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### 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/
- X(3872) more decay modes, determination of JPC
- Summary and prospect

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

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-

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.

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)

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)

Mll - Mll (GeV)

Second scoop, B→ K distribution 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)

X(3872)→ J/ distribution

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(X3pJ/y)

Br(X2pJ/y)

Large isospin(at least G-parity)

violation!!

= 1.0 ± 0.5

X(3872)→ J/ distribution

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(XgJ/y)

Br(XppJ/y)

Belle 275M BB

hep-ex/0505037

=0.14 ± 0.05

X(3872)’s J distribution PC

- 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!

X(3872)’s J distribution PC (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

Let’s test 0 distribution ++ 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|

How about 1 distribution ++?

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|

Look B→ K D distribution 0D00 candidates

D*0→ D00?

Preliminary

M(D0D0p0)

Signal yield 11.3±3.6 events(5)

|DE|

|DE|

Rule out 2++ !

(Strong threshold suppression.)

Properties of X(3872); what is it? distribution

- 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!

Y(3940); what is it? distribution

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

Summary and prospect distribution

- 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

Back up slides distribution

J/ distribution y

Example:1--y’

Use BK 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|

|cos distribution qKl| 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-- !

M distribution 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-+

M( distribution gJ/y) look-back plot

M( distribution 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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