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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). Argonne National Laboratory is managed by The University of Chicago for the U.S. Department of Energy Physics Today, Sept 2003 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. PRL 91 (2003) 012002-1 Predict mass splittings (equal) and widths. M ¼ 1530 MeV < 15 MeV 6 December 2005 Paul E. Reimer, Jefferson Laboratory Hall A Collaboration Meeting SPRing-8 LEPS 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 nonstrange, non-exotic state in anti-decuplet Corners are manifestly exotic— with an unpaired antiquark! 2 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 6 December 2005 Paul E. Reimer, Jefferson Laboratory Hall A Collaboration Meeting 3 Hall A Experiment E04-012 Reaction Mass Range p(e,e0 K+)0 1550-1810 MeV/c2 p(e,e0 +)N* 1600-1830 MeV/c2 p(e,e0 K-)++ 1500-1600 MeV/c2 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 hQ2i ¼ 0.1 (GeV/c)2 In C-M K( )¼ 6± (7±) K()¼ 40 (30) msr 6 December 2005 Paul E. Reimer, Jefferson Laboratory Hall A Collaboration Meeting 4 Kinematics Calibration settings Kin E0 Spect. Mom. (GeV) Central Missing Mass Purpose Left (K/) Right (e) K 1, 2 5.0 2.29 2.50 0.899 0.994 Neutron 3 5.0 2.22 2.50 1.123 1.14 (1116) 4 5.0 2.10 2.00 1.523 1.585 (1520) 14 5.0 0.55 1.85 2.094 2.359 RICH Eff. ++ settings Kin E0 Spect. Mom. (GeV) Central Missing Mass Left (K/) Right (e) K Purpose 8 5.0 2.10 2.00 1.523 1.585 ++ 9 5.0 1.93 2.00 1.611 1.680 ++ 17 5.0 2.06 2.00 1.550 1.613 ++ 6 December 2005 Paul E. Reimer, Jefferson Laboratory Hall A Collaboration Meeting 5 Kinematics 0, N0 Settings Kin E0 Spect. Mom. (GeV) Central Missing Mass Left (K/) Right (e) K Purpose 5 5.0 1.93 2.00 1.611 1.680 0, N* 6 5.0 1.93 1.93 1.648 1.718 0, N* 7 5.0 1.90 1.70 1.778 1.851 0, N* 10 5.0 1.93 1.83 1.700 1.770 0, N* 11 5.0 1.93 1.89 1.622 1.691 0, N* 12 5.0 1.93 2.02 1.600 1.669 0, N* 13 5.0 1.89 1.85 1.713 1.785 0, N* 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 ++) 6 December 2005 Paul E. Reimer, Jefferson Laboratory Hall A Collaboration Meeting 6 PID and Coincidence System 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 6 December 2005 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 Paul E. Reimer, Jefferson Laboratory Hall A Collaboration Meeting 7 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 accidental p(e,e0K+)X 6 December 2005 Paul E. Reimer, Jefferson Laboratory Hall A Collaboration Meeting 8 Acceptance Correction—Matching Spectrometer settings Total and 4 of the 8 spectra, corrected for efficiencies, effective charge and acceptance 6 December 2005 Paul E. Reimer, Jefferson Laboratory Hall A Collaboration Meeting 9 Missing Mass Calibration High resolution missing mass = 1.5 MeV/c2 Missing Mass Uncertainty < 3 MeV/c2 (absolute) 6 December 2005 Paul E. Reimer, Jefferson Laboratory Hall A Collaboration Meeting 10 Parameters of (1520) M(1520) = 1519.8§ 0.6 MeV/c2 = 16.6 § 1.5 MeV/c2 6 December 2005 Measured cross section at forward angle Paul E. Reimer, Jefferson Laboratory Hall A Collaboration Meeting 11 Resonance Search: 0 Within 50 MeV/c2 window, fit spectra twice 1. Linear, “background” only fit (2b) 2. 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) 2 2 a0 2 s b b , 2 2 ( s b b ) a 0 Most significant peak, 2 ¼ -6 6 December 2005 Paul E. Reimer, Jefferson Laboratory Hall A Collaboration Meeting 12 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. 6 December 2005 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. 2 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 6 December 2005 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 6 December 2005 Paul E. Reimer, Jefferson Laboratory Hall A Collaboration Meeting 16 N0 Upper Limits p(e,e0 )N + 0 Probability of Real Peak < 50% For N0, least restrictive upper limit at M=1.65, 1.68, 1.73, 1.86 GeV/c2 0 N 90% CL upper limit: 4 to 9 nb/sr for = 1 to 8 MeV/c2 6 December 2005 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 6 December 2005 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. 6 December 2005 Paul E. Reimer, Jefferson Laboratory Hall A Collaboration Meeting 19