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Analysis of the D + s  K + K - π + channel in the ALICE experiment

Analysis of the D + s  K + K - π + channel in the ALICE experiment. (4050 m. asl). Serhiy Senyukov Universit à & INFN di Torino. Open charm and QGP. π. D 0. A. K. c. QGP. π. -. c. D s. A. K. K. Detection of products. Primary production. Interaction with QGP.

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Analysis of the D + s  K + K - π + channel in the ALICE experiment

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  1. Analysis of theD+sK+K -π+ channel in the ALICE experiment (4050 m. asl) Serhiy Senyukov Università & INFN di Torino ALICE Italia 2008

  2. Open charm and QGP π D0 A K c QGP π - c Ds A K K Detection of products Primary production Interaction with QGP Decay of D mesons ALICE Italia 2008

  3. Results for D0 and D+ Pb-Pb @ 5.5TeV p-p @ 14 TeV 2<pT<3 GeV/c ALICE Italia 2008

  4. Why Ds? • Question: • We know that D0 and D+ can be reconstructed with high significance. Why do we need also Ds? • Answer: • To measure charm yield more precisely we need to measure as many channels as we can • Study of different ways of hadronization: • String fragmentation:Ds+ (cs) / D+ (cd) ~ 0.6 • it should be easier to take a light meson from a vacuum than the strange one • Recombination: • Ds+ (cs) / D+ (cd) ~ N(s)/N(d) (~ 1 at LHC?) • recombination occurs inside the medium. ALICE Italia 2008

  5. ALICE setup Inner Tracking System: Vertexing, Tracking,PID Time Projection Chamber: Tracking, PID Time-of-Flight detector: PID ALICE Italia 2008

  6. DsKKp Ds flight line p Primary Vertex K K Secondary vertex Selection strategy • invariant-mass analysis of fully-reconstructed topologies originating from displaced vertices • build triplets of tracks with correct combination of charge signsandlarge impact parameters • particle identification to tag the decay products • calculate the vertex (DCA point) of the tracks • good pointing of reconstructed D momentum to the primary vertex ALICE Italia 2008

  7. Ds vs. D+ & D0 * - without cuts, with Ideal PID at dη/dy=6000 ** - PbPb (0-5% central), NLO pQCD + Binary Scaling + EKS98, in central acceptance ALICE Italia 2008

  8. Cut tuning scheme • Signal – 2500 PYTHIA events with full simulation each containing 9100* Ds generated in the barrel acceptance (-0.9<η<0.9) forced to decay into hadronic channels: • D+sK+K0*K+K -π+ • D+sφπ+K+K-π+ • Background – 15000 HIJING • (Number of signal is negligible) • Significance– calculated with respect to 107 central events (1 year) * Number is tuned in order to have the same performance of the detector as in BKG event ALICE Italia 2008

  9. Single track selection • Cut: Pt>0.5 GeV/c • Cut: Pt>0.5 GeV/c • Cut: d0>35 μm 3 variables: • Pt(K) – Transverse momentum of Kaon* • Pt(π) – Transverse momentum of Pion* • d0 – impact parameter of track * Ideal PID is assumed Before cuts After cuts Pt of Ds (GeV/c) Pt of Ds (GeV/c) ALICE Italia 2008

  10. Combining tracks to pairs • Single tracks are combined to pairs with opposite sign (K+K- & K+π-) or (K-K+ & K-π+) • Crossing point is found using vertexing algorithm • Two values are calculated: • Dispersion of tracks around the cross-point: • Distance from cross-point to primary vertex • First cut is made on dispersion: σ<300 μm • Second cut is made on the distance: d(pair)<300 μm ALICE Italia 2008

  11. Triplet selection • Triplet of 3 tracks is formed • Secondary vertex is calculated • Dispersion of tracks around the vertex is found • Cuts are tuned in for Pt bins: ALICE Italia 2008

  12. Resonances separation • Ds decays via resonances • Calculation of Inv Mass for KK and Kπ pairs • Accept triplet if |M(KK)-m(φ)|<Δm1 OR |M(Kπ)-m(K0*)|<Δm2 Inv Mass (Kπ) Inv Mass (Kπ) Inv Mass (KK) Inv Mass (KK) ALICE Italia 2008

  13. Final multicut Θpoint π+ D+s Pt(Ds) Variables considered: • Cos Θpoint • Cos Φopening • Distance between primary and secondary vertex • Sum of impact parameters squared • Dispersion of secondary vertex (additional tuning) K+ Φopening K- Cos Point φ-like BKG Signal Ds via φ Cos Opening K0*-like BKG Signal Ds via K0* ALICE Italia 2008

  14. Results for Ideal PID φ K0* ALICE Italia 2008

  15. Conclusion and To-Do • Monte-Carlo simulation shows that reconstruction of the DsKKπ is feasible in the range of Pt down to 3 GeV/c. • Study of Real PID is in progress. Reduction of significance by factor of ~2 is expected • Bigger statistics for background events is needed to reduce the error and better tuning of cuts. • Case of pp collisions is under study. Some preliminary results without multicut are present. ALICE Italia 2008

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