Λ reconstruction in the magnetic field

1. Λ reconstruction in the magnetic field Evgeny Kryshen (PNPI, SPbSPU)

2. 10 000 central Au-Au collisions at 25 AGeV UrQMD generator CBMROOT framework OCT04 Magnetic field v03b Strip hits with 10 μm resolution No particle ID Ideal track finding (more than 3 MC points) Momentum and vertex reconstruction with Kalman filter (4-order Runge-Kutta extrapolation in magnetic field) Simulation framework Simulation meeting

3. Acceptance for Λ Initial distribution Acceptance Total acceptance STS: 15.8% Simulation meeting

4. Momentum fit performance Simulation meeting

5. Secondary vertex fit performance Z-vertex resolution: 340 μm Momentum resolution: 0.64% Invariant mass resolution: 0.78 MeV 0.86 MeV for 1% momentum resolution assumption 1.3 MeV for parabolic approximation (TSR) Simulation meeting

6. Applying cuts • The following variables were considered to cut the background: • bpp – impact parameter of accepted particles • pca – z position of secondary vertex • dca – distance of closest approach • bla – impact parameter of pair momentum Simulation meeting

7. Impact parameter of Λdaughter candidates Positively charged particles Negatively charged particles Simulation meeting

8. Vertex parameters Z position of the fitted vertex Distance of closest approach Simulation meeting

9. Pair impact parameter (bla) Simulation meeting

10. Selection of the first cut Conclusion: impact parameter cut is the strongest one Simulation meeting

11. Selection of the second cut Simulation meeting

12. Selection of the optimal cut value Simulation meeting

13. Invariant mass spectra Simulation meeting

14. Reconstruction of initial distributions Corrected signal Initial distribution Simulation meeting

15. Reconstructed pT distributions y = 1.0 – 1.2 y = 1.8 – 2.0 Simulation meeting

16. Reconstructed rapidity spectrum Initial yield: 40.46 Reconstructed: 40.30 Simulation meeting