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New results from B A B AR

This seminar presentation discusses new results from the BABAR experiment at Brookhaven National Laboratory, focusing on CP violation in charmless B decays. The CKM matrix, detector performance, and analysis strategies are also discussed.

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New results from B A B AR

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  1. New results from BABAR Brookhaven National Laboratory Particle Physics Seminar May 20, 2002 Marie-Hélène Schune Laboratoire de l’Accélérateur Linéaire Orsay, France All numbers are preliminary New results from BABAR, Marie-Hélène Schune, BNL, May 20th 2002 1

  2. 56 fb-1 New results from BABAR sin2b = 0.750.09 0.04 Winter 2002 conferences I will not talk about sin2b in charmonium modes : BABAR and PEPII Charmless B decays : B0, K or KK B000 The “B recoil” physics : semileptonic branching fractions of B+ and B0 D meson production in B decays New results from BABAR, Marie-Hélène Schune, BNL, May 20th 2002 2

  3. CKM matrix for 3 generations Bdp+p-,r+p-, … BdBd, Bdrg B pp, rp, pln, rln,… B  D(*)ln,D(*)p,… Bd J/yKs, D*+D*-,… BD*p, DK, Kp • CKM matrix has 4 real parameters (one phase included) • 2 are well known : • l=|Vus|=sin(qCabbibo)=0.22050.0018 • A =|Vcb|/l2 =0.83 0.06 • unitarity of the CKM matrix leads to constraints that can be tested: h Unitarity Triangle r New results from BABAR, Marie-Hélène Schune, BNL, May 20th 2002 3

  4. The BABAR detector 1.5Tsolenoid CsI(Tl)EMC e+ (3.1GeV) DIRC (PID) DriftChamber SiliconVertexTracker e- (9GeV) InstrumentedFluxReturn • SVT: 97% efficiency, 15mm z resol. (inner layers, perpendicular tracks) • Tracking : s(pT)/pT = 0.13% PT 0.45% • DIRC : K-p separation >3 s for P<3.5GeV/c • EMC: E/E = 1.33% E-1/4  2.1% New results from BABAR, Marie-Hélène Schune, BNL, May 20th 2002 4

  5. New results from BABAR, Marie-Hélène Schune, BNL, May 20th 2002 5

  6. PEP-II asymmetric B Factory 9GeV e- on 3.1GeV e+ : s~10.58 GeV • for B0 : coherent neutral B pair production and decay (p-wave) • boost of (4S) in lab frame : bg=0.55 New results from BABAR, Marie-Hélène Schune, BNL, May 20th 2002 6

  7. Running at the (4S) PEP-II BABAR Off On New results from BABAR, Marie-Hélène Schune, BNL, May 20th 2002 7

  8. B factory performances • May 2nd : • PEPII delivered : 87 fb-1 • BABAR recorded : 83 fb-1 (including 9 fb-1 off peak ) • results for 55 fb-1 daily integrated luminosity New results from BABAR, Marie-Hélène Schune, BNL, May 20th 2002 8

  9. 2 - Charmless B decays Study of penguins diagrams Possible direct CP violation a g • B0, K or KK • Branching fractions (aeff a, g) • CP violations measurements (aeff , a ) • B000 (aeff a) h (r,h) a g b r New results from BABAR, Marie-Hélène Schune, BNL, May 20th 2002 9

  10. B0 and CP violation (1) Hadronic Penguin Amplitude (P) Tree amplitude (T) BF(B0) << BF(B0K) penguins contributions may be large mixing e-2ib Tree only : l=hfe2ia (a = p-b -g) Cpp=0 Spp=sin(2a) Tree+Peng. Cpp 0 Spp=sin(2aeff) New results from BABAR, Marie-Hélène Schune, BNL, May 20th 2002 10

  11. B0 and CP violation (2) f+ : B0 tag Spp=0.7and Cpp=0. perfect flavour tagging & time resolution realistic mis-tagging & finite time resolution New results from BABAR, Marie-Hélène Schune, BNL, May 20th 2002 11

  12. B0, K or KKkinematics Axis of “Rest Event” Candidate Candidate • Main variables : • |cosqS| : angle between the B0 sphericity axis and the sphericity axis of the rest of the event • F : Fisher discriminant based on “energy flow cones” (CLEO) Axis of “Rest Event” “Jets” Candidate |cosqS| New results from BABAR, Marie-Hélène Schune, BNL, May 20th 2002 12

  13. B0, K or KK: mES and DE Signal MC s~2.6 MeV background • Energy substituted mass : • dominated by the beam energy knowledge • DE : assume pp mass • dominated by the tracking resolution s(DE)~26 MeV ~325 MeV mES KK Kp pp background 45 MeV New results from BABAR, Marie-Hélène Schune, BNL, May 20th 2002 13

  14. B0, K or KK : the PID (1) The DIRC Quartz bar Active Detector Surface • Measure Angle of Cherenkov Cone in quartz • Transmitted by internal reflection • Detected by PMTs Cherenkov light Particle New results from BABAR, Marie-Hélène Schune, BNL, May 20th 2002 14

  15. DIRC PMT +light catchers DIRC stand-off box, magnetic shielding and electronic crates  New results from BABAR, Marie-Hélène Schune, BNL, May 20th 2002 15

  16. B0, K or KK : the PID (2) • DIRC performances measured on data using D*D0p and D0 Kp s(qc)  2.2 mrad K/p separation 2.5s p range of 2-body B decays at BABAR New results from BABAR, Marie-Hélène Schune, BNL, May 20th 2002 16

  17. B0, K or KK : analysis strategy mES 5.2 5.24 5.28 Start with a B0h+h- (no PID) unbinned max L with DE, mES, F, q1c, q2c measure Npp NKp NKK and ~17600 events for ~56 fb-1 add Dt and tagging information (as for sin2b ), fix the yields extract Spp and Cpp New results from BABAR, Marie-Hélène Schune, BNL, May 20th 2002 17

  18. B0, K or KK :branching fractions results B0 B0K Likelihood projections : remove one 1 variable from fit ; cut on L proba small cross-feed ~83 B0 small cross-feed ~356 B0K mES DE mES DE New results from BABAR, Marie-Hélène Schune, BNL, May 20th 2002 18

  19. B0, K or KK : BF comparison BF(B0) << BF(B0K) New results from BABAR, Marie-Hélène Schune, BNL, May 20th 2002 19

  20. B0, K or KK : CP analyses Dt • Time information Dt : • resolution dominated by Btag vtx (s(Dz) ~ 180 mm) • extracted from data Breco sample (D(*)p,D(*)r,D(*)a1…) • Background shape : side bands Similar to sin(2b) analyses New results from BABAR, Marie-Hélène Schune, BNL, May 20th 2002 20

  21. B Flavour tagging methods NN output Not Used B0 d B0 d Prob(B0) d d Hierarchical, mutually exclusive, tagging categories For electrons, muons and kaons use the charge correlation l- W+ n W- b c s W- c b K*0 D, D* Lepton Tag Kaon Tag Neural Network Multivariate analysis exploiting the other kinematic information of the event, e.g., • Momentum spectrum of the charged particles • Information from non-identified leptons and kaons • Soft p from D* decay Each category is characterized by the probability of giving the wrong answer (mistag fraction w) New results from BABAR, Marie-Hélène Schune, BNL, May 20th 2002 21

  22. B0, K or KK : CP analyses tagging • Split the events into 4 tagging categories : • leptons • kaons • NT1 • NT2 • Performances obtained on data (Breco sample) mES leptons NN type tagging kaons Similar to sin(2b) analyses NT1 NT2 New results from BABAR, Marie-Hélène Schune, BNL, May 20th 2002 22

  23. B0, K or KK : CP analyses validation • Validation : measure tB on pp/Kp sample : • Validation : measure Dmd tB=1.66 0.09 ps Select the Kp events and plot Amix Dmd=0.517 0.062 ps-1 New results from BABAR, Marie-Hélène Schune, BNL, May 20th 2002 23

  24. B0, K or KK : CP analyses results Spp =-0.010.370.07 Spp [-0.66,+0.62] at 90 % CL Cpp =-0.020.290.07 Cpp [-0.54,+0.48] at 90 % CL ~27B0 Select the B0 events Plot the asymmetry between B0 tag and B0tag events ~9Background ~25B0 ~9Background New results from BABAR, Marie-Hélène Schune, BNL, May 20th 2002 24

  25. (r,h) constraints from Spp and Cpp BBNS: QCD FACTORISATION APPROACH: M. Beneke, G. Buchalla, M. Neubert and C.T. Sachrajda Nucl.Phys.B606 (2001) 245 CKM Fitter H. Höcker, H. Lacker, S. Laplace and F. Le Diberder Eur. Phys. J. C21 225-259 (2001) http://ckmfitter.in2p3.fr/ New results from BABAR, Marie-Hélène Schune, BNL, May 20th 2002 25

  26. B0, K or KK : CP comparisons Belle (K Trabelsi Moriond): -Cpp (BABAR) App c2(Spp,Cpp)=9 (~2.5 s) New results from BABAR, Marie-Hélène Schune, BNL, May 20th 2002 26

  27. Search for B000 • BF(B000) : • measured  isospin analysis to get a from B0+- (M. Gronau, D. London Phys Rev Lett. 65 3381-3384 (1990)) • upper bound  still a useful constraint: (Y. Grossman, H. Quinn Phys Rev D 58 017504 (1998)) • Experimentally challenging : • low BF expected (th. predictions : 10-7 - few 10-6) • purely neutral final state • Recent results : New results from BABAR, Marie-Hélène Schune, BNL, May 20th 2002 27

  28. Search for B000 : analysis (1) Candidate • Main variables : • |cosqS| : angle between the B0 sphericity axis and the sphericity axis of the rest of the event • F : Fisher discriminant based on the “energy flow cones” • mEC : energy constrained mass • DE = E*B –s/2 in the CMS Axis of “Rest Event” “Jets” Candidate F New results from BABAR, Marie-Hélène Schune, BNL, May 20th 2002 28

  29. Search for B000 : analysis (2) Brp0 B0p0p0 -.4 -.2 0 .2 .4 -.4 -.2 0 .2 .4 DE (GeV) DE (GeV) • The Brp0background : • event shape similar to the signal one • mEC only slightly wider (small p missing) • DE is the only discriminating variable • in the fit : fix BF(Brp0)=2.410-5(from CLEO upper limit) New results from BABAR, Marie-Hélène Schune, BNL, May 20th 2002 29

  30. Search for B000 : results • Unbinned maximum L fit using F PDFand(mEC , DE ) PDF • Compare with an optimized cut and count analysis : • Fit yield : • Main systematics : • neutral efficiency • continuum mEC param. • F param. • Brp0 yield BF(B000) < 3.4 10-6 at 90 % CL 54 fb-1 New results from BABAR, Marie-Hélène Schune, BNL, May 20th 2002 30

  31. 3 - The “B recoil” physics generic B decay B type known should allow (in principle !) to measure all B BF Will show : leptonic studies D0 and D production New results from BABAR, Marie-Hélène Schune, BNL, May 20th 2002 31

  32. The “B recoil” physics • B factories : the world’s largest sample of reconstructed B mesons 56 fb-1 Nsignal=13743125 Reconstruct the Cabibbo-favored hadronic decays : B0 sample Nsignal=12909120 B+ sample New results from BABAR, Marie-Hélène Schune, BNL, May 20th 2002 32

  33. Inclusive semileptonic B decays • Inclusive rate is large • Sides of the unitarity triangle |Vcb| and |Vub| • BXcen is large • BXuenis an experimental challenge • (r,h) a g b (1,0) (0,0) New results from BABAR, Marie-Hélène Schune, BNL, May 20th 2002 33

  34. Inclusive semileptonic B decays • Compare b+/b0 with t(B+)/t(B0) : • Extract the prompt and cascade lepton spectrum from the charge correlation with the Breco : • B-Xce-n • B+Xce+n • B0 : correct for mixing CLEO results (2.4 fb-1) using B0 tagged sample and (4S)l: • b0 = (10.78 0.600.69)% • b+ = (10.25 0.570.65)% • b+/b0 = New results from BABAR, Marie-Hélène Schune, BNL, May 20th 2002 34

  35. Electron identification • Variables : • E/p • Shower shapes • DCH and DIRC • Performances measured on data: 90% • Backgrounds : •  conversions • p0 dalitz decays • J/ decays 10-3 p (GeV) New results from BABAR, Marie-Hélène Schune, BNL, May 20th 2002 35

  36. Background subtracted electrons spectra Right sign Wrong sign B N right sign= N+p results on 21 fb-1 B0 Nright sign=N0p(1-cd)+N0ccd Nwrong sign=N0pcd+N0c(1-cd) New results from BABAR, Marie-Hélène Schune, BNL, May 20th 2002 36

  37. b0 and b+ results b+/b0=.950  .080  .091 b+/b0=.99  .10  .03 • BF results : ratio : B+ B0 New results from BABAR, Marie-Hélène Schune, BNL, May 20th 2002 37

  38. D production in B decays c q s D0,D-,Ds-,Lc-,… WRONG b ( ) c B0 or B- D0,D+,Ds+,Lc+,… RIGHT • Inclusive branching fractions of B0 and B+ to charmed hadrons • Enters in the nc (= mean charm per B decay ) computation • For each B specie two measurements are performed : • The absolute BF : BF(BDX) with D = D0 or D+ • “large statistics” • Need e(D) from MC • The wrong D ratio : • Wrong D sample statistically limited • Need to correct for mixing for the B0 • More MC independant New results from BABAR, Marie-Hélène Schune, BNL, May 20th 2002 38

  39. D production in B decays reconstruction Hadronic : B0D*p, D*r, D*a1 Semileptonic: B0 D* l n fit to cosqB-D*l variable 50 fb-1 mES cosqB-D*l • D reconstruction : D0Kp and DKpp New results from BABAR, Marie-Hélène Schune, BNL, May 20th 2002 39

  40. BF(BDX) ( ) ( ) ( ) M(Kp) M(Kpp) • Fit N(D) and correct for Brec background  BF(BDX) Brec : B0D*ln M(Kp) M(Kpp) Brec : B0D*p, D*r, D*a1 (*) Correlated syst. (**) Uncorrelated syst. New results from BABAR, Marie-Hélène Schune, BNL, May 20th 2002 40

  41. w(D) for neutral B mesons • Correlate the D and the B flavours : • For B0 : should correct for mixing • done on an optimized time interval (|Dt|<2.5 ps) reduced statistical uncertainty, Dmd dependance Mix cobs= = cd + w (1 - 2 cd) Mix+Unmix w( B0  D 0X) (%) Semilept. 15.9  3.5  2.4 Hadronic 9.6  4.7  1.1 Combined 13.1  2.8  1.5  0.6 Brec : B0D*ln Brec : B0D*p, D*r, D*a1 Unmix w( B0  DX)(%) Semilept. 7.3  3.7  1.9 Hadronic 8.9  7.1  1.8 Combined 7.7  3.3  1.4  0.8 Mix M(Kp) New results from BABAR, Marie-Hélène Schune, BNL, May 20th 2002 41

  42. D production in B decays BF( B0  D0X) = ( 50.3  3.0  3.7 ) % BF( B0  D0X) = ( 7.6  1.7  1.1 ) % BF( B0  D+X) = ( 32.8  2.5  3.5 ) % BF( B0  D-X) = ( 2.7  1.2  0.6 ) % • Results suggest B0 spectator quark effect negligible in wrong D production • Results consistent with world data (“B admixture”) • In the future : • Add the B sample • 100 fb-1 • start to look for Ds and Lc (looser Breco selection ?) 30 or 51 fb-1 Compare BF( B0  D0+ D+ X) = (83.1  6.4) % with world data: BF( Badmixt D0+ D+ X) = (78.5  3.4) % Better understanding of the overall picture of the B decays New results from BABAR, Marie-Hélène Schune, BNL, May 20th 2002 42

  43. Summary BF( B0  D0X) = ( 50.3  3.0  3.7 ) % BF( B0  D0X) = ( 7.6  1.7  1.1 ) % BF( B0  D+X) = ( 32.8  2.5  3.5 ) % BF( B0  D-X) = ( 2.7  1.2  0.6 ) % • A true factory of B mesons : • BF(B0+-) = (5.40.70.4) 10-6 • BF(B0K+-) = (17.81.10.8) 10-6 Unfortunately not enough to get B000 • BF(B000) < 3.4 10-6 at 90 % CL • CP violation results : • Spp =-0.010.370.07 • Cpp =-0.020.290.07 • “B recoil” physics is starting : • Semi leptonic measurements • D mesons production in B decays New results from BABAR, Marie-Hélène Schune, BNL, May 20th 2002 43

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