From: Dana Beavis (Beavis@sgs1.hirg.bnl.gov)
Date: Thu Jan 30 2003 - 08:41:05 EST
Ian, We believe that the backgounds are higher this year. We are not sure of the reasons but have some guesses. There ahs been substantial reduction in the backgounds although even for the best runs we think they are higher than previous years. Runs with "good collision rates to background" typically have TOFW singles to ZDC coincident rate of about 10. These scalers are in the data stream. Bad run have this ratio as 40 or more. The backgounds in our experiment have always been dominated by the beam current and not beam collisions, at least for most detector systems. I think for the FS this implies if the backgrounds are the same as last year you would have less signal to noise in the FS. In addition, with the tune for d-Au the beam is closer to the walls of the beam pipe in the D0 end of the DX magnet. It is possible (a guess) that a new scraping scource is here and increases the backgound for the same beam current. Next week I will try to do measurements to check this out. I have spent substantial time "beating" on the machine people to reduce backgrounds and understand the source. Hopefully, will will be constinued progress. I think people need to think about H1/C1 removal. Once H2 is in the trigger and we have concentrated runs with P>5 GeV/c it would be my "guess" that the best data would be with both H1 and C1 removed. ----- Original Message ----- From: "Ian Bearden" <bearden@nbi.dk> To: <brahms-l@bnl.gov> Sent: Thursday, January 30, 2003 8:03 AM Subject: Re: C1 > Hi Dana, > Do you understand why the background is so much worse now than last > year? > We ran last year with C1 down to 3 degrees with no big problems (at > least they were not so big that we became aware of them...), and now > there are fewer 'real' tracks per event (that is, in Au+Au at small > angles last year, we had a mean # of reconstructed tracks of almost 2, > i think, whereas this year it is roughly 1 and now we can actually > trigger on tracks) so the problems must come exclusively from the large > background. > It seems really odd to me, since I would expect (naively) less > background from d than from Au, and less background with shielding than > without. > I am not arguing that we should keep C1 in, though I would argue that > we should keep H1. Still, I wonder if anyone has any explanation for > the worse environment and whether there is anything that we can do to > ameliorate the situation. > Cheers, > Ian > > On Thursday, January 30, 2003, at 01:59 PM, Dana Beavis wrote: > > > There may be an additonal thing to consider. At what angle/ field > > settings > > should C1 be removed. I am sure that the material causes interactions > > and > > multiple scattering. A new set of extension bars were made for this > > years > > run which allows both C1 and the multiplicity array to be moved > > out/serviced > > at the same time. The same thought may occur for H1. > > dana > > > > ----- Original Message ----- > > From: "Ian Bearden" <bearden@nbi.dk> > > To: <brahms-l@bnl.gov> > > Sent: Thursday, January 30, 2003 2:34 AM > > Subject: C1 > > > > > >> I am sending this to the list to 'advertise' the usefulness of the > >> elog, and so that other people who are involved in this can see what > >> happened. We have had some problems with calibrating C1, but looking > >> on Wed. day entry in the elog I find a nice writeup with scope > >> pictures, explaining that the problems may come simply from the number > >> of particles in C1. The calibration was attempted using data with the > >> FFS trigger (trigger 6), but in such events there are (evidently) too > >> many pions in C1. We will try to look for the 1 p.e. in min bias > >> events. > >> So, thanks to Ramiro for clearing this up. > >> And thanks to Hiro for providing the wonderful elog. Now if we could > >> just pry that paper log book out of Flemming's hands, all would be > >> well:-) > >> Cheers, > >> Ian > >> > > > > >
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