Hi Ian, The binning question should only be an issue if you are looking at the most 1 or 2% most central events-- even by 3% we have sufficient statistics in the min-biased spectra to reasonably describe the functional behavior. Your question invites a misleading answer: For near central events (say 20% central or better) I think your 1% is probably high (that is, a good conservative estimate) for what we might see in variations in the centrality cut from one run to the next. Our main overall uncertainty is in the total min-biased yields which, remember, requires a correction for "missed" low-multiplicity events. HOWEVER, for any given event, a centrality of, say, 5% will have an uncertainty of several percent. You might want to have a look at Fig. 5 in my Park City contribution http://www.sdcc.bnl.gov/brahms/pubs/parkcity.pdf. A picture showing what different centrality "cuts" correspond to in inpact parameter space is found in the analysis note that Hiro and I wrote on the dNdEta analysis: http://www.sdcc.bnl.gov/brahms/private/AnNotes/dNdeta_analysis.pdf On an event-by-event basis it is also possible to have a very long "tail" for the distribution of "measured"-"real" centrality (based on geant, of course...). This is clear by inspection of the figures cited above. Regards, Steve Ian Bearden wrote: >Hi Steve, Hiro, >Have you guys got a good idea of the error on the centrality? >That is, if I select the 5% most central, I really select (5+/-X)%, and I'd >like to know, roughly, what is X? I suppose it is around one, since Steve >says we cannot bin more finely than 2%. Is this supposition correct? >Ian > >>-----Original Message----- >>From: owner-brahms-dev-l@bnl.gov [mailto:owner-brahms-dev-l@bnl.gov]On >>Behalf Of Stephen J. Sanders >>Sent: 27. juni 2002 19:12 >>To: brahms-dev-l@bnl.gov >>Subject: Re: FW: MA Calibrations update >> >> >>Hi Claus, >> >>I haven't gotten up to the 5900's yet (I should get there sometime >>tomorrow), >>but I suspect this looks much worst than it is. In order to calibrate the >>centrality I need to start with a min-biased multiplicity spectrum. These >>essentially don't exist for the later runs with any reasonable >>statistics. A very small >>change at the high multiplicity end of the spectrum will be STRONGLY >>magnified when looking at the centrality histogram. For these runs I >>would suggest bin sizes of no less than 2% in centrality to avoid >>nightmares of bad calibrations... >> >>Having said this, I am noticing some differences in the centrality >>behavior when I compare the 0-20% range a centrality spectrum based on >>min-biased events, and one using trigger 6. >>Hiro and Flemming have also noted this and the behavior is currently >>being explored. The effect of concern is a dip in the centrality >>spectrum for the most central events when >>using trigger 6. Until this latest replay using the reduced event files >>I have only been looking at trigger 4 events since these are the ones >>needed for the calibrations. >> >>Regards, >>Steve >>Claus O. E. Jorgensen wrote: >> >>>Hi Steve >>> >>>I've looked at the centrality for the high field runs (5901-5983) and >>>I found this: >>> >>>http://www.nbi.dk/~ekman/centTest.gif >>>http://www.nbi.dk/~ekman/centTestZoom.gif >>> >>>which worries me a bit. I should say that to produce these plots >>>I've made a vertex cut (+- 15cm) and requiring good zdc-bb correlation. >>>It looks like the calibrations are not optimal. >>> >>>However, I don't think that there's much to do about it now. The reduced >>>files are produced and I don't think we have time to do more >>> >>calibrations >> >>>and reductions before QM. And I guess that 5% central is more >>> >>or less the >> >>>most central events. >>> >>>Cheers, >>> >>>Claus >>> >>>+-------------------------------------------------------------+ >>>| Claus Jørgensen | >>>| Cand. Scient. Phone : (+45) 33 32 49 49 | >>>| Cell : (+45) 27 28 49 49 | >>>| Niels Bohr Institute, Ta-2, Office : (+45) 35 32 53 07 | >>>| Blegdamsvej 17, DK-2100, E-mail : ekman@nbi.dk | >>>| University of Copenhagen Home : www.nbi.dk/~ekman/ | >>>+-------------------------------------------------------------+ >>> >>>On Thu, 27 Jun 2002, Stephen J. Sanders wrote: >>> >>>>This may come across twice...or not at all. I sent it yesterday but it >>>>never showed up on the server.... >>>> >>>>---------- >>>>From: "Stephen J. Sanders" <ssanders@ku.edu> >>>>Date: Wed, 26 Jun 2002 13:41:45 -0500 >>>>To: <brahms-l@bnl.gov> >>>>Subject: MA Calibrations update >>>> >>>>Hi, >>>>Now that we have the beautiful reduced event files (thanks >>>> >>Claus, Ian, and >> >>>>whoever else helped to produce these files!!!), I've started >>>> >>to replay the >> >>>>runs to: a) get all of the MA pedestals correct and b) check >>>> >>that we don't >> >>>>have any serious problems with the array calibrations. >>>> >>>>To check the MA calibration, I'm calculating dN/dEta (SiMA) >>>> >>for the 0-5% and >> >>>>30-40% centrality cuts, with the centrality calculated using >>>> >>the combined >> >>>>TMA and SiMA data as done for our multiplicity papers. The >>>> >>calculations are >> >>>>identical to what was done for the 200 GeV paper. >>>> >>>>Although I still have a number of runs to complete, I think a fairly >>>>reasonable picture is started to emerge and I wanted to relate >>>> >>this to the >> >>>>Collaboration as people get started on "final" passes. >>>> >>>>A figure of the dN/dEta results vs. run number is at >>>> >>>>http://kuphsx2.phsx.ukans.edu/~sanders/MACalib/dNdEta.jpg >>>> >>>>I've fixed the error bars at +/-4%. >>>> >>>>I have some other figures that might be of interest at >>>> >>>>http://kuphsx2.phsx.ukans.edu/~sanders/MACalib >>>> >>>>In particular, there is pretty clear evidence of a slope to >>>> >>the BB Vertex - >> >>>>TPM1 Tracking Vertex vs. Multiplicity plots for most runs. >>>> >>The same is true >> >>>>with the ZDC vertex. I've been doing these calculations since >>>> >>Monday and so >> >>>>any very recent changes in the DB may not be included in the present >>>>results. >>>> >>>>I hope to have new pedestals for all of the runs where we have >>>> >>reduced event >> >>>>files by this weekend. Unfortunately, these will be added to >>>> >>brat as ascii >> >>>>calibration files... >>>> >>>>Regards, >>>>Steve >>>> >>>> >>>> >> >> >> >
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