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M. L. Sperduto

Publications and source records attributed to M. L. Sperduto.

18 recordsLinked to original sources
arXiv2021

Deeply virtual Compton scattering off the neutron

The three-dimensional structure of nucleons (protons and neutrons) is embedded in so-called generalized parton distributions, which are accessible from deeply virtual Compton scattering. In this process, a high energy electron is scattered off a nucleon by exchanging a virtual photon. Then, a highly-energetic real photon is emitted from one of the quarks inside the nucleon, which carries information on the quark's transverse position and longitudinal momentum. By measuring the cross-section of deeply virtual Compton scattering, Compton form factors related to the generalized parton distributions can be extracted. Here, we report the observation of unpolarized deeply virtual Compton scattering off a deuterium target. From the measured photon-electroproduction cross-sections, we have extracted the cross-section of a quasi-free neutron and a coherent deuteron. Due to the approximate isospin symmetry of quantum chromodynamics, we can determine the contributions from the different quark flavours to the helicity-conserved Compton form factors by combining our measurements with previous ones probing the proton's internal structure. These results advance our understanding of the description of the nucleon structure, which is important to solve the proton spin puzzle.

hep-ph↗
arXiv2017

New Narrow $N(1685)$ and $N(1726)$? Remarks on the Interpretation of the Neutron Anomaly as an Interference Phenomenon

Different interpretations of narrow structures at $W\sim 1.68$ and $W\sim 1.72$ GeV observed in several reactions are discussed. It is questionable whether interference phenomena could explain the whole complex of experimental findings. More probable hypotheses would be the existence of one or two narrow resonances $N(1685)$ and $N(1726)$ and/or the sub-threshold virtual $KΣ$ and $ωp$ production (cusps).

nucl-ex↗
arXiv2017

A Glimpse of Gluons through Deeply Virtual Compton Scattering on the Proton

The proton is composed of quarks and gluons, bound by the most elusive mechanism of strong interaction called confinement. In this work, the dynamics of quarks and gluons are investigated using deeply virtual Compton scattering (DVCS): produced by a multi-GeV electron, a highly virtual photon scatters off the proton which subsequently radiates a high energy photon. Similarly to holography, measuring not only the magnitude but also the phase of the DVCS amplitude allows to perform 3D images of the internal structure of the proton. The phase is made accessible through the quantum-mechanical interference of DVCS with the Bethe-Heitler (BH) process, in which the final photon is emitted by the electron rather than the proton. We report herein the first full determination of the BH-DVCS interference by exploiting the distinct energy dependences of the DVCS and BH amplitudes. In the high energy regime where the scattering process is expected to occur off a single quark in the proton, these accurate measurements show an intriguing sensitivity to gluons, the carriers of the strong interaction.

hep-ex↗
arXiv2017

Rosenbluth separation of the $π^0$ Electroproduction Cross Section off the Neutron

We report the first longitudinal/transverse separation of the deeply virtual exclusive $π^0$ electroproduction cross section off the neutron and coherent deuteron. The corresponding four structure functions $dσ_L/dt$, $dσ_T/dt$, $dσ_{LT}/dt$ and $dσ_{TT}/dt$ are extracted as a function of the momentum transfer to the recoil system at $Q^2$=1.75 GeV$^2$ and $x_B$=0.36. The $ed \to edπ^0$ cross sections are found compatible with the small values expected from theoretical models. The $en \to enπ^0$ cross sections show a dominance from the response to transversely polarized photons, and are in good agreement with calculations based on the transversity GPDs of the nucleon. By combining these results with previous measurements of $π^0$ electroproduction off the proton, we present a flavor decomposition of the $u$ and $d$ quark contributions to the cross section.

hep-ex↗
arXiv2016

Rosenbluth separation of the $π^0$ electroproduction cross section

We present deeply virtual $π^0$ electroproduction cross-section measurements at $x_B$=0.36 and three different $Q^2$--values ranging from 1.5 to 2 GeV$^2$, obtained from experiment E07-007 that ran in the Hall A at Jefferson Lab. The Rosenbluth technique was used to separate the longitudinal and transverse responses. Results demonstrate that the cross section is dominated by its transverse component, and thus is far from the asymptotic limit predicted by perturbative Quantum Chromodynamics. An indication of a non-zero longitudinal contribution is provided by the interference term $σ_{LT}$ also measured. Results are compared with several models based on the leading twist approach of Generalized Parton Distributions (GPDs). In particular, a fair agreement is obtained with models where the scattering amplitude is described by a convolution of chiral-odd (transversity) GPDs of the nucleon with the twist-3 pion distribution amplitude. Therefore, neutral pion electroproduction may offer the exciting possibility of accessing transversity GPDs through experiment.

hep-ex↗
arXiv2015

First Measurement of the $Σ$ Beam Asymmetry in $η^{\prime}$ Photoproduction off the Proton near Threshold

The $Σ$ beam asymmetry in $η^{\prime}$ photoproduction off the proton was measured at the GrAAL polarised photon beam with incoming photon energies of 1.461 and 1.480 GeV. For both energies the asymmetry as a function of the meson production angle shows a clear structure, more pronounced at the lowest one, with a change of sign around 90$^o$. The observed behaviour is compatible with P-wave D-wave (or S-wave F-wave) interference, the closer to threshold the stronger. The results are compared to the existing state-of-the-art calculations that fail to account for the data.

nucl-ex↗
arXiv2015

Evidence for narrow resonant structures at $W \approx 1.68$ and $W \approx 1.72$ GeV in real Compton scattering off the proton

First measurement of the beam asymmetry $Σ$ for Compton scattering off the proton in the energy range $E_γ=0.85 - 1.25$ GeV is presented. The data reveals two narrow structures at $E_γ= 1.036$ and $E_γ=1.119$ GeV. They may signal narrow resonances with masses near $1.68$ and $1.72$ GeV, or they may be generated by the sub-threshold $KΛ$ and $ωp$ production. Their decisive identification requires additional theoretical and experimental efforts.

nucl-ex↗
arXiv2014

The MOLLER Experiment: An Ultra-Precise Measurement of the Weak Mixing Angle Using Møller Scattering

The physics case and an experimental overview of the MOLLER (Measurement Of a Lepton Lepton Electroweak Reaction) experiment at the 12 GeV upgraded Jefferson Lab are presented. A highlight of the Fundamental Symmetries subfield of the 2007 NSAC Long Range Plan was the SLAC E158 measurement of the parity-violating asymmetry $A_{PV}$ in polarized electron-electron (Møller) scattering. The proposed MOLLER experiment will improve on this result by a factor of five, yielding the most precise measurement of the weak mixing angle at low or high energy anticipated over the next decade. This new result would be sensitive to the interference of the electromagnetic amplitude with new neutral current amplitudes as weak as $\sim 10^{-3}\cdot G_F$ from as yet undiscovered dynamics beyond the Standard Model. The resulting discovery reach is unmatched by any proposed experiment measuring a flavor- and CP-conserving process over the next decade, and yields a unique window to new physics at MeV and multi-TeV scales, complementary to direct searches at high energy colliders such as the Large Hadron Collider (LHC). The experiment takes advantage of the unique opportunity provided by the upgraded electron beam energy, luminosity, and stability at Jefferson Laboratory and the extensive experience accumulated in the community after a round of recent successfully completed parity-violating electron scattering experiments

nucl-ex↗
arXiv2013

Measurement of the Σ beam asymmetry for the ω photo-production off the proton and the neutron at GRAAL

We report on new measurements of the beam asymmetry for ω photo-production on proton and neutron in Hydrogen and Deuterium targets from the GRAAL collaboration. The beam asymmetry values are extracted from the reaction threshold (E_γ = 1.1 GeV in the free nucleon kinematics) up to 1.5 GeV of incoming photon energy. For the first time both the radiative and the three-pion decay channels are simultaneously investigated on the free proton. Results from the two decay channels are in agreement and provide important constraints for the determination of resonant state contributions to the ω production mechanism. First experimental results on the deuteron allow the extraction of the Σ beam asymmetry on quasi-free nucleons. Comparison of the results for free and quasi-free kinematics on the proton shows a generally reasonable agreement, similar to the findings in pseudo-scalar meson photo-production reactions. For the first time measurements on quasi-free neutrons are available, showing that both the strength and the angular distributions of the beam asymmetry are sensibly different from the results on the proton target.

nucl-ex↗
arXiv2011

Evidence for Narrow N*(1685) Resonance in Quasifree Compton Scattering on the Neutron

The first study of quasi-free Compton scattering on the neutron in the energy range of $E_γ=0.75 - 1.5$ GeV is presented. The data reveals a narrow peak at $W\sim 1.685$ GeV. This result, being considered in conjunction with the recent evidence for a narrow structure at $W\sim 1.68$GeV in the $η$ photoproduction on the neutron, suggests the existence of a new nucleon resonance with unusual properties: the mass $M\sim 1.685$GeV, the narrow width $Γ\leq 30$MeV, and the much stronger photoexcitation on the neutron than on the proton.

hep-ex↗
arXiv2010

Limits on light-speed anisotropies from Compton scattering of high-energy electrons

The possibility of anisotropies in the speed of light relative to the limiting speed of electrons is considered. The absence of sidereal variations in the energy of Compton-edge photons at the ESRF's GRAAL facility constrains such anisotropies representing the first non-threshold collision-kinematics study of Lorentz violation. When interpreted within the minimal Standard-Model Extension, this result yields the two-sided limit of 1.6 x 10^{-14} at 95% confidence level on a combination of the parity-violating photon and electron coefficients kappa_{o+} and c. This new constraint provides an improvement over previous bounds by one order of magnitude.

hep-ex↗
arXiv2007

Measurement of eta photoproduction on the proton from threshold to 1500 MeV

Beam asymmetry and differential cross section for the reaction gamma+p->eta+p were measured from production threshold to 1500 MeV photon laboratory energy. The two dominant neutral decay modes of the eta meson, eta->2g and eta->3pi0, were analyzed. The full set of measurements is in good agreement with previously published results. Our data were compared with three models. They all fit satisfactorily the results but their respective resonance contributions are quite different. The possible photoexcitation of a narrow state N(1670) was investigated and no evidence was found.

nucl-ex↗
arXiv2003

Isospin effects on two-particle correlation functions in E/A = 61 MeV 36Ar + 112,124Sn reactions

Small-angle, two-particle correlation functions have been measured for 36Ar+ 112,124Sn collisions at E/A = 61 MeV. Total momentum gated neutron-proton (np) and proton-proton (pp) correlations are stronger for the 124Sn-target. Some of the correlation functions for particle pairs involving deuterons or tritons (nd, pt, and nt) also show a dependence on the isospin of the emitting source.

nucl-ex↗
arXiv1996

Statistical Binary Decay of $^{35}$Cl + $^{24}$Mg at 8 MeV/nucleon

The properties of the two-body channels in the $^{35}$Cl + $^{24}$Mg reaction at a bombarding energy of 275 MeV have been investigated by using fragment-fragment coincident techniques. The exclusive data show that the majority of events arises from a binary-decay process. The rather large number of secondary light charged-particles emitted from the two excited exit fragments are cnsistent with the expectations of the Extended Hauser-Feshbach Method. No evidence for the occurence of ternary break-up events is observed.

nucl-ex↗
arXiv1996

$^{35}$Cl+$^{12}$C Asymmetrical fission excitation functions

The fully energy-damped yields from the $^{35}$Cl+$^{12}$C reaction have been systematically investigated using particle-particle coincidence techniques at a $^{35}$Cl bombarding energy of $\sim$ 8 MeV/nucleon. The fragment-fragment correlation data show that the majority of events arises from a binary-decay process with rather large numbers of secondary light-charged particles emitted from the two excited exit fragments. No evidence is observed for ternary break-up events. The binary-process results of the present measurement, along with those of earlier, inclusive experimental data obtained at several lower bombarding energies are compared with predictions of two different kinds of statistical model calculations. These calculations are performed using the transition-state formalism and the Extended Hauser-Feshbach method and are based on the available phase space at the saddle point and scission point of the compound nucleus, respectively. The methods give comparable predictions and are both in good agreement with the experimental results thus confirming the fusion-fission origin of the fully-damped yields. The similarity of the predictions for the two models supports the claim that the scission point configuration is very close to that of the saddle point for the light $^{47}$V mass-asymmetry-dependent fission barriers needed in the transition-state calculation.

nucl-th↗