ABC Effect in Double Pionic Fusion

Transcription

1 Fachbereich Physik CERN Courier September 2011 BLINDBILD ABC Effect in Double Pionic Fusion Facets of Strong-Interaction Physics Hirschegg Jan , 2012 Heinz Clement

2 Outline Two-Pion Production in general Double-Pionic Fusion: the ABC Effect from the ABC Effect to the ABC Resonance consequences what is it? 2

3 NN NNππ pure isovector pp ppπ 0 π 0 / π + π pnπ + π 0 nnπ + π + d π + π 0 pure isoscalar. pn d π 0 π 0 pd 3 He π 0 π 0 dd 4 He π 0 π 0 ABC effect / π + π 3

4 First Observation of ABC Alexander Abashian, Norman E. Booth and Kenneth M. Crowe, rowe, Phys. Rev. Lett. 5,, 258 (1960) enhancement just at ππ threshold T p pd 3 He X = GeV Θ = He 2 π Phase Space lab P 3 He 4 π

5 ABC effect Inclusive measurements: pd 3 He X Abashian et al. Berkeley (Abashian, Both, Crowe ) Banaigs et al. Saclay Missing mass [ GeV/c 2 ] low-mass enhancement! Θ = 0.3 deg NP B67 (1973)1 p d = 3.14 GeV/c T p = 893 MeV 5

6 WASA Detector γ γ d COSY/ γ γ 6

7 The ABC Gallery pn d π 0 π 1.0 GeV pd 3 He π 0 π 0.9 GeV dd 4 He π 0 π 1.0 GeV dσ/dm π o π o [µb/gev] heavier nuclei?? [GeV/c ] M π o π o PRL 102 (2009) PL B 637 (2006) 223 NP A 825 (2009) 71 CELSIUS-WASA measurements WASA-at-COSY: new exclusive measurements over the full region! 7

8 The no-abc no-abc 1.3 GeV dσ/dmπ0π GeV GeV 800 Mπ0π pp GeV GeV dσ/dmπ0π0 [µb/(gev)] pp pp π0π0 pp d π++π00 Mπ0π Mπ0π0 [GeV/c ] Phys.Lett. B 684 (2010) Mπ0π0 [GeV] Phys. Lett. B 695 (2011) 115 fully described by t-channel process H. Clement ABC Effect in Double-Pionic Fusion 8

9 ABC Conclusions I ABC effect occurs only in the production of an scalar-isoscalar pion-pair pair (σ) at an isoscalar nucleon pair, and correlated with excitation energy dependence? 9

10 Isoscalar : Results from WASA at COSY M 2.37 GeV Γ 70 MeV ABC resonance Γ intr 50 MeV Phys.Rev.Lett.106, (2011) 10

11 Isovector : Total Cross Sections isospin decomposition N*(1440) (1600) (?) Phys. Lett. B 679 (2009) 30 11

12 Isovector : pp pp π 0 π 0 Roper dominated T p = 0.9 GeV dominated T p = 1.3 GeV )] 2 [µb/(gev/c M π 0 0π π 0 dσ/dm π 0 π M π [GeV/c ] 0 π 0 phase space Phys. Lett. B 695 (2011) 115 Eur. Phys. J. A 35 (2008)

13 Isovector Fusion (no ABC) pp dπ + π 0 O on proton target on deuteron target with n-spectator 2Γ t-channel Phys.Lett. B 684 (2010) 110 and 702 (2011)

14 Isoscalar Channels Which energy dependence do we expect? pn d π 0 π 0 pd 3 He π 0 π 0 dd 4 He π 0 π 0 / π + π from t-channel t processes we may expect 14

15 Isoscalar : this is what we expect! 15

16 Isoscalar : and this is what we find experimentally CELSIUS/WASA Phys.Rev.Lett.102, (2009) 16

17 Isoscalar : and these are the new measurements WASA@COSY Phys.Rev.Lett.106, (2011) m = 2.37 GeV Γ = 70 MeV 17

18 Dalitz plots Phys.Rev.Lett.106, (2011) 18

19 ππ-invariant mass M ππ ππ Phys.Rev.Lett.106, (2011) ABC effect t-channel 19

20 dπ 0 invariant mass M dπ 0 Phys.Rev.Lett.106, (2011) M dπ 0 M dπ 0 M dπ 0 20

21 Angular distributions Phys.Rev.Lett.106, (2011) cosθ * d cosθ * d cosθ * d 21

22 Angular distribution at the peak cross section σ ( Θ) = J l = 0 D P 2l 2l ( Θ) Phys.Rev.Lett.106, (2011) J=3 J=1 22

23 Quantum numbers of the structure pn R d π 0 π 0 Antisymmetrization: J P =1 + or 3 + : if L =0 σ (cos Θ * d ) = D 0 P0 + D 2 P2 + D 4 P4 + D 6 P Spin-Parity: J P = 3 + Isospin : pn d π 0 π 0 I= 0,1 0 0,2 I=0 23

24 Assume pn R dπ 0 π 0 p model π n π d I(J P ) = 0(3 + ) M, Γ, Γ i Γ f, F(q ) Phys.Rev.Lett.106, (2011) M ππ ππ M dπ 0 Θ d * 24

25 Conclusions II Two-pion production in pp collisions: basically understood by t-channel t excitations of N*, and (1600) Two-pion production in pn collisions: ABC: low mass enhancement in M ππ resonance strcuture in σ tot I(J P ) = 0(3 + ) M 2370 MeV = 2M - 80 MeV Γ 70 MeV << 2 Γ 230 MeV and 25

26 survives even in heavier nuclei! preliminary dd 4 He π 0 π 0 4 He t-channel [arb. units] ππ threshold d 26

27 Consequences and Outlook To-do list: Search for resonance effects in all possible channels: pn d π + π pn pn π 0 π 0 pn pp π 0 π NN NNπ ( I = 0 ) pn scattering (polarized beam) 27

28 1.2 GeV data Sep09 p d d π + π + p spectator d π + π 0 + n spectator d π 0 π 0 + p spectator pp π + p spectator pp π 0 + n spectator

29 Total cross section pn dππ DESY dπ + π - JINR 1 2 dπ + π 0 29

30 Isospin factors σ [ ] 1 [ ] pn dπ + π ( I = 1) = σ pp dπ + π

31 Total cross section pp dπ + π 0 Shimizu et al. F. Kren et al. 31

32 Total cross section pn dππ dπ + π - I=0 = dπ + π 2 32

33 Total cross section pn dππ dπ + π - dπ 0 π 0 I=0 : = - 1 dπ + π

34 Consequences and Outlook To-do list: Search for resonance effects in all possible channels: pn d π + π pn pn π 0 π 0 pn pp π 0 π NN NNπ ( I = 0 ) pn scattering (polarized beam) 34

35 Resonance Effects in pn Scattering Total cross sections [mb] σ tot 40 σ tot SAID (I=0) [mb] σ tot σ tot (I=0) SAID + ABC resonance [GeV] T n [GeV] T n 35

36 so what is it? 36

37 so what is it? Some hint? 37

38 so what is it? Some hint? 38