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The ALICE group

Midwest critical mass 2010. Toledo, Ohio. Measurement of two-particle correlations in pp collisions at sqrt(s) = 900 GeV as well as at sqrt(s) = 7 TeV with ALICE. The ALICE group. 23. October 2010. first paper on HBT by ALICE. two particle correlations in pp at sqrt(s) = 900 GeV.

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The ALICE group

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  1. Midwest critical mass 2010 Toledo, Ohio Measurement of two-particle correlations in pp collisions at sqrt(s) = 900 GeV as well as at sqrt(s) = 7 TeV with ALICE The ALICE group 23. October 2010

  2. first paper on HBT by ALICE two particle correlations in pp at sqrt(s) = 900 GeV 1 dimensional Sebastian Huber

  3. motivation • measuring space-time dimensions in pp collisions at sqrt(s) = 900 GeV with • ALICE • investigating collective behaviour in pp collisions at LHC energies • reference for heavy ion measurements starting in Nov 2010 • using Bose-Einstein enhancement of identical pion pairs to • get access to size of pion emitting source • dependance of source size as function of event multiplicity dNCH/dη • an transverse momentum kT Sebastian Huber – s.huber@gsi.de

  4. HBT – Bose-Einstein correlations „The only way to get access to space-time properties of the emitting source in elementary particle collisions is through the measurement of Bose-Einstein correlations (BEC) between identical pions“ • building the correlation function (CF) • transformation in relative momenta q • correlation function in the experiment A(q) is the measured distribution of the pair momentum difference q, whereas B(q) is a reference distribution build by using pairs of particles from different events (event-mixing) or by rotating on particle of the pair in the transverse ebene (rotation) Reference distribution should be without Bose-Einstein correlations Sebastian Huber – s.huber@gsi.de

  5. Extracting the HBT radii To get the HBT-radii out of the correlations one has to use a propper parametrization If one asumes that the source function has a gaussian shape also the parametrization has a gaussian shape A common parametrization is the following R is the effective size of the emission region λ is the coherence parameter measuring the strength of the Bose-Einstein correlation Bose-Einstein correlation allows to distinguish between collision systems HBT in pp at sqrt(S) = 7 TeV will be interconnection between small systems (pp) and heavy systems (AA) at lower energies Sebastian Huber – s.huber@gsi.de

  6. correlation of non-identical pions at sqrt(S) = 900 GeV • π+π- correlations in comparisson with • PHOJET simulations • description of the background of the CF • rich spectrum of meson resonances • coulomb effect in the first bins • using the background of the CF later for the • parametrization of the CF of identical pions • proper treatment of baseline very important • when studying the dependancy of the radii from • transverse momentum and multiplicity • parametrization of the background Phys. Rev. D 82, 052001 (2010) Sebastian Huber – s.huber@gsi.de

  7. correlation of identical pions at sqrt(S) = 900 GeV • π+π- correlations in one dimension • 2009 data not enough statistics for 3D • 3 bins in event multiplicity • 5 bins in transverse momentum • Bose-Einstein effect clearly visible • fixing the baseline with simulations (see slide • before) • used parametrization • developing of long range correlations with • increasing kT Sebastian Huber – s.huber@gsi.de

  8. multiplicity dependance • source radii increase with multiplicity • same dependance like older measurements • HBT radii seem to depend more on • multiplicity than on geometry (pp) • grey shadowed band Systematic error from: • baseline assumption • fitting • background construction • UNICOR vs ALIFEMTO Sebastian Huber – s.huber@gsi.de

  9. kT dependance - baseline • source radii independant of kT a • no sign of collective behaviour (presence of a bulk) • in pp • very sensitive to basline assumption • if fitted free (flat baseline) – dependance emerges Sebastian Huber – s.huber@gsi.de

  10. results Parametrization with a gaussian dNCH/dη λ RInv/fm 3.2 0.386 (0.022) 0.874 (stat 0.047) (sys 0.181) 7.7 0.331 (0.023) 1.082 (stat 0.068) (sys 0.206) 11.2 0.310 (0.026) 1.184 (stat 0.092) (sys 0.168) Parametrization with an exponential RInv/fm dNCH/dη λ 3.2 0.704 (0.048) 0.808 (stat 0.061) (sys 0.208) 7.7 0.577 (0.054) 0.967 (stat 0.095) (sys 0.206) 11.2 0.548 (0.051) 1.069 (stat 0.104) (sys 0.203) Sebastian Huber – s.huber@gsi.de

  11. ongoing work two particle correlations in pp at sqrt(s) = 7 TeV 1 dimensional 3 dimensional Sebastian Huber

  12. motivation • measuring space-time dimensions in pp collisions at sqrt(s) = 900 GeV and at • sqrt(s) = 7 TeV at ALICE • investigating collective behaviour in pp collisions at LHC energies • more statistics makes it possible to go into more than one dimension • getting deeper into the physics of the system • using Bose-Einstein enhancement of identical pion pairs to • get access to size of pion emitting source • dependance of source size as function of event multiplicity dNCH/dη • and transverse momenta kT • cartesian parametrization in out side and long (Bertsch-Pratt) • expansion in spheriacal harmonics • difference between 900 GeV and 7 TeV • understanding the background – non BE correlations – EMCIC • no gaussian shape of the CF • collective behaviour of the pion emitting fireball Sebastian Huber – s.huber@gsi.de

  13. 1 dim 7TeV – kT and dNCh/dη 7 TeV π+π- 7 TeV π+π+ • coulomb • minijets Sebastian Huber – s.huber@gsi.de

  14. out holes due to combination of single track acceptance pT and Pair kT cut parametrization Sebastian Huber – s.huber@gsi.de

  15. side Sebastian Huber – s.huber@gsi.de

  16. long edges due to acceptance of the detector in η Sebastian Huber – s.huber@gsi.de

  17. ROut &&RSide && RLong • measurement of BE of identical pions at 900 GeV (newest results not shown) and 7 TeV with dependance on • multiplicity dNCh/dη and pair momentum kT • 7 TeV data provide link between multiplicities in pp and AA • 3D CF not gaussian • non femtoscopic correlations in 7 TeV as well as in 900 GeV – minijets – simulated with PHOJET - baseline Sebastian Huber

  18. ROut &&RSide && RLong link to the AA data • radii in 900 GeV and 7 TeV grow with multiplicity • 900 GeV and 7 TeV behave equaly • dependance of the radii with pair momentum – very sensitive to baseline • using spherical harmonics to get a full sight of what is going on (Mikes idea!) Sebastian Huber

  19. Backup Backup Sebastian Huber

  20. holes and edges holes in qout • qlong and qside vanish • pT is sum of pT1 and pT2 • kT is difference of pT1 and pT2 combination of single particle acceptance and two particle cut leads to holes edges in qlong η acceptance of the detector Sebastian Huber – s.huber@gsi.de

  21. UNICOR 7 TeV pass2 event and track selectio 900 GeV runs by mistake? Sebastian Huber – s.huber@gsi.de

  22. UNICOR 7TeV HBT – UNICOR 7000 GeV p+p Sebastian Huber

  23. UNICOR 7 TeV pass2 one dimensional CF in LCMS • red – Pythia-Perugia LHC10d4 • red line – final parametrization • blue line – peak fit • green line – baseline fit • no difference between fixed baseline fit and free fit • baseline not as good fixed as in the 900GeV data • only parts of the simulation LHC10d4 (Pythia-Perugia) taken Sebastian Huber – s.huber@gsi.de

  24. UNICOR 7 TeV pass2 one dimensional CF in LCMS with kt-binning first and two last bins not usable – kT > 0.7 no HBT correlation! new kT binning (see slide 10) Sebastian Huber – s.huber@gsi.de

  25. UNICOR 7 TeV pass2 one dimensional CF in LCMS with multiplicity-binning • two highest multiplicity bins missing (by decission) Sebastian Huber – s.huber@gsi.de

  26. UNICOR 7 TeV pass2 one dimensional CF in LCMS with kt- and multiplicity-binning binning in kt (7 bins) dNCh/dη Sebastian Huber – s.huber@gsi.de

  27. UNICOR 7 TeV pass2 three dimensional CF in LCMS – out side long • red – Pythia-Perugia LHC10d4 • red line – final parametrization • blue line – peak fit • green line – baseline fit • baseline fits do not match the Pythia-Perugia simulation • please ignore the peak fit  Sebastian Huber – s.huber@gsi.de

  28. UNICOR 7 TeV pass2 three dimensional CF in LCMS with kt-binning – out side long binning in kt (5 bins) out side long Sebastian Huber – s.huber@gsi.de

  29. UNICOR 7 TeV pass2 three dimensional CF in LCMS with kt and multiplicity binning – out binning in kt (5 bins) dNCh/dη Sebastian Huber – s.huber@gsi.de

  30. UNICOR 7 TeV pass2 three dimensional CF in LCMS with kt and multiplicity binning – side binning in kt (5 bins) dNCh/dη Sebastian Huber – s.huber@gsi.de

  31. UNICOR 7 TeV pass2 three dimensional CF in LCMS with kt and multiplicity binning – long binning in kt (5 bins) dNCh/dη Sebastian Huber – s.huber@gsi.de

  32. Systematic error Paper preparation • comparison mixing and rotation • comparison π+π+ and π-π- • CMS vs LCMS • LHC10c vs LHC10b (7TeV) • comparison of different magnetic field orientations (only in LHC10d) • different background estimations (fixing the baseline out of simulations or π+π+) • different fitting ranges • comparison UNICOR and ALIFEMTO (ALIFEMTO results from Adam and own results) • variation of the event cuts • variation of the track cuts • variation of the pair cuts • mixing (vertex binning and multiplicity binning) Sebastian Huber – s.huber@gsi.de

  33. dNCH and kT dependancy Sebastian Huber

  34. ROut &&RSide && RLong Sebastian Huber

  35. ROut &&RSide && RLong Sebastian Huber

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