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Izabella Zychor EPIPHANY, Krakow, January 6-8, 2005 1
Hyperon production in pp collisions with ANKE at COSY
I. Zychor ( IPJ Świerk ) for the ANKE Collaboration
FZ Jülich, University: Erlangen, Giessen, Köln, Münster, FZ Rossendorf IPJ Świerk, UJ Cracow, INP Cracow PNPI Gatchina, JINR Dubna, Moscow : ITEP, INR, LPI, State UniversityUniversity Tbilisi University College London
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Izabella Zychor EPIPHANY, Krakow, January 6-8, 2005 2
MOTIVATION
• new results in hadron spectroscopy
• e.g. Σ(1480)– 1-star “bump” in PDG– ZEUS: an indication in the invariant mass
– Crystal Ball: not observed in K -pπ0 π0 Λ
• COSY – a unique possibility to search for hyperons in hadron induced reactions
)(_
0 ppKS
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Izabella Zychor EPIPHANY, Krakow, January 6-8, 2005 3
COoler SYnchrotron (Jűlich, Germany)
•protons and deuterons•polarized and unpolarized•pbeam = 0.3 – 3.7 GeV/c
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Izabella Zychor EPIPHANY, Krakow, January 6-8, 2005 4
ANKE: magnetic spectrometer at internal target position of COSY
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Izabella Zychor EPIPHANY, Krakow, January 6-8, 2005 5
XpKYpKpp
• 3.65 GeV/c proton beam• Y hyperon mass < 1540 MeV/c2
• two final states: Y0* π + X - and Y0* π - X +
• three-particle coincidences (pK +π ±)
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Izabella Zychor EPIPHANY, Krakow, January 6-8, 2005 6
CHARGED PARTICLE IDENTIFICATION
• time-of-flight : in scintillators
• delayed signals from stopped K+ :
in telescopes
• momentum reconstruction in MWPCs
FORWARD GOING PARTICLES
ns0.5)(12.9τ
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Izabella Zychor EPIPHANY, Krakow, January 6-8, 2005 8
XpKpp
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Izabella Zychor EPIPHANY, Krakow, January 6-8, 2005 9
EXPERIMENTAL RESULTSYpKpp
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Izabella Zychor EPIPHANY, Krakow, January 6-8, 2005 10
(i) pp pK+ Y
Y = (1385), (1405), (1520)
(ii) non-resonant production pp NK+X, NK+ π X, NK+ π π X X = hyperon
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Izabella Zychor EPIPHANY, Krakow, January 6-8, 2005 11
Comparison of Monte Carlo simulations and experimental data
pp pK+Y and non-resonant production
pp pKXpp pKX
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Izabella Zychor EPIPHANY, Krakow, January 6-8, 2005 12
(i) pp pK+ Y
Y = (1385), (1405), (1520)
(ii) pp NK+X, NK+ π X, NK+ π π X X = hyperon
(iii) additional contribution pp pK+ Y0*( M, Γ )
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Izabella Zychor EPIPHANY, Krakow, January 6-8, 2005 13
RESULTS
Y0*: M=1480 MeV/c2, Γ=60 MeV/c2
pp pKXpp pKX
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Izabella Zychor EPIPHANY, Krakow, January 6-8, 2005 14
WHAT IS Y0*(1480) ?• Λ or Σ0 resonance ?
• 3-valence quark models: no room for Y0* (?)no additional excited Λ or Σ resonances ≤1600 MeV/c2
( e.g. S.Capstick and N.Isgur, U. Loehring et al. )
• 5-quark configurations • 1480 MeV/c2 by Ya.I.Azimov, 1970• 1440 MeV/c2 by H.Högaasen and P.Sorba, 1978• 1495 MeV/c2 by Y.Oh et al., Phys. Rev. D 69, 035208 (2004)
• 1446 MeV/c2 and width of 343 MeV/c2 in kaon-nucleon quasibound state C.Garcia, M.Lutz and J.Nieves, Phys. Lett. B 582, 49 (2004)
no clear theoretical picture !
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Izabella Zychor EPIPHANY, Krakow, January 6-8, 2005 15
• Y0* mass: ( 1480 ± 15 ) MeV/c2
• Y0* width: ( 60 ± 15 ) MeV/c2
• cross section of a few hundred nanobarns consistent for both final states• statistical significance at the 4.8 σ level
• Y0* non-3 quark candidate ?
Summary
• Y0* observed in pp collisions
in two final states: Y0* π+ X - and Y0* π- X +
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Izabella Zychor EPIPHANY, Krakow, January 6-8, 2005 16
OUTLOOK
• measurement at higher beam momentum 3.70 GeV/c
• charged Y* at ANKE with deuterium target
• Y* decays with photons in final states with WASA at COSY