Transcript EPIPHANY

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 University
University Tbilisi
University College London
Izabella Zychor
EPIPHANY, Krakow, January 6-8, 2005
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MOTIVATION
• new results in hadron spectroscopy
• e.g. Σ(1480)
– 1-star “bump” in PDG
_
– ZEUS: an indication in the K S0 p ( p ) invariant mass
– Crystal Ball: not observed in K -pπ0 π0 Λ
• COSY – a unique possibility to search for
hyperons in hadron induced reactions
Izabella Zychor
EPIPHANY, Krakow, January 6-8, 2005
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COoler SYnchrotron (Jűlich, Germany)
•protons and deuterons
•polarized and unpolarized
•pbeam = 0.3 – 3.7 GeV/c
Izabella Zychor
EPIPHANY, Krakow, January 6-8, 2005
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ANKE: magnetic spectrometer at internal target position of COSY
Izabella Zychor
EPIPHANY, Krakow, January 6-8, 2005
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pp  pK Y  pK  X
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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 ±)
Izabella Zychor
EPIPHANY, Krakow, January 6-8, 2005
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CHARGED PARTICLE IDENTIFICATION
• time-of-flight :
in scintillators
• delayed signals
from stopped K+ :
in telescopes
FORWARD GOING
PARTICLES
τ  (12.9  0.5) ns
• momentum
reconstruction in
MWPCs
Izabella Zychor
EPIPHANY, Krakow, January 6-8, 2005
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pp  pK  X

Izabella Zychor

EPIPHANY, Krakow, January 6-8, 2005
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EXPERIMENTAL RESULTS

pp  pK Y
Izabella Zychor
EPIPHANY, Krakow, January 6-8, 2005
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(i) pp  pK+ Y
Y = S(1385), L(1405), L(1520)
(ii) non-resonant production
pp  NK+X, NK+ π X, NK+ π π X
X = hyperon
Izabella Zychor
EPIPHANY, Krakow, January 6-8, 2005
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Comparison of Monte Carlo simulations and experimental data
pp  pK+Y and non-resonant production
pp  pKX-
Izabella Zychor
pp  pK-X
EPIPHANY, Krakow, January 6-8, 2005
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(i) pp  pK+ Y
Y = S(1385), L(1405), L(1520)
(ii) pp  NK+X, NK+ π X, NK+ π π X
X = hyperon
(iii) additional contribution
pp  pK+ Y0*( M, Γ )
Izabella Zychor
EPIPHANY, Krakow, January 6-8, 2005
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RESULTS
Y0*: M=1480 MeV/c2,
pp  pKX-
Izabella Zychor
Γ=60 MeV/c2
pp  pK-X
EPIPHANY, Krakow, January 6-8, 2005
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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 !
Izabella Zychor
EPIPHANY, Krakow, January 6-8, 2005
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Summary
• Y0* observed in pp collisions
in two final states: Y0* π+ X - and Y0*  π- X +
• 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 ?
Izabella Zychor
EPIPHANY, Krakow, January 6-8, 2005
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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
Izabella Zychor
EPIPHANY, Krakow, January 6-8, 2005
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