BOSEN 2005 Λ(1405) Photoproduction at CB-ELSA Vera Kleber Physikalisches Institut Universität Bonn 1
Outline Motivation Access to Λ(1405) and available data Λ(1405) at CB-ELSA Outlook 2
What s known PDG Σ 0 (1385) Λ(1405) S=-1, Σ 0 = uds S=-1, Λ 0 = uds I(J P ) 1(3/2 + ) Mass 1383.7 ± 1.0 [MeV] Width 36 ± 5 [MeV] Decay 0(1/2 - ) 1406.5±4.0 50 ± 2 Σ 0 π 0 (33%) S. Eidelman et al., Phys. Lett. B 592, 1 (2004) Σ + π - ( 6%) Σ - π + ( 6%) Λπ 0 (88%) Σ + π - (33%) Σ - π + (33%) 3
Where does it come from Data: m(π+σ) m(k+n) R.J. Hemingway, NP B 253 (1985) 742 Analysis: m(π Σ + ) R.H. Dalitz, A. Deloff, JPG 17 (1991) 289, M-Matrix fit 1406.5± 4.0 50±2 Σ * (1670) + π + Λ(1405) π + (πσ) 0 4
Strange Particle located close to many thresholds Λ(1405) πλ π 0 Σ 0 π + Σ K 0 n π Σ + K - p Mass Dalitz and Tuan predicted (1959) a subthreshold KN resonance from K - p scattering data Λ(1405) was discovered a few years later; only 30 MeV below KN threshold 5
Lambda States in Quark Model S=1/2 L=1 6
Structure of the Λ(1405) large theoretical effort J P =1/2 - J P =3/2 - quark model state with orbital excitation mass degenerated partner with J P =3/2 - Λ(1405) Λ(1520) Λ(1520): 115 MeV away KN molecule, dynamically generated another J P =1/2 - Λ near the Λ(1520) unobserved Λ(?) Λ(1520) a.u. χ symmetry: double structure @ 1405 MeV D. Jido et al., Nucl. Phys. A725 (2003) 181 7
Access to Λ(1405) above KN threshold K - p scattering data at KN threshold kaonic hydrogen below KN threshold πσ mass distribution 8
K - p Scattering K - p available data above KN threshold: K - p K 0 n KN scattering length π + Σ π Σ + Hemingway data can be described π 0 Λ π 0 Σ 0 J. A. Oller, U.-G. Meissner, Phys. Lett. B 500 (2001) 263 9
Kaonic Hydrogen DEAR@DAΦNE Kaonic Hydrogen energy shift and width M. Cargnelli et al., Int. Mod. Phys. A20 (2005) 341 Γ [ev] DEAR KEK Borasoy et al., E [ev] arxiv:hep-ph/0505239 K - p scattering length Consequences for Λ(1405) line shape 10
πσ Mass Distribution: LEPS γp K + X LEPS J.K. Ahn, Nucl. Phys. A 721 (2003) 715c 11
πσ Mass Distribution: LEPS γp K + π +/ Σ /+ J.K. Ahn, Nucl. Phys. A 721 (2003) 715c cut on m(x) = m(σ) Λ(1405) (Σ(1385)) Σ 0 12% 66% (1385) πσ Λ(1405) Λ(1520) π + Σ - π Σ + 12
πσ Mass Distribution: Crystal Ball Σ cut and bg subtraction K - p Σ 0 π 0 π 0 Λγ π 0 n 7γ n Σ 0 p K- = 581 MeV/c 687 MeV/c 714 MeV/c -- phase space Λ(1405) Λ(1520) 750 MeV/c 13
Two Λ(1405) Resonances V.K. Magas et al., hep-ph/0503043 Two Λ(1405): in experiments superposition is seen different reactions can pick up the poles with different strength 14
Plans for Λ(1405) at CB-ELSA γp K + Λ(1405) K + n5γ Σ 0 π 0 mass distribution invariant mass of (Σ 0 π 0 ) system or missing mass of K + Λγ nπ 0 t-distribution momentum transfer to Λ(1405) if t-channel dominant access to pk - scattering amplitude below threshold 15
Dominant Production Mechanism Λ(1405) M. Lutz, M. Soyeur, arxiv:nucl-th/0407115 16
Photondetection with Crystal Barrel 1380 CsJ(Tl) crystals angular range 12 o 168 o solid angle 0.95 x 4π δe/e 2.5% @ 1 GeV δθ/θ ±2 o 17
Kaon Identification kaon identification via its mass experimentally difficult equvialent: velocity and momentum velocity via time-of-flight (TOF) (and known distances) momentum via magnetic field deflection momentum 18
Crytal Barrel + Magnetic Spectrometer Crystal Barrel Dipole 0.6 Tm Track Detectors MOMO: 673 scintillating fibers 2.5 mm diameter 3 layers TOF: plastic scintallator bars 3 x 3 x 0.2 m 3 19
TOF versus Momentum Simulation: Andre Süle K+ identification up to 1200 MeV (black line) 20
Alternative: CB + MOMO + TOF Crystal Barrel MOMO: 673 fibers 2.5 mm diameter TOF: plastic scintallator bars 3 x 3 x 0.8 m 3 21
K + Identification with TOF Wall TOF @ 5.3 m Stefan Höffgen K+ identification up to 600 MeV (black line) 22
Summary I Λ(1405): well established state of unknown structure 3q state KN molecule two Λ(1405) not much experimental data so far Plan for CB-ELSA: γp K + Λ(1405) K + n5γ 5γ well suited for CB K+ (and n) ID with TOF / Magn. Spectr. 23
Summary II Benefit of this measurement: clean channel (no contribution from Σ(1385)) t-distribution if t-channel dominates access to K - p scattering amplitude below threshold one more channel to test mass distributions 24