First Observation of the Baryon;Properties of , , , and Baryons

Andreas WarburtonCornell University

CLEO Collaboration

XXXth International Conference on High Energy PhysicsICHEP 2000, Osaka, JapanJuly 27 August 2, 2000

PA01c50

*c

0c c

c 0

c

July 27 - August 2, 2000

ICHEP 2000 A. Warburton Cornell University 2

CLEO

Talk Overview

Charmed-Baryon Spectroscopy

CLEO Charmed-Baryon Reconstruction Techniques

Mass and Width Measurements of the and Baryons

Discovery of and Mass Measurement of the Baryon

First CLEO Observation of the Baryon

0cc

*cc

0c

All new results are preliminary!

July 27 - August 2, 2000

ICHEP 2000 A. Warburton Cornell University 3

CLEOThe Charmed Baryons

Charmed baryons consist of a heavy c quark and a light diquark

Many JP states

To date, all L=0 states seen except and

None of the JP quantum numbers has been measured!

diquarkantisymmetricunder SU(3) diquark

symmetricunder SU(3)

*c 0

c

July 27 - August 2, 2000

ICHEP 2000 A. Warburton Cornell University 4

CLEO

and Spectroscopyc c

Not yetobserved# #

#

#

# #

July 27 - August 2, 2000

ICHEP 2000 A. Warburton Cornell University 5

CLEO

Data Set and CLEO II/II.V Detector

e+e Collisions near Resonance (~10.5 GeV)

(4 )S

114 fbLdt

Charm-quark Production: B-meson decays e+e cc jets

Two Configurations: CLEO II (1989 1995) CLEO II.V (1996 1999)

July 27 - August 2, 2000

ICHEP 2000 A. Warburton Cornell University 6

CLEOReconstructed Candidate Modes

0c c

c

c *

c

and

0c and

15c modes

0

0

0c

K

K

0c K K

Mode found by E-687

p

p

0

Hyperon Channels

July 27 - August 2, 2000

ICHEP 2000 A. Warburton Cornell University 7

CLEO

Event Selection and Background Suppression Principles

candidates are reconstructed in the CsI calorimeter barrel region

candidates are identified using time-of-flight and dE/dx info

Displaced vertices are used to identify candidates

Scaled Momentum criterion: xp > 0.5 or 0.6, where xp p/pmax

and

reduces combinatorial background Note: charmed baryons with B-meson parents have xp < 0.4

max beam cand.p E M2 2

p, K ,

, , , ,

0

July 27 - August 2, 2000

ICHEP 2000 A. Warburton Cornell University 8

CLEO

Mass M c –

15 Modesc

• xp > 0.5

• Signal region: 1.6

• Yield ~ 58 000 candidates

• S:N ~ 1 : 1.2

July 27 - August 2, 2000

ICHEP 2000 A. Warburton Cornell University 9

CLEO

Inclusive Hyperon Samples

K

p

26723 207 742 34

18606 527 69484 731

July 27 - August 2, 2000

ICHEP 2000 A. Warburton Cornell University 10

CLEO

and Massand Width Fits

+ + 2c cM M GeV c

c

0c

• Double-Gaussian resolution function ( ~ 0.6 MeV/c2)

• Yields: ~ 2000 events

• Fit to p-wave Breit-Wigner convolved with resolution function

• xp > 0.5

c 0

c

ResolutionFunction

ResolutionFunction

July 27 - August 2, 2000

ICHEP 2000 A. Warburton Cornell University 11

CLEOc

c

6360661 Events

7873327 Events

+ 0 + 2c cM M MeV c

• Mass Fits to p-wave Breit-Wigner convolved with resolution function

• xp > 0.6

• First observation of resonance

and Yields

cc

c

July 27 - August 2, 2000

ICHEP 2000 A. Warburton Cornell University 12

CLEO

CLEO Mass and Width Measurements

3.7

3.0

0

167.2 0.1 0.2 166.4 0.2 0.3 167.4 0.1 0.2

2.4 0.2 0.4 4.6 (90% CL) 2.5 0.2 0.4

231.0 1.1 2.0

17 (90% CL)

Observable

232.6 1.0 0.8 234.5 1.1 0

Is

.8

13

osp

M

M

i

0

n

. 4.0

c c

c

c c

c

c c c

+3.83.217.9 4.0

c

PRELIMINARY CLEO results G. Brandenburg et al. (CLEO), Phys. Rev. Lett. 78, 2304 (1997)

All quantities are in .First uncertainties are statistical; second are systematic.

2MeV c

P 12J

P 32J

July 27 - August 2, 2000

ICHEP 2000 A. Warburton Cornell University 13

CLEO

Search Modes

2Invariant Mass GeV c

0c

xp > 0.5 or 0.6

0

0K

K K K

July 27 - August 2, 2000

ICHEP 2000 A. Warburton Cornell University 14

CLEO

Sum of 5 Search Modes

Wrong-Sign Daughter CombinationsWrong-Sign Daughter CombinationsHyperon-Sideband DistributionsHyperon-Sideband Distributions

0c

Total Fitted Yield:

40.4 9.0 (stat.) candidates

0 2 Candidate Mass GeVc c

July 27 - August 2, 2000

ICHEP 2000 A. Warburton Cornell University 15

CLEO

Summary of Preliminary Results

0c

0

0

1.0

4.2 2.2

Mode Fitted

1.2

11.3 3.9 2.3

47.6 18.0 2.8

5.1 90% CL

45.1 23.2 4.1

13.3 4.1

11.8 4.9

0.9 1.4

9.2 4.9

7.0

0.6 90% CL

3

4.0 2.5 0.6

1.6 1.1

Yield Relative

K

fb

7 ..

K

0

B B f

K K 9.5 90% CL 4.8 90% CL 53.8 90%

Combi

CL

n

18.2 10.6

ed 40.4 9.0

3.84

Unbinned maximum likelihood fit mass:

0 2M stat.2694.6 2.6 2 syst. . MeV4c c

July 27 - August 2, 2000

ICHEP 2000 A. Warburton Cornell University 16

CLEO

We present the most statistically accurate measurements of the , , and masses.

We have made preliminary measurements of the and widths.

We report the first observation of the baryon and measure its mass to be

Conclusions

0c c

c

0c

c

c

2M sta231.0 1. t. syst. M1 0 eV2.c c c

July 27 - August 2, 2000

ICHEP 2000 A. Warburton Cornell University 17

CLEO

CLEO has now, for the first time, observed a significant number of candidates. We present a preliminary mass measurement of

Supporting documentation can be found in hep-ex/0007041 hep-ex/00070

CLEO continues to contribute to knowledge of the charmed baryon sector.

Conclusions, cont’d

0 2M stat.2694.6 2.6 2 syst. . MeV4c c

0c