Baryon Spectroscopy at ELSA

Transcription

1 Baryon Spectroscopy at ELSA recent results and future plans Hartmut Schmieden Physikalisches Institut Rheinische Friedrich-Wilhelms-Universität Bonn ECT* Trento, July 2005 Resonances in QCD SFB-TR 16

2 Outline Spectroscopy why and how? ELSA facility & Crystal Barrel detector Selected results from ELSA π0 η π0 π 0 / π 0 η ω Future plans ω K+ Λ(1405) polarisation / detector extension

3 Spectroscopy Ba Ca atom nucleon

4 Lowest lying states Lattice QCD S. Aoki et al. (CP-PACS collab.) PRL 84 (2000) 238 D. Richards Wedn. non-perturbative regime LQCD (quenched) lowest states deriving the low-lying hadron spectrum is a key step of LQCD in order to gain a convincing demonstration on the validity of QCD... in the low energy domain models! incorporate symmetries of QCD

5 Quark model N* resonances overall pattern Roper unresolved also S11(1535) too many states Löhring, Metsch, Petry, EPJ A10, 395(2001)

6 Quark model Δ* resonances overall pattern Δ(1600) Roper state? neg. parity Δ(~1900)? too many states?

7 Quark model Λ states Λ(1405)

8 Quark model - conclusions Constituent quark models describe gross features of Baryon spectrum models can be discriminated sequence N(3/2)+ - Δ(3/2)+ Δ(~1900) parity doublets individual problems N(1/2)+(1440) Roper & relatives quark-gluon hybrid pentaquark Λ(1405) L=1 uds-singlet NK molecule ick t s ap n. C. d S We Δm( )? large spin-orbit? nearby multipletpartner of Λ(1520)? proliferation of model-states Missing Resonances alternatives quark-correlations solitons dynamically generated resonances sev t i me et o l Ko & Os πn-coupling? width?

9 Experimental tools meson photoproduction broad & overlapping states isospin separation production mechanism partial wave analysis, dyn. models specific channels 4π - detectors energy range polarisation

10 Experimental tools meson photoproduction prob. to hit meson in cloud σ T 2 ρ(q-k) ρ(r) = e-mr/r ρ(q-k) = 1/[m2+(k-q)] 1/[m2-t] dσ/dt σ 0, 1+,... 0+, 1,... σ Σ = σ - σ σ + σ photon asymmetry 1/[m2-t]

11 ELSA facility

12 Crystal ELSA Crystal Barrel 1380 CsI tagger Tagger radiator Radiator Goniometer Beam-dump TAPS 528 BaF TAPS LH 2 CB 30 Pγmax e - beam Eγ /MeV 30o TOF TOF flux monitor γ-veto

13 Crystal ELSA 1380 CsJ(Tl) crystals 16 X0 (30 cm) angular range solid angle δe/e δθ/θ ΔE readout typ. signal CsJ(Tl) density X0 RM decay time light output λmax 4.53 g/cm cm 3.8 cm 0.9 & 7 μs 0.85 x NaJ 550 nm 12o 168o 0.95 x 4π 1 GeV ±2o 8 MeV 2 GeV wavelength shifter & photodiodes 2000 photoelectr./mev

14 Crystal ELSA

15 Overview of recent results charged final states SAPHIR neutral final states CB MAMI ELSA

16 selected results multi-photon final states γ+p γ+a p + π0 p+η p + η' p+ω p + π0 + π0 p + π0 + η p+η +η p + ω + π0 p + K0 + K0 Σ++ Ks0 K++ Λ(1405) 2γ 2/6 γ π0π0η π0γ 4γ 4/8 γ 2/6 γ π0π0γ 4π0 3π0 π0 Σ0 ω+x π0γ 6/10 γ 3γ 5γ 8γ 6γ 5γ+n 3γ

17 counts γγ final state

18 γ p p π0

19 γ p p π0

20 γ p p π0 Partial Wave Analysis isobar analysis Breit-Wigner/K-matrix & u- and t-channel A. Anisovich et al., EPJ A24 (2005) 111 relativistically invariant operator expansion method analyticity & unitarity Input fit of angular distributions TAPS/MAMI π0 & η low energy GRAAL π0 & η incl. polarization Bonn γp nπ+ ( isospin)

21 γ p p π0 Δ(1232) D33(1700) F15(1680) S11(1650) F37(1950) P33(1920) S11(1535) D13(1520) 2-3% P11(1440) O. Bartolomy, V. Crede, H. van Pee, PRL 94 (2005)

22 γp pη Γ3π/Γ2γ = ± 0.001stat ± 0.005syst exactly PDG!

23 γp pη

24 γp pη S11(1535) GRAAL S11(1650) MAMI CB-ELSA D15(2070) CLAS PWA V. Crede, O. Bartolomy et al., PRL 94 (2005)

25 γp pη results PWA all 3/4* PDG N* and Δ* in PWA S11(1535) & S11(1650) no evidence for 3rd S11(1780/1846) new N(2070) D15 (M,Γ) = (2068±22, 295±40) MeV symmetry in N* quartets / doublets L=1 L=2 L=3 N(1650)S11 N(1535)S11 N(1700)D13 N(1720)D13 N(1675)D15 N(2100)P11 N(1900)P13 N(1720)P13 N(2000)F15 N(1680)F15 N D13 N(2200)D15 N(2190)G17 N(2070)D15 N(2080)G17 S=3/2 ½ N(1990)F17 on k tal d We E. Klempt N(2250) G19 S = ½ J = L-S n.

26 double polarisation: long. pol. target & lin. pol. beam 15?D (2 07 0)? γp pη G 1/2+ 1/2- } instead with D15(2070) -1 0 cos Θ +1 A. Sarantsev, priv. comm.

27 γ p p π0η/π0π0 sequential decays missing resonances? π0π events ηπ0 π0η events ] ev [M m γγ ] V e M m γ[ γ

28 γ p p π0η/π0π0 total cross sections M. Fuchs, I. Horn Diss. (2004/05)

29 γ p p π0η Partial Wave Analysis decay channels Δ+(1232) η a0(980) p N+(1535) η N+(1535) π0 N+(1520) η N+(1710) π0 N+(1440) η γp X p π0η fitted resonance rad.-excitation to Δ(1700) m(q-models) 2150 MeV low as N(1440) & P33(1600) strongest contributions ~ % from ~ % from ~ 3% from Δ+(1232) η with L=0: Δ+(1232) η with L=1: Δ+(1232) η with L=2: Δ(1700)D33 and Δ(1940)D33 Δ(1905)F35 and Δ(2150)F35 Δ(2600)G37

30 γ p p π0η need 2 D33 resonances? χ2 fit w/ 1 resonance maximum 1686 MeV χ2 fit w/ 2nd resonance 1910 MeV

31 γ p/a p/a ω in medium modifications? massless quarks chiral symmetry breaking on hadron level 1 +,1 2 2 mass split comparable to nucleon mass! χ-sym. 1 ( 1535 ) MeV 1 + ( 938 ) 2 hadrons T. Renk et al., PRC 66 (2002) in medium: mv lower mv broader

32 γ p/a p/a ω in medium modifications? experimental: di-lepton spectroscopy ρ,ω,φ e+e- mv = (p1+p2)2 no (strong) final state interaction ELSA: γ γ+a ω+x π0 γ p A γ ω γγ π % π0γ branching γ mω = γ (p π + p γ ) 2 + no ρ π0γ 7x π0 rescattering?

33 γ p/a p/a ω in medium modifications? π0 η η' D. Trnka et al., PRL94 (2005)

34 γ p/a p/a ω in medium modifications? J.G. Messchendorp EPJA 11 (2001) 95 γ p A ω γ π 0 Δ-decay kinematics pω < 0.5 GeV/c decay in nucleus first indication for inmedium ω mass shift γ γ

35 γp pω resonances? N* SU(6)xO(3) exp. status Isgur-Karl assignment coupling πn ωn tot. width JP S11(1535) **** N(1535) 1/ P11(1710) *** N(1710) 1/ P13(1870) * N(1870) 3/ P13(1950) missing N(1955) 3/ P13(2030) missing N(2060) 3/ D15(1675) **** N(1670) 5/ F15(1680) **** N(1715) 5/ N(1955) 5/ N(2025) 5/ F15(1995) F15(2000) missing * 77

36 γp pω t-channel dσ/dt dσ/dt t=t min e -b t π0 (0-) P (0+) s-channel + dσ/dt t-tmin J. Barth et al. EPJ A18, 117 (2003)

37 γp pω resonances? Shklyar et al. (Giessen group) nucl-th/ v2 on k l ta Penner et al., PR C66 (2002) Jres 3/2 Jres 5/2 P11(1710) main thresh. P11(1710) negligible ay d i fr

38 γp pω polarisation observables beam asymmetry beam-target asymmetry non-res. only full calc w/ N* preliminary data from GRAAL J. Ajaka et al., AIP conf. proc. 570 (2001) 198 F15(1680) dominating contrib. A. I. Titov and T.-S.H. Lee PR C66 (2002)

39 γp pω kinematics & polarisation observables photon - plane ˆ zdecay reaction -plane decay -plane Σx Σdec = = σ - σ σ + σ ~ cos 2Φ Gx,dec σ - σ σ + σ doublepolarisation ˆ zdecay E singlepolaris. Pγ,lin PT,z Σx,dec = σ3/2 - σ1/2 σ3/2 + σ1/2 Pγ,circ PT,z

40 γp pω Bonn PWA A. Sarantsev, priv. comm. polarisation observables Σπ E Gπ π-exchange solution 2a 5/2+ -1/2+ -3/2+ solution 5b 3/2+ -5/ cos θ

41 γp pω 8.5% π0 γ γγγ Missing Mass J. Barth et al. EPJ A18, 117 (2003) ΘωCMS Invariant Mass (π0 γ) 7% of data (γ, LH2) Eγ / GeV

42 γ p K Λ/Σ missing resonances? small coupling to Nπ large K Λ/Σ D13(1900) SAPHIR/Bennhold individual states Λ(1405) KN bound state L=1 SU(3) singlet uds double resonance ChPT LS splitting -??? - Λ1/2 (1405) - Λ3/2 (1520) - - N1/2 (1535) - N3/2 (1520) ch.coupl. ; <ss>/<uu>

43 Λ(1405) DAΦNE Γ (ev) M. Cargnelli et al. Int. Mod. Phys. A20 ('05) 341 χ meson-baryon interaction 2 poles KEK Jido, Oller, Oset, Ramos, Meißner NP A725 (2003) 181 DEAR B. Borasoy, R. Nißler, W. Weise hep-ph/ K p scatt. length? - lk a t on ay d fri ΔEs (ev)

44 γ p K+ Λ(1405) LEPS collab., PRL 91 (2003) Σ( separation ) [σ(π+ Σ-) - σ(π- Σ+)] (4/3 [σ(π+ Σ-) + σ(π- Σ+)] Λ(1405) π0 Σ0 π ± Σ unique assumption: 6% σ(σ1385) = σ(λ1405) 33% π ± Σ Jido, Oller, Oset, Ramos, Meißner NP A725 (2004) 181 M. Lutz & M. Soyeur NP A748 (2005) 499 Data from J.K. Ahn et al., NP A721 (2003) 715c

45 γ p K+ Λ(1405) y lk a t on f a d i r M. Lutz & M. Soyeur NP A748 (2005) 499 reaction dynamics sub-threshold K-p scattering

46 γ p K+ Λ(1405) planned ELSA SFB/Transregio 16 double polarization beam/target reaction specific forward extensions K+ id time-of-flight det. MOMO Λ(1405) π0 Σ0 mag. dipole 0.6 Tm tracker 100% Λγ 36% n π0 ideal for Crystal Barrel

47 Baryon ELSA Summary SFB-TR 16 Crystal ELSA 4π multi-photon detector & forward extensions first results single π0/η production sequential decays π0π0/ π0η ω medium modification PWA N(2070)D15 Δ(1940)D33 incomplete experiments linear & circular beam polarisation target & recoil polarisation future plans Λ(1405) π0 Σ0 γ+p N* ω/η+p (double) polarisation