排序方式: 共有16条查询结果,搜索用时 31 毫秒
1.
McKinnon B Hicks K Baltzell NA Carman DS Mestayer MD Mibe T Mirazita M Niccolai S Rossi P Stepanyan S Tedeschi DJ Ambrozewicz P Anghinolfi M Asryan G Avakian H Bagdasaryan H Baillie N Ball JP Batourine V Battaglieri M Bedlinskiy I Bellis M Benmouna N Berman BL Biselli AS Bouchigny S Boiarinov S Bradford R Branford D Briscoe WJ Brooks WK Bültmann S Burkert VD Butuceanu C Calarco JR Careccia SL Chen S Cole PL Collins P Coltharp P Crabb D Crede V Dale D De Masi R DeVita R De Sanctis E 《Physical review letters》2006,96(21):212001
A search for the Theta+ in the reaction gammad --> pK-K+n was completed using the CLAS detector at Jefferson Lab. A study of the same reaction, published earlier, reported the observation of a narrow Theta+ resonance. The present experiment, with more than 30 times the integrated luminosity of our earlier measurement, does not show any evidence for a narrow pentaquark resonance. The angle-integrated upper limit on Theta+ production in the mass range of 1.52-1.56 GeV/c2 for the gammad --> pK-Theta+ reaction is 0.3 nb (95% C.L.). This upper limit depends on assumptions made for the mass and angular distribution of Theta+ production. Using Lambda(1520) production as an empirical measure of rescattering in the deuteron, the cross section upper limit for the elementary gamman --> K-Theta+ reaction is estimated to be a factor of 10 higher, i.e., approximately 3 nb (95% C.L.). 相似文献
2.
Niccolai S Mirazita M Rossi P Baltzell NA Carman DS Hicks K McKinnon B Mibe T Stepanyan S Tedeschi DJ Adams G Ambrozewicz P Anefalos Pereira S Anghinolfi M Asryan G Avakian H Bagdasaryan H Baillie N Ball JP Batourine V Battaglieri M Bedlinskiy I Bektasoglu M Bellis M Benmouna N Berman BL Biselli AS Boiarinov S Bouchigny S Bradford R Branford D Briscoe WJ Brooks WK Bültmann S Burkert VD Butuceanu C Calarco JR Careccia SL Carnahan B Chen S Cole PL Collins P Coltharp P Crabb D Crannell H Crede V 《Physical review letters》2006,97(3):032001
For the first time, the reaction gammad-->DeltanK+ has been analyzed in order to search for the exotic pentaquark baryon Theta+(1540). The data were taken at Jefferson Laboratory, using the Hall-B tagged-photon beam of energy between 0.8 and 3.6 GeV and the CEBAF Large Acceptance Spectrometer (CLAS). No statistically significant structures were observed in the nK+ invariant-mass distribution. The upper limit on the gammad-->DeltaTheta+ integrated cross section has been calculated and found to be between 5 and 25 nb, depending on the production model assumed. The upper limit on the differential cross section is also reported. 相似文献
3.
Strauch S Berman BL Adams G Ambrozewicz P Anghinolfi M Asavapibhop B Asryan G Audit G Avakian H Bagdasaryan H Baillie N Ball JP Baltzell NA Barrow S Batourine V Battaglieri M Beard K Bedlinskiy I Bektasoglu M Bellis M Benmouna N Bennhold C Biselli AS Boiarinov S Bouchigny S Bradford R Branford D Briscoe WJ Brooks WK Bültmann S Burkert VD Butuceanu C Calarco JR Careccia SL Carman DS Carnahan B Chen S Cole PL Coleman A Coltharp P Cords D Corvisiero P Crabb D Crannell H Cummings JP Degtyarenko PV 《Physical review letters》2005,95(16):162003
4.
Nasseripour R Wood MH Djalali C Weygand DP Tur C Mosel U Muehlich P Adams G Amaryan MJ Ambrozewicz P Anghinolfi M Asryan G Avakian H Bagdasaryan H Baillie N Ball JP Baltzell NA Barrow S Battaglieri M Bedlinskiy I Bektasoglu M Bellis M Benmouna N Berman BL Biselli AS Blaszczyk L Bouchigny S Boiarinov S Bradford R Branford D Briscoe WJ Brooks WK Bültmann S Burkert VD Butuceanu C Calarco JR Careccia SL Carman DS Carnahan B Casey L Chen S Cole PL Collins P Coltharp P Crabb D Crannell H Crede V 《Physical review letters》2007,99(26):262302
The photoproduction of vector mesons on various nuclei has been studied using the CLAS detector at Jefferson Laboratory. The vector mesons, rho, omega, and varphi, are observed via their decay to e;{+}e;{-}, in order to reduce the effects of final-state interactions in the nucleus. Of particular interest are possible in-medium effects on the properties of the rho meson. The rho mass spectrum is extracted from the data on various nuclei, 2H, C, Fe, and Ti. We observe no significant mass shift and some broadening consistent with expected collisional broadening for the rho meson. 相似文献
5.
Chen S Avakian H Burkert VD Eugenio P Adams G Amarian M Ambrozewicz P Anghinolfi M Asryan G Bagdasaryan H Baillie N Ball JP Baltzell NA Barrow S Batourine V Battaglieri M Beard K Bedlinskiy I Bektasoglu M Bellis M Benmouna N Berman BL Biselli AS Bonner BE Bouchigny S Boiarinov S Bosted P Bradford R Branford D Briscoe WJ Brooks WK Bültmann S Butuceanu C Calarco JR Careccia SL Carman DS Carnahan B Cazes A Cole PL Collins P Coltharp P Cords D Corvisiero P Crabb D Crannell H Crede V Cummings JP 《Physical review letters》2006,97(7):072002
The longitudinal target-spin asymmetry AUL for the exclusive electroproduction of high-energy photons was measured for the first time in ep-->e;'pgamma. The data have been accumulated at JLab with the CLAS spectrometer using 5.7 GeV electrons and a longitudinally polarized NH3 target. A significant azimuthal angular dependence was observed, resulting from the interference of the deeply virtual Compton scattering and Bethe-Heitler processes. The amplitude of the sinvarphi moment is 0.252+/-0.042stat+/-0.020sys. Theoretical calculations are in good agreement with the magnitude and the kinematic dependence of the target-spin asymmetry, which is sensitive to the generalized parton distributions H and H. 相似文献
6.
Dugger M Ball JP Collins P Pasyuk E Ritchie BG Adams G Ambrozewicz P Anciant E Anghinolfi M Asavapibhop B Asryan G Audit G Avakian H Bagdasaryan H Baillie N Baltzell NA Barrow S Batourine V Battaglieri M Beard K Bedlinskiy I Bektasoglu M Bellis M Benmouna N Berman BL Bianchi N Biselli AS Bonner BE Bouchigny S Boiarinov S Bradford R Branford D Briscoe WJ Brooks WK Bültmann S Burkert VD Butuceanu C Calarco JR Careccia SL Carman DS Carnahan B Chen S Cole PL Coleman A Coltharp P Cords D 《Physical review letters》2006,96(6):062001
Differential cross sections for the reaction gamma p --> eta' p have been measured with the CLAS spectrometer and a tagged photon beam with energies from 1.527 to 2.227 GeV. The results reported here possess much greater accuracy than previous measurements. Analyses of these data suggest for the first time the coupling of the eta'N channel to both the S11(1535) and P11(1710) resonances, known to couple strongly to the etaN channel in photoproduction on the proton, and the importance of J = 3/2 resonances in the process. 相似文献
7.
SL Mironov E Skorova G Taschenberger N Hartelt VO Nikolaev MJ Lohse S Kügler 《BMC neuroscience》2009,10(1):29-11
Background
cAMP is an ubiquitous second messenger mediating various neuronal functions, often as a consequence of increased intracellular Ca2+ levels. While imaging of calcium is commonly used in neuroscience applications, probing for cAMP levels has not yet been performed in living vertebrate neuronal tissue before. 相似文献8.
Battaglieri M De Vita R Kubarovsky V Guo L Mutchler GS Stoler P Weygand DP Ambrozewicz P Anghinolfi M Asryan G Avakian H Bagdasaryan H Baillie N Ball JP Baltzell NA Batourine V Bedlinskiy I Bellis M Benmouna N Berman BL Biselli AS Bouchigny S Boiarinov S Bradford R Branford D Briscoe WJ Brooks WK Bültmann S Burkert VD Butuceanu C Calarco JR Careccia SL Carman DS Chen S Clinton E Cole PL Coltharp P Crabb D Crannell H Cummings JP Dale D De Sanctis E Degtyarenko PV Deur A Dharmawardane KV 《Physical review letters》2006,96(4):042001
The exclusive reaction gammap-->K0K+n was studied in the photon energy range between 1.6 and 3.8 GeV searching for evidence of the exotic baryon Theta+ (1540)-->nK+. The decay to nK+requires the assignment of strangeness S=+1 to any observed resonance. Data were collected with the CLAS detector at the Thomas Jefferson National Accelerator Facility corresponding to an integrated luminosity of 70 pb-1. No evidence for the Theta+ pentaquark was found. Upper limits were set on the production cross section as function of center-of-mass angle and nK+ mass. The 95% C.L. upper limit on the total cross section for a narrow resonance at 1540 MeV was found to be 0.8 nb. 相似文献
9.
Ungaro M Stoler P Aznauryan I Burkert VD Joo K Smith LC Adams G Amarian M Ambrozewicz P Anghinolfi M Asryan G Audit G Avakian H Bagdasaryan H Ball JP Baltzell NA Barrow S Batourine V Battaglieri M Bedliski I Bektasoglu M Bellis M Benmouna N Berman BL Biselli AS Bonner BE Bouchigny S Boiarinov S Bradford R Branford D Briscoe WJ Brooks WK Bültmann S Butuceanu C Calarco JR Careccia SL Carman DS Cazes A Chen S Cole PL Coltharp P Cords D Corvisiero P Crabb D Cummings JP Sanctis ED Devita R 《Physical review letters》2006,97(11):112003
We report a new measurement of the exclusive electroproduction reaction gamma(*)p-->pi(0)p to explore the evolution from soft nonperturbative physics to hard processes via the Q(2) dependence of the magnetic (M(1+)), electric (E(1+)), and scalar (S(1+)) multipoles in the N-->Delta transition. 9000 differential cross section data points cover W from threshold to 1.4 GeV/c(2), 4pi center-of-mass solid angle, and Q(2) from 3 to 6 GeV(2)/c(2), the highest yet achieved. It is found that the magnetic form factor G(M)(*) decreases with Q(2) more steeply than the proton magnetic form factor, the ratio E(1+)/M(1+) is small and negative, indicating strong helicity nonconservation, and the ratio S(1+)/M(1+) is negative, while its magnitude increases with Q(2). 相似文献
10.
Ireland DG McKinnon B Protopopescu D Ambrozewicz P Anghinolfi M Asryan G Avakian H Bagdasaryan H Baillie N Ball JP Baltzell NA Batourine V Battaglieri M Bedlinskiy I Bellis M Benmouna N Berman BL Biselli AS Blaszczyk L Bouchigny S Boiarinov S Bradford R Branford D Briscoe WJ Brooks WK Burkert VD Butuceanu C Calarco JR Careccia SL Carman DS Casey L Chen S Cheng L Cole PL Collins P Coltharp P Crabb D Crede V Dashyan N De Masi R De Vita R De Sanctis E Degtyarenko PV Deur A Dickson R Djalali C 《Physical review letters》2008,100(5):052001
We examine the results of two measurements by the CLAS collaboration, one of which claimed evidence for a Theta(+) pentaquark, while the other found no such evidence. The unique feature of these two experiments was that they were performed with the same experimental setup. Using a Bayesian analysis, we find that the results of the two experiments are in fact compatible with each other, but that the first measurement did not contain sufficient information to determine unambiguously the existence of a Theta(+). Further, we suggest a means by which the existence of a new candidate particle can be tested in a rigorous manner. 相似文献