New charm resonances

Transcription

1 New charm resonances Tadeusz Lesiak Institute of Nuclear Physics Polish Academy of Sciences Kraków, Poland Representing the Belle collaboration Results from: 8-th International Workshop on Heavy Quarks and Leptons (HQL2006) Munich 16. October 2006

2 X(3872) X(3940) Y(3940) Z(3930) Y(4260) h c (3524) HQL06 D sj Σ c (2800) Ξ cx Ω* c Λ c (2940) +

3 B-factories in ina nutshell CESR: symmetric in beam energies KEKB: 8 GeV (e - ) 3.5 GeV (e + ) PEP-II: 9 GeV(e^-) x 3.1 GeV (e^+) Belle detector RF cavity different event topologies e + source Beauty AND charm factory T.Lesiak New charm resonances 3

4 B-factories in a nutshell B-factories in a nutshell CESR (CLEO): 16 fb -1 at the Υ(4S) over 20 years CESR-c (CLEO-c): work at the ψ(3770) peak since 2003 As of July 24, 2006 KEKB (Belle)I KEKB & PEP-II Surpasses all expectations Excellent performace of both accelerators world record world record PEP-II (BaBar) Results presented below correspond to smaller data samples T.Lesiak New charm resonances 4

5 B-factories in a nutshell B-factories in a nutshell Luminosity: world record Luminosity: world record T.Lesiak New charm resonances 5

6 First observation of X(3872) First observation of X(3872) decays studied 140 fb -1 PRL 91, (2003) Events/0.01 GeV/c 2 First Belle measurement: Current world average: T.Lesiak New charm resonances 6

7 PRL 93, (2004) (Rapid) confirmation of X(3872) (Rapid) confirmation of X(3872) 11.6σ The existence of X(3872) out of question However, X parameters (M, Γ and decay pattern) does not fit with any standard, vacant charmonium state PRL 93, (2004) Possible C=+1 charmonium assignements PRD 71, (2005) (rev) events (6.9σ) m X =( ) MeV 3 1 S 0 (η c ) - mass far too high and width wrong: Γ 20MeV) 2 3 P 0, 2 3 P 2, - cannot be that narrow as Γ < 2.3MeV; 2 3 P 2 =Z(3930) 2 3 P 1 Γ(γ J/ψ) 40 (0.14 for X) 1 1 D (η 2 c2 ) B(π + π - J/ψ) should be very small T.Lesiak New charm resonances 7

8 Theoretical interpretation of X(3872) Theoretical interpretation of X(3872) M X coincides with M(D 0 )+M(D 0* ) = MeV Deuson - a DD * bound state (molecule) predicted J PC = 1 ++ (or 0 -+ ) Wave function (S wave bound state): F.E.Close, P.R.Page PLB 578, 119 (2004) N.A.Tornquist. PLB 590, 209 (2004) E.S.Swanson, PLB 588, 189 (2004); ibid 598, 197 (2004) isospin violation (a substantial admixture of I=1 ) for C=+1 the decay to π + π - J/ψ would proceed via an isovector ρ 0 -J/ψ intermediate state prediction: m(ππ) peaked at high masses (as observed by Belle) Tetraquark L.Maiani et al., PRD 71, (2005) open charm diquark-antidiquark states [c q][c q ] Hybrid cc-gluon B.A.Li, PLB 605, 306 (2005) Glueball with a cc admixture K.K.Seth, PLB 612, 1 (2005) Cusp effect D.Bugg, PLB 598, 8 (2004) try tryto to find find (other (otherthan thanπ + J/ψ) decay modes + π J/ψ) decay modes determine the the (J (J PC ) etc. PC ) angular distributions etc. Both Bothpoints pointsdiscussed below below more moreconclusive interpretation of of X(3872) T.Lesiak New charm resonances 8

9 Evidence for X(3872) γ J/ψ Evidence for X(3872) γ J/ψ hep-ex/ fb -1 the energy difference: the beam-energy constrained mass: Inside of the signal box corresponding to the decay B - K - γ J/ψ look at the M(γJ/ψ) T.Lesiak New charm resonances 9

10 Evidence for X(3872) γ J/ψ Evidence for X(3872) γ J/ψ The yield of B mesons obtained from the fit to M bc in bins of M(γ J/ψ): Theory: 40 for the χ, c1 2 3P 1 assignement 260 fb -1 hep-ex/ C(X(3872))=+1 unambiguosly established!! cc cc component in inthe thex wave wavefunction T.Lesiak New charm resonances 10

11 Evidence for X(3872) π + π π 0 J/ψ Evidence for X(3872) π + π π 0 J/ψ Signal of: hep-ex/ fb -1 fit M bc in bins of M(π + π π 0 ): yield of B mesons A virtual ω(782) (sub-threshold) decay X -> ω J/ψ? The kinematical limit for M(π + π - π 0 ) is 7.5MeV below the ω mass (Γ(ω) = 8MeV) Large (near max.) isospin violation: Large (near max.) isospin violation: events (4.3σ) for M(π + π - π 0 )> 750 MeV X(3872) = a mixture of I = 0 and I=1 state The substantial I=1 component there must be uu/dd pairs in addition to cc Both X -> γ J/ψ and X -> π + π - π 0 J/ψ support the DEUSON hypothesis Both X -> γ J/ψ and X -> π + π - π 0 J/ψ support the DEUSON hypothesis T.Lesiak New charm resonances 11

12 Spin-parity of X(3872) hep-ex/ fb -1 Studies of angular distributions of X π + π - J/ψ according to 1 ++ clearly favoured; ++ 1 cannot ++ clearly favoured; 2 ++ cannot be be ruled ruledout outcompletely J.L.Rosner, Phys. Rev. D (2004) D.V.Bugg, Phys. Rev D (2005) 1 ++ expectation tests of all relevant J P assignments Sibebands 360 pb -1 PRL 96, (2006) Study of M(π + π - ): the ρ dominance expected for C=+1; cannot distinguish between 1 ++ and 2 -+ using high statistics (N(X)=3000 ev.); (2 -+ corresponds to L=1, η c2, 1 1 D 2 ) Additional check: look for the decay T.Lesiak New charm resonances 12

13 Evidence for X(3872) D 0 D 0 π 0 Evidence for X(3872) D 0 D 0 π 0 Observation of a near threshold enhancement in 414 fb -1 hep-ex/ Accepted by PRL (2σ higher than M(X) PDG ) 1 ++ or 2 ++? 1 ++ or 2 ++? (dominant decay mode) requires at least one pair of final state particles to be in a D-wave The near threshold production of D 0 D 0 π 0 would be suppressed by an l=2 centrifugal barrier If the peak observed at 3875 MeV/c 2 is due to X(3872) J=2 possibility unlikely If the peak observed at 3875 MeV/c 2 is due to X(3872) J=2 possibility unlikely X(3872): J PC = 1 ++ strongly favoured (2 ++ and 2 -+ cannot be discarded) X(3872): J PC = 1 ++ strongly favoured (2 ++ and 2 -+ cannot be discarded) T.Lesiak New charm resonances 13

14 Observation of Y(3940) Observation of Y(3940) PRL 94, (2005) 253 fb -1 decays studied: B Kπ + π - π 0 J/ψ Observation of B J/ψ ωk, ω π + π - π 0 M(ωK) > 1.6 GeV (removal of strange resonances like K * ωk, KX = K1(1270), K1(1400), K2 * (1430) ) SIGNAL REGIONS: < M bc < GeV/c 2 E < 0.03 GeV < M(π + π - π 0 ) < GeV/c 2 Next slide T.Lesiak New charm resonances 14

15 Observation of Y(3940) Observation of Y(3940) M(ωK) > 1.6 GeV Fit the ( E,M bc ) distribution in bins of M(J/ψ ω) Threshold function S wave Breit-Wigner Differs from phase-space by 8.1σ Conventional charmonium χ cc-g hybrid cj (+) mass above DD (*) threshold F.Close,S.Godfrey, PLB 574, 210 (2003) χ b1,2 observed in ωy(1s) then B(χ cj K) <B(χ cj K) , Belle result implies:b(y J/ψω) 20% - very unusual for a conventional (cc) above the open charm threshold Should predominantly decay to D * D * not observedyet but no decay to DD (*) (+) Large B(Y J/ψ X) (+) partial width consistent with Lattice QCD predictions for ccg (-) expected mass: ( ) GeV/c 2 F.Close, PLB 432, 369 (1995) X.Liao, T.Manke, hep-lat/ , (2002) C.Banner et al., PRD56, 7039, (1997) Interpretation: a χ c1 (2 3 P 1 ) or a cc-qluon hybrid meson Interpretation: a χ c1 (2 3 P 1 ) or a cc-qluon hybrid meson T.Lesiak New charm resonances 15

16 Observation of X(3940) 357 fb -1 a new charmonium state observed by Belle in the process: hep-ex/ , subm. to PRL The signal seen in the J/ψ recoil mass M(X) > DD (*) Does DoesX(3940) decay decayinto intodd (*) (*)? T.Lesiak New charm resonances 16

17 Observation of X(3940) Observation of X(3940) Select the D (D 0, D + ) and look at the M recoil (J/ψ) after the kinematical constraint: improves resolution on M recoil (J/ψ) by a factor of 2.5 (σ(m recoil (J/ψ)) 10 MeV/c 2 ) D sidebands No evidence for for X(3940) J/ψω X(3940)=Y(3940) unlikely X(3940)=Y(3940) unlikely Possible interpretation X(3940) = η c (3S) =η C Possible interpretation X(3940) = η c (3S) =η C T.Lesiak New charm resonances 17

18 Observation of χ c2 =Z(3930) Observation of χ c2 =Z(3930) 395 fb -1 PRL 96, (2006) zero-tag two-photon processes D 0 K - π +, K - π + π 0,K - π + π - π + ; D + K - π + π + P t (DD) < 0.05 GeV/c Z(3930) matches predictions for the unobserved yet radially excited states χ c0 (2P) (χ c0 ) and χ c2 (2P) (χ c2 ): Masses in the range GeV (above DD and around DD * thresholds) χ cj -> DD(*) should be dominant (S.Godfrey, N.Isgur, PRD 32, 189, (1985) E.J.Eichten, K.Lane, C.Quigg, PRD (2004)) (among charmonia, radial excitation states known only for the ψ ( 3 3S 1 ) and η c ( 1 S 0 ) ) D sidebands T.Lesiak New charm resonances 18

19 Observation of χ c2 =Z(3930) Observation of χ c2 =Z(3930) Z=χ cj, J = 0,2? look at angular distributions (efficiency corrected) θ * - angle of a D meson relative to the beam axis in the γγ c.m. frame D sidebands J=2 hypothesis clearly favoured J=2 hypothesis clearly favoured Consistent with expectations for χ c2 All Allproperties of ofz(3930): mass, mass, angular distributions and andγ γγ (Z) are γγ (Z) Br(Z DD) are consistent with withexpectations for for χ χ c2 ( ) state c2 ( P 2 ) charmonium state T.Lesiak New charm resonances 19

20 observed in ISR events e + e - γ ISR π + π - J/ψ detection of γ ISR is not required (most of them are produced along the beam pipe) Observation of Y(4260) Observation of Y(4260) 233 fb -1 PRL 95, (2005) Signatures: - small mass recoiling against the π + π - J/ψ - low missing transverse momentum e + e - ψ(2s)γ provides a reference confirmed by CLEO and Belle BUT Measurements Measurementsof ofmass massand andwidth widthof of Y(4260) Y(4260) are aremarginally marginallyconsistent T.Lesiak New charm resonances 20

21 PRL 96, (2006) 11σ CLEO Observation of Y(4260) Observation of Y(4260) Expected from BaBar result 5.1σ First observation 3.7σ First evidence Y(4260) disfavours some exotic interpretations: χ cj ρ molecule, baryonium, glueball Y(4260) located at a dip in e + e - hadrons) Why has not been observed before? BaBar: σ(e + e - ππj/ψ) 50pb at 4.26 GeV R-0.05 << δσ(e + e - hadrons) hep-ex/ fb -1 Similar dip around 4.26 GeV/c 2 in M(D *+ D *- ) Conventional interpretation:y(4260)=ψ(4s); Conventional interpretation:y(4260)=ψ(4s); the dip in R is due to the interference with ψ(3s); the latter must have a large coupling to π + π - J/ψ Possible exotic interpretations: Possible exotic interpretations: Hybrid meson tetraquark 4.26 GeV can be tested by studying Y decays to open charm (difficult task!) T.Lesiak New charm resonances 21

22 Observation of Y(4260) Observation of Y(4260) BaBar-CONF-06/33 SLAC-PUB fb -1 Study of exclusive production of DD system through ISR radiation D 0 K - π + (π 0 ), D + K - π + π + No No evidence evidencefor for Y(4260) Y(4260) DD DD A 3.9GeV/c 2 not seen in hadronic cross-section but in qualitative agreement with coupled channels model predictions order of magnitude smaller than the value measured for the ψ(3770) against a conventional interpretation of Y BABAR-CONF-06/03, SLAC-PUB Study of e + e - (J/ψπ + π - )γ ISR and e + e - (J/ψγγ)γ ISR 230 fb -1 The ISR photon IS DETECTED (reduction of background; improvement of signal/background ratio) The signal of Y(4260) π + π - J/ψ (consistent with previous BaBar s result, corresponding to undetected γ ISR ) No sign of Y(4260) J/ψη, J/ψπ 0, χ c2 γ Two candidates of Y(4260) χ c1 γ T.Lesiak New charm resonances 22

23 Observation of h c ( 1 P 1 ) Observation of h c ( 1 P 1 ) CLEO III & CLEO-c PRL 95, (2005) ψ(2s) Observation of an enhancement in the π 0 recoil mass 1. EXCLUSIVE reconstruction of the η c (10% of η c decays): 2. INCLUSIVE η c Consistent with 1+ cos 2 θ distr., (E1 transition from a spin 1 state) Theory: 3518 MeV T.Barnes,S.Godfrey,E.Swanson, hep-ph/ st measurement of the hyperfine splitting in the P wave: Expectation: max a few MeV Test of spin dependence and spatial behaviour of the QQ force Test of spin dependence and spatial behaviour of the QQ force T.Lesiak New charm resonances 23

24 cs spectroscopy: cs spectroscopy: framework: HQS based potential models S.Godfrey, N.Isgur, PRD 32, 189 (1985) M.Di Pierro, E.Eichten PRD 64, (2001) L=1: two doublets j q =1/2: 0 +, 1 + j q =3/2: 1 +, 2 + All four states above M(D)+M(K) Γ(j q =3/2) << Γ(j q =1/2) Experimental observation of the J q =3/2 doublet: D s1 (2536) (1 + ) Argus 1989 D s2 (2573) (2 + ) Cleo 1994 j=1/2 doublet wide not seen until 2003? Theoretical expectations Theoretical expectations L = 2.. L = 1 spin-orbit j q = s q + L, J = j q + s Q j q = 3/2 j q = 1/2 tensor s-o spin-spin J P mix L = 0 j q = 1/ D s * D s Golden year of cs spectroscopy Golden year of cs spectroscopy D s2 (2573) D s1 (2536)? D*K? D K D sj (2317) D s π 0 PRL 90, (2003) CLEO CLEO D sj (2460) D s* π 0 PRD 68, (2003) confirms both, also in B decays PRL 92, (2004) T.Lesiak New charm resonances 24

25 cs spectroscopy: cs spectroscopy: PDG 2006 Masses below D (*) K thresholds Isospin-violation in the decay Very narrow Rules out spin zero Other decay modes: D sj (2460) D s γ, D sj (2460) D s π + π - PDG 2006 Are they the, eagerly and long awaited, 0 + and 1 + (cs) states or something exotic? DK molecule Chiral doublers Spin-orbit & tensor forces qq + qqqq mixing qq mixing with DK (*) T.Barnes, F.Close, H.Lipkin, PRD 68, (2003) A.Szczepaniak, PLB 567, 23 (2003) M.Nowak, M.Rho, I.Zahed, PRD 48, 4370 (1993) W.Bardeen, C.Hill PRD 49, 409 (1994) B.Cahn, J.Jackson, PRD 68, (2003) T.Browder, S.Pakvasa, A.Petrov, PLB 578, 365 (2004) D.Hwang, D-W.Kim, PLB 601, 137 (2004) T.Lesiak New charm resonances 25

26 B D sj D (*) decays B D sj D (*) decays b ccs tree-level transitions First observation PRL 91, (2003) Belle-CONF-0461 (2004) 253 fb fb -1 PRL 93, (2004) Spin-parity of D sj Spin-parity of D sj D sj sideband θ Ds π, θ D s γ angles between the D sj momentum in the B rest frame and the D s momentum in the D sj rest frame Surprise: Official name: D * s0 (2317)+ Official name: D s1 (2460) + T.Lesiak New charm resonances 26

27 A new D sj in B + D 0 D 0 K + decays? A new D sj in B + D 0 D 0 K + decays? hep-ex/ fb -1 Dalitz plot M(D 0 D 0 ) vs M(D 0 K) differs from 3-body phase space sideband efficiency 2-dim. fit to the plane ( E, M bc ) in 50 MeV bins of M(D 0 K + ) ψ(4160) reflection Phase space Threshold comp. Sum of three comp. Spin χ 2 /dof J=0 185/5 J=1 7/5 J=2 250/5 ψ(4160) reflection J P = 1 - J P = 1 - (cs) radial excitation 2 3 S 1 of D s* (2112) or chiral doubler to the 1 + state D s1 (2536) angle between the K momentum in the DK rest frame and the DK momentum in the B rest frame T.Lesiak New charm resonances 27

28 A new D sj ( DK) at 2.86 GeV/c 2 A new D sj ( DK) at 2.86 GeV/c 2 Processes studied: 240 fb -1 hep-ex/ Reflection from D s1 (2536) + D * K 2.86 GeV/c 2 region D-mass sideband New structures MC with all previously known D s Background subtracted sum of all three channels: coincides with the Belle state (from the previous slide)??? Needs more study - Needs more study - A radial radialexcitation of ofd * * s0 (2317)? s0 (2317)? T.Lesiak New charm resonances 28

29 Observation of isotriplet Σ c (2800) Observation of isotriplet Σ c (2800) Σ c0 (2800), Σ c+ (2800), Σ c ++ (2800) observed in Λ c π (Λ c p K π) PRL 94, (2005) Background subtracted spectra 281 fb -1 Λ c+ π - Λ c+ π 0 Λ c+ π + Feed-down from Λ c (2880) -> Λ c ππ Σ c0 (2800) Σ c+ (2800) Σ c ++ (2800) Sidebands of Λ c -> p K π Feed-down from Λ c (2880) -> Λ c ππ Interpretation: as the Σ c2 as the Σ c2 membersof the the J P P =3/2 =3/2 - - isospin isospintriplet T.Lesiak New charm resonances 29

30 Observation of Λ c (2940) + hep-ex/ fb -1 BaBar: a new baryon seen in the D 0 p final state (also the Λ c (2880) p D 0 is being observed for the first time) CLEO: PRL , (2001) First observation of Λ + c (2880) Λ c + π - π + Wrong sign D p D sidebands hep-ex/ fb -1 Belle: confirmation (Σ c π final state) N / 2.5 MeV /c 2 Mass and width measurements consistent: BaBar vs Belle Belle favours J P =5/2 + T.Lesiak New charm resonances 30

31 Observation of Ξ cx (2980) + and Ξ cx (3077) + Observation of Ξ cx (2980) + and Ξ cx (3077) + First observation 462 fb -1 hep-ex/ , accepted by PRL 316 fb -1 Confirmation BABAR-CONF-06/01, subm. to PRL AND evidence for Ξ cx Σ c (2455) ++ ( Λ c+ π + )K - Wrong-sign combinations M and Γ: good (Ξ cx (3077)) and marginal (Ξ cx (2980)) consistency Belle vs BaBar T.Lesiak New charm resonances 31

32 Observation of Ξ cx (3077) 0 Observation of Ξ cx (3077) 0 hep-ex/ , Accepted by PRL 462 fb -1 Observation of isospin partner(s) makes even more plausible: interpretation of ofthe Ξ cx and cx cx (2980) and Ξ cx (3077) as as excited charmed strange baryons Ξ c c Ξ cx (csu) Λ c Kπ c and s quarks are carried away by different final state particles T.Lesiak New charm resonances 32

33 Looking for doubly charmed baryons Ξ cc+ and Ξ cc ++ Looking for doubly charmed baryons Ξ cc+ and Ξ cc ++ SELEX Evidence for the Ξ + cc in the decay modes: Evidence for the Ξ ++ cc Λ c+ K - π + π + : ICHEP02 Λc + K - π + PRL 89, (2002) p D + K - PLB 628, 18 (2005) Both states NOT confirmed by FOCUS, in spite of much more abundant sample of Λ c s hep-ex/ , accepted by PRL BABAR-CONF-06/31, SLAC-PUB fb fb -1 More extensive search: Ξ cc+ Λ c+ K - π + Ξ cc+ Ξ c0 π +, Ξ c 0 Ξ - π + Ξcc ++ Λc + K - π + π + SELEX BaBar Belle: no for + BaBar & Belle: no evidence for Ξ cc + cc BaBar: no for ++ BaBar: no evidence for Ξ cc cc ++ T.Lesiak New charm resonances 33

34 Observation of Ω c *0 Observation of Ω c *0 BABAR-CONF-06/31 SLAC-PUB fb -1 the last single-charm baryon with zero orbital angular momentum, not observed so far Theoretical expectations span the range MeV/c 2 *0 Ω c *0 in c observed in agreement with withexpectations T.Lesiak New charm resonances 34

35 The renaissance of charm spectroscopy at B-factories Several new states observed (both mesons and baryons): X(3872), X(3940), Y(3940), Z (3930), Y(4260) a by-product provided important results Theoretical studies reinvigorated (231 answers to the query new charm particle in the CERN document server for the period ) Still much work to be done: Summary Experiment: more detailed and extensive studies of new particles Theory: more precise estimates & new ideas I hope that B-factories will deliver new charming discoveries soon T.Lesiak New charm resonances 35