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U. D'Alesio

Publications and source records attributed to U. D'Alesio.

85 records · Page 5Linked to original sources
arXiv2001

Transverse Lambda polarization in unpolarized semi-inclusive DIS

The long-standing problem of transverse Lambda polarization in high-energy collisions of unpolarized hadrons can be tackled by considering new, spin and k_T-dependent quark fragmentation functions for an unpolarized quark into a polarized, spin-1/2 hadron. Simple phenomenological parameterizations of these new "polarizing fragmentation functions", which describe quite well the experimental data on Lambda and Lambda-bar hyperons produced in p-A processes, are utilized and extended here to give predictions for transverse Lambda polarization in semi-inclusive DIS

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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.

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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.

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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).

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arXiv2000

Phenomenology of single transverse spin asymmetries

A unified and consistent phenomenological approach to single transverse spin asymmetries in the framework of perturbative QCD, with the inclusion of a new class of spin and k_T dependent distribution and fragmentation functions, is presented. As an example, results on A_N(p(pol) p --> pion X) and P_Lambda(p p -->Lambda(pol) X) are shown.

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arXiv2000

Spin effects in the fragmentation of transversely polarized and unpolarized quarks

We study the fragmentation of a transversely polarized quark into a non collinear (k_T not= 0) spinless hadron and the fragmentation of an unpolarized quark into a non collinear transversely polarized spin 1/2 baryon. These nonperturbative properties are described by spin and k_T dependent fragmentation functions and are revealed in the observation of single spin asymmetries. Recent data on the production of pions in polarized semi-inclusive DIS and long known data on Lambda polarization in unpolarized p-N processes are considered: these new fragmentation functions can describe the experimental results and the single spin effects in the quark fragmentation turn out to be surprisingly large.

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arXiv2000

Lambda polarization in unpolarized hadron reactions

The transverse polarization observed in the inclusive production of Lambda hyperons in the high energy collisions of unpolarized hadrons is tackled by considering a new set of spin and kT dependent quark fragmentation functions. Simple phenomenological expressions for these new ``polarizing fragmentation functions'' are obtained by a fit of the data on Lambda's and Lambdabar's produced in p-N processes.

hep-ph↗
arXiv2000

Lambda polarization from unpolarized quark fragmentation

The longstanding problem of explaining the observed polarization of Lambda hyperons inclusively produced in the high energy collisions of unpolarized hadrons is tackled by considering spin and k_T dependent quark fragmentation functions. The data on Lambda's and Lambda-bar's produced in p-N processes are used to determine simple phenomenological expressions for these new "polarizing fragmentation functions", which describe the experiments remarkably well.

hep-ph↗
arXiv2000

Target Fragmentation of the Nucleon at High Energies

We calculate target fragmentation in $p p \to n X$ and $γp \to n X $ reactions in the meson cloud picture of the nucleon. The $p p \to n X$ reaction is used to fix the $pnπ^+$ form factor for two different models. We take into account the possible destruction of the residual neutron by the projectile. Using the form factor from the hadronic reaction we calculate photoproduction and small $x_{Bj}$ electroproduction of forward neutrons at HERA. In photoproduction we observe about the same amount of absorption as in the hadronic reaction. For deep inelastic events ($Q^2>10$ GeV$^2$) screening is weaker but still present at large $Q^2$. The signature for this absorptive rescattering is a shift of the $dσ/dE_n$ distribution to higher neutron energies for photofragmentation.

hep-ph↗
arXiv2000

Target Fragmentation in $pp$, $ep$ and $γp$ Collisions at High Energies

We calculate target fragmentation in $p p \to n X$ and $γp \to n X $ reactions in the meson cloud picture of the nucleon. The $p p \to n X$ reaction is used to fix the $pnπ^+$ form factor for three different models. We take into account the possible destruction of the residual neutron by the projectile. Using the form factor from the hadronic reaction we calculate photoproduction and small $x_{Bj}$ electroproduction of forward neutrons at HERA. Here the $q \bar q$ dipoles in the photon can rescatter on the residual neutron. In photoproduction we observe slightly less absorption than in the hadronic reaction. For deep inelastic events ($Q^2>10$ GeV$^2$) screening is weaker but still present at large $Q^2$. The signature for this absorptive rescattering is a shift of the $dσ/dE_n$ distribution to higher neutron energies for photofragmentation.

hep-ph↗
arXiv1999

Soft and Hard Pomeron in the Structure Function of the Proton at Low x and Low Q^2

We study inclusive electroproduction on the proton at low $x$ and low $Q^2$ using a soft and a hard Pomeron. The contribution of the soft Pomeron is based on the Stochastic Vacuum Model, in which a nonperturbative dipole-dipole cross section can be calculated by means of a gauge invariant gluon field strength correlator. To model the hard Pomeron exchange we phenomenologically extend the leading order evolution of a power-behaved structure function, $F_2 \propto x^{- λ}$, proposed by López and Ynduráin. This extension allows to consider both the case $Q^2 = 0$ and the region of higher $Q^2$ on the basis of the same parametrization. A good simultaneous fit to the data on $F_2$ and on the cross section $σ_{γp}$ of real photoproduction is obtained for $λ=0.37$. With four parameters we achieve a $χ^2/\textrm{d.o.f.} = 0.98$ for 222 data points. In addition, we use our model of the inclusive $γ^{\ast} p$ interaction to compute the longitudinal structure function $F_L$.

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