12 degrees is GREAT was:RE: 12 degrees is GOOD, was: RE: run plans and rates...

From: Ian Bearden (bearden@nbi.dk)
Date: Tue Nov 13 2001 - 10:43:05 EST

  • Next message: Ramiro Debbe: "Re: 12 degrees" 

    Dear All,
One problem with the more forward angles is that there is a much higher
background, particularly in T5 since it 'sees' essentially the entire RHIC
tunnel.
High pt seems also to be where the exciting physics might be, and even
though we have the excruciatingly beautiful RICH, we can only do PID up to
roughly 25 GeV/c.
At 4 degrees this is only pt of 1.7.
The problem with 20 degrees (at least to my mind) is that it is (as the
Danes say) neither fish nor bird.  That is, we are not so far out in
rapidity, and we can only do ID'd pion spectra to 3 GeV/c in pt, and p/K up
to (roughly) 2GeV/c.
At 12 (this is better than 15 because we already have some data at this
setting),
we can do a high p measurement with protons from 14-25 GeV/c (using the
exquisite RICH), a pt of 2.9-5.  I attach a gif of RICH ring radius vs
reconstructed momentum from four degrees 1/3 field, showing the nice PID.
Here the momentum was reconstructed using t4-d4-t5, but could as well come
from another matching station.
I don't have a similar figure from 12 degrees as we do not have high field
data for this setting.

Ian

> -----Original Message-----
> From: owner-brahms-l@bnl.gov [mailto:owner-brahms-l@bnl.gov]On Behalf Of
> Ramiro Debbe
> Sent: Tuesday, November 13, 2001 1:49 PM
> To: brahms-l@bnl.gov
> 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
> >
>
>
>
    PbPRICH.gif

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