LISTSERV mailing list manager LISTSERV 16.5

Help for HPS-SOFTWARE Archives


HPS-SOFTWARE Archives

HPS-SOFTWARE Archives


HPS-SOFTWARE@LISTSERV.SLAC.STANFORD.EDU


View:

Message:

[

First

|

Previous

|

Next

|

Last

]

By Topic:

[

First

|

Previous

|

Next

|

Last

]

By Author:

[

First

|

Previous

|

Next

|

Last

]

Font:

Monospaced Font

LISTSERV Archives

LISTSERV Archives

HPS-SOFTWARE Home

HPS-SOFTWARE Home

HPS-SOFTWARE  October 2012

HPS-SOFTWARE October 2012

Subject:

d0 sign convention consistency

From:

"Hansson Adrian, Per Ola" <[log in to unmask]>

Reply-To:

Software for the Heavy Photon Search Experiment <[log in to unmask]>

Date:

Tue, 16 Oct 2012 22:22:42 -0700

Content-Type:

multipart/mixed

Parts/Attachments:

Parts/Attachments

text/plain (49 lines) , winmail.dat (49 lines)

Hey,

I finally was able to get my "fake" hit code to work for HelicalTrackHits. It took a lot of sweat and tears and made me go through the entire tracking code pretty much :(

Especially for Norman who might not be updated on this work (and has his name on some of the relevant classes mentioned below): I have written some code that allows us to generate a helix, trace it through the detector and add hits at any given point, in particular at the points where the helix and sensor plane intercept. What I'm talking about below is the generation of "fake" HelicalTrackHits. I also have code to generate strip hits but that has some unsolved problems I need to get back to. Omar has offered to implement a version that created SimTrackerHits. All this is to be able to debug and verify that our software chain is working as expected. It might come in handy for the Kalman fitter once that is up and running!?

Anyway, the last of the many issues I had was the fact that the circle fitter has the opposite sign convention for d0 which I didn't realize at first. The way I spotted that was actually that the line fitter sometimes gave a chi2 contribution of order 10. Going through some specific examples where that happened and actually fit a straight line myself in manually I realized that it wasn't that the hits where at the wrong place it was the path length calculation which differed slightly. I checked the circle fit part of the track parameters was identical and so I knew that they should be the same. The difference was of the order of a few microns in path length which sounds ridiculous but I assign a 1nm error on the hits so anything is important which is the reason I do this in the end :)

Anyway, when I compared the methods used to calculate the path lengths in the code there are a few variations, and these are all in "org.lcsim.fit.helicaltrack.HelixUtils.java":


1. In the lcsim HelicalTrackFitter where the actual fit is done we use : public static double PathLength(CircleFit cfit, HelicalTrackHit hit)

2. In general in hps-java we typically use: public static List<Double> PathToXPlane(HelicalTrackFit helix, double x,double smax, int mxint)


Internally both of them compute a couple of helix parameters and then call the *same* function to calculate the path length via:

private static double PathCalc(double xc, double yc, double RC, double x1, double y1, double x2, double y2)

This is all good. However, the d0 convention of the circle fit doesn't seem to be reflected in the formulas in the lcsim HelixUtils? If you look at line 564-570:
-------
   private static double xc(CircleFit cfit) {
       return cfit.xref() + (RC(cfit) - cfit.dca()) * Math.sin(cfit.phi());
   }

   private static double yc(CircleFit cfit) {
       return cfit.yref() - (RC(cfit) - cfit.dca()) * Math.cos(cfit.phi());
   }
-------
you can see that this has the same definition as the "normal L3" sign convention.

I think this can be a problem as all the path lengths that are saved with the HelicalTrackFit (in the member Map "_smap") is done using the circle fitter at the point of the fit (in the HelicalTrackFitter) and is never changed as far as I understand. So this means that if one uses the HelicalTrackFit.PathMap() function the path lengths are calculated with the wrong sign for DCA. I think.

Note that the sign of d0 is flipped only when the HelicalTrackFit is saved from the combination of the circle fit and straight line fit, but again, the path length maps are not updated as far as I can tell.

I implemented a new method in the lcsim HelixUtils that turns the circle fit into a HelicalTrackFit with the correct d0 sign convention and I then I get perfect agreement for the generated and fitted result, not only in track parameters but the residuals look as expected.

This is not exciting stuff but I'd be good if someone can sit down (with me) and help me verify what I'm saying above at some point.

/Pelle

########################################################################
Use REPLY-ALL to reply to list

To unsubscribe from the HPS-SOFTWARE list, click the following link:
https://listserv.slac.stanford.edu/cgi-bin/wa?SUBED1=HPS-SOFTWARE&A=1

Top of Message | Previous Page | Permalink

Advanced Options


Options

Log In

Log In

Get Password

Get Password


Search Archives

Search Archives


Subscribe or Unsubscribe

Subscribe or Unsubscribe


Archives

February 2024
January 2024
December 2023
November 2023
October 2023
September 2023
August 2023
July 2023
June 2023
May 2023
April 2023
March 2023
February 2023
January 2023
December 2022
November 2022
October 2022
September 2022
August 2022
June 2022
April 2022
March 2022
February 2022
January 2022
December 2021
November 2021
October 2021
September 2021
August 2021
July 2021
June 2021
May 2021
April 2021
March 2021
February 2021
January 2021
December 2020
November 2020
October 2020
September 2020
August 2020
July 2020
June 2020
May 2020
April 2020
March 2020
February 2020
January 2020
December 2019
November 2019
October 2019
September 2019
August 2019
July 2019
June 2019
May 2019
April 2019
March 2019
February 2019
January 2019
December 2018
November 2018
October 2018
September 2018
August 2018
July 2018
June 2018
May 2018
April 2018
March 2018
February 2018
January 2018
December 2017
November 2017
October 2017
September 2017
August 2017
July 2017
June 2017
May 2017
April 2017
March 2017
February 2017
January 2017
December 2016
November 2016
October 2016
September 2016
August 2016
July 2016
June 2016
May 2016
April 2016
March 2016
February 2016
January 2016
December 2015
November 2015
October 2015
September 2015
August 2015
July 2015
June 2015
May 2015
April 2015
March 2015
February 2015
January 2015
December 2014
November 2014
October 2014
September 2014
August 2014
July 2014
June 2014
May 2014
April 2014
March 2014
February 2014
January 2014
December 2013
November 2013
October 2013
September 2013
August 2013
July 2013
June 2013
May 2013
April 2013
March 2013
February 2013
January 2013
December 2012
November 2012
October 2012
September 2012
August 2012
July 2012
June 2012
May 2012
April 2012
March 2012
February 2012
January 2012
December 2011
November 2011
October 2011
September 2011
August 2011
July 2011
June 2011
May 2011
April 2011
March 2011

ATOM RSS1 RSS2



LISTSERV.SLAC.STANFORD.EDU

Secured by F-Secure Anti-Virus CataList Email List Search Powered by the LISTSERV Email List Manager

Privacy Notice, Security Notice and Terms of Use