84 research outputs found
Beyond Collins and Sivers: further measurements of the target transverse spin-dependent azimuthal asymmetries in semi-inclusive DIS from COMPASS
In semi-inclusive DIS of polarized leptons on a transversely polarized target
eight azimuthal modulations appear in the cross-section. Within QCD parton
model four azimuthal asymmetries can be interpreted at leading order, two of
them being the already measured Collins and Sivers asymmetries. The other two
leading twist asymmetries, related to different transverse momentum dependent
quark distribution functions, and also additional four asymmetries which can be
interpreted as twist-three contributions have been measured for the first time
at COMPASS, using a 160 GeV/c longitudinally polarized ()
muon beam and a transversely polarized target. We present here the
preliminary results from the 2002-2004 data.Comment: Talk given on XV Internetional Workshop on Deep-Inelastic Scattering
and Related Subjects, April 16-20, 2007, Munich, German
Double hadron lepto-production in the current and target fragmentation regions
We study the inclusive production of two hadrons in deep inelastic processes,
l N ---> l h_1 h_2 X, with h_1 in the current fragmentation region (CFR) and
h_2 in the target fragmentation region (TFR). Assuming a factorized scheme, the
recently introduced polarized and transverse momentum dependent fracture
functions couple to the transverse momentum dependent fragmentation functions.
This allows the full exploration of the fracture functions for transversely
polarized quarks. Some particular cases are considered.Comment: 14 pages, 2 figure
The Proton Spin Puzzle and Polarization in Deep--Inelastic Scattering
We point out that measurements of longitudinal polarization in the
target fragmentation region of deep--inelastic and or scattering may test dynamical mechanisms invoked to explain the proton spin
puzzle. A previously-proposed model for polarized pairs in the
proton wave function reproduces successfully the negative
polarization found in the WA59 experiment, and makes
predictions that could be tested in future and experiments.Comment: 16 pages, LaTeX, 9 eps figures uuencoded in separate file,
typographical errors correcte
SIDIS in the target fragmentation region: polarized and transverse momentum dependent fracture functions
The target fragmentation region of semi-inclusive deep inelastic scattering
is described at leading twist, taking beam and target polarizations into
account. The formalism of polarized and transverse-momentum dependent fracture
functions is developed and the observables for some specific processes are
presented.Comment: 18 pages, 2 figures. Some equations modified and text shortened; main
conclusions unchange
Intrinsic Polarized Strangeness and Lambda Polarization in Deep-Inelastic Production
We propose a model for the longitudinal polarization of Lambda baryons
produced in deep-inelastic lepton scattering at any xF, based on static SU(6)
quark-diquark wave functions and polarized intrinsic strangeness in the nucleon
associated with individual valence quarks. Free parameters of the model are
fixed by fitting NOMAD data on the longitudinal polarization of Lambda hyperons
in neutrino collisions. Our model correctly reproduces the observed dependences
of Lambda polarization on the kinematic variables. Within the context of our
model, the NOMAD data imply that the intrinsic strangeness associated with a
valence quark has anticorrelated polarization. We also compare our model
predictions with results from the HERMES and E665 experiments using charged
leptons. Predictions of our model for the COMPASS experiment are also
presented
Studies of Azimuthal Modulations in Two Hadron Fragmentation of a Transversely Polarised Quark
We study the azimuthal modulations of dihadron fragmentation functions
(DiFFs) of a transversely polarised quark using an NJL-jet based model that
incorporates the Collins effect for single hadron emission. The DiFFs are
extracted as Monte Carlo (MC) averages of corresponding multiplicities using
their probabilistic interpretation. To simplify the model and highlight the
possible mechanisms that create this modulation, we choose the elementary
Collins function to be proportional to the elementary unpolarised fragmentation
and a constant probability () for the quark to flip its spin after a
single hadron emission. Moreover, as a leading order calculation, only one of
the produced hadrons in the decay chain of the quark is produced with
elementary Collins modulation. We calculate the dependence of the polarised
DiFFs on various angles such as the azimuthal angle of the single hadron and
the angle of the two hadron production plane for several values of
. We observe that the polarised DiFFs for oppositely charged pion pairs
exhibit a modulation. This effect is induced purely via the
elementary Collins effect and persists even when the quark completely
depolarises after a single hadron emission (). Moreover, similar
sine modulations are present in the distribution of pion pairs with respect to
the azimuthal angle of their total transverse momentum, .Comment: 10 pages, 12 figures - small updates and added references, to comply
with the version to be published in PL
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