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M. Boglione

Publications and source records attributed to M. Boglione.

At least 91 records · Page 5Linked to original sources
arXiv2004

Parton intrinsic motion: suppression of the Collins mechanism for transverse single spin asymmetries in p(transv. polarised) p --> pion + X

We consider a general formalism to compute inclusive polarised and unpolarised cross sections within pQCD and the factorisation scheme, taking into account parton intrinsic motion in distribution and fragmentation functions, as well as in the elementary dynamics. Surprisingly, the intrinsic partonic motion, with all the correct azimuthal angular dependences, produces a strong suppression of the transverse single spin asymmetry arising from the Collins mechanism. As a consequence, and in contradiction with earlier claims, the Collins mechanism is unable to explain the large asymmetries found in p(transv. polarised) p --> pion + X at moderate to large Feynman x_F. The Sivers effect is not suppressed.

hep-ph↗
arXiv2004

Accessing Sivers gluon distribution via transverse single spin asymmetries in p(transv. polarized) p --> D X processes at RHIC

The production of D mesons in the scattering of transversely polarized protons off unpolarized protons at RHIC offers a clear opportunity to gain information on the Sivers gluon distribution function. D production at intermediate rapidity values is dominated by the elementary g g --> c cbar channel; contributions from q qbar --> c cbar s-channel become important only at very large values of x_F. In both processes there is no single spin transfer, so that the final c or cbar quarks are not polarized. Therefore, any transverse single spin asymmetry observed for D's produced in p(transv. polarized) p interactions cannot originate from the Collins fragmentation mechanism, but only from the Sivers effect in the distribution functions. In particular, any sizeable spin asymmetry measured in p(transv. polarized) p --> D X at mid-rapidity values will be a direct indication of a non zero Sivers gluon distribution function. We study the p(transv. polarized) p --> D X process including intrinsic transverse motion in the parton distribution and fragmentation functions and in the elementary dynamics, and show how results from RHIC could allow a measurement of the Sivers gluon distribution function.

hep-ph↗
arXiv2003

Towards a model independent determination of the phi -> f_0 - gamma coupling

A guide to the composition of the enigmatic f_0(980) and a_0(980) states is their formation in phi-radiative decays. Precision data are becoming available from the KLOE experiment at the DAPHNE machine at Frascati, as well as results from SND and CMD-2 at VEPP-2M at Novosibirsk. We show how the coupling of the f_0(980) to this channel can be extracted from these, independently of the background provided by sigma production. To do this we use the fact that the behaviour of both the f_0(980) and sigma cannot be determined by these data alone, but is strongly constrained by experimental results from other hadronic processes as required by unitarity. We find that the resulting coupling for the phi -> gamma f_0(980) is about 10^{-4} GeV with a background that is quite unlike that assumed if unitarity is neglected. This provides an object lesson in how unitarity teaches us to add resonances. Not surprisingly the result is crucially dependent on the pole position of the f_0(980), for which there are still sizeable uncertainties. At present this leads to an uncertainty in the phi -> f_0 gamma branching ratio which can only be fixed by further precision data on the f_0(980).

hep-ph↗
arXiv2002

Dynamical Generation of Scalar Mesons

Starting with just one bare seed for each member of a scalar nonet, we investigate when it is possible to generate more than one hadronic state for each set of quantum numbers. In the framework of a simple model, we find that in the I=1 sector it is possible to generate two physical states with the right features to be identified with the a_0(980) and the a_0(1450). In the I=1/2 sector, we can generate a number of physical states with masses higher than 1 GeV, including one with the right features to be associated with the K_0^*(1470), but none which can be identified with the light kappa scalar meson. The I=0 sector is the most complicated and elusive: since all outcomes are very strongly model dependent, we cannot draw any robust conclusion. Nevertheless, we find that in that case too, depending on the coupling scheme adopted, the occurrence of numerous states can be achieved. This shows that dynamical generation of physical states is a possible solution to the problem of accounting for more scalar mesons than can fit in a single nonet, as experiments clearly deliver.

hep-ph↗
arXiv2001

Origins of single transverse spin asymmetries

Single transverse spin asymmetries in p-p -> pion + X and l-p -> l-pion + X processes have been observed; their possible origins and connections are investigated. A phenomenological description within a pQCD generalized factorization scheme is discussed.

hep-ph↗
arXiv2001

Longitudinal Lambda polarization in polarized semi-inclusive DIS

We calculate, within pQCD parton model at leading orders, the expression of the longitudinal polarization of Lambda baryons produced in polarized semi-inclusive DIS, including weak interaction effects. We present some numerical estimates in few cases for which data are or will soon be available and discuss how to gather new information on polarized fragmentation functions.

hep-ph↗
arXiv2001

Weak interactions in polarized semi-inclusive DIS

We calculate, within pQCD parton model at leading orders, the expression of the polarization P of spin 1/2 hadrons (typically Lambda baryons), produced in polarized semi-inclusive DIS in all possible cases in which weak interactions are involved. We discuss how to gather new information on fragmentation and distribution functions and give numerical estimates in the cases for which data are or will soon be available.

hep-ph↗
arXiv2001

Physics at the front-end of a neutrino factory: a quantitative appraisal

We present a quantitative appraisal of the physics potential for neutrino experiments at the front-end of a muon storage ring. We estimate the forseeable accuracy in the determination of several interesting observables, and explore the consequences of these measurements. We discuss the extraction of individual quark and antiquark densities from polarized and unpolarized deep-inelastic scattering. In particular we study the implications for the undertanding of the nucleon spin structure. We assess the determination of alpha_s from scaling violation of structure functions, and from sum rules, and the determination of sin^2(theta_W) from elastic nu-e and deep-inelastic nu-p scattering. We then consider the production of charmed hadrons, and the measurement of their absolute branching ratios. We study the polarization of Lambda baryons produced in the current and target fragmentation regions. Finally, we discuss the sensitivity to physics beyond the Standard Model.

hep-ph↗
arXiv2001

Parton Densities and Fragmentation Functions from Polarized Lambda Production in Semi-Inclusive DIS

We consider the longitudinal polarization of Lambda and Lambda-bar produced in the current fragmentation region of polarized deep inelastic scattering. We show how the various cross sections can be used to test the underlying parton dynamics, and how one can extract information about certain parton densities which are poorly known, in particular the polarized strange density sum Delta-s(x) + Delta-s-bar(x), and about fragmentation functions which are totally unknown and which are difficult to access by other means. We show also how one can obtain information concerning the intriguing question as to whether s(x) = s-bar(x) and whether Delta-s(x) = Delta-s-bar(x).

hep-ph↗
arXiv2000

Azimuthal and Single Spin Asimmetries in Deep Inelastic Scattering

Azimuthal and single spin asymmetries play a crucial role in the study of the spin structure of hadrons in terms of their elementary constituents. Exploiting them to uncover information over subtle distribution and fragmentation functions, which cannot easily be accessed in other ways, is what this talk is about.

hep-ph↗
arXiv2000

Bounds on transverse momentum dependent distribution and fragmentation functions

We give bounds on the distribution and fragmentation functions that appear at leading order in deep inelastic 1-particle inclusive leptoproduction or in Drell-Yan processes. These bounds simply follow from positivity of the defining matrix elements and are an important guidance in estimating the magnitude of the azimuthal and spin asymmetries in these processes.

hep-ph↗
arXiv2000

The full spin structure of quarks in the nucleon

We discuss bounds on the distribution and fragmentation functions that appear at leading order in deep inelastic 1-particle inclusive leptoproduction or in Drell-Yan processes. These bounds simply follow from positivity of the quark-hadron scattering matrix elements and are an important guide in estimating the magnitude of the azimuthal and spin asymmetries in these processes. We focus on an example relevant for deep inelastic scattering at relatively low energies.

hep-ph↗
arXiv2000

Semi-inclusive hadron-hadron transverse spin asymmetries and their implication for polarized DIS

We discuss a possible explanation of the 25 year old mystery of the large transverse spin asymmetries found in many semi-inclusive hadron-hadron reactions. We obtain the first reliable information about the transverse polarized quark densities Delta_T q(x) and we find surprising implications for the usual, longitudinal, polarized DIS. The plan of the presentation is as follows: 1) A brief reminder about the internal structure of the nucleon. 2) The transverse asymmetries. 3) Why it is so difficult to explain the asymmetries. 4) Failure and then success using a new soft mechanism. 5) implications for polarized DIS.

hep-ph↗
arXiv2000

Phenomenology of transverse single spin asymmetries in inclusive processes

A phenomenological description of single transverse spin asymmetries for the inclusive production of hadrons in proton-proton and lepton-proton processes is discussed within pQCD and a straightforward generalization of the factorization theorem with the inclusion of parton intrinsic transverse motion. Fits to existing data, predictions for new processes and interpretation of recent results are presented.

hep-ph↗
arXiv2000

Reassessment of the Collins Mechanism for Single-spin Asymmetries and the behavior of Delta d(x) at large x

It is shown that the Collins mechanism explanation of the transverse single-spin asymmetries in p^{\uparrow} p -> πX leads to a transversely polarized d quark density Delta_T d(x) which violates the Soffer bound when one uses several standard forms for the longitudinally polarized d quark density Delta d(x) obtained from polarized deep inelastic scattering. Imposition of the Soffer bound with these Delta d(x) yields results in hopeless disagreement with the data. Remarkably, imposition of the Soffer bound, but using parametrizations of Delta d(x) that respect the PQCD condition Delta q(x) / q(x) -> 1 as x -> 1, leads to an excellent fit to most of the data. The implications for the polarized DIS neutron longitudinal asymmetry A_1^n at large x are dramatic.

hep-ph↗