| EvtGen Output Fixed Point Precision [message #9003] |
Thu, 16 July 2009 16:57  |
Marius Mertens
Messages: 55
Registered: January 2009
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continuous participant |
From: *ikp.kfa-juelich.de
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Hi all,
to my understanding the canonical way to use EvtGen generated events within pandaroot means that one firstly generates the corresponding .evt file which is then imported into pandaroot.
My problem is that the output file format uses 4 digit fixed point precision for the non-integral values. Since these numbers are given in GeV, the potential rounding errors can cause a mass error in the order of more than an MeV.
Since the mass is clamped to the PDG mass for each particle once it crossed the interface to pandaroot, I am not sure about the actual impact of this behaviour.
However, is it be possible to increase precision in the output file or (as Ralf suggested in an earlier post) add another interface to pandaroot which then provides higher precision?
Best regards,
Marius
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| Re: EvtGen Output Fixed Point Precision [message #9008 is a reply to message #9007] |
Thu, 16 July 2009 18:07  |
Marius Mertens
Messages: 55
Registered: January 2009
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continuous participant |
From: *ikp.kfa-juelich.de
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Hi Stefano,
one example I just took from an event file looks like this:
Toggle Spoiler
8 24
N Id Ist M1 M2 DF DL px py pz E t x y z
0 88888 2 -1 -1 1 2 0.0001 -0.0000 9.8081 10.7911 0.0000 0.0000 0.0000 0.0000
1 431 2 0 0 3 4 -0.1031 0.1937 6.0957 6.4094 0.0000 0.0000 -0.0000 0.0000
2 -10431 2 0 0 9 10 0.1032 -0.1937 3.7124 4.3817 0.0000 0.0000 -0.0000 0.0000
3 331 2 1 1 5 6 0.1644 -0.2514 1.6517 1.9331 0.5596 -0.0090 0.0169 0.5322
4 211 1 1 1 -1 -1 -0.2675 0.4451 4.4439 4.4764 0.5596 -0.0090 0.0169 0.5322
5 113 2 3 3 7 8 -0.2246 -0.2185 1.0231 1.1931 0.5596 -0.0090 0.0169 0.5322
6 22 1 3 3 -1 -1 0.3890 -0.0329 0.6286 0.7399 0.5596 -0.0090 0.0169 0.5322
7 211 1 5 5 -1 -1 -0.2382 -0.0779 0.2085 0.3546 0.5596 -0.0090 0.0169 0.5322
8 -211 1 5 5 -1 -1 0.0137 -0.1406 0.8147 0.8385 0.5596 -0.0090 0.0169 0.5322
9 -431 2 2 2 11 12 -0.1946 -0.0838 3.2330 3.7911 0.0000 0.0000 0.0000 0.0000
10 111 2 2 2 22 23 0.2978 -0.1098 0.4794 0.5906 0.0000 0.0000 0.0000 0.0000
11 331 2 9 9 13 15 0.0849 0.2089 0.6670 1.1896 0.1595 -0.0082 -0.0035 0.1361
12 -211 1 9 9 -1 -1 -0.2796 -0.2927 2.5660 2.6015 0.1595 -0.0082 -0.0035 0.1361
13 111 2 11 11 16 17 0.0688 0.1769 0.3666 0.4343 0.1595 -0.0082 -0.0035 0.1361
14 111 2 11 11 18 19 0.0061 0.0425 0.0925 0.1691 0.1595 -0.0082 -0.0035 0.1361
15 221 2 11 11 20 21 0.0101 -0.0104 0.2079 0.5861 0.1595 -0.0082 -0.0035 0.1361
16 22 1 13 13 -1 -1 0.0887 0.1447 0.3570 0.3953 0.1595 -0.0082 -0.0035 0.1361
17 22 1 13 13 -1 -1 -0.0199 0.0322 0.0096 0.0390 0.1595 -0.0082 -0.0035 0.1361
18 22 1 14 14 -1 -1 -0.0405 0.0659 0.0199 0.0798 0.1595 -0.0082 -0.0035 0.1361
19 22 1 14 14 -1 -1 0.0465 -0.0234 0.0726 0.0893 0.1595 -0.0082 -0.0035 0.1361
20 22 1 15 15 -1 -1 -0.2346 -0.0364 -0.0355 0.2400 0.1595 -0.0082 -0.0035 0.1361
21 22 1 15 15 -1 -1 0.2447 0.0259 0.2434 0.3461 0.1595 -0.0082 -0.0035 0.1361
22 22 1 10 10 -1 -1 0.2973 -0.1216 0.4813 0.5786 0.0000 0.0000 0.0000 0.0000
23 22 1 10 10 -1 -1 0.0005 0.0118 -0.0019 0.0120 0.0000 0.0000 0.0000 0.0000
When you calculate the mass of particle 4, it evaluates to 142.266MeV.
The maximum error in mass due to rounding at 4 digits precision is
err_max=0.05MeV*(E+px+py+pz)/sqrt(E^2-px^2-py^2-pz^2)
It is admittedly not very likely that the maximum error is indeed achieved, but it does happen.
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