Misalignment
Page maintainer: Caro
 |
Important note: This page has not yet been reviewed by an expert! Use the information below with caution.
Other pages that have not been reviewed yet can be found in the category FORREVIEW. |
Inhaltsverzeichnis
- 1 Intro
- 2 Essentials
- 2.1 MC productions with misalignment "switched on (off)"
- 2.2 New alignment from last detector survey
- 2.3 Systematic uncertainty due to misalignment in the inclusive and Fehler beim Parsen (MathML mit SVG- oder PNG-Rückgriff (empfohlen für moderne Browser und Barrierefreiheitswerkzeuge): Ungültige Antwort („Math extension cannot connect to Restbase.“) von Server „https://wikimedia.org/api/rest_v1/“:): {\displaystyle b_1} analyses
- 2.4 Systematic uncertainty due to misalignment in the exclusive analyses
- 2.5 Other tests people do
- 3 More Info
- 4 Code Repository
Intro
If the detector positions differ from their ideal places, an error is introduced into the track reconstruction, i.e. momentum, angles and vertices potentially come out wrongly.
For the past few years, the misalignment of the Hermes spectrometer and the beam has been simulated in "misaligned" Monte-Carlo productions. The extent of the detector misalignment has been obtained from a study of electromagnetic showers from the detector frames (aka "Hermes-effect"). The systematic uncertainties of the asymmetries, amplitudes etc. measured by Hermes which are introduced by the misalignment can be estimated with the help of such MC productions.
New data productions (in fact all productions after and including 07c1) are produced with the new alignment file from Alexander's last survey of the detector elements with the idea of minimizing effects of misalignment in the track reconstruction.
Essentials
MC productions with misalignment "switched on (off)"
Need description of exact combination of (mis)aligned geometry file on GMC and HRC level to get (mis)aligned MC. Detector as one piece misaligned or individual part. NEEDEXPERT:Elke
- There are several misaligned MC Productions available, see e.g. [20].
New alignment from last detector survey
- Don't need misali studies with new alignment? (new htc tracking)
- Comment: when one compares in one of the new productions (e.g. 07c1) the HTC and HRC (in save table) results, one should keep in mind that the track SEARCH is the same in HRC and HTC (i.e. based on the same alignment file), only the track FIT is new in HTC. No huge differences between HRC and HTC are expected within the same production. It will be interesting to compare the old and new 2004 production once it is available. See also Tracking Corrections.
Systematic uncertainty due to misalignment in the inclusive and Fehler beim Parsen (MathML mit SVG- oder PNG-Rückgriff (empfohlen für moderne Browser und Barrierefreiheitswerkzeuge): Ungültige Antwort („Math extension cannot connect to Restbase.“) von Server „https://wikimedia.org/api/rest_v1/“:): {\displaystyle b_1} analyses
The inclusive asymmetries Fehler beim Parsen (MathML mit SVG- oder PNG-Rückgriff (empfohlen für moderne Browser und Barrierefreiheitswerkzeuge): Ungültige Antwort („Math extension cannot connect to Restbase.“) von Server „https://wikimedia.org/api/rest_v1/“:): {\displaystyle A_{\_}}
and Fehler beim Parsen (MathML mit SVG- oder PNG-Rückgriff (empfohlen für moderne Browser und Barrierefreiheitswerkzeuge): Ungültige Antwort („Math extension cannot connect to Restbase.“) von Server „https://wikimedia.org/api/rest_v1/“:): {\displaystyle \left.A_{zz}\right.}
were corrected for kinematic bin migrations due to detector smearing and QED radiative effects (see Unfolding of Detector Smearing and QED Radiative Effects). Also misalignment of the detector and the beam causes kinematic bin migrations, but to correct by unfolding for detector misalignment is not considered to be the right procedure because the misalignment doesn't produce a statistically distributed bin misidentification, rather it shifts events systematically. This causes a blow-up of the statistical error (main diagonal of covariance matrix) when one tries to unfold the measured asymmetry with a misaligned MC because the unfolding algorithm doesn't correct for the effective bin migration, but it punishes migration into and out of a given bin.
In principle, one could correct for the misalignment by a track-by-track algorithm. Without such an algorithm, rather the difference (misaligned-aligned) of the reconstructed MC asymmetries was chosen to be assigned as systematic uncertainty, both asymmetries unfolded with a perfectly aligned MC. In such a way, one accounts exactly for what is being done wrongly in the experimentally extracted asymmetries.
Further reading: G1/b1 page
Systematic uncertainty due to misalignment in the exclusive analyses
For the DVCS and other exclusive analyses, the effect of the misalignment and the beam is not studied as a stand-alone effect, but in the context of at the same time (detector) smearing, Hermes acceptance and bin width, resulting in the "4-in-1" systematic uncertainty in DVCS.