Ben Nefkens (UCLA) presented a list of collaboration issues to be discussed at the Steering Committee meeting on Saturday.

Transcription

1 Minutes of the Collaboration Meeting Mainz, March 2004 Attendance: John Annand (Glasgow), Hans Jürgen Arends (Mainz), Reinhard Beck (Mainz), Benedicte Boillat (Basel), Derek Branford (Edinburgh), Bill Briscoe (GWU), Jason Brudvik (UCLA), Sergey Cherepnya (LPI Moscow), Richard Codling (Glasgow), Evie Downie (Glasgow), Lev Fil'kov (Lebedev Phys. Inst.), Peter Grabmayr (Tübingen), Ralf Gregor (Giessen), Dave Hornidge (Mount Allison Univ.), Henry Juengst (GWU), Viktor Kashevarov (LPI Moscow), Rudolf Kondratiev (INR RAS, Moscow), Milorad Korolija (RBI Zagreb), Martin Kotulla (Basel), Dirk Krambrich (Mainz), Segei Kruglov (Petersburg/Gatchina), Bernd Krusche (Basel), Stefan Lugert (Giessen), Mark Manley (Kent State Univ.), Cameron McGeorge (Glasgow), Mariana Nanova (Giessen), Ben Nefkens (UCLA), Rainer Novotny (Giessen), Paolo Pedroni (INFN Pavia), Marco Pfeiffer (Giessen), John Price (UCLA), Günther Rosner (Glasgow), Matthias Rost (Mainz), Sven Schumann (Mainz), Daniel Sober (Catholic Univ.), Hans Martin Staudenmaier (Karlsruhe), Ivan Supek (RBI Zagreb), Claire Tarbert (Edinburgh), Ulrike Thoma (Giessen), Marc Unverzagt (Mainz), Harald van Pee (Giessen), Thomas Walcher (Mainz), Daniel Watts (Edinburgh), Fabien Zehr (Basel) Friday 19 March AM Reinhard Beck (Mainz) reported briefly on the status of the hardware. He reported that the December 2003 PAC had recommended beam time for 7 new proposals, 3 in parallel with already approved experiments (600 hours), 3 more for MAMI-B (1000 hours), and one for MAMI-C (1000 hours.) He reported that several new students had joined the collaboration. Ben Nefkens (UCLA) presented a list of collaboration issues to be discussed at the Steering Committee meeting on Saturday. Thomas Walcher (Mainz) reported on the accelerator upgrade schedule. Primarily because of delays in the contracts for production of the 2.45 GHz and new 4.9 GHz cavities, the first beam is now expected at the end of He pointed out that despite the delays, the MAMI-C facility remains a uniquely valuable facility in its energy region because of the unique experimental resources (spectrometers, CBTAPS) available at Mainz. Cameron McGeorge (Glasgow) reported on the high-energy upgrade of the Tagger magnet from 1.0 to 1.8 T. The iron has been bought and tested. The yoke template will be compared with the yoke immediately after this meeting, and final drawings should be ready by the end of April, with the machined iron parts expected in Mainz by August. The current schedule is: dissassembly August-December 2004, re-assembly December 2004-April The new scintillation counter system is being constructed in Gatchina, and will be ready to install in autumn The entire system should be ready in August Sasha Starostin (UCLA) reported on the status of the Crystal Ball. Data have been taken with CH2 and CD2 targets, and, in the week preceding this meeting, with a liquid H2 target. A plot of photon hits shows that there is no beam-background-related enhancement in the forward or 1

2 0 backward directions. A clean peak with a resolution of 13 MeV (1 ) was obtained from the hydrogen target, using only preliminary calibration of the crystals. Within the past two days, a 0 clean preliminary measurement of the photon polarization asymmetry in production was obtained in only a few hours of running. Sasha discussed the question of whether an outside cover for the CB was required to protect it against possible vacuum leaks in the long periods between run times. Bernd Krusche (Basel) summarized the status of the TAPS installation, with more details to be provided by the following two speakers. About 320 crystals (about 2/3 of the total) are now installed, with about 250 cabled. The new electronics and readout system has been successfully installed and tested, with the only problem being with the synchronization of the TAPS and CB data streams. The future run schedule was discussed, because of the commitment to use TAPS in an experiment at KVI Groningen in early Rainer Novotny (Giessen) provided more details on the problems with the TAPS detectors after they arrived at Mainz at the end of There are 2 separate problems: (1) aging of the oldest photomultiplier tubes, some of which have been in service for 15 years, because of the diffusion of atmospheric helium through the fused silica windows; (2) bad optical contact because of the leakage of the optical coupling oil from many modules. The units are being tested and repaired, with the full forward wall expected to be complete by 19 April. The TAPS veto system is currently at Giessen, where the readout system is being reconfigured; it should also be ready in April. Ralf Gregor (Giessen) gave details on the status of the new TAPS data acquisition system. The first tests of combined TAPS-CB data acquisition have been successful but with some problems remaining. John Annand (Glasgow) reported on the new data acquisition system for CB@MAMI, using the the new flash ADCs and TDCs developed for COMPASS at CERN. He described the VME crate layout and the programmable trigger logic. The ADCs are currently not being used in flash mode because the event size would be too large; instead, 3 sums of 30 samples each are recorded for the pedestal, peak and tail regions. The question of maximum rate was discussed; the goal is 1 khz, but the large number of CB hits (typically 40, but only about 9 belonging to real clusters) is making this goal difficult without raising thresholds. Friday 19 March PM Dirk Krambrich (Mainz) discussed the status of the new CB electronics. The splitters, discriminators, and TDCs are all working. The ADCs are working well at 40 MHz, with the 80 MHz mode still being tested. Remaining to be done: the MWPC setup, and a decision on using scalers. Stefan Lugert (Giessen) presented the status of the TAPS readout electronics. The ADCs have been read out in the beam, and the TDCs tested in the lab. Some hardware for the Veto system is still missing. 2

3 Andreas Thomas (Mainz) reported on the status of the H2/D2 target system. A new 48 mm cell, giving full angular acceptance, has been in operation since February. A precise measurement of the length of the filled target was made using X-ray photographs. Andreas Thomas (Mainz) also spoke about the status of the new frozen spin polarized target system. The new horizontal cryostat is being designed and constructed in collaboration with the Dubna/Moscow polarized target group. The thin holding coil will be built using the Bonn concept, and the NMR and materials studies will be done in collaboration with Bochum. The cryostat is expected to be tested and delivered to Mainz by August 2006, and the target should be ready to install in the CB by April Paolo Pedroni (Pavia) reported on the status of the wire chambers. The chamber being prepared at Pavia was damaged by a high-voltage accident in January, so the chambers from DAPHNE have been modified to be used instead. The chambers were brought from Pavia this week, and will be installed after the meeting. New chamber construction continues for use after the energy upgrade. Evie Downey (Glasgow) described the PID (Particle Identification) detector which was constructed at Glasgow. A barrel of 24 thin scintillators is supported by an aluminium ring at each end, with PMT readout at the downstream end. In a January test, the PID showed good timing and clear pion and proton bands in the de/dx spectra. The PID will be fitted into the MWPC after this meeting. Erik Heid (Mainz) reported on the status of the coherent bremsstrahlung beam. He described the mainz goniometer and the alignment process. A polarized photon run was taken with the LH2 target just prior to this meeting. Sasha Starostin (UCLA) spoke about the various possibilities for triggering the system. The February CH2 data have been analyzed to test the effects of the single-crystal discriminator threshold on the acceptance of 2- and 3-cluster events. A threshold of 15 MeV for single crystals and 150 MeV for the total energy seems close to optimal. Martin Kotulla (Basel) described the possible trigger inputs from TAPS. The TAPS electronics was been wired in 8 segments, which can be combined in to 4 logical blocks for triggering. Final decisions must still be made on the thresholds and pre-trigger format. Saturday 20 March AM John Annand (Glasgow) reported on progress with the new data analysis system, which will be a fully ROOT-integrated system. The main analyzer class, TA2Analysis, decodes the ADC and scaler information, and farms it out to the detector and apparatus classes. Apparatus-level reconstruction is well under way, and physics-level reconstruction has begun. A time spectrum of tagger-taps coincidences, resulting from a few minutes of analysis, was shown. John Price (UCLA) reported on the status of the Monte Carlo simulation. A new official version was made final in September, but was not easily accessible to non-expert users. Since 3

4 then, the simulation code has been stored in CVS and furnished with clear user instructions. A few tasks remain to be completed. Conversion of the simulation code from GEANT3 to GEANT4 is planned during the MAMI-C upgrade. Sasha Starostin (UCLA) presented some first analysis results using the new analysis code. Spectra of hits and clusters for the recent LH2 target data were shown. For the final state p, 0 0 clear and peaks were seen, and 3 6 was also observed and reconstructed. A very 0 preliminary cross section for p p was obtained from the February data (CH2 - C subtraction) with low statistics, but in agreement with the known cross section. In the March run with 0 polarized photons, a clean ( ) distribution was obtained for the ratio of polarized/unpolarized cross section using about 1 hour of data for each beam. Marc Unverzagt (Mainz) described the status of the CB calibration. A new procedure has been developed using a Am- Be source, which produces 4.4 MeV rays from C*. The source was placed inside the ball, surrounded by either unborated or borated CH2 blocks to reduce the neutron background. A clear spectrum of background plus 4.4 MeV peak is observed in single 60 crystals. The procedure must now be repeated for all crystals, and compared with the Co calibration reported by Jason Brudvik (UCLA) to see whether the latter gives a useful second point. Benedicte Boillat (Basel) described the status of the TAPS calibration. Since all the crystals have identical dimensions and orientation, relative calibration can be done with cosmic-ray muons. The absolute calibration is then done using the tagged photon beam at MAMI. Saturday 20 March PM Bernd Krusche (Basel) reported on the status of the mass measurement with TAPS (B. Krusche et al., Z. Phys. A 351, 237 (1995)) and its application for tagger energy calibration. Rainer Wanke (Mainz) described a new measurement of the mass from the NA48 experiment at CERN, using a liquid krypton calorimeter. Steering Committee Meeting Led by Reinhard Beck (Mainz) and Ben Nefkens (UCLA), discussions covered the following points: 1. The financial situation, including both short-term ( 100 ki) and intermediate-term ( 500 ki) requirements. To cover the most immediate needs, commitments were made by Pavia, Basel, Mainz and Edinburgh. 2. People power requirements. Data acquisition and data analysis require more personnel. A procedure is needed to set up at training session in data acquisition before each run period. 3. Run plan. The 7 approved pre-upgrade experiments will require about 22 weeks of beam time. It was proposed that CBTAPS run 2 weeks per month for 10 months, beginning in 4

5 June This schedule conflicts with both the tagger upgrade and the planned TAPS run in Groningen in early No immediate solution was found. 4. Travel. The management has strongly requested that all collaborators planning travel to Mainz send their travel plans by to so that the Institute knows who is on site. The Institute secretaries can help in finding housing. 5. Policies and protocols. 1) Ph.D. thesis topics. A list of topics was presented for the 12 students currently attached to the project. 2) Responsibilities (of a good citizen). Hardware work, collect data, analyze data, write reports and papers. 3) Privileges. Access to data and logbooks, propose new experiments, present data at conferences, co-author on first-round experiments. 4) Authorship on first-round publications should be based on a substantial contribution to installation/operation/running of the experiment. A subcommittee must ultimately make decisions on this. 5) Publication protocol. A draft of each publication should be sent to the Steering Committee, whose members will be responsible for distributing it to their groups. The Steering Committee response should be provided within 2 weeks. The final draft will then be posted on the Web, and collaborators must respond to the Steering Committee within 2 weeks. 6) Conferences. Collaborators wishing to make a conference presentation should make their request via or phone to the Conference Coordinator, who will interact with the Project Leaders and the experiment spokespersons in making the decision. Bernd Krusche (Basel) was elected Conference Coordinator. 7) New proposals (for MAMI-C). New proposals should be presented on the final day of each collaboration meeting, with support from a theorist when appropriate. Drafts of proposals should be sent to the Steering Committee, who will reply within 2 weeks. The proposal will then be posted on the Web for the full collaboration, who should reply within 1 week. 6. Next meeting. It was proposed that the next collaboration meeting (September/October 2004) take place in Giessen, pending discussion with the full Giessen group; and that the Spring 2005 meeting take place in Los Angeles in late March. [Note: After the meeting, the date for the Fall 2004 meeting was set for October 4-5 in Giessen.] Sunday 21 March: New Physics Ideas Pentaquark physics Alexander Fix (Mainz) presented theoretical aspects of the reaction d, whose threshold energy of 0.95 GeV makes it suitable for MAMI-C. The cross section should have a broad maximum of the order of 5 nb at about 1.1 GeV. The sensitivity of various measurements to the parity of the was discussed; only polarized-target experiments are sensitive to P in the region 5

6 of maximum cross section. Viktor Kashevarov ( Moscow, Lebedev) discussed the experimental feasibility of this measurement at MAMI-C. He concluded that with the full CBTAPS and both nucleons detected, a run of 500 hours should yield , with a mass resolution of about 11 MeV. John Price (UCLA) gave a review of the status of pentaquark searches at Jefferson Lab, including two published papers, several analyses in progress, and 5 new approved experiments looking for 0, the,, and. S missing Harald van Pee (Giessen) reported on the search in p pk S K L using the Crystal Barrel and TAPS at ELSA. A partial analysis of the data taken in March 2003 was shown, with some evidence of the. A new run in November-December 2003 provides a factor of 15 more data, as well as polarized photons and a higher endpoint energy. 0 Mariana Nanova (Giessen) discussed the search for in the final state pk S K S p 4 in the above experiment. This is expected to have a branching fraction of 1/72, compared to 1/12 for the final state discussed in the previous talk. Analysis is still preliminary. Other new physics Lev Fil kov (Moscow, Lebedev) spoke about the search for SND s (supernarrow dibaryons) in the reaction d NN. Evidence for such 6-quark states was found in a 2000 INR (Institute of Nuclear Research, Moscow) measurement of pd ppx. Measuring all 3 charge states in NN would give important information on the isospin and spin of the SNDs. Energy calibration issues Andreas Reiter (Mainz) described the calibration of the Tagger using the Microscope (movable high-resolution detector system) in coincidence with Tagger channels Three sets of measurements were made. (1) A very low-intensity (dark current) electron beam was run directly through the Tagger magnet onto the detectors at 180, 195 and 210 MeV electron energy. (2) Coincidences between the Microscope and Tagger double hits were analyzed. (3) The beam was scanned through the Microscope by changing the Tagger dipole magnet field. Repeating this process looks like a very promising way of determining the photon energy to about 150 kev, which is close to the uncertainty in the MAMI beam energy. 16 Peter Grabmayr (Tübingen) reported on results of a high-resolution measurement of O(, pp) 16 and O(, np) using the Microsope. The trigger required a coincidence between Tagger and a HPGe detector, and the data analysis required a 4-fold coincidence which also included the Microscope and either a second HPGe or the TOF wall. The correlation between Tagger and Microscope was very good, but some background and luminosity-related problems are still being investigated. Dave Hornidge (Mt. Allison Univ.) described a measurement of photon asymmetry in 0 photoproduction from the proton near threshold. A first version of this experiment was perfomed 6

7 at MAMI with TAPS in 2001 (Ph.D. thesis of A. Schmidt), and provided only one energy bin ( MeV) with large error bars. Experiment A2/6-03 will remeasure this process over a larger energy range with much better statistics. Simulated results for 2 MeV energy bins were shown, and compared with theoretical predictions. Minutes submitted by D. Sober, sober@cua.edu, who asks your forgiveness for any inaccuracies. Washington, 21 April 2004 Revised 22 April