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" $\Lambda$ 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 $x$- and in $z$-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 $\Lambda$ polarisation in the reaction $\mu N \rightarrow \mu' \Lambda X$. 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

Work on the interplay among h+h^+, h−h^{-} 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 $\mu N \rightarrow \mu ' h^{+} h^{-} X$. 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

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

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

Phenomenological Extraction of Transversity from COMPASS SIDIS and Belle e+e- Data

The valence transversity distributions of the u- and the d-quarks have been extracted point-by-point from single-hadron production and dihadron production data measured in semi-inclusive deep inelastic scattering and in e+e annihilation. The extraction is based on some simple assumptions and does not require any parametrization. The transversity distributions are found to be compatible with each other and with previous analyses

Extraction of Transversity from COMPASS and Belle Data

The valence transversity distributions of the u- and the d-quarks have been extracted point-by-point from single-hadron production and dihadron production data measured in semi-inclusive deep inelastic scattering and in [Formula: see text] annihilation. The transversity distributions are found to be compatible with each other and with previous analyses

Long term experience with CsI photocathodes in gas photon detectors

RICH-1 is a Cherenkov Imaging detector in operation at the COMPASS experiment at CERN SPS since 2001. MWPCs equipped with CsI photocathodes have been used as photon detectors, for the full detection area in the first years of operation, and for 75% of the area after a detector upgrade in 2006. The mean number of detected photons per particle has been extracted from the data collected during six years of COMPASS data taking. An indirect measurement of possible variations of the CsI quantum efficiency versus time is obtained from this analysis