1. V.Petracek TU Prague, UNI Heidelberg 18.10.03 GSI Detection of D +/- hadronic 3-body decays in the CBM experiment ● D +/- K  B. R.  c  = 317  m, 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. V.Petracek TU Prague, UNI Heidelberg 18.10.03 GSI Detector setup in simulation ● 7 tracking stations ● First two used for track reconstruction ●  acceptance 110 – 433 mrad ● No magnetic field ● Ideal P reconstruction ● Ideal PID ● Pixel position resolution  = 20  m ● Pixel geom. ~ 60 x 300  m

3. V.Petracek TU Prague, UNI Heidelberg 18.10.03 GSI Signal and Background simulation ● D +/- K  generated in kinematic decay generator  Thermal Pt spectrum T = 175 MeV  Gaussian rapidity with  = 0.6  Decay exponential in CMS, boosted to LAB SIGNAL

4. V.Petracek TU Prague, UNI Heidelberg 18.10.03 GSI Signal and Background simulation ● Pt and y parametrization based on uRQMD – same as used for D0 ● = 13 / event (in 4  ) ● = 328 / event (in 4  ) ● Still only limited statistics BACKGROUND

5. V.Petracek TU Prague, UNI Heidelberg 18.10.03 GSI Acceptance ● Geometrical acceptance for signal is 18% (all 3 products accepted) ● Geometrical acceptance for background tracks 0.462 ● In acceptance = 6, = 151  K Triplets

6. V.Petracek TU Prague, UNI Heidelberg 18.10.03 GSI S/B, Detection limit, Significance ● 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 GeV b Signal b Background 4.79% 30%,23%,17% 8.16 10 -3 2.75 10 -3 1.1 10 -3

7. V.Petracek TU Prague, UNI Heidelberg 18.10.03 GSI S/B, Detection limit, Significance ● Probability to 2  K with b>b_max in event is given by B e = ( N  )p 3 (1-p) N  -2 N K = 0.5N K N   N   p 3 (1-p) N  -2 ● B e = 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 ) 2 BACKGROUN D ● B.R. 9%, ~10-2, ~0.3, 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 ● S/B = 0.056, 0.505, 4.16 (for the respective b_max ) ● significance = 1.3, 3.5, 8 (for 1Mevt ), for b_max=0.2mm is the detection limit ~6Mevt (for significance >3) SIGNAL/BACKGROUND & SIGNIFICANCE

8. V.Petracek TU Prague, UNI Heidelberg 18.10.03 GSI Effects of pixel geometry and tracking ● Pixel size 60 x 300  m ● 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. V.Petracek TU Prague, UNI Heidelberg 18.10.03 GSI 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. V.Petracek TU Prague, UNI Heidelberg 18.10.03 GSI Effects of pixel geometry and tracking Pixel 60 x 300  m orientation 3-4 Isotropic hit resolution 20  m

11. V.Petracek TU Prague, UNI Heidelberg 18.10.03 GSI Effects of pixel geometry and tracking Isotropic hit resolution 20  m ● 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

12. V.Petracek TU Prague, UNI Heidelberg 18.10.03 GSI Other possible cuts Mean distance between tracks in their closest point. This cut is effective on fake tracks Isotropic hit resolution 20  m

13. V.Petracek TU Prague, UNI Heidelberg 18.10.03 GSI Other possible cuts 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 ~  x(y) SV Isotropic hit resolution 20  m

14. V.Petracek TU Prague, UNI Heidelberg 18.10.03 GSI 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. V.Petracek TU Prague, UNI Heidelberg 18.10.03 GSI 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