V.Petracek TU Prague, UNI Heidelberg 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

V.Petracek TU Prague, UNI Heidelberg 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

V.Petracek TU Prague, UNI Heidelberg 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

V.Petracek TU Prague, UNI Heidelberg 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

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

V.Petracek TU Prague, UNI Heidelberg 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%

V.Petracek TU Prague, UNI Heidelberg 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 = , , (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 = , , (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 = , , (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

V.Petracek TU Prague, UNI Heidelberg 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

V.Petracek TU Prague, UNI Heidelberg 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

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

V.Petracek TU Prague, UNI Heidelberg 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

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

V.Petracek TU Prague, UNI Heidelberg 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

V.Petracek TU Prague, UNI Heidelberg 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)

V.Petracek TU Prague, UNI Heidelberg 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