I guess we are a sufficeint small collaboration to get everybody involved in the considerations
for the paper so here I offer a set of comments, not a re-write or re-analysis
Dear Collaborator,
In reading the first draft of the p-bar/p letter it become that
in writting the presentation several issues many detailed points (mostly technical) has been
brought to light, as also indicated to large degree by Jens Jorgens own footnotes.
We certainly have an interesting measurement, but we must make clear in the abstract
conclusion, that this has implications eg. for understanding theoretical descriptions of
the collisions. As it stand it looks very much like what is/will be in the STAR letter. Also
even though the transperency is not complete it is substantial, and as shown at QM
correspond to a small baryon chemical potentil of 40-50 MeV.
It is very useful to compare to other energies. Of these the only available are the AGS, and SPS
heavy ion data and pp data from ISR to the best of my knowledge. I could not look
up the (NPB87,19(75) ?) & ISR [(NPB70,1(74) ?]reference from home - too old to be in the
NuclearPhysics B electronics archives,
but at the FNAL collider E735 (C0) looked at identified particles at mid-rapidity.
I would expect that p-pbar collisions to have pbar/p = 1 since the baryon number is 0 to begin
with, and thus not relevant for the HI discussion. I do not recall the ISR number (0.4?) - it is a measurement at
everal fixed (.2 -1.0) pt -values for a large range of rapidity. At ISR sqrt(s)=63 the p-bar/(pi++pi-) is ~0.04 while
at E735 see 0.07. (200GeV)
E735 does not give a p/pi ratio because of a large contamination of slow protons from pi-beampipe interaction,
precisely the same issue STAR shows in the letter. This important up to probaly .5-.6 GeV/c at
mid-rapidity. This should be calculated and is not hard - we are pretty much setup to do it. It is in fact a
larger effect than the p-bar absorbtion. Open question is this part of 'background' in FS data
on the positive side.
On the description of the spectrometer setting running.
"The spectrometer were operated in field settings and with both polarities resulting in an acceptance from
0.2-3 , and 1 -6 GeV/c respectively. Track matching and momentum calculation is done with an
effective edge approximation to the fields and applying 3 \sigma cuts on the matching parameters.
[Note is this what was done in FS?]
During the rhic running the beam vertex is typical 60cm in beginning of fill and growing to 75 cm.
For the data presented here it was further required that the track originated from a position less tha
+-15 and +-35 for MRS, FS respectively.
The numbers given for the vertex/ip description in general should be changed to reflect the final
rerun of analysis
In regard to the Tiles and also used in the other draft I will suggest we agree on naming for
the centrality detector. Tiles and Si-det are not so great, but I do not like the proposed PTMA and SiMA
either - why not just TMA and SMA .
In evaluating the ratios it is important it is important to make clear the systematic effects
considered (and review if there can be others)
- anti-proton absorbtion
- evaluation of background within the PID cuts.
- background from pion induced protons
Most systematic effects from tracking of opposite polarity do cancel out, under the assumption
the run conditions were similar. One very important place is to review the normalization between
the A and B pol runs. The assumption is when normalizing to a given centrality cut that the
vertex distribution of those events (taken from BB alone, not tracks) is the same. The acceptance does
depend quite strongly on vertex position. This can be easily evaluated by inspection of this
distribution for the runs and triggers used in the analysis.
Event though there is not much evidence for centrality dependence, we should present the data not as
the inclusive centrality cuts done at QM but as exclusive cuts. From the MRS we can probaly do two values
some thing like 0-15 and 15-40(50) which should have similar statistics. The FS cuts should be same.
The crosssection to which the tiles are normalized (estimated) should also be quoted using either JHs or Steves
calculations of this.
I will like us to consider wheter the results should be presented primarely in pseudo-rapidity \eta
for which data are taken (MRS eta~0.05) and FS (eta~3.1). For MRS the change to y is insignificant, but
in FS the different pt bins do not correspond to the same y. My suggestion would be to present data in \eta
and make a conversion to y for the most probably <pt> value for the models comparisons.
A final editorial note.
I will strongly suggest the next revision be written using latex
and the corresponding phys rev style.
It has also been agreed with
in experiments that the consistent way of lableling the energy is \sqrt{s_{nn}}=130 GeV
and seperately the discussion on hyperons (as done)
------------------------------------------------------
Flemming Videbaek
Physics Department
Brookhaven National Laboratory
tlf: 631-344-4106
fax 631-344-1334
e-mail: videbaek@bnl.gov
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