(γ,2N) reaction inC12

The $^{12}$C(\ensuremath{\gamma},pn) and $^{12}$C(\ensuremath{\gamma},pp) reactions have been measured for photon energies between 80 and 157 MeV using a photon tagging spectrometer and plastic scintillator detectors. The overall energy resolution was \ensuremath{\sim}7 MeV, sufficient to determine the initial shells of the emitted nucleons. Corrections were made for solid angle and threshold effects by means of Monte Carlo simulations. For the (\ensuremath{\gamma},pn) reaction both the missing energy and recoil momentum distributions are largely consistent with a two-nucleon absorption process on p-shell an sp nucleon pairs. For the much smaller $^{12}$C(\ensuremath{\gamma},pp) cross secti…

Compton Scattering by the Proton

Compton scattering by the proton has been measured over a wide range covering photon energies 250 MeV < E_\gamma < 800 MeV and photon scattering angles 30^0 < \theta^{lab}_\gamma < 150^0, using the tagged-photon facility at MAMI (Mainz) and the large-acceptance arrangement LARA. The data are in good agreement with the dispersion theory based on the SAID-SM99K parameterization of photo-meson amplitudes. From the subset of data between 280 and 360 MeV the resonance pion-photoproduction amplitudes were evaluated leading to the multipole E2/M1 ratio EMR(340 MeV) =(-1.6 \pm 0.4(stat+syst) \pm 0.2(model)%. From all data below 455 MeV the proton's backward spin polarizability was determined to be …

Study of three-nucleon mechanisms in the photodisintegration of 3He

Abstract The cross section of the 3He(γ,pp)n reaction has been measured for the first time over a wide photon energy and proton angular range (200 MeV ≤ Eγ ≤ 800 MeV; 20° ≤ ϑplab ≤ 160°) using the large acceptance detector DAPHNE at the tagged photon facility of the MAMI microtron in Mainz. The wide kinematical coverage of the measurement has allowed a detailed analysis of three-nucleon absorption mechanisms. A model developed by Laget explains the main characteristics of the data in the Δ resonance region.

C(,pn) photon asymmetry for Eγ=180–340 MeV

The photon asymmetry (Σ) of the 12C(,pn) reaction has been measured using linearly polarised tagged photons at the Mainz microtron MAMI for Eγ=180–340 MeV. The data have been analysed in separate missing energy (Em) regions corresponding to the ejection of nucleons from (1p)2 and (1p)(1s) shells. The measured Σ values for both Em regions are smaller in magnitude than corresponding 2H data, but the (1p)2 results have a similar Eγ dependence. Calculations of direct two-nucleon emission overestimate the magnitude of Σ at all photon energies.

Near threshold photoproduction of eta mesons off the proton.

We have measured precise total and differential cross sections for the reaction $\ensuremath{\gamma}p\ensuremath{\rightarrow}p\ensuremath{\eta}$ from threshold to 790 MeV at the MAMI accelerator in Mainz with the neutral meson spectrometer TAPS. Resonance parameters of the ${S}_{11}$(1535) resonance and the electromagnetic coupling $\ensuremath{\gamma}p\ensuremath{\rightarrow}{S}_{11}$ have been extracted from the data. Contributions from the ${D}_{13}$(1520) resonance to $\ensuremath{\eta}$ photoproduction in the threshold region have been identified for the first time via interference terms in the angular distributions.

Quasifreeπ+production studied using theC12(γ, π+n)B11reaction in theΔ(1232)resonance region

Results are presented from a coincidence study of the {sup 12}C({gamma},{pi}{sup +}{ital n}){sup 11}B quasifree pion production reaction made in the {Delta}-resonance region using tagged photons. Cross sections for reactions originating on 1{ital p}-shell protons are found to be significantly larger than predicted by calculations based on quasifree pion production. It is suggested that more sophisticated calculations, perhaps including medium effects, may be required to reproduce the data. {copyright} {ital 1996 The American Physical Society.}

Photon Asymmetry of Deuteron Photodisintegration Between 160 and 410 MeV

The photon asymmetry Σ of the reaction has been measured across the photon energy range 160–410 MeV at the Mainz Microtron MAMI. Linearly polarized photons were obtained from coherent bremsstrahlung and their energies were determined with the Glasgow tagging spectrometer. The large acceptance detector DAPHNE enabled the outgoing protons to be measured over the complete azimuthal range and for polar angles from 35° to 155° in the c.m. system. The data are compared with existing results and recent theoretical calculations.

Photofission of235U and238U at intermediate energies: absolute cross sections and fragment mass distributions

The total photofission cross section σγ,F for235U and238U has been measured in the energy range 50≤E γ≤800 MeV at the 855 MeV Mainz Microtron MAMI using energy and time tagged photons (Glasgow Tagger) and a 4π arrangement of position sensitive fragment detectors. Besides the absolute photofission cross section σγF , which almost completely exhausts the total photon absorption cross section for these nuclei, fragment mass distributions in this energy domain were determined via time of flight techniques (TOF). The results for the total photofission cross sections σγ,F normalized to the atomic numberA for both isotopes coincide, and agree in theΔ-resonance region, within the systematic errors,…

Investigation of multiparticle final states in12C photoreactions

The ${}^{12}\mathrm{C}(\ensuremath{\gamma},pn)$, ${}^{12}\mathrm{C}(\ensuremath{\gamma},pp)$, ${}^{12}\mathrm{C}(\ensuremath{\gamma},ppp)$, ${}^{12}\mathrm{C}(\ensuremath{\gamma},pp{\ensuremath{\pi}}^{\ifmmode\pm\else\textpm\fi{}})$, ${}^{12}\mathrm{C}(\ensuremath{\gamma},p{\ensuremath{\pi}}^{\ifmmode\pm\else\textpm\fi{}})$ reactions have been studied using tagged photons of energy ${E}_{\ensuremath{\gamma}}=250$--600 MeV. A model which includes all major absorption mechanisms and final state interactions gives results that agree well with the shapes of missing energy spectra, but for some channels the predicted cross sections are too large.

The 16O(γ, 2N) reaction measured with tagged photons

The results of tagged-photon measurements of the 4He(γ, pn)d, 4He(γ, pn)pn and 4He(γ, pp)nn reactions, carried out with photons of energies 80–131 MeV, are presented. The (γ, pn)d three-body-breakup cross section dominates the four-body-breakup cross section. The three-body-breakup cross section and the corresponding deuteron recoil-momentum spectrum are reasonably accounted for by a mechanism of photon absorption on correlated proton-neutron pairs. In contrast the four-body-breakup mechanism appears to have two components: absorption on correlated proton-neutron pairs and a more complex additional component which has a distribution similar to phase space. The data rule out substantial phot…

Measurement of the p(γ,π^{0}) cross section at threshold

Differential and absolute cross sections for the reaction {ital p}({gamma},{pi}{sup 0}) have been measured with energy-defined photons in the threshold region ({ital E}{sub {gamma}}=131.4--157.2 MeV). The {ital E}{sub 0+} amplitude has been extracted out of the data. The values found are in disagreement with predictions of low-energy theorems.

Compton scattering by the proton through θcms = 75° and 90° in the Δ-resonance region

Abstract Differential cross sections for Compton scattering by the proton have been measured in the energy interval between 200 and 500 MeV at scattering angles of θcms = 75° and θcms = 90° using the CATS, the CATS/TRAJAN, and the COPP setups with the Glasgow Tagger at MAMI (Mainz). The data are compared with predictions from dispersion theory using photo-meson amplitudes from the recent VPI solution SM95. The experiment and the theoretical procedure are described in detail. It is found that the experiment and predictions are in agreement as far as the energy dependence of the differential cross sections in the Δ-range is concerned. However, there is evidence that a scaling down of the reso…

Krusche et al. reply.

Differential cross sections for coherent and incoherent neutral-pion photoproduction from calcium

Differential and absolute cross sections for the coherent reaction $^{40}\mathrm{Ca}$(\ensuremath{\gamma},${\ensuremath{\pi}}^{0}$${)}^{40}$Ca g.s., as well as for the incoherent reaction $^{40}\mathrm{Ca}$(\ensuremath{\gamma},${\mathrm{\ensuremath{\pi}}}^{0}$${)}^{40}$Ca(g.s.), have been measured with monochromatic photons in the threshold region (${E}_{\ensuremath{\gamma}}$=157--169 MeV). The differential cross section for the coherent process exhibits a diffraction minimum due to the nuclear mass form factor while the incoherent cross section is rather structureless. The cross sections are in good agreement with recent distorted-wave impulse-approximation calculations.

The angular distribution of the 12C(γ,pn) reaction for Eγ=120−150 MeV

The angular distribution of nucleons emitted in the 12C(γ,pn) reaction has been measured using tagged photons at the Mainz microtron MAMI. The variation of the reaction strength with the polar angles of the two emitted nucleons is reported for Eγ=120−150 MeV. The proton angular distribution peaks at more backward angles than the 2H(γ,p) differential cross section indicating a departure from the simple quasi-deuteron model of 2N photo-emission. The distribution shape is in reasonable agreement with microscopic theoretical models which include both π- and ρ-exchange.

First measurement of the polarisation transfer on the proton in the reactions $$H(\vec e,e'\vec p)$$ and $$D(\vec e,e'\vec p)$$

The measurement of the polarisation transfer to the proton in the reactions\(H(\vec e,e'\vec p)\) and\(D(\vec e,e'\vec p)\) performed with longitudinally polarised electrons in quasi-free kinematics is presented. The coincidence measurement was executed atQ2≈8fm−2 using the 855 MeV, c.w. beam of the Mainz Microtron MAMI. The recoil polarisation was determined by means of a carbon analyser. The experiment shows that the binding of the nucleon does not modify the polarisationPx of the recoil proton within an error ofΔPx/Px≈10%. The measured polarisation agrees with recent theoretical predictions. Implications for the measurement of the electric form factor of the neutron using the\(D(\vec e,e…

Mechanisms in theC12(γ,pn)and(γ,pp)Reactions

${}^{12}\mathrm{C}(\ensuremath{\gamma},pn)$ and $(\ensuremath{\gamma},pp)$ cross sections have been measured in kinematics which emphasize direct $2N$ knockout for ${E}_{\ensuremath{\gamma}}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}120--400\mathrm{MeV}$ and ${\ensuremath{\theta}}_{p}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}23\ifmmode^\circ\else\textdegree\fi{}--152\ifmmode^\circ\else\textdegree\fi{}$. The cross sections for both reactions peak strongly in the $\ensuremath{\Delta}$-resonance region. Theoretical calculations that account for the medium dependence of the $\ensuremath{\Delta}$ propagator predict a similar photon energy dependence to the data and describe the …

Proton photoproduction from 12C

Abstract The 12 C(γ,p) differential cross-section in the Δ-resonance region has been measured using tagged photons. Data are presented for 20 MeV wide photon energy bins at 200, 300, 400 and 500 MeV and for proton angles from 52° to 128°. The present 12 C(γ,p) measurements are compared with previous experiments carried out at Frascati, Tokyo and Bonn. Comparisons are also made with theoretical calculations developed at Gent and Valencia which provide an interpretation of the photon reaction mechanism in terms of the major contributing processes. Coincidence data with correlated neutrons, protons and pions are also presented.

The12C(γ,NN)reaction studied over a wide kinematic range

The ${}^{12}\mathrm{C}(\ensuremath{\gamma},np)$ and ${}^{12}\mathrm{C}(\ensuremath{\gamma},pp)$ reactions have been studied using the Glasgow photon tagging spectrometer at the Mainz MAMI electron microtron for ${E}_{\ensuremath{\gamma}}=150--700$ MeV over a kinematic range which extends well beyond the approximately back-to-back detector arrangements of previous work. For ${}^{12}\mathrm{C}(\ensuremath{\gamma},np)$ the general trends of the missing energy distributions are reproduced over a wide range of kinematics and photon energies by the theory developed by the Valencia group. The corresponding ${}^{12}\mathrm{C}(\ensuremath{\gamma},pp)$ channel is overestimated by a factor of \ensurem…

Two-body photodisintegration of the deuteron from 100 to 800 MeV

Abstract The total and the differential cross sections for the D(γ,p)n reaction have been measured over the photon energy range 100-800 MeV at the 855 MeV MAMI Microtron in Mainz. Using the large acceptance detector DAPHNE in conjunction with the Glasgow tagging spectrometer, high precision results with small systematic errors were obtained. The data are presented in the form of thirty-five angular distributions at c.m. proton angles between 30°–160° in 10° intervals and at photon energies in steps of 20 MeV. Previous experimental work is reassessed in the light of the present results and comparison with some recent theoretical calculations.

Mass and Γ3π0/Γγγ decay branching ratio of theη-meson from the p(γ, η)p reaction

Near threshold photoproduction ofη-mesons from the proton has been measured at the MAMI accelerator with the TAPS spectrometer. The mass of theη-meson was deduced from the threshold energy forη-photoproduction. The result of m η =(547.12 ± 0.06 ± 0.25) MeV supports the low value of theη-mass reported from a dp →3Heη measurement at SATURNE in 1992. Theη-decay branching ratio Γ3π0/Γγγ was measured to be (0.832±0.005±0.012).

Determination of the neutron electric form factor in the D(e,e′n)p reaction and the influence of nuclear binding

The electric form factor of the neutron GE,n has been determined at the Mainz Microtron MAMI at the low momentum transfer Q2= 0.15 (GeV/c)2 in a measurement of the recoil polarisation ratio Px/Pz in the quasifree reaction D(e,e′n)p. At this Q2 the influence of the nuclear binding is strong. A purely kinematical model is used to get some insight into the effect of the initial Fermi momentum distribution of the neutron. The influence of the final state interaction is determined quantitatively by a model of Arenhovel et al.. After the corresponding corrections a value of GE,n(0.15 (GeV/c)2) = 0.0481±0.0065stat±0.0053syst is obtained.

The Electric Formfactor of the Neutron Determined by Quasielastic Scattering of Longitudinally Polarized Electrons from 3He and 2D

The recent availability of polarized electron beams at electron accelerator laboratories adds another technique to probing the electromagnetic structure of nuclear matter [1]. The present paper discusses the application of polarized electron scattering to the determination of the electric formfactor of the neutron. Its value at medium energies is only poorly known hitherto. Electron scattering is dominated by interaction with the neutron magnetic moment. Therefore the contribution of the charge distribution to the scattering cross section is scarcely detectable in case of unpolarized collision partners. The elastic scattering of longitudinally polarized electrons from a polarized neutron ta…

12C(γ,π+n) and 12C(γ,π+p) reactions across the Δ resonance region

Abstract Differential cross-sections from (γ,π+n) and (γ,π+p) experiments on 12C are presented together with a microscopic model calculation. The comparison of experimental data with theory confirms that quasifree pion production is the dominant process for the (γ,π+n) reaction. The comparison of (γ,π+p) with (γ,π+n) data shows the importance of final state interactions. first time to experimentally study the strength and the possible mechanisms involved in the final state interaction.

Nuclear pion photoproduction in theΔresonance region

A measurement of the /sup 12/C( gamma , pi /sup +/n)/sup 11/B reaction in quasifree pi -production kinematic regimes has been performed using tagged photons in conjunction with large solid angle pi and n detectors. The aim of the experiment was to investigate predicted modifications to the Delta excitation of nucleons and their subsequent propagation and decay, brought about by the nuclear medium. Differential cross sections are presented for photon energies spanning the Delta (1232) excitation region. The measurements are consistent with distorted wave impulse approximation calculations in which the amplitude for proton Delta excitation, followed by Delta propagation and decay to pi /sup +…

Differential cross section for the reaction 2H(γ, p)n from 133 to 158 MeV

The cross section for the reaction 2H(γ, p)n has been measured at laboratory photon energies Eγ = 133−158 MeV and c.m. angles between 30° and 150°. The reaction was induced by a tagged bremsstrahlung photon beam incident on a liquid deuterium target. The uncertainty in the absolute cross sections is ⩽ 5%. There is now reasonable agreement between recent measurements in this energy region and the overall data set now defines the cross section sufficiently well to provide a test of current models of the reaction.

First measurement of the electric formfactor of the neutron in the exclusive quasielastic scattering of polarized electrons from polarized 3He

Abstract A first measurement of the asymmetry in quasielastic scattering of longitudinally polarized electrons from a polarized 3 He gas target in coincidence with the knocked out neutron is reported. This measurement was made feasible by the cw beam of the 855 MeV Mainz Microtron MAMI. It allows a determination of the electric formfactor of the neutron G E n independent of binding effects to first order. At Q 2 =0.31 ( GeV /c) 2 two asymmetries A ∥ ( S He ∥ q ) and A ⊥ ( S He ⊥ q ) have been measured giving A ∥ =(−7.40±0.73)% and A ⊥ =(0.89±0.30)% . The ratio A ⊥ / A ∥ is independent of the absolute value of the electron and target polarization and yields G E n =0.035±0.012±0.005.

Scaling of the 4He(γ,p)t reaction in the Eγ = 80–160 MeV region

The 4He(γ,p) 3H reaction cross section has been measured with tagged photons of energy 81–158 MeV. Protons were detected over the angular range 55°–125°. The scaling of the data as a function of momentum mismatch has been examined for two reaction models, the modified quasideuteron mechanism and quasifree knockout. Both models show clear scaling behaviour but comparison of the predicted and measured scaling function shapes favours the modified quasideuteron mechanism at momenta up to ≈500 MeV/c.

Single and double πo-photoproduction from the deuteron

Photoproduction of neutral pions from the deuteron has been studied for incident photon energies from 200 MeV to 792 MeV with the TAPS detector at the Mainz MAMI accelerator. Total and differential cross sections covering the full angular range have been obtained for coherent and incoherent single πo-photoproduction. Good agreement between model predictions and the data was found for the coherent process. The incoherent cross section in the energy region of the Δ(1232)-resonance is overestimated by existing models. A comparison to model predictions indicates that final state interaction effects are much more important than for the coherent reaction. However, the angular dependence of the da…

Measurement of theE2/M1Ratio in theN→ΔTransition Using the Reactionp(γ→,p)π0[Phys. Rev. Lett. 78, 606 (1997)]

The small electric quadrupole $E2$ amplitude of the predominantly magnetic dipole $M1$ $p\ensuremath{\rightarrow}\ensuremath{\Delta}(1232)$ transition has been measured using 270 to 420 MeV tagged linearly polarized photons in the $p(\stackrel{\ensuremath{\rightarrow}}{\ensuremath{\gamma}},p){\ensuremath{\pi}}^{o}$ reaction at the Mainz Microtron MAMI. Differential cross sections and photon asymmetries were determined by measuring the recoil proton in the cylindrically symmetric $4\ensuremath{\pi}$ detector DAPHNE. From the proton angular distributions the ratio $E2/M1\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}\ensuremath{-}(2.5\ifmmode\pm\else\textpm\fi{}0.2\ifmmode\pm\else\textpm\…

Elastic and inelastic photon scattering from 12C

Abstract The elastic and inelastic photon scattering from 12 C was investigated in the energy range of the Δ-resonance ( E γ = 200–500 MeV) at a scattering angle of 40°. The experiment was performed with the tagged photon facility at the cw electron accelerator MAMI ( E e − = 855 MeV). By using a large NaI(Tl) detector having an energy resolution of 1.5%, the elastic scattering could be separated from the inelastic process to the first excited state ( E x = 4.44 MeV of 12 C. The differential cross section for the coherent scattering is compared with a simple static ansatz, that uses the known charge form factor, and with a recent Δ-hole calculation.

Polarized photon measurements of the12C(γ→,pp)and12C(γ→,pn)reactions forEγ=160−350MeV

The ${}^{12}\mathrm{C}(\stackrel{\ensuremath{\rightarrow}}{\ensuremath{\gamma}},pp)$ and ${}^{12}\mathrm{C}(\stackrel{\ensuremath{\rightarrow}}{\ensuremath{\gamma}},pn)$ reactions have been studied for ${E}_{\ensuremath{\gamma}}=160\ensuremath{-}350$ MeV using linearly polarized photons from the Glasgow tagged photon spectrometer at the Mainz microtron MAMI. Both reaction channels show a negative photon asymmetry $\ensuremath{\Sigma}$ for missing energies ${E}_{m}$ below 70 MeV, where direct emission nucleon pairs is expected. A strong peak at low ${E}_{m}$ is observed in ${\ensuremath{\Sigma}}_{(\ensuremath{\gamma},pp)},$ but not in ${\ensuremath{\Sigma}}_{(\ensuremath{\gamma},pn)}.$ Furth…

C12(γ,p)11B cross section from 80 to 157 MeV

The $^{12}\mathrm{C}$(\ensuremath{\gamma},p${)}^{11}$B differential cross section has been measured over proton angles ranging from 58\ifmmode^\circ\else\textdegree\fi{} to 128\ifmmode^\circ\else\textdegree\fi{}, using tagged photons of energy 80--157 MeV, for low-lying regions of residual excitation energy in $^{11}\mathrm{B}$. The data have been compared with four different types of calculation. It is shown that scaling of the cross section with momentum mismatch occurs for both the ground-state and excited-state data.

Near threshold photoproduction of η mesons from 4 He

Photoproduction of η mesons from 4He has been measured for the first time. The experiment was performed at the Mainz Microtron (MAMI) using the TAPS photon spectrometer and the Glasgow/Mainz tagged photon facility. η mesons were identified in coincidence with recoil nucleons. Total and differential cross sections are presented in the photon energy range between threshold and 818 MeV. The exclusive data are used to determine the ratio of the elementary production cross sections on bound neutrons and protons, σn/σp= 0.68 ± 0.02 ± 0.09. In addition, upper limits for the total coherent cross section have been derived.

"Table 1" of "Differential cross section for the reaction $^2$H(��,p)n from 133 to 158 MeV"

No description provided.

"Table 2" of "C-12 (gamma,p) B-11 cross-section from 80 to 157 MeV"

EX = 7 (FROM 6.5 TO 8.0 MEV). ANGULAR BINS OF 5 DEG WIDTH.

"Table 3" of "Scaling of the $^{4}$He(��,p)t reaction in the $E_\gamma$ = 80���160 MeV region"

No description provided.

"Table 2" of "The 16O(��, 2N) reaction measured with tagged photons"

PROPOSED THAT THE REACTION IS DUE TO A QUASI DEUTERON MECHANISM AND P N PAIRS E]ECT FROM THE 1P SHELL.

"Table 6" of "Scaling of the $^{4}$He(��,p)t reaction in the $E_\gamma$ = 80���160 MeV region"

No description provided.

"Table 3" of "C-12 (gamma,p) B-11 cross-section from 80 to 157 MeV"

EX = 13 (FROM 12.0 TO 13.5 MEV). ANGULAR BINS OF 5 DEG WIDTH.

"Table 4" of "Scaling of the $^{4}$He(��,p)t reaction in the $E_\gamma$ = 80���160 MeV region"

No description provided.

"Table 1" of "Scaling of the $^{4}$He(��,p)t reaction in the $E_\gamma$ = 80���160 MeV region"

No description provided.

"Table 7" of "Scaling of the $^{4}$He(��,p)t reaction in the $E_\gamma$ = 80���160 MeV region"

No description provided.

"Table 1" of "First measurement of the polarization transfer on the proton in the reactions H (e (polarized), e-prime p (polarized)) and D (e (polarized), e-prime p (polarized))"

No description provided.

"Table 1" of "C-12 (gamma,p) B-11 cross-section from 80 to 157 MeV"

EX IN 0 MEV REGION (FROM 0 TO 1.5 MEV). ANGULAR BINS OF 5 DEG WIDTH.

"Table 2" of "Differential cross section for the reaction $^2$H(��,p)n from 133 to 158 MeV"

No description provided.

"Table 2" of "Scaling of the $^{4}$He(��,p)t reaction in the $E_\gamma$ = 80���160 MeV region"

No description provided.

"Table 5" of "Scaling of the $^{4}$He(��,p)t reaction in the $E_\gamma$ = 80���160 MeV region"

No description provided.

"Table 1" of "The 16O(��, 2N) reaction measured with tagged photons"

PROPOSED THAT THE REACTION IS DUE TO A QUASI DEUTERON MECHANISM AND P N PAIRS E]ECT FROM THE 1P SHELL.