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Garibaldi, F.

Publications and source records attributed to Garibaldi, F..

70 records · Page 4
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DOE OSTI2014

Single spin asymmetries of inclusive hadrons produced in electron scattering from a transversely polarized 3 He target

We report the first measurement of target single-spin asymmetries (A N ) in the inclusive hadron production reaction, e + 3 He↑→h+X, using a transversely polarized 3 He target. This experiment was conducted at Jefferson Lab in Hall A using a 5.9-GeV electron beam. Three types of hadrons (π ± , K ± and proton) were detected in the transverse hadron momentum range 0.54 < p T < 0.74 GeV/c. The range of x F for pions was -0.29 < x F < -0.23 and for kaons -0.25 < x F <-0.18. The observed asymmetry strongly depends on the type of hadron. A positive asymmetry is observed for π + and K + . A negative asymmetry is observed for π–. The magnitudes of the asymmetries follow |A π – |<|A π + |<|A K + |. The K – and proton asymmetries are consistent with zero within the experimental uncertainties. The π + and π – asymmetries measured for the 3 He target and extracted for neutrons are opposite in sign with a small increase observed as a function of p T .

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2014

Measurement of parity violation in electron–quark scattering

Symmetry permeates nature and is fundamental to all laws of physics. One example is parity (mirror) symmetry, which implies that flipping left and right does not change the laws of physics. Laws for electromagnetism, gravity and the subatomic strong force respect parity symmetry, but the subatomic weak force does not1, 2. Historically, parity violation in electron scattering has been important in establishing (and now testing) the standard model of particle physics. One particular set of quantities accessible through measurements of parity-violating electron scattering are the effective weak couplings C2q, sensitive to the quarks’ chirality preference when participating in the weak force, which have been measured directly3, 4 only once in the past 40 years. Here we report a measurement of the parity-violating asymmetry in electron–quark scattering, which yields a determination of 2C2u-C2d (where u and d denote up and down quarks, respectively) with a precision increased by a factor of five relative to the earlier result. These results provide evidence with greater than 95 per cent confidence that the C2q couplings are non-zero, as predicted by the electroweak theory. They lead to constraints on new parity-violating interactions beyond the standard model, particularly those due to quark chirality. Whereas contemporary particle physics research is focused on high-energy colliders such as the Large Hadron Collider, our results provide specific chirality information on electroweak theory that is difficult to obtain at high energies. Our measurement is relatively free of ambiguity in its interpretation, and opens the door to even more precise measurements in the future.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2013

Electroproduction of K+ Λ at JLab Hall-C

A Λ hypernuclear spectroscopic experiment, JLab E05-115 was performed at JLab Hall-C in 2009 by the (e, e' K + ) reaction. Data of Λ hypernuclei with mass numbers from A = 7 to A = 52 were successfully taken, and the analyses are in progress. A polyethylene (CH 2 ) target was used as a proton target to calibrate energy scales, and to study elementary process of the p(e, e' K + )Λ, Σ 0 reaction. We report a preliminary differential cross section of K + Λ electro-production at low Q 2 [~0.01 (GeV/c) 2 ] and at small kaon angles (cosΘ$CM\atop{K}$ ~0.97) in the present article.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2012

Polarization components in π 0 photoproduction at photon energies up to 5.6 GeV

We present new data for the polarization observables of the final state proton in the 1 H(→ γ, → p)π 0 reaction. These data can be used to test predictions based on hadron helicity conservation (HHC) and perturbative QCD (pQCD). These data have both small statistical and systematic uncertainties, and were obtained with beam energies between 1.8 and 5.6 GeV and for π 0 scattering angles larger than 75{sup o} in center-of-mass (c.m.) frame. The data extend the polarization measurements data base for neutral pion photoproduction up to E γ = 5.6 GeV. The results show non-zero induced polarization above the resonance region. The polarization transfer components vary rapidly with the photon energy and π 0 scattering angle in the center-of-mass frame. This indicates that HHC does not hold and that the pQCD limit is still not reached in the energy regime of this experiment.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2012

Final analysis of proton form factor ratio data at Q 2 = 4.0, 4.8, and 5.6 GeV 2

Recently published measurements of the proton electromagnetic form factor ratio R = μ p G E p /G M p at momentum transfers Q 2 up to 8.5 GeV 2 in Jefferson Lab Hall C deviate from the linear trend of previous measurements in Jefferson Lab Hall A, favoring a slower rate of decrease of R with Q 2 . While statistically compatible in the region of overlap with Hall A, the Hall C data hint at a systematic difference between the two experiments. This possibility was investigated in a reanalysis of the Hall A data. We find that the original analysis underestimated the background in the selection of elastic events. The application of an additional cut to further suppress the background increases the results for R, improving the consistency between Halls A and C.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2012

New Precision Limit on the Strange Vector Form Factors of the Proton

The parity-violating cross-section asymmetry in the elastic scattering of polarized electrons from unpolarized protons has been measured at a four-momentum transfer squared Q 2 = 0.624 GeV 2 and beam energy E b = 3.48 GeV to be A PV = -23.80 ± 0.78 (stat) ± 0.36 (syst) parts per million. This result is consistent with zero contribution of strange quarks to the combination of electric and magnetic form factors G E s + 0.517 G M s = 0.003 ± 0.010 (stat) ± 0.004 (syst) ± 0.009 (ff), where the third error is due to the limits of precision on the electromagnetic form factors and radiative corrections. With this measurement, the world data on strange contributions to nucleon form factors are seen to be consistent with zero and not more than a few percent of the proton form factors.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2012

Beam-Target Double-Spin Asymmetry A LT in Charged Pion Production from Deep Inelastic Scattering on a Transversely Polarized He 3 Target at 1.4 < Q 2 < 2.7 GeV 2

We report the first measurement of the double-spin asymmetry A LT for charged pion electroproduction in semi-inclusive deep inelastic electron scattering on a transversely polarized 3 He target. The kinematics focused on the valence quark region, 0.16 < x < 0.35 with 1.4 < Q 2 < 2.7 GeV 2 . The corresponding neutron A LT asymmetries were extracted from the measured 3 He asymmetries and proton/ 3 He cross section ratios using the effective polarization approximation. These new data probe the transverse momentum dependent parton distribution function g 1T q and therefore provide access to quark spin-orbit correlations. Our results indicate a positive azimuthal asymmetry for π - production on 3 He and the neutron, while our π + asymmetries are consistent with zero.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Probing the High Momentum Component of the Deuteron at High Q{sup 2}

The {sup 2}H(e,e{sup '}p)n cross section at a momentum transfer of 3.5 (GeV/c){sup 2} was measured over a kinematical range that made it possible to study this reaction for a set of fixed missing momenta as a function of the neutron recoil angle {theta}{sub nq} and to extract missing momentum distributions for fixed values of {theta}{sub nq} up to 0.55 GeV/c. In the region of 35 deg. {<=}{theta}{sub nq}{<=}45 deg. recent calculations, which predict that final-state interactions are small, agree reasonably well with the experimental data. Therefore, these experimental reduced cross sections provide direct access to the high momentum component of the deuteron momentum distribution in exclusive deuteron electrodisintegration.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗