DELPHI Inner Detector (ID)
The Inner Detector (ID) is a tracking and triggering detector.
It consists of two parts:
the JET chamber and the Trigger Layers (TL).
The JET chamber is a driftchamber, subdivided into 24 sectors of 15 degrees
in phi. Each sector consists of 24 sense wires,
The driftgas used is CO2 with a small admixture of Isobutane. This together
with the special shaping of the driftfield, makes that for >1.0 GeV
tracks coming from the interactionpoint, all 24 signals on the sense wires
arrive more or less at the same time.
The TL consist of 5 cylindrical layers of 192 Straw tubes. The tubes
in subsequent planes are staggered by half a cell.
The cell width is about 8 mm. Pulse heights are measured, and drift times.
Full angular coverage is down to 15 (165) degrees in theta.
It looks like (here with a Z0 in it!)
For each event, 3 types of information are produced :
- The JET chamber measures up to 24 R*PHI points on a track.
- The TL measure up to 5 points in R*PHI.
- trigger : see below.
- JET: the single wire resolution is of the order of 90 microns. Combined
into a TE and after careful calibration and 'fixing', the TE resolution
is of the order of 40 microns in R*PHI and about 1.2 mrad in the angle phi.
The 2-track separation is of the order of 1 mm.
- TL: the R*PHI measurement is used in the trigger and to provide an
R*PHI TE of approx. 150 micron resolution. It therefore also resolves
the left/right ambiguity in the JET chamber.
Dedicated electronics is used to produce the local trigger
results for the first and second level. ID trigger data are correlated
with the OD ones in order to reduce the rate due to cosmic and beam gas
events. The third level is done by software. The IDOD trigger is
very useful to cover the cracks between the TPC sectors.
- T1: The signals on the 5 (staggered) tubes of the TL are used in a
track-finding chip to define a track pointing roughly to the interaction
point. The OR of a group of 8 (times 5) tubes defines a trigger bit per
'sector'. The OR of all 24 sectors is the first level trigger ID used in DF4_I.
The majority (>12) coincidence of the 24 wire signals in a JET sector defines
a JET trigger bit per sector. The TL bit can be hardware ANDed with the
corresponding bit from the Jet and defines an ID bit for sector i. This bit
is then ANDed with the OR of the three OD sectors i-1, i, i+1. It is this
ID.AND.OD for the 6 sectors covering the TPC sector gaps that is used in
IDOD6 at the 2nd level trigger. The OR of the 24 TL bits forms the IDMJ1
trigger which is used at several places in DELPHI in coincidence with other
- T2: No special T2 trigger is being made. The T1 part ID.AND.OD for the
6 sectors covering the TPC sector gaps is used in the socalled IDOD6.
- T3: The basis of the T3 is a fast track search using histogramming of the
drifttimes on the 24 wires in a JET sector, thus mimicing the hardware
majority coincidence of T1. But now the average drifttime defines a rough
PHI coordinate. This track candidate has then to be confirmed in space
by a track found in the trigger chips of the TL. The output of the T3 is
not only a bit per sector, but also the PHI of the track (resolution about
1 degree, corresponding to about 3 mm in R*PHI).