233 research outputs found
Double production in pion-nucleon scattering at COMPASS
No full textWe present the study of the production of double mesons using
COMPASS data collected with a 190 GeV/ beam scattering off NH,
Al and W targets. Kinematic distributions of the collected double
events are analysed, and the double production cross section is
estimated for each of the COMPASS targets. The results are compared to
predictions from single- and double-parton scattering models as well as the
pion intrinsic charm and the tetraquark exotic resonance hypotheses. It is
demonstrated that the single parton scattering production mechanism gives the
dominant contribution that is sufficient to describe the data. An upper limit
on the double intrinsic charm content of pion is evaluated. No significant
signatures that could be associated with exotic tetraquarks are found in the
double mass spectrum.Comment: 12 pages, 4 figure
A low momentum tagged antineutron beam
No full textThe operating performances of a low-momentum (< 270 MeV/c) tagged beam are reported. The beam is obtained by means of the charge exchange reaction n on a liquid hydrogen target. The neutron associated to the in the two-body reaction is used for the determination of the energy and direction. The measured total rate of tagged is 8.02 ± 0.03 × 10−5 per incident at 300 MeV/c
Future Measurements of Spin Structure Function with Polarized Collisions and Determination of
No full textExcitation of low lying natural parity levels in<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:mmultiscripts><mml:mrow><mml:mi mathvariant="normal">Pb</mml:mi></mml:mrow><mml:mprescripts /><mml:mrow /><mml:mrow><mml:mn>208</mml:mn></mml:mrow><mml:mrow /><mml:mrow /></mml:mmultiscripts></mml:mrow></mml:math>by inelastic electron scattering
No full textObservation of a J**PC = 1-+ exotic resonance in diffractive dissociation of 190-GeV/c pi- into pi- pi- pi+
No full textAlekseev M, Alexakhin VY, Alexandrov Y, et al. Observation of a J**PC = 1-+ exotic resonance in diffractive dissociation of 190-GeV/c pi- into pi- pi- pi+. Phys.Rev.Lett. 2010;104(24): 241803.The COMPASS experiment at the CERN SPS has studied the diffractive dissociation of negative pions into the pi- pi- pi+ final state using a 190 GeV/c pion beam hitting a lead target. A partial wave analysis has been performed on a sample of 420000 events taken at values of the squared 4-momentum transfer t' between 0.1 and 1 GeV^2/c^2. The well-known resonances a1(1260), a2(1320), and pi2(1670) are clearly observed. In addition, the data show a significant natural parity exchange production of a resonance with spin-exotic quantum numbers J^PC = 1-+ at 1.66 GeV/c^2 decaying to rho pi. The resonant nature of this wave is evident from the mass-dependent phase differences to the J^PC = 2-+ and 1++ waves. From a mass-dependent fit a resonance mass of 1660 +- 10+0-64 MeV/c^2 and a width of 269+-21+42-64 MeV/c^2 is deduced
Exotic meson with and its decay into
No full textWe study the spin-exotic JPC=1-+ amplitude in single-diffractive dissociation of 190 GeV/c pions into π-π-π+ using a hydrogen target and confirm the π1(1600)→ρ(770)π amplitude, which interferes with a nonresonant 1-+ amplitude. We demonstrate that conflicting conclusions from previous studies on these amplitudes can be attributed to different analysis models and different treatment of the dependence of the amplitudes on the squared four-momentum transfer and we thus reconcile these experimental findings. We study the nonresonant contributions to the π-π-π+ final state using pseudodata generated on the basis of a Deck model. Subjecting pseudodata and real data to the same partial-wave analysis, we find good agreement concerning the spectral shape and its dependence on the squared four-momentum transfer for the JPC=1-+ amplitude and also for amplitudes with other JPC quantum numbers. We investigate for the first time the amplitude of the π-π+ subsystem with JPC=1-- in the 3π amplitude with JPC=1-+ employing the novel freed-isobar analysis scheme. We reveal this π-π+ amplitude to be dominated by the ρ(770) for both the π1(1600) and the nonresonant contribution. These findings largely confirm the underlying assumptions for the isobar model used in all previous partial-wave analyses addressing the JPC=1-+ amplitude.We study the spin-exotic amplitude in single-diffractive dissociation of 190 GeV pions into using a hydrogen target and confirm the amplitude, which interferes with a nonresonant amplitude. We demonstrate that conflicting conclusions from previous studies on these amplitudes can be attributed to different analysis models and different treatment of the dependence of the amplitudes on the squared four-momentum transfer and we thus reconcile their experimental findings. We study the nonresonant contributions to the final state using pseudo-data generated on the basis of a Deck model. Subjecting pseudo-data and real data to the same partial-wave analysis, we find good agreement concerning the spectral shape and its dependence on the squared four-momentum transfer for the amplitude and also for amplitudes with other quantum numbers. We investigate for the first time the amplitude of the subsystem with in the amplitude with employing the novel freed-isobar analysis scheme. We reveal this amplitude to be dominated by the for both the and the nonresonant contribution. We determine the resonance parameters within the three-pion final state. These findings largely confirm the underlying assumptions for the isobar model used in all previous partial-wave analyses addressing the amplitude
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