# Presentation: 273333

## BaBar Results on the Ds System

- R. Cahn
- LBNL
- Hadron 2003
- Aschaffenburg, Sept. 4, 2003

## Event Selection

- Ds → K+ K- +

- K id from DIRC, dE/dx

- 0 from primary
- or secondary vertex

- Χ2 prob > 1%

- E >100 MeV

- P(K+ K- +0)>2.5 GeV

- K+

-  K-

- +

- 0

****

****

- e+

- e-

## Suppress background

- Require K*K or 

- Cut on decay angle:      |cos θ|>0.5

- Sidebands

- Ds+

- D+

- Ds+

## Add 0 to Ds:

- DsJ*(2317)

- D0K threshold

- D*+s(2112)

- m(K+K-+0) GeV

## Not there for fake 0

- m() GeV

- m(Ds) GeV

## Fit to mass, width:

- M = 2316.8 ± 0.4 MeV

-  = 8.6 ± 0.4 MeV

- (Statistical errors only)

**** consistent with resolution.

- Ds(2112)

- DsJ*(2317)

-              m(Ds )    (GeV)

*p** > 3.5 GeV

## Angular distribution featureless

- DsJ(2317) spinless or unaligned

- efficiency

- uncorrected

- corrected

- cos θ

- cos θ

- cos θ

## Consistent results in second mode:Ds→K+K-+0

- M = 2317.6 ± 1.3 MeV

-  = 8.8 ± 1.1 MeV

- (Statistical errors only)

- DsJ*+(2317)

- Ds*+(2112)

-        m(Ds )    (GeV)

## State Confirmed byCLEO and Belle

## Ds(2317):Immediate conclusions

- Ds 0  has charm, strangeness, isospin.
- If initial state is c-sbar,                                                   strong isospin-violating decay.
- Explains narrowness.
- Must be natural spin-parity.

## Deja Vu

- Heavy-quark light-quark = the hydrogen atom!
- DeRujula, Georgi, Glashow 1975
- Heavy quark’s spin doesn’t matter much
- Add light quark’s spin ***s***,  orbital*** l ***angular momentum: ***j***= ***l*** + ***s******light***
***j *** nearly conserved
***J*** =*** j*** + ***s******heavy****** ***really conserved

## Interactions split energy levelsof p-wave states

## New State 170 MeV Below Potential Model Predictions

- Predictions of potential models

- New state

- Ds

- Ds*

- Ds1

- Ds2

- 0_

- 1_

## Looking in other channelsBaBar PRL90,242001(2003)

- Ds  : only the Ds(2112)

- Ds :  nothing

- Ds 0 :  some sort of peak

- Events with a   Ds  = Ds*

- m (GeV)

- 2.2

- 2.4

- 2.0

- 2.6

## Is peak a real effect?

- All selected
- Ds  events

- Ds sidebands

- Potential peak

***BaBar Preliminary***

- m(Ds+ 0 ) (GeV)

## Real effect or overlapping bands?

- m(Ds*+ )    (GeV)

- m(Ds+) (GeV)

- m(Ds*+ )=m(Ds+)-m(Ds+)

- m(Ds+)=m(Ds+)-m(Ds+)

- Ds* + random 0

- DsJ*(2317) + random 

***BaBar Preliminary***

- Ds 0 events

## Background small, peaks higher than signal

- Ds* band

- Ds* sideband

- DsJ*(2317)  + 

***BaBar Preliminary***

- m(Ds*+ 0)  (GeV)

## Sideband-Subtracted Spectrum

- m=346.2 ± 0.9 MeV

- (statistical error only)

***BaBar Preliminary***

- m(Ds*+ 0)  (GeV)

## What is decay path for DsJ(2458)?

- If DsJ(2458) → DsJ*(2317)  then
- DsJ*(2317) narrow, Ds*(2112) wide
-  If DsJ(2458) → DsJ*(2112)  then
- DsJ*(2317) wide, Ds*(2112) narrow
- Need to fit full distributions to disentangle

## Channel Likelihood Fit

- Variant on maximum likelihood.
- Model the competing decay channels, bkgd
- Ds(2458)→Ds(2317) 
- Ds(2458)→Ds*(2112) 0
- Ds(2317) + ()
- Ds*(2112) + (0)
- For each event, assign likelihoods to hypotheses.
- A posteriori, assign weights to events.
- Convenient way to plot results.

## Separate Contributionsto Ds0 Events

- Ds0 

- Ds*0
- weighted

- Ds(2317) 
- weighted

- Ds0
- projection

- Ds 
- projection

***BaBar Preliminary***

- Lots !

- Little

**m(D****s*********+**** ********0 ********)  (GeV)**

**m(D****s****+**** ********0 ****)  (GeV)**

**m(D****s*****(2112)********0 ****) (GeV)**

**m(D****s**** **** ********)  (GeV)**

**m(D****s***** (2317) **** ********)  (GeV)**

## Ds  structure is narrow

- MC assuming
- Ds(2458)→Ds(2317) 

- MC assuming
- Ds(2458)→Ds*(2112) 

***BaBar Preliminary***

-     m(Ds+ )  (GeV)

## Ds  structure is broad

- MC assuming
- Ds(2458)→Ds*(2112) 

- MC assuming
- Ds(2458)→Ds(2317) 

***BaBar Preliminary***

- Conclude: decay is
- Ds(2458)→Ds*(2112) 

- m(Ds+ 0)  (GeV)

## Spin of Ds(2458)

- 

- Ds

- Ds*

- θ

- 0 - disfavored, 1 - ok, 2 + ok;
-  1 +, 2 -,... can’t say anything

- cos θ

## BaBar’s Quantitative Results for Ds(2458)

- DsJ+(2458)→Ds*+(2112)0:         174 ± 22 evts
- DsJ+(2458)→DsJ*+(2317):             0 ± 19 evts
- m=2458.0 ± 1.0 ± 1.0 MeV;   = 8.5 ± 1.0 MeV
*Belle 2456.5 ± 1.3 ± 1.1 MeV      CLEO 2463.6 ± 1.7 ± 1.0 MeV ** *
- m=2317.3 ± 0.4 ± 0.8 MeV;
*       **Belle 2317.2** **± 1.3 ± 1.1 MeV      CLEO 2318.5 ± 1.2 ± 1.0 MeV** *

***BaBar Preliminary***

## BaBar rate ratios

- =

***BaBar Preliminary***

*Belle 0.26 ± 0.08;        CLEO 0.44 ± 0.11*

## Consistent Picture of 2317 and 2458

- Isospin conserving decays to DK and D*K unavailable

- Isospin violation:
- View as  mixing.

## Belle: Exclusive B Decays

- B→DDsJ*(2317),
- DsJ*(2317) →Ds 0

- B→DDsJ(2458),
- DsJ(2458) →Ds*(2112) 0

- B→DDsJ(2458),
- DsJ(2458) →Ds 

## Belle: B→DDsJ(2458), DsJ(2458) →Ds 

- Spin-1

- Spin-2

- Spin-0 forbidden

- Belle
- – hep-ex/0308019

## Current Picture Challenges Experiment and Theory

*Other radiative decays?*

-  *decays?*

*Are masses of broad states right?*

*Can any potential model describe the spectra?*

*Equal 0**-**1**-** and 0**+**1**+** splittings*
*Coincidental?*