I don't see any problem with using the Cerenkov in the trigger except
that we have to understand the efficiencies very well. To do this we
would need another trigger which would produce an identifable electron
in each of the Cerenkov's without explicitly using the Cerenkov's.
This extra trigger could of course be prescaled by a large factor but
should still allow 1% statistics over a reasonable time frame.
Karen, is it possible to prescale combinations of hits which make up
the trigger or only the final trigger?
Cheers,
Douglas
26-415 M.I.T.
Tel: +1 (617) 258-7199
77 Massachusetts Avenue Fax: +1 (617)
258-5440
Cambridge, MA 02139, USA E-mail:
hasell@mit.edu
On Mar 5, 2004, at 8:46 AM, Karen Dow wrote:
>
> I believe the logic of (first 12 TOFS AND Cerenkov) OR (last 4
> TOFS) is all within the sector MLU, it's just a pattern lookup. So
> there should not be timing issues, because the logic operations are
> not sequential. The only problem would be if the Cerenkov signal to
> the MLU came so late that (TOF AND Cerenkov) came very late, after the
> TOF Meantime signal, which is what really provides the event timing.
> However, that was checked ages ago and shouldn't be a problem. We'd
> see it now in the PHYS6 singles events, as a shifted TOF timing peak.
>
> One thing we might want to worry about is whether the last TOF
> behind a Cerenkov (#11) should REQUIRE a Cerenkov or not, since there
> might be an edge effect. For inbending electrons I wouldn't think
> there would be a problem. Also, the way the TOFs go into the sector
> MLU (paired after the first 4), you'd actually need to allow TOF10 to
> also not require a Cerenkov.
>
> I'll keep thinking about other consequences, especially if
> they could produce a false asymmetry, or some kind of additive
> background.
>
> Karen
>
>
> At 08:22 AM 3/5/2004 -0500, 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
>> > > > > >
>> > > > >
>> ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
>> ^^^^^^^^^^
>> > > > > >
>> > > > > >
>> > > > >
>> > > > >--
>> > > >
>> > > >
>> > >
>> > >
>> >
>> >
>>
>> --
>> 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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