Upgrade of JLab 12 GeV

Deeply Virtual Compton Scattering experiment at  Jefferson Lab Hall B , with CLAS12, large acceptance spectrometer.


Theoretical concepts as Generalized Parton Distributions (GPD), enable to probe with a dramatic accuracy the nucleon structure, and access the quark confinement in hadrons.  

These distributions might be determined through exclusive reactions measurements as DVCS (Deeply Virtual Compton Scattering) and the upgrade in energy of the CEBAF accelerator at Jefferson Lab is also aiming at this goal. The SPhN CLAS group considers these topics as its scientific priority.


DVCS experiments and their kinematic coverages


Elastic scattering experiments enabled in the past to access the nucleon space structure by measuring form factors. Deep inelastic scattering, through parton distribution functions, improved the knowledge about momentum distributions. GPDs are the new tool which will reach the quarks and gluons space distributions inside the nucleons. The DVCS experiments are fit to extract GPDs and the 11 GeV kinematic domain foreseen at JLab is a crucial step forward following the pionneering experiments performed in Hall A and B at JLab, at Hermes and H1.

The  COMPASS collaboration at CERN also prepares an experimental program on the GPDs starting in 2015.


Vertex detector (Micromegas part)

Irfu contribution

 Dapnia is implied in the construction of the vertex detector of the futur CLAS12 spectrometer in Hall B. A tracker equipped with Micromegas detectors will be installed around the target, in the barrel and forward regions. This project gathers teams from Sedi, SIS and SPhN, and fhave been delivered in 2015-2016 of about 4 m² of Micromegas. In parallel, Irfu has been asked by a group from INFN to build another Micromegas tracker, for the detection of electrons at very small angles


Status of the project

The accelerator upgrade is finished. The installation of CLAS12 equipments will take place in 2017, with the aim to start the data taking in 2018.







Jefferson Lab is located in the US,  Newport-News  Virginia, 350 km South East fromWashington DC









Franck SABATIÉ: co-spokesman of an approved CLAS12 DVCS experiment and scientific leader of the CLAS12-Micromegas project



Last update : 12/19 2017 (2264)

More ...
  Deeply Virtual Compton Scattering (DVCS) is the simplest hard exclusive process related to Generalized Parton Distributions (GPDs): the scattering of an electron off a proton through the exchange of a photon of virtuality Q2, accompanied by the re-emission of a real photon. At large Q2 and low transfer t the GPD formalism may be applied.
Transverse Momentum-dependent Distributions (TMD)
  Drell-Yan Process and transverse parton distributions in the nucleon Using a high energy pion beam and a transversally polarized nucleon target, COMPASS is the first experiment  measuring directly  spin dependent Drell-Yan events. The Drell-Yan process (annihilation of a quark and an anti-quark in a lepton pair q qbarà l+ l-) has been used in the past to study simple distributions of quarks in the nucleon.
  Theory and phenomenology studies at LSN are focussed on a better understanding of the quark and gluon structure of hadrons, and of the mechanisms of elementary reactions.


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