Latest developments in the Spectroscopy of Heavy Hadrons

Transcription

1 Latest developments in the Spectroscopy of Heavy Hadrons Fulvia De Fazio INFN - Bari Question: recent discoveries in charm(onium) and bottom (onium) spectra might be exotic states? Collaborators: P. Colangelo, R. Ferrandes, S. Nicotri, A. Ozpineci, M. Rizzi F. De Fazio INFN Bari Hadron

2 Open charm/beauty states D (38), D (44) D s* (37), D s (46) D(55), D(6), D(75), D(76) D sj (63) D sj (86), D sj (7), D sj (34) B (5734), B * (5738) B s (583), B * s (584) F. De Fazio INFN Bari Hadron

3 Open charm/beauty states D (38), D (44) D s* (37), D s (46) D(55), D(6), D(75), D(76) D sj (63) Seen only by SELEX, never confirmed D sj (86), D sj (7), D sj (34) B (5734), B * (5738) B s (583), B * s (584) F. De Fazio INFN Bari Hadron 3

4 Open charm/beauty states D (38), D (44) D s* (37), D s (46) D(55), D(6), D(75), D(76) D sj (63) Seen only by SELEX, never confirmed D sj (86), D sj (7), D sj (34) B (5734), B * (5738) B s (583), B * s (584) F. De Fazio INFN Bari Hadron 4

5 Hadrons containing a single heavy quark Q Spin of the heavy quark and of the light degrees of freedom decoupled in the m Q limit J = s spin angular momentum s = L s q of the light degrees of freedom (conserved) M s Q Mesons classified as doublets In the HQ limit: - states with the same s lp degenerate finite m Q corrections - remove degeneracy between the states of the same doublet - induce mixing between states with the same J P F. De Fazio INFN Bari Hadron 5

6 P J Qq multiplets 3 D-wave doublets: L = s = 5/ l (D (s), D (s)3 ), (B (s), B (s)3 ) (D * (s),d (s) ), (B * (s),b (s) ) L = s =/ l P-wave doublets: (D (s), D * (s)), (B (s), B * (s)) (D * (s),d (s)), (B * (s),b (s)) L = s =/ l fundamental doublet: (D (s), D * (s)), (B (s), B * (s)) F. De Fazio INFN Bari Hadron 6

7 L = s = 5/ l P J 3 Qq multiplets Strong transitions between multiplets L = L = s =/ l s =/ l 3 3 F. De Fazio INFN Bari Hadron pseudoscalar meson d-wave transition mesons are expected to be narrow pseudoscalar meson s-wave transition mesons are expected to be broad 7

8 P J 3 cq multiplets Low lying Rad. Excitations L = s = 5/ l D(75), D(76)? L = s =/ l D * ±, (46) D ± (4) D (43) Γ * D Γ D Γ D MeV MeV MeV D * (38) Γ D 6 MeV L = s =/ l D D *± ± (), (869), D D (865) F. De Fazio INFN Bari Hadron * (7) D(6)? D(55)? 8

9 P J 3 cs multiplets Low lying L = s = 5/ l D * s(573) Γ * D s MeV L = s =/ l D s (536) Γ < D s.3 MeV L = s =/ l D * s D s () (968) F. De Fazio INFN Bari Hadron 9

10 Narrow peak in the D s π mass distribution: D sj (37) BaBar CLEO.3 GeV Belle M ( D π ) M ( D s s ) production also observed at a fixed target exp observed width consistent with exp. Resolution (< MeV) intrinsic width smaller F. De Fazio INFN Bari Hadron

11 D sj (37) quantum numbers The narrow width suggests Isospin violating decay i.e. confirmed by the absence of isospin partners eventually decaying in, ± D s π ± π ± D s I I= is the preferred assignment J P = D ( 37) π sj D s The observation of the mode D sj (37) D s π favours the assignment J P = Also suggested by the helicity angle distribution Consistent with being flat F. De Fazio INFN Bari Hadron

12 Another narrow peak in the D s * π mass distribution: D sj (46) CLEO.46 GeV M(D s * π ) - M(D s * ) Belle BaBar width consistent with exp resolution F. De Fazio INFN Bari Hadron

13 D sj produced in B decays: B D D sj D s (37) π o D s D s (46) π o D s * D s (46) γd s Belle observes radiative decay of D sj (46) rules out J= Analysis of helicity angle distribution suggests J= spin F. De Fazio INFN Bari Hadron 3

14 D sj (37) & D sj (46) The two narrow states identified as the J P =(, ) lowest lying cs states with L= are data consistent with this interpretation? are data consistent with other interpretations? Understanding if D sj (37) and D sj (46) can be identified with the J P =(, ) lowest lying cs states with L= means checking that the isospin violating decays to D s (*) π proceed at a rate larger than the radiative modes the total rate should not exceed the exp upper bound Γ MeV F. De Fazio INFN Bari Hadron 4

15 Hadronic modes The decays D * s (D s ) D (*) s π as the result of the strong transition followed by the π-η mixing can be described D s (D s ) D (*) s η D s (D s * ) P. Colangelo, FDF PLB57, 8 P. Colangelo, R. Ferrandes, FDF MPLA9, 83 D * ' s (D s ) h η π Γ computed by sum rules Isospin violation enters here M * h D m d m s u π 3 ( Ds Dsπ ) = ( ) p π 6π f M m m * d u p Ds m π s Γ( D Γ( D sj sj (37) (46) D π ) = 7 ± s D s π ) = 7 ± * m KeV KeV F. De Fazio INFN Bari Hadron 5

16 Radiative modes: Light-cone sum rule predictions PDG (m c ) P. Colangelo, A. Ozpineci, FDF PRD 7, 744 The largest computed rate corresponds to the largest measured radiative branching ratio D sj (37) and D sj (46) behave as ordinary cs mesons F. De Fazio INFN Bari Hadron 6

17 P J 3 cs multiplets Low lying L = s = 5/ l D * s(573) L = s =/ l D s (536) L = s =/ l D * s D s () (968) F. De Fazio INFN Bari Hadron 7

18 P J 3 cs multiplets Low lying L = s = 5/ l D * s(573) L = s =/ l D s (536) D s(46) ' D * s(37) L = s =/ l D * s D s () (968) F. De Fazio INFN Bari Hadron 8

19 P J 3 cs multiplets Low lying L = s = 5/ l L = L = s =/ l s =/ l D * s(573) D s (536) D ' s(46) D * s(37) D * s D s () (968) F. De Fazio INFN Bari Hadron Γ < 3.5 Γ < 3.8 D*K threshold MeV D K threshold MeV 9

20 D sj (86) Discovered by BaBar Collab. Reconstructed in D K ( K ( K π ) K π π ) K and in D K S M = ±.5 ± 5. Γ = 48 ± 7 ± MeV MeV BaBar Collab., PRL 97 (6) Quantum number assignment required in order to identify it Possibilities: - low lying state not yet observed - radial excitation of an already observed state Only states that can decay to the observed mode DK are allowed F. De Fazio INFN Bari Hadron

21 P J cs multiplets Low lying Rad excitations 3 L = s = 5/ l L = s =/ l D * s(573) D s (536) D s(46) ' D * s(37) L = s =/ l D * s D s () (968) F. De Fazio INFN Bari Hadron

22 P J cs multiplets Low lying Rad excitations 3 L = s = 5/ l forbidden forbidden L = s =/ l D * s(573) D s (536) D s(46) ' forbidden forbidden D * s(37) L = s =/ l D * s D s () (968) F. De Fazio INFN Bari Hadron forbidden

23 P J cs multiplets Low lying Rad excitations 3 allowed L = s = 5/ l forbidden forbidden allowed L = s =/ l D * s(573) D s (536) D s(46) ' allowed forbidden forbidden D * s(37) allowed L = s =/ l D * s D s () (968) F. De Fazio INFN Bari Hadron allowed forbidden 3

24 D sj (7) B D D K Belle Collab.: analysis of the mode New resonance decaying to D K with: M = 78 ± 9 ± MeV Γ = 8 ± 3± 36 3 MeV implies P=- J= J= J= J P = - favoured A broad structure at M=688 MeV with Γ= MeV was found by BaBar in the DK mass distribution F. De Fazio INFN Bari Hadron 4

25 P J cs multiplets Low lying Rad excitations 3 L = s = 5/ l L = s =/ l D * s(573) D s (536) D s(46) ' D * s(37) L = s =/ l D * s D s () (968) F. De Fazio INFN Bari Hadron 5

26 P J cs multiplets Low lying Rad excitations 3 L = s = 5/ l * D s L = s =/ l D * s(573) D s (536) D ' s(46) D * s(37) L = s =/ l D * s D s () (968) F. De Fazio INFN Bari Hadron * D s 6

27 D sj (86) & D sj (7) predictions on allowed decay rates can help to distinguish among the various possibilities HQ limit: the members of the doublets are described by effective fields: L= s P = L= s P s P = 3 = L= s P s P 3 = = 5 F. De Fazio INFN Bari Hadron 7

28 D sj (86) & D sj (7) Interactions with the emission of a light pseudoscalar meson described by effective Lagrangian terms H S H π H π T H π X H π X H π Analogous terms describe interactions involving radial excitation doublets: g g ~, h h ~,... F. De Fazio INFN Bari Hadron 8

29 D sj (86) : results for width ratios P. Colangelo, S. Nicotri, FDF PLB 64, Would explain the observed narrowness F. De Fazio INFN Bari Hadron 9

30 D sj (86) Our supported option: 5 Signal expected in D * K Small signal expected also in D s η In this case the small width can be attributed to the suppression due to the kaon momentum factor: f-wave transition Assuming the experimentally measured width would predict in the typical range of these couplings k k. 5 The spin partner could decay in p-wave due to the effect of /m Q corrections may escape detection Our conclusion: D sj (86) is likely to be a J P =3 - state Should decay to D*K F. De Fazio INFN Bari Hadron 3

31 Identifying D sj (7) through its decay modes P. Colangelo, S. Nicotri, M. Rizzi, FDF Phys. Rev. D77, 4 the dependence on the (unknown) couplings drops out The D * K decay is the signal that must be investigated in order to distinguish the two possible assignments F. De Fazio INFN Bari Hadron 3

32 BaBar Analysis of D * K final states D * K invariant mass spectrum (background-subtracted) m( D * s Three peaks are visible: (7) ) = 7 ± stat ± 7 syst MeV Γ( D * s (7) ) = 49 ± 7 stat ± 39 5syst MeV angular analysis m( D Γ( D sj sj (86) (86) ) = 86 ± ) = 48 ± 3 stat stat ± 6 ± 5 syst syst MeV MeV m( D Γ( D sj sj (34) (34) ) = 344 ± 8 ) = 39 ± 35 stat stat ± ± 3 5 syst 46 4syst MeV MeV The angular distribution is consistent with the expectations for states with natural parity (, -,,3 -, ) for D s (7) and D sj (86) excluded by the observation of the D * K mode F. De Fazio INFN Bari Hadron BaBar, PRD8 (9 )93 3

33 BaBar Analysis of D * K final states D * K invariant mass spectrum (background-subtracted) m( D * s Three peaks are visible: (7) ) = 7 ± stat ± 7 syst MeV Γ( D * s (7) ) = 49 ± 7 stat ± 39 5syst MeV angular analysis m( D Γ( D sj sj (86) (86) ) = 86 ± ) = 48 ± 3 stat stat ± 6 ± 5 syst syst MeV MeV m( D Γ( D sj sj (34) (34) ) = 344 ± 8 ) = 39 ± 35 stat stat ± ± 3 5 syst 46 4syst MeV MeV The angular distribution is consistent with the expectations for states with natural parity (, -,,3 -, ) for D s (7) and D sj (86) excluded by the observation of the D * K mode F. De Fazio INFN Bari Hadron BaBar, PRD8 (9 )93 to be discussed later 33

34 BaBar Analysis of D * K final states Branching fractions B( D B( D s s (7) (7) * D K) DK) =.9±.3 stat ±. syst Supports the identification of D s (7) with 3 S (first radial excitation of D s* ) B( D B( D sj sj (86) (86) * D K) DK) =. ±.5 stat ±.9 syst Does not support or discard unambiguously any interpretation: still to be understood F. De Fazio INFN Bari Hadron 34

35 P J cs multiplets Low lying Rad excitations 3 L = s = 5/ l L = s =/ l D * s(573) D s (536) D s(46) ' D * s(37) L = s =/ l D * s D s () (968) F. De Fazio INFN Bari Hadron 35

36 P J cs multiplets Low lying Rad excitations 3 D sj (86)? L = s = 5/ l L = s =/ l D * s(573) D s (536) D s(46) ' D * s(37) L = s =/ l D * s D s () (968) F. De Fazio INFN Bari Hadron D sj (7) 36

37 D sj (34) The only additional information is that it decays D*K YES DK NO J P =, -, 3, F. De Fazio INFN Bari Hadron 37

38 P J cs multiplets Low lying Rad excitations 3 D sj (86)? L = s = 5/ l L = s =/ l D * s(573) D s (536) D s(46) ' D * s(37) L = s =/ l D * s D s () (968) F. De Fazio INFN Bari Hadron D sj (7) 38

39 P J cs multiplets Low lying Rad excitations 3 D sj (86)? L = s = 5/ l D sj (34) D sj (34) L = s =/ l D * s(573) D s (536) D ' s(46) D sj D sj (34) (34) D * s(37) L = s =/ l D * s D s () (968) F. De Fazio INFN Bari Hadron D sj (7) 39

40 P J cs multiplets Low lying Rad excitations 3 D sj (86)? L = s = 5/ l D sj (34) D sj (34) would imply an (unlikely) mass inversion if D sj (86) has been properly placed L = s =/ l D * s(573) D s (536) D ' s(46) D sj D sj (34) (34) D * s(37) L = s =/ l D * s D s () (968) F. De Fazio INFN Bari Hadron D sj (7) 4

41 D sj (34): how to discriminate among the four possibilities? info from Relativistic Quark Model (RQM) Allowed strong decays: - to D * (s) light pseudoscalar meson D * K, D * sη - to members of higher doublets a light pseudoscalar meson D * K, D * s, D K D K, D * K - to D (s) a light vector meson DK *, D s φ F. De Fazio INFN Bari Hadron 4

42 D sj (34): how to discriminate among the four possibilities? ~ D s decays in s-wave to D * K, D s* η (broader), has the largest R, the largest width to light vector mesons P. Colangelo, FDF PRD8, 94 F. De Fazio INFN Bari Hadron 4

43 D sj (34): how to discriminate among the four possibilities? ~ D s decays in s-wave to D * K, D s* η (broader), has the largest R, the largest width to light vector mesons P. Colangelo, FDF PRD8, 94 the two - states should not be observed in the decay to light vector mesons F. De Fazio INFN Bari Hadron 43

44 D sj (34): how to discriminate among the four possibilities? ~ D s decays in s-wave to D * K, D s* η (broader), has the largest R, the largest width to light vector mesons P. Colangelo, FDF PRD8, 94 the two - states should not be observed in the decay to light vector mesons D s cannot decay to D K but should have the largest width to D * K F. De Fazio INFN Bari Hadron 44

45 D sj (34): how to discriminate among the four possibilities? ~ D s decays in s-wave to D * K, D s* η (broader), has the largest R, the largest width to light vector mesons P. Colangelo, FDF PRD8, 94 the two - states should not be observed in the decay to light vector mesons D s cannot decay to D K but should have the largest width to D * K look at the features of the spin partner F. De Fazio INFN Bari Hadron 45

46 D sj (34): how to discriminate among the four possibilities? ~ D s decays in s-wave to D * K, D s* η (broader), has the largest R, the largest width to light vector mesons P. Colangelo, FDF PRD8, 94 the two - states should not be observed in the decay to light vector mesons D s cannot decay to D K but should have the largest width to D * K look at the features of the spin partner F. De Fazio INFN Bari Hadron 46

47 Hidden charm (conventional) states Belle, BaBar 5 F. De Fazio INFN Bari Hadron 47

48 Hidden charm states (?) From N. Brambilla et al. EPJ C7 () 534 F. De Fazio INFN Bari Hadron 48

49 Hidden beauty states BaBar & CLEO (8) to be confirmed Belle, to be confirmed BaBar & CLEO (4) To be confirmed and interpreted: Y b (888) very recently discovered puzzling states: Z b (6) & Z b (65) decaying to ϒ(nS) π ± (n=,,3) and h b (mp) π ± (m=,) in ϒ(5S) decays in association with a single charged pion favoured quantum numbers I=, J P = decays to ϒ and h b occur with comparable rates no spin-flip suppression F. De Fazio INFN Bari Hadron 49

50 Exotic interpretations Molecular state: loosely bound state of a pair of mesons. The dominant binding mechanism should be pion exchange. Being weakly bound, mesons tend to decay as if they were free Tetraquark: Bound state of four quarks (diquark-antidiquark) quarks grouped into colour triplet scalar or vector clusters. Strong decays via rearrangement processes Distinctive featuresof multiquarkpicture with respectto charmonium: - prediction of many new states - possible existence of states with non-zero charge, strangeness or both Charmonium hybrids States with an excited gluonic degree of freedom -, -, - quantum numbers are not possible for cc states but are possible for hybrids would unambiguously signal an exotic state Lattice predictions for the lowest lying hybrid: M 4. GeV Threshold effects Virtual enhancement of cross section that may not indicate a resonance. F. De Fazio INFN Bari Hadron 5

51 X(387): discovery and properties Observed in 3 by four experiments in two production channels: From R. Van Kooten, D mass very close to D D * threshold: M(X(387) ) (M D M D* ) = -.3 ±.35 GeV very small width: Γ <.3 9% c.l. X J/ψ π π consistent with originating from X J/ψ ρ C= from angular distributions in X J/ψ π π (CDF) J PC = ( χ c ) or J PC = - ( η c ) search for charged partners produced no result I= F. De Fazio INFN Bari Hadron 5

52 X(387): decays to two or three pions Two and three pion modes were found with: B( X J / ψπ π π ) B( X J / ψπ π ) =. ±.4 ±.3 Isospin violation Possible explanation: phase space severely suppressed B( X J / ψπ π π ) B( X J / ψπ π ) phace space not very suppressed =. ±.4 ±.3 Suzuki, PRD 7, 43 A( X A( X J / ψρ). J / ψω) BaBar studies the πππ distribution in X J/ψ ω which seeems too favour a p-wave decay J P = - however in contrast with other properties of X F. De Fazio INFN Bari Hadron 5

53 X(387): radiative decays to J/ψ γ and ψ(s) γ May help in distinguishing the different possibilities Barnes et al, PRD 7, 546 Swanson, PLB 598, 97 if X= χ c X ψ(s) γ should have a rate larger than X J/ψ γ if X= η c or X=composite object X ψ(s) γ is suppressed with respect to X J/ψ γ BaBar gives: Γ( X (387) ψ (S) γ ) Γ( X (387) J / ψ γ ) = 3.4 ±.4 while Belle: Γ( X (387) ψ (S) γ ) Γ( X (387) J / ψ γ ) <. F. De Fazio INFN Bari Hadron 53

54 X(387): molecule vs charmonium X proximity to DD * threshold may suggest that a molecular state made of charmed mesons contributes to the structure of X c u u c Swanson, Brateen, Voloshin Mixing of the molecule (dominant component) with other states such as pure charmonium no definite isospin radiative decays In the molecular scenario X D D γ & X D D γ arise from the radiative decays of the individual vector mesons Voloshin D * D γ, and the decay D * X D D D γ γ & D * ± D is strongly suppressed with respect to ± γ X D D γ If observed, the suppression of X D D γ would support the molecular interpretation? with respect to X D D γ F. De Fazio INFN Bari Hadron 54

55 X(387) as the first radial excitation of χ c : radiative decays Standard mechanism for radiative X transitions into charmed states Pole diagrams Intermediate ψ (377) Unknown coupling c g ψdd known from exp data Intermediate D* Unknown coupling ĝ c Can be obtained from data on radiative D * decays 55

56 X(387) as the first radial excitation of χ c : radiative decays P. Colangelo, S. Nicotri, FDF PLB 65, 66 Can be evaluated as a function of the ratio of the two unknown couplings c ĝ Very small values of R R<.7 in the cc description R is very small for small values of (when the ψ pole contribution is negligible) c ĝ the suppression of R is not peculiar of the molecular scenario F. De Fazio INFN Bari Hadron 56

57 X(387) as the first radial excitation of χ c : hadronic decays ĝ Exp bound Values of ĝ typical of hadronic couplings can reproduce the small width of X(387) F. De Fazio INFN Bari Hadron 57

58 Heavy quark mass limit for heavy quarkonium states Usual classification for the states: s = spin s n LJ L = orbital angular momentum radial quantum number J = total angular momentum with: P C = ( ) = ( ) L L s L= S- wave states L= P- wave states L= D- wave states.. HQ spin simmetry YES HQ flavour symmetry NO F. De Fazio INFN Bari Hadron 58

59 Multiplets for heavy quarkonium states L= multiplet spin state spin state n= n= ( ηc (S ), ψ (S )) ( η (S), ψ (S)) c L= multiplet triplet n= spin spin spin singlet spin [( χ P), χ (P ), χ (P )), h ( )] c( c c c P L= multiplet triplet spin 3 triplet spin [( n D n D, n D ), n D ], 3 triplet spin singlet spin F. De Fazio INFN Bari Hadron 59

60 Effective Lagrangian for radiative transitions of heavy quarkonia P S F. De Fazio, PRD 79, 545 a single constant describes all the transitions among the various members of the P and S multiplets photon - reduced theoretical uncertainty - model independence D P idem for transitions among members of D and P multiplets F. De Fazio INFN Bari Hadron 6

61 P S transitions Exploting known data: total widths of χ cj states spin symmetry turns out to be experimentally well satisfied averaged result: can be used to predict: F. De Fazio INFN Bari Hadron 6

62 possibility to exploit data in the beauty sector: S P transitions define width ratio and coupling ratio even though the coupling might be different passing from beauty to charm, it is reasonable to assume that the ratios of the couplings stay stable we can predict analogous charm ratios (c) R J F. De Fazio INFN Bari Hadron 6

63 S P transitions prediction for J=: Identifing X(387) with χ c (P) and using the data: R ( c) R and are close enough to consider the assumption X(387) = χ c (P) plausible X to be contrasted with composite scenarios in which X(387) ψ(s)γ is suppressed with respect to X(387) ψ(s)γ F. De Fazio INFN Bari Hadron 63

64 Concluding remarks open charm mesons: - all the observed cs states classified as ordinary mesons - the most intriguing challenge remains to understand why D * s (37) and D s (46) have masses below the D (*) K threshold - HQ symmetry predicts analogous states in the beauty system : M(B * s)=57 MeV decaying to B s π M(B s )=576 MeV decaying to B * s π P. Colangelo et al. MPLA 9, 83 quarkonium like states: - X(387) still puzzling state - identification with χ c plausible ( according to my analysis of radiative decays) Many other states not discussed Strongly required independent confirmation of charged quarkonium-like states (at present only Belle has evidence) F. De Fazio INFN Bari Hadron 64