376 research outputs found
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Determination of the quadratic slope parameter in eta -> 3 pi(0) decay
No full textWe have determined the quadratic slope parameter α for η→3π0 to be α = -0.031(4) from a 99% pure sample of 106η→3π0 decays produced in the reaction π-p→nη close to the η threshold using the Crystal Ball detector at the AGS. The result is four times more precise than the present world data and disagrees with current chiral perturbation theory calculations by about four standard deviations
Photoproduction of pion pairs off nucleons
No full textIn the absence of a solution for Quantum Chromodynamics (QCD) in the low energy regime, so called effective models are being used to describe the nucleon and
its excited states. These models include the basic symmetries from QCD, but on the other hand, compared to quarks and gluons, use higher lying degrees of freedom.
Experimental contributions are mandatory to validate these models and fix free parameters. Today still most of the world-data in this field was obtained by
meson-induced excitation of the nucleon. Even though numerous excited states of the nucleon could be identified, the number of model predicted states is much
higher. This is known as the missing resonance problem. One explanation could be that some excited states just couple weakly to pion-N (kaon-N) and hence the
excitation via photons was proposed to further test the model predictions.
During the last 15 years, much experimental effort was made at various photoproduction facilities like MAMI, ELSA, JLab or ESRF and a large number of states
could be confirmed, but the missing resonance problem could not be solved. Higher lying resonances (M > 1.6 GeV) decay preferably via sequential decays with
many meson final states, and especially double pion decay channels are assumed to dominate in this region. The reactions investigated in this work, namely
g+p(n)->pion^0+pion^0+p(n), g+n(p)->pion^0+pion^0+n(p), g+p->pion^0+pion^0+p, g+p(n)->pion^++pion^0+n(n), g+n(p)->pion^-+pion^0+p(p), g+p->pion^++pion^0+n
thus form the primary source of information on photocouplings of higher lying resonances.
This work explores neutral and mixed-charge double pion production channels up to invariant masses of the final state center-of-mass system of about 1.9 GeV
and presents unpolarized as well as single-polarized observables. All results have high precision, are compared to different model predictions, and will
considerably constrain future model analyses in the field of double pion photoproduction and beyond.
The data of this work were taken at MAMI in four different experiments with liquid hydrogen and deuterium targets in 2007 and 2009 and include over 600 hours
of beam time. A longitudinally polarized electron beam was used to produce circularly polarized bremsstrahlung photons with energies up 1.4 GeV. The reaction
products, charged pions, photons and nucleons, were detected in the combined calorimeter consisting of Crystal Ball and TAPS.
Total and differential cross sections, invariant mass distributions of N-pion and pion-pion and beam helicity asymmetries were computed in the fully reconstructed
final state center-of-mass system. Effects from Fermi motion in the deuteron target could be reliably defolded leading to a good agreement between free and
quasifree proton data, and thus the neutron results can be interpreted as a good approximation of free neutron data.
Beam-helicity asymmetries for g+n(p)->pion^0+pion^0+n(p) and g+n(p)->pion^-+pion^0+p(p) have been measured for the first time and published together with the
results from the proton data. Especially for the mixed-charge results, the available model calculations fail to reproduce the data, and for the neutral channel
data, an unexpected similarity for proton and neutron results was observed.
Total and differential cross sections as well as invariant mass distributions of N-pion and pion-pion for g+n(p)->pion^-+pion^0+p(p) have also been measured for
the first time and previous results for g+p(n)->pion^++pion^0+n(n) could be reproduced and extended into the third resonance region
Prethodni diferencijalni udarni presjeci za reakciju izmjene naboja
No full textThe Crystal Ball Collaboration measured differential cross sections for pion-nucleon charge-exchange reaction at seven different pion momenta in the momentum region between 105 MeV/c and 180 MeV/c. When analyzed, these data will represent the highest-precision differential cross sections in this energy region. They will be essential for providing the necessary constrains on partial-wave analysis so that pion-nucleon sigma term can be extracted more reliably, and also provide a determination of the mass difference of the up and down quarks. Preliminary results for these differential cross sections are presented.Grupa Crystal Ball načinila je mjerenja diferencijalnih udarnih presjeka izmjene naboja u reakciji pion-nukleon za sedam impulsa piona u području od 105 MeV/c do 180 MeV/c. Kad se završe analize, ti će podaci predstavljati najtočnije diferencijalne udarne presjeke u ovom području. Oni su bitni za određivanje granica u analizama parcijalnih valova kako bi se član sigma odredio pouzdanije, i također radi određivanja razlike masa kvarkova gore i dolje. Predstavljaju se prethodni ishodi mjerenja tih diferencijalnih udarnih presjeka
Prethodni diferencijalni udarni presjeci za reakciju izmjene naboja
No full textThe Crystal Ball Collaboration measured differential cross sections for pion-nucleon charge-exchange reaction at seven different pion momenta in the momentum region between 105 MeV/c and 180 MeV/c. When analyzed, these data will represent the highest-precision differential cross sections in this energy region. They will be essential for providing the necessary constrains on partial-wave analysis so that pion-nucleon sigma term can be extracted more reliably, and also provide a determination of the mass difference of the up and down quarks. Preliminary results for these differential cross sections are presented.Grupa Crystal Ball načinila je mjerenja diferencijalnih udarnih presjeka izmjene naboja u reakciji pion-nukleon za sedam impulsa piona u području od 105 MeV/c do 180 MeV/c. Kad se završe analize, ti će podaci predstavljati najtočnije diferencijalne udarne presjeke u ovom području. Oni su bitni za određivanje granica u analizama parcijalnih valova kako bi se član sigma odredio pouzdanije, i također radi određivanja razlike masa kvarkova gore i dolje. Predstavljaju se prethodni ishodi mjerenja tih diferencijalnih udarnih presjeka
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Recent results from the Crystal Ball experiment
No full textSeveral recent analyses from the Crystal Ball collaboration are reviewed. The major topics discussed are the search for new states in radiative UPSILON(1S) decays, the search for lepton number-violating and inclusive eta decay modes of the tau, and results from ..gamma gamma.. physics
Mjerenja izmjene naboja pion-nukleon u području ∆(1232) rezonancije
No full textMeasurements of differential cross sections for pion-nucleon scattering, π −p → π 0n, in the region of the ∆(1232) resonance are presented. These data were obtained as part of the baryon spectroscopy program using the Crystal Ball detector in the C6 beam line of the Alternating Gradient Synchrocyclotron at Brookhaven National Laboratory. The results reported here are limited to the momenta at which the beam contaminations could be deduced by TOF. Data at higher momenta require the use of special normalization runs completed in 2002 and are still under analysis.Opisujemo mjerenja diferencijalnih udarnih presjeka za raspršenje pion-nukleon, π −p → π 0n, u području ∆(1232) rezonancije. Podatke smo dobili u okviru programa barionske spektroskopije s detektorom Crystal Ball na snopu C6 sinkrociklotrona s izmjeničnim gradijentom u Nacionalnom laboratoriju u Brookhavenu. Podaci su ograničeni na impulse za koje se onečišćenje u snopu moglo razlučiti vremenom proleta. Podaci za više impulse zahtijevaju posebna normalizacijska mjerenja koja su izvršena u 2002. godini, ali analize još nisu dovršene
Mjerenja izmjene naboja pion-nukleon u području ∆(1232) rezonancije
No full textMeasurements of differential cross sections for pion-nucleon scattering, π −p → π 0n, in the region of the ∆(1232) resonance are presented. These data were obtained as part of the baryon spectroscopy program using the Crystal Ball detector in the C6 beam line of the Alternating Gradient Synchrocyclotron at Brookhaven National Laboratory. The results reported here are limited to the momenta at which the beam contaminations could be deduced by TOF. Data at higher momenta require the use of special normalization runs completed in 2002 and are still under analysis.Opisujemo mjerenja diferencijalnih udarnih presjeka za raspršenje pion-nukleon, π −p → π 0n, u području ∆(1232) rezonancije. Podatke smo dobili u okviru programa barionske spektroskopije s detektorom Crystal Ball na snopu C6 sinkrociklotrona s izmjeničnim gradijentom u Nacionalnom laboratoriju u Brookhavenu. Podaci su ograničeni na impulse za koje se onečišćenje u snopu moglo razlučiti vremenom proleta. Podaci za više impulse zahtijevaju posebna normalizacijska mjerenja koja su izvršena u 2002. godini, ali analize još nisu dovršene
Najvažniji ishodi programa s kristalnom loptom u AGS-u
No full textResults are presented for π −- and K−-induced reactions on a proton target leading to all-neutral final states. Also shown are new data on rare and forbidden eta-meson decays. The detector is the Crystal Ball multi-photon spectrometer, which until recently was located in the C-6 secondary beam line at the AGS. Special emphasis is given to 2π 0 production.Opisujemo ishode mjerenja reakcija izazvanih π −- i K−-mezonima na protonima koje vode na stanja samih neutralnih čestica. Prikazujemo također nove podatke o rijetkim i zabranjenim raspadima eta mezona. Primjenjuje se više-fotonski spektrometar Crystal Ball koji je do nedavno bio na sekundarnom snopu C-6 u AGSu. Posebna se pažnja pridaje tvorbi 2π 0
Najvažniji ishodi programa s kristalnom loptom u AGS-u
No full textResults are presented for π −- and K−-induced reactions on a proton target leading to all-neutral final states. Also shown are new data on rare and forbidden eta-meson decays. The detector is the Crystal Ball multi-photon spectrometer, which until recently was located in the C-6 secondary beam line at the AGS. Special emphasis is given to 2π 0 production.Opisujemo ishode mjerenja reakcija izazvanih π −- i K−-mezonima na protonima koje vode na stanja samih neutralnih čestica. Prikazujemo također nove podatke o rijetkim i zabranjenim raspadima eta mezona. Primjenjuje se više-fotonski spektrometar Crystal Ball koji je do nedavno bio na sekundarnom snopu C-6 u AGSu. Posebna se pažnja pridaje tvorbi 2π 0
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