COmmon Muon Proton Apparatus for Structure and Spectroscopy

Issue 2015/55-05
Issue 2015/55-02
Issue 2010/09
Issue 46-6
Issue 46-4
Issue 39-7

2006/06 | scan

AMBER/COMPASS++: A new QCD Facility at the M2 beam line of the CERN SPS
Workshop: Beyond 2020
Goldstone nature of the pion confirmed (Press)
Science Ticker: a1(1420) (pdf)
Welt der Physik
SPS experiment NA58 safety


COMPASS is a high-energy physics experiment at the Super Proton Synchrotron (SPS) at CERN  in Geneva, Switzerland. The purpose of this experiment is the study of hadron structure and hadron spectroscopy with high intensity muon and hadron beams. 

On February 1997 the experiment was approved by CERN and the final Memorandum of Understanding was signed in September 1998. The spectrometer was installed in 1999–2000 and commissioned during a technical run in 2001. The physics experiments started in summer 2002 with a muon beam and polarised proton and deuteron targets. These semi-inclusive deep inelastic scattering (SIDIS) experiments reveal details of the quark-gluon structure of the nucleon, in particular the gluon polarisation and transverse-momentum-dependent correlations. After the shutdown in 2005, COMPASS resumed the SIDIS experiments in 2006 and 2007 with a new large-aperture target magnet. The spin structure measurements were continued in 2010 and 2011.

The years 2008 and 2009 were dedicated to the hadron spectroscopy programme with pion and proton beams scattering off a liquid hydrogen target and nuclear targets. An unprecedented amount of data was collected and has allowed for a much refined analysis of the final states, and is still revealing subtle details of the light-meson spectrum. Part of 2009 was dedicated to the study of the pion polarisability using Primakoff scattering of pions from heavy nuclei. This measurement had been prepared by a pilot run in 2004. The programme was continued in 2012 under COMPASS phase-II.

Phase-II of COMPASS is primarily dedicated to the transverse and 3D structure of nucleons using Deeply Virtual Compton scattering (DVCS), Hard Exclusive Meson Production (HEMP), SIDIS and polarised Drell-Yan (DY) reactions. Approved in 2010, it started in 2012 with a Primakoff run and a DVCS pilot run using a muon beam and a long liquid hydrogen target with a huge recoil detector. The first-ever polarised Drell-Yan measurement with a beam of negative pions and a polarised proton target was successfully performed in 2015 and the data taking was resumed in 2018. The years 2016 and 2017 were dedicated to DVCS measurement and simultaneously data on HEMP and SIDIS were collected. For 2021 after long shut-down 3, further measurements of SIDIS off transversely polarised deuterons were approved.

About 200 physicists from 13 countries and 25 institutions work in COMPASS.



Drell-Yan run 2018 (2015, 2014)

Who is who and Responsibilities

GPD run 2017 (2016)


Muon   run 2011 (2010)

Members (COMPASS I)

Hadron run 2012, 2009, 2008, old
  Collaboration Board       Muon   run 2007, 2006, 2004
  Technical Board       An online event display

Home Pages

The M2 beam line
  Summer Students       Electronic logbook (old logbook)
  Compass Phonebook       DAQ
  Mailing & Discussions       COMPASS Wiki
  Election 2019 2017 2015 2013       CDR status
  Visits       DCS
      Beam Monitoring

Artistic view of the 60 m long COMPASS two-stage spectrometer. The two dipole magnets are indicated in red.



  Compass Set-up       Analysis Meetings
  Hadron Calorimeters       Software
  EM Calorimeters       Seminars
  GEM detectors       ELOG logbooks
  Trigger       PUBLICATIONS
  RICH       Publications-all page

RICH Upgrade

  W45       Target Papers
  SM1 Magnet       Theses
  Polarized Target       Talks
  Cedars       Conference Papers
  Compass Gallery       Compass Notes
          Released results
  Transversity       Collaboration Meetings
      Weekly meetings
  Drell-Yan       TB meetings
  Hadron analysis       FE meetings
        Meetings database
  My Mail and More       CERN Map/Buildings
  CERN       Experiments at CERN
  High Energy Physics       CERN Stores
  WWW       Document Server


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