FTPC Physics: Past & Future

1. FTPC Physics: Past & Future Frank Simon and Peter Seyboth Max-Planck-Institut für Physik, Munich, Germany (for the FTPC group) STAR Upgrade Workshop, Yale, June 16, 2004 FTPC review, BNL, July 19, 2004 • The forward rapidity region • Bulk properties: Flow and <pt> • Strangeness • Future Plans • Summary & Outlook

2. The Forward Rapidity Region • At mid-rapidity: • Many observables (almost) boost-invariant: • dN/dy, <pt>, v2 • Very small v1 • Antiparticle/particle ratios ~ 1, low baryon density • The FTPCs: 2.5 < |h| < 4.0 • Closer to the fragmentation region • Sizeable v1 • Significant baryon transport to this region • In d+Au collisions: Collision asymmetry and low-x phenomena • Two detectors: Large rapidity gap for correlation analysis

3. The Forward TPCs 2 FTPCs 2.5 < || < 4.0 6 azimuthal sectors (~60 deg.) with 10 rows in z- direction Electron drift radial and perpendicular to the magnetic field Spatial res.  200-300 mm Two track res.  2-2.5 mm

4. FTPC Calibration • Main Calibration issues understood (we hope ) • Detector alignment • Cathode offset • Gas composition calibration with lasers • Calibration done for AuAu (2001), pp (2002&2003) and dAu (2003), almost complete for 2004 • Simulations and Embedding working • Efficiency corrections for spectra and strangeness • Study of momentum resolution

5. Efficiency and Momentum Resolution • Efficiency and momentum resolution for AuAu MinBias studied with embedding efficiency momentum resolution

6. Tracking efficiency d+Au Au+Au Trackfinding eff. constant in pt and 3<|h|<3.5. In d+Au eff. around 90% mainly determined by the electronic loss in the FTPCs. In Au+Au top 5% central not fully understood yet.

7. Au+Au dN/dh • Good agreement with PHOBOS: Corrections under control! • So far no subtraction of background, especially central events need more work

8. <pt>: RHIC vs SPS • <pt> in the FTPCs consistent with mean pt at mid-rapidity in SPS -> Same particle density at given h - ybeam

9. Directed Flow in Au+Au • v1 shows a strong rise with rapidity • Limiting fragmentation applies (comparison to NA49 data) • Already published: Phys. Rev. Lett. 92 (2004) 062301

10. Elliptic Flow in Au+Au • Good agreement of different analysis methods -> Non-flow effects in the FTPCs not very pronounced • PRC in preparation • Consistent with PHOBOS results

11. Directed Flow v1(η) at 62 GeV Aihong Tang Three particle cumulants v1{3} by Aihong Tang • v1 is a smooth and almost linear function of η • No wiggle visible (slope in the TPC should be opposite to the FTPC slope)! Mixed harmonics event plane method v1{EP1,EP2} • Not even the full statistics yet (only about 3.5 M events) • Good agreement with the cumulant method v1{3} for all centrality bins

12. Limiting Fragmentation? Aihong Tang • STAR’s v1 @ 200 GeV data plotted together with shifted* NA49 data • The new STAR v1 @ 62.4 GeV is shifted accordingly. • Limiting fragmentation seems to work in forward regions • However, there might be a discrepancy around η = 2. * Shifted by the difference in beam rapidities

13. Elliptic Flow v2(η) at 62 GeV minimum bias (0-80%) • Usual event plane method works fine for elliptic flow v2. • The second order event plane is measured in the TPC and all particles (TPC and FTPC) are correlated to this event plane. • Statistics is very good, even for the different centrality bins. • The two most peripheral centrality bins need more work due to the bad event plane resolution.

14. The Sign of Elliptic Flow v2 62.4 GeV (4.20 ± 0.35) · 10-5 Average over all centralities with error bar • With the high statistics the ‘positiveness’ is very prominent and the mean of v12·v2 = (4.20 ± 0.35) · 10-5 • Elliptic flow at 62.4 GeV is in-plane (as expected) • The observed rise comes from the rising v1 vs. centrality. 0

15. dN/dh in d+Au • Clear asymmetry of the events • FTPCs sit in an interesting region: used for centrality definition for mid-rapidity analysis (Published in the d+Au high-pt PRL) • Consistent with PHOBOS (difference in central due to centrality def)

16. Nuclear Modification Factor • Rcp independent of centrality on the Au side • Strong centrality dependence on the d side, has been discussed as a potential signal for saturation, but might also be due to multiple collisions of d projectiles • RdAu needs an analysis of the pp data, not done yet

17. L in d+Au • No particle ID via dE/dx -> strict geometric cuts needed • Remaining background from K0 taken from simulations • Shape of invariant mass distribution reproduced by simulations • High multiplicity problematic, analysis might not be possible in Au+Au L, FTPC W

18. Anti-L/L Ratio • Differences for Au and d side due to different contributions of baryon transport and pair production • Poster at QM04, nucl-ex/0403017

19. Anti-L and L Yields • Preliminary corrections for efficiency and feeddown • Systematic errors not estimated yet, big contributions from extrapolation expected • Look at different centralities

20. Future Physics Projects • Existing analyses (flow) for other collision systems and energies • Strangeness maybe not possible in larger systems • Forward/Backward Correlations: use both FTPCs to span a large rapidity gap • Use FTPC tracks to correlate with PMD (charged particles from FTPC, neutrals from the PMD). Search for Disoriented Chiral Condensate. • Correlation of FTPC tracks and FPD π0 • Reaction plane for HBT analysis ? • Extend tracking in UPC studies ?

21. F/B Correlations: Motivation ( Pudue group particularly interested in this topic) • The Study of correlations among particles produced in different rapidity regions helps to understand the mechanisms of particle production. • Many experiments show strong positive short-range correlations: Particles cluster over ~1 unit of rapidity • Central rapidity is dominated by these short-range correlations • Long-range correlations should be much stronger in p+A and A+A compared to p+p at the same energy • String fusion: Particles are produced by color strings. In high-density environments, the strings might fuse and lead to long-range correlations • Use the FTPC to study correlations over 6 units in rapidity

22. <nf nb> - <nf > <nb> b = <nf 2> - <nf >2 F/B Multiplicity Correlations: p+p • 2.5 M minbias events • |h| < 1.3 • Correlation strength increases with energy, STAR consistent with other experiments = Correlation Strength

23. Correlation Strength and Rapidity Gap • Study in the TPC dominated by short-range correlation • Does it go to 0 with larger rapidity gaps? Or might there be percolation/string fusion? d+Au and Au+Au: 10% most central

24. Summary • FTPC calibration mostly understood: Ready for physics • Final or near final results: • dN/dh, <pt> for Au+Au and d+Au • v1 and v2 for Au+Au • Analysis in progress: • Lambdas in d+Au • F/B correlation studies with FTPCs (string fusion studies) • FTPC results have been published in several papers and are included in paper drafts in preparation • Future: • Provide reaction plane for high pt and HBT studies in TPC • Provide independent centrality selection via FTPC multiplicities • Look for jets accompanying high ptp0 in FPD • Charged particle multiplicity in PMD acceptance (DCC study)

25. Who was/is doing it? • Volker Eckardt (MPI) • Alexei Lebedev (BNL) • Markus Oldenburg (LBL) • Jörn Putschke (MPI) • Janet Seyboth (MPI) • Peter Seyboth (MPI) • Frank Simon (MPI) • Brijesh Srivastava (Purdue) • Terry Tarnowsky (Purdue) Invaluable support (database, embedding, production, slow control, …) • Lidia Didenko • Eric Hjort • Jerome Lauret • Jeff Porter / Michael DePhilips • Bill Waggoner/ Dennis Reichhold • ....