discovery of d sj (2463) + (part ii) jc wang cleo meeting 06/20/03 authors dave cinabro selina li...

Discovery of DsJ(2463)+

(part II)

JC WangCLEO Meeting

06/20/03

Authors

Dave CinabroSelina Li

Sheldon StoneJon Urheim

Jianchun Wang

Committees

Roy Briere (chair)

David MillerDavid BessonJohn Yelton

900

06/20/03 Jianchun (JC) Wang 2

BaBar Discovery

BaBar observed a narrow Ds0 resonance at 2.317 GeV, possibly a JP = 0+ state (hep-ex/0304021). They reconstructed 1267 53 events, with P(Ds0) > 3.5 GeV using 91 fb data.

M( Ds0 )

BaBar

M( Ds0 )

They also noticed a peak at 2.46 GeV. “This mass corresponds to the overlap region of the Ds

* Ds and Ds(2317)Ds0 signal bands that, because of the small width of both mesons, produces a narrow peak in the Ds mass distribution that survives a Ds

* selection” .

Reflections?


Possible Explanations Four Ds**(L=1) states: JP = 0+, 1+, 1+ & 2+. One 1+ & 2+ seen. Others are

predicted to be above DK threshold and have large ~200 MeV widths. This state is way below DK threshold.

The Dso decays from an initial cs state violates iso-spin conservation. Hence the decay is suppressed and the decay width is narrow. So the low mass ensures the narrow width.

Bardeen, Eichten and Hill (hep-ph/0305049) couple chiral perturbation theory with a quark model representing HQET. They infer that Ds*(2317) is the 0+ state. The theory also predict the existence of the 1+ partner of this state, and has mass splitting identical to that of Ds*(2112) and Ds ( M(1+) M(0+) = M(1) M(0) ). The branching fraction of other possible modes are also calculated.

Many other theoretical explanations appeared (see references in the paper): For example, it could be a D / DK molecule (see Adam Szczepaniak’s talk).


The Ds0 Final State

Fit resultN = 165 20

= 8.0 1.3 MeVM> = 349.4 1.0 MeV

Brief selection criteria

All CLEO II and II.V data P(Ds0) > 3.5 GeV

Ds, KK

|cos| > 0.3 Invariant mass cuts ~ 2.5 Photons in good barrel.

Ds*


The Ds*0 Final State

Fit resultN = 55.3 10.1

= 6.1 1.0 MeVM> = 349.8 1.3 MeV

Brief selection criteria

All CLEO II and II.V data P(Ds*0) > 3.5 GeV

Ds, KK

|cos| > 0.3 Invariant mass cuts ~ 2.5 Photons in good barrel.

Ds* sideband

Ds* signal

!?


Ds0 Scatter Plot


Ds0 Monte Carlo SimulationsDs(2463)Ds*0

signal MC

= 6.5 0.2 MeV

Ds(2317) does “feed up” to the Ds(2463) by attaching to a random .

However, the probability is low (~17% with floating width, ~9% with width fixed to that of data), and the width is 14.9 MeV rather than 6.5.

Ds(2317)Ds0 signal + random

= 14.9 0.6 MeVMuch wider than 6.1±1.0 MeV


Feed Down: Ds(2463) Candidates Reconstructed as Ds(2317)

All events in the Ds*0 mass

spectrum are used to show the Ds(2463) signal “feed down” to

the Ds(2317) spectrum.


Reconstruct Ds0 from MC

Ds(2317)Ds0 signal MC

= 6.5 0.3 MeV

Ds(2463)Ds*0 signal with photon skipped

= 14.9 0.4 MeV

Ds(2463) also “feed down” to Ds(2317) with very large probability (~0.84 with

width fixed to that of data). The width is 14.9 MeV rather than 6.5 MeV.


Yield Unfolding

R0 reconstructed DsJ(2317)Ds0 excluding feed-down.

R1 reconstructed DsJ(2463)Ds*0 excluding feed-up.

N0 = R0 + feed-down = R0 + R1 f1

N1 = R1 + feed-up = R1 + R0 f0

R0 = 154.8 23.4

R1 = 41.2 11.5

f feed-up probability relative to true Ds0 yield. (0.091±0.007±0.015)

f feed-down probability relative to true Ds*0 yield. (0.84±0.04±0.10)

N0 number of events extracted from fit to Ds0 mass spectrum. (189.518.9)

N1 number of events extracted from fit to Ds*0 mass spectrum. (55.310.1)


Double Gaussian Fit Fit the spectrum with double

Gaussian functions for the peak.

Narrow Width

Broad width

Single Gaussian

Data 6.01.2 16.56.3 8.01.3

MC 6.00.3 14.90.4

Eve

nts/

5MeV

/c2

Determine the mass without the effect of reflection.

<M> = (350.0 ± 1.2 ± 1.0) MeV

M = 2318.5 ± 1.7 MeV

The amount of reflection in the fit is consistent with calculation.


Sideband Subtraction

Sideband subtraction

Unfoldingmethod

Number of events 45.7 ± 11.6 41.2 ± 11.1

M(Ds*0) M(Ds*) in MeV

351.2 ± 1.7 349.8 ± 1.3

Signal width () in MeV

5.5 ± 1.1 6.1 ± 1.0

<M> = (351.2 ± 1.7 ± 1.0) MeV

M = 2463.6 ± 2.1 MeV


Significance of Ds(2463) Signal

Fit the spectrum with:

Single Gaussian for true signal.

Sideband spectrum for feedup and part of combinatorial bkg.

2nd order polynomial for bkg.

We can get the significance of signal: sqrt( 32.4) = 5.7

Number of true signals: 42.4 9.7


Production Rate of DsJ Mesons

Yield(P>3.5)

Efficiency(%)

ProductionRatio

Ds(2463)Ds(Ds)

Ds(2317)Ds

DsDs

Ds(1969)

The final DsJ candidates are required to be P>3.5 GeV.

Ds is reconstructed in Ds, KKmode. The efficiency is

the value in the table times BR of the decay chain listed.


Kinematically Allowed DsJ Decay ChannelsDecay Channel Spin parity Possible JP of DsJ

Ds(2317)

Ds0

Ds , OZI suppressed

Ds

Ds0

Ds

Ds(2463)

Ds0

Ds OZI

suppressed

Ds

Ds 0

Ds OZI suppressed

Ds

Ds(2317) 0

Ds(2317)


Search For Ds and DsDecay odes

N(2317) =

N(2463) =

Ds(2317) Ds(2463)

N(2317) =

N(2463) =

Ds(2317)

Ds(2463)


Search For Dsand Ds(2317) Decay Modes

Ds(2317)

Ds(2463)

N(2317) =

N(2463) =

Ds(2463)

N(2463) =

Ds(2463)Ds(2317)(Ds0)

has reflection from mode

Ds(2463) Ds*0(Ds)0


The 90% C.L. Upper Limits

Decay Channel Yield Efficiency (%)

Ratio (90% C.L.)

Prediction

Ds(2317)

Ds0 0.6

Ds 2.3 0.8

Ds 13 0.1

Ds0 3.9 0.3

Ds 5.2 0.5

Ds(2463)

Ds0 12 0.2

Ds 7.7 0.3

Ds 5.4 1.5

Ds 17 0.4

Ds(2317) 3.0 0.1


Nature of Ds(2317) and Ds(2463)

Ds(2317) and Ds(2463) fit in well the quark model as 0+ and 1+ cs mesons except for maybe the mass.

Chiral perturbation + HQET lower mass.

Ds(2317) is below DK threshold. Ds(2463) is below D*K threshold and above DK, which is suppressed (1+).

The <M> measurements also back up chiral perturbation + HQET model.

It is nature to think that they are 0+ and 1+ Ds states.

Ds(2463)Ds0

<M> = (351.2 ± 1.7 ± 1.0) MeVM = 2463.6 ± 2.1 MeV

Width < 7.0 MeV at 90% C.L.

Ds(2317) Ds0

<M> = (350.0 ± 1.2 ± 1.0) MeVM = 2318.5 ± 1.7 MeV

Width < 7.0 MeV at 90% C.L.


Search For Ds+and Ds

+Modes

Ds(2317)Ds(2463)Ds(2317) Ds(2463)

Resonant Ds+or Ds

+ surely will be interesting for other models (e.g. D atom)


Summary Confirmed DsJ

(2317): Mass = 2318.5 1.7 MeV/c2, <M> = (350.0 ± 1.2 ± 1.0) MeV Very narrow intrinsic width. Decaying to Ds 0 , as expected for JP = 0+.

Observed a new state DsJ(2463): Mass = 2463.6 2.1 MeV, <M> = (351.6 1.2 1.0) MeV. Very narrow intrinsic width. Decaying to Ds*0 , as expected for JP = 1+.

The results are compatible with model (Chiral perturbation+HQET) predictions of 0+ and 1+ Ds states, and mass splitting.

Obtained upper limits of branching fraction for the other decay modes relative to the observed states.

Submitted to PRD (hep-ex/0305100).

discovery of d sj (2463) + (part ii) jc wang cleo meeting 06/20/03 authors dave cinabro selina li...

Documents

mev d s

gev d s

narrow d s

mc d s

sideband d s

d s mass distribution

d s m1 m0

d s o decays