Browsing by Author "Lin, P. Y."

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Anomalous anticrossing of neutral exciton states in GaAs/AlGaAs quantum dots
(2014-03-12)
Kumar, S.
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Zallo, E.
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Liao, Y. H.
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Lin, P. Y.
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Trotta, R.
We study the effects of heavy hole-light hole (HH-LH) mixing on fine-structure and polarization properties of neutral excitons ( X-0) confined in single GaAs/AlGaAs quantum dots (QDs) under the application of anisotropic biaxial stress. In the large HH-LH mixing regime, these properties are substantially different from the usually observed properties in the case of small or no mixing. By varying the applied stress, the mixing in the initially strain-free QDs changes from similar to 0 to similar to 70% and an anomalous anticrossing of the X-0 bright states is observed. The latter is attributed to stress-induced rotation of the in-plane principal axis of the QD confinement potential. We show that the analysis of free-excitonic emission of bulk GaAs surrounding the QDs not only allows estimation of the stress and mixing in the QDs, but also provides the quantum-confinement-induced HH-LH splitting of the as-grown QDs.
Charmful two-body antitriplet b-baryon decays
(2015-12-08)
Hsiao, Y. K.
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Lin, P. Y.
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Lih, C. C.
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Geng, C. Q.
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電子物理學系
We study the charmful decays of the two-body B-b -> BnMc decays, where B-b represents the antitriplet of (Lambda(b), Xi(0)(b), Xi(-)(b)), B-n stands for the baryon octet, and M-c denotes the charmed meson of D-(s)((*)), eta(c) and J/psi. Explicitly, we predict that B(Lambda(b) -> D(s)(-)p) = (1.8 +/- 0.3) x 10(-5), which is within the measured upper bound of B(Lambda(b) -> D(s)(-)p) < 4.8(5.3) x 10(-4) at 90% (95%) C.L., and reproduce B(Lambda(b) -> J/psi Lambda) = (3.3 +/- 2.0) x 10(-4) and B(Xi(-)(b) -> J/psi Xi(-)) = (5.1 +/- 3.2) x 10(-4) in agreement with the data. Moreover, we find that B(Lambda(b) -> Lambda eta(c)) = (1.5 +/- 0.9) x 10(-4), B(Xi(-)(b) -> Xi(-)eta(c)) = (2.4 +/- 1.5) x 10(-4) and B(Xi(0)(b) -> Xi(0)eta(c), Xi(0)J/psi) = (2.3 +/- 1.4, 4.9 +/- 3.0) x 10(-4), which are accessible to the experiments at the LHCb.
Fragmentation fractions of two-body b-baryon decays
(2015-12-17)
Hsiao, Y. K.
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Lin, P. Y.
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Luo, L. W.
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Geng, C. Q.
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電子物理學系
We study the fragmentation fractions (f(Bb)) of the b-quark to b-baryons (B-b). By the assumption of f(Lambda b)/(f(u) + f(d)) = 0.25 +/- 0.15 in accordance with the measurements by LEP, CDF and LHCb Collaborations, we estimate that f(Lambda b)= 0.175 +/- 0.106 and f(Xi b)(-),0 = 0.019 +/- 0.013. From these fragmentation fractions, we derive B(Lambda(b) -> J/psi Lambda) =(3.3 +/- 2.1) x10(-4), B(Xi(-)(b) -> J/psi Xi(-)) = (5.3 +/- 3.9) x10(-4) and B(Omega(-)(b) -> J/psi Omega(-)) > 1.9 x10(-5). The predictions of B(Lambda(b) -> J/psi Lambda) and B(Xi(-)(b) -> J/psi Xi(-)) clearly enable us to test the theoretical models, such as the QCD factorization approach in the b-baryon decays. (C) 2015 The Authors. Published by Elsevier B.V.
Independent measurement of the neutrino mixing angle theta(13) via neutron capture on hydrogen at Daya Bay
(2014-10-03)
An, F. P.
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Balantekin, A. B.
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Band, H. R.
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Beriguete, W.
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Bishai, M.
A new measurement of the theta(13) mixing angle has been obtained at the Daya Bay Reactor Neutrino Experiment via the detection of inverse beta decays tagged by neutron capture on hydrogen. The antineutrino events for hydrogen capture are distinct from those for gadolinium capture with largely different systematic uncertainties, allowing a determination independent of the gadolinium-capture result and an improvement on the precision of the theta(13) measurement. With a 217-day antineutrino data set obtained with six antineutrino detectors and from six 2.9 GWth reactors, the rate deficit observed at the far hall is interpreted as sin(2)2 theta(13) = 0.083 +/- 0.018 in the three-flavor oscillation model. When combined with the gadolinium-capture result from Daya Bay, we obtain sin(2)2 theta(13) = 0.089 +/- 0.008 as the final result for the six-antineutrino-detector configuration of the Daya Bay experiment.
Measurement of the Reactor Antineutrino Flux and Spectrum at Daya Bay
(2016-02-12)
An, F. P.
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Balantekin, A. B.
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Band, H. R.
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Bishai, M.
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Blyth, S.
This Letter reports a measurement of the flux and energy spectrum of electron antineutrinos from six 2.9 GW(th) nuclear reactors with six detectors deployed in two near (effective baselines 512 and 561 m) and one far (1579 m) underground experimental halls in the Daya Bay experiment. Using 217 days of data, 296 721 and 41 589 inverse beta decay (IBD) candidates were detected in the near and far halls, respectively. The measured IBD yield is (1.55 +/- 0.04) x 10(-18) cm(2) GW(-1) day(-1) or (5.92 +/- 0.14) x 10(-43) cm(2) fission(-1). This flux measurement is consistent with previous short-baseline reactor antineutrino experiments and is 0.946 +/- 0.022 (0.991 +/- 0.023) relative to the flux predicted with the Huber-Mueller (ILL-Vogel) fissile antineutrino model. The measured IBD positron energy spectrum deviates from both spectral predictions by more than 2 sigma over the full energy range with a local significance of up to similar to 4 sigma between 4-6 MeV. A reactor antineutrino spectrum of IBD reactions is extracted from the measured positron energy spectrum for model-independent predictions.
New Measurement of Antineutrino Oscillation with the Full Detector Configuration at Daya Bay
(2015-09-11)
An, F. P.
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Balantekin, A. B.
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Band, H. R.
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Bishai, M.
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Blyth, S.
We report a new measurement of electron antineutrino disappearance using the fully constructed Daya Bay Reactor Neutrino Experiment. The final two of eight antineutrino detectors were installed in the summer of 2012. Including the 404 days of data collected from October 2012 to November 2013 resulted in a total exposure of 6.9 x 10(5) GW(th) ton days, a 3.6 times increase over our previous results. Improvements in energy calibration limited variations between detectors to 0.2%. Removal of six Am-241-C-13 radioactive calibration sources reduced the background by a factor of 2 for the detectors in the experimental hall furthest from the reactors. Direct prediction of the antineutrino signal in the far detectors based on the measurements in the near detectors explicitly minimized the dependence of the measurement on models of reactor antineutrino emission. The uncertainties in our estimates of sin(2)2 theta(13) and vertical bar Delta m(ee)(2)vertical bar were halved as a result of these improvements. An analysis of the relative antineutrino rates and energy spectra between detectors gave sin(2)2 theta(13) = 0.084 +/- 0.005 and vertical bar Delta m(ee)(2)vertical bar = (2.42 +/- 0.11) x 10(-3) eV(2) in the three-neutrino framework.
Search for a Light Sterile Neutrino at Daya Bay
(2014-10-01)
An, F. P.
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Balantekin, A. B.
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Band, H. R.
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Beriguete, W.
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Bishai, M.
A search for light sterile neutrino mixing was performed with the first 217 days of data from the Daya Bay Reactor Antineutrino Experiment. The experiment's unique configuration of multiple baselines from six 2.9 GW(th) nuclear reactors to six antineutrino detectors deployed in two near (effective baselines 512 m and 561 m) and one far (1579 m) underground experimental halls makes it possible to test for oscillations to a fourth (sterile) neutrino in the 10(-3) eV(2) < vertical bar Delta m(41)(2)vertical bar < 0.3 eV(2) range. The relative spectral distortion due to the disappearance of electron antineutrinos was found to be consistent with that of the three-flavor oscillation model. The derived limits on sin(2) 2 theta(14) cover the 10(-3) eV(2) less than or similar to vertical bar Delta m(41)(2)vertical bar less than or similar to 0.1 eV(2) region, which was largely unexplored.
Structural and optical properties of buried InAs/GaAs quantum dots on GaAsSb buffer layer
(2009-09-21)
Wu, Y. H.
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Chang, Li
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Lin, P. Y.
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Chiang, C. H.
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Chen, J. F.
In this work, we investigated the effect of a 1 nm thick GaAs(94.3)Sb(0.57) buffer layer on structural and optical properties of buried InAs quantum dots (QDs) and wetting layers (WLs) in GaAs using photoluminescence (PL) and transmission electron microscopy (TEM). The density and emission wavelength of the QDs on the buffer were increased due to the size and the shape modification in comparison with those without a buffer. PL analysis of the ground-state (GS) peak of the QDs on the buffer showed a red-shift of 18 meV with an enhanced intensity. In addition, PL and TEM show that the buffer has a weak effect on the WLs and no apparent changes occur for the buffer during QD deposition and the capping process.
The detector system of the Daya Bay reactor neutrino experiment
(2016-03-01)
An, F. P.
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Bai, J. Z.
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Balantekin, A. B.
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Band, H. R.
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Beavis, D.
The Daya Bay experiment was the first to report simultaneous measurements of reactor antineutrinos at multiple baselines leading to the discovery of (nu) over bar (e) oscillations over km-baselines. Subsequent data has provided the world\'s most precise measurement of sin 2 2013 and the effective mass splitting Delta m(ee)(2). The experiment is located in Daya Bay, China where the cluster of six nuclear reactors is among the world\'s most prolific sources of electron antineutrinos. Multiple antineutrino detectors are deployed in three underground water pools at different distances from the reactor cores to search for deviations in the antineutrino rate and energy spectrum due to neutrino mixing. Instrumented with photomultiplier tubes, the water pools serve as shielding against natural radioactivity from the surrounding rock and provide efficient muon tagging. Arrays of resistive plate chambers over the top of each pool provide additional muon detection. The antineutrino detectors were specifically designed for measurements of the antineutrino flux with minimal systematic uncertainty. Relative detector efficiencies between the near and far detectors are known to better than 0.2%. With the unblinding of the final two detectors\' baselines and target masses, a complete description and comparison of the eight antineutrino detectors can now be presented. This paper describes the Daya Bay detector systems, consisting of eight antineutrino detectors in three instrumented water pools in three underground halls, and their operation through the first year of eight detector data-taking. (C) 2015 Elsevier B.V. All rights reserved.
The muon system of the Daya Bay Reactor antineutrino experiment
(2015-02-11)
An, F. P.
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Balantekin, A. B.
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Band, H. R.
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Beriguete, W.
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Bishai, M.
The Daya Bay experiment consists of functionally identical antineutrino detectors immersed in pools of ultrapure water in three well-separated underground experimental halls near two nuclear reactor complexes. These pools serve both as shields against natural, low-energy radiation, and as water Cherenkov detectors that efficiently detect cosmic muons using arrays of photomultiplier tubes. Each pool is covered by a plane of resistive plate chambers as an additional means of detecting muons. Design, construction, operation, and performance of these muon detectors are described. (C) 2014 Elsevier By. All rights reserved.