1 / 48

Radiative Decays of the X(3872) in BaBar

Radiative Decays of the X(3872) in BaBar. Bryan Fulsom University of British Columbia SLAC Experimental Seminar March 3, 2009. Outline. Background Information Introduction to Charmonium and the X(3872) Recent Experimental Results Theoretical Predictions Analysis Description

olive
Download Presentation

Radiative Decays of the X(3872) in BaBar

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Radiative Decays ofthe X(3872) in BaBar Bryan Fulsom University of British Columbia SLAC Experimental Seminar March 3, 2009 Radiative Decays of the X(3872) in BaBar, SLAC Experimental Seminar Bryan Fulsom, March 3, 2009

  2. Outline • Background Information • Introduction to Charmonium and the X(3872) • Recent Experimental Results • Theoretical Predictions • Analysis Description • The BaBar Experiment • Event Reconstruction and Selection • Fit Strategy and PDFs • Results • Validation (MC and B cc1,2 K) • Systematic Uncertainties • X(3872) Results and Implications Radiative Decays of the X(3872) in BaBar, SLAC Experimental Seminar Bryan Fulsom, March 3, 2009

  3. Background Information Radiative Decays of the X(3872) in BaBar, SLAC Experimental Seminar Bryan Fulsom, March 3, 2009

  4. Introduction • November Revolution: discovery of the J/y in 1974 • First evidence of the charm quark • Strong confirmation of the quark model • Charmonium is a bound state of cc • Described by phenomenological models: • Analogous to hydrogen, positronium • Theory has enjoyed fairly good success • Several recent results from the B Factories: • Some discoveries fit naturally into the charmonium system • Many others cannot be accommodated by the model • QCD allows for more “exotic” possibilities • hybrids, tetraquark states, four-quark molecules Radiative Decays of the X(3872) in BaBar, SLAC Experimental Seminar Bryan Fulsom, March 3, 2009

  5. Basic Theoretical Description • Charmonium potential models (phenomenological): • non-relativistic (charm quarks are “heavy” compared to binding energy) • strong force potential via one gluon exchange (similar to Coulomb force) • quark confinement (increases linearly with separation) • Typical representation: plus extensions to include spin-dependent terms, relativistic corrections, etc. • Many successful predictions on masses, widths, branching fractions • Lattice QCD has made great advancements, but won’t be discussed here Radiative Decays of the X(3872) in BaBar, SLAC Experimental Seminar Bryan Fulsom, March 3, 2009

  6. Charmonium Production • Colour-suppressed b  c decay • Predominantly from B  cc K • e+e- annihilation/Initial State Radiation (ISR) • e+e- collision at/below nominal c.m. energy • JPC = 1-- • Double charmonium production • Typically one J/y or y(2S), plus second cc state • Two-photon production • Access to C = + states • pp annihilation • All quantum numbers available Radiative Decays of the X(3872) in BaBar, SLAC Experimental Seminar Bryan Fulsom, March 3, 2009

  7. Charmonium Decays • Annihilation: • Generally suppressed for bound state • Decay to leptons is a clean experimental signal • J/y  e+e-, m+m-, y(2S)  e+e-, m+m- • Radiative: • EM radiative transition emitting photon • Emit gluons producing light quarks • cc1,2 J/yg, y(2S)  J/yp+p- • Strong interaction: • Dominant above ~3.72 GeV (DD threshold) • OZI-suppressed below this mass Radiative Decays of the X(3872) in BaBar, SLAC Experimental Seminar Bryan Fulsom, March 3, 2009

  8. Exotic QCD • Meson Molecules • Weakly bound state of two mesons • Binding at long distance via pion exchange • Mesons decay as though free • “Tetraquarks” • Diquark-antidiquark bound by spin-spin interactions • Multiplets with non-zero charge and strangeness • Decay via rearrangement and dissociation • Charmonium hybrids • Charmonium with excited gluon • Doubly degenerate octet of states with exotic JPC • Decays similar to charmonium, though predictions vary Radiative Decays of the X(3872) in BaBar, SLAC Experimental Seminar Bryan Fulsom, March 3, 2009

  9. Charmonium Spectrum Spectroscopic notation: N2S+1LJ where L=S,P,D,F,... Angular momentum: J = L+S S(qq) = 0 or 1 Parity: P = (-1)L+1 Charge conjugation C=(-1)L+S Radiative Decays of the X(3872) in BaBar, SLAC Experimental Seminar Bryan Fulsom, March 3, 2009

  10. The X(3872) Radiative Decays of the X(3872) in BaBar, SLAC Experimental Seminar Bryan Fulsom, March 3, 2009

  11. Discovery of the X(3872) • Belle discovered a signal in B  J/yp+p- K; confirmed by CDF, D0 and BaBar • Narrow (G<2.3MeV) particle with mass m(X)=3871.4+/-0.6 MeV/c2 Radiative Decays of the X(3872) in BaBar, SLAC Experimental Seminar Bryan Fulsom, March 3, 2009

  12. X(3872)  J/yp+p- Dipion Mass • Belle and CDF analysed the p+p- mass distribution from X  J/yp+p- • Both seem to favour a “r-like” shape, with J/y-r in an S-wave • Shape in BaBar is similar, no attempt to fit Radiative Decays of the X(3872) in BaBar, SLAC Experimental Seminar Bryan Fulsom, March 3, 2009

  13. X(3872) Angular Analyses • CDF analysed angular distribution of daughters, and tested against various JPC assignments • Angular analysis compatible with both 1++ and 2-+ • c2 prob.(1++)=27.8%, (2-+)=25.8% Note: Angular analysis from Belle favours 1++ disfavours 0++, 0-+, 1+- Radiative Decays of the X(3872) in BaBar, SLAC Experimental Seminar Bryan Fulsom, March 3, 2009

  14. Evidence for X(3872)  J/y g • Both BaBar and Belle have found evidence for this radiative decay • J/y and g have charge parity C = –, implies X(3872) C = + Radiative Decays of the X(3872) in BaBar, SLAC Experimental Seminar Bryan Fulsom, March 3, 2009

  15. X(3872)  D0D0*K • Belle discovered X(3872) in B  D0D0p0K • Found mass 2.0s higher than W.A. for X(3872) • Recent update confirms D0D0* decay (8.8s) • Compute m(X)=3872.60.50.4 MeV/c2 • BaBar search confirms X(3872) signal (4.9s) • Ratio of D0D0p0/D0D0g matches D0* expectation • Mass ~4.5s above X(3872) • Angular study inconclusive Radiative Decays of the X(3872) in BaBar, SLAC Experimental Seminar Bryan Fulsom, March 3, 2009

  16. X(3872) Interpretation • Summary of X(3872) Properties: • Narrow with mass m(X)=3871.4+/-0.6 MeV/c2 • Observed in X(3872) J/ypp, dipion mass is “r-like” • Also seen in decays X(3872)  D0D0* and X(3872)  J/y g • Spin-parity identified as either JPC = 1++ or 2-+ • Charmonium Hybrid • Lightest mass prediction m(ccg)>4.2GeV/c2 • Tetraquark State • No evidence for charged/neutral mass splitting • No evidence for charged partners Radiative Decays of the X(3872) in BaBar, SLAC Experimental Seminar Bryan Fulsom, March 3, 2009

  17. X(3872) Interpretation • Conventional Charmonium • Angular analysis: cc1(23P1) (1++) or hc2(11D1) (2-+) • Not expected to violate isospin, X J/y r • X(3872) is narrow and does not decay X DD • Expect hc2 J/y g to be suppressed • cc1(2P) somewhat inconsistent with predicted mass • D0D0* Molecular interpretation • m(D0) + m(D0*) = 3871.8+/-0.4 MeV/c2 • Decays to X(3872) J/y r, D0D0*, J/y w expected • Compatible with JPC = 1++ assignment • Successful predictions vary by model Study radiative decays as a diagnostic! Radiative Decays of the X(3872) in BaBar, SLAC Experimental Seminar Bryan Fulsom, March 3, 2009

  18. X(3872)  cc g Theoretical Predictions • Electromagnetic transitions for charmonium: • hc2 (11D1) y(nS)g forbidden (M2) • cc1 (23P1)  [J/y,y(2S)]g allowed (E1) • Predictions for relative rate varies, but are of similar order Radiative Decays of the X(3872) in BaBar, SLAC Experimental Seminar Bryan Fulsom, March 3, 2009

  19. X(3872)  cc g Theoretical Predictions • Radiative decays of the D0D0* molecule: • Decay to J/yg is possible in vector meson dominance scenario • y(2S)g proceeds via annihilation, highly disfavoured • Caveat: Theory-dependent, few definite predictions exist Radiative Decays of the X(3872) in BaBar, SLAC Experimental Seminar Bryan Fulsom, March 3, 2009

  20. X(3872)  cc g Theoretical Predictions • Radiative decays may discriminate between hc2, cc1(2P), and D0D0* “Perhaps the most robust diagnostic is the gy’ decay mode...Clearly a measurement of the gJ/y and gy’ decay modes of the X(3872) will provide compelling clues to its internal structure.” Radiative Decays of the X(3872) in BaBar, SLAC Experimental Seminar Bryan Fulsom, March 3, 2009

  21. Analysis Description Radiative Decays of the X(3872) in BaBar, SLAC Experimental Seminar Bryan Fulsom, March 3, 2009

  22. The BaBar Experiment Radiative Decays of the X(3872) in BaBar, SLAC Experimental Seminar Bryan Fulsom, March 3, 2009

  23. The BaBar Experiment Radiative Decays of the X(3872) in BaBar, SLAC Experimental Seminar Bryan Fulsom, March 3, 2009

  24. Analysis Description • Search for radiative decays X(3872)  [J/y,y(2S)]g • Refit event with B mass constrained • Variables of interest: mmiss = |pe+e- – pB|,mX, mK* • Select candidate with best unconstrained mB • Optimize selection cuts on MC using FOM: Radiative Decays of the X(3872) in BaBar, SLAC Experimental Seminar Bryan Fulsom, March 3, 2009

  25. Event Selection • B Meson Variables • B Vertex P(c2) • Reconstructed B mass • Kinematic Variables • mmiss, mX • cc Masses • Unconstrained J/y, y(2S) mass • Event shape • Isotropy of momenta • Photon variables • Energy and shower-related • Kaon variables • Mass selection • Decay length and vertexing Radiative Decays of the X(3872) in BaBar, SLAC Experimental Seminar Bryan Fulsom, March 3, 2009

  26. Signal Extraction Strategy • Fit strategy: 1. Unbinned 1(2)-D ML fit to mmiss (and mK* if applicable) 2. Use sPlot technique to get projection of signal events in mX 3. Fit to mX to extract number of signal events • sPlot useful for isolating signal-like events for “bump-hunting” • Test on well-known B cc1,2 (J/yg)K decays first, then unblind for X(3872) • Determine PDFs from truth-matched MC • Fix most parameters except for normalization and background in mX fit Radiative Decays of the X(3872) in BaBar, SLAC Experimental Seminar Bryan Fulsom, March 3, 2009

  27. PDF Definitions - Signal • Selected the following PDF shapes: • mmiss: Crystal Ball (s ~ 5 MeV/c2) • mX: Double Gaussian (s ~ 5, 10 MeV/c2) • mK*: BW * Gaussian (s ~ 45, 10 MeV/c2) Radiative Decays of the X(3872) in BaBar, SLAC Experimental Seminar Bryan Fulsom, March 3, 2009

  28. PDF Definition – Background • Bkgd. PDFs: mmiss: ARGUS + peak, mX: Linear (+ peak), mK*: Linear (+ peak) Radiative Decays of the X(3872) in BaBar, SLAC Experimental Seminar Bryan Fulsom, March 3, 2009

  29. sPlot Procedure • sPlot technique uses information from discriminant variables (mmiss) to unfold the distribution in uncorrelated control variable (mX) by species (signal, background) 1. Conduct ML fit using PDFs (F) in variable (y) to get Nb events of species (b) 2. For species (a), each event (i) is assigned weight: where Vaa is the covariance matrix between two species (a, a) 3. Produce a histogram of the control variable using the weights w for species a Radiative Decays of the X(3872) in BaBar, SLAC Experimental Seminar Bryan Fulsom, March 3, 2009

  30. Signal Extraction Example • Begin with mixture of events • Perform fit to mmiss to get Nsig and Nbkgd • Generate sPlots based on the yield and distributions • Can examine signal or background species • Fit sPlot for signal to get X(3872) yield Radiative Decays of the X(3872) in BaBar, SLAC Experimental Seminar Bryan Fulsom, March 3, 2009

  31. Fit Validation • Test fit with MC toys: • Insert expected number of signal events from MC • Generate background samples from distributions • Repeat N times • Truth-matched MC trials • Measure of bias: PDFs determined on truth, “true” events should work • Non-truth-matched MC trials • Measure “fit efficiency” (ie: how well PDFs match data and extract results) • Other trials • X(3872) with null result, 8 times estimated BF (y(2S)g), varying number of cc2 events, with and without NR backgrounds, crossfeed from other K and cc modes, X(3872)  J/ y p+p- background, etc. Radiative Decays of the X(3872) in BaBar, SLAC Experimental Seminar Bryan Fulsom, March 3, 2009

  32. Efficiency • Determine signal extraction efficiency in two stages • Cut/Reconstruction efficiency • Number of events from MC reconstructed and passing all selection cuts • Fit efficiency from MC toy trials • Described on previous slide • General comment: • e decreases as N tracks increases • Fit e decreases as N p increases and Eg decreases Radiative Decays of the X(3872) in BaBar, SLAC Experimental Seminar Bryan Fulsom, March 3, 2009

  33. Results and Implications Radiative Decays of the X(3872) in BaBar, SLAC Experimental Seminar Bryan Fulsom, March 3, 2009

  34. B cc1,2 K Results • Observe signals in all decay modes • Consistent with PDG, and best measurement for K+, KS and K*+ modes • Unexpected B0 cc2 K*0 • Analysis of Run 1-3 subset consistent with previous BaBar result • Set limits on other modes Radiative Decays of the X(3872) in BaBar, SLAC Experimental Seminar Bryan Fulsom, March 3, 2009

  35. B cc1,2 K Systematic Uncertainties • Primarily for B cc1 K; statistics-dominated for B cc2 K • Systematic uncertainties on the B cc1 K yield are small • Generally dominated by effects beyond this analysis Radiative Decays of the X(3872) in BaBar, SLAC Experimental Seminar Bryan Fulsom, March 3, 2009

  36. Summary ofcc1,2 K Results Radiative Decays of the X(3872) in BaBar, SLAC Experimental Seminar Bryan Fulsom, March 3, 2009

  37. X(3872)  J/y g Results • Find ~3.6s evidence for X(3872)  J/y g • No evidence in other decay modes • Measure: BF(B+ X(3872) K+) x (X(3872)  J/y g ) = (2.8+/-0.8+/-0.2) x 10-6 • Consistent with previous: (3.3+/-1.0+/-0.3) x 10-6 Radiative Decays of the X(3872) in BaBar, SLAC Experimental Seminar Bryan Fulsom, March 3, 2009

  38. X(3872) y(2S)g Results • First evidence for X(3872) y(2S) g (~3.5s significance) • Measure: BF(B+ X(3872) K+) x (X(3872) y(2S) g ) = (9.5+/-2.7+/-0.9) x 10-6 • Ratio of BFs: (X(3872) y(2S) g) / (X(3872) J/y g) = 3.4  1.4 Radiative Decays of the X(3872) in BaBar, SLAC Experimental Seminar Bryan Fulsom, March 3, 2009

  39. X(3872) Systematic Uncertainties • Entirely statistics-dominated in the X(3872) modes • Most effects are related to the signal yield, not the BF calculation • Largest concern is uncertainties in MC/data modeling Radiative Decays of the X(3872) in BaBar, SLAC Experimental Seminar Bryan Fulsom, March 3, 2009

  40. Summary of X(3872) Results Radiative Decays of the X(3872) in BaBar, SLAC Experimental Seminar Bryan Fulsom, March 3, 2009

  41. Full mX Range Radiative Decays of the X(3872) in BaBar, SLAC Experimental Seminar Bryan Fulsom, March 3, 2009

  42. Results and Implications • Results • Best B cc1K measurement, limits on cc2, possible B cc2 K*0 evidence • Updated BF(B+  X(3872)K+)(X(3872)  J/y g) • First evidence for X(3872) y(2S) g • Accepted to PRL, to appear soon • Implications: • Hybrids and tetraquark already ruled out • X(3872) y(nS) g disfavours 2-+hc2(1D) charmonium • Large [y(2S) g / J/y g] ratio unexpected for D0D0* • Consistent with 1++cc1(2P) charmonium Radiative Decays of the X(3872) in BaBar, SLAC Experimental Seminar Bryan Fulsom, March 3, 2009

  43. Conclusions? • Can X(3872) = cc1(2P)fit into the charmonium model? • cc1(2P) mass prediction is too high • Explanation for isospin violation and cc1(2P)  DD suppression • Can X(3872) y(2S)g be reconciled with molecular model? • Theoretical work needed to explain large BF(D0D*0y(nS) g) • What do we learn regarding X(3872) structure from this? • Perhaps neither purely molecular nor charmonium • D0D*0 – cc1(2P) mixing or other phenomena? The X(3872) saga continues... Radiative Decays of the X(3872) in BaBar, SLAC Experimental Seminar Bryan Fulsom, March 3, 2009

  44. Backup Slides Radiative Decays of the X(3872) in BaBar, SLAC Experimental Seminar Bryan Fulsom, March 3, 2009

  45. Charmonium Spectrum Radiative Decays of the X(3872) in BaBar, SLAC Experimental Seminar Bryan Fulsom, March 3, 2009

  46. X(3872)  J/yp+p- Updates • Both Belle and BaBar have updated B  X(3872)[XJ/yp+p-] K results • Belle finds no mass splitting, equal ratio between the B0 and B+ decay modes: BaBar measurement confirms, though suffers statistically Sets limit on width: G<3.3 MeV Radiative Decays of the X(3872) in BaBar, SLAC Experimental Seminar Bryan Fulsom, March 3, 2009

  47. X(3872)  J/yw Conflict • Belle searched for B  X(3872)[XJ/yp+p-p0] K • 3p-invariant mass shows enhancement assumed to be w p+p-p0 • Separate BaBar analysis of B  KwJ/y • Observe Y(3940), no evidence for X(3872) • ie: X  J/yp+p-p0 not necessarily X  J/yw Radiative Decays of the X(3872) in BaBar, SLAC Experimental Seminar Bryan Fulsom, March 3, 2009

  48. X(3872) Null Results • Upper limits and null results: • X  J/yh = consistent with “molecule” • X  DD = rules out 0+, 1-, 2+, ... • X  cc1,2g = rules out charmonium possibilities • X J/y p- p0 = no charged partner Radiative Decays of the X(3872) in BaBar, SLAC Experimental Seminar Bryan Fulsom, March 3, 2009

More Related