Dear Collaborator,
I think the question on settings to measdure in the last (1.5 week- taken into account the STAR problems) of the run comes to a choice, not so much related to rates for higher pt values but as a matter of detector performance vs. physics goals.
Ian has mentioned rates vs pt /triggers in a couple of e-mails. My own evaluation are very close to his. It should be noted that for the same pt- range and dy bin the rates per trigger 6 are not so different.
- the covered dy range gets wider at more forward angles.
- the effective p range covered at any angle setting is ~ Pref 60%-200% with Pref= 23 GeV* Field fraction.
Some typical values are
20 deg ~ 12 per 75 MeV/c pt bin at 2 GeV/ce
30 deg ~6 per 100 MeV/c pt bin at 2 GeV/c (outside Pref range)
12 deg ~14 per 100 MeV/c pt bin at 2GeV/c
all for 70K triggers 6.
So the choice of angles is much more governed by other factor as PID than rate
30 deg K/p (H1) 6 GeV --> 3.0 GeV/c
K/pi (C1) 9 --> 4.5 GeV/c
20 deg 1.5
3.0
12-15 deg (p*.2-.25) K/p H1 1.5
k/pi C1 2.0
H2,RiCH K/P 5.0
H2/rich pi/K 3.5-4.
At theta < 12 the pt range just get less.
Thus to get to the highest pt for identified particles with FS there are two choices
a) 30 deg with well working C1, H1 -> 4.0 GeV/c
b) 12-15 deg using the full spectrometer -> 4 GeV/c too.
The rates in the BFS are ~ 1`/3 just for solid angle/accpt , with the added problem that
we have only T4 + 2/3T5 working at present.
The physics issue is briefly that 30 deg is approximately like 90 (i.e. on the plateau) while the
12-15 deg is actually on the edge/turn over , and might show real diference. Have we enought time the choice is clearly to do both settings, but with an expected 40h*60k*1.6== 6M events this is not expected to be enough for both settings, including others that will have to be redone .
I will point out that my personal physics preference is to do the 12 deg, as I have advocated for several years), but is concerned that the lack of tracking in FFS (T5 problems, no T3 and less than 100% eff) will make it a not guarenteed measurement and thus carries a risk of not getting a result.
I will finally point out that the present 30 deg 2*300k trigger 6 are for valuable cross chekcs with the MRS data.
My suggestion will be in the near term to complete the 30 deg measurements, move to 12 deg, take data at the 1/2 field setting ~500k trigger and get at the same time documented feedback in terms of actuall tracks reconstructed in full FFS (for 12 deg) with PID , as well as for the 30 deg data so we can judge rates etc for the last week or so
best regards
Flemming
------------------------------------------------------
Flemming Videbaek
Physics Department
Brookhaven National Laboratory
tlf: 631-344-4106
fax 631-344-1334
e-mail: videbaek@bnl.gov
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