arXiv subjects

V. Mascagna

Publications and source records attributed to V. Mascagna.

At least 73 records · Page 4Linked to original sources

arXiv2021

Improved $Λp$ Elastic Scattering Cross Sections Between 0.9 and 2.0 GeV/c and Connections to the Neutron Star Equation of State

Strange matter is believed to exist in the cores of neutron stars based on simple kinematics. If this is true, then hyperon-nucleon interactions will play a significant part in the neutron star equation of state (EOS). Yet, compared to other elastic scattering processes, there is very little data on $Λ$-$N$ scattering. This experiment utilized the CLAS detector to study the $Λp \rightarrow Λp$ elastic scattering cross section in the incident $Λ$ momentum range 0.9-2.0 GeV/c. This is the first data on this reaction in several decades. The new cross sections have significantly better accuracy and precision than the existing world data, and the techniques developed here can also be used in future experiments.

hep-ex↗

arXiv2021

Light dark matter searches with positrons

We discuss two complementary strategies to search for light dark matter (LDM) exploiting the positron beam possibly available in the future at Jefferson Laboratory. LDM is a new compelling hypothesis that identifies dark matter with new sub-GeV "hidden sector" states, neutral under standard model interactions and interacting with our world through a new force. Accelerator-based searches at the intensity frontier are uniquely suited to explore it. Thanks to the high intensity and the high energy of the CEBAF (Continuous Electron Beam Accelerator Facility) beam, and relying on a novel LDM production mechanism via positron annihilation on target atomic electrons, the proposed strategies will allow us to explore new regions in the LDM parameters space, thoroughly probing the LDM hypothesis as well as more general hidden sector scenarios.

hep-ex↗

arXiv2021

Observation of Beam Spin Asymmetries in the Process $e p \rightarrow e π^{+}π^{-}X$ with CLAS12

The observation of beam spin asymmetries in two-pion production in semi-inclusive deep inelastic scattering off an unpolarized proton target is reported. The data presented here were taken in the fall of 2018 with the CLAS12 spectrometer using a 10.6 GeV longitudinally spin-polarized electron beam delivered by CEBAF at JLab. The measured asymmetries provide the first opportunity to extract the parton distribution function $e(x)$, which provides information about the interaction between gluons and quarks, in a collinear framework that offers cleaner access than previous measurements. The asymmetries also constitute the first ever signal sensitive to the helicity-dependent two-pion fragmentation function $G_1^\perp$. A clear sign change is observed around the $ρ$ mass that appears in model calculations and is indicative of the dependence of the produced pions on the helicity of the fragmenting quark.

hep-ex↗

arXiv2021

Beam charge asymmetries for deeply virtual Compton scattering off the proton

The unpolarized and polarized Beam Char\-ge Asymmetries (BCAs) of the $\vv{e}^{\pm}p \to e^{\pm}p γ$ process off unpolarized hydrogen are discussed. The measurement of BCAs with the CLAS12 spectrometer at the Thomas Jefferson National Accelerator Facility, using polarized positron and electron beams at 10.6 GeV is investigated. This experimental configuration allows to measure azimuthal and $t$-dependences of the unpolarized and polarized BCAs over a large $(x_B,Q^2)$ phase space, providing a direct access to the real part of the Compton Form Factor (CFF) ${\mathcal H}$. Additionally, these measurements confront the Bethe-Heitler dominance hypothesis and eventual effects beyond leading twist. The impact of potential positron beam data on the determination of CFFs is also investigated within a local fitting approach of experimental observables. Positron data are shown to strongly reduce correlations between CFFs and consequently improve significantly the determination of $\Re {\rm e} [\mathcal{H}]$.

nucl-ex↗

arXiv2021

Exploiting the wide dynamic range of Silicon photomultipliers for Quantum Optics applications

Silicon photomultipliers are photon-number-resolving detectors endowed with hundreds of cells enabling them to reveal high-populated quantum optical states. In this paper, we address such a goal by showing the possible acquisition strategies that can be adopted and discussing their advantages and limitations. In particular, we determine the best acquisition solution in order to properly reveal the nature, either classical or nonclassical, of mesoscopic quantum optical states.

quant-ph↗

arXiv2021

Differential cross sections for Λ(1520) using photoproduction at CLAS

The reaction $γp \rightarrow K^{+} Λ(1520)$ using photoproduction data from the CLAS $g12$ experiment at Jefferson Lab is studied. The decay of $Λ(1520)$ into two exclusive channels, $Σ^{+}π^{-}$ and $Σ^{-}π^{+}$, is studied from the detected $K^{+}$, $π^{+}$, and $π^{-}$ particles. A good agreement is established for the $Λ(1520)$ differential cross sections with the previous CLAS measurements. The differential cross sections as a function of CM angle are extended to higher photon energies. Newly added are the differential cross sections as a function of invariant 4-momentum transfer $t$, which is the natural variable to use for a theoretical model based on a Regge-exchange reaction mechanism. No new $N^*$ resonances decaying into the $K^+Λ(1520)$ final state are found.

hep-ex↗

arXiv2020

Photoproduction of $η$ mesons off the proton for $1.2 < E_γ< 4.7$ GeV using CLAS at Jefferson Laboratory

Photoproduction cross sections are reported for the reaction $γp\to pη$ using energy-tagged photons and the CLAS spectrometer at Jefferson Laboratory. The $η$ mesons are detected in their dominant charged decay mode, $η\to π^+π^-π^0$, and results on differential cross sections are presented for incident photon energies between 1.2 and 4.7 GeV. These new $η$ photoproduction data are consistent with earlier CLAS results but extend the energy range beyond the nucleon resonance region into the Regge regime. The normalized angular distributions are also compared with the experimental results from several other experiments, and with predictions of $η$ MAID\,2018 and the latest solution of the Bonn-Gatchina coupled-channel analysis. Differential cross sections $dσ/dt$ are presented for incident photon energies $E_γ> 2.9$ GeV ($W > 2.5$ GeV), and compared with predictions which are based on Regge trajectories exchange in the $t$-channel (Regge models). The data confirm the expected dominance of $ρ$, $ω$ vector-meson exchange in an analysis by the Joint Physics Analysis Center.

nucl-ex↗

arXiv2020

Investigation on radiation generated by Sub-GeV electrons in ultrashort Si and Ge bent crystals

We report on the measurements of the spectra of gamma radiation generated by 855 MeV electrons in bent silicon and germanium crystals at MAMI (MAinzer MIkrotron). The crystals were 15 μm thick along the beam direction to ensure high deflection efficiency. Their (111) crystalline planes were bent by means of a piezo-actuated mechanical holder, which allowed to remotely change the crystal curvature. In such a way it was possible to investigate the radiation emitted under planar channeling and volume reflection as a function of the curvature of the crystalline planes. We show that using volume reflection, one can produce intense gamma radiation with comparable intensity but higher angular acceptance than for channeling. We studied the trade-off between radiation intensity and angular acceptance at different values of the crystal curvature. The measurements of radiation spectra have been carried out for the first time in bent Germanium crystals. In particular, the intensity of radiation in the Ge crystal is higher than in the Si one due to the higher atomic number, which is important for the development of the X-ray and gamma radiation sources based on higher-Z deformed crystals, such as crystalline undulator.

physics.acc-ph↗

arXiv2020

The ENUBET Beamline

The ENUBET ERC project (2016-2021) is studying a narrow band neutrino beam where lepton production can be monitored at single particle level in an instrumented decay tunnel. This would allow to measure $ν_μ$ and $ν_{e}$ cross sections with a precision improved by about one order of magnitude compared to present results. In this proceeding we describe a first realistic design of the hadron beamline based on a dipole coupled to a pair of quadrupole triplets along with the optimisation guidelines and the results of a simulation based on G4beamline. A static focusing design, though less efficient than a horn-based solution, results several times more efficient than originally expected. It works with slow proton extractions reducing drastically pile-up effects in the decay tunnel and it paves the way towards a time-tagged neutrino beam. On the other hand a horn-based transferline would ensure higher yields at the tunnel entrance. The first studies conducted at CERN to implement the synchronization between a few ms proton extraction and a horn pulse of 2-10 ms are also described.

physics.acc-ph↗

arXiv2020

The hadronic beamline of the ENUBET neutrino beam

The ENUBET ERC project (2016-2021) is studying a facility based on a narrow band beam capable of constraining the neutrino fluxes normalization through the monitoring of the associated charged leptons in an instrumented decay tunnel. A key element of the project is the design and optimization of the hadronic beamline. In this proceeding we present progress on the studies of the proton extraction schemes. We also show a realistic implementation and simulation of the beamline.

physics.acc-ph↗

arXiv2020

Investigation on steering of ultrarelativistic $e^{\pm}$ beam through an axially oriented bent crystal

An investigation on stochastic deflection of high-energy charged particles in a bent crystal was carried out. In particular, we investigated the deflection efficiency under axial confinement of both positively and negatively charged particles as a function of the crystal orientation, the choice of the bending plane, and of the charge sign. Analytic estimations and numerical simulations were compared with dedicated experiments at the H4 secondary beam line of SPS North Area, with 120 GeV/$c$ electrons and positrons. In the work presented in this article, the optimal orientations of the plane of bending of the crystal, which allow deflecting the largest number of charged particles using a bent crystal in axial orientation, were found.

physics.acc-ph↗

arXiv2020

Measurement of the Principal Quantum Number Distribution in a Beam of Antihydrogen Atoms

The ASACUSA (Atomic Spectroscopy And Collisions Using Slow Antiprotons) collaboration plans to measure the ground-state hyperfine splitting of antihydrogen in a beam at the CERN Antiproton Decelerator with initial relative precision of 10-6 or better, to test the fundamental CPT (combination of charge conjugation, parity transformation and time reversal) symmetry between matter and antimatter. This challenging goal requires a polarised antihydrogen beam with a sufficient number of antihydrogen atoms in the ground state. The first measurement of the quantum state distribution of antihydrogen atoms in a low magnetic field environment of a few mT is described. Furthermore, the data-driven machine learning analysis to identify antihydrogen events is discussed.

physics.atom-ph↗

arXiv2020

Beam spin asymmetry in semi-inclusive electroproduction of a hadron pair

A first measurement of the longitudinal beam spin asymmetry ALU in the semi-inclusive electroproduction of pairs of charged pions is reported. ALU is a higher-twist observable and offers the cleanest access to the nucleon twist-3 parton distribution function e(x). Data have been collected in the Hall-B at Jefferson Lab by impinging a 5.498 GeV electron beam on a liquid-hydrogen target, and reconstructing the scattered electron and the pion pair with the CLAS detector. One-dimensional projections of the sin(phiR) moments of ALU are extracted for the kinematic variables of interest in the valence quark region. The understanding of di-hadron production is essential for the interpretation of observables in single hadron production in semi-inclusive DIS, and pioneering measurements of single spin asymmetries in di-hadron production open a new avenue in studies of QCD dynamics.

hep-ex↗

arXiv2020

Extraction of beam-spin asymmetries from the hard exclusive $π^{+}$ channel off protons in a wide range of kinematics

We have measured beam-spin asymmetries to extract the $\sinϕ$ moment $A_{LU}^{\sinϕ}$ from the hard exclusive $\vec{e} p \to e^\prime n π^+$ reaction above the resonance region, for the first time with nearly full coverage from forward to backward angles in the center-of-mass. The $A_{LU}^{\sinϕ}$ moment has been measured up to 6.6 GeV$^{2}$ in $-t$, covering the kinematic regimes of Generalized Parton Distributions (GPD) and baryon-to-meson Transition Distribution Amplitudes (TDA) at the same time. The experimental results in very forward kinematics demonstrate the sensitivity to chiral-odd and chiral-even GPDs. In very backward kinematics where the TDA framework is applicable, we found $A_{LU}^{\sinϕ}$ to be negative, while a sign change was observed near 90$^\circ$ in the center-of-mass. The unique results presented in this paper will provide critical constraints to establish reaction mechanisms that can help to further develop the GPD and TDA frameworks.

nucl-ex↗

arXiv2020

The ENUBET positron tagger prototype: construction and testbeam performance

A prototype for the instrumented decay tunnel of ENUBET was tested in 2018 at the CERN East Area facility with charged particles up to 5 GeV. This detector is a longitudinal sampling calorimeter with lateral scintillation light readout. The calorimeter was equipped by an additional "$t_0$-layer" for timing and photon discrimination. The performance of this detector in terms of electron energy resolution, linearity, response to muons and hadron showers are presented in this paper and compared with simulation. The $t_0$-layer was studied both in standalone mode using pion charge exchange and in combined mode with the calorimeter to assess the light yield and the 1 mip/2 mip separation capability. We demonstrate that this system fulfills the requirements for neutrino physics applications and discuss performance and additional improvements.

physics.ins-det↗

arXiv2020

Decay tunnel instrumentation for the ENUBET neutrino beam

The uncertainty in the initial neutrino flux is the main limitation for a precise determination of the absolute neutrino cross section. The ERC funded ENUBET project (2016-2021) is studying a facility based on a narrow band beam to produce an intense source of electron neutrinos with a ten-fold improvement in accuracy. Since March 2019 ENUBET is also a Neutrino Platform experiment at CERN: NP06/ENUBET. A key element of the project is the instrumentation of the decay tunnel to monitor large angle positrons produced together with $ν_e$ in the three body decays of kaons ($K_{e3}$) and to discriminate them from neutral and charged pions. The need for an efficient and high purity e/$π$ separation over a length of several meters, and the requirements for fast response and radiation hardness imposed by the harsh beam environment, suggested the implementation of a longitudinally segmented Fe/scintillator calorimeter with a readout based on WLS fibers and SiPM detectors. An extensive experimental program through several test beam campaigns at the CERN-PS T9 beam line has been pursued on calorimeter prototypes, both with a shashlik and a lateral readout configuration. The latter, in which fibers collect the light from the side of the scintillator tiles, allows to place the light sensors away from the core of the calorimeter, thus reducing possible irradiation damages with respect to the shashlik design. This contribution will present the achievements of the prototyping activities carried out, together with irradiation tests made on the Silicon Photo-Multipliers. The results achieved so far pin down the technology of choice for the construction of the 3 m long demonstrator that will take data in 2021.

physics.ins-det↗

arXiv2020

Study of muon pair production from positron annihilation at threshold energy

The muon collider represents one of the most promising solutions for a future machine exploring the high energy frontier, but several challenges due to the 2.2 $μ$sec muon lifetime at rest have to be carefully considered. The LEMMA project is investigating the possibility of producing low emittance muon/antimuon pairs from the e$^+$e$^-$ annihilation process at threshold energy, resulting in small transverse emittance beams without any additional beam cooling. However most of the measurements available are performed at higher $\sqrt{s}$ values. It is therefore necessary to measure muons production in positron annihilation at threshold energy and compare the experimental results with the predictions in this specific energy regime. Apart from being a topic of physical interest by itself, these near to threshold measurements can have a sizeable impact on the estimation of the ultimate luminosity achievable in a muon collider with the LEMMA injection scheme.

hep-ex↗

arXiv2020

Polysiloxane-based scintillators for shashlik calorimeters

We present the first application of polysiloxane-based scintillators as active medium in a shashlik sampling calorimeter. These results were obtained from a testbeam campaign of a $\sim$6$\times$6$\times$45 cm$^3$ (13 $X_0$ depth) prototype. A Wavelength Shifting fiber array of 36 elements runs perpendicularly to the stack of iron (15 mm) and polysiloxane scintillator (15 mm) tiles with a density of about one over cm$^2$. Unlike shashlik calorimeters based on plastic organic scintillators, here fibers are optically matched with the scintillator without any intermediate air gap. The prototype features a compact light readout based on Silicon Photo-Multipliers embedded in the bulk of the detector. The detector was tested with electrons, pions and muons with energies ranging from 1 to 7 GeV at the CERN-PS. This solution offers a highly radiation hard detector to instrument the decay region of a neutrino beam, providing an event-by-event measurement of high-angle decay products associated with neutrino production (ENUBET, Enhanced NeUtrino BEams from kaon Tagging, ERC project). The results in terms of light yield, uniformity and energy resolution, are compared to a similar calorimeter built with ordinary plastic scintillators.

physics.ins-det↗