HLT1 Reconstruction algorithms
Velo clusters
Format needed by one RawEvent for masked clustering code:
-----------------------------------------------------------------------------
name | type | size | array_size
=============================================================================
number_of_rawbanks | uint32_t | 1
-----------------------------------------------------------------------------
raw_bank_offset | uint32_t | number_of_rawbanks
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
sensor_index | uint32_t | 1 |
------------------------------------------------------------------------------
count | uint32_t | 1 | number_of_rawbanks
------------------------------------------------------------------------------
word | uint32_t | count |
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++x
raw_bank_offset: array containing the offsets to each raw bank, this array is currently filled when running Brunel to create this output; it is needed to process several raw banks in parallel
sp = super pixel
word: contains super pixel address and 8 bit hit pattern
Velo tracks
Primary vertices
Velo-UT tracks
To configure the number of candidates to search for go to CompassUTDefinitions.cuh and change:
constexpr unsigned max_considered_before_found = 4;
A higher number considers more candidates but takes more time. It saves the best found candidate.
Standalone UT tracks
Standalone SciFi tracks (seeding)
Short Introduction in geometry
The SciFi Tracker Detector, or simple Fibre Tracker (FT) consits out of 3 stations. Each station consists out of 4 planes/layers. Thus there are in total 12 layers, in which a particle can leave a hit. The reasonable maximum number of hits a track can have is thus also 12 (sometimes 2 hits per layer are picked up).
Each layer consists out of several Fibre mats. A fibre has a diameter of below a mm.(FIXME) Several fibres are glued alongside each other to form a mat. A Scintilating Fibre produces light, if a particle traverses. This light is then detected on the outside of the Fibre mat.
Looking from the collision point, one (X-)layer looks like the following:
y 6m
^ ||||||||||||| Upper side
| ||||||||||||| 2.5m
| |||||||||||||
-|--||||||o||||||----> -x
|||||||||||||
||||||||||||| Lower side
||||||||||||| 2.5m
All fibres are aranged parallel to the y-axis. There are three different kinds of layers, denoted by X,U,V. The U/V layers are rotated with respect to the X-layers by +/- 5 degrees, to also get a handle of the y position of the particle. As due to the magnetic field particles are only deflected in x-direction, this configuration offers the best resolution. The layer structure in the FT is XUVX-XUVX-XUVX.
The detector is divided into an upeer and a lower side (>/< y=0). As particles are only deflected in x direction there are only very(!) few particles that go from the lower to the upper side, or vice versa. The reconstruction algorithm can therefore be split into two independent steps: First track reconstruction for tracks in the upper side, and afterwards for tracks in the lower side.
Due to construction issues this is NOT true for U/V layers. In these layers the complete(!) fibre modules are rotated, producing a zic-zac pattern at y=0, also called “the triangles”. Therefore for U/V layers it must be explicetly also searched for these hit on the “other side”, if the track is close to y=0. Sketch (rotation exagerated!):
_.*
y ^ _.* _.*
| .*._ Upper side _.*._
| *._ _.* *._
|--------*._ _.* *._----------------> x
| *._ _.* *._ _.*
*._.* Lower side *._.*
Zone ordering:
y ^
| 1 3 5 7 9 11 13 15 17 19 21 23
| | | | | | | | | | | | |
| x u v x x u v x x u v x <-- type of layer
| | | | | | | | | | | | |
|------------------------------------------------> z
| | | | | | | | | | | | |
| | | | | | | | | | | | |
| 0 2 4 6 8 10 12 14 16 18 20 22
Velo-UT-SciFi tracks
With Looking forward algorithm
A detailed introduction in Forward tracking (with real pictures!) can be found here: