arXiv subjects

G. Chen

Publications and source records attributed to G. Chen.

At least 703 records · Page 39Linked to original sources

arXiv2019

Improved measurements of the absolute branching fractions of the inclusive decays $D^{+(0)}\toϕX$

By analyzing 2.93 fb$^{-1}$ of $e^+e^-$ annihilation data taken at the center-of-mass energy $\sqrt s=$ 3.773 GeV with the BESIII detector, we determine the branching fractions of the inclusive decays $D^+\toϕX$ and $D^0\toϕX$ to be $(1.135\pm0.034\pm0.031)\%$ and $(1.091\pm0.027\pm0.035)\%$, respectively, where $X$ denotes any possible particle combination. The first uncertainties are statistical and the second systematic. We also determine the branching fractions of the decays $D\toϕX$ and their charge conjugate modes $\bar{D}\toϕ\bar{X}$ separately for the first time, and no significant CP asymmetry is observed.

hep-ex↗

arXiv2019

Insight-HXMT observations of 4U~1636-536: Corona cooling revealed with single short type-I X-ray burst

Corona cooling was detected previously from stacking a series of short type-I bursts occurred during the low/had state of atoll outburst. Type-I bursts are hence regarded as sharp probe to our better understanding on the basic property of the corona. The launch of the first Chinese X-ray satellite Insight-HXMT has large detection area at hard X-rays which provide almost unique chance to move further in this research field. We report the first detection of the corona cooling by Insight-HXMT from single short type-I burst showing up during {\bf flare} of 4U 1636-536. This type-I X-ray burst has a duration of $\sim$13 seconds and hard X-ray shortage is detected with significance 6.2~$σ$ in 40-70 keV. A cross-correlation analysis between the lightcurves of soft and hard X-ray band, shows that the corona shortage lag the burst emission by 1.6 $\pm$1.2~s. These results are consistent with those derived previously from stacking a large amount of bursts detected by RXTE/PCA within a series of {\bf flares} of 4U 1636-536. Moreover, the broad bandwidth of Insight-HXMT allows as well for the first time to infer the burst influence upon the continuum spectrum via performing the spectral fitting of the burst, which ends up with the finding that hard X-ray shortage appears at around 40 keV in the continuum spectrum. These results suggest that the evolution of the corona along with the outburst{\bf /flare} of NS XRB may be traced via looking into a series of embedded type-I bursts by using Insight-HXMT.

astro-ph.HE↗

arXiv2019

Measurement of branching fractions for $D$ meson decaying into $ϕ$ meson and a pseudoscalar meson

The four decay modes $D^{0}\toϕπ^{0}$, $D^{0}\toϕη$, $D^{+}\toϕπ^{+}$, and $D^{+}\toϕK^{+}$ are studied by using a data sample taken at the centre-of-mass energy $\sqrt{s} = 3.773$~GeV~with the BESIII detector, corresponding to an integrated luminosity of 2.93 fb$^{-1}$. The branching fractions of the first three decay modes are measured to be ${\cal B}(D^{0}\toϕπ^{0})=(1.168\pm0.028\pm0.028)\times10^{-3}$, ${\cal B}(D^{0}\toϕη)=(1.81\pm0.46\pm0.06)\times10^{-4}$, and ${\cal B}(D^{+}\toϕπ^{+})=(5.70\pm0.05\pm0.13)\times10^{-3}$, respectively, where the first uncertainties are statistical and the second are systematic. No significant signal is observed of the decay $D^+\toϕ{K^+}$ and the upper limit of its branching fraction is set for the first time, to be $2.1\times10^{-5}$ at the $90\%$ confidence level. The ratio of ${\cal B}(D^0\toϕπ^0)$ to $\cal B(D^+\toϕπ^+)$ is calculated to be $(20.49\pm0.50\pm0.45)\%$, which is consistent with the theoretical prediction based on isospin symmetry between these two decay modes.

hep-ex↗

arXiv2019

Study of the decays $ψ(3686)\rightarrowγχ_{cJ}\rightarrowγ\bar{p}K^{+}Λ+c.c.$ and $ψ(3686)\rightarrow\bar{p}K^{+}Λ+c.c.$

Based on the data sample of $448.1\times10^{6}$ $ψ(3686)$ events collected with the BESIII detector at BEPCII, we present a study of the decays $ψ(3686)\rightarrowγχ_{cJ}\rightarrowγ\bar{p}K^{*+}Λ+c.c.$ and $ψ(3686)\rightarrow\bar{p}K^{*+}Λ+c.c.$. The branching fractions of $χ_{cJ}\rightarrow\bar{p}K^{*+}Λ+c.c.$ ($J$=0, 1, 2) are measured to be $(4.8\pm0.7\pm0.5)\times10^{-4}$, $(5.0\pm0.5\pm0.4)\times10^{-4}$, and $(8.2\pm0.9\pm0.7)\times10^{-4}$, respectively, where the first uncertainties are statistical and the second systematic. The branching fraction of $ψ(3686)\rightarrow\bar{p}K^{*+}Λ+c.c.$ is measured to be $(6.3\pm0.5\pm0.5)\times10^{-5}$. All these decay modes are observed for the first time.

hep-ex↗

arXiv2019

Timing analysis of 2S 1417-624 observed with NICER and Insight-HXMT

We present a study of timing properties of the accreting pulsar 2S 1417-624 observed during its 2018 outburst, based on Swift/BAT, Fermi/GBM, Insight-HXMT and NICER observations. We report a dramatic change of the pulse profiles with luminosity. The morphology of the profile in the range 0.2-10.0keV switches from double to triple peaks at $\sim2.5$ $\rm \times 10^{37}{\it D}_{10}^2\ erg\ s^{-1}$ and from triple to quadruple peaks at $\sim7$ $\rm \times 10^{37}{\it D}_{10}^2\ erg\ s^{-1}$. The profile at high energies (25-100keV) shows significant evolutions as well. We explain this phenomenon according to existing theoretical models. We argue that the first change is related to the transition from the sub to the super-critical accretion regime, while the second to the transition of the accretion disc from the gas-dominated to the radiation pressure-dominated state. Considering the spin-up as well due to the accretion torque, this interpretation allows to estimate the magnetic field self-consistently at $\sim7\times 10^{12}$G.

astro-ph.HE↗

arXiv2019

Constant cyclotron line energy in Hercules X-1 -- Joint Insight-HXMT and NuSTAR observations

The long-term evolution of the centroid energy of the CRSF in Her X-1 is still a mystery. We report a new measurement from a campaign between {\sl Insight}-HXMT and {\sl NuSTAR} performed in February 2018. Generally, the two satellites show well consistent results of timing and spectral properties. The joint spectral analysis confirms that the previously observed long decay phase has ended, and that the line energy instead keeps constant around 37.5 keV after flux correction.

astro-ph.HE↗

arXiv2019

Hot disk of the Swift J0243.6+6124 revealed by Insight-HXMT

We report on analysis of observations of the bright transient X-ray pulsar \src obtained during its 2017-2018 giant outburst with Insight-HXMT, \emph{NuSTAR}, and \textit{Swift} observatories. We focus on the discovery of a sharp state transition of the timing and spectral properties of the source at super-Eddington accretion rates, which we associate with the transition of the accretion disk to a radiation pressure dominated (RPD) state, the first ever directly observed for magnetized neutron star. This transition occurs at slightly higher luminosity compared to already reported transition of the source from sub- to super-critical accretion regime associate with onset of an accretion column. We argue that this scenario can only be realized for comparatively weakly magnetized neutron star, not dissimilar to other ultra-luminous X-ray pulsars (ULPs), which accrete at similar rates. Further evidence for this conclusion is provided by the non-detection of the transition to the propeller state in quiescence which strongly implies compact magnetosphere and thus rules out magnetar-like fields.

astro-ph.HE↗

arXiv2019

Observation of $ψ(3686)\rightarrowΞ(1530)^{-}\barΞ(1530)^{+}$ and $Ξ(1530)^{-}\barΞ^{+}$

Using 448.1 $\times$ $10^{6}$ $ψ(3686)$ events collected with the BESIII detector at BEPCII, we employ a single-baryon tagging technique to make the first observation of $ψ(3686)\rightarrowΞ(1530)^{-}\barΞ(1530)^{+}$ and $Ξ(1530)^{-}\barΞ^{+}$ decays with a statistical significance of more than 10$σ$ and 5.0$σ$, respectively. The branching fractions are measured to be $\cal{B}$$[ψ(3686)\rightarrowΞ(1530)^{-}\barΞ(1530)^{+}] $ = (11.45 $\pm$ 0.40 $\pm$ 0.59) $\times$ $10^{-5}$ and $\cal{B}$$[ψ(3686)\rightarrowΞ(1530)^{-}\barΞ^{+}]$ = (0.70 $\pm$ 0.11 $\pm$ 0.04) $\times$ $10^{-5}$. The angular distribution parameter for $ψ(3686)\rightarrowΞ(1530)^{-}\barΞ(1530)^{+}$ is determined to be $α$ = 0.40 $\pm$ 0.24 $\pm$ 0.06, which agrees with the theoretical predictions within 1$σ$. The first uncertainties are statistical, and the second systematic.

hep-ex↗

arXiv2019

First observation of the decay $χ_{cJ}\to Σ^{+}\bar{p}K_{S}^{0}+c.c. ~(J = 0, 1, 2)$

Using E1 radiative transitions $ψ(3686) \to γχ_{cJ}$ from a sample of $(448.1 \pm 2.9)\times10^{6}$ $ψ(3686)$ events collected with the BESIII detector, the decays $χ_{cJ}\to Σ^{+}\bar{p}K_{S}^{0}+c.c.~(J = 0, 1, 2)$ are studied. The decay branching fractions are measured to be $\mathcal{B}(χ_{c0}\to Σ^{+}\bar{p}K_{S}^{0}+c.c.) = (3.52 \pm 0.19\pm 0.21)\times10^{-4}$, $\mathcal{B}(χ_{c1}\to Σ^{+}\bar{p}K_{S}^{0}+c.c.) = (1.53 \pm 0.10\pm 0.08)\times10^{-4}$, and $\mathcal{B}(χ_{c2}\to Σ^{+}\bar{p}K_{S}^{0}+c.c.) = (8.25 \pm 0.83 \pm 0.49)\times10^{-5}$, where the first and second uncertainties are the statistical and systematic ones, respectively. No evident intermediate resonances are observed in the studied processes.

hep-ex↗

arXiv2019

The highly inflated giant planet WASP-174b

The transiting exoplanetary system WASP-174 was reported to be composed by a main-sequence F star (V=11.8 mag) and a giant planet, WASP-174b (orbital period 4.23 days). However only an upper limit was placed on the planet mass (<1.3 Mj), and a highly uncertain planetary radius (0.7-1.7 Rj) was determined. We aim to better characterise both the star and the planet and precisely measure their orbital and physical parameters. In order to constrain the mass of the planet, we obtained new measurements of the radial velocity of the star and joined them with those from the discovery paper. Photometric data from the HATSouth survey and new multi-band, high-quality (precision reached up to 0.37~mmag) photometric follow-up observations of transit events were acquired and analysed for getting accurate photometric parameters. We fit the model to all the observations, including data from the TESS space telescope, in two different modes: incorporating the stellar isochrones into the fit, and using an empirical method to get the stellar parameters. The two modes resulted to be consistent with each other to within 2 sigma. We confirm the grazing nature of the WASP-174b transits with a confidence level greater than 5 sigma, which is also corroborated by simultaneously observing the transit through four optical bands and noting how the transit depth changes due to the limb-darkening effect. We estimate that ~76% of the disk of the planet actually eclipses the parent star at mid-transit of its transit events. We find that WASP-174b is a highly-inflated hot giant planet with a mass of 0.330 Mj and a radius of 1.435 Rj, and is therefore a good target for transmission-spectroscopy observations. With a density of 0.135 g/cm^3, it is amongst the lowest-density planets ever discovered with precisely measured mass and radius.

astro-ph.EP↗

arXiv2019

Search for the rare decay $η'\rightarrowπ^{0}π^{0}π^{0}π^{0}$ at BESIII

Based on a sample of 1.31 billion $J/ψ$ events collected with the BESIII detector, we perform a search for the rare decay $η'\rightarrow 4π^{0}$ via $J/ψ\rightarrowγη'$. No significant $η'$ signal is observed in the invariant mass spectrum of 4$π^{0}$. With a Bayesian approach, the upper limit on the branching fraction of $η'\rightarrow 4π^{0}$ is determined to be $\mathcal{B}(η'\rightarrow 4π^{0})$ $< 4.94\times10^{-5}$ at the 90\% confidence level, which is a factor of six smaller than the previous experimental limit.

hep-ex↗

arXiv2019

In-orbit demonstration of X-ray pulsar navigation with the Insight-HXMT satellite

In this work, we report the in-orbit demonstration of X-ray pulsar navigation with Insight-Hard X-ray Modulation Telescope (Insight-HXMT), which was launched on Jun. 15th, 2017. The new pulsar navigation method 'Significance Enhancement of Pulse-profile with Orbit-dynamics' (SEPO) is adopted to determine the orbit with observations of only one pulsar. In this test, the Crab pulsar is chosen and observed by Insight-HXMT from Aug. 31th to Sept. 5th in 2017. Using the 5-day-long observation data, the orbit of Insight-HXMT is determined successfully with the three telescopes onboard - High Energy X-ray Telescope (HE), Medium Energy X-ray Telescope (ME) and Low Energy X-ray Telescope (LE) - respectively. Combining all the data, the position and velocity of the Insight-HXMT are pinpointed to within 10 km (3 sigma) and 10 m/s (3 sigma), respectively.

astro-ph.IM↗

arXiv2019

Planetary system around the nearby M dwarf GJ 357 including a transiting, hot, Earth-sized planet optimal for atmospheric characterization

We report the detection of a transiting Earth-size planet around GJ 357, a nearby M2.5V star, using data from the Transiting Exoplanet Survey Satellite (TESS). GJ 357 b (TOI-562.01) is a transiting, hot, Earth-sized planet (Teq=525+-11 K) with a radius of Rb=1.217+-0.084 Re and an orbital period of Pb=3.93 d. Precise stellar radial velocities from CARMENES and PFS, as well as archival data from HIRES, UVES, and HARPS also display a 3.93-day periodicity, confirming the planetary nature and leading to a planetary mass of Mb=1.84+-0.31 Me. In addition to the radial velocity signal for GJ 357 b, more periodicities are present in the data indicating the presence of two further planets in the system: GJ 357 c, with a minimum mass of Mc=3.40+-0.46 Me in a 9.12 d orbit, and GJ 357 d, with a minimum mass of Md=6.1+-1.0 Me in a 55.7 d orbit inside the habitable zone. The host is relatively inactive and exhibits a photometric rotation period of Prot=78+-2 d. GJ 357 b is to date the second closest transiting planet to the Sun, making it a prime target for further investigations such as transmission spectroscopy. Therefore, GJ 357 b represents one of the best terrestrial planets suitable for atmospheric characterization with the upcoming JWST and ground-based ELTs.

astro-ph.EP↗

arXiv2019

Evidence for the decays of $Λ^+_{c}\toΣ^+η$ and $Σ^+η^\prime$

We study the hadronic decays of $Λ_{c}^{+}$ to the final states $Σ^{+}η$ and $Σ^+η^\prime$, using an $e^{+}e^{-}$ annihilation data sample of 567 pb$^{-1}$ taken at a center-of-mass energy of 4.6 GeV with the BESIII detector at the BEPCII collider. We find evidence for the decays $Λ_{c}^{+}\rightarrowΣ^{+}η$ and $Σ^+η^\prime$ with statistical significance of $2.5σ$ and $3.2σ$, respectively. Normalizing to the reference decays $Λ_c^+\toΣ^+π^0$ and $Σ^+ω$, we obtain the ratios of the branching fractions $\frac{{\mathcal B}(Λ_c^+\toΣ^+η)}{{\mathcal B}(Λ_c^+\toΣ^+π^0)}$ and $\frac{{\mathcal B}(Λ_c^+\toΣ^+η^\prime)}{{\mathcal B}(Λ_c^+\toΣ^+ω)}$ to be $0.35 \pm 0.16 \pm 0.03$ and $0.86 \pm 0.34 \pm 0.07$, respectively. The upper limits at the 90\% confidence level are set to be $\frac{{\mathcal B}(Λ_c^+\toΣ^+η)}{{\mathcal B}(Λ_c^+\toΣ^+π^0)}<0.58$ and $\frac{{\mathcal B}(Λ_c^+\toΣ^+η^\prime)}{{\mathcal B}(Λ_c^+\toΣ^+ω)}<1.2$. Using BESIII measurements of the branching fractions of the reference decays, we determine $\mathcal B({Λ_{c}^{+}\rightarrowΣ^{+}η})=(0.41\pm0.19\pm0.05)\%$ ($<0.68\%$) and $\mathcal B({Λ_{c}^{+}\rightarrowΣ^{+}η'})=(1.34\pm0.53\pm0.21)\%$ ($<1.9\%$). Here, the first uncertainties are statistical and the second systematic. The obtained branching fraction of $Λ_c^+\toΣ^+η$ is consistent with the previous measurement, and the branching fraction of $Λ_{c}^{+}\rightarrowΣ^{+}η^{\prime}$ is measured for the first time.

hep-ex↗

arXiv2019

Cross section measurements of $e^{+}e^{-} \to K^{+}K^{-}K^{+}K^{-} $ and $ ϕK^{+}K^{-}$ at center-of-mass energies from 2.10 to 3.08 GeV

We measure the Born cross sections of the process $e^{+}e^{-} \to K^{+}K^{-}K^{+}K^{-}$ at center-of-mass (c.m.) energies, $\sqrt{s}$, between 2.100 and 3.080 GeV. The data were collected using the BESIII detector at the BEPCII collider. An enhancement at $\sqrt{s}= 2.232$ GeV is observed, very close to the $e^{+}e^{-} \to Λ\overlineΛ$ production threshold. A similar enhancement at the same c.m. energy is observed in the $e^{+}e^{-} \to ϕK^{+}K^{-}$ cross section. The energy dependence of the $K^{+}K^{-}K^{+}K^{-}$ and $ϕK^{+}K^{-}$ cross sections differs significantly from that of $e^{+}e^{-} \to ϕπ^{+}π^{-}$.

hep-ex↗

arXiv2019

Search for the decay $η'\toγγη$

Using a data sample of $1.31\times10^{9} ~J/ψ$ events collected with the BESIII detector, a search for $η'\toγγη$ via $J/ψ\toγη'$ is performed for the first time. No significant $η'$ signal is observed in the $γγη$ invariant mass spectrum, and the %upper limit of the branching fraction of $η'\toγγη$ is determined to be less than $1.33 \times 10^{-4}$ at the 90$\%$ confidence level.

hep-ex↗

arXiv2019

Observation and study of the decay $J/ψ\rightarrowϕηη'$

We report the observation and study of the decay $J/ψ\rightarrowϕηη'$ using $1.3\times{10^9}$ $J/ψ$ events collected with the BESIII detector. Its branching fraction, including all possible intermediate states, is measured to be $(2.32\pm0.06\pm0.16)\times{10^{-4}}$. We also report evidence for a structure, denoted as $X$, in the $ϕη'$ mass spectrum in the $2.0-2.1$ GeV/$c^2$ region. Using two decay modes of the $η'$ meson ($γπ^+π^-$ and $ηπ^+π^-$), a simultaneous fit to the $ϕη'$ mass spectra is performed. Assuming the quantum numbers of the $X$ to be $J^P = 1^-$, its significance is found to be 4.4$σ$, with a mass and width of $(2002.1 \pm 27.5 \pm 21.4)$ MeV/$c^2$ and $(129 \pm 17 \pm 9)$ MeV, respectively, and a product branching fraction $\mathcal{B}(J/ψ\rightarrowηX)\times{}\mathcal{B}(X\rightarrowϕη')=(9.8 \pm 1.2 \pm 1.7)\times10^{-5}$. Alternatively, assuming $J^P = 1^+$, the significance is 3.8$σ$, with a mass and width of $(2062.8 \pm 13.1 \pm 7.2)$ MeV/$c^2$ and $(177 \pm 36 \pm 35)$ MeV, respectively, and a product branching fraction $\mathcal{B}(J/ψ\rightarrowηX)\times{}\mathcal{B}(X\rightarrowϕη')=(9.6 \pm 1.4 \pm 2.0)\times10^{-5}$. The angular distribution of $J/ψ\rightarrowηX$ is studied and the two $J^P$ assumptions of the $X$ cannot be clearly distinguished due to the limited statistics. In all measurements the first uncertainties are statistical and the second systematic.

hep-ex↗

arXiv2019

Search for heavy Majorana neutrino in lepton number violating decays of D-> K pi e+ e+

Using the data sample of an integrated luminosity of 2.93 fb$^{-1}$ taken at the center-of-mass energy of 3.773 GeV, we search for the Majorana neutrino in the lepton number violating decays $D\to K πe^+ e^+$. No significant signal is observed, and the upper limits on the branching fraction at the 90\% confidence level are set to be $\mathcal{B}\,(D^0 \to K^- π^- e^+ e^+)<2.8\times10^{-6}$, $\mathcal{B}\,(D^+ \to K_S^0 π^- e^+ e^+)<3.3\times10^{-6}$ and $\mathcal{B}\,(D^+ \to K^- π^0 e^+ e^+)<8.5\times10^{-6}$. The Majorana neutrino is searched for with different mass assumptions ranging from 0.25 to 1.0 GeV/$c^2$ in the decays $D^0\to K^- e^+ ν_N(π^- e^+)$ and $D^+\to K_S^0 e^+ ν_N(π^- e^+)$, and the upper limits on the branching fraction at the 90\% confidence level are extracted to be at the level of $10^{-7} \sim 10^{-6}$, depending on the mass of Majorana neutrino. The constraints on the mixing matrix element $|V_{eN}|^2$ are also evaluated.

hep-ex↗