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2003 work in BaBar

2003 work in BaBar. The apparatus Physics with BaBar Data analysis. The accelerator PEP-II @ SLAC. PEP-II is a high luminosity , asymmetric , e + e - collider filled by the 3 km long, linear accelerator ( Linac ). E CM = 10.58 GeV , bg = 0.55. L int =160 fb -1.

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2003 work in BaBar

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  1. 2003 work in BaBar The apparatus Physics with BaBar Data analysis

  2. The accelerator PEP-II @ SLAC PEP-II is a high luminosity, asymmetric, e+e- collider filled by the 3 km long, linear accelerator (Linac) ECM = 10.58 GeV , bg = 0.55 Lint=160 fb-1 Ldesign = 3 x 1033 cm-2s-1 Lpeak = 6.93 x 1033 cm-2s-1

  3. The BaBar dectector • BaBar is mounted on the interaction point of PEP-II • Layers of subdetectors: • Silicon Vertex Tracker • Drift CHamber • Detector of Internal Reflected Cherenkov light • Electro Magnetic Calorimeter • Instrumented Flux Return • Magnetic Solenoid (1,5T) between EMC and IFR

  4. SVT commissioner work During the Apr-Jul 2003 period of data taking at SLAC, I was responsible for the correct working status of the innermost part of the BaBar detector: the Silicon Vertex Tracker

  5. Physics at a B factory • CP violation • Test of standard model • b quark physics • …

  6. 11 Apr 2003 BaBar discovery of DsJ(2317)! Observation of a Narrow Meson Decaying to Ds+p0 at a Mass of 2.32 GeV/c2 Phys.Rev.Lett. 90 (2003) 242001 DsKKp SLAC press-release http://www.slac.stanford.edu/slac/media-info/20030428/index.html INFN announcement http://www.infn.it/comunicati/detail.php?id=299 Nature http://www.nature.com/nsu/030428/030428-18.html DsKKpp0 soon after another particle was discovered: DsJ(2460)!

  7. cs spectroscopy - Godfrey-Isgurmodel • Known particles: Ds+, Ds*+, Ds1+(2536), DsJ+(2573) • New discoveries: DsJ+(2317), DsJ+(2460) • below the treshold for the DK decay process • isospin violating decay process Ds(*)p • narrow states S-wave P-wave

  8. Interpretation of these narrow states? • 38 theoretical preprints between 1st May to 30th Sep • Among others also exotic explanations like: • 4-quark states? • DK molecule? • …

  9. Study of BDsJD(*) decays • The other B-factory experiments, Cleo and Belle, confirmed the discovery and started to study the new particles • Belle announced the observation of the decays BDsJD(*) • on 1st Sept I started to work with the French group of Annecy on this topic • I will spend ~10 months in Annecy • The results will be an important part of my thesis hep-ex/0305100 hep-ex/0307052 hep-ex/0308019

  10. DsJ in B decays c _ s _ _ _ b c D d, u Vcs DsJ Vcb B d, u • Cabibbo favored • B, D pseudoscalar • possibility of quantum number measurement for the DsJ from the angular distribution of the decay products

  11. Analysis Strategy • look for decays B  DsJ+ D(*) • consider 24 decays • D(*) Ds+(*) • D(*) (Ds+(*)p0) • D(*) (Ds+(*)g) Control sample, used to test the analysis chain DsJ+  Ds+(*)p0 DsJ+  Ds+(*)g • reconstruct the daughters: D*0 D0p0, D0g D*+  D0p+,D+p0 D*s  Dsg D0  Kp, Kpp0, K3p D+ Kpp DS+  fp, K*0K 6 Ds+D0or 2 Ds+D-submodes/B Studies on simulated data to evaluate efficiencies and background • establish signals, measure BRs • perform angular analysis ( DsJquantum numbers)

  12. Analysis strategy (II) • Resolution studies • Event Selection Optimization • Background studies • Efficiency and significance • Multiple candidates problem • Cross-feed between different decay modes Total: 16 D(*)Ds(*) p0,g final states

  13. DsJ mass resolutions (simulation) s(m(Dsp0)) 8 MeV/c2 s(m(Dsg)) 14 MeV/c2 Signal estimates from a fit to these distributions on real data m(Dsp0) (GeV/c2) m(Dsg) (GeV/c2)

  14. Cut optimization: m(Dg) For B  DDsJ+ (DsJ+ Dsg) m(Dg) is a good discriminating variable Red is background Blue is simulated signal The curve is the fraction of events rejected by m(Dg) > m(Dg)_cut Optimal selection: m(Dg) > 2.3 GeV/c2 (D) m(Dg) > 2.4 GeV/c2 (D*)

  15. Background estimates in the DsJ signal region (from real data) To compute the background in the DsJ mass region we average the number of events observed in the data into two symmetric (6s wide) sidebands around the DsJ mass region (-4 to -10 s and 4 to 10s) m(Dsg) (GeV/c2)

  16. Candidate multiplicity studies • Several candidates per event: • Choosing the candidate with the best DEgives the largest efficiency on simulated signal (1 candidate per mode) DE, mES quantities constructed using kinematic variables * assuming Br(B DsJD)xBr(DsJ Dp0,g)=10-3

  17. 2 body decays used as a calibration sample (data) compute the branching fractions of all decays B  Ds(*)D(*) to test if we understand well our selection efficiencies

  18. Signal example: m(Dsg) for BD(*)Dsg candidates (data) m(D(*)g)>2.3(2.4)GeV/c2 1 best B candidate/mode all B candidates

  19. B D(*)DsJ MC  Data Helicity analysis • Data is compatible with J=1 • Comparison with other hypotheses (J=0,J=2) still to be done Events cosqh

  20. Conclusions (I) • The analysis work is going on • A preliminary BR measurement was shown at the BaBar collaboration meeting • An example: • A preliminary angular analysis was also done Br(B0DsJ+2460D-)  Br(DsJ+Dsg)) =( 0.75 ±0.19) 10-3 Br(B+DsJ+2460D0)  Br(DsJ+Dsg)) =( 0.65 ±0.19) 10-3 Br(B0DsJ+2460D*-)  Br(DsJ+Dsg)) =( 2.04 ±0.29) 10-3 Br(B0DsJ+2460 D*0)  Br(DsJ+Dsg)) =( 1.63 ±0.32) 10-3

  21. Conclusions (II) • More work done, not described here • efficiencies studies • published paper on B0D*+D*- • Plan for this year: • more work to do on cross-feed, estimate systematic uncertainties • Write an internal document and submit a paper

  22. Event Selection Optimization • Tested many combination of different criteria • Used standard discriminating variables to separate quark b production from other quarks • Select a window in the invariant mass around the mass of the particles from the B and the DsJ • Vertexing, particle identification, etc • computed the significance S/(S+B) for each set, with S from simulated signal and B from the real data • choose the criteria that results in higher significance • a different set of criteria for each submode will be considered S=signal B=background

  23. Expected signal and background with the current selection Mode S B B [m(Dp0,g) cut] S/(S+B) S/(S+B) [m(Dp0,g)cut] D+ Ds-p0 9.2 50.0 14.5 1.19 1.88 D+ Ds*-p0 3.5 18.5 6.0 0.75 1.14 D*+ Ds-p0 8.5 43.0 14.5 1.19 1.78 D*+ Ds*- p0 3.4 8.0 2.0 1.00 1.45 D0 Ds-p0 14.6 235.0 71.0 0.92 1.58 D0 Ds*-p0 4.9 83.5 24.0 0.52 0.91 D*0 Ds-p0 4.9 74.0 25.0 0.55 0.90 D*0 Ds*- p0 1.6 16.5 6.5 0.39 0.58 D+ Ds-g 15.9 21.0 3.5 2.61 3.60 D*+ Ds- g 14.0 19.5 4.0 2.41 3.30 D0 Ds- g 23.2 119.5 44.0 1.94 2.83 D*0 Ds-g 7.2 40.5 16.5 1.04 1.47 assuming Br(B DsJD)xBr(DsJ Dp0,g)=10-3

  24. MC: efficiency • With the best DE (1 candidate per mode) The rest of the table here: http://www.slac.stanford.edu/~grancagn/internal/DsJD/de-a-2s.txt

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