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Detection of D +/- hadronic 3-body decays in the CBM experiment

Detection of D +/- hadronic 3-body decays in the CBM experiment. D +/- K p p , B. R. 9 % , c t = 317 m m , 25 AGeV Au-Au. Detector setup in simulation Signal and Background simulation Acceptance S/B , Detection limit, Significance

sydney-fleming
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Detection of D +/- hadronic 3-body decays in the CBM experiment

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  1. Detection of D+/- hadronic 3-body decays in the CBM experiment • D+/- K p p , B. R. 9 % , c t = 317 mm , 25 AGeV Au-Au • Detector setup in simulation • Signal and Background simulation • Acceptance • S/B , Detection limit, Significance • Effects of pixel geometry and tracking • Other possible cuts

  2. Detector setup in simulation • 7 tracking stations • First two used for track reconstruction • Q acceptance 110 – 433 mrad • No magnetic field • Ideal P reconstruction • Ideal PID • Pixel position resolution s = 20 mm • Pixel geom. ~ 60 x 300 mm

  3. Signal and Background simulation SIGNAL • D+/- Kp p generated in kinematic decay generator • Thermal Pt spectrum T = 175 MeV • Gaussian rapidity with s = 0.6 • Decay exponential in CMS , boosted to LAB

  4. Signal and Background simulation BACKGROUND • Pt and y parametrization based on uRQMD – same as used for D0 • <K-> = 13 / event (in 4p) • <p+> = 328 / event (in 4p) • Still only limited statistics

  5. Acceptance K p • Geometrical acceptance for signal is 18% (all 3 products accepted) • Geometrical acceptance for background tracks 0.462 • In acceptance <K> = 6 , <p> = 151 Triplets

  6. S/B , Detection limit, Significance b Background b Signal 8.16 10-3 2.75 10-3 • Main cut on track impact parameter b • Done before triples are made – reduces CPU time • B estimate based on fit of the b distribution • B triplets = all 3 tracks have b>b_max and invariant mass <1.8,2> GeV 1.1 10-3 4.79% 30%,23%,17%

  7. S/B , Detection limit, Significance BACKGROUND 2 • Probability to 2p + K with b>b_max in event is given by Be = (Np)p3(1-p)Np-2 NK = 0.5NKNp(Np-1)p3(1-p)Np-2 • Be = 1.1 10-2 , 9.37 10-4 , 7.6 10-5 (for b_max 0.2 , 0.25 ,0.3 mm) • Combined with probability, that background triplet will be found in signal region we obtain B = 5.14 10-4 , 4.42 10-5 , 3.58 10-6 (for the respective b_max ) SIGNAL • B.R. 9% , <D0> ~10-2, <D+> ~0.3 <D0>, Geometrical acceptance 18%, 30%-17% of signal remains after the b_cut 0.2, 0.25, 0.3 mm • S = 2.916 10-5 , 2.235 10-5 , 1.652 10-5 (for the respective b_max ) SIGNAL/BACKGROUND & SIGNIFICANCE • S/B = 0.056 , 0.505 , 4.16(for the respective b_max ) • significance = 1.3 , 3.5 , 8 (for 1Mevt) , for b_max=0.2mmis the detection limit ~6Mevt (for significance >3)

  8. Effects of pixel geometry and tracking • Pixel size 60 x 300 mm • Pixel orientation in first 3 layers optimizes resolution in non-bending plane ... precise determination of y-z projection of the displaced track • In Stations 4-7 optimized for momentum resolution

  9. Effects of pixel geometry and tracking • Implemented “Toy” tracking in idealized dipole magnetic field • Studied influence of tracking and pixel size on SV reconstruction resolution and on reconstructed invariant mass

  10. Effects of pixel geometry and tracking Pixel 60 x 300 mm orientation 3-4 Isotropic hit resolution 20 mm

  11. Effects of pixel geometry and tracking • Effect of multiple scattering dominates • Mass resolution with ideal hit resolution is very similar • With this resolution would be possible to decrease width of the mass window and to improve S/B Isotropic hit resolution 20 mm

  12. Other possible cuts Mean distance between tracks in their closest point. This cut is effective on fake tracks Isotropic hit resolution 20 mm

  13. Other possible cuts Isotropic hit resolution 20 mm Triplet impact parameter distance between PV and intersection of the line defined by reconstructed SV and total momentum 3-vector of products. This cut is effectively momentum conservation cut smeared by position resolution of the SV Maximum of this distribution ~ sx(y) SV

  14. Other possible cuts Cuts in Dalitz plane Better to avoid Use with great care Selection of resonant decays via K*(892) and K*(1430)

  15. Conclusions • Reconstruction of D 3-body hadronic decays is possible under idealized conditions considered in this study • The main unknown factor is amount of fake tracks produced by tracking • In the next phase will be used the tracking algorithm from Ivan Kisel • There is still uncertainty in the fit of background b due to statistics – more background events are needed

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