Physics
1
Abstract：
Magnetars have been proposed to be the origin of the fast radio bursts (FRBs) soon after its initial discovery. The detection of the first Galactic FRB 200428 from SGR 1935+2154 has made this hypothesis more convincing. In October 2020, this source was supposed to be in an extremely active state again. We then carried out a 1.6-hours follow-up observation of SGR 1935+2154 using the new ultra-wideband low (UWL) receiver of the Parkes 64 m radio telescope covering a frequency range of 704-4032 MHz. However, no convincing signal was detected in either of our single pulse or periodicity searches. We obtained a limit on the flux density of periodic signal of 3.6 μJy using the full 3.3 GHz bandwidth data sets, which is the strictest limit for that of SGR 1935+2154. Our full bandwidth limit on the single pulses fluence is 35 mJy ms, which is well below the brightest single pulses detected by the FAST radio telescope just two days before our observation. Assuming that SGR 1935+2154 is active during our observation, our results suggest that its radio bursts are either intrinsically narrow-band or show a steep spectrum.
Magnetars have been proposed to be the origin of the fast radio bursts (FRBs) soon after its initial discovery. The detection of the first Galactic FRB 200428 from SGR 1935+2154 has made this hypothesis more convincing. In October 2020, this source was supposed to be in an extremely active state again. We then carried out a 1.6-hours follow-up observation of SGR 1935+2154 using the new ultra-wideband low (UWL) receiver of the Parkes 64 m radio telescope covering a frequency range of 704-4032 MHz. However, no convincing signal was detected in either of our single pulse or periodicity searches. We obtained a limit on the flux density of periodic signal of 3.6 μJy using the full 3.3 GHz bandwidth data sets, which is the strictest limit for that of SGR 1935+2154. Our full bandwidth limit on the single pulses fluence is 35 mJy ms, which is well below the brightest single pulses detected by the FAST radio telescope just two days before our observation. Assuming that SGR 1935+2154 is active during our observation, our results suggest that its radio bursts are either intrinsically narrow-band or show a steep spectrum.
2
Abstract：
Our research proposes a new scheme to build a controlled-NOT(C-NOT) gate between two adjacent nitrogen-vacancy (NV) color centers in diamond, using electric dipole coupling between adjacent NVs and selective resonant laser excitation.The electric dipole coupling between two NVs causes the state dependent energy shift.This allows to apply resonant laser excitation to realize the C-phase gate.Combined with a single qubit operation, C-NOT gate can be implemented quickly.Between two adjacent 10 nm NVs, the C-NOT gate can operate up to 120 ns faster than the traditional magnetic dipole coupling method by 2 magnitudes.In order to reduce the effect of a spontaneous emission,we propose to use a non-resonant cavity to suppress the spontaneous emission.The simulation results show that the C-phase gate fidelity can reach 98.88%.Finally, the scheme is extended to a one-dimensional NV spin chain.
Our research proposes a new scheme to build a controlled-NOT(C-NOT) gate between two adjacent nitrogen-vacancy (NV) color centers in diamond, using electric dipole coupling between adjacent NVs and selective resonant laser excitation.The electric dipole coupling between two NVs causes the state dependent energy shift.This allows to apply resonant laser excitation to realize the C-phase gate.Combined with a single qubit operation, C-NOT gate can be implemented quickly.Between two adjacent 10 nm NVs, the C-NOT gate can operate up to 120 ns faster than the traditional magnetic dipole coupling method by 2 magnitudes.In order to reduce the effect of a spontaneous emission,we propose to use a non-resonant cavity to suppress the spontaneous emission.The simulation results show that the C-phase gate fidelity can reach 98.88%.Finally, the scheme is extended to a one-dimensional NV spin chain.
3
Abstract：
High-resolution soft X-ray microscopy has been widely adopted for obtaining the three-dimensional structure of physical objects. However, the limited depth of focus may cause sample defocusing and, subsequently, lead to blurring of images. A defocused image restoration method was proposed based on an optical transfer function (OTF) of a Fresnel zone plate (FZP). Using this restoration method the defocused image of Siemens star was restored. The results show that the restoration method based on OTF is capable of suppressing the blurring effect and restore defocus images caused by defocusing of the object. Furthermore, related simulations have been carried out to demonstrate the effectiveness of this method in overcoming the limitations to focal depth and accomplishing three dimensional imaging of samples.
High-resolution soft X-ray microscopy has been widely adopted for obtaining the three-dimensional structure of physical objects. However, the limited depth of focus may cause sample defocusing and, subsequently, lead to blurring of images. A defocused image restoration method was proposed based on an optical transfer function (OTF) of a Fresnel zone plate (FZP). Using this restoration method the defocused image of Siemens star was restored. The results show that the restoration method based on OTF is capable of suppressing the blurring effect and restore defocus images caused by defocusing of the object. Furthermore, related simulations have been carried out to demonstrate the effectiveness of this method in overcoming the limitations to focal depth and accomplishing three dimensional imaging of samples.
4
Abstract：
Recently, grating-based phase contrast X-ray imaging has become a hot spot, and it is considered the key technology for future clinical medical nondestructive diagnosis due its high compatibility with the conventional X-ray source. Compared with the existing X-ray absorption contrast imaging technology, phase-contrast imaging has the unique ability to distinguish soft tissues. Here the grating-based phase contrast X-ray imaging was used to nondestructively detect the structure of local crucian carp treated by formalin. The structure of the intestine tissues are shown clearly, the very first time using such imaging technology.
Recently, grating-based phase contrast X-ray imaging has become a hot spot, and it is considered the key technology for future clinical medical nondestructive diagnosis due its high compatibility with the conventional X-ray source. Compared with the existing X-ray absorption contrast imaging technology, phase-contrast imaging has the unique ability to distinguish soft tissues. Here the grating-based phase contrast X-ray imaging was used to nondestructively detect the structure of local crucian carp treated by formalin. The structure of the intestine tissues are shown clearly, the very first time using such imaging technology.
5
2016, 46(6): 449-455.
DOI: 10.3969/j.issn.0253-2778.2016.06.001
Abstract：
The BESⅢ Collaboration has recently embarked on a two-photon physics program. Its main motivation is given by the large uncertainty of the contribution of hadronic light-by-light scattering to the anomalous magnetic moment of the muon αμ, and the need of electromagnetic transition form factors(TFF) as experimental input to improve the calculations. Data acquired with the BESⅢ detector at center-of-mass energies from 3.77 to 4.6 GeV allow for the determination of TFFs of light pseudoscalar mesons. The measurements are performed with a single-tag technique and result in unprecedented accuracy at momentum transfers below 2 GeV2, the region of highest importance for the calculations of αμ. Employing the same approach, the first double-tagged measurement of the pion transition form factor has been started. It is the first step towards a model independent parameterization of the TFF of the π0. Additionally, measurements of multi-meson final states have been engaged.
The BESⅢ Collaboration has recently embarked on a two-photon physics program. Its main motivation is given by the large uncertainty of the contribution of hadronic light-by-light scattering to the anomalous magnetic moment of the muon αμ, and the need of electromagnetic transition form factors(TFF) as experimental input to improve the calculations. Data acquired with the BESⅢ detector at center-of-mass energies from 3.77 to 4.6 GeV allow for the determination of TFFs of light pseudoscalar mesons. The measurements are performed with a single-tag technique and result in unprecedented accuracy at momentum transfers below 2 GeV2, the region of highest importance for the calculations of αμ. Employing the same approach, the first double-tagged measurement of the pion transition form factor has been started. It is the first step towards a model independent parameterization of the TFF of the π0. Additionally, measurements of multi-meson final states have been engaged.
6
Abstract：
The hadronic corrections to the muon anomalous magnetic moment αμ, due to the full gauge-invariant set of diagrams with dynamical quark loop and intermediate pseudoscalar and scalar states light-by-light scattering insertions, are calculated in the framework of the nonlocal chiral quark model. These diagrams correspond to all hadronic light-by-light scattering contributions to αμ in the leading order of the 1/Nc expansion in quark model. The result of the quark loop contribution is μHLbL,Loop=(11.0±0.9) ·10-10, and the total result is αμHLbL,NχQM=(16.8±1.2) ·10-10.
The hadronic corrections to the muon anomalous magnetic moment αμ, due to the full gauge-invariant set of diagrams with dynamical quark loop and intermediate pseudoscalar and scalar states light-by-light scattering insertions, are calculated in the framework of the nonlocal chiral quark model. These diagrams correspond to all hadronic light-by-light scattering contributions to αμ in the leading order of the 1/Nc expansion in quark model. The result of the quark loop contribution is μHLbL,Loop=(11.0±0.9) ·10-10, and the total result is αμHLbL,NχQM=(16.8±1.2) ·10-10.
7
Abstract：
A combined analysis of the space- and time-like experimental data for the η transition form factor is performed in a model-independent way by means of rational approximants. The recent measurement of the e+e- invariant mass spectrum of the η→e+e--γ decay provided by the A2 Collaboration allowed us to extract the most precise and up-to-date slope and curvature parameters of the form factor. The impact of this new analysis on the ηη′ mixing parameters and the VPγ couplings is also discussed.
A combined analysis of the space- and time-like experimental data for the η transition form factor is performed in a model-independent way by means of rational approximants. The recent measurement of the e+e- invariant mass spectrum of the η→e+e--γ decay provided by the A2 Collaboration allowed us to extract the most precise and up-to-date slope and curvature parameters of the form factor. The impact of this new analysis on the ηη′ mixing parameters and the VPγ couplings is also discussed.
8
2016, 46(6): 470-475.
DOI: 10.3969/j.issn.0253-2778.2016.06.004
Abstract：
After briefly discussing the importance of the precise measurement of the weak mixing angle, the implication of the dark Z on the low-Q2 parity tests is discussed. The dark Z is a very light (roughly, MeV-GeV scale) gauge boson, which couples to the electromagnetic current as well as the weak neutral current.
After briefly discussing the importance of the precise measurement of the weak mixing angle, the implication of the dark Z on the low-Q2 parity tests is discussed. The dark Z is a very light (roughly, MeV-GeV scale) gauge boson, which couples to the electromagnetic current as well as the weak neutral current.
9
Abstract：
Forward-backward asymmetry in the muon pairs production in electron-positron annihilation is caused by the interference of the photon and Z-boson already at leading order. A high precise measurement of the value of this asymmetry, AFB, at the Super B-factory will provide stringent limitations on the New Physics effects. Even though AFB≈0.01 at 10 GeV center-of-mass energy of B-factory operation, a huge statistics expected at the BelleⅡ experiment will provide an opportunity to obtain high precision. This report briefly describes perspectives as well as obstacles on the way to achieve the precise results.
Forward-backward asymmetry in the muon pairs production in electron-positron annihilation is caused by the interference of the photon and Z-boson already at leading order. A high precise measurement of the value of this asymmetry, AFB, at the Super B-factory will provide stringent limitations on the New Physics effects. Even though AFB≈0.01 at 10 GeV center-of-mass energy of B-factory operation, a huge statistics expected at the BelleⅡ experiment will provide an opportunity to obtain high precision. This report briefly describes perspectives as well as obstacles on the way to achieve the precise results.
10
Abstract：
The P2 experiment in Mainz aims to measure the weak mixing angle sin2θW in electron- proton scattering to a precision of 0.13%. In order to suppress uncertainties due to proton structure and contributions from box graphs, both a low average momentum transfer Q2 of 4.5×10-3GeV2/c2 and a low beam energy of 155 MeV are chosen. In order to collect the enormous statistics required for this measurement, the new Mainz energy recovery superconducting accelerator(MESA) is being constructed. These proceedings describe the motivation for the measurement, the experimental and accelerator challenges and plans to tackle them.
The P2 experiment in Mainz aims to measure the weak mixing angle sin2θW in electron- proton scattering to a precision of 0.13%. In order to suppress uncertainties due to proton structure and contributions from box graphs, both a low average momentum transfer Q2 of 4.5×10-3GeV2/c2 and a low beam energy of 155 MeV are chosen. In order to collect the enormous statistics required for this measurement, the new Mainz energy recovery superconducting accelerator(MESA) is being constructed. These proceedings describe the motivation for the measurement, the experimental and accelerator challenges and plans to tackle them.
11
2016, 46(6): 488-493.
DOI: 10.3969/j.issn.0253-2778.2016.06.007
Abstract：
EM Dalitz decays could be sensitive and provide very rich information about meson structures, and they play an important role in constraining the uncertainties to (g-2)μ. BEPCⅢ has performed and published several Dalitz decays,including η′→γe+e-, J/ψ→Pe+e-(P=η′,η /π0), η′→ωe+e- etc. These processes are all observed and measured for the first time, furthering our knowledge about meson structures and meson interactions. Many more related work is ongoing and there will be more results to come, which will further test the theory against the measurements and could be sensitvie to the new physics beyond the standard model.
EM Dalitz decays could be sensitive and provide very rich information about meson structures, and they play an important role in constraining the uncertainties to (g-2)μ. BEPCⅢ has performed and published several Dalitz decays,including η′→γe+e-, J/ψ→Pe+e-(P=η′,η /π0), η′→ωe+e- etc. These processes are all observed and measured for the first time, furthering our knowledge about meson structures and meson interactions. Many more related work is ongoing and there will be more results to come, which will further test the theory against the measurements and could be sensitvie to the new physics beyond the standard model.
12
Abstract：
A comprehensive phenomenological study is carried out of the decay processes with the η or η′ in the initial/final states within the effective field theory approach. Two primary types of processes are analyzed: The ones only with lightflavor hadrons and those involving the J/ψ. The couplings from the effective Lagrangian, together with the ηη′ mixing parameters from the two-mixing-angle scheme, are fitted to a large number of experimental data, including the various decay widths and the form factors. With the phenomenological mixing parameters and the lattice simulation data of the masses and decay constants of the light pseudoscalar mesons as inputs, a next-to-next-to-leading order study is performed of the ηη′ mixing system in U(3) chiral perturbation theory. Updated values of the relevant low energy constants are obtained.
A comprehensive phenomenological study is carried out of the decay processes with the η or η′ in the initial/final states within the effective field theory approach. Two primary types of processes are analyzed: The ones only with lightflavor hadrons and those involving the J/ψ. The couplings from the effective Lagrangian, together with the ηη′ mixing parameters from the two-mixing-angle scheme, are fitted to a large number of experimental data, including the various decay widths and the form factors. With the phenomenological mixing parameters and the lattice simulation data of the masses and decay constants of the light pseudoscalar mesons as inputs, a next-to-next-to-leading order study is performed of the ηη′ mixing system in U(3) chiral perturbation theory. Updated values of the relevant low energy constants are obtained.
13
Abstract：
The results of the study of e+e--→Ф(1020)η process with the CMD-3 detector are reported. The analysis is based on an integrated luminosity of 22 pb-1 collected by the CMD-3 in 2011-2012. It was established that only Ф(1020)η intermediate state can be recognized at the current level of CMD-3 statistics. The cross section of e+e--→Ф(1020)η process was measured at 30 center-of-mass energy points in the range from 1.59 up to 2.0 GeV. The η meson was treated as a recoil particle and all the modes of η decay were used. A total of 1454±48 events of signal process were selected. The measured cross section was approximated according to vector meson dominance model as a sum of Ф(1680) and nonresonant amplitudes, and the preliminary results for Ф(1680) meson parameters have been obtained.
The results of the study of e+e--→Ф(1020)η process with the CMD-3 detector are reported. The analysis is based on an integrated luminosity of 22 pb-1 collected by the CMD-3 in 2011-2012. It was established that only Ф(1020)η intermediate state can be recognized at the current level of CMD-3 statistics. The cross section of e+e--→Ф(1020)η process was measured at 30 center-of-mass energy points in the range from 1.59 up to 2.0 GeV. The η meson was treated as a recoil particle and all the modes of η decay were used. A total of 1454±48 events of signal process were selected. The measured cross section was approximated according to vector meson dominance model as a sum of Ф(1680) and nonresonant amplitudes, and the preliminary results for Ф(1680) meson parameters have been obtained.
14
Abstract：
The e+e-→KS0+KL0 and e+e-→K-K+ cross sections have been measured in the center-of-mass energy range 1004-1060 MeV for 25 energy points with about 2%3% systematic uncertainties. The analysis is based on 5.5 pb-1 of integrated luminosity collected with the CMD-3 detector at the VEPP-2000 e+e- collider. The measured cross section is approximated according to vector meson dominance model as a sum of Ф, ω, ρ like amplitudes and their excitations, and Ф(1020) meson parameters have been obtained.
The e+e-→KS0+KL0 and e+e-→K-K+ cross sections have been measured in the center-of-mass energy range 1004-1060 MeV for 25 energy points with about 2%3% systematic uncertainties. The analysis is based on 5.5 pb-1 of integrated luminosity collected with the CMD-3 detector at the VEPP-2000 e+e- collider. The measured cross section is approximated according to vector meson dominance model as a sum of Ф, ω, ρ like amplitudes and their excitations, and Ф(1020) meson parameters have been obtained.
15
Abstract：
The processes +e-→ηπ+π-→γγπ+π-,e+e-→ηπ+π-→π0π+π-π+π- and e+e-→ωπ+π-→π0π+π-π+π- have been studied with the CMD-3 detector at the VEPP2000 collider. For analysis data collected in the center-of-mass energy range from 1.2 to 2.0 GeV is used. Studied data corresponding to an integrated luminosity of 3×104 nb-1 were recorded in 2011 and 2012. The Born cross section of e+e-→ηπ+π- has been measured in the η→γγ channel and is in good agreement with results obtained in other experiments. There are also preliminary results for the e+e--→ηπ+π- and e+e-→ωπ+π- Born cross sections in the η→π+π-π0 and ω→π+π-π0 final states, respectively. The e+e-→ηπ+π- Born cross section data have been used to determine the τ-→ηπ-π0ντ decay branching fraction.
The processes +e-→ηπ+π-→γγπ+π-,e+e-→ηπ+π-→π0π+π-π+π- and e+e-→ωπ+π-→π0π+π-π+π- have been studied with the CMD-3 detector at the VEPP2000 collider. For analysis data collected in the center-of-mass energy range from 1.2 to 2.0 GeV is used. Studied data corresponding to an integrated luminosity of 3×104 nb-1 were recorded in 2011 and 2012. The Born cross section of e+e-→ηπ+π- has been measured in the η→γγ channel and is in good agreement with results obtained in other experiments. There are also preliminary results for the e+e--→ηπ+π- and e+e-→ωπ+π- Born cross sections in the η→π+π-π0 and ω→π+π-π0 final states, respectively. The e+e-→ηπ+π- Born cross section data have been used to determine the τ-→ηπ-π0ντ decay branching fraction.
16
Abstract：
The reactions e+e-→ρπ, ωπ,ρη, ωη have been studied in the energy region 1.05-2.00 GeV. The experiment has been carried out at the VEPP-2000 e+e- collider with the SND detector. The measured cross sections have been fitted in the vector meson dominance model.
The reactions e+e-→ρπ, ωπ,ρη, ωη have been studied in the energy region 1.05-2.00 GeV. The experiment has been carried out at the VEPP-2000 e+e- collider with the SND detector. The measured cross sections have been fitted in the vector meson dominance model.
17
Abstract：
A search for the rare decay η′→e+e- has been performed with the SND detector at the VEPP-2000 e+e- collider. The inverse reaction e+e-→η′ and η′ five decay chains have been used for this search. The upper limit Γη′→e+e-＜0.002 eV at the 90% confidence level has been set. A sensitivity of SND in a search for η→e+e- decay has been studied. For this purpose a data sample with an integrated luminosity of 108 nb-1 collected in the centerofmass energy range 520580 MeV was analyzed. No background events for the reaction e+e-→η with decay η→π0π0π0 have been found. In the absence of background, a sensitivity to B(η→e+e-) of 10-6 can be reached during two weeks of VEPP-2000 operation.
A search for the rare decay η′→e+e- has been performed with the SND detector at the VEPP-2000 e+e- collider. The inverse reaction e+e-→η′ and η′ five decay chains have been used for this search. The upper limit Γη′→e+e-＜0.002 eV at the 90% confidence level has been set. A sensitivity of SND in a search for η→e+e- decay has been studied. For this purpose a data sample with an integrated luminosity of 108 nb-1 collected in the centerofmass energy range 520580 MeV was analyzed. No background events for the reaction e+e-→η with decay η→π0π0π0 have been found. In the absence of background, a sensitivity to B(η→e+e-) of 10-6 can be reached during two weeks of VEPP-2000 operation.
18
Abstract：
In order to study the acceptance and calculate cross sections for CSR experiment, one needs to obtain target variables on the target plane of the spectrometer. Target variables can be reconstructed from focal plane variables with optics. In principle, the optics is the mathematical expression of the magnetic field of HRS. The optics optimization method which minimizes χ2 of TgVardata-TgVatheory to determine the better optics matrix elements for CSR experiment was studied. The optimization results show a good agreement between the data and theoretical values.
In order to study the acceptance and calculate cross sections for CSR experiment, one needs to obtain target variables on the target plane of the spectrometer. Target variables can be reconstructed from focal plane variables with optics. In principle, the optics is the mathematical expression of the magnetic field of HRS. The optics optimization method which minimizes χ2 of TgVardata-TgVatheory to determine the better optics matrix elements for CSR experiment was studied. The optimization results show a good agreement between the data and theoretical values.
