New states in B decays

2006 Mar. BINP to WSKenkichi Miyabayashi

Nara Women’s University(for Belle collaboration)

-with “hidden charm”-

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

IntroductionB decays as a source of “hidden charm”(charm anti-charm )

B“hidden charm”

Kaon

Cabbibo-favored diagram (Vcb and Vcs)→ commonly produced!

Spectroscopy↓

Mass, Width?New states?

Reconstruction of charmonium

+-

e+e-

J/→di-lepton decaysare 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.

Reconstruction of charmonium(cont.)

c1, c2 → J/(2S)→ J/ +-

c1

c2

Higher charmonium states((2S), c) are reconstructed using mass difference.

Reconstruction of B decays

Using Υ(4S)→ BB kinematics

Mbc = { (ECM/2)2 - ( Pi)2}1/2

Signal peaks at B mass (5.28GeV)

E = Ei - ECM/2Signal peaks at 0.

Example; B0→ J/ KS

E(GeV)

Mbc(GeV)

First sensation, peak at 3872 MeV in “look-back” distributi

on

Mll - Mll (GeV)

•K +- 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)

Second scoop, B→ KJ/ enhancement; Y(3940)

Mbc for each MJ/ bin B signal yield as a func. of MJ/

Y(3940)M=3943±11 MeV=87±22 MeV(stat. error only)

Belle, 275M BB, PRL94,182002(2005)

X(3872)→ J/

Mbc in each MJ/ bin

Signal yield as a func. of M

12.4±4.2 events

A virtual ?

Br(X3J/)Br(X2J/)

= 1.0 ± 0.5Large isospin(at least G-parity)violation!!

Belle 275M BB,hep-ex/0505037

X(3872)→ J/ B→ K J/candidates

c1→ J/“landmark”

Mbc in each MJ/ binMJ/ (MeV)

B signal yield as a func. of MJ/

13.6±4.4 events

(4 signif.)

Br(XJ/)

Br(XJ/)=0.14 ± 0.05 Belle 275M BB

hep-ex/0505037

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!

X(3872)’s JPC (cont.)Angular distribution of X(3872)’s decay products → determination of spin.

Rosner, PRD70,094023, Bugg, PRD71,016006,

Suzuki&Pakvasa, PLB579,67

K

J/J=0

J=0X3872

Jz=0

z

l

In the limit where X(3872), , & J/rest frames coincide:

d/dcosl sin2l

|cosl|

2/dof = 34/9

Let’s test 0++ hypothesis.

Rule out 0++!

l

dN/dcosdcos sin2l sin2

K|cosl|

2/dof = 11/9

|cos|

2/dof = 5/9

1++ looks OK!

Compute angles in X(3872) rest frame.

How about 1++?

Look B→ K D0D00 candidates

|E| |E|

Preliminary

D*0→ D00?

M(D0D00)

Signal yield 11.3±3.6 events(5) Rule out 2++ !

(Strong threshold suppression.)

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 hy

pothesis. → 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?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 prospectX(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

Example: 1--

dN/dcos sin2K

K

compute angles inJ/ restframe

D.V. Bugg hep-ph/0410168v2

Use BK ’

’ is 1--

K

J/’

z

’2/dof = 8.9/9

|cosK|

|cosKl| for X(3872) events

X(3872) is not 1-- !

fit with1--MC + bkgd

expect 1&3evts/bin

see 8 evts/bin

2/dof = 45/9

backgroundscaled fromsidebands

0-+

0-+ : sin2 sin2

safe to rule out 0-+

|cos|

|cos|

2/dof=34/9

2/dof=18/9

M pJ/· (J/ x

M(J/) look-back plot

M() can distinguish -J/ S- & P-waves

S-wave: 2/dof = 43/39 P-wave: 2/dof = 71/39

q*roll-off

q*3

roll-off

(CL=0.1%)(CL= 28%)

Shape of M() distribution nearthe kinematic limit favors S-wave