I want to add my vote to the choice of forward angles. If Ian's optimism is accepted, why not go even further and think about 3 or 4 degrees, after all the community is expecting BRAHMS to study the highest rapidities as possible and that doesn't require high Pt. Ramiro On Tue, 13 Nov 2001, Ian Bearden wrote: > 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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