Hi All, I would like to add a strong second to Flemming suggestion to run at 12 degrees for as long as possible. I think, though, that we should not be so pessimistic as to say that the BFS has only T4 and 2 of 3 T5 modules. We can certainly use T2 tracks as a 'seed' to find tracks in T3, rather than relying on T3 alone (that is, one uses T3 to validate and extend T2 tracks) and this will increase the T3 efficiency by a large factor that I don't know yet (but which Pawel and Radek are working on). We can play the same game using T4 and T5, with the small added complication that we have to rely on the momentum from D2 and D3 and lose the third momentum determination. In fact, even without T5 at all we could do this by matching tracks from FFS+T3+T4 to hits on H2 and rings in the (extremely beautiful!) RICH. Since this is only necessary at high p where there are few tracks per event on average, there should not be large losses due to double hits on H2. Again, we lose a little momentum resolution, but probably not enough that we should lose a lot of sleep over it. Summary: 12 degree high field is GOOD. Ian -----Original Message----- From: owner-brahms-l@bnl.gov [mailto:owner-brahms-l@bnl.gov]On Behalf Of Flemming Videbaek Sent: Tuesday, November 13, 2001 2:47 AM To: brahms-l@bnl.gov Subject: run plans and rates... 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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