1,189 research outputs found
Recent COMPASS results on Transverse Spin Asymmetries in SIDIS
After reviewing the most important COMPASS results on transverse spin effects
in SIDIS, I will present the recent work we have done on weighted Sivers
asymmetries and "transversity induced" polarisation. Using the high
statistics data collected in 2010 on a transversely polarised proton target
COMPASS has evaluated the transverse momentum weighted Sivers asymmetries both
in - and in -bins. The results are also compared with the standard
unweighted asymmetries. Using the whole data sample collected over the years on
transversely polarised deuteron and proton targets COMPASS has measured the
transversity induced polarisation in the reaction . Possible future SIDIS COMPASS measurements will also be
briefly mentioned.Comment: 8 pages, 7 figures, proceedings of the XVII Workshop on High Energy
spin Physics DSPIN-17 Dubna, Russia, September 11 - 15, 201
The future SIDIS measurement on transversely polarized deuterons by the COMPASS Collaboration
Since 2005, measurements of Collins and Sivers asymmetries from the HERMES
and COMPASS experiments have allowed to assess that the transversity and the
Sivers PDFs are different from zero and measurable in semi-inclusive DIS on
transversely polarised targets. Most of the data were collected on proton
targets, only small event samples were collected in the early phase of the
COMPASS experiment on a deuteron (LiD) target and more recently at JLab, on
He, so that the -quark and the sea-quarks PDFs are much more poorly
known than the -quark PDFs. This constitutes an important limitation to the
knowledge of the transverse spin structure of the nucleon. For this reason the
COMPASS Collaboration has proposed to measure semi-inclusive DIS on
transversely polarised deuterons with good accuracy, comparable with that of
the existing transverse spin asymmetry data on protons. The proposal has been
accepted by CERN and the experiment will run in 2021, as soon as the Long
Shut-down 2 is over, providing measurements which will stay unique for many
years to come. Projections will be given for the extraction of the transversity
PDFs, and for the evaluation of the isovector tensor charge of the nucleon.Comment: 9 pages, 5 figure and 2 table
Work on the interplay among , and hadron pair transverse spin asymmetries in SIDIS
In the fragmentation of a transversely polarized quark a left-right
asymmetry, the Collins asymmetry, is expected for each hadron produced in the
process . Similarly, an asymmetry is
also expected for the hadron pair, the dihadron asymmetry. Both asymmetries
have been measured to be different from zero on transversely polarised proton
targets and have allowed for first extractions of the transversity
distributions. From the high statistics COMPASS data we have further
investigated these asymmetries getting strong indications that the two
mechanisms are driven by a common physical process.Comment: 6 pages, 4 figure
Transverse spin and transverse momentum structure of the nucleon from the COMPASS experiment
A selection is presented of recent results from the COMPASS Collaboration on
transverse spin and transverse momentum effects in semi-inclusive deeply
inelastic scattering (SIDIS) of 160 GeV/c muons off proton and deuteron
targets.Comment: 10 pages, 6 figures, proceedings of the invited talk at the XV
Workshop on High Energy Spin Physics DSPIN-13, Dubna, Russia, October 8-12,
201
Single hadron transverse spin asymmetries from COMPASS
Transverse spin physics is an important part of the scientific programme of
the COMPASS experiment at CERN. The analysis of the data taken with the target
polarized orthogonally to the 160 GeV/c muon beam momentum has allowed to
measure for the first time the Collins and Sivers asymmetries of the deuteron.
Both for the positive and the negative hadrons produced in semi-inclusive DIS
the measured asymmetries are small and, within errors, compatible with zero.
New results for charged pions and kaons are presented here.Comment: To be published in Proceedings of 17th International Spin Physics
Symposium (SPIN06), 2-7 October 2006, Kyoto, Japa
Why there is no crisis of the "spin crisis"
In a recent eprint [1] it is argued that the experimental determinations of
the spin-dependent structure function g1 have been done incorrectly and that a
reanalysis of those data suggests that the original motivation to argue fora
"spin crisis", namely the small contribution of quark spins to the nucleon
spin, is invalid. In a subsequent note [2] the theoretical understanding, as it
has evolved from almost 30 years of theoretical and experimental scrutiny, has
been shortly summarised. In this short note, arguments are presented that the
line of reasoning in Ref. [1] does not apply, at least not for the Compass
data.Comment: 2 pages, no figure
Transverse-Spin and Transverse-Momentum Effects in High-Energy Processes
The state of the art concerning transverse-spin and transverse-momentum
phenomena in hard hadronic reactions is reviewed. An account is given of
single-spin and azimuthal asymmetries in semiinclusive deep inelastic
scattering, e^+ e^- annihilation, Drell-Yan production, and hadroproduction.
The ongoing experiments and the main theoretical frameworks are described in
the first part of the paper. The second part is devoted to the experimental
findings and their phenomenological interpretations. A brief discussion of the
perspectives of future measurements is finally presented.Comment: 95 page
Extracting the transversity distributions from single-hadron and dihadron production
We present a point-by-point determination of the valence transversity
distributions from two different types of processes: single-hadron production
and dihadron production, both in semi-inclusive deep inelastic scattering and
e+e- annihilation. The extraction is based on some simple assumptions and does
not require any parametrization. The transversity distributions obtained from
Collins effect in single-hadron production and from interference effects in
dihadron production are found to be compatible with each other.Comment: 16 pages, 7 figures; added reference
The spin structure of the nucleon: A phenomenological introduction
Abstract The investigation of the spin structure of the nucleon via semi-inclusive deep inelastic scattering on polarised nucleons is updated with the most recent results of the JLab, HERMES, and COMPASS experiments. A short description is given of these experiments, which are complementary in phase space and use sophisticated and different techniques to polarise the nucleon targets. The cases of target spin parallel or orthogonal to the direction of the incoming lepton require different experimental techniques, have a different phenomenology and need a different theoretical treatment. After reviewing these differences, the most recent transverse spin advances are presented, and evidence is given that the new data already allow for a rather precise extraction of the transversity and of the Sivers PDFs
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