The differential cross sections \sigma_0=\sigma_T+\epsilon \sigma_L, \sigma_{LT}, and \sigma_{TT} of \pi^0 electroproduction from the proton were measured from threshold up to an additional center of mass energy of 40 MeV, at a value of the photon four-momentum transfer of Q^2= 0.05 GeV^2/c^2 and a center of mass angle of \theta=90^\circ. By an additional out-of-plane measurement with polarized electrons \sigma_{LT'} was determined. This showed for the first time the cusp effect above the \pi^+ threshold in the imaginary part of the s-wave. The predictions of Heavy Baryon Chiral Perturbation Theory are in disagreement with these data. On the other hand, the data are somewhat better predicted by the MAID phenomenological model and are in good agreement with the dynamical model DMT.
The separated cross section SIG(0), SIG(LT) and SIG(TT).
Beam helicity asymmetry.
To determine nonspherical angular momentum amplitudes in hadrons at long ranges (low Q^2), data were taken for the p(\vec{e},e'p)\pi^0 reaction in the Delta region at Q^2=0.060 (GeV/c)^2 utilizing the magnetic spectrometers of the A1 Collaboration at MAMI. The results for the dominant transition magnetic dipole amplitude and the quadrupole to dipole ratios at W=1232 MeV are: M_{1+}^{3/2} = (40.33 +/- 0.63_{stat+syst} +/- 0.61_{model}) (10^{-3}/m_{\pi^+}),Re(E_{1+}^{3/2}/M_{1+}^{3/2}) = (-2.28 +/- 0.29_{stat+syst} +/- 0.20_{model})%, and Re(S_{1+}^{3/2}/M_{1+}^{3/2}) = (-4.81 +/- 0.27_{stat+syst} +/- 0.26_{model})%. These disagree with predictions of constituent quark models but are in reasonable agreement with lattice calculations with non-linear (chiral) pion mass extrapolations, with chiral effective field theory, and with dynamical models with pion cloud effects. These results confirm the dominance, and general Q^2 variation, of the pionic contribution at large distances.
Measured value of SIG(C=T) + EPS*SIG(C=L) as a function of the pion angle relative to the virtual photon direction.
Measured value of SIG(C=TT) as a function of the pion angle relative to thevirtual photon direction.
Measured value of SIG(C=LT) as a function of the pion angle relative to thevirtual photon direction.
A search for single top quark production is performed in e^\pm p collisions at HERA. The search exploits data corresponding to an integrated luminosity of 118.3 pb^-1. A model for the anomalous production of top quarks in a flavour changing neutral current process involving a t-u-gamma coupling is investigated. Decays of top quarks into a b quark and a W boson are considered in the leptonic and the hadronic decay channels of the W. Both a cut-based analysis and a multivariate likelihood analysis are performed to discriminate anomalous top quark production from Standard Model background processes. In the leptonic channel, 5 events are found while 1.31 \pm 0.22 events are expected from the Standard Model background. In the hadronic channel, no excess above the expectation for Standard Model processes is found. These observations lead to a cross section \sigma (ep -> e t X) = 0.29 +0.15 -0.14 pb at \sqrt{s} = 319 GeV. Alternatively, assuming that the observed events are due to a statistical fluctuation, upper limits of 0.55 pb on the anomalous top production cross section and of 0.27 on the t-u-gamma coupling \kappa_{t-u-gamma} are established at the 95% confidence level.
Cross section from a combination of electron, muon and hadron channels.
A combination of fifteen top quark mass measurements performed by the ATLAS and CMS experiments at the LHC is presented. The data sets used correspond to an integrated luminosity of up to 5 and 20$^{-1}$ of proton-proton collisions at center-of-mass energies of 7 and 8 TeV, respectively. The combination includes measurements in top quark pair events that exploit both the semileptonic and hadronic decays of the top quark, and a measurement using events enriched in single top quark production via the electroweak $t$-channel. The combination accounts for the correlations between measurements and achieves an improvement in the total uncertainty of 31% relative to the most precise input measurement. The result is $m_\mathrm{t}$ = 172.52 $\pm$ 0.14 (stat) $\pm$ 0.30 (syst) GeV, with a total uncertainty of 0.33 GeV.
Polarization transfer in the 4He(e,e'p)3H reaction at a Q^2 of 0.4 (GeV/c)^2 was measured at the Mainz Microtron MAMI. The ratio of the transverse to the longitudinal polarization components of the ejected protons was compared with the same ratio for elastic ep scattering. The results are consistent with a recent fully relativistic calculation which includes a predicted medium modification of the proton form factor based on a quark-meson coupling model.
No description provided.
No description provided.
The reactione+p →> e+π++n at c.m. energyW=1125MeV and momentum transfer Q2=0.117GeV2/c2 has been measured. The transverse and longitudinal structure functions have been separated by varying the polarization of the virtual photon (Rosenbluth plot) with a 3 to 4% error. In addition the longitudinal-transverse interference term has been determined measuring the right-left asymmetry with an accuracy of 3%. The experimental data are compared to model calculations, and the sensitivity of the results to the axial and pion formfactors is discussed.
Angle PHI(P=4) is the angle between the scattering plane (defined by 1 and 3 particles) and the reaction plane (defined by 4 and 5 particles).
Angle PHI(P=4) is the angle between the scattering plane (defined by 1 and 3 particles) and the reaction plane (defined by 4 and 5 particles).
Angle PHI(P=4) is the angle between the scattering plane (defined by 1 and 3 particles) and the reaction plane (defined by 4 and 5 particles).
We have measured the absolute unpolarized cross sections for photon electro-production off the proton ep → epγ with the Three-Spectrometer-Setup at MAMI at a momentum transfer q=600 MeV/c and a virtual photon polarization ɛ=0.62. The momentum q ′ of the outgoing real photon range from 33 to 111 MeV/c. We extracted two combinations of the recently introduced generalized polarizabilities [1,2].
First data on coherent threshold \pi^0 electroproduction from the deuteron taken by the A1 Collaboration at the Mainz Microtron MAMI are presented. At a four-momentum transfer of q^2=-0.1 GeV^2/c^2 the full solid angle was covered up to a center-of-mass energy of 4 MeV above threshold. By means of a Rosenbluth separation the longitudinal threshold s wave multipole and an upper limit for the transverse threshold s wave multipole could be extracted and compared to predictions of Heavy Baryon Chiral Perturbation Theory.
Differential cross-section d(SIG(PI0))/d(OMEGA) is related to electron-deuteron one by the relation as follows: d(SIG)/d(OMEGA_e)/d(E_e)/d(OMEGA) = Gamma *d(SIG)/d(OMEGA), where the virtual photon flux is give by: Gamma = (alpha/2*pi**2) * (E'/E) * (k_gamma/Q2) / (1-epsilon). Here epsilon is transverse degree of polarization of the virtual photon. See article for details.
Differential cross-section d(SIG(PI0))/d(OMEGA) is related to electron-deuteron one by the relation as follows: d(SIG)/d(OMEGA_e)/d(E_e)/d(OMEGA) = Gamma *d(SIG)/d(OMEGA), where the virtual photon flux is give by: Gamma = (alpha/2*pi**2) * (E'/E) * (k_gamma/Q2) / (1-epsilon). Here epsilon is transverse degree of polarizatiuon of the virtual photon. See article for details.
Differential cross-section d(SIG(PI0))/d(OMEGA) is related to electron-deuteron one by the relation as follows: d(SIG)/d(OMEGA_e)/d(E_e)/d(OMEGA) = Gamma *d(SIG)/d(OMEGA), where the virtual photon flux is give by: Gamma = (alpha/2*pi**2) * (E'/E) * (k_gamma/Q2) / (1-epsilon). Here epsilon is transverse degree of polarizatiuon of the virtual photon. See article for details.
Cross sections for the production of two isolated muons up to high di-muon masses are measured in ep collisions at HERA with the H1 detector in a data sample corresponding to an integrated luminosity of 71 pb^-1 at a centre of mass energy of sqrt{s} = 319 GeV. The results are in good agreement with Standard Model predictions, the dominant process being photon-photon interactions. Additional muons or electrons are searched for in events with two high transverse momentum muons using the full data sample corresponding to 114 pb^-1, where data at sqrt{s} = 301 GeV and sqrt{s} = 319 GeV are combined. Both the di-lepton sample and the tri-lepton sample agree well with the predictions.
Integrated cross sections for electroweak muon pair production in the evaluated phase space. The cross section has the di-muon contributions from UPSILON, TAU-PAIR and QUARK-QUARKBAR decay subtracted.
Cross section for the production of two muons in e p interactions as a function of the di-muon mass. This data sample includes di-muons from UPSILON, TAU-PAIR and QUARK-QUARKBAR decays.
Cross section for the production of two muons as a function of the muon transverse momentum (two entries per event).
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ABSENT OF AN ABSOLUTE NEUTRON FLUX NORMALIZATION DIDN'T ALLOWED TO DEFINE THE CROSS-SECTION OF LAMBDA-K0-PARE PRODUCTION,SO IT WAS DEFINED THE RELATION OF CARBON AND CUPRUM CROSS-SECTION.
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