Improved search of COSY-TOF on Ө +

Transcription

1 Pentaquark 05 International Worksho, October 20-22, 2005, Jefferson Lab, U.S. Imroved search of COSY-TOF on Ө + Wolfgang Eyrich Physikalisches Institut, University of Erlangen-Nuremberg, Germany for the COSY-TOF collaboration suorted by German BMBF and Forschungszentrum Jülich

2 Content Introduction The COSY-TOF exeriment Evidence on Θ + from Σ + K 0 Ongoing and new activities Outlook

3 Introduction Strangeness roduction at COSY-TOF: N KYN Information: dynamics + structure degrees of freedom different reaction channels : N =, n Y = Λ, Σ o, Σ +, Σ - Meson Exchange Model final state interaction R? π,ρ,... Λ K + + Κ,Κ,... K + Λ Search for exotic Θ + Θ +? K,K* K* Σ + Κ 0 Σ +

4 Introduction Strangeness roduction at COSY-TOF: N KYN Information: dynamics + structure degrees of freedom different reaction channels : N =, n Y = Λ, Σ o, Σ +, Σ - Meson Exchange Model final state interaction R? π,ρ,... Λ K + + Θ ++? Κ,Κ,... K + Λ Search for exotic Θ + Θ +? K,K* K* Σ + Κ 0 Σ +

5 Introduction Strangeness roduction at COSY-TOF: exclusive observables full hase-sace Dalitz Plots olarization: Hyeron-olarization, olarized beam, olarized target threshold region only few artial waves, no Y*, strangeness tagging FSI FSI

6 COSY - Facility Cooler Synchrotron Jülich Circumference: 180 m Phase sace cooling: electron and stochastic TOF Beam momentum: maximum: 3.6 GeV/c

7 COSY - beam Beam-Quality Veto-detector with 2 mm hole 0.1% intensity Beam-Intensity used 1-3 x 10 7 /s

8 COSY - TOF Large-angle Time-of-Flight sectrometer (modular vacuum vessel) Barrel Hodoscoe Starttorte Si μ-stri SciFi- Hodo 1 SciFi- Hodo 2 Erlangen Startdetector system "Erlangen" Startdetektor System Veto Target LH 2 Target Ring Hodoscoe Central Hodoscoe Quirl Folie 3.4 m 3329 Quirl orderkante Start detector system vertex reconstruction designed for strangeness roduction Λ K +, Σ + K 0, Σ 0 K +, Σ + K + n, n Λ K 0,...

9 COSY-TOF - Sto-Detector TOF Quirl

10 Erlangen Start Detector : Ring microstri detector Frontside 100 rings Rearside 128 sectors

11 Erlangen Start Detector : Fibre Hodoscoes Fibre Hodoscoe 1 Fibre Hodoscoe 2

12 The Erlangen Start Detector K + Λ π- delayed decay of Λ charged multilicity 2 4 trigger K + vertex reconstruction identification of Λ : decay V comlete geometric reconstruction 4π coverage

13 K + Λ: Dalitz lot analysis counts 2.95 GeV/c Data 2.95 GeV/c Λ-mass

14 The Erlangen Start Detector K 0 Σ + π π + π 0 π + n delayed decay of K 0 charged multilicity 2 4 trigger vertex reconstruction identification of K 0 s : decay V Σ + a identification of Σ + : decay kink in track comlete geometric reconstruction 4π coverage

15 Σ + K 0 : reconstructed masses P beam = 2.95 GeV/c events Runs K 0 mass (GeV/c 2 ) Σ + - mass (GeV/c 2 )

16 Σ + K 0 : Dalitz lots P beam = 2.95 GeV/c M 2 (K 0 ) in GeV 2 /c M 2 (K 0 ) in GeV 2 /c M 2 (Σ + ) in GeV 2 /c 4 M 2 (K 0 Σ + ) in GeV 2 /c 4

17 K 0 Σ + : K 0 mass sectra P beam = 2.95 GeV/c efficiency corrected significance: 4 6 σ (deending on method) NS / NB NS / NS + NB 5.9 σ 4.7σ Mass 1530 ± 5 MeV/c² Width 18 ± 4 MeV/c² (FWHM) Strangeness S = + 1 Cross section: 0.4 ± 0.1 stat ±0.1 sys µb NS / ( NS + NB) + NB 3.7σ he-ex/ , Phys. Lett. B 595 (2004), 127

18 2 nd Round: COSY-TOF run Oct. / Nov Reaction: Σ + K 0 beam = 3.05 GeV/c Goal: Decision on the existence of the Θ + in the investigated channel Exerimental ugrade: New fibre hodoscoe with three layers Two layers increase of reconstruction efficiency Three layers

19 Measurement Oct./Nov. 2004: K 0 Σ + Estimate of outut: P beam = 3.05 GeV/c Reference: reaction channel K + Λ (similar attern) Preliminary analyses of 4 hours run: Λ missing mass Exected overall gain for K 0 Σ + : Factor of ~ 5 more events comared to existing data (in agreement with the roosal)

20 COSY-TOF run October / November 2004 Ongoing analysis: Imroved Monte Carlo simulations Blind analysis Indeendent analyses at several institutes: - common calibration database - different codes - emhasising on different detector asects geometric reconstruction time-of-flight information energy loss information Detailed investigation: - K s system - Dalitz lot - background (+ modelling)

21 Related toic: Search for ossible isosin artners Search for Ө ++ : ΛK + P beam : 2.95 GeV/c 3.20 GeV/c 3.30 GeV/c Preliminary: no evidence for Ө ++ in K + sectra New data: 2x10 5 ΛK + events!

22 Related toic: Width of N*(1710) resonance ΛK + P beam : 3.30 GeV/c N * (1710) contributes strongly Influence of Λ-FSI m 2 (KЛ) GeV 2 /c 4 In rogress: Investigation of Dalitz lots width

23 K + Λ: Dalitz lots 2.95 GeV/c 3.20 GeV/c 3.30 GeV/c DATA MODEL d dm 2 KΛ σ dm 2 2 Λ = R ( flux) ( C A ) + C A ( + C A ) R R N N 1 FSI FSI 2 Sibirtsev

24 3rd round : Parity of Θ + - roosed measurement with double olarization Σ + Θ + Proosed by W.A. Thomas et al. Hanhart et al., he-h ; PLB590(04)39; PLB606(05)67 Observable: ( 3 P 0,1 ) 3 σ Σ = ½σ 0 (2+A xx +A yy ) K only K* only K and K* at two energies (+ ( 1 S 0 ) for reference)

25 Polarized frozen sin target for COSY-TOF Accetance: ± 32 Dimensions: Hanhart et al., 9mm he-h ; x 6mm P max PLB590(04)39; (butanol): PLB606(05)67 ~ 80% alternative material in Test - Frozen sin technique well suited for low intensity external beams - High olarization ~90%, d ~80% - PS185/3 set u will be used - rearation at Bochum and Bonn.. Installation at COSY-TOF

26 Polarized frozen sin target for COSY-TOF Set u at COSY-TOF New comonents: - olarized Target - Straw tracker

27 n() K 0 Λ() Test 2004 K 0 Λ π + π π Unique signature: 2 V s corresonding to delayed decays of Λ and K 0 into charged articles Trigger: 1 5 ν 2 6 Successful test: Trigger o.k. First events Well suited for COSY-TOF

28 Reserve

29 Σ + K 0 : background searation Searation of K 0 Σ + from K + Λ and K + Σ 0 ( γ Λ) P beam = 2.95 GeV/c Monte Carlo simulations Θ 2 K 0 S π + π Λ π Λ π K 0 S π + π analysis cuts detector limits Θ 1 Θ 1 + Θ 2

30 Σ + K 0 : cuts on masses P beam = 2.95 GeV/c Run Run 2002 Σ+ K 0 Σ events K events

31 3rd round : Parity of Θ + - roosed measurement double olarized Σ + Θ + K only K* only K + K* Observable: 3 σ Σ = ½σ 0 (2+A xx +A yy ) P = + P = at two excess energies n double olarized Hanhart et al., he-h ; PLB590(04)39; PLB606(05)67 n Λ Θ + n Λ Θ + information on arity (model deendent)

32 K + Λ: Results of analysis I [A.U.] C 1650 Strong contribution of N*-Resonances: π - exchange dominant K exchange small contribution C C 1720 Change of the dominant resonance at about beam =3 GeV/c : N*(1650) N*(1710) / N*(1720) 0 2,8 2,85 2,9 2,95 3 3,05 3,1 3,15 3,2 3,25 3,3 3,35 [GeV/c] Next ste: olarization!

33 Σ + K 0 : K 0 mass sectra P beam = 2.95 GeV/c olynomial fit + = significance: 4 6 σ (deending on method) NS / NB 5.9 σ NS / NS + NB 4.7σ NS / ( NS + NB) + NB 3.7σ

34 Σ + K 0 : efficiency corrected K 0 sectrum 1.53 Background: Polynomial fit Peak: Gaussian fit Mass 1530 ± 5 MeV/c² Width 18 ± 4 MeV/c² (FWHM) Strangeness S = + 1 Cross section: 0.4 ± 0.1 stat ±0.1 sys µb he-ex/ , Phys. Lett. B 595 (2004), 127