Midwest critical mass 2010 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 Midwest critical mass 2010 Toledo, Ohio

Midwest critical mass 2010 Sebastian Huber2 first paper on HBT by ALICE two particle correlations in pp at sqrt(s) = 900 GeV 1 dimensional

Midwest critical mass 2010 motivation Sebastian Huber – 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 dN CH /dη an transverse momentum k T

Midwest critical mass 2010 HBT – Bose-Einstein correlations Sebastian Huber – „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

Midwest critical mass 2010 Extracting the HBT radii Sebastian Huber – 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

Midwest critical mass 2010 correlation of non-identical pions at sqrt(S) = 900 GeV Sebastian Huber – 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, (2010)

Midwest critical mass 2010 correlation of identical pions at sqrt(S) = 900 GeV Sebastian Huber – 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) developing of long range correlations with increasing k T used parametrization

Midwest critical mass 2010 multiplicity dependance Sebastian Huber – 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

Midwest critical mass 2010 k T dependance - baseline Sebastian Huber – source radii independant of k T a no sign of collective behaviour (presence of a bulk) in pp very sensitive to basline assumption if fitted free (flat baseline) – dependance emerges

Midwest critical mass 2010 results Sebastian Huber – Parametrization with a gaussian Parametrization with an exponential dN CH /dη λ λR Inv /fm (0.022) (0.023) (0.026) (0.048) (0.054) (0.051) (stat 0.047) (sys 0.181) (stat 0.068) (sys 0.206) (stat 0.092) (sys 0.168) (stat 0.061) (sys 0.208) (stat 0.095) (sys 0.206) (stat 0.104) (sys 0.203)

Midwest critical mass 2010 Sebastian Huber11 ongoing work two particle correlations in pp at sqrt(s) = 7 TeV 1 dimensional 3 dimensional

Midwest critical mass 2010 motivation Sebastian Huber – 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 dN CH /dη and transverse momenta k T 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

Midwest critical mass dim 7TeV – k T and dN Ch /dη Sebastian Huber – coulomb minijets 7 TeV π + π + 7 TeV π + π -

Midwest critical mass 2010 out Sebastian Huber – parametrization holes due to combination of single track acceptance p T and Pair k T cut

Midwest critical mass 2010 side Sebastian Huber –

Midwest critical mass 2010 long Sebastian Huber – edges due to acceptance of the detector in η

Midwest critical mass 2010 Sebastian Huber17 R Out && R Side && R Long measurement of BE of identical pions at 900 GeV (newest results not shown) and 7 TeV with dependance on multiplicity dN Ch /dη and pair momentum k T 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

Midwest critical mass 2010 Sebastian Huber18 R Out && R Side && R Long 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!) link to the AA data

Midwest critical mass 2010 Sebastian Huber19 Backup

Midwest critical mass 2010Sebastian Huber – holes and edges q long and q side vanish p T is sum of p T1 and p T2 k T is difference of p T1 and p T2 holes in q out combination of single particle acceptance and two particle cut leads to holes edges in q long η acceptance of the detector

Midwest critical mass 2010Sebastian Huber – event and track selectio UNICOR 7 TeV pass2 900 GeV runs by mistake?

Midwest critical mass 2010 Sebastian Huber22 UNICOR 7TeV HBT – UNICOR 7000 GeV p+p

Midwest critical mass 2010Sebastian Huber – one dimensional CF in LCMS UNICOR 7 TeV pass2 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

Midwest critical mass 2010Sebastian Huber – one dimensional CF in LCMS with kt-binning UNICOR 7 TeV pass2 first and two last bins not usable – k T > 0.7 no HBT correlation! new k T binning (see slide 10)

Midwest critical mass 2010Sebastian Huber – UNICOR 7 TeV pass2 one dimensional CF in LCMS with multiplicity-binning two highest multiplicity bins missing (by decission)

Midwest critical mass 2010Sebastian Huber – UNICOR 7 TeV pass2 one dimensional CF in LCMS with kt- and multiplicity-binning binning in kt (7 bins) dN Ch /dη

Midwest critical mass 2010Sebastian Huber – UNICOR 7 TeV pass2 three dimensional CF in LCMS – out side long baseline fits do not match the Pythia-Perugia simulation please ignore the peak fit red – Pythia-Perugia LHC10d4 red line – final parametrization blue line – peak fit green line – baseline fit

Midwest critical mass 2010Sebastian Huber – UNICOR 7 TeV pass2 three dimensional CF in LCMS with kt-binning – out side long binning in kt (5 bins) out side long

Midwest critical mass 2010Sebastian Huber – UNICOR 7 TeV pass2 three dimensional CF in LCMS with kt and multiplicity binning – out binning in kt (5 bins) dN Ch /dη

Midwest critical mass 2010Sebastian Huber – UNICOR 7 TeV pass2 three dimensional CF in LCMS with kt and multiplicity binning – side binning in kt (5 bins) dN Ch /dη

Midwest critical mass 2010Sebastian Huber – UNICOR 7 TeV pass2 three dimensional CF in LCMS with kt and multiplicity binning – long binning in kt (5 bins) dN Ch /dη

Midwest critical mass 2010 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) Systematic error Sebastian Huber – Paper preparation variation of the event cuts variation of the track cuts variation of the pair cuts mixing (vertex binning and multiplicity binning)

Midwest critical mass 2010 Sebastian Huber33 dN CH and k T dependancy

Midwest critical mass 2010 Sebastian Huber34 R Out && R Side && R Long

Midwest critical mass 2010 Sebastian Huber35 R Out && R Side && R Long