The $\gamma n \to \pi^0 n$ differential cross section evaluated for 27 energy bins span the photon-energy range 290-813 MeV (W = 1.195-1.553 GeV) and the pion c.m. polar production angles, ranging from 18 deg to 162 deg, making use of model-dependent nuclear corrections to extract pi0 production data on the neutron from measurements on the deuteron target. Additionally, the total photoabsorption cross section was measured. The tagged photon beam produced by the 883-MeV electron beam of the Mainz Microtron MAMI was used for the 0-meson production. Our accumulation of 3.6 x 10^6 $\gamma n \to \pi^0 n$ events allowed a detailed study of the reaction dynamics. Our data are in reasonable agreement with previous A2 measurements and extend them to lower energies. The data are compared to predictions of previous SAID, MAID, and BnGa partial-wave analyses and to the latest SAID fit MA19 that included our data. Selected photon decay amplitudes $N^* \to \gamma n$ at the resonance poles are determined for the first time.
Excitation function at pion c.m. angle THETA=18 deg as function of incident photon energy E. The uncertainties are statistical and systematic, combined in quadrature.
Excitation function at pion c.m. angle THETA=32 deg as function of incident photon energy E. The uncertainties are statistical and systematic, combined in quadrature.
Excitation function at pion c.m. angle THETA=41 deg as function of incident photon energy E. The uncertainties are statistical and systematic, combined in quadrature.
The c.m. angular distribution of π+p elastic scattering at 1.6 GeV/c shows a strong forward diffraction peak decreasing exponentially with a slopeA + = (6.9±0.5) GeV−2 comparable to thatA − = (7.2±0.5) GeV−2 observed in a previous experiment for π-p elastic scattering at the same incident momentum. The behaviour of the π+ and the π− angular distributions is quite different beyond the diffraction peak. The π+p total elastic cross-section is found to be Σ01 = (16.70±0.45) mb.
No description provided.
No description provided.
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We report on precision measurements of the elastic cross section for electron-proton scattering performed in Hall C at Jefferson Lab. The measurements were made at 28 unique kinematic settings covering a range in momentum transfer of 0.4 $<$ $Q^2$ $<$ 5.5 $(\rm GeV/c)^2$. These measurements represent a significant contribution to the world's cross section data set in the $Q^2$ range where a large discrepancy currently exists between the ratio of electric to magnetic proton form factors extracted from previous cross section measurements and that recently measured via polarization transfer in Hall A at Jefferson Lab.
Measured values of the electron-proton elastic cross section for beam energy 1.148 GeV.
Measured values of the electron-proton elastic cross section for beam energy 1.882 GeV.
Measured values of the electron-proton elastic cross section for beam energy 2.235 GeV.
A test of the QED process e+e- -> gamma gamma (gamma) is reported. The data analysed were collected with the DELPHI detector in 1998 and 1999 at the highest energies achieved at LEP, reaching 202 GeV in the centre-of-mass. The total integrated luminosity amounts to 375.7 pb^{-1}. The differential and total cross-sections for the process e+e- -> gamma gamma were measured, and found to be in agreement with the QED prediction. 95% Confidence Level (C.L.) lower limits on the QED cut-off parameters of Lambda+ > 330 GeV and Lambda- > 320 GeV were derived. A 95% C.L. lower bound on the mass of an excited electron of 311 GeV/c^2 (for lambda_gamma = 1) was obtained. s-channel virtual graviton exchange was searched for, resulting in 95% C.L. lower limits on the string mass scale, M_S: M_S > 713 GeV/c^2 (lambda = 1) and M_S > 691 GeV/c^2 (lambda = -1).
No description provided.
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No description provided.
The total and differential cross sections of the process e+e- -> n gamma with n >= 2 are measured using data collected by the L3 experiment at centre-of-mass energies of \sqrt{s}=183 and 189 GeV. The results are in agreement with the Standard Model expectations. Limits are set on deviations from QED, contact interaction cut-off parameters and masses of excited electrons.
Measured cross section.
Measured differential cross sections corrected for efficiency and additional photons as a function of cos(theta) where theta is the polar angle of the event defined as. cos(theta)=ABS((sin(theta1-theta2)/2)/(sin(theta1+theta2)/2)).
The total and the differential cross-sections for the reaction e + e − → γγ ( γ ) have been measured with the DELPHI detector at LEP at centre-of-mass energies from 130 to 183 GeV for an integrated luminosity of 78.19 pb −1 . The results agree with the QED predictions. The lower limits (obtained including previously published results at the Z 0 energies) on the QED cutoff parameters are Λ + >253 GeV and Λ − >225 GeV and the lower bound on the mass of an excited electron with an effective coupling constant λ γ =1 is 231 GeV/ c 2 . All the limits are at the 95% confidence level.
The cross section of the previously published data (sqrt(s)=91.25 GeV, see PL 327B, 386) is given at the mean of the CM energies weighted by the luminosityat each point.
Statistical errors only. Additional overall systematic uncertainty is givenabove.
Statistical errors only. Additional overall systematic uncertainty is givenabove.
Total and differential cross sections for the process e + e − → γγ ( γ ), and the total cross section for the process e + e − → γγγ , are measured at energies around 91 GeV using the data collected with the L3 detector from 1991 to 1993. We set lower limits, at 95% CL, on a contact interaction energy scale parameter Λ > 602 GeV, on the mass of an excited electron m e ∗ >146 GeV and on the QED cut-off parameters Λ + > 149 GeV and Λ _ > 143 GeV. Upper limits are also set o branching fractions of Z decaying into γγ , π ° and ηγ of 5.2 × 10 −5 , 5.2 × 10 −5 and 7.6 × 10 −5 respectively. The reactions e + e − → ℓ + ℓ − nγ (ℓ = e , μ , τ ) are studied using the data collected from 1990 to 1994. The data are consistent with the QED expectations.
No description provided.
No description provided.
No description provided.
The total and the differential cross sections for the reaction e + e − → γγ ( γ ) have been measured with the DELPHI detector at LEP using an integrated luminosity of 36.9 pb −1 . The results agree with the QED predictions and consequently there is no evidence for non-standard channels with the same experimental signature. The lower limits obtained on the QED cutoff parameters are Λ + > 143 GeV and Λ − > 120 GeV, and the lower bound on the mass of an excited electron with an effective coupling constant λ γ = 1 is 132 GeV/ c 2 . Upper limits on the branching ratios for the decays Z 0 → γγ , Z 0 → π 0 γ , Z 0 → ηγ and Z 0 → γγγ have been determined to be 5.5 × 10 −5 , 5.5 × 10 −5 , 8.0 × 10 −5 , and 1.7 × 10 −5 respectively. All the limits are at the 95% confidence level.
1990 energies are 88.223, 89.222, 90.217, 91.217, 92.209, 93.208 and 94.202 GeV.. 1991 energies are 88.465, 89.460, 90.208, 91.225, 91.954, 92.953, and 93.703 GeV.. 1992 energy is 91.278 GeV.
Average of all data.
No description provided.
We have measured the total and differential cross sections of the reaction e + e − → γγ ( γ ) at center-of-mass energies around 91 GeV, with an integrated luminosity of 14.2 pb −1 . The results are in good agreement with QED predictions. We set lower limits, at 95% confidence level, on the QED cutoff parameters of Λ + > 139 GeV, Λ − > 108 GeV and on the mass of an excited electron of m e∗ > 127 GeV . We searched for Z 0 rare decays with photonic signitures in the final state. Upper limits, at 95% confidence level, for branching ratio of Z 0 decaying into π 0 γ / γγ , νγ and γγγ are 1.2 × 10 −4 , 1.8 × 10 −4 , 3.3 × 10 −5 respectively.
Measured cross section for the 1991 data.
Measured cross section for the 1990 data.
Measured differential cross sections of combined 1990 and 1991 data.
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THE MOMENTUM OF EACH INCIDENT PION WAS DETERMINED WITH AN ACCURACY 0.2 PCT.
THE MOMENTUM OF EACH INCIDENT PION WAS DETERMINED WITH AN ACCURACY 0.2 PCT.
THE MOMENTUM OF EACH INCIDENT PION WAS DETERMINED WITH AN ACCURACY 0.2 PCT.
The differential cross section for the backward (120° ⩽ θ c.m.s. ⩽ 180°) pion-deuteron elastic scattering was measured at eight incident pion momenta from 0.90 to 2.025 GeV/ c . A distinctive change in the shape of the angular distribution is observed. At 0.9 GeV/ c the differential cross section decreases smoothly to 180° in accordance with predictions of multiple-scattering theory. At 1.31 GeV/ c , i.e. in the region of the hypothetical 1 I 6 dibaryon with a mass of 2.9 GeV, the differential cross section is practically independent of angle. At higher energies a sharp backward peak is clearly seen. Connections of our results with dibaryons and Regge asymptotic behaviour are discussed.
No description provided.
No description provided.
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We report on high statistics Bhabha scattering data taken with the TASSO experiment at PETRA at center of mass energies from 12 GeV to 46.8 GeV. We present an analysis in terms of electroweak parameters of the standard model, give limits on QED cut-off parameters and look for possible signs of compositeness.
Axis error includes +- 1/1 contribution (The overall uncertainty in the bin-to-bin polar acceptance due to shower corrections, trigger and reconstruction efficiencies was estimated to be less than 1% and was added in quadrature to the statistical errorsData have been corrected for qed radiative effects up to order alpha**3 (F.A.Berends, R.Kleiss, Nucl.Phys.B206(1983)61)//Weak radiative corrections have not yet been provided in a form of a Monte Carlo generator program, but are estimated to be negligible at PETRA energies (M.Bohm, A.Denner, W.Hollik, DESY-86-165)).
Axis error includes +- 1/1 contribution (The overall uncertainty in the bin-to-bin polar acceptance due to shower corrections, trigger and reconstruction efficiencies was estimated to be less than 1% and was added in quadrature to the statistical errorsData have been corrected for qed radiative effects up to order alpha**3 (F.A.Berends, R.Kleiss, Nucl.Phys.B206(1983)61)//Weak radiative corrections have not yet been provided in a form of a Monte Carlo generator program, but are estimated to be negligible at PETRA energies (M.Bohm, A.Denner, W.Hollik, DESY-86-165)).
Axis error includes +- 1/1 contribution (The overall uncertainty in the bin-to-bin polar acceptance due to shower corrections, trigger and reconstruction efficiencies was estimated to be less than 1% and was added in quadrature to the statistical errorsData have been corrected for qed radiative effects up to order alpha**3 (F.A.Berends, R.Kleiss, Nucl.Phys.B206(1983)61)//Weak radiative corrections have not yet been provided in a form of a Monte Carlo generator program, but are estimated to be negligible at PETRA energies (M.Bohm, A.Denner, W.Hollik, DESY-86-165)).
Measurements of the differential cross section for π − d elastic scattering in the backward angular region (−1 ⩽ cos θ cms ⩽ −0.98) are presented. These measurements were made at nine incident pion momenta P π ranging from 1.75 to 3.09 GeV/ c and at the largest values of q 2 [up to 7 (GeV/ c ) 2 ] ever reached experimentally; here q 2 is the momentum transfer squared. The differential cross section was found to decrease rapidly with increasing momentum d σ d Ω cms (180°) ∼ P −15.7 π , d σ d t ∼ (q 2 ) −12.8 . The data are compared with predictions of Regge and quark bag models.
Statistical errors only.
We have measured differential cross sections for both π+p and π−p elastic scattering at incident-pion kinetic energies of 30, 50, 70, and 90 MeV in the center-of-mass angular range between 50° and 150°. The experiment detected pions scattered from a liquid-hydrogen target with multiwire proportional chambers and scintillation-counter range telescopes. The relative accuracy of each angular distribution is better than 5%, while the absolute cross sections have uncertainties of 4% to 25%. Our results for the absolute cross section for π+p scattering at 30 and 90 MeV are inconsistent with previous measurements. Our π−p measurements comprise the first extensive set of precision differential cross sections below 90 MeV.
No description provided.
No description provided.
No description provided.
Differential cross sections for backward π − d elastic scattering (−1 ≦ cos θ c.m ≦ −0.98) have been measured at fourteen momenta from 0.98 to 1.76 GeV/ c and at 2.45 GeV/ c . Energy dependence of the cross section exibits a new wide structure at √ s ≈ 2.9 GeV. Possible mechanisms of the reaction accounting for this structure are presented. Experimental data are compared with theoretical calculations.
BEAM ERROR D(P)/P = 0.300 PCT.
BEAM ERROR D(P)/P = 0.300 PCT.
BEAM ERROR D(P)/P = 0.300 PCT.
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No description provided.
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BEAM ERROR D(P)/P = 0.300 PCT.
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X ERROR D(THETA) = 0.2000 DEG.
X ERROR D(TARGET) = 99.60 PCT. X ERROR D(THETA) = 0.2000 DEG.
X ERROR D(THETA) = 0.2000 DEG.
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No description provided.
No description provided.
The experimental data on d-d collisions at 4.3, 6.3 and 8.9 GeV/ c , exhibiting the two-peak structure in the high-momentum parts of the secondary deuteron spectra at momentum transfers | t | ≈ 0.4–0.8 (GeV/ c ) 2 , are presented. An analysis of the results in terms of the multiple nucleon-nucleon scattering model is given. Some conclusions about the mechanism of the elastic and quasielastic d-d scattering at the above-mentioned momentum transfers are made.
No description provided.
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We present differential cross-sections for pp elastic scattering at eight laboratory momenta from 1.50 to 2.06 GeV/c. The data are analysed using an 8-parameter optical modelà la Frahn and Venter. However, the best representation of the differential cross-sections is obtained by combining the glory model with a parametrization of the scattering amplitude in terms of coherent exponentials. Both representations show the dominance of the partial wave with orbital angular momentum equal to four.
No description provided.
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The spectrum and yield of protons produced by 60-, 100-, and 200-MeV π+ and π− beams on targets of He4, C12, Ni62, and Ta181 have been measured at 45° and 90°. A distinct high-energy component is seen in the protons from He4, which is consistent with a two-body absorption mechanism. Its cross section at 220 MeV is somewhat larger than calculated from the π+ + D process. Possible evidence is also seen for multinucleon absorption modes. The data on heavier nuclei are consistent with earlier experiments.
No description provided.
No description provided.
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X ERROR D(TARGET) = 95.80 PCT.
X ERROR D(TARGET) = 97.50 PCT.
Differential cross sections have been measured for the interactions p p → π − π + and p p → K − K + over a centre of mass angular range −0.95 ⩽ cos θ ∗ ⩽ 0.95 at 20 incident momenta between 0.79 and 2.43 GeV/ c . A magnetic spectrometer with wire spark chambers was used. Typically 2000 π − π + and 300 K − K + events were obtained at each momentum. Results are compared with those from related experiments.
No description provided.
No description provided.
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The differential cross section for the reaction π − p→n π ° has been measured with high statistics at six incident beam momenta between 1.0 and 2.4 GeV/ c . The results are compared with predictions of recent phase shift analyses and forward dispersion relations.
No description provided.
FROM EXTRAPOLATING THE LEGENDRE POLYNOMIAL FITS.
THE LEGENDRE POLYNOMIAL FITS WERE CONSTRAINED IN THE EXTREME BACKWARD DIRECTION BY DATA AT THETA = 180 DEG FROM OTHER EXPERIMENTS.
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X ERROR D(TARGET) = 96.97 PCT.
X ERROR D(TARGET) = 93.08 PCT.
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Elastic electron proton scattering has been used to check the validity of the dipole fit of the proton form factors at momentum transfer between 0.05 and 0.30 (GeV/ c ) 2 . The general behaviour of the cross sections is in agreement with previous measurements and is close to the dipole predictions but there is the suggestion of some small amplitude deviations. It is speculated that these deviations may be related to similar effects in the proton formfactor derived from the ISR pp elastic scattering data via a Chou-Yang model.
D(SIG(N=DIPOLE))/D(OMEGA) is cross-section derived in the assumption that both the magnetic and electric form - factors of the proton can be expressed by the dipole formula G(q**2) = 1/(1 + q**2/0.71)**2. Data are read from graph by BVP.
D(SIG(N=DIPOLE))/D(OMEGA) is cross-section derived in the assumption that both the magnetic and electric form - factors of the proton can be expressed by the dipole formula G(q**2) = 1/(1 + q**2/0.71)**2. Data are read from graph by BVP.
Results of fit of the combined data samples of Table 1 and Table 2. Data points was fitted by formula A + B*q**2 + C*sin(OMEGA*q**2 + PHI).
None
No description provided.
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Small-angle differential cross sections are presented here for π−+p→π0+n charge-exchange scattering between 2.4 and 3.8 GeV/c. The differential cross section near t=0 displays two minima and one maximum in this momentum interval, reflecting the presence of the N32*(2420), N32*(2850), and N12*(2650) resonances; at larger t values, the cross sections fall off exponentially as a function of t, just as has been previously observed for charge-exchange scattering above 6 GeV/c. The pion-charge-exchange data reported here at 6 and 10 GeV/c extend out to large angles, showing a maximum near t=0, followed by an exponential falloff as e10t, a minimum near −t=0.6 (GeV/c)2, and then a second maximum near −t=1.0 (GeV/c)2. The π−+p→η0+n differential cross section shows a maximum near t=0, followed by an exponential falloff as e4t, much less steep than the π0 slope. These data are compared to our previously published data and to those of the Saclay-Orsay group.
No description provided.
No description provided.
No description provided.
Report on the investigation of interactions in π−p collisions at a pion momentum of 1.59 GeV/c, by means of the 50 cm Saclay liquid hydrogen bubble chamber, operating in a magnetic field of 17.5 kG. The results obtained concern essentially the elastic scattering and the inelastic scattering accompanied by the production of either a single pion in π−p→ pπ−π0 and nπ−π+ interactions, or by more than one pion in four-prong events. The observed angular distribution for the elastic scattering in the diffraction region, can be approximated by an exponential law. From the extrapolated value, thus obtained for the forward scattering, one gets σel= (9.65±0.30) mb. Effective mass spectra of π−π0 and π−π+ dipions are given in case of one-pion production. Each of them exhibits the corresponding ρ− or ρ0 resonances in the region of ∼ 29μ2 (μ = mass of the charged pion). The ρ peaks are particularly conspicuous for low momentum transfer (Δ2) events. The ρ0 distribution presents a secondary peak at ∼31μ2 due probably to the ω0 → π−π+ process. The branching ratio (ω0→ π+π−)/(ω0→ π+π− 0) is estimated to be ∼ 7%. The results are fairly well interpreted in the frame of the peripheral interaction according to the one-pion exchange (OPE) model, Up to values of Δ2/μ2∼10. In particular, the ratio ρ−/ρ0 is of the order of 0.5, as predicted by this model. Furthermore, the distribution of the Treiman-Yang angle is compatible with an isotropic one inside the ρ. peak. The distribution of\(\sigma _{\pi ^ + \pi ^ - } \), as calculated by the use of the Chew-Low formula assumed to be valid in the physical region of Δ2, gives a maximum which is appreciably lower than the value of\(12\pi \tilde \lambda ^2 = 120 mb\) expected for a resonant elastic ππ scattering in a J=1 state at the peak of the ρ. However, a correcting factor to the Chew-Low formula, introduced by Selleri, gives a fairly good agreement with the expected value. Another distribution, namely the Δ2 distribution, at least for Δ2 < 10 μ2, agrees quite well with the peripheral character of the interaction involving the ρ resonance. π− angular distributions in the rest frame of the ρ exhibit a different behaviour for the ρ− and for the ρ0. Whereas the first one is symmetrical, as was already reported in a previous paper, the latter shows a clear forward π− asymmetry. The main features of the four-prong results are: 1) the occurrence of the 3/2 3/2 (ρπ+) isobar in π−p → pπ+π−π− events and 2) the possible production of the ω0→ π+π−π0 resonance in π−p→ pπ−π+π−π0 events. No ρ’s were observed in four-prong events.
No description provided.
No description provided.
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