First measurement of interference fragmentation on a transversely polarized hydrogen target

The HERMES experiment has measured for the first time single target-spin asymmetries in semi-inclusive two-pion production using a transversely polarized hydrogen target. These asymmetries are related to the product of two unknowns, the transversity distribution function and the interference fragmentation function. In the invariant mass range 0.51 GeV < M_inv < 0.97 GeV the measured asymmetry deviates significantly from zero, indicating that two-pion semi-inclusive deep-inelastic scattering can be used to probe transversity.Comment: 6 pages, 6 figures, contribution to the proceedings of the International Workshop on Transverse Polarisation Phenomena in Hard Processes (Transversity 2005), Como, Italy, Sep 7 - 10, 200

Two-hadron single target-spin asymmetries: first measurement by HERMES

Single target-spin asymmetries in semi-inclusive two-pion production were measured for the first time by the HERMES experiment, using a longitudinally polarized deuterium target. These asymmetries relate to the unknown transversity distribution function $h_1(x)$ through, also unknown, interference fragmentation functions. The presented results are compared with a model for the dependence of one of these interference fragmentation functions on the invariant mass of the pion pair.Comment: 4 pages, 4 figures, contribution to the proceedings for the 16th international spin physics symposium (SPIN'2004

Hedging with stock index futures: downside risk versus the variance

In this paper we investigate hedging a stock portfolio with stock index futures.Instead of defining the hedge ratio as the minimum variance hedge ratio, we considerseveral measures of downside risk: the semivariance according to Markowitz [ 19591 andthe various lower partial moments according to Fishburn's [ 1977] alpha-t model (alphaO).Analytically we show that for normal returns and biased futures markets there is an extracost associated with hedging lower partial moments if the minimum variance hedge ratioinstead of the optimal hedge ratio is used. We prove that the extra cost is different fromzero if a is bigger than or equals 1. Furthermore, in case futures markets are positively biased minimum lower partial moment hedge ratios are smallerthan the minimum variance hedge ratio (strictly smaller in case a is bigger than or equals 1).We used the Dutch FTI contract to hedge three Dutch stock market indexes. The in-sample analysis shows that (i) minimum semivariance and minimumvariance hedge ratiosare almost the same in size, (ii) minimum lower partial moment hedge ratios are smallerthan minimum variance hedge ratios (only slightly smaller for a is bigger than or equals 1) and (iii) except for the lower partial moment with a=0.5,hedging downside risk using the minimum variance hedge ratio instead of the optimal hedge ratio is appropriate. For both strategies risk can be reducedin the same proportion whereas the extra cost of using the minimum variance hedge strategy is negligible. In contrast to (iii), out-of-sample result

Final state interactions and hadron quenching in cold nuclear matter

I examine the role of final state interactions in cold nuclear matter in modifying hadron production on nuclear targets with leptonic or hadronic beams. I demonstrate the extent to which available experimental data in electron-nucleus collisions can give direct information on final state effects in hadron-nucleus and nucleus-nucleus collisions. For hadron-nucleus collisions, a theoretical estimate based on a parton energy loss model tested in lepton-nucleus collisions shows a large effect on mid-rapidity hadrons at fixed target experiments. At RHIC energy, the effect is large for negative rapidity hadrons, but mild at midrapidity. This final state cold hadron quenching needs to be taken into account in jet tomographic analysis of the medium created in nucleus-nucleus collisions.Comment: 14 pages, 7 figure

Transversity in two-hadron fragmentation

Steenhoven, G. van der [Promotor]Lapikas, L. [Copromotor