Observation in BaBar of a narrow resonance in the D+

s 0 system at 2317 MeV

Roger BarlowManchester University

For the BABAR Collaboration

Roger Barlow: FPCP Paris 2003 Slide 2

Data

• 1999-2002• 91 fb-1

• On and off (4S)• Search for D+

s and : Require 3 tracks 2 photons over 100 MeV– FW moments H2/H0 <0.9

Roger Barlow: FPCP Paris 2003 Slide 3

selection

• Both E > 100 MeV

• fit probability >1%

• Neither shared with another candidate

Peak and sidebands

Roger Barlow: FPCP Paris 2003 Slide 4

selection(1

)

• Kaon id from DIRC & dE/dx via Neural network

• Vertex fit P>0.1%

sD

KKDs

Peaks from• D+(1869)

• D+s(1970)

• D*+(2010)D0+

D+

D+s

D*+

Roger Barlow: FPCP Paris 2003 Slide 5

• M(K+K-)<1.84 GeV• M(K+K-)M() or

M(K)M(K*) or K* decays with |

Cos h|>0.5• p*(K+K- + 0)>2.5

GeV

Signal and sidebands shown

80K D+s in signal region

sDselection(2

)

D+s

D+

Roger Barlow: FPCP Paris 2003 Slide 6

The signal

Large (unexpected) peak in D+

smass at 2.32 GeV

Named as D*sJ(2317)+

Small spike from D*+s just on

kinematic limit

?D+sJ(2317)

Roger Barlow: FPCP Paris 2003 Slide 7

Check# 1 Monte Carlo

Reproduces D+sbut no D*sJ(2317)+

D+

D+s

Roger Barlow: FPCP Paris 2003 Slide 8

Check# 2 Sidebands

0sidebands

No signal present

M(K+K- + 0) from sidebands in yellowD+

ssidebands

Roger Barlow: FPCP Paris 2003 Slide 9

Check# 3 Different D+

s

decaysSeen in both D+

s

and D+s K*K

Also in D+sK+K-

at the same mass

D+sJ(2317)

Roger Barlow: FPCP Paris 2003 Slide 10

Check# 4 Reflections

• Particle ID? – Take events: reassign K as . – No sign of D+ or D0 or D*

• D*+s(2112) D+

s+ extra

No: Antiselecting M(D+s 2112)

enhances peak at 2317

Roger Barlow: FPCP Paris 2003 Slide 11

Properties#1 p* dependence

Signal enhanced at high p*

As expected from e+ecc production

(Momentum of

D*+sJ(2317) in CMS)

Roger Barlow: FPCP Paris 2003 Slide 12

Properties#2 Mass

• Take p*>3.5 GeV• Gaussian +

polynomial• Peak at

2316.80.4 MeV• 126753 signal

events• Systematic

uncertainty below 3 MeV

Roger Barlow: FPCP Paris 2003 Slide 13

Properties#3 Width

• Single Gaussian • Standard Deviation

8.60.4 MeV• MC (revised) predicts

7.50.3 MeV• Measurement of

D+sK+K-+0 gives 6.7

0.1 MeV • Observed width

compatible with our mass resolution

10 MeV

Roger Barlow: FPCP Paris 2003 Slide 14

Properties#4 Angular Distribution

• Plot helicity angle of in D*+

sJ(2317) frame

• Correct for efficiency

Consistent with being flat:Suggests J=0. (Or unpolarised

and J=anything)

Roger Barlow: FPCP Paris 2003 Slide 15

Properties#5 Other modes

Not seen in– D+

s

– D*+s (2112)

– D+s

– D+s

– D+s

D*+s(2112)

Roger Barlow: FPCP Paris 2003 Slide 16

Comment onD+

s

Care needed!Peaks at Ds0 (2317) and

Ds(2112) combine to give reflection with M(Ds0 )2460

2112

2317

M(Ds)

M(Ds0)

• No peak at 2317• But new peak

appears at 2460• Enhanced when

M(D+s)2112=M(D

*+s)

Roger Barlow: FPCP Paris 2003 Slide 17

InterpretationA cs state: D*s

Below threshold for DK, D*K Ds decay violates isospin, hence narrowParity conservation JP=0+, 1-,2+…

0+ plausible from Cos distribution L=1 radial excitation. But other L=1 states (1+ and 2+) are at 2536, 2573Qq potential models predict 0+ at M=2480

2317 << 2480 Either re-think theory or include hybrid

Roger Barlow: FPCP Paris 2003 Slide 18

Confirmation

Confirmed by CLEO and BELLEMass and width and decay modes

consistent.

CLEO also claim D*+s(2463) in

D*+s(2112) 0

Roger Barlow: FPCP Paris 2003 Slide 19

The Peak in D*+

s

BaBar• There is a peak at 2.46 GeV• Some of it is a reflection of

the 2317. How much is still under study. Great care is required.

• Even if this peak is a resonance, it cannot account for all the 2317 signal

CLEO• There is a peak at 2.463

GeV• Some, but not all of it,

is a reflection of the 2317

• Some of the 2317 is a reflection of the 2463

If it exists, careful extraction of yields, masses and widths is needed. Work in progress…

Roger Barlow: FPCP Paris 2003 Slide 20

Conclusions

• BaBar has observed an unexpected narrow resonance: the D*+

sJ(2317)

• Decays to D+s

• Spin-parity compatible with 0+

• Confirmed by CLEO and BELLE