Minutes of the E89044 group meeting, January 16, 2000, at Jefferson Lab

List of participants:

Konrad Aniol, CalStateLA
Fatiha Benmokhtar, Algiers
Bill Bertozzi, MIT
Zhengwei Chai, MIT
George Chang, Maryland
Martin Epstein, CalStateLA
Shalev Gilad, MIT
Doug Higinbotham, MIT
Akio Hotta, UMass
Michael Kuss, JLab
Nilanga Liyanage, JLab
Dimitri Margaziotis, CalStateLA
Jean Mougey, Grenoble
Marat Rvachev, MIT
Arun Saha, JLab
Riad Suleiman, MIT
Raphael Tieulent, Grenoble

Arun ...

... opened the meeting. In December, we finished the 845 MeV (#17, #27) and 4.045 GeV (#16, #26) kinematics points. Due to the target problems, we could not run 2.028 GeV. This will be done in February at 1.953 GeV. In general, if we cannot make up the lost time in February/March, we can ask Kees for additional beam time during "facility developement". Important here is that the run coordinators should keep track of the correct logging of the beam accounting table, e.g. that "beam not acceptable" is not logged as "beam in use". The E_miss resolution we have achieved so far for ³He is 1 MeV. For ¹²C it is 0.5 MeV, so we see an effect from the target. It is not clear if the spread is entirely due to straggling, or if the energy loss correction in ESPACE can be improved.
First priority in February are the 4.8 GeV kinematics points. Arun pointed out that we have poor knowledge of the counting rate to expect for high p_miss (and also high E_miss), thus the run times in the experiment run table are kanonical. If the cross section stays flat we should consider to extend p_miss to 1 GeV/c or even 1.2 GeV/c. He pointed out that the high p_miss were a basic reason for the proposal at all. There was a discussion about how to prioritize if we have to continue with lower luminosity. Jean was giving some information on this later in his presentation.
Michael was added as a forth spokesperson to E89044. He gladly accepted. Does this mean there will be a party?

Jean ...

... spoke about modifications to the kinematical settings parts 1 and 2 and parts 3 - 6. His changes are summarized on his transparancies modified kinematics, modified spectrometer setups and proposed run plan modifications.

Doug ...

... lead the analysis session. He gave a general overview of the status of the analysis. Special attention got his plot about the E_miss. It showed that we can separate the deuteron ground state from the break-up. However, in the break-up region the cross-section was almost constant from threshold to about 20 MeV. On the other hand, the spectrum was more or less online analysis.

Michael ...

... will implement the beam position reconstruction into ESPACE, using the burst mode bpm information. He anticipates one day for implementing it and one day for testing.

Fatiha ...

... is checking the detector performances.

• She achieves a tc_cor FWHM resolution of 3 ns. This is wide, but the matrix elements and especially the paddle offsets are not yet optimized. For the paddle offsets, it is known they are off.
• The scintillator ADC and TDC spectra look reasonable.
• The VDC efficiencies look good, close to 100%. However, the vertical axes should be zoomed to check where is the efficiency above 98%.
• The tracking has problems, see Marat's talk later.
• The Cerenkov seemed to work, but the pedestal peaks dominate the scale of the vertical axes; log would be better to check.
• Shower/preshower not yet checked.

Nilanga ...

... will have finished the matrix optimizations by end of the month. Problem was that the previous optimizations were done with point-like targets, but at higher energies extended target have to be used. There were used external optimization routines, which were not very user friendly.

Marat ...

... also checked the detector performances. He reported that he believes for some paddles in HRSH the discriminator thresholds were to high. There only events with an ADC value above a high channel number (e.g. 2000) had a valid TDC value. However, the spectra were looking reasonable, not showing a cusp below the suspected threshold. He made his test with run #1349.
He showed that ESPACE has problems identifying the track that made the trigger if there are multiple hits (about 10% of the events). He also thinks the tracking in general has to be improved. It was not quite clear why ESPACE sometimes considers an obviously wrong track, because unphysical drift times should be excluded (intrisically) before trying to fit. Marat mentioned Ole Hansen will try to fix it. Nilanga mentioned that E93050 (VCS) will ingnore multi-hit events and correct later by a scale factor.
For run #1380 (elastic scattering on ³He) Marat found a bad vertex resolution. Despite the beam raster not being corrected properly, the width FWHM should not exceed 1 cm (15^o spectrometer angle), but he found 3 cm. Has to be checked.
He found a bug in MCEEP. It simulates the radiative tail correctly for recoiling protons and deuterons, but for ³He there seems to be a cut-off (about 5-10 MeV from the peak). Paul Ulmer is informed but has no time to check immediately.

Summary about things to do

ESPACE

• Beam position
• Improve tracking
• Update databases

MCEEP

• ¹²C and ³He elastic cross sections
• put raster profile into MCEEP
• debug MCEEP

General

• LVDT system (Riad)
• Efficiencies
• check MCEEP with ¹²C (Marat)

Michael ...

... spoke about the target performance in December and improvements being made. The start of E89044 was delayed due to fan problems. During the first successful cool-down it was noticed that the neccessary cooling power could not be delivered through the target heat exchanger. At 6.3 K the effective cooling power was about 240 W. 80 W were needed by the fan, the rest of about 160 W was allowing for a beam current of up to 80 µA. This resulted in a maximum luminosity of about 0.5·10³⁸cm^-2s^-1.
Several things were/are being done to increase the mass flow through the heat exchanger:

• connecting the loop 1 and loop 3 heat exchangers in parallel to double the cooling power
• replacing the JT valves with JT valves with larger orifice
• opening the balancing valves at the heat exchanger

Additionally, ³He from Hall C was added to increase the target pressure to the design 220 psi.

Final discussion

Marty concluded we have the following outstanding problems:

• the 10% discrepancy of Konrad's cross sections from the world data
• we still have no good method for the normalization at 4.8 GeV. To reiterate, we cannot detect elastic scattered electrons at the forward angle of 12.5^o because their momentum will exceed 4 GeV, and at more backward angles the cross section is unacceptably small. The two alternatives being discussed:
  • detecting the recoiling ³He in the HRSH. The momentum will be low, and they may undergo scattering in the target or in the various foils.
  • having a scheme where the elastic cross section is measured at a lower beam energy, essentially determining the target density, then changing the beam energy and measuring elastic again. Both measurements can be linked under the assumption that the density hasn't changed during the energy change.

Moreover, in December the pressure transducers were showing radiation damage, making it impossible to determine the target pressure at a given time. It has to be made sure the pressure transducers work and are well calibrated, and/or we need a precise mechanical gauge. But even this seems not to be enough, because it is questionable if the density extracted from data bases is accurate enough.