Update on chi_b studies

Transcript

1. Update on χb studies Alexander (Sasha) Mazurov University of Ferrara,

   Italy & CERN alexander.mazurov@cern.ch 19 December 2012 Sasha Mazurov (University of Ferrara) Update on χb studies 19 December 2012 1 / 11

2. My studies 1 Study of χb production. 2 Measurement of

   χb(3P) mass. Sasha Mazurov (University of Ferrara) Update on χb studies 19 December 2012 2 / 11

3. Study of χb production Cross sections Cross sections formula In

   each pT (Υ) bin calculate: σ(χb→Υγ) σ(Υ) = Nχb→Υγ NΥ × Υ χb→Υγ = Nχb→Υγ NΥ × 1 reco γ Calculate for each Υ(nS), n = 1, 2, 3 and χb(mP), m = 1, 2, 3 Get N from fits: NΥ from m(µ+µ−) and Nχb→Υγ from [m(µ+µ−γ) − m(µ+µ−)] (for better resolution) Compute efficiency from Monte-Carlo simulation Luminosity = 1015 ± 35pb−1, data collected in year 2011. Sasha Mazurov (University of Ferrara) Update on χb studies 19 December 2012 3 / 11

4. Study of χb production Cross sections Reconstruction Models were built

   on top of RooFit toolkit and unbinned maximum likelihood fits were performed. For NΥ: invariant mass Signal: sum of 3 Crystal Ball functions Background: exponential function. For Nχb→Υ(1S)γ : mass difference Signal: 3 Gauss functions Background: √ x × e−τx × (c1 + a1x + a2x2) + e−τx × (c2 + a3x + a4x2) (not enough resolution to separate χb(0,1,2) ) Sasha Mazurov (University of Ferrara) Update on χb studies 19 December 2012 4 / 11

5. Study of χb production Cross sections Number of χb (NP)

   → Υ(1S) decays Sasha Mazurov (University of Ferrara) Update on χb studies 19 December 2012 5 / 11

6. Study of χb production Cross sections Monte-Carlo Decay files were

   released (Gen/DecFiles v25r20). Will be produced during Xmass. Sasha Mazurov (University of Ferrara) Update on χb studies 19 December 2012 6 / 11

7. Study of χb production Cross sections χb → Υ(2S, 3S)

   Sasha Mazurov (University of Ferrara) Update on χb studies 19 December 2012 7 / 11

8. Study of χb production Measurement of χb(3P) mass Measurement of

   χb (3P) mass Sasha Mazurov (University of Ferrara) Update on χb studies 19 December 2012 8 / 11

9. Study of χb production Measurement of χb(3P) mass Selection optimization

   Background subtraction We can reduce the background by tightening cut on pT (γ) Can make a precise measurement of mχb(3P) Sasha Mazurov (University of Ferrara) Update on χb studies 19 December 2012 9 / 11

10. Study of χb production Measurement of χb(3P) mass Very preliminary

    results Next steps: Determine systematic errors Photon energy calibration mχb(2P) [GeV /c2] mχb(3P) [GeV /c2] ATLAS 10.530 ± 0.0050 D0 10.551 ± 0.0140 LHCb (prev) 10.2660 ± 0.0060 10.535 ± 0.0100 This study 10.2709 ± 0.0035stat 10.515 ± 0.0074stat Sasha Mazurov (University of Ferrara) Update on χb studies 19 December 2012 10 / 11

11. Study of χb production Measurement of χb(3P) mass Summary 1

    Studying the production of χb particles in LHCb, through the reconstruction of χb → Υγ decays, with the Υ decaying to µ+µ−. 2 Determined χb → Υ(1S)γ yields as a function of pT (Υ(1S)). 3 Measured mass of the χb(3P) state, which has been recently observed at LHC and TeVatron. 4 Finalize analysis (efficiencies, other decays,...). Sasha Mazurov (University of Ferrara) Update on χb studies 19 December 2012 11 / 11