Speaker
Ana Sofia Nunes
(LIP Laboratorio de Instrumentacao e Fisica Experimental de Part)
Description
The COMPASS experiment at CERN has collected
a large sample of about 700 million events of
quasi-real photoproduction in polarised μ+-p
scattering using a beam momentum of 160
(GeV/c)2 in 2007 and 200 (GeV/c)2 in 2011.
The events have a Bjorken scaling variable in
the range 0.00004<x<0.04
and a four-momentum transfer squared in the range
0.001<Q2<1 (GeV/c)2.
They allow the most accurate determination to date
of the longitudinal double spin asymmetry A1p
and of the spin-dependent structure function g1p
of the proton in the region of low x and low Q2.
These data complement our data for a polarised
deuteron target. They have an order of magnitude
better precision than the previous SMC results.
The preliminary results yield non-zero, positive
asymmetries A1p and structure function g1p
in the full studied ranges of x and ν, the virtual
photon energy. It is the first time that spin effects
are observed at such low x.
Primary author
Ana Sofia Nunes
(LIP Laboratorio de Instrumentacao e Fisica Experimental de Part)
