostly symmetric Gaussian distributions of energy deposit for all energies in the ACCESS range. The energy response is quite linear. The energy resolution is about 35% and nearly energy independent. According to Wolfgang Schmidt (MPI – Lindau)’s study, electrons can be measured in the presence of carbon target with the rejection power expected to be lower than the case with thicker EM calorimeter without target. The bottom line is that the baseline can meet the ACCESS mission goal.
Other reports:
· A few groups’ independent studies (UMD, GSFC, MSFC) agreed that we get about 25% higher geometry factor by including a carbon target in front of the calorimeter.
· High energy simulation speed issue was discussed. Jian-Zhong Wang (UMD) presented results of a study on parametrized GEANT simulations. He presented a method that allowed about x10 faster simulation with almost no degradation in simulation quality, including back-scattered particles.
· Charge measurement: Jian-Zhong also presented results of a simulation study showing how one might be able to flag events that interacted above the calorimeter's Si matrix, using the hit pattern in the Si matrix. In such events the Si charge measurement would be inaccurate.
·
John Watts presented simulation results of a sampling
lead/fiber imaging calorimeter. He presented
results using several different techniques, but none was better than what could
be achieved without resorting to fiber-by-fiber readout.
·
Ulisse Bravar presented tungsten/Si calorimeter. The RMS/mean was about 30%, but the energy
deposit distribution was asymmetric and showed a long low energy tail.
Consensus on alternate configuration to study:
· A totally active design concept (U Mich) was agreed to be abandoned.
· The team chose to study a W sampling calorimeter in addition to the baseline.
· Two configurations of a W calorimeter, one with a carbon target and another one with no target, will be studied.
· For active sampling material, both scintillating fibers and Si strips will be studied.
· For each case, the charge detector needs to be designed to deal with the backscatter effect properly.
· For each configuration, energy resolution, shape of the energy deposit distribution, type of sampling, and electron identification power will be compared.
John Mitchell emphasized that the beam test was approved by CERN for ACCESS R&D and not for a particular instrument calibration. CERN is quite sensitive to the language employed in this regard, and John requested heightened awareness of this from all calorimeter teams. John also said that CERN would expect substantially equal time allocations for the different ACCESS calorimeter prototypes. John asked the attendees if ACCESS should push for a heavy-ion time allocation at the 40 GeV/nucleon beam expected in November. He said CERN is sure to have the full energy beam next year regardless the LHC schedule. He asked if the heavy ion beam test is necessary for the calorimeter selection, and the answer was no. The need is rather to test simulation models. Due to the uncertainties among different heavy ion interaction models, even a data point at the low energy end is valuable. While other prototypes may take advantage of having higher energy heavy ion beam by going to CERN next year, the situation for ATIC is quite different. Getting back to CERN in the fall of year 2000 for a heavy ion beam requires a flight cancellation, which is hard for ATIC to accommodate.