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

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

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

Izabella Zychor EPIPHANY, Krakow, January 6-8, 2005 4

ANKE: magnetic spectrometer at internal target position of COSY

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 ±)

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

Izabella Zychor EPIPHANY, Krakow, January 6-8, 2005 8

XpKpp

Izabella Zychor EPIPHANY, Krakow, January 6-8, 2005 9

EXPERIMENTAL RESULTSYpKpp

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

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

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 )

Izabella Zychor EPIPHANY, Krakow, January 6-8, 2005 13

RESULTS

Y0*: M=1480 MeV/c2, Γ=60 MeV/c2

pp pKXpp pKX

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 !

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 +

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