Argonne National Laboratory is managed by The University of Chicago for the U.S. Department of Energy PQE: The search for Pentaquark partner states at Jefferson Lab Hall A, E 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).

26 December 2005Paul E. Reimer, Jefferson Laboratory Hall A Collaboration Meeting Chiral Soliton Model Physics Today, Sept 2003 Corners are manifestly exotic with an unpaired antiquark! 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 parameterfixed by identifying the J p = (1/2) + N(1710) explicitly with non- strange, non-exotic state in anti-decuplet Predict mass splittings (equal) and widths. M ¼ 1530 MeV < 15 MeV PRL 91 (2003) SPRing-8 LEPS

36 December 2005Paul E. Reimer, Jefferson Laboratory Hall A Collaboration Meeting Physics Today, Sept partner states E 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/c 2 –N * and 0 Physics Today, Sept 2003 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

46 December 2005Paul E. Reimer, Jefferson Laboratory Hall A Collaboration Meeting Hall A Experiment E ReactionMass Range p(e,e 0 K + ) MeV/c 2 p(e,e 0 + )N * MeV/c 2 p(e,e 0 K - ) MeV/c 2 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 h Q 2 i ¼ 0.1 (GeV/c) 2 In C-M K( ) ¼ 6 ± (7 ± ) K( ) ¼ 40 (30) msr

56 December 2005Paul E. Reimer, Jefferson Laboratory Hall A Collaboration Meeting Kinematics Calibration settings KinE0E0 Spect. Mom. (GeV)Central Missing MassPurpose Left (K/ ) Right (e)K 1, Neutron ) ) RICH Eff. ++ settings KinE0E0 Spect. Mom. (GeV)Central Missing MassPurpose Left (K/ ) Right (e)K

66 December 2005Paul E. Reimer, Jefferson Laboratory Hall A Collaboration Meeting Kinematics Last Modified: May 26, , N 0 Settings KinE0E0 Spect. Mom. (GeV)Central Missing MassPurpose Left (K/ ) Right (e)K , N * , N * , N * , N * , N * , N * , 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 ++ )

76 December 2005Paul E. Reimer, Jefferson Laboratory Hall A Collaboration Meeting PID and Coincidence System Single Arm PID 2 Aerogel thres. Cerenkov counters n = 1.015, RICH n = 1.30 Single arm pion reject. 3 £ 10 4 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

86 December 2005Paul E. Reimer, Jefferson Laboratory Hall A Collaboration Meeting Acceptance Correction Missing Mass acceptance is proportional to the (diagonal) length in the 2-D momentum acceptance plot. –e + p ! e 0 + K § + X –M X ¼ const – E e 0 – E K p(e,e 0 + )X accidental p(e,e 0 + )X

96 December 2005Paul E. Reimer, Jefferson Laboratory Hall A Collaboration Meeting Acceptance CorrectionMatching Spectrometer settings Total and 4 of the 8 spectra, corrected for efficiencies, effective charge and acceptance

106 December 2005Paul E. Reimer, Jefferson Laboratory Hall A Collaboration Meeting Missing Mass Calibration High resolution missing mass = 1.5 MeV/c 2 Missing Mass Uncertainty < 3 MeV/c 2 (absolute)

116 December 2005Paul E. Reimer, Jefferson Laboratory Hall A Collaboration Meeting Parameters of (1520) M (1520) = § 0.6 MeV/c 2 = 16.6 § 1.5 MeV/c 2 Measured cross section at forward angle

126 December 2005Paul E. Reimer, Jefferson Laboratory Hall A Collaboration Meeting Within 50 MeV/c 2 window, fit spectra twice 1.Linear, background only fit ( 2 b ) 2.Linear + resonance Breit-Wigner (fixed width of = 1, 3, 5 MeV/c 2 ) convoluted w/Gaussian, = 1.5 MeV/c 2 detector resolution ( 2 b+s ) Test of significance (Where a is the integral of the diff. cross section of the hypothesized resonance) Most significant peak, 2 ¼ -6 Resonance Search: 0

136 December 2005Paul E. Reimer, Jefferson Laboratory Hall A Collaboration Meeting Is this peak significant, or just background noise (heard by an elephant?) Are there any Whos down in Whoville?

146 December 2005Paul E. Reimer, Jefferson Laboratory Hall A Collaboration Meeting 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.

156 December 2005Paul E. Reimer, Jefferson Laboratory Hall A Collaboration Meeting Repeat experiment 1000 times Simulated background spectra with actual experimental statisticsi.e. randomly populate missing mass spectra taking acceptance weights into account. Apply peak search algorithm. Peak Significance: A frequentist approach 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

166 December 2005Paul E. Reimer, Jefferson Laboratory Hall A Collaboration Meeting Upper LimitsHow 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,e 0 K + ) 0 For 0, least restrictive upper limit at M=1.72 GeV/c % CL upper limit: 8 to16 nb/sr for = 1 to 8 MeV/c 2

176 December 2005Paul E. Reimer, Jefferson Laboratory Hall A Collaboration Meeting N 0 Upper Limits p(e,e 0 + ) 0 Probability of Real Peak < 50% For 0, least restrictive upper limit at M=1.65, 1.68, 1.73, 1.86 GeV/c % CL upper limit: 4 to 9 nb/sr for = 1 to 8 MeV/c 2

186 December 2005Paul E. Reimer, Jefferson Laboratory Hall A Collaboration Meeting ++ Upper Limits p(e,e 0 K - ) ++ Low statisticsswitch to log likelihood as estimator. Probability of Real Peak < 80% For ++, least restrictive upper limit at M=1.57 GeV/c % CL upper limit: 3 to 6 nb/sr for = 1 to 8 MeV/c 2

196 December 2005Paul E. Reimer, Jefferson Laboratory Hall A Collaboration Meeting Summary PQE/E has completed a high resolution search for narrow partner states to the +. No strong signal is observed for the ++, 0 or N 0 All bumps are statistically consistent with the background.

206 December 2005Paul E. Reimer, Jefferson Laboratory Hall A Collaboration Meeting Collaboration J. Annand, J. Arrington, Y. Azimov, C. M. Camacho, G. Cates, J. P. Chen, S. Choi, E. Chudakov, F. Cusanno, K. de Jager, M. Epstein, R. Feuerbach, J. Gomez, O. Gayou, F. Garibaldi, R. Gilman, D. Hamilton, O. Hansen, D. Higinbotham, T. Holmstrom, M. Iodice, X. Jiang, M. Jones, J. Lerose, R. Lindgren, N. Liyanage, D. Margaziotis, P. Markowitz, V. Mamyan, R. Michaels, Z. Mezianni, P. Monaghan, V. Nelyubin, K. Paschke, E. Piasetzky, P. Reimer (co- spokesperson), J. Reinhold, B. Reitz, R. Roche, Yi Qiang (Ph.D. student), A. Sarty, A. Saha, E. Schulte, A. Shahinyan, R. Sheyor, J. Singh, I. Strakovsky, R. Subedi, R. Suleiman, V. Sulkovsky, B. Wojtsekhowski (contact and spokesperson), X. Zheng and the Hall A Collaboration

216 December 2005Paul E. Reimer, Jefferson Laboratory Hall A Collaboration Meeting Other resonances in the region 1600)--***--mass range , width from PDG estimate width is only seen in PWA analysis according to PDG. 1670)--****--width only MeV, and mass well determined, only seen in DPWA (some old bubble chamber results also are used in the branching ratios). 1690)--****--width only MeV, only seen in DPWA. 1800)--***--wide mass range of possibly out of our acceptance. Extremely wide MeV. Only seen in partial wave analyses. 1560)--**-- listed as "bumps"--width MeV. 1580)--*--width of 15 MeV 1620)--**--width of MeV from PWA and seen in prod. expt. (bubble chambers). 1660)--***--mass of width of MeV, PWA analysis only 1670)--****--width of MeV PWA only. Formation experiments see bumps here. 1690)--**--listed at "bumps", seen in formation experiments with width of MeV. 1750)--***--mass MeV, width MeV. Primarily seen in PWA, but some bubble chamber results. 1770)--*--width of 70 MeV, partial wave analysis. 1775)--****--width of MeV seen in PWA.

226 December 2005Paul E. Reimer, Jefferson Laboratory Hall A Collaboration Meeting Wide resonances 1520) 350 nb 16.6 MeV/c 2 10 nb 8 MeV/c 2 10 nb 45 MeV/c 2 The key to this experiment is to search for narrow resonances. Sensitivity decreases dramatically at the with grows Same number of counts