Minutes of N-star Meeting
The N-star group met at 9:00 AM on Jan. 11, 1998.
Attendance: W. Bertozzi, V. Burkert, S. Dytman, H. Egiyan, L. Elouadrhiri,
H. Funsten, M. Holtrop, K.Joo, M. Kim, S. Kuhn, B. Mecking, R. Minehart,
R. Miskimen, J. Muell, B. Niczyporuk, J. Price, R. Schumacher,
A. Skabelin, C. Smith, P. Stoler, S. Stepanyan, M. Taiuti,
R. Thompson, J. Zhau
1, Bogdan reported on his data analysis using the program EvRec&SIM.
He reported an analysis rate of 100 Hz, with 30% of the December triggers
containing electron tracks. He reported a reconstruction efficiency
of 96-98%
for time based tracking with electrons. In the reconstruction of elastic
events
he obtains proton mass of 940 MeV with a peak width of sigma=15 MeV.
Details of
his report are appended.
2. Kyung-seon reported on results using his TOF calibration scheme.
His report is appended. One of his interesting results
was the identification of a substantial radiative tail from elastic
scattering in the inelastic region.
3. Stepan showed his analysis of three prong events, in which he is
able
to identify reactions such as ep to e,pi, delta.
4. Ralph reported on his analysis of the CLAS
acceptance for inclusive electrons. He made no cuts in the data,
so that the acceptance functions at fixed electron angle and momentum
have sloped edges due to the imperfect efficiency of the Cerenkov dertectors
at their edges. He used this acceptance to calculate an expected inclusive
electron trigger rate using Brasse's compilation of inelastic electron
scattering cross sections. Richard Thompson reported good agreement
between
these calculations and our absolute data rate.
5. Volker Burkert proposed a plan for dividing the February run period
into three energies. He argued for the importance of obtaining at the
minimum enough data at 1.6 and 2.4 GeV to make a substantial improvement
to the existing data base. His calculations indicate that with the
50%
efficiency factor, we need 4 days at 1.6 and 8 days at 2.4. This would
leave 14 days for 4 GeV. There was considerable discussion of this
plan,
with the primary concern being that we might end up with too little
data
at 4 GeV to obtain interesting, if preliminary, results at that energy.
Volker agreed to re-state his plan making the number of electron triggers
required at each of the lower energies the driving term. This would
lead
to the possibility of running for shorter amounts of time than his
estimate.
There seemed to be a consensus that if the time required for the two
lower
energies became stretched out due to accelerator or apparatus problems,
the question of how to divide up remaining time would have to be revisited.
6. Maurik reported on the status of GSIM. Substantial work is required
to make it use identical parameters as RECSIS. He announced a GSIM
workshop
for Jan. 12.
7. In brief discussion of graduate student participation, we reiterated
the need for more students, and it was pointed out that a list of projects
compiled by Volker was available on the N-star web site.
8. The next meeting will be coordinated
with other activities, but should be soon.
Submitted by: Ralph Minehart
Appendix I. Bogdan Niczyporuk
SHORT STATUS of EVENT RECONSTRUCTION and SIMULATION with SDA
(Bogdan Niczyporuk, Jan.12,1998)
SOME RESULTS (TBT)
==================
Speed: about 100 trig/second on HP (jlabh3)
DST contains: - about (12 - 35)% of original triggers (at least electron)
- event size about 10% of the original event size with the
following BANKS: EVTB(new) and original {CC,SC,EC,CALL} banks
Calibrations
------------
The SDA use only the pedestals from "MAP manager" (SC,EC). Other calibration
constants are derived from the data runs. In major, the success of
time based
tracking (TBT) depends on the knowledge of delays for DC (each signal
wire)
and for SC (each phototube). Those delays can be derived from data
runs taken
with "e1_EC_123456" trigger. At present, the current (preliminary)
resolutions
for the DC delays are about 10 ns and for the SC delays is about 2-3
ns.
I have shown that the resolutions for SC delays can be easy reduced
to the 1 ns
level (work in progress). The resolutions of individual SC phototubes
(Panel 1)
are about (0.20 - 0.25) ns without time walk corrections. That is sufficient
to see the RF beam structure. The SC delays for the Panel 2 and 3 were
derived
from the exclusive elastic and inelastic reactions. The DC delays derived
from
"pulser" runs are not complete and in the big portion are not applicable
for
the December runs (many adjustments has been made). Even using the
pulser
delays for the September runs produces worse DC resolutions.
The 1 ns resolution for SC phototube delays seems to be sufficient
for the successful
completion of the time based tracking (to derive the particle velocity).
DC Alignments
-------------
At present the SDA uses the nominal geometry (design values). Deviations
from the
design values has been clearly observed. Analysis of elastic scattering
(phi acollinearity of opposite sectors) suggests that the three pairs
of sectors
are rotated by about 1 mrad around z-axis (the same sign), but sectors
1 and 4
are acollinear by about 3 mrad. From analysis of electron tracks with
empty
target (Run 7889, trigger e1_CCEC_1456) one can clearly see the walls
of the
target seperated by 4 cm. Following we show the z-positions of the
downstream
target wall and the distances to the beam (z-axis) reconstructed at
different
sectors: Sector#1 Zwall = 1.10 +/- 0.016 cm Dbeam = -2.10 +/- 0.036
cm Sector#4
Zwall = 0.63 +/- 0.018 cm Dbeam = 0.28 +/- 0.031 cm Sector#5 Zwall
= 0.46 +/- 0.025 cm
Dbeam = -0.74 +/- 0.051 cm Sector#6 Zwall = 0.43 +/- 0.023 cm Dbeam
= -1.57 +/- 0.038 cm
Again, the vertex positions data for sectors 1 and 4 seems to be correlated
with the
observed acollinearity.
Track Reconstruction Efficiency (TBT)
-------------------------------------
To obtain the hit based tracking efficiency is a simple task; one needs
only
the list of "dead" wires. The time based tracking efficiency is much
more
complex procedure since that evolves not only DC but also other subsystems
(geometry misalignments, resolutions, time delays, drift cell physics,
etc).
In order to get a feeling how efficient is the TBT I have analyzed
a few
December runs taken with the "e1_EC_123456" trigger. As a denominator
I have used the identified electrons with the DC (HBT), SC (slab matching)
and EC (U,V,W matching and ratio Ecluster/p). A number of survived
electrons
(DC, SC timing and global fiting) gives the estimate of efficiency.
The efficiency, averaged over 6 sectors, is about 96% which is only
about 2%
lower what the MC simulation predicts.
Overall Resolution
------------------
The overall detector resolution can be judged by examining the width
of elastic peak
(ep --> e + X) and the misssing mass width of neutron (ep --> e + pi
+ X).
The resolution (sigma) of elastic peak is about 15 MeV and the position
is
about 945 MeV. The SDA simulation (by definition: perfect alignments
and delays
are ideal) and reconstruction (the same code) gives the sigma of 12
MeV and perfect
position. The analysis of the two prong events (ep --> e + pi + X)
gives the neutron
mass about 945 MeV and sigma about 15 MeV. The above quoted values
are for the
December runs (Ebeam = 1.645 GeV, Itorus = 2250A) and were averaged
over the all sectors.
Appendix II: Kyungseon Joo's report
-----------
Kyungseon Joo reported his study of exclusive reacations
using run 7893 with 1.6 GeV and EC*CC trigger from last DEC 97 run.
For this study, he needed a fairly good particle id.
He assumed that as a starting point, a paddle to paddle calibartion
for panel 1 has been well done so he assumed all paddles in panel 1
for
all sectors for electron side as a single paddle. He calculated all
time constants available for six sectors. He achieved a good separation
between protons and pions with sigmas of 50 MeV for protons and 70
MeV for pions.
Each panel 1 calibration is underway. Using the above particle id,
he showed missing mass spectrum from(e,e'p)pi0, (e,e'p)eta, (e,e'pi+)n
and (e,e'pi+)delta reaction after cut on W( > 1.1). He found a fairly
l
arge contribution of radiative tail from hydrogen elastic scattering
more than he expected. More systematic studies are needed. He also
showed the W dependence of the ratio of (e,e'p)/(e,e'pi+) for single
pion production and noticed that events from (e,e'pi+) were supressed
at low W side probably due to the acceptances.
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