[d2n-analysis-talk] Spike at E/p=0 [SOLVED, but begs a new question]

[David Flay]

On Fri, Dec 17, 2010 at 12:47 PM, Brad Sawatzky <brads at jlab.org> wrote:
>
> Some of your plots seem to indicate E/p is happening for more than 10%
> of physics triggers that have a track.  Is that really the case?
> Are those E/p==0 values correlated with cosmics?  (ie. the frequency of
> the problem will get larger at higher LHRS p0 setting, beta will be
> negative, the track will probably not reconstruct to the target).
>

using EDTM==0,T3 trigger, VDC one cluster (for each plane), I plotted L.tr.n
for each kinematic.  I compared that number to the same histogram with the
same cuts plus the cut E/p==0 (and taking the ratio, with E/p==0 events
being 'bad'):

kin     |       p       |       E       |       Bad/Total (%)
0               0.60            4.73            9.05
1               0.60            5.89            9.43
2               0.80            4.73            8.68
3               0.90            5.89            9.27
4               1.13            5.89            9.83
5               1.20            5.89            10.09
6               1.27            5.89            11.01
7               1.42            4.73            13.21
8               1.42            5.89            12.99
9               1.51            4.73            16.78
10              1.51            5.89            15.15
11              1.60            4.73            22.52
12              1.60            5.89            19.80
13              1.70            5.89            25.07


Now, to investigate the correlation to cosmics, I added the cut L.tr.beta>0
to the above histograms:

kin     |       p       |       E       |       Bad/Total (%)
0               0.60            4.73            8.91
1               0.60            5.89            9.29
2               0.80            4.73            8.39
3               0.90            5.89            8.87
4               1.13            5.89            8.84
5               1.20            5.89            7.92
6               1.27            5.89            8.57
7               1.42            4.73            8.10
8               1.42            5.89            8.68
9               1.51            4.73            9.05
10              1.51            5.89           8.75
11              1.60            4.73           11.37
12              1.60            5.89           10.60
13              1.70            5.89           13.45

So it seems that cosmics do play a role to some degree here.

I've also constructed a raw sum of the PRL ADCs (see file 1, which also has
a sample L.tr.n plot (total events in black, E/p==0 in red, and a sample
beta plot for the E/p==0 events).  I've verified the pedestal subtracted
sums, so I have confidence that this is correct (see second file which shows
the pedestal subtracted sum from my code as a 1D histo, along with the plot
vs. the energy, determined by the analyzer; plots of L.tr.n and beta are
shown again).  The last file shows the ADC pedestal subtracted sum
determined by the analyzer.

The 2D plot of the raw ADC sum vs. the energy (calculated by the analyzer)
shows something that looks to be fairly ok; however, there were instances
(from my output to the screen) where the energy was identically zero while
the ADC sum in either of the layers was not zero.

For instance:

======================== Event: 171472 ========================

PRL1 Block: 16 ADC value: 506.0000
ADC sum value: 506.0000
Energy Sum: 0.0000
======================== Event: 171473 ========================

PRL1 Block: 8 ADC value: 533.0000
ADC sum value: 533.0000
Energy Sum: 0.0000

======================== Event: 1108548 ========================

PRL1 Block: 8 ADC value: 533.0000
ADC sum value: 533.0000
PRL1 Block: 16 ADC value: 508.0000
ADC sum value: 1041.0000
PRL1 Block: 24 ADC value: 489.0000
ADC sum value: 1530.0000
Energy Sum: 0.0000


From my pedestal subtracted sums:

======================== Event: 1408639 ========================

PRL1 Block: 2 ADC value: 11.0000
ADC sum value: 11.0000
Energy Sum: 0.0000

which leads me to believe that the occurrence of E==0 for the raw sum
(above) was pedestal events -- maybe the pedestals for some of these blocks
are not perfectly subtracted so that they sit at zero, or maybe a binning
issue?

I'm still digging around the source code for the ExTgtCor_L.p variable so I
can see how it's set to kBig...

-- 
-----------------------------------------------------------
David Flay
Physics Department
Temple University
Philadelphia, PA 19122

office: Barton Hall, BA319
phone: (215) 204-1331

e-mail: flay at jlab.org
           flay at temple.edu

website: http://www.jlab.org/~flay <http://www.jlab.org/%7Eflay>
             http://quarks.temple.edu
-----------------------------------------------------------
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