Preliminary Agenda for Analysis Workshop

BRAHMS has two short term analysis goals:
1. 'like' particle ratios (i.e. pi-/pi+)
2. 'unlike' particle ratios (i.e. K/pi)

It is the goal of the workshop to extract these ratios as a function
of rapidity.  If we obtain this goal, it should put us in an
excellent position to have exciting new results for QM2002 in July.   

I. Like particle ratios.

We have now preliminary results for like particle ratios
at all spectrometer settings used in the 2001 Au+Au run.  The y=0
values have been obtained for the p+p run data.  All of these results
need to be finalized, requiring the following:

  1. There are some minor acceptance issues in the MRS.  Claus has
     looked at this quite a bit.  The problem seems to be that the ratio
     polA(+)/polB(-)!=polB(+)/polA(-), as one would expect.  The mismatch
     is roughly 5%.  We should try to understand this, or convince
     ourselves that this is an irreducible systematic error.
 
 2. The FS analysis needs to be completed.  This may require reducing
    the data again including the latest changes to the DC tracking
    (which increase efficiency and resolution drastically).  If the
    survey of the forward arm is completed and we get the proper
    positions of the various detectors, we will need to redo the
    global tracking using the surveyors best guess of the geometry. 
    I estimate that the reduction of all data from the Au+Au run will
    take 3-4 days, and the production of DSTs (data summary trees)
    will take a similar amount of time. Most of the needed scripts for
    carrying out this work are already in hand, and with proper
    planning, we could start looking at the first 'final' DSTs a few
    hours after starting the reduction.  This should allow us to
    extract pbar/p in the range y=1 to y=3, pt=200MeV/c to pt=1GeV/c. 
 
 3. We should produce some event generator results for 200GeV Au+Au.
    I have results from AMPT. A comparision of these to HIJING and our
    data would be quite interesting, as it should say whether or not
    AMPT adds the 'correct' amount of rescattering to HIJING to
    reproduce the data.  

 4. Look at correction factors.  In the MRS, the largest contributions
    come from the production of protons in the beam pipe, and the
    absorption of low momentum pbars (giving a large correction at low
    pt). In the MRS, the primary correction to pbar/p is the
    difference in the absorption.  We need also to look into what
    corrections may be needed for kaons.

 5. Produce BRAHMS analysis note on ratio analysis.
 
I. Unlike particle ratios.

Peter Christiansen has produced some preliminary results for K/pi at
y=0.  We should also try to extract this for other field and
spectrometer settings.  As I understand the present state of the
software, the tools Peter used are generally applicable to BRAHMS
data.  One must make some minor changes to take into account that the
spectrometer has a different setting, etc. but the framework seems to
be rather good.  The following is a list of tasks which need to be
completed to allow us to produce the K/pi ratio vs. rapidity. 
 
  1. Final checking of the Christiansen acceptance corrections.  One
     obvious check is to throw a thermal distribution of pions into a
     given spectrometer setting, and check that the slope and yield
     one obtains after reconstruction and corrections is the same as
     the known thrown distribution.  This should probably be done for
     each particle type in each spectrometer setting. One way to
     proceed would be for one person to try to do acceptance corrected
     spectra for each MRS setting.  Also, some development work
     remains to make the process run smoothly for the FS.

  2. Understand the efficiency of the spectrometers.  This is
     necessary to do reasonable efficiency corrections, and is thus a
     vital step toward getting particle yields.  As I see it, this
     step entails expanding the existing TPC efficiency software to
     all TPCs, a clear understanding of how the DCs behave (which
     Pawel has done).  In addition, we should investigate how time
     varying drift velocities (temperature, atm. pressure, etc.)
     affect the TPC efficiency.  The efficiency of the TOF should also
     be characterized (for low mult, it is very nearly determined by
     geometry, but we still need to see about high mult, etc.).
 
  3. Determine the proper pt (or mt) range in which to fit various
     particle species in various spectrometer settings.  Note that
     this will also depend on the choice of functional representation
     of the spectrum.    

  4. Estimate systematic errors associated with the extracted particle
     yields.  One might imagine that many of the acceptance effects
     which cancel when comparing (-) to (+) in the same setting
     (opposite polarity) do not cancel when comparing extracted
     yields. 

  5. BRAHMS Analysis note on Acceptance corrections.

  6. BRAHMS Analysis note on Efficiency.

  7. BRAHMS Analysis note on K/pi ratio.

There will, of course, be tasks which are necessary but which are not
included here.  If you think of any, please let me know.  

My recommendation for  the "agenda" is that those who are at NBI on
Monday 27. Feb. use the opportunity to ask questions of each other,
and, very importantly, to be sure that the latest versions of BRAT and
brahms_apps are installed on the NBI machines and on AFS. Also, those
not familiar with the calibration procedures should take this
opportunity to become familiar with them.  By Tuesday,
then, we should be able to get started with the 'final' analysis.
I propose that we divide ourselves into two teams, one for 'like'
ratios and one for 'unlike' ratios.  We will use the same data files,
but some of the tasks are different and can go, more or less, in
parallel.  I recommend that Peter Christiansen lead the 'unlike' team,
and that Claus Ekman lead the 'like' team.  Djamel Ouerdane is the
local expert on calibration and global reconstruction, and will be
extremely valuable to both teams.  Others should think about what they are
interested in contributing and get back to me.    

The scheduled arrival times, and length of stay (as far as I know...)
Bjorn Samset : 25.02 1200 ~10 days
Jens Ivar :    25.02 ?    2 weeks
Trine T.  :    27.02 ?    3 days
Elin      :    27.02 ?    3 days
Truls     :    27.02      3 days
Mads      :    28.02      3 days
Radek     :    04.03      2 weeks
NNR       :    (04/10) 03 2-3 weeks
IGB       :    26.02      as long as I can stand it!
NBIers    :    25.02      as long as I can keep them

Please add any important corrections.

Best regards,
Ian