First thanks to JJG for sending out the summary from the NBI work. I think a nice addition would be to post significant plots on the web, not that the following report has that either. As Jens Jorgen I encourage these communications, and hope they won't stop because of the holiday season. I am summarizing the work at BNL to the best of my understanding, and hope it is represented accurately. -Spectrometer analysis: Acceptance: EJK has continued the work on setting up procedures to evaluate and use the 'geometric acceptance' for the MRS spectra. It focused on the 90-degree settings. The method is conceptual simple - for each vertex position (in 5 cm steps) create a map in y-pt, and eta-pt that contains the #accepted tracks/#thrown tracks based on gent calculations (using only energy losses, and stopping particles in all magnet iron.) - This done for two field settings, and two polarities (and for pions + protons (the y-pt map)). - Check using known input spectra for calculations. PID: JH is continuing to understand the MRS PID and improve the S/N for the spectra. This includes looking at fiducial cuts, optimizing timing, checking beta-P, mass-p. Taking a closer look at pi+/pi- ratios. The path length issue is not important for MRS. For vertexes in the range of -30->30 the path length distribution has a sigma of <=1 cm in simulations (and from real data). We will take another look at the C1 performance with the hope it can be used in the FS PID analysis done at NBI. The idea is to further develop the software, and evaluate if the response from the detector is good enough to be used to accept/reject pions. We are preparing for a production run of retrieving raw data and performing track reconstruction in MRS and saving as root files that can be rapidly analyzed in terms of PID for MRS. In contrast to the earlier MRS selected events this will be an event sample unbiased requiring only the vertex from BB and ZDC are consistent and within +-30 cm. The logbook, datasheets etc are carefully scanned to identify the sets of runs that will be used in the next analysis step. This is almost done. The results with comments on goodness and problems with runs will be available in a spreadsheet. Hardware: The gas-flow in and out of the TPCs has been studied with the drift-velocity monitors, and filter was put before after chamber to. The tentative conclusion is that the V(in) is about 1.43 cm/microsec, while V(out) is ~1.30 cm/microsecond. Activating the oxysorber following the chamber brought the measurement up to 1.4 again indicating contamination in the chamber (TPM2). Work in continuing in preparations for the calibration wire chamber installation. Centrality- >From Hiro I got the following note " The Following is the summary of the things I am looking in last 2 weeks. 1. I try to understand the delta ray production in GEANT simulation. The delta ray production decreases the tale of energy distribution in si and tile. At this points, I do not know what the threshold of this effect should be. 2. Recalibration of silicon detectors. I am re-fitting each channels since some of previous fits are not that good. 3. Looking at the folding of 1 particle energy distributions to fit the experimental data. For more detail, look at the Steve's Note. " Comment: the note referred to from Steve was send to the brahms-cent-l@bnl.gov listserver. You do not have to subscribe to see the note. They are archived and accessible through the web too. JHLee has also made a filter macro that can be used for common centrality cuts- the listing was posted to this same list-server. It is not a full-fledged analysis module or event filter, but can and should be used in on-going analysis to make a set of well-defined centrality cuts using the tiles. FV- This is a note I wrote the previous weekend doing some additional checking on the dN/dEta from Beam-Beam counters. This is a collection of considerations and evaluation of the beam-beam status. These notes are to be considered work in progress and not a complete analysis. I am trying to address some of the many questions that have been brought up during the collaboration meeting as well as before in discussion. It should also be pointed out that Yury has been looking at many of these questions before and may well have similar evaluations ready in his notes. A major point is to quantify this. I Vertex position dependence The vertex is determined with an accuracy of about 2.0 cm. What is the effect of a misplaced vertex. This was evaluated semi-analytically and found to be about delta(dN/dEta) /dZ ~ +.5 /cm misplaced. This for a dN/deta value of about 280. II Procedure for evaluation acceptance. The average number of hits is converted to multiplicity by the solid angle factor 4R/r/delta(eta) where delta(eta)=eta(R+r,Z) - eta(R-r,Z). A question was raised how accurate this method is. I found in my investigation that it seems even for a 2" tubes to be amazingly accurate. A small ROOT macro was written to check this analytically/numerically without going though the whole simulation - analysis apparatus. It confirms that one should have reproduced the dN/dEta for hijing in the data chain (presented by YB the previous week with and not have had a result about 10-15% above for the large tubes. This indicates some error either in the analysis code, or in the Gbrahms generation for those tubes. Rather than repeating what was written in the macro used for the analysis I enclose the comment that Give some of the results. /* Divide the eta range of the tube into nsteps pieces. For each of these range the contribution to average counts in the tubes is evaluated from the fraction of the 'center eta' value circle i.e. a given radius (rad) that is inside the tube. The equation (rad.cos(phi)-R)**2+(rad.sin(phi))**2 = rtube**2 determines the angle phi that is inside the tube. This is solved by a simple iteration in this program. The contribution is then simple dN/dEta*delta(eta)*phi*2/2*pi. At the end the input dN/dEta at center eta for the tube compared to the value gotten by taking N(hits)/(eta2-eta1)*4*R/rtube, as used in the analysis. dN/dEta is assumed to be linear in the range covered by the tubes and described as Nav - dN*(eta-etaAverage); Conclusion: The size of the tubes has no effect (i.e. < 2 out of 275 ~ .7% ) Accuracy of algorithm is better than .3/300 0.1%; */ Analysis Code and chain. I took a (virtual) walk through the code, and checked some of the crucial places. Other peoples code is usually difficult to read a first time around and this is no exception. I raise a few questions that may be inconsequential, but may require some running of the code. All comments are in regard to what was checked into CVS last week. (~ Dec. 4). The eta range is divided into very small bins (0.02). I would argue this is in fact much too small. The extension of a big tube is about .3 units. This might still work ok (see comment above). For the most inner tube a change in 5 cm changes eta by 0.023, and with a vertex sigma of 2-3 cm this is comparable. There may be good reasons to look at this for systematic effects, but final presentation should be no finer than .1 in my opinion. The analysis code fills event-by-event dN/dEta distributions (each with a .02) bin, and evaluate in the very end the means. This is integrated over all tubes at this point. I had a concern about the binning (bin size 13 units) but made some checks with ROOT histograms and convinced my self that mean, and RMS is calculated properly as long there is no over or underflows. It would be most useful to have all tubes separated in the analysis at this level (eta binning) so each of these can be inspected and compared to the other tube(s) that have same geometry. This way we can also in the end look at the extracted dN/dEta for say the 8 left tubes- calculate a statistically proper Mean for each and Study the deviation between each measurement to get a better understanding of the statistical vs systematic error. >From the RMS and # entries we would expect the stat. Error to be around +-2 out of 300. The syst. Error from above is also very small. I will tentatively as also said at many occasions that the errors shown in the plot so far do not reflect the facts. The statistical errors are much smaller maybe 1-2% and we cannot arbitrarily assign a large systematic error. A crucial missing part is to evaluate the BB dN/dEta using the Tiles as an event selection e.g. with JH's newest selection module. The other very open issue is to a) resolve the Geant puzzles that YB has presented at the collaboration meeting b) Understand quite a better the tube response within geant particular in regard to delta-rays that can be incorporated into geant- cuts and treatment in what materials are difficult to assess without quite a long study c) We have seen that these kind of inclusion can change the background correction by perhaps from .62 to .58 with some pieces included. What are the important one? And how do one check the calculations is reasonable converged? Some tentative conclusions: I think there too much to be done on a rapid time-scale to make this well understood. I do not think there is any trivial error in what is the main code for raw-data analysis, and the most important. ------------------------------------------------------ Flemming Videbaek Physics Department Brookhaven National Laboratory tlf: 631-344-4106 fax 631-344-1334 e-mail: videbaek@bnl.gov
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