PQE: The search for Pentaquark partner states at Jefferson Lab Hall A, E04-012

1. PQE: The search for Pentaquark partner states at Jefferson Lab Hall A, E04-012 An update to the Hall A Collaboration Paul E. Reimer What were we looking for? How did we look? What did we find? (with help from all of my collaborators, especially Y. Qiang and O. Hanson and their talks at PANIC05 and Hadron05).

2. Physics Today, Sept 2003 Corners are manifestly exotic—with an unpaired antiquark! Chiral Soliton Model Diakonov, Petrov and Polyakov, Z. Phys. A 359, 305 (1997) • All baryons are rotational excitations of a rigid object. • Reproduces mass splittings in lowest baryon octet and decuplet. • Apply to 3-flavor, 5-quark states. • Anti-decuplet of states • 1 “free” parameter—fixed by identifying the Jp = (1/2)+ N(1710) explicitly with non-strange, non-exotic state in anti-decuplet • Predict mass splittings (equal) and widths. PRL 91 (2003) 012002-1 SPRing-8 LEPS M¼ 1530 MeV  < 15 MeV Paul E. Reimer, Jefferson Laboratory Hall A Collaboration Meeting

3. Physics Today, Sept 2003 Physics Today, Sept 2003 + partner states • E04-012 was approved to search for partner states to the + pentaquark. • Antidecuplet, non-exotic states • From Soliton Model, mass is set by M = M+ + (1-s) £ 107 MeV/c2 • N* and 0 • Isospin Partners (Capstick 2003) • Narrow width in terms of isospin-violating strong decays • Predicts set of narrow, exotic partners • ++ • Narrow, Low mass, states of specific strangeness Paul E. Reimer, Jefferson Laboratory Hall A Collaboration Meeting

4. Hall A Experiment E04-012 • Beam Energy: 5 GeV/c (Proposed 6 GeV/c) • Spectr. Angle: 6± (left and right w/septa) • Spectr. Momenta: 1.8 to 2.5 GeV/c • hQ2i¼ 0.1 (GeV/c)2 • In C-M  K()¼ 6± (7±) K()¼ 40 (30) msr Paul E. Reimer, Jefferson Laboratory Hall A Collaboration Meeting

5. Kinematics Paul E. Reimer, Jefferson Laboratory Hall A Collaboration Meeting

6. Kinematics Kinematics Tasks • Event identification (/K separation, random rejection) • Acceptance correction between different separate spectrometer settings • Mass calibration • Search for resonances (non-exotic 0, N*, and exotic ++) Paul E. Reimer, Jefferson Laboratory Hall A Collaboration Meeting Last Modified:  May 26, 2004

7. Single Arm PID • 2 Aerogel thres. Cerenkov counters n = 1.015, 1.055 • RICH n = 1.30 • Single arm pion reject. 3£104 • K/ ratio > 20 Coincidence Time • ToF resolution, FWHM ¼ 0.60 ns • Coincidence time difference ¼ 2 ns Reaction Vertex Z • FWHM ¼ 2.5 cm • 15 cm target reduces background by factor of 2 PID and Coincidence System Paul E. Reimer, Jefferson Laboratory Hall A Collaboration Meeting

8. p(e,e0K+)X accidental Acceptance Correction • Missing Mass acceptance is proportional to the (diagonal) length in the 2-D momentum acceptance plot. • e + p ! e0 + K§ + X • MX ¼ const – Ee0 – EK p(e,e0K+)X Paul E. Reimer, Jefferson Laboratory Hall A Collaboration Meeting

9. Acceptance Correction—Matching Spectrometer settings Total and 4 of the 8 spectra, corrected for efficiencies, effective charge and acceptance Paul E. Reimer, Jefferson Laboratory Hall A Collaboration Meeting

10. High resolution missing mass = 1.5 MeV/c2 • Missing Mass Uncertainty < 3 MeV/c2 (absolute) Missing Mass Calibration Paul E. Reimer, Jefferson Laboratory Hall A Collaboration Meeting

11. Parameters of (1520) • M(1520) = 1519.8§ 0.6 MeV/c2 •  = 16.6 § 1.5 MeV/c2 • Measured cross section at forward angle Paul E. Reimer, Jefferson Laboratory Hall A Collaboration Meeting

12. Resonance Search: 0 • Within 50 MeV/c2 window, fit spectra twice • Linear, “background” only fit (2b) • Linear + resonance Breit-Wigner (fixed width of  = 1, 3, 5 MeV/c2) convoluted w/Gaussian,  = 1.5 MeV/c2 detector resolution (2b+s) • Test of significance (Where a is the integral of the diff. cross section of the hypothesized resonance) • Most significant peak, 2¼ -6 Paul E. Reimer, Jefferson Laboratory Hall A Collaboration Meeting

13. Peak Significance: A frequentist approach • Simulate smooth mass spectra (left) • To achieve this, must consider acceptance/luminosity weight factors for 8 spectrometer settings, so randomly populate right distribution and weight events just as in analysis. Paul E. Reimer, Jefferson Laboratory Hall A Collaboration Meeting

14. Peak Significance: A frequentist approach Repeat experiment 1000 times • Simulated background spectra with actual experimental statistics—i.e. randomly populate missing mass spectra taking acceptance weights into account. • Apply peak search algorithm. • Find largest 2 improvement in each spectrum • Use distribution of “greatest 2 improvement” to determine probability such an improvement being a background fluctuation. • For 0, =5 MeV, a 2 improvement of -6 corresponds to a < 55% probability of not being a background fluctuation Paul E. Reimer, Jefferson Laboratory Hall A Collaboration Meeting

15. Upper Limits—How small is too small to be observed (heard)? Repeat experiment 1000 times • Add small resonance. • How large must resonance be for search procedure to find beam at 90% CL p(e,e0 K+)0 • For 0, least restrictive upper limit at M=1.72 GeV/c2 • 0 90% CL upper limit: 8 to16 nb/sr for  = 1 to 8 MeV/c2 Paul E. Reimer, Jefferson Laboratory Hall A Collaboration Meeting

16. N0 Upper Limits p(e,e0+)N0 • Probability of Real Peak < 50% • For N0, least restrictive upper limit at M=1.65, 1.68, 1.73, 1.86 GeV/c2 • N0 90% CL upper limit: 4 to 9 nb/sr for  = 1 to 8 MeV/c2 Paul E. Reimer, Jefferson Laboratory Hall A Collaboration Meeting

17. ++ Upper Limits p(e,e0 K-)++ • Low statistics—switch to log likelihood as estimator. • Probability of Real Peak < 80% • For ++, least restrictive upper limit at M=1.57 GeV/c2 • ++ 90% CL upper limit: 3 to 6 nb/sr for  = 1 to 8 MeV/c2 Paul E. Reimer, Jefferson Laboratory Hall A Collaboration Meeting

18. Summary • PQE/E04-012 has completed a high resolution search for narrow partner states to the +. • No strong signal is observed for the ++, 0 or N0 • All “bumps” are statistically consistent with the background. Paul E. Reimer, Jefferson Laboratory Hall A Collaboration Meeting