Non-identified Two Particle Correlations from Run I

1. Non-identified Two Particle Correlations from Run I • Understanding drift chamber tracking • Tracker and candidatory • Two particle efficiencies/ghosts • A first look. Momentum distributions, etc. • First correlation function • Gamow corrections • And from here…

2. The current status of DC tracking • As I understand it. • Tracker (old): • Assumes x wires parallel to beam. • Works in nominal dc position, even with minor changes in geometry • Large fraction of tracks with reconstructed UV wires • Candidatory (new): • Same pattern recognition philosophy as above. • Built to withstand major changes in geometry (I.e. retracted arms) • Better interface to the rest of dc software • Cleaner separation of pattern recognition from hit association • Most tracks are not reconstructed through UV wires (‘simple’ bug) • currently bypasses this problem by boot-strapping with PC1 • What we need to use in the long run – but unusable now. (?)

3. DC tracking variables: • Use bounded, natural variables for pattern recognition (I.e. not slope and intercept) • Two particle effects occur at low f and a with the x wires and b and zed with the uv. • Can see from this that two particle inefficiencies occur at low relative f and a => almost no two track inefficiency in opposite charged tracks. • 3-momentum reconstructed from fit to associated hits in PHDchTrackModel

4. Ghosting in tracker: • Small (but measurable) fraction of tracks have a ghost pair at low f and a. (=> low q) • 3 solutions: • 1. Fix tracker to remove ghosts (in progress by DC group) • 2. Quantitatively understand 2-particle in/over-efficiencies and correct for it • 3. Cut it out • You don’t have to think to hard to know which choice I made here … • Cut in 2-dimensional a-f space. Real Mixed df

5. Ghosting in zed Real Mixed • A look at the raw d(zed) distribution [top] also shows a clear ghosting problem. • After cutting on |df|<.005 && |da|<.005, however, the peak in zed disappears • I should probably make a full 3d cut, but this will do for this talk… dzed Real Mixed dzed

6. [A reminder or impetus for further personal study…] Amplitude for detecting two bosons (pions in my case) in above configuration is: Then the probability is the amplitude squared, and integrating over the source: The 2 particle counting rate is related to the Fourier transform of the source. The normalization of r requires C(q=0) -> 2. Then for a simple Gaussian source: Want to know more? Motivation for studying correlation functions* (r1,p1) x y (r2,p2) * This slide stolen almost completely from W. Zajc, Proc. Of 4th Intersections Conference (1991)

7. Event characterization • Runs: • 9979, 9981, 9987, 9988, 9992 • 20 files • Events: ~20k • <½ in pairs I’ll show today • Some naïve cuts just to get us started • |BBC zvtx| < 30cm (Track model works out to +/- 45 cm • > 50 tracks reconstructed (~central) • => Pairs: • 760K + + • 430K - - • 1.1M + -

8. Kinematic distributions • DC pattern recognition and track model built to work above 180 MeV. • Cut out low pt part • Unphysical • Bug in track model (?) • And a kt distribution … • <kt>~700 MeV for all tracks • <kt>~400 MeV for all tracks with q<100MeV kt(GeV/c)

9. q distributions Real Mixed • q=|p1-p2| • Before the ghost tracks cut the real distribution shows a strong peak at low q. After the ghosting cut in both the real and mixed the distributions are similar. (though we hope they’re not identical) • Now as experimentalists, we determine the probability of detecting pairs at relative momentum q by measuring the ratio: A(q)/B(q) • A(q) => distribution of measured q from same event pairs • B(q) => from different (uncorrelated) events q (GeV/c) Real Mixed q (GeV/c)

10. Raw correlation function ++ • Recall: in ideal case, C(q)->2 • But we don’t have ideal bosons since they are charged • leads to a depletion at low q due to the coulomb repulsion of the pair --

11. Gamow Correction • First correction: Gamow correction for particles from point source: • Dependent on mass of particles in pair … • Ratios of particles from Min Bias hijing as a function of q • pp = 87.6% • pK = 9.3% • pp = 2.5% • KK = .3%

12. Gamow correcting opposites • In red: • raw correlation function for opposite pairs • In blue: • corrected for Gamow assuming a point source. • It appears to be an over correction • not surprising since we don’t have a point source • or if we did we should call a CERN press conference. +-

13. And Gamow Corrected… -- • Now same charge pairs corrected for Gamow. • Again, an over-correction at low q. (off scale) • Low statistics. • But, heck … let’s fit a Gaussian to that and see what we get. ++

14. Analysis Note #7 • Simple study of PHENIX’s ability to resolve source size: • Throw two tracks into acceptance. • Impose artificial correlation on pair. • Reconstruct R from correlation. Questions: http://www.phenix.bnl.gov/p/info/an/007/

15. Slight beam energy dependence strong centrality and kt dependence. What’s shown here is for higher <kt> than most previous experiments. In the end we’ll do it as a function of kt for direct comparison The point: First study Correlation function is visible with a small fraction of the data set Results of 1D fit are in the ballpark Comparisons

16. Lots still to do: • Understand two particle ghosts/efficiencies/etc • p/q resolutions • PID! • Requires working DC code, track model and TOF • Multi-dimensional anaysis • Full coulomb correction • Centrality/kt dependence • Etc, etc, etc. • Another postdoc at LLNL (Mike Heffner) has just begun additional studies on correlations • David Brown, source imaging guru, joining theory effort in October • Schedule to have publishable results by QM 2001