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Yi Qiang, The search for pentaquarks at JLab Hall A 1 June 2006 The Search for PentaQuarks at Jefferson Lab Hall A: E Yi Qiang Massachusetts Institute of Technology for JLab E Collaboration Hall A Collaboration Meeting, June 2006

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Yi Qiang, The search for pentaquarks at JLab Hall A2June 2006 PentaQuark Model Chiral Quark Soliton Model (Diakonov et al., 1997) predicts an anti-decuplet of pentaquarks Iso-spin Partners (Capstick et al., 2003): Narrow width in terms of isospin-violating strong decays Following theoretical and experimental studies suggested: – Narrow ( 1~8 MeV) – Low mass (Θ~1530 MeV) – Physics Today, Sept 2003 Corners are manifestly exotic with an unpaired antiquark! Spring-8 LEPS PRL 91 (2003)

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Yi Qiang, The search for pentaquarks at JLab Hall A3June 2006 Hall A Experiment E – 1810 MeV 1610 – 1880 MeV 1470 – 1590 MeV 15cm Beam Energy: 5GeV Left and Right HRS angle: 6° Left HRS (hadron): 1.85 ~ 2.0 GeV/c Right HRS (e): 1.89 ~ 2.10 GeV/c Q 2 : ~ 0.1 (GeV/c) 2 High Resolution and Statistics!

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Yi Qiang, The search for pentaquarks at JLab Hall A4June 2006 Particle Identification Left HRS: Aerogel 1 & 2 Cherenkov Counters; Ring Imaging Cherenkov detector: RICH; Lead Glass Pion Rejector. Right HRS: Gas Cherenkov RICH detector has very good Cherenkov angle resolution: ~ 6 mrad, which reduced pion contamination from kaon events to less than 5 % K Freon Radiator (n=1.28) CsI Pad Photocathode MWPC

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Yi Qiang, The search for pentaquarks at JLab Hall A5June 2006 Coincidence System TOF Resolution : FWHM 600 ps CT difference ~ 2 ns Longitudinal target vertex resolution: FWHM 2.5 cm 15 cm extended Target removes background by a factor of 2

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Yi Qiang, The search for pentaquarks at JLab Hall A6June 2006 Missing Mass Calibration High Missing Mass Resolution mm = 1.5 MeV Mass Uncertainty < 3 MeV Better than ANY previous experiment!

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Yi Qiang, The search for pentaquarks at JLab Hall A7June 2006 Combine Kinematics Settings Small momentum acceptance of HRS requires combined kinematics settings Pure Counts in individual missing mass spectra was transformed into differential cross-section of virtual photoproduction in CMS: The Combination was very smooth!

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Yi Qiang, The search for pentaquarks at JLab Hall A8June 2006 Γ=16.5 ± 1.7 MeV/c 2 (PDG: 15.6 ± 1.0 MeV/c 2 ) Parameters of

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Yi Qiang, The search for pentaquarks at JLab Hall A9June 2006 First glance of all three channels No observation of significant narrow structure in any of them Need further attempt to settle down the problem: Feldman- Cousins approach

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Yi Qiang, The search for pentaquarks at JLab Hall A10June 2006 Feldman-Cousins Approach A way which will automatically determine confidential interval type: pure upper limit or interval Test statistics: 80% 90% 0 90% upper limit 80% interval For each ordering of 2 will find out 2 90% (from M.C.): Create 90% CL interval: the collection of satisfying

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Yi Qiang, The search for pentaquarks at JLab Hall A11June 2006 Fit and Monte-Carlo We selected four different fixed widths: 0.5, 2, 5, 10 MeV; At each point of M X, we first determined the background level by fitting the side bands: both 20 MeV above and below the 90% resonance window; Fix the background level, then fit in the resonance window with only cross- section varying and get 2 exp ( ) 1000 M.C. experiments with resonace was generated to get 2 90% ( ) Compare 2 exp ( ) and 2 90% ( ) to get 90% CL interval 20 MeV side bands 90% Resonance window

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Yi Qiang, The search for pentaquarks at JLab Hall A12June 2006 Upper Limits Blue: upper limit Red: lower limit Green: 90% background flucuation Maximum upper limit: 7 nb/sr ~ 17.5 nb/sr

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Yi Qiang, The search for pentaquarks at JLab Hall A13June 2006 Upper Limits 90% CL upper limit at that position ranges: 4.5 nb/sr ~ 10.5 nb/sr for 0.5~10 MeV width

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Yi Qiang, The search for pentaquarks at JLab Hall A14June 2006 Upper Limits 90% CL upper limit at that position ranges: 3.0 nb/sr ~ 4.0 nb/sr for 0.5~10 MeV width

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Yi Qiang, The search for pentaquarks at JLab Hall A15June 2006 Summary Theres no significant narrow pentaquark structures observed in Hall A experiment E04-012; All signals seen are consistent to statistical fluctuation. The maximum upper limits and ratio to (1520) production are listed at a function of selected width. (MeV/c 2 ) Mass Range (MeV/c 2 ) (nb/sr) 7.0 (1.7%)9.0 (2.1%)13.0 (3.1%)17.5 (4.2%) (nb/sr) 4.5 (1.1%)5.5 (1.3%)6.0 (1.4%)10.5 (1.5%) (nb/sr) 3.0 (0.7%)3.5 (0.8%) 4.0 (1.0%)

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Yi Qiang, The search for pentaquarks at JLab Hall A 16 June 2006 Thank you

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Yi Qiang, The search for pentaquarks at JLab Hall A17June 2006 Collaboration J. Annand, J. Arrington, Y. Azimov, W. Bertozzi, 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 (run coordinator), F. Garibaldi, R. Gilman, D. Hamilton, O. Hansen (analysis coordinator), D. Higinbotham, T. Holmstrom, M. Iodice, X. Jiang, M. Jones, J. Lerose, R. Lindgren, N. Liyanage, D. Margaziotis, P. Markowitz, V. Mamyan (analysis guru), 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. Rachek I. Strakovsky, R. Subedi, R. Suleiman, V. Sulkovsky, B. Wojtsekhowski (contact and spokesperson), X. Zheng. and the Hall A Collaboration

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