This e-mail discusses several subjects
- ZDC/Beam trigger rates
- commissioning of vertex trigger
- background measurements
- vote to dump policy
- adding of Vdrift monitors in DataStream
a) So far the institutedpolicy has been to scale trigger(4) to trigger(1) at at ratio of 3:1. As pointed out, this in fact means since
tr(1)/tr(4) ~ 1:3.5 that about 18% of all events are very peripheral events (ZDC's) with out BB (i.e. ~ 60-70% nucl cross-section).do to
This fraction is probably more than enough for normalizations etc. If the scaledown ratios is changed to 1:5 the ratio will be about 5%, surely enough for normalizations. If you have an opinion of this please comment.
b) A 'fast' trigger that relies on making a precise overlap between times from left/right ZDC's derived from Constant Fraction Discr.
This overlap is based on a simple, circuit proposed (and tested) by Chellis, and seems so far to work quite well. For the last couple of days this trigger has been added to the 'latch' in trigger2 (bit 5), and today timed in with the BB. It is thus
CDF overlap * BB(trig1). and it pick a region -30-+20 cm around the real IP with an efficiency close to 1/11 of ZDC counts.
(the actual region can both be adjusted a bit better as well as made narrower)
It will be trivial to also add it for the central collision trigger, and it seem to make a very good improvement to the data collected.
A dedicated run was made this afternoon with only this trigger just to check the performance and rates. The latch bit is set all the
time now.
c) a set of background meas. was done today (we had beam during the day !!!) by fv+dana+eun-joo recording rates in a subsection of H1,H2 and currents in T3,T4,t5. The results should be presented on a web pages soon, but the interesting feature is that
at 3 deg. both H1 and T3 sees less rate than at 5-7 deg apparently due to a 'shielding effect from D3) while the H2,T5 rates just
falls off with the distance from the beam.The singles rates are quite large e.g 7 slats in H2 with a top-bot coinc see a 'singles' rate of
~10K with I(blue) ~ 15*10*9 ions total and ZDC rate ~100. ZDC singles ~
d) There is a disucssion how to implement the vote to dump store policy. AT present we(I) have said that
ZDC(rate)< 50/sec ==>dump
Since RHIC is getting better at getting stores back following a voluntary dump one should not let the store run to long either
- the vertex gets wider, as well as having more de-bounched beam so my suggestion would be to requiere
if zdc/zdc(inital)<1/3 =>dump.er
e) The drifft velocity monitors has been added on a continuous basis- as trigger 7-3 scale down ~50 to record the mainly outpiut stream value. There is mounting evidence (that has only come after careful analysis) that the tpc's has positional dependences that may come from the gas-exchange problems (tpm1, tpm2) that makes tracking difficult. Again I hope some additional plots illustrating this will be posted.
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Flemming Videbaek
Physics Department
Brookhaven National Laboratory
tlf: 631-344-4106
fax 631-344-1334
e-mail: videbaek@bnl.gov
This archive was generated by hypermail 2b30 : Tue Sep 25 2001 - 22:28:51 EDT