From: W.J. Llope (llope_at_physics.rice.edu)
Date: Wed Feb 19 2003 - 11:43:20 EST
hello zhangbu,
i take from the thread below that, with some additional
changes presumably happening today, the timing-in of a pVPD-based
trigger seems possible - barely.
this raises a concern regarding the possible triggering
on TOFr. pelase note that the times at which the earliest signals arrive
at the platform discriminators is roughly the same (to <10ns)
for each of paths (i.e. pVPD, TOFp and TOFr).
as i understand it, the proposal is to take the
second outputs from the platform discs for TOFr, run these
into NIM multiplicity counting logic (w.g. three LeCroy 380A's,
plus a logic fan, plus a discriminator, plus lemo cabling...).
concern part A: let's assume all TOFr signals are prompt
(which they are not - see part B below).
the logic needed to form the TOFr multiplicity sum
takes no less than ~32ns after the signals arrive at the platform
discriminators. so, the TOFr multiplicity signal
at Rack Row A cannot arrive earlier than ~32ns *after*
the pVPD trigger signals arrives at this same location.
-> if the pVPD-to-trigger timing is "tight" as you
implied below, the TOFr trigger signal is even later, and
significantly so.
concern part B: i assume the point of this trigger is
to result in a high statistics sample of pVPD physics
triggers that also have at least one TOFr hit, so that one
can produce a Big Nice 1/beta vs momentum plots for all of the
individual TOFr channels.
if that's the goal, bear in mind that one has to wait
30-40ns more (relative to the prompt pVPD signals at
the plat discs) to allow TOFr hits from slow things
like ~500MeV protons at eta~1... if your trigger
is not open/active this whole time, then you will
only be triggering on the promptest particles, and
full bands in 1/beta vs p will not exist in these data.
of course this is beyond the time needed for part A of
my concerns...
anyway, it seems to me that one needs ~32 + ~35 = **70ns** of
additional head-room (as compared to the pVPD trigger timing)
to base an effective multiplicity trigger on TOFr.
comments? regards, bill
>Hi, Frank and John:
> Sorry, I refered to John as "Jeff".
> Yes, I can get rid of a 8ns cable and a logical fan. It will
>give us -15ns. This together will get rid of about 30ns. If the
>one you sent me was the inverted signal with 20ns, this would delay
>it by another 20ns. If we can put all this back, this will fix it.
>
>Thanks!
> Zhangbu
>
>
>>-----Original Message-----
>>From: Frank Geurts
>>To: John Mitchell
>>Cc: Xu, Zhangbu; tofp_at_physics.rice.edu
>>Sent: 2/11/03 12:08 AM
>>Subject: pvpd trigger in STAR
>>
>>John,
>> are you available somewhere tomorrow so Zhangbu and I can call. The
>>issue still revolves around getting the pvpd east and west coincidences
>>available at the STAR trigger. You know who things are currently set up
>>(fanning out the EAST and WEST signals, and sending them on a 40ns cable
>>
>>to Zhangbu's stuff). As it turns out the signals arive too late ...
>>zhangbu sees them in the zdc post one clock tick. Meaning that we are
>>too late by at least some 40ns (Zhangbu??). I couldn't see any timing
>>measurements on your trigger logic diagram for the path from the output
>>of the ps706s until the outputs of the EAST or WEST coincidence units.
>>
>>* What would you guess this timing would be?
>>
>>* From the diagram I read that we had enough outputs for both
>>coincidences so we could provide Zhangbu with regular negative logic,
>>right? Or did we give him positive logic (w/ a pulsewidth of 20ns)?
>>
>>In order to push the timing back, we could reconsider removing the fan
>>unit which we placed to protect ourselved from reflections. I suppose
>>removing the cable to that unit + the unit itself could safe us 8ns
>>(cable length?) + 6-7ns (transient time, according to specs for the
>>LC428) about 15ns. Not much, but maybe Zhangbu can get his 40ns cable
>>somewhat shorter too ...
>>
>>In any case, the reflections for which the fan-out unit should protect
>>us could also be minimized by a attenuator in Zhangbu's signal path.
>>Currently, he already has an 14dB attenuator in it.
>>
>>With the scheduled access, we just want to ran with you through some
>>options before we touch anything. Maybe we could use the TOF phone
>>bridge so Bill and Geary can join if they want to (if these guys can
>>keep their meeting short :) ... )
>>
>>-frank
--W.J. Llope, Ph.D. Res. Assoc. Professor T.W. Bonner Nuclear Laboratory phone: 713-348-4741 Rice University, MS-315 fax: 713-348-5215 6100 S. Main St. Houston, TX 77005-1892 e-mail: llope_at_physics.rice.edu WWW home: http://wjllope.rice.edu/default.html
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