1 E895  - correlation analysis - Status Report Mike Lisa, The Ohio State University E895 Motivation and Measurement Status of HBT analysis Summary and plans

2 Lawrence Berkeley Lab D. Best, T. Case, K. Crowe, D. Olson, G. Rai, H.-G. Ritter, L. Schroeder, J. Symons, T. Wienold Brookhaven National Lab S. Gushue, N. Stone Carnegie Mellon UniversityM. Kaplan, Z. Milosevich, J. Whitfield Columbia University I. Chemakin, B. Cole, H. Hiejima, X. Yang, Y. Zhang U.C. Davis P. Brady, B. Caskey, D. Cebra, J. Chance, J. Draper, M. Heffner, J. Romero, L. Wood St. Mary’s CollegeJ. Kintner Harbin Institute (China)L. Huo, Y. Liu, W. Zhang Kent State UniveristyM. Justice, D. Keane, H. Liu, S. Panitkin, S. Wang, R. Witt Lawrence Livermore LabV. Cianciolo, R. Sotlz Ohio State UniversityA. Das, M. Lisa, R. Wells University of Auckland (NZ)D. Krofcheck Purdue University M. Gilkes, A. Hirsch, E. Hjort, N. Porile, R. Scharenberg, B. Srivastava S.U.N.Y. Stony Brook N.N. Ajitanand, J. Alexander, P. Chung, R. Lacey, J. Lauret, E. LeBras, B. McGrath, C. Pinkenburg

3 Systematics/meta-analysis suggest approach to maximum AGS energy interesting... P. Braun-Munzinger and J. Stachel, NPA606, 320 (1996)

4 Perhaps some signals only apparent near threshold D. Rischke, NPA 610, c88 (1996) E895 flow status discussed by R. Lacey

5 Ideally, HBT gives a measure of source size

6 HBT systematics at AGS interesting in themselves, & can look for suprises “”“” “c”“c” Rischke & Gyulassy NPA 608, 479 (1996) May miss signal at “too high” E beam

7 HBT - another handle on mean field effects at AGS Generated by H. Liu and S. Panitkin

8 AGS  Bevalac Particle reconstruction upgrades have taken huge effort, but have born fruit...

9 PID via dE/dx for primaries (negative particles cleaner) 2 AGeV 4 AGeV 8 AGeV

10 Strange neutrals reconstructed (& provide sensitive diagnostic of data quality) plots from P. Chung, SUNY-SB   p +   K 0    

11 Non-uniform trigger in dataset analysed Will be possible to select top ~5% for all energies offline Current analysis: 2 GeV: b  0-8 fm 4 GeV: b  0-8 fm 8 GeV: b  0-3 fm Otherwise seems OK e.g. log increase of multiplicity with E beam : E beam  E beam M max  M max + 50 M  max  M  max + 15

12 Singles coverage for pions

13 Large acceptance  many  - But...phase space means most are at large Q Background (denominator) generated with standard event-mixing (15 previous) 4 GeV central

14 Pairwise cuts to remove track splitting effects “Raw” correlation function shows encouraging structure at low Q inv Simulations: requirement that > 50% of track is seen kills truly found pairs. (Au+Be event)

15 Pairwise cuts, cont’ Track-splitting virtually eliminated by pairwise cut: require that sum of % track seen > 100% (applied to “real” and “mixed” pairs) Next low-Q problem: track-merging.

16 Merging effect reduced by cut on projected seperation at exit of TPC. Real pairs Mixed pairs

17 Require particles to exit TPC 10 cm apart. 0 cm cut 5 cm cut 10 cm cut 15 cm cut

18 Overview of E895 HBT Analysis raw data (pass1) TRKS HBT_SW HBT_EVENT_CUT HBT_TRK_CUT HBT_PAIR_CUT Embed MC pairs into raw data perform pass1 correlate embedded, extracted particles fit of singles distribution generation of MC pairs (kuip macro files) EMBED_PARTS TRKS AM_PIDAM_HBT histograms acceptance corrections coulomb correction diagnostic ntuples correlation functions

19 Corrections - I Ideally... “Background” pair distribution contains all physics and detector effects except for the BE symmetrization Well-known deviation from this is due to final-state Coulomb repulsion... Approximate correction - Gamow factor: (Better to do full Coulomb integration)

20 Corrections - II Detector acceptance effects are more subtle, especially with a tracking detector Original pion pair k1k1 k2k2 MC Scattering Pattern recognition Digitization, thresholds Pixel noise Measured particle(s) k 1 ’, k 2 ’, (k 3 ’...) Track merging and splitting and momentum resolution and distortion. Hit the low-Q pairs hardest, and affect the correlation signal significantly. Effects depend on k 1, k 2 (six-dimensional!), as well as track and pair cuts!!! Correcting for or minimizing these 2-particle effects requires detailed simulation.

21 Generating the Acceptance /Resolution Correction - I C 2 (ideal) C 2 (reconstructed) = R(k 1,k 2 ) B(k 1,k 2 ) R(k 1,k 2 ) B(k 1,k 2 ) K acceptance = B(k 1,k 2 ) = d6Nd6N d3k1d3k2d3k1d3k2 R(k 1,k 2 ) = d6Nd6N d3k1d3k2d3k1d3k2 C 2 (k 1,k 2 ) for some set of cuts: only phase space (k) cut applied (no track quality or 2-track cuts) B(k 1,k 2 ) = d6Nd6N d3k1d3k2d3k1d3k2 R(k 1,k 2 ) = d6Nd6N d3k1d3k2d3k1d3k2 C 2 (k 1,k 2 ) apply same track and pair cuts as applied to data (weighting by C 2 (k 1,k 2 ) implies foreknowledge of correlation function  iterative approach)

22 Understanding close pairs Close pairs are embedded into real data events at pixel level with measured momentum distribution, to get correct noise track density environment Full event reconstruction run Gives momentum distortions, pair loss...

23 Resolution from the 4 GeV simulations MeV/c resolution (includes MCS) finite resolution + phase space give Q distortion at low Q (Q in > 40 MeV/c)

24 Pair loss from 4 GeV simulations Pair loss constant above 50 MeV/c (statistical loss of single track) Single pair in... Lost pairSplit track

25 Finally: “Correction to the Coulomb Correction” In the measured ratios, we apply the Coulomb correction (currently the Gamow correction) according to the measured Q, not the true Q. With the simulated pairs, we have the true and reconstructed momenta, so can account for this. Then, the full acceptance/resolution correction function is: R(k 1,k 2 ) B(k 1,k 2 ) R(k 1,k 2 ) B(k 1,k 2 )  G(k 1,k 2 )

26 Corrections for 10 cm exit seperation

27 Corrections for 2 cm exit separation

28 Acceptance/resolution well understood & accounted for 2 cm exit separation cut10 cm exit separation cut Different cuts give very different raw correlation functions. But corrected correlation function is robust. 2 GeV results

29 Data points consistent - fits are sensitive

30 4 GeV results stable (and reasonable) as well 10 cm exit separation cut2 cm exit separation cut

31 8 GeV results not stable or reasonable (under study) 10 cm exit separation cut 2 cm exit separation cut

32 Summary E895 can measure low-Q correlations well Difficulties of close pairs (splitters/mergers) largely addressed through pairwise cuts Detailed simulations generate corrections that track with cuts –These corrections are significant and important Different quality cuts –  very different measured correlation functions –  very different measured corrections –  NOT different corrected correlation functions Must figure out what is going on at high energy Multi-dimensional HBT and phase space cuts come next (present analysis on < 5% of data)