Hi Ramiro The motivation for the 12 deg is to study jet-(or no jet) quenching. This requires high pt. Sin(12)=0.2 and makes this possible (pt up to 4GeV). 12 deg is sufficiently forward that the physics might be different from that at the mid-rap plateau. Obviously we would also like to do this closer to midrap, but I feel that it is more important to see a deviation from the PHENIX-STAR story at the present time than it is to validate it. If we validate it , we are just one in the crowd, if we don't see it we have validated our existence. cheers JJ ________________________________ Jens Jørgen Gaardhøje Assoc. prof. Dr. Scient. Chair Ph.D: school of Physics NBI.f.AFG. (secretariat. 35 32 04 41) Chair science committee. UNESCO Natl. Commission. (secretariat. 33 92 52 16) Office: Niels Bohr Institute, Blegdamsvej 17, 2100, Copenhagen, Denmark. Tlf: (+45) 35 32 53 09 Fax: (+45) 35 32 50 16 ________________________________ ----- Original Message ----- From: "Ramiro Debbe" <debbe@sgs1.hirg.bnl.gov> To: <brahms-l@bnl.gov> Sent: Tuesday, November 13, 2001 1:48 PM Subject: Re: 12 degrees is GOOD, was: RE: run plans and rates... > 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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