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Studies of the Branching Ratio for η  µ + µ - decay

Studies of the Branching Ratio for η  µ + µ - decay. Frascati, Phi Decay Meeting 5.02.2008. Jarosław Zdebik. PLAN. Physics motivation, previous experiments and results. Simulation studies for the signal and background with Geanfi. Physic motivation.

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Studies of the Branching Ratio for η  µ + µ - decay

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  1. Studies of the Branching Ratio for ηµ+µ- decay Frascati, Phi Decay Meeting 5.02.2008 Jarosław Zdebik

  2. PLAN Physics motivation, previous experiments and results. Simulation studies for the signal and background with Geanfi.

  3. Physic motivation 1. The dilepton pair production decays can serve to study the structure of decaying hadrons (Form Factor shape) 2. These decays gives a chance to study the physics beyond the Standard Model (searching a candidate for the dark matter particle) 3. Recent BR value measured by SATURNE is equal to 1.3±0.2 (~20% ,~100 events) times the unitarity bound (4.3*10-6) [calculated with VDM] 4. Rare decay - BR= 5.8 * 10-6

  4. Previous measurements of the BR(ηµ+µ- ) 1968 – BROOKHAVEN upper bound for ηµ+µ- 1969 – CERN Thefirst observation of this decay. 1980 (published) – SERPUKHOV [Institute for High Energy Physics, USSR] Phys. Lett. B V. 97, Pages 471-472 Measured result is: 27±8 events Phys. Rev. Lett. V70, N7

  5. Previous measurements of the BR(ηµ+µ- ) (2) 1993 (published) - SATURNE Measured 100 events of and 8 events of background 1994 (published) – SATURNE II Phys. Rev. D 50, 92-103 Measured 114 events of and 14 events of background

  6. How many events for we expect? KLOE data = 100 000 000 η mesons (L=2.5 fb-1) BR(ηµ+µ-) = 5.8 * 10-6 PDG(2008) If reconstruction efficiency=100% Number of reactions = 100 000 000 * 5.8 * 10-6 = 580 events (reactions) (5 x Saturne events) Need to perform efficiency studies in order to estimate how many events we should see. Very important background rejection (especially from e+e-u+u-g)

  7. The value in PDG 2008, Was calculated as the average for Serpukhov and Saturne II results

  8. SERPUKHOV [Institute for High Energy Physics, USSR] near Moscov CEA at Saclay, near Paris, SATURNE synchrotron

  9. Reaction mechanism C parity: +1 -1 η γ l+ γ* η F(q12,q22) l- γ* Dominant mechanism within the Standard Model: second order electromagnetic process, F(q12,q22) arXiv:0711.3531v3

  10. Expected background channels for ϕ  ηγ 1.304% ηµ+µ- 5.8 *10-6 collision: e+e-µ+µ-γ Signature of signal: One neutral cluster in calorimeter, Two charged tracks in Drift Chamber e+e-µ+µ- e+e- ?? e+e-e+e- e+e- γ?? e+e-π+π-γ e+e-π+π- π0  π+π-γ γ e+e-e+e-γ ?? eta decays: phi decays: ηπ+π- π0π+π-γ γ 22.73% ηπ+π-γ 4.6% ϕe+e- 2.97 *10-4 ?? ϕµ+µ- 2.86 *10-4 ηe+e-γ 6.8 *10-3 ηµ+µ-γ 3.1 *10-4 ϕ π+π- 7.3 *10-5 ϕ π+π- γ 4.1 *10-5 η  π+π- 1.3 *10-5 ϕµ+µ- γ 1.4 *10-5

  11. Simulations Signal: simulated with the standard GEANFI package, (stand alone simulation) Background : GEANFI + phokara generator (e+e-µ+µ-γ) Reconstruction and production prod2ntu.hbook was performed using standard kloe „datarec.exe” program

  12. Geanfi studies [NTMC - KINE] 50 000 events Cut: 541.0 < Inv mass µ+µ- < 554.0 e+e-µ+µ-γ ηµ+µ-

  13. GeanFi studies [NTV – tracks connected with vertex] 50 000 events Cut: 541.0 < Inv mass µ+µ-< 554.0 ηµ+µ- s=1.7 MeV e+e-µ+µ-γ

  14. Background from e+e-µ+µ-γ σ(e+e- ϕ η γ µ+µ- γ) ~ 3.1 *10-6 * 1.304 *10-2 * 5.8 *10-6 = 2.3 *10-4 [nb] σ(e+e-µ+µ-γ) ~ 30.7 [nb] Ratio S/B~10-5 before any cut.

  15. Inv mass studies – kine MC Cut: 541.0 < Inv mass < 554.0 B/S ~ 62.5 Inv mass studies – Recon Tracks connected with vertex – DC signal Cut: 541.0 < Inv mass < 554.0 B/S ~ 300

  16. Angular distributions for muons+

  17. Angular distributions for photon Statistic: 50000 events

  18. How we reconstructed „gamma quanta” (neutral) cluster ? 1. Extracted neutral cluster using TRACK to CLUSTER association BANK 2. Time window condition: If(time_window > 2.0) smaller_window = 2.0 If(time_window < 2.0) smaller_window = time_window if(delta_time_clu < smaller_window)  calculate:

  19. Energy distributions for photon Strongly correlated with the invariant mass for eta

  20. Cuts efficiency studies

  21. Conclusions and futher steps -- perform efficiency studies in the respect to estimate a realistic number of reactions -- good cut: invariant mass of the muons (541 < Inv mass < 554) -- additional background recjection should be given by: optimizing invariant mass of the muon (Dm =5 MeV) and angular cuts -- perform p/mu separation

  22. Thanks for attention

  23. BACKUP SLIDES

  24. TRACKS to VERTEX reconstruction LOOP of tracks connected to the vertex, „vv” LOOP of all reconstructed tracks, „tt” If(trkind[tt]==trknumv[vv]) If(trtype1 == 5  mion+) If(trtype1 == 6  mion-)

  25. Why we need this BR ? • The real part of the amplitude of ηe+e- decay can be estimated using the measured value of BR(ηµ+µ-), etc. arXiv:0711.3531v3

  26. Dark matter – cluster bullet • Evidence for existing Dark Matter in Universe. Galactic gas (red color), Dark matter (blue color). Year: 2006

  27. Analysis goals Present measurement: 16% precision on the BR etamu+mu- Goal of the analysis: Measurement of the BR at 8% precision level or better. Enhancement on respect the predicted value of 5.11 ± 0.20 is expected from the KTev result on

  28. Inv mass studies – kine MC Cut: 541.0 < Inv mass < 554.0 62.5 times higher background than signal

  29. Inv mass studies – ntv MC Tracks connected with vertex – DC signal Cut: 541.0 < Inv mass < 554.0 250 times higher background than signal

  30. Unitarity bound Y and X are the imaginary (absorptive) and real (dispersive) components, respectively, of the normalized dimensionless amplitude in Pl+l- decay for unitarity bound: BR(ηµ+µ-)unit.= BR(ηγγ)*1.07*10-5=4.3*10-6 Electromagnetic decays of light mesons Institute for High Energy Physics, Serpukhov, U.S.S.R Physics Reports 128. No. 6 (1985) 301-376

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