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K 0 s reconstruction in ALICE

Investigating K0s reconstruction in ALICE experiment through realistic simulation. Evaluating algorithm efficiency, resolution, and impact of different selection criteria. Future work includes studying Λs reconstruction.

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K 0 s reconstruction in ALICE

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  1. K0s reconstruction in ALICE Giuseppe Lo Re INFN, Sezione di Catania, and Dipartimento di Fisica e Astronomia, Università di Catania, Italy, March 2002

  2. Summary • Introduction • Simulation • Optimization of cuts • Results • Conclusions

  3. Introduction V0 position = middle point between the two tracks at the distance of closest approach Dpn = distance of closest approach Sec. vertex Dpn Radial distance Primary vertex

  4. Simulation • B = 0.2 T • Aliroot v 3.06 • Event generator: HIJING (full) • - generated 31 events with b = 3 fm • “Slow” simulation of the ITS • Tracking V1 in the ITS (with 6 points) • - step 1: with vertex constraint • - rejection of the “primary tracks” • - step 2: without vertex constraint • Straight line approximation from the beam pipe backwards to the primary vertex • Combination of + and - tracks and application of the cuts • - search of K0S within a fiducial region (R=0.5-2.5 cm)

  5. List of the cuts used • Cut 1: product of the radial impact parameter (Dr-  Dr+) • Cut 2: distance of closest approach (Dpn) • Cut 3: angle between the K0s position vector and the K0s momentum () • Cut 4: impact parameter of the daughters (D) • Cut 5: 2 of the daughters

  6. Cut 1: product of the radial impact parameter Dr-  Dr+ < 0 Sec. vertex  - + Primary vertex Dr- Dr+

  7. Cut 2: distance of closest approach (Dpn) Dpn < 0.14 cm

  8. Cut 3: angle between the K0s position vector (R) and the K0s momentum (PK)  Cos  > 0.9985 PK Sec. vertex Primary vertex R

  9. Effect of cuts Dr-  Dr+ < 0 Without any cut Mass (GeV/c2) Dpn < 0.14 cm Cos  > 0.9985

  10. Results N. found K0S  2.5 per event

  11. x, y and z resolution of secondary vertices

  12. ,  and Pt resolution  = 5 mrad  = 3 mrad

  13. Efficiency of algorithm and cuts Eff = no. of found K0s / no. of findable K0s after the TPC-ITS tracking Found Eff. = 32 % Fake Prob. = 11 %

  14. Total found efficiency Eff = no. of found K0s / no. of generated K0s Found Eff. = 0.37 % Fake Prob. = 0.12 %

  15. Reconstructed Pt spectrum Reconstructed spectrum Generated spectrum

  16. Conclusions and future work • The problem of reconstructing K0S in ALICE is under investigation in a realistic simulation framework • An algorithm for Aliroot has been written and its resolution and efficiency have been evaluated • Evaluation of the effect of a different choice of the fiducial region • Simulations with a magnetic field of 0.4 T • Studies for reconstructing the s are already started

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