From: W.J. Llope (llope_at_physics.rice.edu)
Date: Tue Feb 25 2003 - 12:09:03 EST
hi zhangbu et al...
i have some comments on the trigger proposal - i just wanted to
get them down - let's discuss tonight, thanks, bill
> TOFr Trigger Proposal in d+Au run
very small point - the trigger really should be called TOF, or
"pVPD+TOFr"...
one can't really use TOFr hits unless the pVPD fired in the
same events, so the pVPD has to be involved in the decision
too....
>
>Motivation:
>
>i) Measure proton/pbar spectra upto pt=2.->3.GeV/c
> dE/dx from TPC only covers proton dN/dy of ~50\% in narrow
> rapidity window. TOF is the only detector in STAT which
> can extends this to >99\%
>ii) Resolve the proton/pion ratio ``puzzle'' seen in AuAu data,
> distinguish flow effect from other mechanism and
> Address flow effects from partonic versus hadronic stages.
i worry about these being the first motivation listed.... as
worded, the implication is that these goals are not possile
without this tofr trigger. this is not true really.
TOFp already has tens of k hits per channel, and is roughly
three times the total area... i.e. the TOFp results are
also in play here, and given the present state of the
TOFp vs TOFr offlien software, the TOFp results are
likely to be "out" much sooner than from TOFr.
so, perhaps these bullets could have a slightly different spin.
i.e.
a TOFr trigger would allow the formation of full 1/beta
vs momentum spectra from ~70 TOFr cells. This will provide
a modest increase in acceptance w/ TOF PID, and the ability to
make important cross-checks of the charged hadron spectra obtained
by TOFp and TOFr. this will lead to more precise & detailed
analyses towards charged hardon spectra, and ratios of
these (->"pion/proton puzzle").
also taking enough TOFr data to form full 1/beta vs p
spectra for each cell will allow for more detailed investigations
of the performance of TOFr - which is the primary focus of
this TOFr "engineering" run. without a TOFr trigger, it will
be possible to extract the time resolution (for pions) and
the efficiency, satisfying the basic goal of the run. however,
with an event sample enriched by triggering on TOFr, it
will be possible to collect enough kaons and protons to
extend our understanding of the basic detector performance
even further. this will be a large boost to the full barrel
TOF project, especially in fighting concerns that this
technology is finicky, unstable, whatever....
>iii) Good pVPD (4 pVPD with adc>300, dt<50ps) is absolutely
> necessary to be able to measure the TOFr timing resolution
> expected at 60-80 ps.
i don't see how you can employ an ADC threshold on the pVPD
ADCs with the present cabling...
>Trigger Details:
>
>i) require at least 4 pVPDs fire in the event with high pulse
> and at least one TOFr channel has signal. The enhancement factor
> is about 122 compared with minbias.
besides my concern about the ability to requirelarge ADC signals
i am also worried that requiring so many pVPD hits is not
necessary...
from a technical perspective, it would require an access
to change (increase) the local trigger requirement, then star
runs the tofr special trigger, then another access is
required to change (decrease back to 1.and.1) the local trigger
condition again. since i think we want to run this
special trigger at least two different times (see below),
all these accesses to keep changing the local trigger
condition will be a problem.
if we leave the pvpd local trigger as is during
tofr trigger runs, none of these accesses are needed and
presumably everything can be controlled from the control room...
remember the 1.and.1 local trigger is the most wide open possible,
but it happens to also be one for which there is already
enough hits in just the minbias data as is
to get a good total start resn.... so higher
requirements on the No of pvpd hits seems unneccessarily
strict. we can use the events such a trigger would pitch!
also, i'd like to use the special trigger data to improve
the analyses of all the other "normal" data we have so far.
in that case, i'd like to have so-called "1.and.1" and
"1.and.2" events in the tofr triggered events so
that i (we) can directly compared the performance of the
detectors in the different data sets...
so one thing we should discuss tonight is if
raising the pvpd local trigger condition during tofr triggered
runs is really necessary...
BTW i made a plot this mornign... the number of tofr hits per
event is uncorrelated with the number of pvpd hits. so
requiring a lot of pvpd hits does not increase the
probability that there is >=1 tofr hit in the event...
>ii) Logically OR the TOFr signals from the discriminators which has
> 2-bridge output (one to TDC).
agreed - this seems like the best option....
>Another option is to split the
> analog signals to ADC.
this would better be done in the manner i described a few days
ago to startrg... we could gain 30-40 ns in the arrival time
of the pvpd signals at the trigger racks by building and runnign
new cables. but this would take some work and i kind of doubt
we could pull it off during tomorrows access. let's
discuss tonight
>iii)The pVPD.AND.TOFr signal will be sent to the ZDC CDB and use the
> spare channels in the ZDC Digitizer Board with the CTBMult register
> in DSM.
> The timing of the signal is about 300ns which is perfectly in time
> with ZDC.
>
[snip]
>4) We should switch to the default TOFr gas (Freon and Isobutane) ASAP.
could i propose something else. how about we work into the
request that we want to run this special trigger on two separate
occassions.
first (soon) we run it for the present freon-only gas. we have
a lot of that data and the tofr triggered data would really help us
understand that.
then, in about a week hopefully we are finally cleared to turn
on the isobutane, and then some days later we run the tofr
special trigger *again*...
one could also mentioned we are still hoping, time permitting, to try
implementing SF6 during this run. we have anecdotal eveidence
that SF6 may not be necessary for the full system, but now
is the time really prove this.,.. we would then want to run the special
trigger a third time - since by then i doubt there's enough
beam time left to collect enough events to calibrate TOFr
without such a special trigger.......
--
_________________________________________________________
W.J. Llope, Ph.D. Res. Assoc. Professor
http://wjllope.rice.edu/default.html
llope_at_physics.rice.edu
T.W. Bonner Nuclear Lab.
Rice University, MS-315
6100 S. Main phone: 713-348-4741
Houston, TX 77005-1892 fax: 713-348-5215
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