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R. De Vita

Publications and source records attributed to R. De Vita.

At least 127 records · Page 7Linked to original sources
arXiv2011

Precise Measurements of Beam Spin Asymmetries in Semi-Inclusive $π^0$ production

We present studies of single-spin asymmetries for neutral pion electroproduction in semi-inclusive deep-inelastic scattering of 5.776 GeV polarized electrons from an unpolarized hydrogen target, using the CEBAF Large Acceptance Spectrometer (CLAS) at the Thomas Jefferson National Accelerator Facility. A substantial $\sin ϕ_h$ amplitude has been measured in the distribution of the cross section asymmetry as a function of the azimuthal angle $ϕ_h$ of the produced neutral pion. The dependence of this amplitude on Bjorken $x$ and on the pion transverse momentum is extracted with significantly higher precision than previous data and is compared to model calculations.

hep-ex↗
arXiv2010

Near-threshold Photoproduction of Phi Mesons from Deuterium

We report the first measurement of the differential cross section on $ϕ$-meson photoproduction from deuterium near the production threshold for a proton using the CLAS detector and a tagged-photon beam in Hall B at Jefferson Lab. The measurement was carried out by a triple coincidence detection of a proton, $K^+$ and $K^-$ near the theoretical production threshold of 1.57 GeV. The extracted differential cross sections $\frac{dσ}{dt}$ for the initial photon energy from 1.65-1.75 GeV are consistent with predictions based on a quasifree mechanism. This experiment establishes a baseline for a future experimental search for an exotic $ϕ$-N bound state from heavier nuclear targets utilizing subthreshold/near-threshold production of $ϕ$ mesons.

nucl-ex↗
arXiv2010

Measurement of the atmospheric muon flux with the NEMO Phase-1 detector

The NEMO Collaboration installed and operated an underwater detector including prototypes of the critical elements of a possible underwater km3 neutrino telescope: a four-floor tower (called Mini-Tower) and a Junction Box. The detector was developed to test some of the main systems of the km3 detector, including the data transmission, the power distribution, the timing calibration and the acoustic positioning systems as well as to verify the capabilities of a single tridimensional detection structure to reconstruct muon tracks. We present results of the analysis of the data collected with the NEMO Mini-Tower. The position of photomultiplier tubes (PMTs) is determined through the acoustic position system. Signals detected with PMTs are used to reconstruct the tracks of atmospheric muons. The angular distribution of atmospheric muons was measured and results compared with Monte Carlo simulations.

astro-ph.IM↗
arXiv2009

Measurement of unpolarized semi-inclusive pi+ electroproduction off the proton

Semi-inclusive pi+ electroproduction on protons has been measured with the CLAS detector at Jefferson Lab. The measurement was performed on a liquid-hydrogen target using a 5.75 GeV electron beam. The complete five-fold differential cross sections were measured over a wide kinematic range including the complete range of azimuthal angles between hadronic and leptonic planes, phi, enabling us to separate the phi-dependent terms. Our measurements of phi-independent term of the cross section at low Bjorken x were found to be in fairly good agreement with pQCD calculations. Indeed, the conventional current fragmentation calculation can account for almost all of the observed cross section, even at small pi+ momentum. The measured center-of-momentum spectra are in qualitative agreement with high energy data, which suggests a surprising numerical similarity between the spectator diquark fragmentation in the present reaction and the anti-quark fragmentation measured in e+e- collisions. We have observed that the two phi-dependent terms of the cross section are small. Within our precision the cos(2phi) term is compatible with zero, except for low-z region, and the measured cos(phi) term is much smaller in magnitude than the sum of the Cahn and Berger effects.

hep-ex↗
arXiv2009

Photoproduction of $π^+ π^-$ meson pairs on the proton

The exclusive reaction $γp \to p π^+ π^-$ was studied in the photon energy range 3.0 - 3.8 GeV and momentum transfer range $0.4<-t<1.0$ GeV$^2$. Data were collected with the CLAS detector at the Thomas Jefferson National Accelerator Facility. In this kinematic range the integrated luminosity was about 20 pb$^{-1}$. The reaction was isolated by detecting the $π^+$ and proton in CLAS, and reconstructing the $π^-$ via the missing-mass technique. Moments of the di-pion decay angular distributions were derived from the experimental data. Differential cross sections for the $S$, $P$, and $D$-waves in the $M_{π^+π^-}$ mass range $0.4-1.4$ GeV were derived performing a partial wave expansion of the extracted moments. Besides the dominant contribution of the $ρ(770)$ meson in the $P$-wave, evidence for the $f_0(980)$ and the $f_2(1270)$ mesons was found in the $S$ and $D$-waves, respectively. The differential production cross sections $dσ/dt$ for individual waves in the mass range of the above-mentioned mesons were extracted. This is the first time the $f_0(980)$ has been measured in a photoproduction experiment.

hep-ex↗
arXiv2009

Exclusive photoproduction of $f_1(1285)$ meson off proton in the JLab kinematics

Within the Regge approach, we calculated the exclusive $f_1(1285)$ meson photoproduction cross section at energy of few GeV. The calculation shows that the cross section is sizable, being in the range of 100 nb, and much larger than the the expected cross section of the $η(1295)$ meson photoproduction at the same energy. These two facts make possible to use this reaction to study the poor known properties of the $f_1(1285)$ meson in the JLab kinematics.

nucl-th↗
arXiv2008

First measurement of direct $f_0(980)$ photoproduction on the proton

We report on the results of the first measurement of exclusive $f_0(980)$ meson photoproduction on protons for $E_γ=3.0 - 3.8$ GeV and $-t = 0.4-1.0$ GeV$^2$. Data were collected with the CLAS detector at the Thomas Jefferson National Accelerator Facility. The resonance was detected via its decay in the $π^+ π^-$ channel by performing a partial wave analysis of the reaction $γp \to p π^+ π^-$. Clear evidence of the $f_0(980)$ meson was found in the interference between $P$ and $S$ waves at $M_{π^+ π^-}\sim 1$ GeV. The $S$-wave differential cross section integrated in the mass range of the $f_0(980)$ was found to be a factor of 50 smaller than the cross section for the $ρ$ meson. This is the first time the $f_0(980)$ meson has been measured in a photoproduction experiment.

hep-ex↗
arXiv2007

Cascade production in the reactions gamma p --> K+ K+ (X) and gamma p --> K^+ K^+ pi- (X)

Photoproduction of the cascade resonances has been investigated in the reactions $γp \to K^+ K^+ (X)$ and $γp \to K^+ K^+ π^- (X)$. The mass split of the $Ξ$ doublet is measured to be $5.4\pm 1.8$ MeV/c$^2$, consistent with existing measurements. The differential (total) cross sections for the $Ξ^{-}$ have been determined for photon beam energies from 2.75 to 3.85 (4.75) GeV, and are consistent with a possible production mechanism of $Y^*\to K^+Ξ^-$ through a $t$-channel process. The reaction $γp \to K^+ K^+ π^-[Ξ^0]$ has also been investigated in search of excited cascade resonances. No significant signal of excited cascade states other than the $Ξ^-(1530)$ is observed. The cross section results of the $Ξ^-(1530)$ have also been obtained for photon beam energies from 3.35 to 4.75 GeV.

nucl-ex↗
arXiv2006

Search for the $Θ^+$ pentaquark in the reactions $γp \to \bar K^0K^+n$ and $γp \to \bar K^0K^0p$

The exclusive reactions $γp \to \bar K^0 K^+ n$ and $γp \to \bar K^0 K^0 p$ have been studied in the photon energy range 1.6--3.8 GeV, searching for evidence of the exotic baryon $Θ^+(1540)$ in the decays $Θ^+\to nK^+$ and $Θ^+\to p K^0$. Data were collected with the CLAS detector at the Thomas Jefferson National Accelerator Facility. The integrated luminosity was about 70 pb$^{-1}$. The reactions have been isolated by detecting the $K^+$ and proton directly, the neutral kaon via its decay to $K_S \to π^+ π^-$ and the neutron or neutral kaon via the missing mass technique. The mass and width of known hyperons such as $Σ^+$, $Σ^-$ and $Λ(1116)$ were used as a check of the mass determination accuracy and experimental resolution. Approximately 100,000 $Λ^*(1520)$'s and 150,000 $ϕ$'s were observed in the $\bar K^0 K^+ n$ and $\bar K^0 K^0 p$ final state respectively. No evidence for the $Θ^+$ pentaquark was found in the $nK^+$ or $pK_S$ invariant mass spectra. Upper limits were set on the production cross section of the reaction $γp \to Θ^+ \bar K^0$ as functions of center-of-mass angle, $nK^+$ and $pK_S$ masses. Combining the results of the two reactions, the 95% C.L. upper limit on the total cross section for a resonance peaked at 1540 MeV was found to be 0.7 nb. Within most of the available theoretical models, this corresponds to an upper limit on the $Θ^+$ width, $Γ_{Θ^{+}}$, ranging between 0.01 and 7 MeV.

hep-ex↗
arXiv2006

Search for $Θ^{++}$ Pentaquarks in the Exclusive Reaction $γp\to K^+K^-p$

The reaction $γp \to pK^+K^-$ was studied at Jefferson Lab with photon energies from 1.8 to 3.8 GeV using a tagged photon beam. The goal was to search for a $Θ^{++}$ pentaquark, a narrow doubly charged baryon state having strangeness S=+1 and isospin I=1, in the $pK^+$ invariant mass spectrum. No statistically significant evidence of a $Θ^{++}$ was found. Upper limits on the total and differential production cross section for the reaction $γp \to K^-Θ^{++}$ were obtained in the mass range from 1.5 to 2.0 GeV/c$^2$, with an upper limit of about 0.15 nb, 95% C.L. for a narrow resonance with a mass $M_{Θ^{++}}=1.54$ GeV/c$^2$. This result places a very stringent upper limit on the $Θ^{++}$ width.

hep-ex↗
arXiv2005

Search for $Θ^+(1540)$ pentaquark in high statistics measurement of $γp \to \bar K^0 K^+ n$ at CLAS

The exclusive reaction $γp \to \bar K^0 K^+ n$ was studied in the photon energy range between 1.6-3.8 GeV searching for evidence of the exotic baryon $Θ^+(1540)\to nK^+$. The decay to $nK^+$ requires the assignment of strangeness $S=+1$ to any observed resonance. Data were collected with the CLAS detector at the Thomas Jefferson National Accelerator Facility corresponding to an integrated luminosity of 70 $pb^{-1}$. No evidence for the $Θ^+$ pentaquark was found. Upper limits were set on the production cross section as function of center-of-mass angle and $nK^+$ mass. The 95% CL upper limit on the total cross section for a narrow resonance at 1540 MeV was found to be 0.8 nb.

hep-ex↗
arXiv2004

Experimental determination of the evolution of the Bjorken integral at low Q^2

We extract the Bjorken integral Gamma^{p-n}_1 in the range 0.17 < Q^2 < 1.10 GeV^2 from inclusive scattering of polarized electrons by polarized protons, deuterons and 3He, for the region in which the integral is dominated by nucleon resonances. These data bridge the domains of the hadronic and partonic descriptions of the nucleon. In combination with earlier measurements at higher Q^2, we extract the non-singlet twist-4 matrix element f_2.

hep-ex↗
arXiv2004

The CLAS Electromagnetic Calorimeter at Large Angles

The study of the response of the two modules of the large-angle electromagnetic shower calorimeter (LAC) of the CLAS detector to charged and neutral particles is reported. The results agree very well with the Monte Carlo simulation. The procedures adopted for the energy and timing calibration are also discussed, proving that the module geometry allows for simple self-calibrating energy and timing algorithms.

nucl-ex↗
arXiv2003

Measurement of the Proton Spin Structure Function $g_1(x,Q^2)$ for $Q^2$ from 0.15 to 1.6 GeV$^2$ with CLAS

Double-polarization asymmetries for inclusive $ep$ scattering were measured at Jefferson Lab using 2.6 and 4.3 GeV longitudinally polarized electrons incident on a longitudinally polarized NH$_3$ target in the CLAS detector. The polarized structure function $g_1(x,Q^2)$ was extracted throughout the nucleon resonance region and into the deep inelastic regime, for $Q^2 = 0.15 -1.64 $GeV$^2$. The contributions to the first moment $Γ_1(Q^2) = \int g_1(x,Q^2)dx$ were determined up to $Q^2=1.2$ GeV$^2$. Using a parametrization for $g_1$ in the unmeasured low $x$ regions, the complete first moment was estimated over this $Q^2$ region. A rapid change in $Γ_1$ is observed for $Q^2 < 1 $GeV$^2$, with a sign change near $Q^2 = 0.3 $GeV$^2$, indicating dominant contributions from the resonance region. At $Q^2=1.2$ GeV$^2$ our data are below the pQCD evolved scaling value.

nucl-ex↗
arXiv2003

Measurement of $ep \to e^{'}pπ^{+}π^{-}$: experimental procedures and baryon resonance analysis

The cross section for the reaction $ e p \to e^{\prime} p π^{+} π^{-}$ was measured in the resonance region for 1.4$<$W$<$2.1 GeV and 0.5$<Q^{2}<$1.5 GeV$^{2}$/c$^{2}$ using the CLAS detector at Jefferson Laboratory. The data show resonant structures not visible in previous experiments. The comparison of our data to a phenomenological prediction using available information on $N^{*}$ and $Δ$ states shows an evident discrepancy. A better description of the data is obtained either by a sizeable change of the properties of the $P_{13}$(1720) resonance or by introducing a new baryon state, not reported in published analyses.

hep-ex↗
arXiv2003

The proton structure function F2 in the resonance region

Unique measurement of the proton structure function F2 in a wide two-dimensional region of x and Q**2 has been reported. The accessible kinematics covers entire resonance region up to W=2.5 GeV in the Q**2 interval from 0.1 to 4.5 GeV**2. Obtained data allowed for the first time an evaluation of moments of the structure function F2 directly from experimental data as well as an intensive study of the Bloom-Gilman duality phenomenon.

hep-ex↗
arXiv2002

Single Quark Transition Model Analysis of Electromagnetic Nucleon Resonance Transitions in the [70,1-] Supermultiplet

We apply the single quark transition model to resonance transition amplitudes extracted from photo-and electroproduction data. We use experimental data on the S11(1535) and D13(1520) nucleon resonances to extract the amplitudes for the electromagnetic transition from the nucleon ground state to the [70,1-] SU(6)xO(3) supermultiplet, and make predictions for the transition amplitudes of all other states associated with the [70,1-]. We find suprisingly good agreement with the data.

hep-ph↗