Centrality Dependence of φ meson production

1. Centrality Dependence of φ meson production Volker Friese NA49 Analysis Meeting, February 2011, Warsaw

2. Centrality Classes as proposed by P. Dinkelacker N.b.: statistics is about a factor 10 less than for events with central trigger NA49 Coll. Meeting, Warsaw, 18 February 2011

3. Analysis • Method (extraction of inv. mass signal, fit, correction, spectra) analogue to analysis of central Pb+Pb data • Re-used acceptance table of 1996 central data (STD+) • Kaon identification by Bethe-Bloch from TNA49DedxFunction::GetRelRise • Assuming constant dE/dx resolution of 4 % • Kaon selection: ± 1.5 σ around expectation value • Inv. mass background subtraction by event mix method • Fit of rel. Breit-Wigner plus residual background to extract signal • No 2d binning: pt spectra integrated over rapidity; correction of y spectra assuming T independent of y NA49 Coll. Meeting, Warsaw, 18 February 2011

4. Centrality Class 1, pt bins NA49 Coll. Meeting, Warsaw, 18 February 2011

5. Centrality Class 1, y bins NA49 Coll. Meeting, Warsaw, 18 February 2011

6. Centrality Class 1, Spectra NA49 Coll. Meeting, Warsaw, 18 February 2011

7. Comparison with preliminary data: slope Looks ok (well, error bars are non-negligible for peripheral classes) NA49 Coll. Meeting, Geneva, 15 October 2010

8. Comparison with preliminary data: yield Looked promising Some issues for classes 4 – 6 ? NA49 Coll. Meeting, Geneva, 15 October 2010

9. News • Increased statistics by some 10 % (2 runs added to analysis) • Introduced parametrisation of dE/dx resolution as fnct. of p(instead constant 4 % • Started to look into systematics / stablibity of results NA49 Coll. Meeting, Warsaw, 18 February 2011

10. Centrality Class 1 y = 2.9 – 4.5 (4 bins, width 0.4) Forward rapidity not well covered: extrapolation unsure 2-Gauß parametrisation failed (too few data points) Make more bins; go to higher rapidities NA49 Coll. Meeting, Warsaw, 18 February 2011

11. Centrality Class 1, new analysis 6 bins, width 0.3 Good signals also in smaller bin, except last one NA49 Coll. Meeting, Warsaw, 18 February 2011

12. Centrality Class 1, new analysis Gives substantially smaller yield ( - 20 %) : N = 6.42 +- 0.47 NA49 Coll. Meeting, Warsaw, 18 February 2011

13. Comparison: yields (new) Not so nice any longer... Better agreement with 2000 analysis but no good agreement with published result for central trigger NA49 Coll. Meeting, Warsaw, 18 February 2011

14. To believe or not to believe... Inclusion of this data makes a 20 % effect on the integrated yield Has the analysis surpassed the limits set by statistics? NA49 Coll. Meeting, Warsaw, 18 February 2011

15. First systematic checks show that the results for integrated yield are not quite stable (to be shown for the peripheral event classes as well) Results on T and dn/dy are much better confined Tools to derive systematc errors, developed for central data sets, seem to fail Change strategy (to minimal): Extract phi signal in full acceptance Correct for global acceptance, assuming spectral distributions in y and pt Known: for central Pb+Pb and for p+p Interpolation between the two? Or using the two as limiting cases and assign corresponding systematic error Status (new) NA49 Coll. Meeting, Warsaw, 18 February 2011

16. Conclusion Contrary to my expectations of last October, there is still some way to go for a publication NA49 Coll. Meeting, Warsaw, 18 February 2011