arXiv subjects

Marco Radici

Publications and source records attributed to Marco Radici.

At least 55 records · Page 3Linked to original sources

arXiv2017

Update on extraction of transversity PDF from inclusive di-hadron production

The transversity was recently extracted from data on the production of hadron pairs in semi-inclusive deep-inelastic scattering. This analysis can be conveniently performed in the framework of collinear factorization where the elementary mechanism is represented by the simple product of transversity and of a suitable chiral-odd function describing the fragmentation of a transversely polarized parton into a pair of hadrons inside the same current jet. The same elementary mechanism was predicted long ago to generate an asymmetry in the azimuthal distribution of the hadron pairs when they are produced in proton-proton collisions with one transversely polarized proton. Recently, the STAR Collaboration has observed this asymmetry. We analyze the impact of these data on our knowledge of transversity and we present its first preliminary extraction from a global fit of all data in hard processes with inclusive di-hadron production.

hep-ph↗

arXiv2017

Extraction of partonic transverse momentum distributions from semi-inclusive deep-inelastic scattering, Drell-Yan and Z-boson production

We present an extraction of unpolarized partonic transverse momentum distributions (TMDs) from a simultaneous fit of available data measured in semi-inclusive deep-inelastic scattering, Drell-Yan and Z-boson production. To connect data at different scales, we use TMD evolution at next-to-leading logarithmic accuracy. The analysis is restricted to the low-transverse-momentum region, with no matching to fixed-order calculations at high transverse momentum. We introduce specific choices to deal with TMD evolution at low scales, of the order of 1 GeV$^2$. This could be considered as a first attempt at a global fit of TMDs.

hep-ph↗

arXiv2016

Exploring universality of transversity in p-p collisions

The transversity distribution was recently extracted from deep-inelastic scattering processes producing hadron pairs in the final state. Together with a specific chiral-odd di-hadron fragmentation function, it is involved in the elementary mechanism that generates a transverse-spin asymmetry in the azimuthal distribution of the detected hadron pairs. The same elementary mechanism was predicted to generate an analogous asymmetry when the hadron pairs are produced in proton-proton collisions with one transversely polarized proton. Recently, the STAR Collaboration has observed this asymmetry. We analyze the impact of these data on our knowledge of transversity.

hep-ph↗

arXiv2016

Reconstructing parton densities at large fractional momenta

Parton distribution functions (PDFs) are nonperturbative objects defined by nonlocal light-cone correlations. They cannot be computed directly from Quantum Chromodynamics (QCD). Using a standard lattice QCD approach, it is possible to compute moments of PDFs, which are matrix elements of local operators. Recently, an alternative approach has been proposed, based on the introduction of quasi-parton distribution functions (quasi-PDFs), which are matrix elements of equal-time spatial correlations and hence calculable on lattice. Quasi-PDFs approach standard PDFs in the limit of very large longitudinal proton momenta $P^z$. This limit is not attainable in lattice simulations, and quasi-PDFs fail to reproduce PDFs at high fractional longitudinal momenta. In this paper, we propose a method to improve the reconstruction of PDFs by combining information from quasi-PDFs and from the Mellin moments of regular PDFs. We test our method using the diquark spectator model for up and down valence distributions of both unpolarized and helicity PDFs. In the future, the method can be used to produce PDFs entirely based on lattice QCD results.

hep-ph↗

arXiv2016

Exploring universality of transversity in proton-proton collisions

We consider the azimuthal correlations of charged hadron pairs with large total transverse momentum and small relative momentum, produced in proton-proton collisions with one transversely polarized proton. One of these correlations directly probes the chiral-odd transversity parton distribution in connection with a chiral-odd interference fragmentation function. We present predictions for this observable based on previous extractions of transversity (from charged pion pair production in semi-inclusive deep-inelastic scattering) and of the interference fragmentation function (from the production of back-to-back charged pion pairs in electron-positron annihilations). All analyses are performed in the framework of collinear factorization. We compare our predictions to the recent data on proton-proton collisions released by the STAR collaboration at RHIC, and we find them reasonably compatible. This comparison confirms for the first time the predicted role of transversity in proton-proton collisions and it allows to test its universality.

hep-ph↗

arXiv2015

Di-hadron fragmentation and mapping of the nucleon structure

The fragmentation of a colored parton directly into a pair of colorless hadrons is a non-perturbative mechanism that offers important insights into the nucleon structure. Di-hadron fragmentation functions can be extracted from semi-inclusive electron-positron annihilation data. They also appear in observables describing the semi-inclusive production of two hadrons in deep-inelastic scattering of leptons off nucleons or in hadron-hadron collisions. When a target nucleon is transversely polarized, a specific chiral-odd di-hadron fragmentation function can be used as the analyzer of the net density of transversely polarized quarks in a transversely polarized nucleon, the so-called transversity distribution. The latter can be extracted through suitable single-spin asymmetries in the framework of collinear factorization, thus in a much simpler framework with respect to the traditional one in single-hadron fragmentation. At subleading twist, the same chiral-odd di-hadron fragmentation function provides the cleanest access to the poorly known twist-3 parton distribution $e(x)$, which is intimately related to the mechanism of dynamical chiral symmetry breaking in QCD. When sensitive to details of transverse momentum dynamics of partons, the di-hadron fragmentation functions for a longitudinally polarized quark can be connected to the longitudinal jet handedness to explore possible effects due to $CP-$violation of the QCD vacuum. In this review, we outline the formalism of di-hadron fragmentation functions, we discuss different observables where they appear and we present measurements and future worldwide plans.

hep-ph↗

arXiv2015

Realistic estimate of valence transversity from dihadron production

We have updated our extraction of the transversity parton distribution based on the analysis of pion-pair production in deep-inelastic scattering off transversely polarized targets in collinear factorization. The most recent COMPASS data for proton and deuteron targets, complemented by previous HERMES data on the proton, make it possible to perform a flavor separation of the valence components of the transversity distribution, using di-hadron fragmentation functions taken from the semi-inclusive production of two pion pairs in back-to-back jets in $e^+ e^-$ annihilation. The $e^+ e^-$ data from BELLE have been reanalyzed to reach a more realistic estimate of the uncertainties on the chiral-odd interference fragmentation function. Our results represent the most accurate estimate of the uncertainties on the valence components of the transversity distribution currently available.

hep-ph↗

arXiv2015

Effects of TMD evolution and partonic flavor on $e^+e^-$ annihilation into hadrons

We calculate the transverse momentum dependence in the production of two back-to-back hadrons in electron-positron annihilations at the medium/large energy scales of BES-III and BELLE experiments. We use the parameters of the transverse-momentum-dependent (TMD) fragmentation functions that were recently extracted from the semi-inclusive deep-inelastic-scattering multiplicities at low energy from HERMES. TMD evolution is applied according to different approaches and using different parameters for the nonperturbative part of the evolution kernel, thus exploring the sensitivity of our results to these different choices and to the flavor dependence of parton fragmentation functions. We discuss how experimental measurements could discriminate among the various scenarios.

hep-ph↗

arXiv2015

Realistic estimate of valence transversity distributions from inclusive dihadron production

We present an updated extraction of the transversity parton distribution based on the analysis of pion-pair production in deep-inelastic scattering off transversely polarized targets in collinear factorization. Data for proton and deuteron targets make it possible to perform a flavor separation of the valence components of the transversity distribution, using di-hadron fragmentation functions taken from the semi-inclusive production of two pion pairs in back-to-back jets in e+e- annihilation. The e+e- data from Belle have been reanalyzed using the replica method and a more realistic estimate of the uncertainties on the chiral-odd interference fragmentation function has been obtained. Then, the transversity distribution has been extracted by using the most recent and more precise COMPASS data for deep-inelastic scattering off proton targets. Our results represent the most accurate estimate of the uncertainties on the valence components of the transversity distribution currently available.

hep-ph↗

arXiv2014

Phenomenology from SIDIS and $e^+e^-$ multiplicities

This study is part of a project to investigate the transverse momentum dependence in parton distribution and fragmentation functions, analyzing (semi-)inclusive high-energy processes within a proper QCD framework. We calculate the transverse-momentum-dependent (TMD) multiplicities for $e^+e^-$ annihilation into two hadrons (considering different combinations of pions and kaons) aiming to investigate the impact of intrinsic and radiative partonic transverse momentum and their mixing with flavor. Different descriptions of the non-perturbative evolution kernel are available on the market and there are 200 sets of flavor configurations for the unpolarized TMD fragmentation functions (FFs) resulting from a Monte Carlo fit of Semi-Inclusive Deep-Inelastic Scattering (SIDIS) data at Hermes. We build our predictions of $e^+e^-$ multiplicities relying on this rich phenomenology. The comparison of these calculations with future experimental data (from Belle and Babar collaborations) will shed light on non-perturbative aspects of hadron structure, opening important insights into the physics of spin, flavor and momentum structure of hadrons.

hep-ph↗

arXiv2014

Dihadron Fragmentation Functions and Transversity

We present preliminary results for an updated extraction of the transversity parton distribution based on the analysis of pion-pair production in deep-inelastic scattering off transversely polarized targets in collinear factorization. Data for proton and deuteron targets by HERMES and COMPASS allow for a flavor separation of the valence components of transversity, while di-hadron fragmentation functions are taken from the semi-inclusive production of two pion pairs in back-to-back jets in $e^+ e^-$ annihilation. The latter data from Belle have been reanalyzed using the replica method and a more realistic estimate of the uncertainties on the chiral-odd interference fragmentation function has been obtained. After encoding this piece of information into the deep-inelastic scattering cross section, the transversity has been re-extracted by using the most recent and more precise COMPASS data for proton target. This picture represents the current most realistic estimate of the uncertainties on our knowledge of transversity. The preliminary results indicate that the valence up component seems smaller and with a narrower error band than in previous extraction.

hep-ph↗

arXiv2014

Production of two hadrons in semi-inclusive Deep Inelatic Scattering

We present the general expression, in terms of structure functions, of the cross section for the production of two hadrons in semi-inclusive deep-inelastic scattering. We analyze this process including full transverse-momentum dependence up to subleading twist and check, where possible, the consistency with existing literature.

hep-ph↗

arXiv2014

Phenomenology of unpolarized TMDs from Semi-Inclusive DIS data

We discuss the dependence on the flavor of the intrinsic transverse momentum in unpolarized transverse-momentum-dependent distribution functions (TMD PDFs) and fragmentation functions (TMD FFs) analyzing data of semi-inclusive deep-inelastic scattering (SIDIS) released by the HERMES collaboration. Adopting a flavor-dependent Gaussian model in the transverse momentum and neglecting QCD evolution, we find interesting evidences concerning the flavor dependence in TMD FFs, whereas the indications are weaker in TMD PDFs and deserve further investigations. Inclusions of new data sets of SIDIS, electron-positron annihilations and and Drell-Yan (DY) events require a proper treatment of QCD evolution. We try to get constraints on the non-perturbative Sudakov factor from electron-positron annihilations into hadrons.

hep-ph↗

arXiv2013

Flavor dependence of unpolarized TMDs from semi-inclusive pion production

Recent data from semi-inclusive deep inelastic scattering collected by the HERMES collaboration allow for the first time to discuss how the transverse-momentum dependence of unpolarized distribution and fragmentation functions is affected by the flavor of the involved partons. A model built with flavor-dependent Gaussian transverse-momentum distributions fits data better than the same flavor-independent model. The current analysis is performed for totally unpolarized scattering of leptons off protons and deuterons, with detected pions in the final state. There are convincing indications of flavor dependence in the fragmentation functions, while for parton distribution functions the evidence is weaker.

hep-ph↗

arXiv2013

Investigations into the flavor dependence of partonic transverse momentum

Recent experimental data on semi-inclusive deep-inelastic scattering from the HERMES collaboration allow us to discuss for the first time the flavor dependence of unpolarized transverse-momentum dependent distribution and fragmentation functions. We find convincing indications that favored fragmentation functions into pions have smaller average transverse momentum than unfavored functions and fragmentation functions into kaons. We find weaker indications of flavor dependence in the distribution functions.

hep-ph↗

arXiv2013

Detecting correlated di-hadron pairs: about the extraction of transversity and beyond

We summarize the latest achievements about the extraction of the transversity parton distribution and proton tensor charge based on an analysis of pion-pair production in deep-inelastic scattering off transversely polarized targets. Recently released data for proton and deuteron targets by HERMES and COMPASS allow for a flavor separation of the valence components of transversity. At variance with the Collins effect, this extraction is performed in the framework of collinear factorization and relies on di-hadron fragmentation functions. The latter have been taken from the first recent analysis of the semi-inclusive production of two pion pairs in back-to-back jets in e+e- annihilation. We also comment on the possibility of isolating new azimuthally asymmetric correlations of opposite pion pairs, which could arise when a fragmenting quark crosses parity-odd domains localized in Minkowski space-time and induced by the topologically nontrivial QCD background (the so-called θ vacuum).

hep-ph↗

arXiv2013

Valence transversities: the collinear extraction

In these proceedings, we propose an extraction of the valence transversity parton distributions. Based on an analysis of pion-pair production in deep-inelastic scattering off transversely polarized targets, this extraction of transversity is performed in the framework of collinear factorization. The recently released data for proton and deuteron targets at HERMES and COMPASS allow for a flavor separation of the valence transversities, for which we give a complete statistical study.

hep-ph↗

arXiv2012

First extraction of valence transversities in a collinear framework

We present an extraction of the valence transversity parton distributions based on an analysis of pion-pair production in deep-inelastic scattering off transversely polarized targets. Recently released data for proton and deuteron targets at HERMES and COMPASS permit a flavor separation of valence transversities. The present extraction is performed in the framework of collinear factorization, where dihadron fragmentation functions are involved. The latter are taken from a previous analysis of electron-positron annihilation measurements.

hep-ph↗