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Rapidity dependence of Bose-Einstein correlations at SPS energies

Rapidity dependence of Bose-Einstein correlations at SPS energies. Stefan Kniege Institut für Kernphysik Johann Wolfgang Goethe Universität Frankfurt a.M. for the NA49 collaboration. Workshop on Particle Correlations and Femtoscopy Kromeriz , 15-17.09.2005. Outline. Analysis.

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Rapidity dependence of Bose-Einstein correlations at SPS energies

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  1. Rapidity dependence of Bose-Einstein correlations at SPS energies Stefan Kniege Institut für KernphysikJohann Wolfgang Goethe Universität Frankfurt a.M. for the NA49 collaboration Workshop on Particle Correlations and Femtoscopy Kromeriz , 15-17.09.2005

  2. Outline Analysis • NA49 detector and data sets • correlation function •  fit method and parametrisation • systematic errors Results • kt- dependence of the HBT radii • Blastwave analysis • (HBT radii + particle mt- spectra) • Y- dependence of HBT radii Stefan Kniege WPCF, 15-17.09.2005, Kromeriz

  3. Analysis: Detector and datasets Setup of the NA49 detector Data sets: Stefan Kniege WPCF, 15-17.09.2005, Kromeriz

  4. Ycm=1.9 Ycm=2.9 Detector and data sets Similar coverage of phase space for different energies due to scaled magnetic field Phase space: (h- -h- pairs) kinematic interval:Ycm: (0.0-2.5) 5 bins kt : (0.0-0.6)GeV/c 5 bins for all energies Stefan Kniege WPCF, 15-17.09.2005, Kromeriz

  5. correlation function Signal distribution Momentum differences of h- h-pairs of tracks from the same event Measurement Background distributionmixed event pairs Bertsch-Pratt Parametrisation Fit function Basic considerations coulomb weight:Phys Lett. B 432 (1998) - extract  - - correlations and  as a physics parameter . determine the purity p of the source by VENUS/GEANT simulation. - coulomb interaction : iterative calculation of mean pair separationr. - consider different statistics in S(q) and B(q) by a normalisation factor n Stefan Kniege WPCF, 15-17.09.2005, Kromeriz

  6. BP- projections : kt-dependence kt dependence Projections of the correlation function onto qout(50 MeV/c) at midrapidity. fit data Stefan Kniege WPCF, 15-17.09.2005, Kromeriz

  7. BP- projections: Y-dependence Ycm dependence Projections of the correlation function onto qout(50 MeV/c) kt=(0.0-0.1)GeV/c. fit data Stefan Kniege WPCF, 15-17.09.2005, Kromeriz

  8. Systematic errors Stefan Kniege WPCF, 15-17.09.2005, Kromeriz

  9. Systematic errors : two track distance (ttd) Two track distance ttd is determined at each pad row of the TPCs (72 (VTPC), 90 (MTPC)) pair accepted if :ttd > ttdcut for a given number of pad rows ( nrows ) determination of cut criterion: variation of ttdcut and nrows ttd Look directly at the correlation function passed pad rows nrows Stefan Kniege WPCF, 15-17.09.2005, Kromeriz

  10. Systematic errors : Two Track Resolution Undershoot of the correlation function in case of to loose cuts (left plot) In the plateau region (blue): results vary by less than 0.2 fm Common cut criterion for all energies: ttdcut:2.2 cm nrows: 50 Stefan Kniege WPCF, 15-17.09.2005, Kromeriz

  11. Systematic errors : Momentum resolution Basic consideration: Momentum resolution is determined for each out-side-long -bin by a reconstruction of simulated events q< 5 MeV/c (158 AGeV) q< 10 MeV/c (20 AGeV) Cideal: obtained by weighting mixed event pairs according to a theoretical Bose-Einstein correlation function (radii taken from fit to the data in the corresponding bin) Csmeared :q value shifted according to momentum resolution q before weighting Stefan Kniege WPCF, 15-17.09.2005, Kromeriz

  12. Systematic errors : Momentum resolution Preliminary results: still uncorrected Very small correction ( <0.2fm) atlow energies Stefan Kniege WPCF, 15-17.09.2005, Kromeriz

  13. Further systematic uncertanties: • Missing particle identification strong influence on  Coulomb-correction: strong influence on Routand  : Normalisation: strong influence on and the Radii in case of small statistics or narrow acceptance Systematic error on the radii 1fm Stefan Kniege WPCF, 15-17.09.2005, Kromeriz

  14. Results kt-dependence Blastwave parametrisation Stefan Kniege WPCF, 15-17.09.2005, Kromeriz

  15. Results: Blastwave analysis Emission function:(Retiere/Lisa nucl-th/0312024) : source velocity: - longitudinal boost invariance - linear increasing transverse flow 0 : freezeout time : emission duration Fit parameters: : weighting function - Transverse radius - surface diffuseness (box- profile assumed) Stefan Kniege WPCF, 15-17.09.2005, Kromeriz

  16. Results: Blastwave analysis calculation of observables pt-spectra: azimuthal angle of momentum HBT –radii : (longitudinal boost invariant source , analysed in the LCMS) Average over the emission function: Combined fit of HBT-radii and particle spectra Stefan Kniege WPCF, 15-17.09.2005, Kromeriz

  17. Results: Blastwave analysis Fit to mt-spectra only Stefan Kniege WPCF, 15-17.09.2005, Kromeriz

  18. Results: Blastwave analysis Fit to mt-spectra only Stefan Kniege WPCF, 15-17.09.2005, Kromeriz

  19. Results: Blastwave analysis Combined fit to spectra and HBT radii at midrapdity Only pand and p - spectra were used to make the results comparable to AGS and RHIC data. Good approximation to the data except for slight deviations in Rside at high kt Stefan Kniege WPCF, 15-17.09.2005, Kromeriz

  20. Results: Blastwave analysis – fit results open symbols: results from fit to mt - spectra only T>Tchem! at AGS energies Tchem J. Cleymans, K. Redlich, Phys. Rev. C60, 054908 (1999) • Further possible improvements: • add further • particles • Take into account • resonance decays • slightly increasing temperature with beam energy at SPS energies • approximately constant transverse geometrical Radii (Rbox 2Rgauss) • finite emission duration at SPS energies Stefan Kniege WPCF, 15-17.09.2005, Kromeriz

  21. Results Ycm-dependence Stefan Kniege WPCF, 15-17.09.2005, Kromeriz

  22. Results : Ycm-dependence Non vanishing cross term for non boost invariant expansion expected:( Phys.Rev.Lett. 74,4400-4403(1995) ) 158 AGeV kt : (0.0-0.1) GeV/c  shift of the correlation function in the qlong - qout- plane Stefan Kniege WPCF, 15-17.09.2005, Kromeriz

  23. Results : Ycm-dependence increasing Routlong kt : (0.0-0.1) GeV/c Stefan Kniege WPCF, 15-17.09.2005, Kromeriz

  24. Results : Ycm-dependence increasing Routlong kt : (0.1-0.2) GeV/c Stefan Kniege WPCF, 15-17.09.2005, Kromeriz

  25. Results : Ycm-dependence increasing Routlong kt : (0.2-0.3) GeV/c Stefan Kniege WPCF, 15-17.09.2005, Kromeriz

  26. Summary and Conclusion • Bose-Einstein correlations at NA49: • 1. measured over a wide region of phase space • 2. measured at 5 different beam energies source parameters extracted from transverse momentum dependence of the HBT radii show no pronouncedenergy dependence at SPS energies. HBT-Radii Rside, Rout show no pronounced rapidity dependenceat SPS energies • rapidity dependence of R outlongreflects • non boost invariant longitudinal expansion •  further investigation (YKP parametrisation) Stefan Kniege WPCF, 15-17.09.2005, Kromeriz

  27. Thanks for your attention Stefan Kniege WPCF, 15-17.09.2005, Kromeriz

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