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User name C. Furget

Log entry time 08:42:43 on September 25, 2006

Entry number 122790

Followups:

keyword=Analysis: Comparison of e/(e+pi) between 5 and 60 muA

Cerenkov current scan Here is the comparison between run 31016 (Beam current at 5 muA) and run 31015 (beam current at 60 muA)

Table 1 : ratio e/(e+pi) on the whole matrix

e/(e+pi) total
 Oct 1
 Oct 2
 Oct 3
 Oct 4
 Oct 5
 Oct 6
 Oct 7
 Oct 8
5 muA
 0.52
 0.50
 0.54
 0.50
 0.49
 0.52
 0.46
 0.51
60 muA
 0.59
 0.56
 0.61
 0.55
 0.57
 0.56
 0.54
 0.56

Table 2 : ratio e/(e+pi) on the elastic locus
e/(e+pi) elastic locus
 Oct 1
 Oct 2
 Oct 3
 Oct 4
 Oct 5
 Oct 6
 Oct 7
 Oct 8
5 muA
 0.65
 0.61
 0.68
 0.60
 0.59
 0.62
 0.60
 0.62
60 muA
 0.70
 0.65
 0.72
 0.64
 0.65
 0.66
 0.66
 0.66

Comments :

1/ The e/(e+pions) ratio is increazing by 10 % on the whole matrix and by 8 % on the elastic at larger beam current .

2/ Let see if this could be explained by pion contamination in the electron pattern at larger beam current :

For Octant 8,  the Cerenkov trigger is increazing from 10000 Hz/muA to 30000 Hz/muA between 5 and 60 muA.
That means that an additional 20000 Hz/muA* 60 muA = 1.2 MHz of Cerenkov trigger can enable CED-FPD coincidences,
which are in the pion pattern. The width of the Cerenkov enable is about 33 ns, which should gives about 4% of the "pions" going into the
electron pattern.
This represents about  4% of change in e/(e+pi) of the whole pattern (here e/(e+pi (oct8 at 5 muA) = 0.5 ).
This has to be compared to a change of (0.56-0.51)/0.51 = 10 %

2/ The calculation should give less on the elastic locus because the e/(e+pi) at 5 muA = 0.62 is larger. The effect of the contamination of "pions"
on the electron pattern is reduced by the ratio pions/electrons = 0.6 and the effect on octant 8 is 0.6*4% = 2.5%.
This should be compared to (0.66-0.62)/0.62 = 6.5%.

So it seems that the contamination of pions in the electron pattern could  explain about half of the change of the electron/(electron+pions) ratio.

Also when the beam is going from 5 to 60 muA, we would expect other effects, like  randoms in the CED-FPD but it's difficult now to say
how they will affect this ratio because we don't know the number of Meantimer in coincidence with true Cerenkov or not.

We can also think to deadtime, but in principle (but not in practice), the effect should be the same on the electrons and pions.
Indeed the deadtime of the CED-FPD electronics don't know about the nature of the particle (electron or pions), and the deadtime
on the Cerenkov trigger has in principle a small effect because the signal which causes the loss of the electron trigger will replace the
signal in the enabling.




3/ Now these values