1 / 16

L and K 0 S production in Pb-Pb collisions with the ALICE experiment

L and K 0 S production in Pb-Pb collisions with the ALICE experiment. Motivation ALICE performance for L and K 0 S L /K ratios in centrality bins (preliminary) Comparison with the STAR measurements Conclusions. I. Belikov for the ALICE Collaboration. Motivation.

nicolejones
Download Presentation

L and K 0 S production in Pb-Pb collisions with the ALICE experiment

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. L and K0S production in Pb-Pb collisions with the ALICE experiment Quark Matter 2011, Annecy, France, May 23 2011 • Motivation • ALICE performance for L and K0S • L/K ratios in centrality bins (preliminary) • Comparison with the STAR measurements • Conclusions I. Belikov for the ALICE Collaboration

  2. Motivation Quark Matter 2011, Annecy, France, May 23 2011 M.A.C.Lamont et al, Eur. Phys. J C49, 39–55 (2007) Why do baryons appear to be produced more easily than mesons, at intermediate pT in AA collisions ? The energy dependence can help with understanding... (The value and the position in pT of the maximum)‏ R.J.Fries and B.Muller, Eur. Phys. J C34, s279–s285 (2004)

  3. ALICE Performance for L and K0S(see M. Putis’ poster about the V0 reconstruction) Quark Matter 2011, Annecy, France, May 23 2011

  4. ALICE Performance for L and K0S Quark Matter 2011, Annecy, France, May 23 2011 The efficiencies change with the event centrality… The ratio of efficiencies changes with the centrality significantly less than the efficiencies themselves, especially at the intermediate pT’s. This is the ratio of the fitting 5-th order polynomials

  5. ALICE Performance for L and K0S Quark Matter 2011, Annecy, France, May 23 2011 • There is an excellent agreement between the K0S and K± spectra. (See also M. Floris’ talk about the ID-ed particle spectra)

  6. Feed-down correction for L Quark Matter 2011, Annecy, France, May 23 2011 p p p L X X -> p + L -> p + p + p- Lraw = LfromXraw + Lprimraw (neglecting the L’s generated in the material, and decays of W’s) Lprimraw = eprimLprim = Lraw – LfromXraw = Lraw (1 – LfromXraw /Lraw) = Lraw F Lprim = 1/eprimLraw (1 – LfromXraw /Lraw) = 1/eprimLrawF F = (1 – LfromXraw /Lraw) feed-down correction factor

  7. ALICE Performance for L and K0S Quark Matter 2011, Annecy, France, May 23 2011 Life-time checks. Implicitly, the shape of these distributions depends on getting correctly the shape of the efficiency function (pT, decay length, etc). We are ~3 % away from the PDG values. With the statistical error < 1 % … Clearly, we are dominated by the systematic uncertainties.

  8. Main sources of systematic uncertainties Quark Matter 2011, Annecy, France, May 23 2011 • Signal extraction: ~3 % (slide #3) • Efficiency correction: [~1 % to ~7 %] (slide #5) • Feed-down correction: ~5 % (slide #6) • L’s generated in the material: ~2 % (MC studies) ~10 % for 2.5 < pT < 5.5 GeV/c

  9. The preliminary results(see A. Toia’s talk about the centrality in ALICE ) Quark Matter 2011, Annecy, France, May 23 2011 ALICE data only Feed-down (from X) corrected The pp data nicely bracket (in energy) the Pb-Pb data ! • The 80-90 % data are corrected with 60-80 % MC data, • fitted to 5-th order polynomial used for these double ratios.

  10. The preliminary results Quark Matter 2011, Annecy, France, May 23 2011 ALICE data only Both the position in pT and the value of the L/K maximum increase with Npart

  11. The preliminary results Quark Matter 2011, Annecy, France, May 23 2011 Comparison with STAR • The L/L ratio is known to be pT-independent in the region of our interest. J. Phys. G 30, S963 (2004) Phys. Rev. Lett. 98 (2007) 062301 arXiv:nucl-ex/0601042 Phys. Rev. C 83, 024901 (2011) _

  12. Conclusions • At intermediate pT, in Pb-Pb collisions at √sNN = 2.76 TeV, the production of L is enhanced compared with the production of K0S. • The magnitude of this enhancement increases with the collision centrality. • The maximum value of the /K ratio measured by ALICE is higher than that observed by STAR at RHIC. • The position in pT of the maximum in ALICE is shifted towards higher transverse momenta compared with the STAR measurements at RHIC energies. Physics Forum 10.05.2011 I. Belikov 12

  13. Quark Matter 2011, Annecy, France, May 23 2011 Extra slides…

  14. Fitting the L and K0S efficiencies Quark Matter 2011, Annecy, France, May 23 2011 The efficiencies are extracted from detailed Monte Carlo simulations. The efficiency points are fitted to 5-th order polynomials. These polynomials are then used for the actual efficiency corrections.

  15. Fitting the L/K ratios The fitting function: max + p2Dx2 + p3Dx3 + p4Dx4 + p5Dx5, Dx = x-pTmax Quark Matter 2011, Annecy, France, 23.05.2011 I. Belikov 15

  16. More on the feed-down correction For each MC L coming from X and satisfying the selections, fill this “matrix”. 2. Divide the matrix columns by the MC raw spectrum of X. For each MC L coming from X and satisfying the selections, fill this “matrix”. 2. Divide the matrix columns by the MC raw spectrum of X. • 3. Multiply the columns by the raw spectrum • of real X. • 4. Sum up the matrix over the rows. • 5. The result is an estimate for LfromXraw • (spectrum of L coming from X) Quark Matter 2011, Annecy, France, 23.05.2011 I. Belikov 16

More Related