New states in B decays

1
New states in B decays
-with hidden charm-

• 2006 Mar. BINP ? to ? WS
• Kenkichi Miyabayashi
• Nara Womens 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.
mm-
ee-
5
Reconstruction of charmonium(cont.)
cc1, cc2 ? J/y g
y(2S) ? J/y pp-
cc1
cc2
Higher charmonium states(y(2S), cc) are
reconstructed using mass difference.
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Reconstruction of B decays
Example B0? J/y KS
Using ?(4S)? BB kinematics Mbc (ECM/2)2 - (S
Pi)21/2 Signal peaks at B mass (5.28GeV) DE
S Ei - ECM/2 Signal peaks at 0.
DE(GeV)
Mbc(GeV)
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First sensation, peak at 3872 MeV in look-back
distribution

• K pp- J/? is combined to form a B candidate.
• Using the B candidates 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) M394311 MeV ?8722 MeV (stat. error
only)
Mbc for each MJ/?? bin
B signal yield as a func. of MJ/??
Belle, 275M BB, PRL94,182002(2005)
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X(3872)? J/? ?
A virtual ??
Signal yield as a func. of M???
Mbc in each MJ/?? bin
Belle 275M BB, hep-ex/0505037
12.44.2 events
Br(X?3pJ/y) Br(X?2pJ/y)
Large isospin(at least G-parity) violation!!
1.0 0.5
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X(3872)? J/? ?
B? K ? J/? candidates
13.64.4 events
(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
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X(3872)s JPC

• C1 is established!
• X(3872)? J/? ? is only allowed for C1.
• 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)? P1!
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X(3872)s JPC (cont.)
Angular distribution of X(3872)s decay products
? determination of spin.
J/y
Jz0
J0
X3872
J0
z
K
pp
Rosner, PRD70,094023, Bugg, PRD71,016006,
SuzukiPakvasa, PLB579,67
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Lets 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
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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
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Look B? K D0D0?0 candidates
D0? D0?0?
Preliminary
M(D0D0p0)
Signal yield 11.33.6 events(5?)
DE
DE
Rule out 2 ! (Strong threshold suppression.)
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Properties of X(3872) what is it?

• JPC1.
• 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?
• JPC1 is favored.
• Isospin violation is predicted
• ?(J/? ?) lt ?(J/? ??) is also predicted.
• ? looks no contradiction!

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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 hadronJ/? widths are predicted
• masses expected to be 4.3 4.4 GeV (higher than
  what we see)
• ? Need more study

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Summary and prospect

• X(3872)
• JPC1 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

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Back up slides
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Example 1--
J/y
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
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cosqKl for X(3872) events
fit with 1--MC bkgd
c2/dof 45/9
see 8 evts/bin
expect 13evts/bin
background scaled from sidebands
X(3872) is not 1-- !
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0-
M ? pJ/y (eJ/y x er)
c2/dof18/9
0- sin2q sin2y
q
cosq
c2/dof34/9
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
(CL0.1)
(CL 28)
q roll-off
q3 roll-off
Shape of M(pp) distribution near the kinematic
limit favors S-wave