Be careful. Now that we have removed CC3 from behind the 4 rearmost TOFs
and put them behind the BATs, a hardware CC requirement restricts the
high Q^2 end, and that's where the ed elastic T20 overlaps the very
interesting region where the old Bates data overlap the recent JLab
data. I don't think we want to sacrifice that, and I definitely want
the high Q^2 end for the ep elastic.
On Thu, 4 Mar 2004, Karen Dow wrote:
>
> Just spoke with Richard on the phone, he requested that someone check how
> much a hardware Cerenkov requirement would cut the trigger rate, hoping to
> reduce the rate of PHYS1 significantly (and possibly also PHYS0). Tavi and
> Baris will look at crunched data while they're on shift, see what a
> Cerenkov cut does to the number of trig==2 and trig==1, also what it does
> to the spectra (z, momentum, theta etc -- presumably we don't lose good
> events).
>
> Karen
>
>
> At 01:42 PM 3/4/2004 -0500, Richard Milner wrote:
> >Following Tancredi's mail, I think we should significantly prescale the
> >inclusive and put more lead shielding in front of the forward LADS. Ernie
> >is working up a modification of the collimator which has the potential to
> >improve the deadtime situation for the inclusive trigger. Until we can
> >implement that, we should optimize running conditions for (e,e'd), (e,e'p)
> >and (e,e'n) both vector and tensor.
> >Richard
> >
> >
> >
> >On Thu, 4 Mar 2004, Tancredi Botto wrote:
> >
> > >
> > > A brief summary of the present understanding of deadtime sources from the
> > > analysis of recent data:
> > >
> > > Deadtime is limiting us in the use of higher beam currents. There are many
> > > components to this: the most significant is "trackless" triggers that pass
> > > the 2nd level trigger thanks to random hits in the wch. The ratio of
> > > these fake 2ndl level triggers (abot 2/3 of total data) is consistent with
> > > the Wch S/N ratios. The ratio of trackless triggers is nearly independent
> > > of trigger type.
> > >
> > > Trackless triggers have no known vertex or momentum distribution of course
> > > but they contribute fully to DAQ deadtime. They are very sensitive to Wch
> > > multiplicity and S/N. Possibly this is related also to the collimator
> > design.
> > > Trackless events really have too few wch hits (often < 3 hits in the tdc
> > > range used in the reconstruction of the wch events). We can't use a
> > > momentum cut to truly speak about deadtime..
> > >
> > > A second contribution is coming from low-momentum particles that originate
> > > mostly upstream of the target. These events constitute the vast majority
> > > of "tracked" triggers, but a smaller fraction of the overall yield. They
> > > are well characterized in momentum (100-200 MeV/c), charge (positrons for
> > > inbending field, electrons for outbedending - both fire the Cerenkovs) and
> > > location in the detector (tof #'s 10-14).
> > >
> > > These events must originate from 300 MeV photons in a EM shower. The
> > shower
> > > having photons (which are not "bent") may contribute again to the Wch S/N.
> > > Note that trackless triggers are instead *uniformly* distributed in the
> > TOF's
> > >
> > > We have never experienced such a harsh environment before because we were
> > > not running with an inclusive trigger (requires a cerenkov) prescaled by 6
> > > and because we did not add the LADS to the e,e'n trigger. Having done so
> > > it offers many more opportunities for trackless and low-energy-background
> > > triggers. Indeed trig==2 and trig==7 are the dominant distribution of
> > > trigger types.
> > >
> > > To make matters worse, any of these trigger rates will show a dependence
> > > on beam current and as mentioned in the prev email it is important to
> > > operate in a linear region. Regards,
> > >
> > >
> > > -- tancredi
> > >
> > ________________________________________________________________________________
> > > Tancredi Botto, phone: +1-617-253-9204 mobile:
> > +1-978-490-4124
> > > research scientist MIT/Bates, 21 Manning Av Middleton MA,
> > 01949
> > >
> > ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
> > >
> > >
> >
> >--
>
>
-- John R. Calarco Dept. of Physics Univ. of New Hampshire Durham, NH 03824 phone: (603)862-2088 FAX: (603)862-2998 email: calarco@unh.edu
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