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M. Anselmino

Publications and source records attributed to M. Anselmino.

At least 109 records · Page 6Linked to original sources
arXiv1999

Predictions for single spin asymmetries in lepton + p(transv. polarized) -> pion + X and gamma^* + p(transv. polarized) -> pion + X

Predictions for the single transverse spin asymmetry A_N in semi-inclusive DIS processes are given; non negligible values of A_N may arise from spin effects in the fragmentation of a polarized quark into a final hadron with a transverse momentum k_T with respect to the jet axis, the so-called Collins effect. The elementary single spin asymmetry of the fragmenting quark has been fixed in a previous paper, by fitting data on p(transv. polarized) + P -> pion + X, and the predictions given here are uniquely based on the assumption that the Collins effect is the only cause of the observed single spin asymmetries in p(transv. polarized) + p -> pion + X. Eventual spin and k_T dependences in quark distribution functions, the so-called Sivers effect, are also discussed.

hep-ph↗
arXiv1999

Single transverse spin asymmetries in inclusive hadron production

A consistent phenomenological approach to the computation of transverse single spin asymmetries in inclusive hadron production is presented, based on the assumed generalization of the QCD factorization theorem to the case in which quark intrinsic motion is taken into account. New k_T and spin dependent quark distribution and fragmentation functions are considered: some of them are fixed by fitting data on p(transv. polarized) + p -> pion + X and predictions are given for single spin asymmetries in l + p(transv. polarized) -> pion + X and gamma^* + p(transv. polarized) -> pion + X processes.

hep-ph↗
arXiv1999

Off-diagonal helicity density matrix elements for vector mesons produced in polarized e+e- processes

Final state quark-antiquark interactions give origin to non zero values of the off-diagonal element rho_{1,-1} of the helicity density matrix of vector mesons produced in e+e- annihilations, as confirmed by recent OPAL data on Phi, D^* and K^*'s. New predictions are given for rho_{1,-1} of several mesons produced at large x_E and small p_T -- i.e. collinear with the parent jet -- in the annihilation of polarized e+ and e-; the results depend strongly on the elementary dynamics and allow further non trivial tests of the Standard Model.

hep-ph↗
arXiv1998

Quark fragmentation and off-diagonal helicity density matrix elements for vector meson production

As confirmed by some recent LEP data on phi, K^* and D^*0 production, final state interactions in quark fragmentation may give origin to non-zero values of the off-diagonal element rho_{1,-1} of the helicity density matrix of vector mesons produced in e^+ e^- annihilations: we give estimates for rho_{1,-1} of vector mesons with a large x_E and collinear with the parent jet, relating its size and sign to the associated hard constituent dynamics. We mention possible non-zero values of rho_{1,-1} in several other processes.

hep-ph↗
arXiv1998

Single spin asymmetries in polarized proton-proton, polarized antiproton-proton inclusive processes

Single spin asymmetries in polarized proton(antiproton) + proton -> pion + X have been measured to be large. They can be understood within perturbative QCD by introducing new k_perp and spin dependences in fragmentation and/or distribution functions. We discuss first how these effects in distribution functions alone can account for existing data and predict single spin asymmetries in other processes; then we see how similar effects in fragmentation functions alone can fit the existing data; finally we devise strategies to discriminate between the two contributions

hep-ph↗
arXiv1998

Off-diagonal helicity density matrix elements for heavy vector mesons inclusively produced in N-N, gamma-N, l-N interactions

Final state interactions in quark fragmentation may give origin to non zero values of the off-diagonal element rho_(1,-1) of the helicity density matrix of vector mesons V produced in current jets, with a large energy fraction x_E; the value of rho_(1,-1)(V) is related to the hard constituent dynamics and tests unusual properties of it. Some recent data on phi, K^* and D^* produced in e^+ e^- annihilations at LEP show such effects. Predictions are given here for rho_(1,-1) of heavy mesons produced in nucleon-nucleon, gamma-nucleon and lepton-nucleon interactions.

hep-ph↗
arXiv1997

Quark fragmentation into vector and pseudoscalar mesons at LEP

Some data on the ratio of vector to vector + pseudoscalar mesons, V/(V+P), and the probability of helicity zero vector states, rho_00, are now available from LEP. A possible relation between these two quantities and their interpretation in terms of polarized fragmentation functions are discussed; numerical estimates are given for the relative occupancies of K and K*, D and D*, B and B* states.

hep-ph↗
arXiv1997

Single spin asymmetries in DIS

We consider possible mechanisms for single spin asymmetries in inclusive Deep Inelastic Scattering (DIS) processes with unpolarized leptons and transversely polarized nucleons. Tests for the effects of non-zero $\bfk_\perp$, for the properties of spin dependent quark fragmentations and for quark helicity conservation are suggested.

hep-ph↗
arXiv1996

Single Spin Asymmetries in Inclusive Hadron Production

We consider a general formalism, previously developed to describe single spin asymmetries (SSA) in inclusive particle production at moderately large $p_T$ in hadron-hadron high-energy processes. In this approach SSA can originate from non perturbative, universal, quark distribution analyzing powers, provided the quark intrinsic motion is taken into account. A fit of the available data on $p^\uparrow p \to πX$ fixes simplified phenomenological expressions of these quark analyzing powers for the dominant (at large $x_F$) $u$ and $d$ quark contributions. We use the results of the fit as input to provide a possible scenario for SSA in a number of interesting processes (e.g. $p p \to γX$, $p p \to K X$) for which experimental results are or will soon be available.

hep-ph↗
arXiv1996

Spin Measurements in lp -> hX Deep Inelastic Scattering

The production of hadrons in polarized lepton-nucleon deep inelastic scattering is discussed. The helicity density matrix of the hadron is computed within the QCD hard scattering formalism and its elements are shown to yield information on the spin structure of the nucleon and the spin dependence of the quark fragmentation process. The case of $ρ$ vector mesons is considered in more detail and estimates are given.

hep-ph↗
arXiv1996

On the Physics Potential of Polarized Nucleon-Nucleon Collisions at HERA

The physics of polarized nucleon--nucleon collisions originating from an internal polarized target in the HERA proton beam is investigated. Based on 240 pb^-1 integrated luminosity at 40 GeV c.m. energy, statistical sensitivities are given over a wide (x_F, p_T) range for a variety of inclusive and exclusive final states. By measuring single spin asymmetries unique information can be obtained on higher twist contributions and their p_T-dependence. From double spin asymmetries in both photon and J/psi production it appears possible to measure the polarized gluon distribution in the range 0.1<x_gluon<0.4 with a good statistical accuracy.

hep-ph↗
arXiv1996

New proton polarized structure functions in charged current processes at HERA

Estimates for longitudinal spin asymmetries which single out new polarized nucleon structure functions in deeply inelastic charged current interactions at HERA energies are given, exploiting their interpretation in terms of polarized quark distributions. These asymmetries turn out to be large and allow a measurement of the new polarized structure functions $g_1^{W}$ and $g_5^{W}$, which would add valuable tests and information on the spin content of quarks inside a polarized proton. We also show that single spin asymmetries in neutral current interactions are very small.

hep-ph↗
arXiv1995

Polarized inclusive leptoproduction, $\ell N \to hX$, and the hadron helicity density matrix, $ρ(h)$: possible measurements and predictions

We discuss the production of hadrons in polarized lepton nucleon interactions and in the current jet fragmentation region; using the QCD hard scattering formalism we compute the helicity density matrix of the hadron and show how its elements, when measurable, can give information on the spin structure of the nucleon and the spin dependence of the quark fragmentation process. The cases of $ρ$ vector mesons and $Λ$ baryons are considered in more details and, within simplifying assumptions, some estimates are given.

hep-ph↗
arXiv1995

Single spin asymmetry for $p^{\uparrow}p \to πX$ in perturbative QCD

Within the QCD-improved parton model and assuming the factorization theorem to hold in the helicity basis and for higher twist contributions, we show how non zero single spin asymmetries in hadron-hadron high energy and moderately large $p_T$ inclusive processes can be obtained, even in massless perturbative QCD, provided the quark intrinsic motion is taken into account. A simple model is constructed which reproduces the main features of the data on the single spin asymmetry observed in inclusive pion production in $p\,p$ collisions.

hep-ph↗
arXiv1994

Polarized deep inelastic scattering at high energies and parity violating structure functions

A comprehensive analysis of deep inelastic scattering of polarized charged leptons on polarized nucleons is presented; weak interaction contributions, both in neutral and charged current processes, are taken into account and the parity violating polarized nucleon structure functions are studied. Possible ways of their measurements and their interpretations in the parton model are discussed.

hep-ph↗