1 / 22

Perspective for the measurement of D + elliptic flow

Perspective for the measurement of D + elliptic flow. F. Prino 1 , E. Bruna 2 , M. Masera 2 1 INFN – Sezione di Torino 2 Dip. Fisica Sperimentale, Università di Torino. Elliptic flow. y. Y RP. x. Elliptic flow.

garrison-meadows
Download Presentation

Perspective for the measurement of D + elliptic flow

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. Perspective for the measurement of D+ elliptic flow F. Prino1, E. Bruna2, M. Masera2 1 INFN – Sezione di Torino 2 Dip. Fisica Sperimentale, Università di Torino Alice Physics Week, December 5-9 2005

  2. Elliptic flow y YRP x Elliptic flow • Anisotropy in particle azimuthal distribution due to collective motion (flow) of particles • Driven by anisotropic pressure gradients originating from the almond-shaped overlap zone of the colliding nuclei in non-central collisions • Fourier expansion of particle azimuthal distribution relative to the reaction plane • Reaction plane (YRP) defined by beam direction and impact parameter Alice Physics Week, December 5-9 2005

  3. Flow and anisotopy • Elliptic Flow not the only source of correlations between D± azimuthal angles and the reaction plane • D± azimuthal anisotropy may also originate from: • Parton energy loss • Smaller in-medium length L in-plane (parallel to reaction plane) than out-of-plane (perpendicular to the reaction plane) • Drees, Feng, Jia, Phys. Rev. C71, 034909 • Dainese, Loizides, Paic, EPJ C38, 461 • Scattering on pions • Due to elliptic flow, azimuthal distribution of pions is anisotropic • more pions in-plane than out-of-plane • What is measured is v2 (which is not only due to flow) Alice Physics Week, December 5-9 2005

  4. Unknown reaction plane Event plane resolution Measurement of v2 • Calculate the 2nd order coefficient of Fourier expansion of particle azimuthal distribution relative to the reaction plane • The reaction plane is unknown. • Estimate the reaction plane from particle azimuthal anisotropy: • Yn = Event plane (nth harmonic) = estimator of the unknown reaction plane • Calculate particle distribution relative to the event plane • Correct for event plane resolution • Resolution contains the unknown YRP • Can be extracted from sub-events Alice Physics Week, December 5-9 2005

  5. Motivation and method • GOAL: Evaluate the statistical error bars for measurements of v2 for D± mesons decaying in Kpp • v2 vs. centrality (pT integrated) • v2 vs. pT in different centrality bins • TOOL: fast simulation (ROOT + 3 classes + 1 macro) • Assume to have only signal • Generate ND±(Db, DpT) events with 1 D± per event • For each event • Generate a random reaction plane (fixed YRP=0) • Get an event plane (with correct event plane resolution) • Generate the D+ azimuthal angle (φD) according to the probability distribution p(φ)  1 + 2v2 cos [2(φ-YRP)] • Smear φDwith the experimental resolution on D± azimuthal angle • Calculate v′2(D+), event plane resolution and v2(D+) Alice Physics Week, December 5-9 2005

  6. PPR chap 6.4 Our simulation Event plane simulation • Simple generation of particle azimuthal angles () according to a probability distribution • Faster than complete AliRoot generation and reconstruction • Results compatible with the ones in PPR chapter 6.4 Alice Physics Week, December 5-9 2005

  7. Ntrack = number of p, K and p in AliESDs of Hijing events with b = <b> Hadron integrated v2 input values (chosen ≈ 2  RHIC v2) Event plane resolution scenario • Event plane resolution depends on v2 and multiplicity Alice Physics Week, December 5-9 2005

  8. D± azimuthal angle resolution • From 63364 recontructed D+ • 200 events made of 9100 D+ generated with PYTHIA in -2<y<2 • Average  resolution = 8 mrad = 0.47 degrees Alice Physics Week, December 5-9 2005

  9. D± statistics • Nevents for 2·107 MB triggers • Ncc = number of c-cbar pairs • Includes shadowing • Shadowing centrality dependence from Emelyakov et al., PRC 61, 044904 • D± yield calculated from Ncc • Fraction ND±/Ncc (≈0.38) from tab. 6.7 in chapt. 6.5 of PPR • Geometrical acceptance and reconstruction efficiency • Extracted from 1 event with 20000 D± in full phase space • B. R. D± Kpp = 9.2 % • Selection efficiency • No final analysis yet • Assume e=1.5% (same as D0) Alice Physics Week, December 5-9 2005

  10. Results: v2 vs. centrality 2·107 MB events • Error bars quite large • Would be larger in a scenario with worse event plane resolution • May prevent to draw conclusions in case of small anisotropy of D mesons Alice Physics Week, December 5-9 2005

  11. Results: v2 vs. pT 2·107 MB events Alice Physics Week, December 5-9 2005

  12. Combinatorial background • Huge number (≈1010) of combinatorial Kpp triplets in a central event • ≈108 triplets in invariant mass range 1.84<M<1.90 GeV/c2 (D± peak ± 3s ) • Final selection cuts not yet ready • Signal almost free from background only for pT>5-6 GeV/c • Need to separate signal from background in v2 calculation • FIRST IDEA: sample candidate Kpp triplets in bins of azimuthal angle relative to the event plane (Dφ= φ-Y2) • Build invariant mass spectra in bins of Dφ and centrality / pT Alice Physics Week, December 5-9 2005

  13. Analysis in bins of Dφ (I) • Extract number of D± in 90º “cones”: • in-plane (-45<Dφ<45 U 135<Dφ<225) • out-of-plane (45<Dφ<135 U 225<Dφ<315) Alice Physics Week, December 5-9 2005

  14. 0<b<3 3<b<6 6<b<9 v2 values and error bars compatible with the ones obtained from <cos(2Dφ)> Analysis in bins of Dφ (II) • Fit number of D± vs. Dφ with A[1 + 2v2cos(2Dφ) ] Alice Physics Week, December 5-9 2005

  15. Other ideas for background Different analysis methods to provide: • Cross checks • Evaluation of systematics • Apply the analysis method devised for Ls by Borghini and Ollitrault [ PRC 70 (2004) 064905 ] • To be extended from pairs (2 decay products) to triplets (3 decay products) • Extract the cos[2(φ-YRP)] distribution of combinatorial Kpp triplets from: • Invariant mass side-bands • Different sign combinations (e.g. K+p+p+ and K-p-p-) Alice Physics Week, December 5-9 2005

  16. Conclusions • Large stat. errors on v2 of D± → Kpp in 2·107 MB events • How to increase the statistics? • Sum D0→Kp and D±→Kpp • Number of events roughly 2 → error bars on v2 roughly /√2 • Sufficient for v2 vs. centrality (pT integrated) • Semi-peripheral trigger • v2 vs. pT that would be obtained from 2·107 semi-peripheral events ( 6<b<9 ) Alice Physics Week, December 5-9 2005

  17. BACKUP SLIDES Alice Physics Week, December 5-9 2005

  18. Worse resolution scenario • Low multiplicity and low v2 Large contribution to error bar on v2 from event plane resolution Alice Physics Week, December 5-9 2005

  19. Glauber calculations (I) • N-N c.s.: • scc from HVQMNR • + shadowing • Pb Woods-Saxon Alice Physics Week, December 5-9 2005

  20. Glauber calculations (II) • N-N c.s.: • scc from HVQMNR • + shadowing • Pb Woods-Saxon Alice Physics Week, December 5-9 2005

  21. Shadowing parametrization • Eskola et al., Eur. Phys. J C 9 (1999) 61. • Emel’yanov et al., Phys. Rev. C 61 (2000) 044904. Rg(x~10-4,Q2=5 GeV2) = 65% from EKS98 Alice Physics Week, December 5-9 2005

  22. More details on v2 error bars High resolution scenario Low resolution scenario Alice Physics Week, December 5-9 2005

More Related