Hi Steve, Thanks for the quick (and clear!) answer. I have one more thing, and I am not sure if it is a question or a statement. Read and decide! Can we really look at the 1 or 2% most central? I would guess that once we are in this regime, we are looking at fluctuations (of detector response) and not really centrality. What then, is the 'most' central we can look at? I would say that we can safely (and correctly) look at the most 5%. And, I would not venture to discuss single events using the spectrometers, as ensembles are my friends. Anybody else say something different? And now, since I am not so conservative, what should X be? 0.5%? > -----Original Message----- > From: owner-brahms-dev-l@bnl.gov [mailto:owner-brahms-dev-l@bnl.gov]On > Behalf Of Stephen J. Sanders > Sent: 28. juni 2002 15:08 > To: brahms-dev-l@bnl.gov > Subject: Re: FW: MA Calibrations update > > > 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 > >>>> > >>>> > >>>> > >> > >> > >> > > > > > > >
This archive was generated by hypermail 2b30 : Fri Jun 28 2002 - 09:30:43 EDT
