1 / 18

Measurement of D 0 production in pp

Measurement of D 0 production in pp. Andrea Dainese University of Padova. Outline. One step back: study of feed-down from beauty (b  B  D 0 ), important also for systematic error Estimation of statistical error on dN(D 0 )/dp T Estimation of systematic errors :

fay
Télécharger la présentation

Measurement of D 0 production in pp

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Measurement of D0 production in pp Andrea Dainese University of Padova PPR Meeting - May 16, 2003 Andrea Dainese

  2. Outline • One step back: study of feed-down from beauty (b  B  D0), important also for systematic error • Estimation of statistical error on dN(D0)/dpT • Estimation of systematic errors: • contribution from beauty • uncertainty on D0 ct • MC corrections & uncertainty on B.R. to Kp • Combination of errors and error on total cross section PHYSICS PERFORMANCE: SENSITIVITY TO PPR Meeting - May 16, 2003 Andrea Dainese

  3. Feed-down from Beauty (1) • At LHC energies • Fraction of D0 from chain b  B0/B+ D0 not negligible • “Standard” NLO pQCD + Pythia fragmentation + PDG: • Important to use the correct ratio “D from b” / “D from c”: • Selection may change the ratio • Results have to be eventually corrected for feed-down estimate systematic error from b cross section 0.0017 0.64 0.0196 PPR Meeting - May 16, 2003 Andrea Dainese

  4. Feed-down from Beauty (2) • How D0 signal was generated: • generate standard pp minimum 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 pQCD • In that sample: factor 4 too high! All candidates have been re-weighted: • c  D: to reproduce pT distr. by NLO • b  D: to have correct ratio (5.5%) AND reproduce THEIR pT distr. by NLO (harder than for c  D !) PPR Meeting - May 16, 2003 Andrea Dainese

  5. Feed-down from Beauty (3) After event reconstruction (tracking + vertexing): D0 from b / D0 from c = 5.8 % Different pT slopes After selection (impact parameter + pointing angle): D0 from b / D0 from c = 16 % PPR Meeting - May 16, 2003 Andrea Dainese

  6. K p K D p B D V1 V1 Resolution on pointing angle is worse for D from c pointing angle enhances D from b Feed-down from Beauty (4) Selection on pointing angle expected to suppress D0 from b (they point to the decay vertex of the B and not to the primary vertex) 2<pT<3 GeV/c PPR Meeting - May 16, 2003 Andrea Dainese

  7. 20% ! D0 from b / D0 from c = 16 % Systematic error from b = uncertainty on b cross section  fraction of D0 from b Feed-down from Beauty (5) Also selection based on impact parameter enhances beauty PPR Meeting - May 16, 2003 Andrea Dainese

  8. D0 from b / D0 from c = 10 % Feed-down from Beauty (6) impact parameter distribution after selection new cut |d0|< 500 mm can suppress beauty PPR Meeting - May 16, 2003 Andrea Dainese

  9. K id Results • Essentially unchanged w.r.t. to last shown (March) PPR Meeting - May 16, 2003 Andrea Dainese

  10. Binning & “Smoothing” in dN/dpT • Optimize binning in the range 0-14 GeV/c: bin size increasing with pT • good precision on measurement of pT slope • small statistical error up to high pT • Fit pT distributions to remove fluctuations due to reduced statistics of simulation at high pT (especially for Bkg) • Use fitted function to obtain “smooth” dN/dpT for S and B PPR Meeting - May 16, 2003 Andrea Dainese

  11. Statistical Error (1) • Rel. Statisitical error on S expected to be 1/Significance: S = (S+B)observed – Bestimated error on (S+B)observed = sqrt(S+B) error on Bestimated negligible (uses info from wide range mass distr.) error on S = error on (S+B)observed = sqrt(S+B) relative error on S = sqrt(S+B)/S = 1/Significance • This has been checked by generating and fitting a large number of invariant mass distributions, using as input parameters the results of the simulation, namely: • statistics for S and B VS pT • width of D mass distribution VS pT • slope of exponential bkg VS pT PPR Meeting - May 16, 2003 Andrea Dainese

  12. 0.5<pT<1 GeV/c Significance = 11 2<pT<2.5 GeV/c significance = 21 12<pT<14 GeV/c significance = 11 no systematic shift of integral (S) Pulls analysis err. given by fit = stat. err. on S Statistical Error (2) • Fit with expo + gaus • with 4 free parameters: • expo slope • gaus integral (S) • gaus mean • gaus sigma • (total integral fixed) • Many (10,000) iterations: • study resolution on S (statistical error) • study robustness of fit PPR Meeting - May 16, 2003 Andrea Dainese

  13. ~10% 2.4% Systematic Errors • When the data are corrected for efficiency, acceptance, etc… systematic errors are introduced • Main sources of systematic errors have been considered PPR Meeting - May 16, 2003 Andrea Dainese

  14. Systematic from b subtraction • Fraction of D0 from b will be estimated from MC and subtracted to obtain D0 from c • Input to MC: • Beauty cross section in pp will be measured by all 4 expts • Now: pessimistic case use theoretical uncertainty (80%) • Error on N(c  D0) = 0.8  N(b  D0) • Relative error = 0.8  N(b  D0)/N(c  D0)  0.810% = 8% presentth. uncertainty PPR Meeting - May 16, 2003 Andrea Dainese

  15. depends on ct in MC input assuming it is primary error ~ 0.5 %  negligible lower cut on d0 upper cut on d0 charm beauty Systematic from ct = (123.4  0.8)mm • From selected to reconstructed D0: • For each D, calculated “equivalent” true value of ct = LM/p PPR Meeting - May 16, 2003 Andrea Dainese

  16. Errors combined dN(D0)/dy for |y| < 1 and pT > 0.5 GeV/c (91% of pT > 0) statistical error = 3 % systematic error = 13 % from b = 8 % MC correction = 10% B.R. = 2.4 % Note: Error from MC may be lower than 10% and dep. on pT Error from b may be much lower after direct measure Error on BR doesn’t alter pT shape PPR Meeting - May 16, 2003 Andrea Dainese

  17. Comparison with CDF-Run II • CDF Run II: preliminary measurement of charm cross section using the Secondary Vertex Trigger • sigma(D0, pT >= 5.5 GeV/c) = (13.3 ± 0.2 ± 1.5) µb 1.5% 11% • “We could measure the charm cross section in pp @ LHC from pT > 0.5 with the ~ same precision/accuracy” PPR Meeting - May 16, 2003 Andrea Dainese

  18. Conclusions • Feed-down from b studied – important for systematic error • Statistical errors on pT distribution estimated • Main systematic errors considered • Physics performance on charm X section measurement in pp: • statistical error: 3 % • systematic error: 13 % (only indicative value) Systematic error from MC corrections will dominate • Next steps: • try D0 impact parameter to measure (b  D0) / (c  D0) “a la CDF” • sensitivity for comparison with NLO pQCD and/or Pythia • error analysis for Pb-Pb • play a bit with comparisons (RAA (pT) ….) PPR Meeting - May 16, 2003 Andrea Dainese

More Related