1. Sergio Grancagnolo Activity Summary 9 Jan 2003 2003 work in BaBar The apparatus Physics with BaBar Data analysis

2. 2 E CM  GeV,  = 0.55 PEP-II is a high luminosity, asymmetric, e + e - collider filled by the 3 km long, linear accelerator (Linac) The accelerator PEP-II @ SLAC L design = 3 x 10 33 cm -2 s -1 L peak = 6.93 x 10 33 cm -2 s -1 L int =160 fb -1

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

4. 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. 5 Physics at a B factory n CP violation n Test of standard model n b quark physics n …

6. 6 BaBar discovery of D sJ (2317)! Observation of a Narrow Meson Decaying to D s +  0 at a Mass of 2.32 GeV/c 2 Phys.Rev.Lett. 90 (2003) 242001 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 11 Apr 2003 D s  KK  D s  KK   soon after another particle was discovered: D sJ (2460)!

7. 7 n Known particles: D s +, D s *+, D s1 + (2536), D sJ + (2573) n New discoveries: D sJ + (2317), D sJ + (2460) u below the treshold for the DK decay process  isospin violating decay process D s (*)  u narrow states Godfrey-Isgur model - cs spectroscopy S-waveP-wave

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

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

10. 10 n Cabibbo favored n B, D pseudoscalar n possibility of quantum number measurement for the D sJ from the angular distribution of the decay products D sJ B b _ d, u D _ V cb V cs c _ s c _ d, u D sJ in B decays

11. 11 Analysis Strategy look for decays B  D sJ + D (*) n consider 24 decays  D (*) D s +(*)  D (*) ( D s +(*)  0 )  D (*) ( D s +(*)  ) D 0  K  K  0, K3  D   K  D S +      Ds + D 0  or  Ds + D -  submodes/B D *0  D 0  0, D 0  D *+  D 0  +, D +  0 D * s  D s  n establish signals, measure BRs n perform angular analysis (  D sJ quantum numbers) n reconstruct the daughters: Studies on simulated data to evaluate efficiencies and background Control sample, used to test the analysis chain D sJ +  D s +(*)  0 D sJ +  D s +(*) 

12. 12 Analysis strategy (II) n Resolution studies n Event Selection Optimization n Background studies n Efficiency and significance n Multiple candidates problem n Cross-feed between different decay modes Total: 16 D (*) D s (*)  ,  final states

13. 13  (m  D s  )  14 MeV/c 2 DsJ mass resolutions (simulation)  (m  D s    )  8 MeV/c 2 m(D s  ) (GeV/c 2 ) Signal estimates from a fit to these distributions on real data m(D s   ) (GeV/c 2 )

14. 14 Cut optimization: m  D  For B  DD sJ + (D sJ +  D s  m  D  is a good discriminating variable Red is background Blue is simulated signal The curve is the fraction of events rejected by m  D  m  D  cut Optimal selection: m  D  2.3 GeV/c 2 (D) m  D  2.4 GeV/c 2 (D*)

15. 15 To compute the background in the D sJ mass region we average the number of events observed in the data into two symmetric (6  wide) sidebands around the D sJ mass region (-4 to -10  and 4 to 10  ) Background estimates in the D sJ signal region (from real data) m(D s  ) (GeV/c 2 )

16. 16 Candidate multiplicity studies n Several candidates per event: Choosing the candidate with the best  E gives the largest efficiency on simulated signal (1 candidate per mode) * assuming Br(B  D sJ D)xBr(D sJ  D  0,  )=10 - 3  E, m ES quantities constructed using kinematic variables

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

18. 18 Signal example: m(D s  ) for B  D (*) D s  candidates (data) all B candidates 1 best B candidate/mode m(D (*)  )>2.3(2.4)GeV/c 2

19. 19  Data is compatible with J=1  Comparison with other hypotheses (J=0,J=2) still to be done Helicity analysis cos  h Events B  D (*) D sJ MC  Data

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

21. 21 Conclusions (II) n More work done, not described here u efficiencies studies  published paper on B 0  D *+ D *- n Plan for this year: u more work to do on cross-feed, estimate systematic uncertainties u Write an internal document and submit a paper

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

23. 23 ModeS BB [m(D    ) cut]S/  (S+B)S/  (S+B) [m(D    )  cut] D + D s -  0 9.2 50.0 14.5 1.191.88 D + D s *-  0 3.5 18.5 6.0 0.751.14 D *+ D s -  0 8.5 43.0 14.5 1.19 1.78 D *+ D s *-  0 3.4 8.0 2.0 1.00 1.45 D 0 D s -  0 14.6 235.071.0 0.92 1.58 D 0 D s *-  0 4.9 83.524.0 0.52 0.91 D *0 D s -  0 4.9 74.0 25.0 0.55 0.90 D *0 D s *-  0 1.6 16.5 6.5 0.39 0.58 D + D s -  15.9 21.0 3.5 2.61 3.60 D *+ D s -  14.0 19.5 4.0 2.41 3.30 D 0 D s -  23.2 119.5 44.0 1.94 2.83 D *0 D s -  7.2 40.5 16.5 1.04 1.47 Expected signal and background with the current selection assuming Br(B  D sJ D)xBr(D sJ  D  0,  )=10 -3

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