Study of Two-Photon Exchange via the Beam Transverse Single Spin Asymmetry in Electron-Proton Elastic Scattering at Forward Angles over a Wide Energy Range.

We report on a new measurement of the beam transverse single spin asymmetry in electron-proton elastic scattering, A_{⊥}^{ep}, at five beam energies from 315.1 to 1508.4 MeV and at a scattering angle of 30°<θ<40°. The covered Q^{2} values are 0.032, 0.057, 0.082, 0.218, 0.613 (GeV/c)^{2}. The measurement clearly indicates significant inelastic contributions to the two-photon-exchange (TPE) amplitude in the low-Q^{2} kinematic region. No theoretical calculation is able to reproduce our result. Comparison with a calculation based on unitarity, which only takes into account elastic and πN inelastic intermediate states, suggests that there are other inelastic intermediate states such as ππN, KΛ, and ηN. Covering a wide energy range, our new high-precision data provide a benchmark to study those intermediate states.

New Measurements of the Beam Normal Spin Asymmetries at Large Backward Angles with Hydrogen and Deuterium Targets.

New measurements of the beam normal single spin asymmetry in the electron elastic and quasielastic scattering on the proton and deuteron, respectively, at large backward angles and at ⟨Q^{2}⟩=0.22 (GeV/c)^{2} and ⟨Q^{2}⟩=0.35 ( GeV/c)^{2} are reported. The experimentally observed asymmetries are compared with the theoretical calculation of Pasquini and Vanderhaeghen [Phys. Rev. C 70, 045206 (2004).PRVCAN0556-281310.1103/PhysRevC.70.045206]. The agreement of the measurements with the theoretical calculations shows a dominance of the inelastic intermediate excited states of the nucleon, πN and the Δ resonance. The measurements explore a new, important parameter region of the exchanged virtual photon virtualities.

Measurement of the charged-pion polarizability.

The COMPASS collaboration at CERN has investigated pion Compton scattering, π(-)γ→π(-)γ, at center-of-mass energy below 3.5 pion masses. The process is embedded in the reaction π(-)Ni→π(-)γNi, which is initiated by 190 GeV pions impinging on a nickel target. The exchange of quasireal photons is selected by isolating the sharp Coulomb peak observed at smallest momentum transfers, Q(2)<0.0015 (GeV/c)(2). From a sample of 63,000 events, the pion electric polarizability is determined to be α(π)=(2.0±0.6(stat)±0.7(syst))×10(-4) fm(3) under the assumption α(π)=-ß(π), which relates the electric and magnetic dipole polarizabilities. It is the most precise measurement of this fundamental low-energy parameter of strong interaction that has been addressed since long by various methods with conflicting outcomes. While this result is in tension with previous dedicated measurements, it is found in agreement with the expectation from chiral perturbation theory. An additional measurement replacing pions by muons, for which the cross-section behavior is unambiguously known, was performed for an independent estimate of the systematic uncertainty.

Measurement of strange quark contributions to the vector form factors of the proton at Q2 = 0.22 (GeV / c)2.

A new measurement of the parity violating asymmetry in elastic electron scattering on hydrogen at backward angles and at a four momentum transfer of Q;{2} = 0.22 (Ge V / c);{2} is reported here. The measured asymmetry is A_{LR} = (-17.23 +/- 0.82_{stat} +/- 0.89_{syst}) x 10;{-6}. The standard model prediction assuming no strangeness is A_{0} = (-15.87 +/- 1.22) x 10;{-6}. In combination with previous results from measurements at forward angles, it is possible to disentangle for the first time the strange form factors at this momentum transfer, G_{E};{s} = 0.050 +/- 0.038 +/- 0.019 and G_{M};{s} = -0.14 +/- 0.11 +/- 0.11.

Evidence for strange-quark contributions to the nucleon's form factors at Q2=0.108 (GeV/c)2.

We report on a measurement of the parity violating asymmetry in the elastic scattering of polarized electrons off unpolarized protons with the A4 apparatus at MAMI in Mainz at a four momentum transfer value of Q(2)=0.108 (GeV/c)(2) and at a forward electron scattering angle of 30 degrees p)=[-1.36+/-0.29(stat)+/-0.13(syst)]x10(-6). The expectation from the standard model assuming no strangeness contribution to the vector current is A(0)=(-2.06+/-0.14)x10(-6). We have improved the statistical accuracy by a factor of 3 as compared to our previous measurements at a higher Q2. We have extracted the strangeness contribution to the electromagnetic form factors from our data to be G(s)(E)+0.106G(s)(M)=0.071+/-0.036 at Q(2)=0.108 (GeV/c)(2). We again find the value for G(s)(E)+0.106G(s)(M) to be positive, this time at an improved significance level of two sigma.

Measurement of the transverse beam spin asymmetry in elastic electron-proton scattering and the inelastic contribution to the imaginary part of the two-photon exchange amplitude.

We report on a measurement of the asymmetry in the scattering of transversely polarized electrons off unpolarized protons, A( perpendicular), at two Q2 values of 0.106 and 0.230 (GeV/c)(2) and a scattering angle of 30 degrees

Measurement of strange-quark contributions to the nucleon's form factors at Q(2) = 0.230 (GeV/c)(2).

We report on a measurement of the parity-violating asymmetry in the scattering of longitudinally polarized electrons on unpolarized protons at a Q2 of 0.230 (GeV/c)(2) and a scattering angle of theta (e) = 30 degrees - 40 degrees. Using a large acceptance fast PbF2 calorimeter with a solid angle of delta omega = 0.62 sr, the A4 experiment is the first parity violation experiment to count individual scattering events. The measured asymmetry is A(phys)=(-5.44+/-0.54(stat)+/-0.26(sys))x10(-6). The standard model expectation assuming no strangeness contributions to the vector form factors is A(0) = (-6.30+/-0.43) x 10(-6). The difference is a direct measurement of the strangeness contribution to the vector form factors of the proton. The extracted value is G(s)(E) + 0.225G(s)(M) = 0.039+/-0.034 or F(s)(1) + 0.130F(s)(2) = 0.032+/-0.028.

Utility of ascitic fluid analysis in patients with malignancy-related ascites.

One-hundred and thirty-three consecutive ascitic patients hospitalized in our Liver Unit were prospectively investigated, to define the accuracy of ascitic fluid analysis in identifying malignancy. Patients with extrahepatic cancer and peritoneal carcinomatosis were characterized by positive cytology and higher ascitic levels of fibronectin, lactic dehydrogenase, carcinoembryonic antigen, and total protein than both patients with uncomplicated cirrhosis and patients with cirrhosis and liver cancer. Ascitic cytology, fibronectin, and lactic dehydrogenase (LDH) were the most sensitive and specific markers of extrahepatic malignancy. In contrast, none of these markers was useful in identifying patients with primary liver cancer complicating cirrhosis. For them, the only alteration of the ascitic fluid was an elevated alpha-fetoprotein concentration. The sensitivity, specificity, and accuracy of ascitic alpha-fetoprotein for detecting liver cancer were 87%, 95%, and 94%, respectively. Combining cytology with the determinations of fibronectin (or LDH) and alpha-fetoprotein in ascitic fluid satisfactorily differentiated 28 of 32 cases of malignancy-related ascites, with very low incidence of false-positives (4-6%). Therefore, in view of the frequent difficulties in detecting liver cancer as a complication of cirrhosis in patients with ascites, it is advisable to determine all these three markers in the same ascitic sample.

Paracentesis: a re-evaluated procedure in the management of cirrhotic patients with ascites.

Paracentesis is the oldest method for treating patients with ascites, but the fear of serious side-effects and the coincident introduction of effective non-toxic diuretic drugs led to its abandonment during the fifties. In recent years, several studies have investigated whether abdominal evacuation of ascitic fluid is truly dangerous for cirrhotic patients. The results of some randomized controlled trials comparing paracentesis with a traditional diuretic therapy showed that the rate of complications after paracentesis, particularly when the procedure was combined with a sufficient plasma expansion, was equal to or lower than that of diuretic treatment. Moreover, the ability of paracentesis to resolve tense ascites, both in terms of number of successes and of time required to obtain ascites resolution, was similar or even higher. These data and the recent new interest of several investigators in employing ascitic fluid examination for diagnostic purposes have increased the use of this procedure in the clinical practice.

Renal response to atrial natriuretic peptide in patients with advanced liver cirrhosis.

Sodium retention in liver cirrhosis is thought to be due to, among other things, lack of a natriuretic factor or failure to respond to one. alpha-Human-atrial natriuretic peptide is a peptide that accounts partly or entirely for the circulating natriuretic activity in man. In the present study, we have evaluated the effects of the bolus administration of synthetic alpha-human-atrial natriuretic peptide (1 microgram per kg) to patients with liver cirrhosis and variable degrees of sodium retention. alpha-Human-atrial natriuretic peptide induced rapid and marked increases of diuresis and natriuresis in patients without sodium retention or with moderate retention. The results were comparable to those obtained in six healthy control subjects. Conversely, the diuretic and natriuretic effects of alpha-human-atrial natriuretic peptide were attenuated or completely blunted in patients with avid sodium retention. The two groups of patients differed not only in basal sodium excretion, but also in plasma renin activity and in plasma aldosterone levels, suggesting that the reduced responsiveness to atrial natriuretic peptide might be due to excessive antagonism by antinatriuretic factors. The direct relationship between baseline sodium excretion rate and that stimulated by human-atrial natriuretic peptide administration was consistent with this interpretation. In none of the subjects did plasma renin activity peptide and cortisol levels change after human-atrial natriuretic peptide, while plasma aldosterone slightly declined in cirrhotics. Blood pressure fell after the administration of the peptide, with the drug greater in cirrhotic than in normal subjects.(ABSTRACT TRUNCATED AT 250 WORDS)