Alexander Leopold Felicitas Breibeck Christoph Schwanda. for the Belle Collaboration

Transcription

1 Full reconstruction of hadronic B 0 S decays at Belle Alexander Leopold Felicitas Breibeck Christoph Schwanda for the Belle Collaboration Insitute of High Energy Physics Austrian Academy of Sciences under Grant Nr. P26794-N20 Jahrestagung der Österreichischen Physikalischen Gesellschaft 2. September 2015 A. Leopold (HEPHY) Full reconstruction ÖPG 2015/09/02 1 / 11

2 Outline 1 Belle Detector Data Sample 2 Full Reconstruction Tag side/signal Side Hierarchical Approach Neural Networks 3 First Results 4 Outlook A. Leopold (HEPHY) Full reconstruction ÖPG 2015/09/02 2 / 11

3 Belle Detector Belle Detector at e + e collider KEKB in Tsukuba, Japan 1. Silicon Vertex Detector 2. Central Drift Chamber 3. Aerogel Cherenkov Counter 4. Time of Flight Counter 5. CsI Calorimeter 6. KLM Detector 7. Superconducting Solenoid 8. Superconducting Final Focussing System main scientific goals: measurement of CKM parameters and CP violating effects Nobel Price for Kobayashi and Maskawa in 2008 Charmonium states (X(3872)) A. Leopold (HEPHY) Full reconstruction ÖPG 2015/09/02 3 / 11

4 The Belle Data Sample - Υ(5S) Resonance hadronic Υ(5S) events σ b b 300pb udsc continuum b b events non-b B B 0, B + events B 0 S events f s 20% World s largest B meson dataset ( 770 million B B events) Also collected 121fb 1 at Υ(5S) Resonance (E CM = GeV), unique BS 0 dataset at lepton collider with σ b b = ± nb and f s = 17.2 ± 3.0 N B 0 s = f s σ b b Ldt = 7.1 ± 1.3 million B S B S B S B 0 S B 0 S B 0 S 90% 7% 3% B s B 0 s γ A. Leopold (HEPHY) Full reconstruction ÖPG 2015/09/02 4 / 11

5 Full Reconstruction final state particles: e ±, π ±, π 0, µ ±, K ±, K 0 s, γ hadronic decay: B 0 S leptonic decay: B 0 S π + D S τ τ + Φ π µ + ν µ ν τ π + ν τ K + K neutrinos not detected missing information on energy and momentum high combinatorial background A. Leopold (HEPHY) Full reconstruction ÖPG 2015/09/02 5 / 11

6 Full Reconstruction final state particles: e ±, π ±, π 0, µ ±, K ±, K 0 s, γ hadronic decay: B 0 S leptonic decay: B S 0 π + D S τ τ + Φ π ν µ µ + ν τ π + ν τ K + K neutrinos not detected missing information on energy and momentum high combinatorial background A. Leopold (HEPHY) Full reconstruction ÖPG 2015/09/02 5 / 11

7 Signal and Tag Side measure four-momentum of hadronically decaying tag side B 0 S t 1 ν l ν l t 2 Υ(5S) l B tag B sig t 3 t4 price to pay: reduces efficiency by factor of 1000 ν l π dertermines missing mass of signal side reduces combinatorial background A. Leopold (HEPHY) Full reconstruction ÖPG 2015/09/02 6 / 11

8 Hierarchical Approach use only events with < 12 charged tracks all intermediate particles individually reconstructed use neural networks in reconstruction, one for every mode of each particle preselection: charged tracks: cut on interaction point photons: minimum energy threshold π 0 : mass cut mass cut mass cut E = E B E beam M bc = E 2 beam (p B )2 A. Leopold (HEPHY) Full reconstruction ÖPG 2015/09/02 7 / 11

9 Neural Networks (NeuroBayes R ) Input layer Hidden layer Energy p t Likelihood p... Output Use network output for particle characterization. Get rid of background by cutting on network output. µ training A. Leopold (HEPHY) Full reconstruction ÖPG 2015/09/02 8 / 11

10 Preliminary Results training result for K 0 K + π Level 1&2 finished currently working on level 3 mass spectrums show good results comparing mass spectrum of K 0 achieved with preselection and with NN 0* K mass determine cut value, maximize FoM= S S+B entries preselection selection with NN mass [GeV] A. Leopold (HEPHY) Full reconstruction ÖPG 2015/09/02 9 / 11

11 Summary & Outlook Level 1 & 2 finished currently working on Level 3 once tag complete, verify validity with well known decay (e.g. B s D s π) tool will be used for Bs 0 τ + τ more analyses possible (Bs 0 D s lν, Bs 0 lτ) will gain experience for Belle 2 A. Leopold (HEPHY) Full reconstruction ÖPG 2015/09/02 10 / 11

12 Thank you for your attention. A. Leopold (HEPHY) Full reconstruction ÖPG 2015/09/02 11 / 11

13 backup Figure : Example of E/M bc distribution of a B 0 s decay. A. Leopold (HEPHY) Full reconstruction ÖPG 2015/09/02 1 / 4

14 Top 8 variables of remaining particles for NN training Table : e Variables Name Description ATC02 Particle ID e vs π PIDeid Particle ID ATC03 Particle ID e vs K trkpid PID info from TRK only pt transversal momentum accpid PID info from ACC only PIDmuid Particle ID µ, if it exists tofpid PID info from TOF only Table : Ks 0 Variables Name Description mass Particle mass dr r from K s finder Chi2 χ 2 of the fit dphi φ from K s finder PMag p from K s finder pt transversal momentum Zdist Zdist of the two helices px p x energy Energy Table : K Variables Name Description ATC32 Particle ID K+ vs π+ ATC30 Particle ID K vs e (de/dx) dedx-pull measured (de/dx)exp σ(de/dx) accpid Particle ID from ACC only energy Particle energy pidmuid Particle ID µ, if it exists tofpid Particle ID from TOF only ATC 31 Particle ID K vs µ Table : π 0 Variables Name Description Pi0Mass mass Pi0ChildAngle Angle of the two γ Pi01EAciD ECL AUX γ 1 ID of seed cell Pi00EAseed ECL AUX γ 0 energy of seed cell Pi01EAseed ECL AUX γ 1 energy of seed cell Pi0GammaMatch ECL γ 0 & γ 1 info if clusers match with CDC tracks pt p t energy Energy A. Leopold (HEPHY) Full reconstruction ÖPG 2015/09/02 2 / 4

15 Top 8 variables of remaining particles for NN training Table : π Variables Name Description ATC23 Particle ID π vs K PIDeid Particle ID e PIDmuid Particle ID µ dedxpull {(de/dx) measured (de/dx) exp}/σ(de/dx) ATC21 Particle ID π vs µ energy Energy dedxratio (de/dx) measured /(de/dx) expected tofpid Particle ID from TOF only Name EAe9 EAwidth EAseed EAnhits EAe9unf EAcID energy Table : γ Variables Description photon-like and isolation cut RMS shower width energy of seed cell crystals in the cluster photon-like & isolation cut unfolded ID of seed cell Energy A. Leopold (HEPHY) Full reconstruction ÖPG 2015/09/02 3 / 4

16 Level 2 NN training - training variables Table : Training variables used for level 2. Name Description sumchildnb Sum of NB output of all children. prodchildnb Product of NB of all children. ptot p of particle. ptotn p of child n. NBn NeuroBayes R output of child n. pseudoangn Angle between child momentum in mother s rest frame and mother s direction in Υ(5S) rest frame. energyn Energy of child n. daughterangle Angle between children n & m. distancevxip Distance of the fitted vertex and the interaction point. A. Leopold (HEPHY) Full reconstruction ÖPG 2015/09/02 4 / 4