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Exploration of New States in B Decays with Hidden Charm

This study explores B decays as a source of "hidden charm," focusing on reconstructing B-mesons and charmonium states like X(3872) and Y(3940). The discoveries, decay modes, and properties of these states are examined, shedding light on their nature and potential implications. The research involves reconstructing di-lepton decays of charmonium and investigating mass differences to identify new states. The results suggest the presence of unique states like X(3872) and Y(3940) with intriguing characteristics, prompting further analysis and future studies. Key points include angular distributions, decay products, and theoretical predictions, offering valuable insights into the mysterious realm of hidden charm physics.

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Exploration of New States in B Decays with Hidden Charm

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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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