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New states in B decays

New states in B decays. -with “hidden charm”-. 2006 Mar. BINP  to  WS Kenkichi Miyabayashi Nara Women’s University (for Belle collaboration). Outline. Introduction B-meson/charmonium reconstruction First sensation, discovery of X(3872)→ J/   +  - Second scoop, Y(3940)→ J/  

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New states in B decays

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  1. New states in B decays -with “hidden charm”- 2006 Mar. BINP  to  WS Kenkichi Miyabayashi Nara Women’s University (for Belle collaboration)

  2. Outline • Introduction • B-meson/charmonium reconstruction • First sensation, discovery of X(3872)→ J/+- • Second scoop, Y(3940)→ J/ • X(3872) more decay modes, determination of JPC • Summary and prospect

  3. Introduction B decays as a source of “hidden charm”(charm anti-charm ) Cabbibo-favored diagram (Vcb and Vcs)→ commonly produced! “hidden charm” B Spectroscopy ↓ Mass, Width? New states? Kaon

  4. Reconstruction of charmonium J/y→di-lepton decays are reconstructed as a prominent peak. In di-electron channel, include photons detected near electron/positron tracks to recover Brems. as much as possible in order to reduce radiative tail. m+m- e+e-

  5. Reconstruction of charmonium(cont.) cc1, cc2 → J/y g y(2S) → J/yp+p- cc1 cc2 Higher charmonium states(y(2S), cc) are reconstructed using mass difference.

  6. Reconstruction of B decays Example; B0→ J/y KS Using Υ(4S)→ BB kinematics Mbc = { (ECM/2)2 - (S Pi)2}1/2 Signal peaks at B mass (5.28GeV) DE = S Ei - ECM/2 Signal peaks at 0. DE(GeV) Mbc(GeV)

  7. First sensation, peak at 3872 MeV in “look-back” distribution • K p+p- J/ is combined to form a B candidate. • Using the B candidate’s daughter particles, the mass difference distribution is checked. • Narrow unknown peak is there, above DD threshold! (2S) “landmark” Belle, 152M BB, PRL91,261801(2003) Mll - Mll (GeV)

  8. Second scoop, B→ KJ/ enhancement; Y(3940) Y(3940) M=3943±11 MeV =87±22 MeV (stat. error only) Mbc for each MJ/ bin B signal yield as a func. of MJ/ Belle, 275M BB, PRL94,182002(2005)

  9. X(3872)→ J/ A virtual ? Signal yield as a func. of M Mbc in each MJ/ bin Belle 275M BB, hep-ex/0505037 12.4±4.2 events Br(X3pJ/y) Br(X2pJ/y) Large isospin(at least G-parity) violation!! = 1.0 ± 0.5

  10. X(3872)→ J/ 13.6±4.4 events B→ K  J/ candidates (4 signif.) c1→  J/ “landmark” B signal yield as a func. of MJ/ Mbc in each MJ/ bin MJ/ (MeV) Br(XgJ/y) Br(XppJ/y) Belle 275M BB hep-ex/0505037 =0.14 ± 0.05

  11. X(3872)’s JPC • C=+1 is established! • X(3872)→ J/ is only allowed for C=+1. • X(3872)→ J/supports this picture. • X(3872)→ J/, M looks like a  Shape of M distribution favors S-wave btw J/ and (different centrifugal barrier for P, D-wave)→ P=+1!

  12. X(3872)’s JPC (cont.) Angular distribution of X(3872)’s decay products → determination of spin. J/y Jz=0 J=0 X3872 J=0 z K pp Rosner, PRD70,094023, Bugg, PRD71,016006, Suzuki&Pakvasa, PLB579,67

  13. Let’s test 0++ hypothesis. In the limit where X(3872), pp, & J/y rest frames coincide: dN/dcosqlp sin2qlp qlp c2/dof = 34/9 Rule out 0++! |cosqlp|

  14. How about 1++? dN/dcosqdcosc sin2ql sin2c c2/dof = 11/9 ql K |cosql| c c2/dof = 5/9 Compute angles in X(3872) rest frame. 1++ looks OK! |cosc|

  15. Look B→ K D0D00 candidates D*0→ D00? Preliminary M(D0D0p0) Signal yield 11.3±3.6 events(5) |DE| |DE| Rule out 2++ ! (Strong threshold suppression.)

  16. Properties of X(3872); what is it? • JPC=1++. • That means c1’ if it is usual charmonium, but • Mass is 100MeV off from the prediction. • Small (J/) /(J/) disfavors this hypothesis. • → not likely to be c1’! • DD* bound state? • JPC=1++ is favored. • Isospin violation is predicted • (J/) < (J/) is also predicted. • → looks no contradiction!

  17. Y(3940); what is it? No obvious charmonium assignment. Is it ccg hybrid? • Predicted by QCD, • Decays to DD and DD* are suppressed (“open-charm” thresh = mD + m D** = 4.3 GeV) • large hadron+J/ widths are predicted • masses expected to be 4.3 ~ 4.4 GeV (higher than what we see) → Need more study

  18. Summary and prospect • X(3872) • JPC=1++ established. • Properties are consistent with expectations of DD* bound state. • Y(3940) • No obvious charmonium assignment. • Might be ccg hybrid. • Need more study to have conclusive picture. • The studies shown today are based on 275M BB, while 447M BB have been accumulated by 2005 summer. • → following would appear soon, • More precise measurements of their properties • Attempts to hunt something new

  19. Back up slides

  20. J/y Example:1-- y’ Use BK y’ K z y’is 1-- dN/dcosq  sin2qKm pp y’: c2/dof = 8.9/9 qKm K compute angles in J/y restframe D.V. Bugg hep-ph/0410168v2 |cosqKm|

  21. |cosqKl| for X(3872) events fit with 1--MC + bkgd c2/dof = 45/9 see 8 evts/bin expect 1&3evts/bin background scaled from sidebands X(3872) is not 1-- !

  22. M  pJ/y· (eJ/yxer) 0-+ c2/dof=18/9 0-+ : sin2q sin2y q |cosq| c2/dof=34/9 y |cosy| safe to rule out 0-+

  23. M(gJ/y) look-back plot

  24. M(pp) can distinguish r-J/y S- & P-waves P-wave: c2/dof = 71/39 S-wave: c2/dof = 43/39 (CL=0.1%) (CL= 28%) q* roll-off q*3 roll-off Shape of M(pp) distribution near the kinematic limit favors S-wave

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