Dihadron fragmentation functions and their relevance for transverse spin studies

Journal of Physics Conference Series 11/2010; 295(1). DOI:10.1088/1742-6596/295/1/012053
Source: arXiv

ABSTRACT Dihadron fragmentation functions describe the probability that a quark
fragments into two hadrons plus other undetected hadrons. In particular, the
so-called interference fragmentation functions describe the azimuthal asymmetry
of the dihadron distribution when the quark is transversely polarized. They can
be used as tools to probe the quark transversity distribution in the nucleon.
Recent studies on unpolarized and polarized dihadron fragmentation functions
are presented, and we discuss their role in giving insights into transverse
spin distributions.

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    ABSTRACT: We reconsider the option of extracting the transversity distribution by using interference fragmentation functions into two leading hadrons inside the same current jet. To this end, we perform a new study of two-hadron fragmentation functions. We derive new positivity bounds on them. We expand the hadron pair system in relative partial waves, so that we can naturally incorporate in a unified formalism specific cases already studied in the literature, such as the fragmentation functions arising from the interference between the s- and p-wave production of two mesons, as well as the production of a spin-one hadron. In particular, our analysis clearly distinguishes two different ways to access the transversity distribution in two-hadron semi-inclusive leptoproduction. Comment: 23 pages, 3 figures
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    ABSTRACT: New results on single spin asymmetries of charged hadrons produced in deep-inelastic scattering of muons on a transversely polarised LiD target are presented. The data were taken in the years 2002, 2003 and 2004 with the COMPASS spectrometer using the muon beam of the CERN SPS at 160 GeV/c. Preliminary results are given for the Sivers asymmetry and for all the three ``quark polarimeters'' presently used in COMPASS to measure the transversity distributions. The Collins and the Sivers asymmetries for charged hadrons turn out to be compatible with zero, within the small (~1%) statistical errors, at variance with the results from HERMES on a transversely polarised proton target. Similar results have been obtained for the two hadron asymmetries and for the Lambda polarisation. First attempts to describe the Collins and the Sivers asymmetries measured by COMPASS and HERMES allow to give a consistent picture of these transverse spin effects.
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    ABSTRACT: We present a model for dihadron fragmentation functions, describing the fragmentation of a quark into two unpolarized hadrons. We tune the parameters of our model to the output of the PYTHIA event generator for two-hadron semi-inclusive production in deep inelastic scattering at HERMES. Once the parameters of the model are fixed, we make predictions for other unknown fragmentation functions and for a single-spin asymmetry in the azimuthal distribution of pi+ pi- pairs in semi-inclusive deep inelastic scattering on a transversely polarized target at HERMES and COMPASS. Such asymmetry could be used to measure the quark transversity distribution function.
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