29/08/2008ALICE Italia Analysis of the D + s  K + K - π + channel in the ALICE experiment Serhiy Senyukov Università & INFN di Torino (4050 m. asl)

Open charm and QGP 29/08/2008ALICE Italia QGP A A c DsDs K K π D0D0 π K Primary production Interaction with QGP Decay of D mesons Detection of products c -

Results for D 0 and D + 29/08/2008ALICE Italia <p T <3 GeV/c 14 TeV 5.5TeV

29/08/2008ALICE Italia Question: We know that D 0 and D + can be reconstructed with high significance. Why do we need also D s ? Answer: 1.To measure charm yield more precisely we need to measure as many channels as we can 2.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. Why D s ?

ALICE setup 29/08/2008ALICE Italia Inner Tracking System: Vertexing, Tracking,PID Time Projection Chamber: Tracking, PID Time-of-Flight detector: PID

Selection strategy 6 invariant-mass analysis of fully- reconstructed topologies originating from displaced vertices  build triplets of tracks with correct combination of charge signs and large 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 Primary Vertex D s flight line Secondary vertex  K K D s  KK  29/08/2008ALICE Italia 2008

29/08/2008ALICE Italia D s vs. D + & D 0 D0D0 D+D+ DsDs Combinations * 10 6 pairs10 9 triplets 10 8 triplets cτcτ123 μm312 μm150 μm Hadronic branching ratio 3.8%9.2%4.3% Abundance** 3095 * - without cuts, with Ideal PID at dη/dy=6000 ** - PbPb (0-5% central), NLO pQCD + Binary Scaling + EKS98, in central acceptance

29/08/2008ALICE Italia Cut tuning scheme o Signal – 2500 PYTHIA events with full simulation each containing 9100* D s generated in the barrel acceptance (-0.9<η<0.9) forced to decay into hadronic channels: o D + s  K + K 0 *  K + K - π + o D + s  φπ +  K + K - π + o Background – HIJING (Number of signal is negligible) o Significance – calculated with respect to 10 7 central events (1 year) * Number is tuned in order to have the same performance of the detector as in BKG event

29/08/2008ALICE Italia Single track selection 3 variables: P t (K) – Transverse momentum of Kaon* P t (π) – Transverse momentum of Pion* d 0 – impact parameter of track Before cutsAfter cuts  Cut: P t >0.5 GeV/c  Cut: d 0 >35 μm * Ideal PID is assumed P t of Ds (GeV/c)

29/08/2008ALICE Italia 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

29/08/2008ALICE Italia 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 P t bins:

29/08/2008ALICE Italia Resonances separation D s decays via resonances Calculation of Inv Mass for KK and Kπ pairs Accept triplet if |M(KK)-m(φ)|<Δm 1 OR |M(Kπ)-m(K 0 *)|<Δm 2 Inv Mass (K π) Inv Mass (KK) Inv Mass (K π) Inv Mass (KK)

29/08/2008ALICE Italia Final multicut Variables considered: 1.Cos Θ point 2.Cos Φ opening 3.Distance between primary and secondary vertex 4.Sum of impact parameters squared 5.Dispersion of secondary vertex (additional tuning) Signal D s via φ Signal D s via K 0* K 0 *-like BKG φ-like BKG Cos Point Cos Opening D+sD+s π+π+ K+K+ K-K- Φ opening P t (D s ) Θ point

29/08/2008ALICE Italia Results for Ideal PID φK 0*

29/08/2008ALICE Italia Conclusion and To-Do Monte-Carlo simulation shows that reconstruction of the D s  KKπ is feasible in the range of P t 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. 3-5 GeV/c>5 GeV/c φ channel 5.1±0.419±5 K 0* channel 2.0±0.79±3