共查询到10条相似文献,搜索用时 0 毫秒
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Hwang SH Hicks K Ahn JK Nakano T Ahn DS Chang WC Chen JY Daté S Ejiri H Fujimura H Fujiwara M Fukui S Gohn W Hotta T Imai K Ishikawa T Joo K Kato Y Kohri H Kon Y Lee HS Maeda Y Miyabe M Mibe T Morino Y Muramatsu N Nakatsugawa Y Niiyama M Noumi H Oh Y Ohashi Y Ohta T Oka M Parker J Rangacharyulu C Ryu SY Sawada T Sugaya Y Sumihama M Tsunemi T Uchida M Ungaro M Yosoi M;LEPS Collaboration 《Physical review letters》2012,108(9):092001
The exclusive reaction γp→K(+)π(-)Σ(+) was measured for the first time using linearly polarized photons at beam energies from 1.85 to 2.96 GeV. Angular distributions in the rest frame of the K(+)π(-) system were fitted to extract spin-density matrix elements of the K(*0) decay. The measured parity spin asymmetry shows that natural-parity exchange is dominant in this reaction. This result clearly indicates the need for t-channel exchange of the κ(800) scalar meson. 相似文献
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Aaltonen T Álvarez González B Amerio S Amidei D Anastassov A Annovi A Antos J Apollinari G Appel JA Apresyan A Arisawa T Artikov A Asaadi J Ashmanskas W Auerbach B Aurisano A Azfar F Badgett W Barbaro-Galtieri A Barnes VE Barnett BA Barria P Bartos P Bauce M Bauer G Bedeschi F Beecher D Behari S Bellettini G Bellinger J Benjamin D Beretvas A Bhatti A Binkley M Bisello D Bizjak I Bland KR Blumenfeld B Bocci A Bodek A Bortoletto D Boudreau J Boveia A Brigliadori L Brisuda A Bromberg C Brucken E 《Physical review letters》2011,107(19):191801
A search has been performed for B(s)(0) → μ+ μ- and B(0) → μ+ μ- decays using 7 fb(-1) of integrated luminosity collected by the CDF II detector at the Fermilab Tevatron collider. The observed number of B(0) candidates is consistent with background-only expectations and yields an upper limit on the branching fraction of B(B(0) → μ+ μ-) < 6.0 × 10(-9) at 95% confidence level. We observe an excess of B(s)(0) candidates. The probability that the background processes alone could produce such an excess or larger is 0.27%. The probability that the combination of background and the expected standard model rate of B(s)(0) → μ+ μ- could produce such an excess or larger is 1.9%. These data are used to determine B(B(s)(0)→ μ+ μ-) = (1.8(-0.9) (+1.1)) × 10(-8) and provide an upper limit of B(B(s)(0) → μ+ μ-) < 4.0 × 10(-8) at 95% confidence level. 相似文献
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José Luis Sánchez Bote Antonio Pedrero González Juan José Gómez Alfageme 《Applied Acoustics》2012,73(4):440-453
The International Standard ISO 140-5 on field measurements of airborne sound insulation of façades establishes that the directivity of the measurement loudspeaker should be such that the variation in the local direct sound pressure level (ΔSPL) on the sample is ΔSPL < 5 dB (or ΔSPL < 10 dB for large façades). This condition is usually not very easy to accomplish nor is it easy to verify whether the loudspeaker produces such a uniform level. Direct sound pressure levels on the ISO standard façade essentially depend on the distance and directivity of the loudspeaker used. This paper presents a comprehensive analysis of the test geometry for measuring sound insulation and explains how the loudspeaker directivity, combined with distance, affects the acoustic level distribution on the façade.The first sections of the paper are focused on analysing the measurement geometry and its influence on the direct acoustic level variations on the façade. The most favourable and least favourable positions to minimise these direct acoustic level differences are found, and the angles covered by the façade in the reference system of the loudspeaker are also determined. Then, the maximum dimensions of the façade that meet the conditions of the ISO 140-5 standard are obtained for the ideal omnidirectional sound source and the piston radiating in an infinite baffle, which is chosen as the typical radiation pattern for loudspeakers.Finally, a complete study of the behaviour of different loudspeaker radiation models (such as those usually utilised in the ISO 140-5 measurements) is performed, comparing their radiation maps on the façade for searching their maximum dimensions and the most appropriate radiation configurations. 相似文献
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Study of n-γ discrimination for 0.4-1 MeV neutrons using the zero-crossing method with a BC501A liquid scintillation detector 下载免费PDF全文
CHEN Yong-Hao LEI Jia-Rong ZHANG Xiao-Dong AN Li ZHENG Pu WANG Xin-Hua ZHU Chuan-Xin HE Tie 《中国物理C(英文版)》2013,37(4):046202-046202
An experimental system aimed at n-γ discrimination using the zero-crossing method with a φ3"× 2" BC501A liquid scintillation detector was established and tested with an Am-Be neutron source. Two-dimensional plots of energy versus zero-crossing time were obtained. The quality of n-γ discrimination was checked by the figure-of-merit (FOM), the neutron peak-to-valley ratio, and the proportion of leaked neutrons over all neutron events. The performance of n-γ discrimination in terms of FOM was compared with previous work done by other groups. The n-γ discrimination in four different energy regions with an interval of 0.1 MeV between 0.3 MeV and 0.7 MeV was studied, and the results indicate that the n-γ discrimination threshold can go down to 0.4 MeV. 相似文献
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Abouzaid E Arenton M Barker AR Bellantoni L Blucher E Bock GJ Cheu E Coleman R Corcoran MD Cox B Erwin AR Escobar CO Glazov A Golossanov A Gomes RA Gouffon P Hsiung YB Jensen DA Kessler R Kotera K Ledovskoy A McBride PL Monnier E Nguyen H Niclasen R Phillips DG Ping H Ramberg EJ Ray RE Ronquest M Santos E Slater W Smith D Solomey N Swallow EC Toale PA Tschirhart R Velissaris C Wah YW Wang J White HB Whitmore J Wilking MJ Winston R Worcester ET Worcester M Yamanaka T Zimmerman ED 《Physical review letters》2011,107(20):201803
The KTeV E799 experiment has conducted a search for the rare decays, K(L)→π(0)π(0)μ(+)μ(-) and K(L)→π(0)π(0)X(0)→π(0)π(0)μ(+)μ(-), where the X(0) is a possible new neutral boson that was reported by the HyperCP experiment with a mass of (214.3 ± 0.5) MeV/c(2). We find no evidence for either decay. We obtain upper limits of Br(K(L)→π(0)π(0)X(0)→π(0)π(0)μ(+)μ(-)) < 1.0 × 10(-10) and Br(K(L)→π(0)π(0)μ(+)μ(-)) < 9.2 × 10(-11) at the 90% confidence level. This result rules out the pseudoscalar X(0) as an explanation of the HyperCP result under the scenario that the dsX(0) coupling is completely real. 相似文献
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