Centrality Dependence of φ meson production

NA49 Analysis Meeting, February 2011, Warsaw

Volker Friese

Centrality Classes

Volker Friese NA49 Coll. Meeting, Warsaw, 18 February 2011 2

class Eveto centrality # events

C1 0 – 10,770 0 – 5 % 27,103

C2 10,770 – 19,270 5 – 12,5 % 32,739

C3 19,270 – 25,510 12.5 – 23.5 % 33,750

C4 25,510 – 28,230 23.5 – 33.5 % 20,747

C5 28,230 – 30,330 33,5 – 43,5 % 19,379

C6 30,330 – 38,000 43,5 - ? % 51,833

as proposed by P. Dinkelacker

N.b.: statistics is about a factor 10 less than for events with central trigger

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

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Centrality Class 1, pt bins

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Centrality Class 1, y bins

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Centrality Class 1, Spectra

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Comparison with preliminary data: slope

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Looks ok (well, error bars are non-negligible for peripheral classes)Looks ok (well, error bars are non-negligible for peripheral classes)

Comparison with preliminary data: yield

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Looked promisingSome issues for classes 4 – 6 ?Looked promisingSome issues for classes 4 – 6 ?

News

• Increased statistics by some 10 % (2 runs added to analysis)

• Introduced parametrisation of dE/dx resolution as fnct. of p(instead constant 4 %

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• Started to look into systematics / stablibity of results

Centrality Class 1

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y = 2.9 – 4.5 (4 bins, width 0.4)Forward rapidity not well covered: extrapolation unsure2-Gauß parametrisation failed (too few data points)

Make more bins; go to higher rapidities

Centrality Class 1, new analysis

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6 bins, width 0.3

Good signals also in smaller bin, except last one

Centrality Class 1, new analysis

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Gives substantially smaller yield ( - 20 %) : N = 6.42 +- 0.47

Comparison: yields (new)

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Not so nice any longer...

Better agreement with 2000 analysis

but no good agreement with published result for central trigger

To believe or not to believe...

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Inclusion of this datamakes a 20 % effect on the integrated yield

Has the analysis surpassed the limits set by statistics?

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Status (new)

• 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

Conclusion

Contrary to my expectations of last October, there is still some way to go for a publication

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