High precision measurements of the differential cross sections for π0 photoproduction at forward angles for two nuclei, 12C and 208Pb, have been performed for incident photon energies of 4.9-5.5 GeV ...to extract the π0→γγ decay width. The experiment was done at Jefferson Lab using the Hall B photon tagger and a high-resolution multichannel calorimeter. The π0→γγ decay width was extracted by fitting the measured cross sections using recently updated theoretical models for the process. The resulting value for the decay width is Γ(π0→γγ)=7.82±0.14(stat)±0.17(syst) eV. With the 2.8% total uncertainty, this result is a factor of 2.5 more precise than the current Particle Data Group average of this fundamental quantity, and it is consistent with current theoretical predictions.
Full text
Available for:
CMK, CTK, FMFMET, IJS, NUK, PNG, UM
High precision photon flux determination for photon tagging experiments Teymurazyan, A.; Ahmidouch, A.; Ambrozewicz, P. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
12/2014, Volume:
767, Issue:
C
Journal Article
Peer reviewed
The Jefferson Laboratory PrimEx Collaboration has developed and implemented a method to control the tagged photon flux in photoproduction experiments at the 1% level over the photon energy range from ...4.9 to 5.5GeV. This method has been successfully implemented in a high precision measurement of the neutral pion lifetime. Here, we outline the experimental equipment and the analysis techniques used to accomplish this. These include the use of a total absorption counter for absolute flux calibration, a pair spectrometer for online relative flux monitoring, and a new method for post-bremsstrahlung electron counting.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
3.
The CLAS forward electromagnetic calorimeter Amarian, M.; Asryan, G.; Beard, K. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
03/2001, Volume:
460, Issue:
2
Journal Article
Peer reviewed
Open access
The CEBAF Large Acceptance Spectrometer (CLAS) at Jefferson Lab utilizes six iron-free superconducting coils to provide an approximately toroidal magnetic field. The six sectors are instrumented ...individually to form six independent spectrometers. The forward region (8°<
θ<45°) of each sector is equipped with a lead–scintillator electromagnetic sampling calorimeter (EC), 16
radiation lengths thick, using a novel triangular geometry with stereo readout. With its good energy and position resolution, the EC is used to provide the primary electron trigger for CLAS. It is also used to reject pions, reconstruct π° and η decays and detect neutrons. This paper treats the design, construction and performance of the calorimeter.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
New Measurement of the {pi}{sup 0} Radiative Decay Width Larin, I.; North Carolina A and T State University, Greensboro, North Carolina 27411; McNulty, D. ...
Physical review letters,
04/2011, Volume:
106, Issue:
16
Journal Article
Peer reviewed
High precision measurements of the differential cross sections for {pi}{sup 0} photoproduction at forward angles for two nuclei, {sup 12}C and {sup 208}Pb, have been performed for incident photon ...energies of 4.9-5.5 GeV to extract the {pi}{sup 0}{yields}{gamma}{gamma} decay width. The experiment was done at Jefferson Lab using the Hall B photon tagger and a high-resolution multichannel calorimeter. The {pi}{sup 0}{yields}{gamma}{gamma} decay width was extracted by fitting the measured cross sections using recently updated theoretical models for the process. The resulting value for the decay width is {Gamma}({pi}{sup 0}{yields}{gamma}{gamma})=7.82{+-}0.14(stat){+-}0.17(syst) eV. With the 2.8% total uncertainty, this result is a factor of 2.5 more precise than the current Particle Data Group average of this fundamental quantity, and it is consistent with current theoretical predictions.
Full text
Available for:
CMK, CTK, FMFMET, IJS, NUK, PNG, UM
High precision measurements of the differential cross sections for $\pi^0$ photoproduction at forward angles for two nuclei, $^{12}$C and $^{208}$Pb, have been performed for incident photon energies ...of 4.9 - 5.5 GeV to extract the ${\pi^0 \to \gamma\gamma}$ decay width. The experiment was done at Jefferson Lab using the Hall~B photon tagger and a high-resolution multichannel calorimeter. The ${\pi^0 \to \gamma\gamma}$ decay width was extracted by fitting the measured cross sections using recently updated theoretical models for the process. The resulting value for the decay width is $\Gamma{(\pi^0 \to \gamma\gamma)} = 7.82 \pm 0.14 ~({\rm stat.}) \pm 0.17 ~({\rm syst.}) ~{\rm eV}$. With the 2.8\% total uncertainty, this result is a factor of 2.5 more precise than the current PDG average of this fundamental quantity and it is consistent with current theoretical predictions.
Full text
Available for:
CMK, CTK, FMFMET, IJS, NUK, PNG, UM
A technique is presented for precision measurements of the area densities,
ρT, of approximately 5% radiation length carbon and
208Pb targets used in an experiment at Jefferson Laboratory to measure ...the neutral pion radiative width. The precision obtained in the area density for the carbon target is ±0.050%, and that obtained for the lead target through an X-ray attenuation technique is ±0.43%.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Electromagnetic calorimeter modules are being constructed for the CEBAF Large Acceptance Spectrometer that will utilize plastic plate scintillators that can be over 4 meters in length. At shower ...maximum, it is expected that up to 100 Gray may be deposited over a ten year lifetime in the detector elements. Although it is believed that PVT-based scintillators are radiation-hard at that level, the large size of the plates motivated an ageing test of a 2 meter long sample so as to gain a realistic estimate of the loss in intrinsic light output and especially in attenuation performance of the chosen scintillator (Bicron BC412). A test setup was designed so that the sample was irradiated (by a /sup 60/Co line source) at a rate sufficiently low (0.5 Gray/hr) to allow complete diffusion of oxygen into the material during the irradiation. Additionally, in order to ensure complete diffusion and to gain a pessimistic estimate of damage, a pure oxygen atmosphere was circulated through the sample container during the irradiation, and the total dose was increased to a total of 160 Gray. Within the same setup, tests were also made of two additional materials: (1) a 1 meter long sample of an uniquely bright, fast green scintillator with superior attenuation properties, and (2) a customized acrylic scintillator (with a high doping level of fluors) read out by embedded (into smooth grooves cut into the surface of the scintillator) wavelength shifting fibers doped with the same green fluor as the aforementioned scintillator. The data indicates that the BC412 shows no loss in intrinsic light output, but does have an attenuation loss amounting to 10% at 1 meter and 16% at 2 meters. The fast green scintillator (and fibers) showed no damage. When read out by WLS fibers, the acrylic scintillator displayed a loss in intrinsic light output, but no change in attenuation.< >
Measurements are presented of inclusive charm and beauty cross sections in e$^+$p collisions at HERA for values of photon virtuality Q$^2$ > 150 GeV$^2$ and of inelasticity 0.1 < y < 0.7. The charm ...and beauty fractions are determined using a method based on the impact parameter, in the transverse plane, of tracks to the primary vertex, as measured by the H1 vertex detector. The data are divided into four regions in Q$^2$ and Bjorken x, and values for the structure functions $F_2^{c\overline{c}}$ and $F_2^{b\overline{b}}$ are obtained. The results are found to be compatible with the predictions of perturbative quantum chromodynamics.
Full text
Available for:
DOBA, FZAB, GEOZS, IJS, IMTLJ, IZUM, KILJ, KISLJ, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, SIK, UILJ, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
PDF
