Service d'astrophysique
Laboratoire AIM

Physics case and context

Compass= Common Muon and Proton Apparatus for Structure and Spectroscopy
The COMPASS experimental programme consists in two parts :
- Spin structure of the nucleon : gluon polarization des gluons, transversity, quark polarization...
- Hadron spectroscopy : charmed hadrons, exotic states, glueballs,...

Place:  At CERN SPS accelerator , Geneva

Collaboration: The Compass Collaboration : 28 institutes from 12 countries, (Germany, Italy, France, Russia,...)

 Means of investigation

Spin structure of the Nucleon: a muon beam naturally polarized  (2 10⁸ μ/s,  160 GeV) is scattered on a polarized nucleon target (Li6D or NH3).
Gluon polarization is measured through spin asymmetry of 'photon gluon fusion' events.

A high resolution spectrometer, for high particle flux, has been built to identify and reconstruct the trajectory of outgoing muons, pions and kaons. It has been operating since 2002. It is a two stage spectrometer (for large and small angles). Each stage being equipped with a dipole magnet and particle detectors (scintillating fibers, microstrip detectors- GEMs and Micromegas-, MWPCs, and electromagnetic and hadronic calorimeters. A RICH (Rich Imaging Cerenkov) detector is used to separate pions, kaons and protons.




Spécificities

- Large volume solid polarized target (3 cells of 30, 60 and 30 cm long) in a superconducting solenoid.
- Muons, pion, kaons, protons identification.
- Micromegas detectors- largest size ever built to date 40x40 cm2 active area. High flux, resolution  <90 µm; GEMs detectors 30x30 cm2 high flux, high resolution.
- Drift chambers 1.2x1.2m2 high flux, spatial resolution ~200µm.
- Rich (Rich Imaging Cerenkov)
- Data Acquisition System ( > 300 megabytes per 16.8s cycle).

Dapnia Contribution

Technical responsibilities since 2002:

- Conception, realization  12 Micromégas microstrip detectors 40x40 cm², High flux (450 kHz) rspatial resolution: 70um at low  flux, 90um at high  flux, time resolution 9ns.
- conception, realisation of associated FE electronics (12000 channels), including conception of chip ampli-discri SFE16.
- realization  of 3 Drift Chambers  1.2x1.2 m² (8 planes per detector, high flux, spatial resolution ~200um) and FE electronics ( Amplis ASD8 + TDC F1).
- commissionning of  'old' SMC superconducting solenoid , and operation from 2001 to 2004
- development of tracking software
- developement of software for analytical error calculations in order to optimize detector geometry.

SCIENTIFIC RESPONSABILITIES OF THE GROUP

- spokesperson of the collaboration 02/2003 to 02/2009.
- run coordination  (2002, 2003, 2006 and 2007).
- physics analysis coordination 10/1999 to 06/2001.
- technical coordination  (07/2003-07/2006).
- publication committee  (07/2001-12/2007).

RECENT TECHNICAL DEVELOPMENTS for 2006 run and after:

- Large aperture target magnet solénoide supra cold tests, repair and instrumentation (see specific project)
-  Large drift chamber 2x2 m2 (8 planes) adaptée à l'ouverture du nouvel aimant Compass.
- new FE electronics APV: 60000 channels for  RICH chambers
- remake of Micromegas with amagnetic copper grids

Contact:

Fabienne KUNNE