X(3872) Review

X(3872) Review

T.AushevLPHE seminar

8 February 2010 T.Aushev, LPHE seminar 2

Introduction

• Era of the new family of particles, named XYZ, started from the observation of X(3872) in the J/ψ π+π- final state by the Belle experiment

• Many new states have been found/observed/studied by Belle and other experiments, BaBar, CDF, D0, CLEO after that

• This is just a short list of them X(3872), X(3940), Y(3940), X(4160), Y(4008), Y(4260), Y(4350), Y(4660), Z(3930), Z(4415), Z(4430)+, Yb(10580), …• These particles are not fittable to any of the known or predicted states• Most probably it is new type of quark particles in addition to mesons

and baryon, although it is not proved yet

Observation of X(3872)


X(3872)'

M(+-l+l-)- M(l+l-) It did not fit to any known cc-bar statesMass of X(3872) is close to DD*

What is it: charmonium, DD*-molecule, tetraquark...?

Observed by Belle in B± → K± +-J/ 2003

Belle data: 152 M BB eventsMass = 3872.0±0.6±0.5 MeVSignificance = 10 σ

152M BB, PRL91, 262001(2003)

Most recent measurements

0803.2838 (2008)

0809.1224 (2008)

0906.5218 (2009)

0405004 (2004)

5.2σ

12.8σ (K+) + 5.9σ (KS)

(>> or = ∞) σ

8.6σ (K+) + 2.3σ (KS)


X(3872) mass measurements


Current mass is below the DD* threshold

• Recent CDF’s result is the most precise measurement of X(3872) mass• Together with CLEO’s update on the D0 mass gives hint on the X(3872) mass to be below the D0D*0 threshold

M(X(3872)), MeV/c2 Γ(X(3872)), MeV/c2

B→XK 3871.46±0.37±0.07 <2.3 @ 90% C.L. (2003)

B→XK 3871.4±0.6±0.1 <3.3 @ 90% C.L. (2008)

X→J/ψπ+π– 3871.61±0.16±0.19 1.34 (fixed from first two)

Our average 3871.50±0.19

M(D0)+M(D*0) 3871.81±0.36

Determination ofJPC

quantum numbersof the X(3872)

8 February 2010 6T.Aushev, LPHE seminar

JPC possibilities (for J ≤ 2)

0--

exotic

violates parity

0-+

(c”)

0++

DD allowed

(c0’)

0+-

exotic

DD allowed

1- -

DD allowed

((3S))

1-+

exotic

DD allowed

1++

(c1’)

1+-

(hc’)

2- -

(2)

2- +

(c2)

2++

DD allowed

c2’)

2+-

exotic

DD allowed8 February 2010 7T.Aushev, LPHE seminar

Existence of X(3872) J/established:

C(X(3872))=+1

Belle, 275M BB, hep-ex/0505037(2005)

X(3872) C-parity

B± → K± J/

€

Br(X →γJ /ψ )

Br(X →π +π −J /ψ )= 0.14 ± 0.05

no. of B’s in M(J/) bins13.6±4.4 ev. (4)

M=3872 MeV=13 MeV

J/ (2S)

€

Br(X →ψ (2S)γ)

Br(X →J /ψγ)= 3.4 ±1.4

Relatively large fraction of (2S) supports D*D molecule hypothesis and possible admixture of cc-bar component

BaBar, 465M BB, 0809.0042 (2009)


Isospin violation

B± → K± ( + - 0)J/

Further evidence for C(X(3872))=+1

If 3 come from , 2 – from large isospin violation, difficult to explain if X=cc state

5.200

virtual → + - 0

€

Br(X →π +π −π 0J /ψ )

Br(X →π +π −J /ψ )=1.0 ± 0.4 ± 0.3



0--

exoticviolates parity

0-+

(c”)

0++

DD allowed

(c0’)

0+-

exotic

DD allowed

1- -

DD allowed

(y(3S))

1-+

exotic

DD allowed

1++

(c1’)

1+-

(hc’)

2- -

(y2)

2- +

(c2)

2++

DD allowed

c2’)

2+-

exotic

DD allowed

8 February 2010 10T.Aushev, LPHE seminar

X(3872) P-parity

Looks like X(3872)→J/

P(X(3872))=+1

J/ : S wave

P wave

M( + -) from B± → K± + -J/

S wave: 2/dof=43.1/39 (CL=28%)

P wave: 2/dof=71.0/39 (CL=0.1%)

For C=+1: if P=+1 L({+-},J/)=0,2,…

P=-1 L({+-},J/)=1,3,…

M( + -) upper boundary is modulated by q2L+1 centrifugal barrier: S,P waves should dominate

55%7.7%



0--


0-+

(c”)

0++

DD allowed

(c0’)

0+-

exotic

DD allowed

1- -

DD allowed

(y(3S))

1-+

exotic

DD allowed

1++

(c1’)

1+-

(hc’)

2- -

(y2)

2- +

(c2)

2++

DD allowed

c2’)

2+-

exotic


X(3872) properties (cont')

Angular distributions in B± → K± + -J/

Belle, hep-ex/0505038

side band

expectedJPC=0++

0++ (S, D waves)

+

-l+ l-

X(J/)

-

+K B

X(J/)

1++ (S, D waves)

Opposite parity 0-+ (P wave) has been also ruled out

JPC=0++, 1++, 2++ ?

|cos|

|cos|

JPC=1++

is disfavored

is favored



0--


0-+

(c”)

0++

DD allowed

(c0’)

0+-

exotic

DD allowed

1- -

DD allowed

(y(3S))

1-+

exotic

DD allowed

1++

(c1’)

1+-

(hc’)

2- -

(y2)

2- +

(c2)

2++

DD allowed

c2’)

2+-

exotic


CDF study of quantum numbers



0--


0-+

(c”)

0++

DD allowed

(c0’)

0+-

exotic

DD allowed

1- -

DD allowed

(y(3S))

1-+

exotic

DD allowed

1++

(c1’)

1+-

(hc’)

2- -

(y2)

2- +

(c2)

2++

DD allowed

c2’)

2+-

exotic


Quantum numbers summary


JPC = 1++ is the most favored1++ charmonium Xc1’ state is unlikely assignment for X(3872):

Potential model predicts Xc1’ mass to be 3953-3990 MeV/c2

Large isospin violation coming from BR(XJ/ψω)/BR(XJ/ψρ) ~ 1

J/ decay of ’c1 should be much stronger than isospin violating decay J/. Experimentally the ratio is 0.14±0.05.

Possible interpretation: X(3872) =D0D*0 molecule

DD* threshold enhancement in BKDD*


Both saw higher mass &BR(DD*) ≈ 10x BR(π+π-J/ψ)

PRD 77, 011102 (2008)

D0D00

Mass, MeV Width, MeV B+ BR x 104

Belle 3875.4±0.7+1.2-2.0 1.25±0.31±0.30

BaBar 3875.1+0.7-0.5±0.5 3.0+1.9

-1.4±0.9 1.67±0.36±0.47

PRL 97, 162002 (2006)

Higher X mass raised some speculations about new particle X(3875)

B→X(3872) K; X(3872)D*0D0; D*0D0 (γ,π0)


MD*D = (3872.9+0.6-0.4

+0.4-0.5) MeV

BaBar: (3875.1+0.7-0.5±0.5) MeV

Γ(Belle) =(3.9+2.8-1.4

+0.2-1.1) MeV

Γ(BaBar)=(3.0+2.5-1.3

+0.5-0.3) MeV

Nsig = 50.1+14.8-11.1

Significance = 6.4 σ

X(3872) mass shape is also well fittable by Flatte function

BR(BX(3872)(D*0D0)K) = (0.73±0.17±0.13)×10-4

NEW

hep-ex:0810.0358

2++ is rather unlikely (at least one D wave near threshold)

Charged and neutral partners of X(3872)


12.8

B0→XK0s

B+→XK+

5.9

X(3872)→J/ψπ+π–

diquark-antidiquark modelsXu and Xd from B0 and B+ decays

MX= 8±3 MeV Maiani et al PRD71, 014028

cdc dXd =

cdc d

cddcc dXd =

cuc uXu =

cuc u

cuucc uXu =

MX = (+0.18±0.89±0.26 ) MeV/c2 Br(B0→XK0) / Br(B+→XK+) = 0.82 ± 0.22 ± 0.05Br(B0→XK0) Br(J/–+) = (6.65 ± 1.63 ± 1.00)x10–6

Br(B+→XK+) Br(J/–+) = (8.10 ± 0.92 ± 0.66)x10–6

Molecule model


Most advanced theory which can explain all observed decay modes and their parameteris the molecule model.

According to it X(3872) is the D*0D0 state with bounding energy which make its mass below D*0D0 threshold.

It favors ten times larger BR to double charm in comparison with charmonium decays

Different models


X(3872) likely not a charmonium stateRadial excitation of χc1 (JPC = 1++) expected at 3950 MeV/c2

ηc2 (JPC = 2-+) should have X →J/ψγ suppressedNo satisfactory cc assignment

D0D*0 molecule? Phys. Rev. D71, 074005 (2005)

Would explain proximity of the D0D*0 thresholdfavors DD* decay over J/ψππ over J/ψγ (as observed)Expect X →ψ(2S)γ to be suppressed (in contradiction with observation)

tetraquark state? Phys. Rev. D71, 014028 (2005)

Predict 2 neutral states and 2 charged statesNeutral states produced in B0 and B+ decays: Δm ≈ (7 ± 2) MeV/c2

Measurements:Δm = (+0.18±0.89±0.26) MeV/c2 in B →J/ψπ+π-

No evidence for charged partners

Mixing of D0D*0 and χc1? Something else?...

Conclusion

• X(3872) is JPC=1++ state• Normal cc-bar charmonium can not be

assigned to this particle• Most probable nature is D0D*0 molecule with

probably admixture of normal cc-bar state


X(3872) Review

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