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Detection of D 0  K - p + in pp collisions “Propedeutics for a feasibility study”

Detection of D 0  K - p + in pp collisions “Propedeutics for a feasibility study”. Andrea Dainese University of Padova. Table of contents. Reconstruction of pp events determination of z position of primary vertex parameterization of TPC tracking for pp

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Detection of D 0  K - p + in pp collisions “Propedeutics for a feasibility study”

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  1. Detection of D0 K-p+in pp collisions“Propedeutics for a feasibility study” Andrea Dainese University of Padova PPR meeting - November 8, 2002 Andrea Dainese

  2. Table of contents • Reconstruction of pp events • determination of z position of primary vertex • parameterization of TPC tracking for pp • resolution on track parameters (compared to Pb-Pb “6000”) • Status of the generation/reconstruction with AliEn of events for background study • Production of charm particles in pp @ s = 14 TeV • cc cross section from NLO QCD calculation • rates for D mesons • generation of charm signal (D0) with Pythia • Global properties of pp events with charm production • multiplicity • mean pT • event thrust and azimuthal correlations PPR meeting - November 8, 2002 Andrea Dainese

  3. Reminder: D0 detection strategy • Invariant mass analysis of fully-reconstructed topologies originated in secondary vertices • Secondary vertex selection based on: • couple of tracks with large impact parameters • good pointing of reconstructed D0 momentum to the primary vertex Resolution on track parameters and primary vertex is crucial • The feasibility study requires very large statistics (~106 pp events) for signal and background analysis at high pT TPC tracking parameterization makes it possible PPR meeting - November 8, 2002 Andrea Dainese

  4. Primary vertex • Pb-Pb • bending plane: s(x) = s(y)  15 mm given by transverse size of Pb beam • z direction: position measured using the correlation between clusters in the 2 pixel layers (Int. Notes by Ohio/LNL, Catania group) s(z)  1/dNch/dy s(z) = 5.5 mm @ 6000 • pp • bending plane: assume to have the same resolution as in Pb-Pb (for the moment) • z direction: • 1st step: use tracklets from pixels as in Pb-Pb, but … multiplicity lower by factor ~1000 s(z) worse by factor ~ 30 ! • 2nd step: do tracking in TPC+ITS and use tracks to estimate zvtx but not much expectation: tracks are more precise but fewer than tracklets PPR meeting - November 8, 2002 Andrea Dainese

  5. 1st step: zvtx from tracklets • Same method as in Pb-Pb (adapted to pp by M. Masera) s(z) = 155 mm PPR meeting - November 8, 2002 Andrea Dainese

  6. 2nd step: zvtx from ITS tracks • Tracking in TPC+ITS • Selection of tracks from primary vertex (in bending plane): |d0(rf)| < 3 sd0(rf)(pT) • Estimate of zvtx from weighted average of z impact parameters d0(z) [weight is 1/sd0(z)2(pT) ] • Expected result: • average # rec. tracks in pp = 7.5 • average pT of rec. tracks = 0.6 GeV/c • sd0(z)(0.6 GeV/c) = 240 mm PPR meeting - November 8, 2002 Andrea Dainese

  7. Results (1) s(z)1 track = 250 mm s(z) = 105 mm PPR meeting - November 8, 2002 Andrea Dainese

  8. Results (2) PPR meeting - November 8, 2002 Andrea Dainese

  9. Comparison of the two methods • With ITS tracks resolution improves by  50 mm • Reconstruction chain: • vertex from pixels • tracking • use tracks to improve vertex position to be used for analysis (e.g. pointing angle) PPR meeting - November 8, 2002 Andrea Dainese

  10. Parameterization of TPC tracking • Parameterization of TPC Kalman filter response (efficiency, resolutions, covariance matrix, dE/dx) gives a large reduction in time/space for simulation (~factor 40) • New in pp w.r.t. Pb-Pb: • use of AliTrackReferences at inner radius of TPC allows full coverage in f • all particles treated separately (p, K, p, e, m) • “Making of” presented at last Alice Week, here only some interesting “highlights”: • TPC tracking efficiency in pp • tests on tracking performance in ITS for “validation” of the tool PPR meeting - November 8, 2002 Andrea Dainese

  11. Tracking efficiency in the TPC (1) Saturation at 0.93: 7 % of very high pT tracks that enter the TPC are lost no seed at end of TPC ? Effect not seen at low pT PPR meeting - November 8, 2002 Andrea Dainese

  12. Tracking efficiency in the TPC (2) why do we loose tracks in pp ? Muons, with seed, not reconstructed (pT = 0.7 GeV/c) they change sector! <1/2 of the lost tracks don't have seed others are lost when they change sector very low pT: all have seed not lost when change sector PPR meeting - November 8, 2002 Andrea Dainese

  13. Validation: fraction of prolonged tracks PPR meeting - November 8, 2002 Andrea Dainese

  14. Validation: resolutions after complete tracking PPR meeting - November 8, 2002 Andrea Dainese

  15. Resolutions: Pb-Pb VS pp • Momentum resolution ~ 25% better in pp • Impact parameter resolution ~ same in Pb-Pb and in pp primary tracks PPR meeting - November 8, 2002 Andrea Dainese

  16. Background for D0 with • 5 million pp non-diffractive events generated in June: “kinematic” window |y|<2, R < 85 cm (ITS only+AliTrackReferences at TPC) 5000 pp events / file (failures < 5 %) • Reconstruction successfully executed in the last weeks: • TPC tracking parameterized • Fast points in ITS • Vertex determination (smearing with resolution given by ITS tracks) • tracking in ITS with standard Kalman V2 (6 points required) • Analysis and reconstruction of D0 candidates in progress: • analysis macro + compiled library registered in catalogue • candidates built from ITS tracks • only small ROOT file with candidates being copied to my PC (~ 0.5 ‰ of total size) PPR meeting - November 8, 2002 Andrea Dainese

  17. Background for D0 with Thanks to AliEn team (Pablo, Predrag) PPR meeting - November 8, 2002 Andrea Dainese

  18. Charm production in pp @ 14 TeV • NLO QCD calculation (MNR): • Using : (115 in central Pb-Pb @ 5.5 TeV) • Yields for charm hadrons: • D0 Kp with K and p in TPC acc.: 7.16  10-4 / event PPR meeting - November 8, 2002 Andrea Dainese

  19. Generation of D0 signal • Requirements for generation of D0 Kp signal in pp: • pT distribution as given by MNR calculation • the signal has to be generated together with “its own” pp event: • want to study global properties of pp evts with charm • there can be “dangerous” backgrounds (one track from the D0 and one track from the underlying event) • Nicola has tuned Pythia to reproduce pT distribution of MNR • tuning is meant to be used to generate charm stand-alone • if one keeps the full event, the total charged multiplicity in the barrel is lower than that given by pp min. bias • Recipe for generation: • generate standard pp min. bias with Pythia • keep only those events that have a D0 • weight D0s according to their pT in order to reproduce distribution given by NLO QCD PPR meeting - November 8, 2002 Andrea Dainese

  20. Global properties of charm events • Production of heavy quarks requires “hard” hard scattering • Fragmentation of heavy quarks gives large multiplicity Events with a cc pair should have larger multiplicity and larger mean pT w.r.t. to “ordinary” pp events • Maybe this cannot be used for detection of charm particles, but it’s worth having a look • Global event properties inspected: • multiplicity • mean pT • thrust of the event (defined later) • azimuthal correlations of D particle with all other tracks PPR meeting - November 8, 2002 Andrea Dainese

  21. Multiplicity and mean pT • Charged particles in ||<0.9 and pT > 200 MeV/c PPR meeting - November 8, 2002 Andrea Dainese

  22. … as a function of D0 pT pT < 1 GeV/c 1 < pT < 2 GeV/c 2 < pT < 3 GeV/c 3 < pT < 5 GeV/c pT > 10 GeV/c 5 < pT < 10 GeV/c PPR meeting - November 8, 2002 Andrea Dainese

  23. Event Thrust • Definition: • thrust = • = is the thrust axis “axis which maximizes projected momenta” PPR meeting - November 8, 2002 Andrea Dainese

  24. D0 w.r.t. thrust axis pT < 1 GeV/c 1 < pT < 2 GeV/c 2 < pT < 3 GeV/c 3 < pT < 5 GeV/c pT > 10 GeV/c 5 < pT < 10 GeV/c PPR meeting - November 8, 2002 Andrea Dainese

  25. Azimuthal correlations • Df of all particles (in acc.) w.r.t. to D0 flight-line (D0 decay products excluded) • Particles weighted with their momentum • Looks like jets … • Depends on Df(cc)… • could it give informations on this variable? PPR meeting - November 8, 2002 Andrea Dainese

  26. Conclusions • All tools for reconstruction in pp ready • Background (~106 events) being analyzed using ALICE distributed resources exclusively • Signal generation in progress • Survey of pp specific observables (multiplicity, thrust, etc…) • events with charm have larger multiplicity • clear jet topology for pT(D0) > few GeV/c • Possible applications: • use thrust + invariant mass for D0 selection at high pT • can be done on TPC tracks (increase statistics by ~50%) • use azimuthal correlations for study of cc production kinematics PPR meeting - November 8, 2002 Andrea Dainese

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