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Title: pi+- p differential cross sections at low energies

Abstract

Differential cross sections for pi- p and pi+ p elastic scattering were measured at five energies between 19.9 and 43.3 MeV. The use of the CHAOS magnetic spectrometer at TRIUMF, supplemented by a range telescope for muon background suppression, provided simultaneous coverage of a large part of the full angular range, thus allowing very precise relative cross section measurements. The absolute normalization was determined with a typical accuracy of 5 %. This was verified in a simultaneous measurement of muon proton elastic scattering. The measured cross sections show some deviations from phase shift analysis predictions, in particular at large angles and low energies. From the new data we determine the real part of the isospin forward scattering amplitude.

Authors:
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Publication Date:
Research Org.:
Thomas Jefferson National Accelerator Facility (TJNAF), Newport News, VA
Sponsoring Org.:
USDOE - Office of Energy Research (ER)
OSTI Identifier:
862053
Report Number(s):
JLAB-PHY-05-455; DOE/ER/40150-3665; nucl-ex/0512006; 6447759
TRN: US0600108
DOE Contract Number:
AC05-84ER40150
Resource Type:
Journal Article
Country of Publication:
United States
Language:
English
Subject:
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS; ACCURACY; CROSS SECTIONS; DIFFERENTIAL CROSS SECTIONS; ELASTIC SCATTERING; ISOSPIN; MAGNETIC SPECTROMETERS; MUONS; PHASE SHIFT; PROTONS; SCATTERING AMPLITUDES; TELESCOPES

Citation Formats

H. Denz, P. Amaudruz, J.T. Brack, J. Breitschopf, P. Camerini, J.L. Clark, H. Clement, L. Felawka, E. Fragiacomo, E.F. Gibson, N. Grion, G.J. Hofman, B. Jamieson, E.L. Mathie, R. Meier, G. Moloney, D. Ottewell, O. Patarakin, J.D. Patterson, M.M. Pavan, S. Piano, K. Raywood, R.A. Ristinen, R. Rui, M.E. Sevior, G.R. Smith, J. Stahov, R. Tacik, G.J. Wagner, F. von Wrochem, and D.M. Yeomans. pi+- p differential cross sections at low energies. United States: N. p., 2005. Web.
H. Denz, P. Amaudruz, J.T. Brack, J. Breitschopf, P. Camerini, J.L. Clark, H. Clement, L. Felawka, E. Fragiacomo, E.F. Gibson, N. Grion, G.J. Hofman, B. Jamieson, E.L. Mathie, R. Meier, G. Moloney, D. Ottewell, O. Patarakin, J.D. Patterson, M.M. Pavan, S. Piano, K. Raywood, R.A. Ristinen, R. Rui, M.E. Sevior, G.R. Smith, J. Stahov, R. Tacik, G.J. Wagner, F. von Wrochem, & D.M. Yeomans. pi+- p differential cross sections at low energies. United States.
H. Denz, P. Amaudruz, J.T. Brack, J. Breitschopf, P. Camerini, J.L. Clark, H. Clement, L. Felawka, E. Fragiacomo, E.F. Gibson, N. Grion, G.J. Hofman, B. Jamieson, E.L. Mathie, R. Meier, G. Moloney, D. Ottewell, O. Patarakin, J.D. Patterson, M.M. Pavan, S. Piano, K. Raywood, R.A. Ristinen, R. Rui, M.E. Sevior, G.R. Smith, J. Stahov, R. Tacik, G.J. Wagner, F. von Wrochem, and D.M. Yeomans. Sat . "pi+- p differential cross sections at low energies". United States. doi:. https://www.osti.gov/servlets/purl/862053.
@article{osti_862053,
title = {pi+- p differential cross sections at low energies},
author = {H. Denz and P. Amaudruz and J.T. Brack and J. Breitschopf and P. Camerini and J.L. Clark and H. Clement and L. Felawka and E. Fragiacomo and E.F. Gibson and N. Grion and G.J. Hofman and B. Jamieson and E.L. Mathie and R. Meier and G. Moloney and D. Ottewell and O. Patarakin and J.D. Patterson and M.M. Pavan and S. Piano and K. Raywood and R.A. Ristinen and R. Rui and M.E. Sevior and G.R. Smith and J. Stahov and R. Tacik and G.J. Wagner and F. von Wrochem and D.M. Yeomans},
abstractNote = {Differential cross sections for pi- p and pi+ p elastic scattering were measured at five energies between 19.9 and 43.3 MeV. The use of the CHAOS magnetic spectrometer at TRIUMF, supplemented by a range telescope for muon background suppression, provided simultaneous coverage of a large part of the full angular range, thus allowing very precise relative cross section measurements. The absolute normalization was determined with a typical accuracy of 5 %. This was verified in a simultaneous measurement of muon proton elastic scattering. The measured cross sections show some deviations from phase shift analysis predictions, in particular at large angles and low energies. From the new data we determine the real part of the isospin forward scattering amplitude.},
doi = {},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Sat Dec 03 00:00:00 EST 2005},
month = {Sat Dec 03 00:00:00 EST 2005}
}
  • Differential cross sections have been measured for ..pi../sup +/p elastic scattering at incident-pion energies 442, 490, 530, 560, and 600 MeV, and for ..pi../sup -/p elastic scattering at pion energies 425, 465, 490, 530, 560, 600, and 640 MeV. The differential cross sections were measured in the angular range theta/sub ..pi../*=40--176/sup 0/ with an accuracy of about 2--5%. The resulting data were used to calculate the isospin boundaries for the ..pi../sup -/p..--> pi../sup 0/n charge-exchange cross sections. It is shown that the published charge-exchange cross sections for large scattering angles cluster near the lower boundary and that those for energiesmore » above 490 MeV fall outside the region allowed by isotopic invariance. The measured cross sections are compared with the predictions of various phase-shift analyses, and it is shown that none of the existing analyses can describe all the new data in a satisfactory manner. The results of the present experiment together with available accurate data on ..pi.. +- p elastic scattering at lower energies constitute a systematic self-consistent set of accurate data that can serve as a basis for a new phase-shift analysis of ..pi..p scattering in the region of the P/sub 33/, P/sub 11/, S/sub 11/, and D/sub 13/ resonances.« less
  • Differential cross sections of the elementary process Ar/sup + +/(/sup 3/P)+He(/sup 1/S)..-->..Ar/sup +/(/sup 2/P)+He/sup +/(/sup 2/S) at collision energies between 0.6 and 1.6 eV were calculated using the quasiclassical treatment. Analytic potentials providing an approximation of the electronic energy of the system were employed to calculate deflection functions. Coupling of the diabatic terms was evaluated using the asymptotic method, and the Landau--Zener model was applied to account for the transition probability. Semiquantitative agreement of the calculated differential cross sections with those obtained in crossed beam experiments was achieved.
  • We report on measurements of the differential [pi][sup [plus minus]][ital p] cross section at pion energies [ital T][sub [pi]]=32.7, 45.1, and 68.6 MeV. The measurements, covering the angular range 25[degree][le][theta][sub lab][le]123[degree], have been carried out at the Paul-Scherrer-Institute (PSI) in Villigen, Switzerland, employing the magnet spectrometer LEPS. The absolute normalization of the [pi][sup [plus minus]][ital p] cross sections have been achieved by relating them to the electromagnetic cross sections of [mu][sup [plus minus] 12]C scattering. The results are in agreement with those of our preceding measurements at [ital T][sub [pi]]=32.2 and 45.1 MeV insofar as they overlap with the regionmore » of the Coulomb nuclear interference investigated there. A comparison with the predictions of the Karlsruhe-Helsinki phase shift analysis KH80, which has formed the basis for the determination of the experimental'' [sigma] term, reveals considerable deviations. These are most pronounced for the [pi][sup +][ital p] cross sections at [ital T][sub [pi]]=32.7 and 45.1 MeV. Single energy partial wave fits result in [ital S]-wave contributions, which are about 1[degree] lower in magnitude then those specified by the KH80 solution. The data at 68.6 MeV are in good agreement with the phase shift analysis.« less
  • The values of the pion nucleon ([pi][ital N]) [sigma] term, as determined, on the one hand, from experimental pion nucleon scattering by means of dispersion relations and, on the other hand, from baryon masses by means of chiral perturbation theory, differ by 10 to 15 MeV. The origin of this discrepancy is not yet understood. If the difference between the two values is attributed to the scalar current of strange sea quark pairs within the proton, the contribution to the proton mass would be of the order of 120 MeV. The discrepancy may hint at either theoretical deficiencies or anmore » inadequate [pi][ital N] database. In order to provide reliable experimental data we have measured angular distributions of elastic pion proton scattering at pion energies [ital T][sub [pi]]=32.2 and 44.6 MeV using the magnet spectrometer LEPS located at the Paul-Scherrer-Institute (PSI) in Villigen, Switzerland. From the data covering the region of the Coulomb nuclear interference, the real parts of the isospin-even forward scattering amplitude Re[ital D][sup +]([ital t]=0), have been determined as a function of energy. The results have been compared with the predictions of the Karlsruhe-Helsinki phase shift analysis KH80, revealing discrepancies most pronounced for the [pi][sup +][ital p] data. The experimentally determined values for Re[ital D][sup +]([ital t]=0), however, support the KH80 prediction (which is based on [pi][ital N] data available in 1979).« less