Energy Measurement in E9491. Present situation of energy measurementData: 1998, 2002 and 2002 UMC Kp21 monitor samples
Setup cut: n/cut $1 ipiflg.eq.0.and.itgqualt.le.1.and.abs(tpi-tk).gt.2
n/cut $2 $1.and.pr_rf.gt.0.02.and.abs(cos3d).lt.0.15.and.nhz.ge.5
n/cut $3 $2.and.abs(deltarp/sig_p).lt.3.and.b4abm.gt.1.2
n/cut $4 $3.and.abs(ictime-trs).lt.5.and.(eic-eicest).lt.1.5
n/cut $5 $4.and.abs(ptot-205.14).lt.10
Year 2002 1998 Diff. UMC Expected E (MeV) 102.4±0.03 104.9±0.02 - 105.9±0.02 108.5 Res(MeV) 3.79±0.03 3.60±0.02 1.17 1.69±0.03 - P(MeV/c) 205.8±0.01 205.4±0.01 - 205.4±0.02 205.14 Res(MeV/c) 2.37±0.01 2.31±0.01 0.53 2.55±0.03 - Comments: i) A new 2.5 MeV Kp2 energy deficit in the 2002 data is observed and completely from the range stack. ii) The measurement of the Kp2 momentum peak and resolution will be used in the following energy residual study. iii) The observed worse UMC momentum resolution is seen from the target. A clear correlation between the momentum and the target range is observed in UMC but not in the data.Energy residuals: Deltar_E(TG) = sqrt((ptot*205.14/205.8)**2+139.57**2)
-sqrt(( pdc*205.14/205.8)**2+139.57**2)
-eicest-(etot-ers-eic)
Deltar_E(IC) = eicest - eic
Deltar_E(RS) = sqrt(( pdc*205.14/205.8)**2+139.57**2)-139.57-ers
Year 2002 1998 Diff. UMC Expected Target(MeV) 1.86±0.02 2.32±0.01 - 2.06±0.02 0 Res (MeV) 2.03±0.02 1.80±0.01 0.94 1.37±0.02 - IC (MeV) 0.36±0.00 0.39±0.00 - 0.29±0.00 0 Res (MeV) 0.62±0.00 0.36±0.00 0.50 0.19±0.00 - RS(MeV) 3.98±0.03 0.58±0.02 - 0.17±0.02 0 Res (MeV) 3.46±0.02 3.34±0.02 0.93 1.59±0.02 - Comments: i) Energy deficit in the target is less in the 2002 data due to the application of SWATHCCD at a cost of worse target energy resolution. ii) The energy deficit in the I-counter keeps unchanged except the resolution becomes worse. The reason is still unknown. iii) More energy deficit is observed in the 2002 data. After subtracting the contribution from the UTC, a 0.76 MeV new contribution in the 2002 data may be from the more accidental hits in comparing to the 1998 data. iv) Ignoring the UTC contribution to the target and I-counter residual study, one estimates an 1.31 MeV new energy resolution contribution in the 2002 data, which agrees with the observed 1.17 MeV in the total energy study.
2. Work has been done or is underway
The run dependence effect has been fixed with a fine range stack energy calibration. Part of the pion energy deposit in the kaon fibers is found back with SWATHCCD at a cost of a small contribution to the energy resolution. Energy resolutions in the new inner 5 RS layers have been improved as demonstrated in the study of Elayer(meas)/Elayer(exp). Also note that the ratios are almost a constant in the 2002 Kp21 data. However, there is a bump (~5%) from Layer#6 to Layer#11 in 1998 data, corresponding an about 2.5 MeV exceptional RS saturated energy when comparing to the 2002 data. If this pump is wrong, it will support the statement that there is an unknown inactive material effect before the RS Layer#6, accounting for the 3.0 MeV RS energy deficit. The effect should have shown up in the E787 data, but it was blurred by the exceptional energy in Layer#6 to Layer#11. Most of the energy tail is found to be from the I-counter accidental hits. A TD double pulse fit for theI-counter is underway, a gain in the acceptance is anticipated. The muon energy deposit in each RS layer has been checked with Km21 and Km22 monitor samples, all of which are consistent with those from the UMC samples within 1%, indicating a reasonably good RS calibration. The TD muon energy from the stopping pion decay has been checked to be an almost 2.99 MeV constant from Layer# 6 to Layer# 18, disagrees with 1998 data, where the TD muon energy goes beyond 3.05 MeV from Layer#6 to Layer#12 and drops back to 3.0 MeV for the rest layers. Assuming Birks' constant to be 1%, the expected TD muon energy is 3.04 MeV. Birks' constant has been investigated. The 2.99 MeV TD muon energy corresponds to 1.07% instead of 1% used in the present calculation. The observed Kp21 energy deficit is seen to be from the range stack energy measurement. With the piscat monitor sample, the about 3.0 MeV pion energy deficit is seen to be uncorrelated with the stopping layer, the range and the incident momentum and therefore is considered to be from either an unknown inactive material before the RS Layer#6 (equivalent to about an 1.3 cm thickness of scintillators) or an incorrect Birks' constant input. For the later, one finds a 1.8% value is needed, but too big to be swallowed up. An average 0.5 MeV target energy deficit is attributed to the edge fibers. A complicated demutiplexing procedure hinders the application of the edge fibers in SWATHCCD. Also, it is not clear if there is a benefit since it may increase the sensitivity to the accidentals. It is observed that the Kp2 energy is a function of the target and I-counter range. Almost half of this correlation can be explained as the use of the saturated target and I-counter energy, which can contribute a 0.5 MeV to the energy deficit in the target and I-counter measurement. A correlation between the Kp2 energy and the spill timing is observed in both the 2002 data and the previous data. A calibration based on the RSMON information is underway, somewhat improvement on the energy resolution is anticipated. Rate dependent effect is observed in the range stack and the I-counter energy measurement, but it doesn't show up in the target energy measurement. A correction to this effect is underway.