Charm Baryon Studies at BABAR

Transcription

1 Institut für Kern- und Teilchenphysik Technische Universität Dresden Institutsseminar IKTP 15. Juni 006

2 Outline 1 Introduction The BABAR Detector and PEP-II 3 Reconstruction of Charm Baryon Decays 4 Analysis of Charm Baryons Analysis of Ω 0 c Decays Study of Ξ 0 c Charmed Baryons Spin Measurement of the Ω 5 Summary

3 Introduction Introduction SU(4) Multiplet of Baryons = Ξ + cc Ξc 0 0 Ξ (a) J P= 3/ Σ 0 c + Ω + cc Ω ++ ccc????????????????????????? Σ c +???????????????? Ξ ++ cc????????????????????????????????????????? Ω 0 c?????????????????????????????????? Ξ c + + Ω Ξ 0 Σ ++ c?????????????????????????????????????????????????????????????????????????????????????????? Σ????????????????????????????????????????????????? Σ 0 Σ +?????????????????????????????????????????????????????????? (b) Σ 0 c Ξ + cc????????????????????????? Ω + cc Λ + c,σ + c??????????????????????????????????????????????????????????????????????? 0??????????? Ξ Ω c?????? c 0??? Ξ + c Ξ ++ cc?????????????????????????????????????????????????????????????????????????????????????????????????????? Λ,Σ 0????????????????????????????????? Ξ Ξ 0 Σ c ++ n p Σ Σ Ξ c (c) J P= 1/ Λ Λ + c +?????????????????????? Ξ + c

4 Introduction Introduction All Analysis Presented were Developed During my Time with The University of Iowa Group at SLAC Thanks to: Prof. Usha Mallik (P. I.) Dr. Matthew J. Charles Veronique Ziegler (Ph.D. Student) Xuedong Chai (Ph.D. Student)

5 The BABAR Detector and PEP-II Part II The BABAR Detector and PEP-II

6 The BABAR Detector and PEP-II The PEP-II B-Factory

7 ] The BABAR Detector and PEP-II Luminosity (as of 06/14/006) 06/14/006 04:0-1 Integrated Luminosity [fb BaBar Run 1-5 PEP II Delivered Luminosity: /fb BaBar Recorded Luminosity: /fb Off Peak Luminosity: 31.6/fb Delivered Luminosity Recorded Luminosity Off Peak

8 The BABAR Detector and PEP-II The BABAR Detector

9 The BABAR Detector and PEP-II The BABAR Detector Also Charm Factory σ(b B) = 1.1nb σ(c c) = 1.3nb Luminosity (as of 6.Mar.006) L total = fb 1 L off peak = 31.6fb 1 Operated at the PEP-II e + e Storage Ring at SLAC DATA: s = mυ(4s) = 10.58GeV (On Peak) s = 10.54GeV (Off Peak)

10 Reconstruction of Charm Baryon Decays Analysis of Charm Baryons Part III Reconstruction of Charm Baryon Decays

11 Reconstruction of Charm Baryon Decays Analysis of Charm Baryons Event Topology of Charm Baryon Decays Decay into Long-lived Hyperons Flight Length O(cm) Secondary/Tertiary Vertices π p Reconstruction 3σ Mass Window Kinematic Constraint χ Probability > 0.1% Cut on p (Ξc 0 /Ωc) 0 (Center-of-Mass Momentum) Particle ID Protons/Kaons/Primary Pions π Secondary Vertex Tertiary Vertex Ξ Λ 0 Ξ c 0 π +

12 Reconstruction of Charm Baryon Decays Analysis of Charm Baryons Intermediate Hyperons Λ pπ + (1. fb 1 ) Entries/0.3 MeV/c Ξ Λπ (69 fb 1 ) m(pπ - ) (GeV/c ) Ω ΛK (110 fb 1 ) Entries/0.5 MeV/c BABAR preliminary m(λπ ) (GeV/c ) Entries/0.5 MeV/c m(λ K ) (GeV/c )

13 Analysis of Ω 0 c Decays Part IV Study of Ω 0 c (ssc) (hep-ex/ )

14 Analysis of Ω 0 c Decays Experimental Situation (PDG 004)

15 Analysis of Ω 0 c Decays Experimental Situation (PDG 004) Summary of Ω 0 c Studies Experiment WA-6 ARGUS E687 CLEO Belle FOCUS Luminosity (fb 1 ) Ω π + not seen 10.9 ± ± ± ± 7 Ω π + π ± 4.9 Ω π + π π + not seen Evidence not seen 0.9 ± 1.4 Ξ K π + π ± 4.5 not seen 7.0 ± ± 9 Ξ 0 K π + 9. ± 4.9 ΛK K π + π + not seen Σ + K K π ± ± 4.1 Numbers are Signal Events Observed BABAR with its High Statistics can Provide Valuable New Information in the Field of Ω 0 c Studis

16 Ω 0 c Decay Modes Analyzed Analysis of Ω 0 c Decays Intermediate Hyperons Λ pπ Ξ Λπ Ω ΛK Strategy for Selection of Intermediate Hyperons Common to All Decay Modes (see previous slide) Ωc 0 Decay Modes (Dataset: 30 fb 1 ) Ωc 0 Ω π + Ωc 0 Ω π + π π + Ωc 0 Ξ K π + π +

17 Analysis of Ω 0 c Decays Cut Optimization Ξ K π + π + as Example Relative Significance Yield After Selection ~00 ~50 ~ Ξ Flight Length / mm Optimization Based on Monte Carlo Simulation Figure of Merit: S/ (S + B)

18 Analysis of Ω 0 c Decays Cut Optimization Ξ K π + π + as Example Relative Significance Particle ID Relative Significance Ξ Flight Length Yield After Selection ~00 ~50 ~ Yield After Selection ~00 ~50 ~ KaonID Ξ Flight Length / mm Relative Significance CM Momentum (p ) Relative Significance Log(Fit Probability) Yield After Selection ~00 ~50 ~ Yield After Selection ~00 ~50 ~ * p / (GeV/c) Log10(χ )

19 Analysis of Ω 0 c Decays Signal Parametrization Ξ K π + π + as Example ) Entries / (3 MeV/c LINEAR χ / ndf / 5 Prob Yield 5596 ± 75.0 Mean.698 ± Sigma ± Frac ± Frac ± Sigma ± Sigma ± ) Entries / (3 MeV/c LOG m(ξ K π + π + ) / (GeV/c ) m(ξ K π + π + ) / (GeV/c ) Parameters for Signal Shape from MC f 1 f f 3 σ 1 σ σ 3 RMS HWHM χ /NDF Ω 0 c Decay Mode (%) ( MeV/c ) ( MeV/c ) Ω π /53 Ω π + π π /54 Ξ K π + π /5

20 Selection of Ω 0 c Final States Analysis of Ω 0 c Decays Ω 0 c Ω π + p lab (π + ) > 00MeV r trans Ω r 3D Λ >.0mm > 1.5mm (signed) Ω 0 c Ω π + π π + i p i(π) > 650MeV r trans Ω r 3D Λ >.5mm >.0mm (signed) Ω 0 c Ξ K π + π + rξ trans rξ trans > 4.5mm < r trans Λ (signed)

21 Analysis of Ω 0 c Decays Ω 0 c Invariant Mass Spectra (p >.8 GeV/c) ) Entries / (5 MeV/c Ω π + π π + ) Entries / (7 MeV/c m(ω π + π - π + ) / (GeV/c ) Ω π + ) Entries / (5 MeV/c BABAR preliminary m(ω π + ) (GeV/c ) BABAR preliminary BABAR preliminary Ξ K π + π m(ξ K π + π + ) (GeV/c )

22 Ω 0 c Results Analysis of Ω 0 c Decays Fit Procedure Unbinned Maximum Likelihood Fit Sum of Gaussians for Signal (Signal Shape taken from Monte Carlo) 1 st / nd Order Polynomial for Background Numerical Results (L = 30fb 1 ) Preliminary Results Decay Mode Signal Yield Efficiency (%) prob(χ ) S ( ) Ω π ± ± Ω π + π π ± ± Ξ K π + π ± ± ( ) S = log L

23 Measurement of the p Spectrum Analysis of Ω 0 c Decays Measurement Strategy Obtain Invariant Mass Spectrum in p Intervals (Width 400 MeV/c) Unbinned Maximum Likelihood Fit to Obtain Yield Ωc 0 Mass Fixed for all p Bins (to Weighted Mean over p Intervals) Yield / 0.44 GeV/c χ / ndf 4.74 / 37 Prob Yield ± Background at Peak 38.5 ± 1.1 Background Slope -8.7 ± Yield / 0.44 GeV/c χ / ndf 7.15 / 37 Prob Yield ± Background at Peak ± Background Slope ± m(ω π + )/(GeV/c ) (0.4 < p < 0.8)GeV/c m(ω π + )/(GeV/c ) (.8 < p < 3.)GeV/c

24 Analysis of Ω 0 c Decays Measurement of the p Spectrum (Not Corrected for Efficiency) Full DATA Set Off-Peak DATA Yield / (400 MeV/c ) BABAR preliminary Yield / (880 MeV/c) BABAR preliminary * 0 p (Ω c ) (GeV/c ) * 0 p (Ω c ) (GeV/c ) Conclusion Measurement from Ω 0 c Ω π + Channel First Evidence for Ω 0 c Production from B-Decays Good MC-DATA Agreement for Continuum Production (p >. GeV/c)

25 Systematic Uncertainties Analysis of Ω 0 c Decays Monte Carlo Simulation Extraction of Signal Yield Multiple Candidates One or more Final State Particles are not Correctly Assigned Peaking Backgrounds Particle ID & Tracking 1% per Additional Pion and 1% per Primary Pion Tracking: Standard Recipe 0.5% per Track with 1.4% Systematic Uncertainty Branching Fractions PDG Error on Ω Branching Ratio (68.7 ± 0.7%) Λ Branching Fraction cancels in Ratio

26 Analysis of Ω 0 c Decays Systematic Uncertainties MC Simulation Monte Carlo Statistics p Reweighting Possible Resonance Structure e.g. in Ξ K π + π + Ξ K (89)π + Ξ (1530)K π + Ξ (1530)K (89) Efficiency Systematic Uncertainties (%) Decay Mode (%) Res. Structure p Reweighting sys total Ω π ± Ω π + π π ± Ξ K π + π ±

27 Analysis of Ω 0 c Decays Systematic Uncertainties Extraction of Signal Yield Change Parameters of the Fit Change the Fit Range.4 < m Ω 0 c < 3.0GeV/c.5 < m Ω 0 c <.9GeV/c.6 < m Ω 0 c <.8GeV/c Change the Fit Function Change Description of Signal Tails Double Width of Broadest Gaussian Drop Third Gaussian from Fit Change in Signal Yield Observed.5% (Ω π + ) up to 10% (Ξ K π + π + )

28 Analysis of Ω 0 c Decays Ω 0 c Decay Modes (p >.8 GeV/c) Systematic Uncertainties (in Units of the Ratio) B(Ω π + π π + ) B(Ω π + ) B(Ξ K π + π + ) B(Ω π + ) Monte Carlo Statistics p Reweighting Resonance Structure Extraction of Signal Yield Particle ID & Tracking Ω Branching Fraction Multiple Candidates Total Systematic Uncertainty

29 Analysis of Ω 0 c Decays Results Ratio of Branching Fractions Preliminary Results B(Ω 0 c Ω π + π π + ) B(Ω 0 c Ω π + ) B(Ω 0 c Ξ K π + π + ) B(Ω 0 c Ω π + ) = 0.16 ± 0.10 (stat.) ± (sys.) PDG = seen = 0.31 ± 0.15 (stat.) ± (sys.) PDG = 1.6 ± 1.1 (stat.) ± 0.4 (sys.) (Bayesian) Upper Limit Preliminary Results B(Ω 0 c Ω π + π π + ) B(Ω 0 c Ω π + ) < 0.30 (90%CL)

30 Analysis of Ω 0 c Decays Limit on the Ω 0 c Ω π + π π + Branching Ratio Input to Toy Experiments Statistical and Systematic Uncertainties All Distributions Assumed to be Gaussian Experiments BABAR preliminary B(Ω π + π π + ) B(Ω π + ) Ratio of Branching Fractions

31 Study of Ξc 0 Charmed Baryons Part V Study of Ξ 0 c (dsc) (Phys.Rev.Lett.95:14003,005)

32 Study of Ξc 0 Charmed Baryons Ξ 0 c Selection Selection of Intermediate Hyperons Similar to Previous Section Invariant Mass Spectra + Ξ π Ξ 0 c Ξ π + r trans Ξ r 3D Λ >.5mm > 3.0mm (signed) Ω Κ + Ξ 0 c Ω K + r trans Ω r 3D Λ > 1.5mm > 3.0mm (signed)

33 Study of Ξc 0 Charmed Baryons Results (L = 116fb 1 ) Extraction of Signal Yield Several Methods Applied Fit With Sum of Gaussians (all Parameters free) plus 1 st Order Polynomial Cut-and-Count Fit with 1 st Order Polynomial to Mass-Sidebands The Ratio of Branching Fractions (p >.15GeV) B(Ξ 0 c Ω K + ) B(Ξ 0 c Ξ π + ) = 0.94 ± (stat.) ± (sys.) CLEO(PL B 85, 161) = 0.5 ± 0.1 (stat.) ± 0.05 (sys.)

34 Results (L = 116fb 1 ) Study of Ξc 0 Charmed Baryons Systematic Uncertainties (%) Extraction of Yield 3.4 Efficiency 3.1 Particle Identification.0 Monte Carlo Statistics 1.4 Multiple Candidates 1.0 Charge Asymmetry 1.0 Ω Helicity 1.0 Ω Branching Fractions 1.0

35 Study of Ξc 0 Charmed Baryons Measurement of the p Spectrum from (Ξ 0 c Ξ π + ) bb Range cc Range Ξ 0 c Ξ π + Results B(B ΞcX) 0 B(Ξc 0 Ξ π + ) = (.11 ± 0.19 (stat.) ± 0.5 (sys.) ) 10 4 σ(e + e c c ΞcX) 0 B(Ξc 0 Ξ π + ) = (388 ± 39 (stat.) ± 41 (sys.) )fb

36 Interpretation of the p Spectrum Study of Ξc 0 Charmed Baryons c c Part (p.gev): Consistent with MC-Prediction B B Part (p.gev): Peak in Data Lower Several Explanations Possible Some Evidence for b cs s?

37 Interpretation of the p Spectrum Study of Ξc 0 Charmed Baryons Obvious Weak Decay b cūd: e. g. B Ξ 0 cλ... Plus a Number of Pions Peak Could be Due to High Multiplicity b cūd Decays

38 Interpretation of the p Spectrum Study of Ξc 0 Charmed Baryons Theorists Claim that b c cs is high: B(B Ξ 0 c X c ) (1 ) 10 3 This Would Naturally Give a Heavy Recoiling System Thesis Topic at The University of Iowa... Stay Tuned!

39 Summary Spin Measurement of the Ω Part VI Spin Measurement of the Ω (to be subm. to PRD-RC)

40 Summary Spin Measurement of the Ω Status of the Spin of the Ω PDG: The quantum numbers have not actually been measured, but follow the assignments of the particles to the baryon decuplet. DEUTSCHMAN 78 and BAUBULER 78 rule out J = 1/ and find consistency with J = 3/ Measurement of the Spin in Assumptions: J(Ξ 0 c /Ω 0 c) = 1/ Ξ 0 c K + Ω ΛK Ω 0 c π + Ω ΛK Ξ 0 c/ω 0 c are Produced Unpolarized

41 Helicity Formalism Summary Spin Measurement of the Ω Boost all decay products in Ξ 0 c rest-frame. In this frame Ω Ω 1, Λ Λ0 1, K ± K ± 1 Boost the Ω 1 decay products in its rest-frame. In this Ω 1 Ω, Λ 0 1 Λ0, K ± 1 K ± Predicted Angular Distribution J(Ω ) = 1/ : dn/dcos θ h 1 J(Ω ) = 3/ : dn/dcos θ h cos θ h J(Ω ) = 5/ : dn/dcos θ h 1 cos θ h + 5 cos 4 θ h

42 Summary Spin Measurement of the Ω Measurement of the Helicity Distribution Analysis Strategy Measure Invariant Mass Spectrum of Ωc 0 in Bins of cos Θ h Yield from Fit to Invariant Mass Spectrum Correct for Selection Efficiency Entries/ BABAR preliminary Ξ 0 c Ω K Fit for J(Ω ) = 3/ Hypothesis cosθ h (Λ)

43 Summary Spin Measurement of the Ω Measurement of the Helicity Distribution Entries/ BABAR preliminary Ξ 0 c Ω K Fit-Probabilities 00 Fit for J(Ω ) = 1/ Hypothesis (solid) Fit for J(Ω ) = 5/ Hypothesis (dashed) cosθ h (Λ) J(Ω )=1/: χ /N.D.F.=100.4/9 Prob= J(Ω )=3/: χ /N.D.F.=6.5/9 Prob=0.69 J(Ω )=5/: χ /N.D.F.=47.6/9 Prob=3 10 7

44 Summary Spin Measurement of the Ω Measurement of the Helicity Distribution Entries/ BABAR preliminary 150 Ω 0 c Ω π Fit for J(Ω ) = 3/ Hypothesis cosθ h (Λ) Conclusion J(Ω ) 3/ Ruled out at > 95%CL Results from Ξc 0 and Ωc 0 Decays Consistent

45 Summary Summary Field of Charm Baryons is Very Interesting BABAR with its High Statistics Offers Ideal Conditions for Charm Baryon Studies Topics Covered in This Talk Studies of Ω 0 c Studies of Ξ 0 c Measurement of Ω Spin A Lot More to Come Study of Excited Charm Baryons Mass Measurements B Decays into Charm Baryons...