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Pages and cover are clean and intact. They vanish in leading twist collinear factorization 4 3. The subtraction terms are computed by convoluting appropriate partonic cross sections with perturbative parton distribution and fragmentation functions relying on the method of mass factorization. In doing so we stress that the photon wavefunctions and dipole cross sections used are precisely those determined in the previous section, without any adjustment of parameters. About this Item: Published for The Skirball Cultural Center Hebrew Union College - Jewish Institute of Religion Californian School by Western States Jewish Historical Association, Los Angeles, 1994. About this Item: Historic Frankfort, 1986. Since the Sivers mechanism involves the transverse momentum of unpolarized quarks in a polarized nucleon a non-zero signal implies non-vanishing orbital angular momenta of the quarks.

Single spin asymmetries Single spin asymmetries are currently under intense investigation from both the experimental and theoretical point of view. About this Item: Published for The Skirball Cultural Center Hebrew Union College - Jewish Institute of Religion Californian School by Western States Jewish Historical Association, Los Angeles, 1993. A detailed discussion of the advantages and drawbacks of the different reactions can be found in Refs. D 7 0 , 074025 2004. The allowed string configurations are those in which each parton index is an element of one of the strings. Apparently this viewpoint was shared by many colleagues and it was therefore not surprising that in response to our invitation everybody who had been invited agreed to come and to present a talk. B o t h B G F and Q C D C depend on as Mz , but the B G F process also depends directly on t h e gluon parton distribution function P D F , whereas Q C D C depends on quark P D F s.

For values of x lower than about 1 0 - 2 F2 is sea-quark dominated and its Q2 dependence is driven by the gluon density. Peterson; Contributor-Raja Parasuraman; Contributor-Mark W. Previously the ratio of di-jet to single-jet cross-sections has been used to extract as. T h u s measuring jet rates Figure 1. He found his models in the farmhouses around Lake Tegernsee. The signature of the Collins Figure 2.

In order to obtain the Collins and Sivers moments in an unbiased way the two sine modulations are extracted simultaneously from the data by fitting the asymmetries in a two dimensional grid of the two azimuthal angles p and s. Airapetian et al , Phys. For the direct cross section we derive the massless limit from the massive theory with the result that this limit differs from the massless version with factorization by finite corrections. The recoiling proton is not detected. For such topics the reader is referred to existing review articles like, e. In the meantime the field has grown tremendously. However, if we are to confront the data at low values of 3, corresponding to large invariant masses mx, it is necessary to also include a contribution from the higher Fock state qqg.

Helicity amplitudes In the handbag diagram, shown on the left hand side in fig. This observation led to the important conclusion that the nucleon cannot be pointlike. Subtracting or adding these corrections allows us to compare the two approaches on equal footing. Here Gp determines the normalization and the W mass entering the formula is the propagator mass M p r o p. Photon radiation off quarks involves a contribution from the quark-to-photon fragmentation function, corresponding to the non-perturbative transition of a hadronic jet into a single, highly energetic photon accompanied by some limited hadronic activity. First results of the azimuthal asymmetries have been reported by the Belle collaboration 7. While for the positive pions we observe a clear positive signal of the order of 0.

The proton and deuteron results are systematically different for both amplitudes of the asymmetry at higher —t bins, which indicates that the asymmetries on protons and neutrons are different. This problem affects also the soft factor appearing in factorization formulae for transverse momentum dependent processes. C h a r 9 e d Current Figure 2. Experimental systematic uncertainties are evaluated by repeating the procedure with the measurement shifted according to each source of systematic uncertainty and theoretical uncertainties are evaluated by repeating the procedure with the predictions shifted according to different theoretical assumptions. Richard Ball: Resummed perturbative evolution at high energy Graham Shaw: Colour dipole phenomenology 2. How to define a conventional shower scheme? Octavo, paper covers, 97-192 pp.

Outlook We can look forward t o improving these P D F fits with more jet d a t a in t h e near future, since the jet d a t a included in the present fit came only from the 96-97 running. See text for explanation on the projections squares,circles. Jet d a t a from the 98-00 running are already becoming available, as described in Sec. Consequently one measures the convolution of the transversity distribution function times the Collins fragmentation function. Now we can define the basis states.

In the handbag diagram this is equivalent to the fact that the helicity of the quark line coupling to the photons does not change. This large value is somewhat surprising as one would expect, due to u-quark dominance, that the negative pions are suppressed similarly as in the longitudinal case. Consequently the theoretical calculations shown in Fig. The value of x at which this occurs is Q2 dependent: as Q2 increases the x value for which jets are well contained increases. About this Item: Published for The Skirball Cultural Center Hebrew Union College - Jewish Institute of Religion Californian School by Western States Jewish Historical Association, Los Angeles, 1994.

However, these d a t a suffer from very large correlated systematic uncertainties from a variety of sources. B 530, 99 2002 J. The signal is positive over the whole measured range. The central values and systematic uncertainties were taken from the published data in each case. About this Item: Published for The Skirball Cultural Center Hebrew Union College - Jewish Institute of Religion Californian School by Western States Jewish Historical Association, Los Angeles, 1994. The chief disadvantage of typical shower Monte Carlo event generators is that they are based on leading order perturbation theory for the basic hard process. About this Item: Published for The Skirball Cultural Center Hebrew Union College - Jewish Institute of Religion Californian School by Western States Jewish Historical Association, Los Angeles, 1997.