arXiv subjects

S. G. Sherman

Publications and source records attributed to S. G. Sherman.

8 recordsLinked to original sources

arXiv2017

Study of the proton-proton collisions at 1683 MeV/c

The new data on the elastic $pp$ and single pion production reaction $pp\to pn π^{+}$ taken at the incident proton momentum 1683 MeV/c are presented. The data on the $pp\to pn π^{+}$ reaction are compared with predictions from the OPE model. To extract contributions of the leading partial waves the single pion production data are analyzed in the framework of the event-by-event maximum likelihood method together with the data measured earlier. The analysis allows us to obtain the assessment with a better precision the contributions from different initial partial waves.

nucl-ex↗

arXiv2011

The study of the proton-proton collisions at the beam momentum 1628 MeV/c

The detailed investigation of the single pion production reactions $pp\to pnπ^{+}$ and $pp\to ppπ^{o}$ at the incident proton momentum 1628 MeV/c has been carried out. The data are analyzed in the framework of the event-by-event maximum likelihood method together with the $pp\to ppπ^{0}$ data measured earlier in the energy region below 1 GeV. At 1628 MeV/c the largest contributions stem from the $^{3}P_{2}$, $^{3}P_{1}$, $^{3}P_{0}$, $^{1}D_{2}$ and $^{3}F_{2}$ initial partial waves.

hep-ex↗

arXiv2009

The study of the negative pion production in neutron-proton collisions at beam momenta below 1.8 GeV/c

A detailed investigation of the reaction np -> ppπ^{-} has been carried out using the data obtained with the continuous neutron beam produced by charge exchange scattering of protons off a deuterium target. A partial wave event-by-event based maximum likelihood analysis was applied to determine contributions of different partial waves to the pion production process. The combined analysis of the np -> ppπ^{-} and pp -> ppπ^{0} data measured in the same energy region allows us to determine the contribution of isoscalar partial waves (I=0) in the momentum range from 1.1 up to 1.8 GeV/c. The decay of isoscalar partial waves into (^1S_0)_{pp}π$ channel provides a good tool for a determination of the pp S-wave scalar scattering length in the final state which was found to be a_{pp}=-7.5\pm 0.3 fm.

hep-ph↗

arXiv1998

Polarization Properties of Low Energy Amplitude for $πN \to ππN$ Reaction

The theoretical study of cross sections for polarized--target measurements of $ πN \to ππN $ reactions gives evidence that the interplay between the strong contribution from OPE mechanism and the one from isobar exchanges, which is equally strong within isobar half--widths energy region, must result in nontrivial polarization phenomena. The Monte--Carlo simulations for asymmetries in $ π^{-} p^{\uparrow} \to π^{-} π^{+} n $ reaction at $ P_{Lab} = 360 $~MeV/c with the use of theoretical amplitudes found as solutions for unpolarized data at $ P_{Lab} < 500 $~MeV/c provide confirmations for significant effect. The effect is capable to discriminate between the OPE and isobar exchanges and it is sensitive to the OPE parameters in question. This leads to the conclusion that the decisive $πN \to ππN$ analysis, aiming at determination of $ ππ$--scattering lengths, must combine both unpolarized data and polarization information. The appropriate measurements are shown to be feasible at the already existing CHAOS spectrometer.

hep-ph↗

arXiv1997

Phenomenological $ πN \to ππN $ Amplitude and Analysis of Low Energy Data on Total Cross Sections and 1--D Distributions

We develop the phenomenological amplitude of the $πN \to ππN$ reaction describing the exchanges of $Δ$ and $N_{*}$ along with the OPE mechanism. The contribution of the latter contains 4 independent low energy parameters (up to $O(k^{4})$ order). The terms of the polynomial background are added to stand for far resonances and for contact terms originating from the off-mass-shell interactions. These terms are introduced with the account of isotopic, crossing, $ C $, $ P $ and $ T $ symmetries of strong interactions. The data consisting of total cross sections in the energy region $ 0.300 \le P_{Lab} \le 500 $~MeV/c and 1D distributions from the bubble-chamber experiments for three reaction channels were undergoing fittings to determine free parameters of the amplitude. The best solutions are characterized by $ χ^{2}_{DF} = $ 1.16. At the considered energies the isobar exchanges are found to be more important than OPE. The obtained solutions reveal the need in more precise data and/or in polarization measurements because of large correlations of isobar parameters with the OPE ones. The theoretical solutions were used for modeling the Chew-Low extrapolation and the Olsson-Turner threshold approach. It is shown that the noncritical application of the former results in 100% theoretical errors, the extracted values being in fact the random numbers. The results of the Olsson-Turner method are characterised by significant systematic errors coming from unknown details of isobar physics.

hep-ph↗

arXiv1996

Cross-Symmetric Expansion of $ππ$ Amplitude Near Threshold

The near-threshold expansion of the $ππ$ amplitude is developed using the crossing-covariant independent variables. The independent threshold parameters entering the real part of the amplitude in an explicitly Lorentz-invariant way are free from restrictions of isotopic and crossing symmetries. Parameters of the expansion of the imaginary part are recovered by the perturbative unitarity relations.

hep-ph↗

arXiv1996

Gauss Integration over Relativistic 3--Body Phase Space for 1--Dimensional Distributions of $ 2 \to 3 $ Reaction

We present the analysis of the phase space geometry of 2 $\rightarrow$ 3 reaction for the general case of nonzero and unequal particle masses. Its purpose is to elaborate an alternative approach to the problem of integration over phase space which does not exploit the Monte Carlo principle. The fast and effective algorithm of integration based on Gauss method is developed for treating 1--dimensional distributions in two--particle invariant variables. The algorithm is characterized by significantly improved accuracy and it can meet requirements of interactive processing.

hep-ph↗

arXiv1995

Analysis of data on low energy piN-->pipiN reaction. I. Total cross sections

This is the first of a series of papers on a consistent model independent analysis of the complete experimental information on the reaction $πN \rightarrow ππN$ at pion momenta up to 500 MeV/c. The paper summarizes the theoretical approach and details of the computational procedure. The complete database on total cross sections in 5 $ππN$ channels is given together with a critical discussion of their model independent analysis.

hep-ph↗