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TrackCand dip treatment where Theta > 90° [message #8312]

Tue, 28 April 2009 14:10

Marius Mertens
Messages: 55
Registered: January 2009

continuous participant

From: *ikp.kfa-juelich.de

Hi all,

since the _dip member of a TrackCand usually stores the cosine of the dip angle relative to the xy-plane, this parameter is only unambiguous for tracks where Theta relative to the z-axis is less than 90°.
I.e., using only the information from the TrackCand, I can't get the correct parameters of tracks which have a Theta > 90°. How can I properly treat such tracks?

Best regards,

Marius

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Re: TrackCand dip treatment where Theta > 90° [message #8314 is a reply to message #8312]

Tue, 28 April 2009 14:24

Sebastian Neubert
Messages: 282
Registered: March 2006
Location: Munich

first-grade participant

From: *natpool.mwn.de

Hi Marius!

TrackCand is actually NOT supposed to carry the starting values of the fit. At least there is no guarantee that the values that are put there are meaningfull.

We still have to design a good interface to carry the fit starting values.

TrackCand acquired the field for dip angel, momentum and so on as a quick and dirty solution.

You are completely right though that there is a fundamental ambiguity in the definition of the dip angle, which arises from the (unknow) direction of motion of the particle. You cannot distinguish a particle that is going into forward direction towards the center of the system (a secondary) from a track that moves from the interaction point outwards but in backward direction.

This ambiguity is not solved at the moment.

Cheers! Sebastian.

Sebastian Neubert
Technische Universität München
Department Physik E18
sneubert@e18.physik.tu-muenchen.de
tel: +49-8928912592

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Re: TrackCand dip treatment where Theta > 90° [message #8315 is a reply to message #8314]

Tue, 28 April 2009 14:51

Marius Mertens
Messages: 55
Registered: January 2009

continuous participant

From: *ikp.kfa-juelich.de

Hi Sebastian,

thank you for the information on that matter.
Since you mentioned the final interface is not yet fixed, it would be nice if it included a way to store the actual angle instead of its cosine in order to keep potential sign information.

Best regards,

Marius

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Re: TrackCand dip treatment where Theta > 90° [message #8316 is a reply to message #8315]

Tue, 28 April 2009 15:05

Anonymous Poster

From: *natpool.mwn.de

Hi,

is the dip angle really measured against the x-y plane? In fact the polar angle is defined against the beam axis. This should be the same...

Christian

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Re: TrackCand dip treatment where Theta > 90° [message #8317 is a reply to message #8316]

Tue, 28 April 2009 15:37

Marius Mertens
Messages: 55
Registered: January 2009

continuous participant

From: *ikp.kfa-juelich.de

Hi Christian,

dip angle (as used by the Riemann track finder) and polar angle (Theta, as used by PndFlatGen and probably other event generators) as they are implemented at the moment, are not the same.
Currently, _dip stores the cosine of the angle between track and xy-plane. Due to this operation the sign is lost (one can argue if "lost" is strictly correct as Sebastian already pointed out that the actual direction of a track is ambiguous unless additional information is present), but I assume its range should be -90°..90° in order to cover the full polar angle range of Theta = 180°..0°.

Best regards,

Marius

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Re: TrackCand dip treatment where Theta > 90° [message #8318 is a reply to message #8317]

Tue, 28 April 2009 15:39

StefanoSpataro
Messages: 2736
Registered: June 2005
Location: Torino

first-grade participant

From: *to.infn.it

Hi,
this is the reason why in PndLheTrack I have decidet to calculate theta.

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