Good morning:
I must have not thought things completely through. A quick check with
Eugene on the phone shows that indeed CC remove all the trackless stuff
in trig==2 just as richard suggested.
We can require CC in trig==2 (e,e'n) which would yield a significant
reduction of that trigger. One can monitor the CC efficiency with ee'p
events from trig==1, which does not contribute to the deadtime as much.
-- t
________________________________________________________________________________
Tancredi Botto, phone: +1-617-253-9204 mobile: +1-978-490-4124
research scientist MIT/Bates, 21 Manning Av Middleton MA, 01949
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
On Fri, 5 Mar 2004, John Calarco wrote:
>
> Hi Richard,
>
> I may be wrong, which is why I opened my comment with "Be careful." ...
> meaning we need to think carefully to not make any mistakes. Unless I'm
> wrong (which may be the case), PHYS0 contains the elastic as well as
> quasielastic e,e'p. Thus a simple hardware AND of the CC takes the
> last 4 TOFs out of the trigger which means we get no triggers for
> elastic events in the last 4 TOFs, the high Q^2 region. It is possible
> of course to work around this and have a hardware trigger of (any TOF
> AND CC) OR (last 4 TOFs). This keeps the last 4 TOFs in the trigger,
> but now I begin to worry about timing. For every logical operation,
> we accumulate a delay of at least 10 ns in the trigger. If the 2
> Boolean operations I just described have to be done sequentially, then
> we have at least 20 ns delay in the trigger relative to the retiming
> signal. At some point we run into trouble. Perhaps Karen or others
> might wish to comment.
>
> So, to reiterate, "Be careful." Any change in the trigger is possible
> but MAY (repeat, MAY) have possible unforeseen consequences which have
> to be assessed before making the change.
>
>
> On Thu, 4 Mar 2004, Richard Milner wrote:
>
> >
> > I am not sure what you mean John. The idea is that where we have Cerenkov
> > detectors in the acceptance we should seriously consider to use them in
> > the electron trigger. They are now highly efficient and should
> > reduce trackless triggers, e.g. in (e,e'n) as a means to reduce the
> > deadtime.
> >
> > Elastic scattering on both the deuteron and proton has the benefit of
> > being completely kinematically correlated. My understanding is that this
> > trigger type is a relatively small contributor to the deadtime.
> >
> > Also, for the proton target we have only the (e,e'p) assuming we prescale
> > the inclusive.
> >
> > Am I missing something?
> >
> > Richard
> >
> > On Thu, 4 Mar 2004, John Calarco wrote:
> >
> > >
> > > 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
> > > > > >
> > > > > ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
> > > > > >
> > > > > >
> > > > >
> > > > >--
> > > >
> > > >
> > >
> > >
> >
> >
>
>
This archive was generated by hypermail 2.1.2 : Mon Feb 24 2014 - 14:07:30 EST