arXiv subjects

Yifei Zhang

Publications and source records attributed to Yifei Zhang.

243 records · Page 14Linked to original sources

arXiv2017

A novel analog power supply for gain control of the Multi-Pixel Photon Counter (MPPC)

Silicon Photo-Multipliers (SiPM) are regarded as novel photo-detectors to replace conventional Photo-Multiplier Tubes (PMTs). However, the breakdown voltage dependence on the ambient temperature results in a gain variation of $\sim$3$\% /^{\circ} \mathrm C$. This severely limits the application of this device in experiments with wide range of operating temperature, especially in space missions. An experimental setup was established to investigate the temperature and bias voltage dependence of gain for the Multi-Pixel Photon Counter (MPPC). The gain and breakdown voltage dependence on operating temperature of an MPPC can be approximated by a linear function, which is similar to the behavior of a zener diode. The measured temperature coefficient of the breakdown voltage is $(59.4 \pm 0.4$ mV)$/^{\circ} \mathrm C$. According to this fact, an analog power supply based on two zener diodes and an operational amplifier was designed with a positive temperature coefficient. The measured temperature dependence for the designed power supply is between 63.65 to 64.61~mV/$^{\circ} \mathrm C$ at different output voltages. The designed power supply can bias the MPPC at an over-voltage with a temperature variation of $\sim$ 5~mV$/^{\circ} \mathrm C$. The gain variation of the MPPC biased at over-voltage of 2~V was reduced from 2.8$\% /^{\circ} \mathrm C$ to 0.3$\% /^{\circ} \mathrm C$ when biased the MPPC with the designed power supply for gain control. Detailed design and performance of the analog power supply in the temperature range from -42.7$^{\circ}\mathrm{C}$ to 20.9$^{\circ}\mathrm{C}$ will be discussed in this paper.

astro-ph.IM↗

arXiv2016

Ripple: Reflection Analysis for Android Apps in Incomplete Information Environments

Despite its widespread use in Android apps, reflection poses graving problems for static security analysis. Currently, string inference is applied to handle reflection, resulting in significantly missed security vulnerabilities. In this paper, we bring forward the ubiquity of incomplete information environments (IIEs) for Android apps, where some critical data-flows are missing during static analysis, and the need for resolving reflective calls under IIEs. We present Ripple, the first IIE-aware static reflection analysis for Android apps that resolves reflective calls more soundly than string inference. Validation with 17 popular Android apps from Google Play demonstrates the effectiveness of Ripple in discovering reflective targets with a low false positive rate. As a result, Ripple enables FlowDroid, a taint analysis for Android apps, to find hundreds of sensitive data leakages that would otherwise be missed. As a fundamental analysis, Ripple will be valuable for many security analysis clients, since more program behaviors can now be analyzed under IIEs.

cs.CR↗

arXiv2015

A Cosmic Ray Test Platform Based on the High Time Resolution MRPC Technology

In order to test the performance of detector/prototype in environment of laboratory, we design and build a larger area ($90\times52$ $cm^2$) test platform of cosmic ray based on well-designed Multi-gap Resistive Plate Chamber (MRPC) with an excellent time resolution and a high detection efficiency for the minimum ionizing particles (MIPs). The time resolution of the MRPC module used is tested to be ~80 ps, and the position resolution along the strip is ~5 mm, while the position resolution perpendicular to the strip is ~12.7 mm. The platform constructed by four MRPC modules can be functional for tracking the cosmic rays with a spatial resolution ~6.3 mm, and provide a reference time ~40 ps.

physics.ins-det↗

arXiv2011

Open charm hadron measurement in p+p and Au+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV in STAR

We present the measurements of $D^0$ and $D^*$ in p+p and $D^0$ in Au+Au collisions via hadronic decays $D^{0}\rightarrow K^{-}π^{+}$, $D^{*+}\rightarrow D^{0}π^{+}\rightarrow K^{-}π^{+}π^{+}$ in mid-rapidity $|y|<1$ at $\sqrt{s_{_{\rm NN}}}$ = 200 GeV, covering $p_T$ from 0.2 to 6 GeV/$c$ in p+p and 0.4 to 5 GeV/$c$ in Au+Au, respectively. The charm pair production cross section per nucleon-nucleon collision at mid rapidity is measured to be 202 $\pm$ 56 (stat.) $\pm$ 40 (sys.) $\pm$ 20 (norm.) $μ$b in p+p and 186 $\pm$ 22 (stat.) $\pm$ 30 (sys.) $\pm$ 18 (norm.) $μ$b in Au+Au minimum bias collisions. The number of binary collisions scaling of charm cross section indicates that charm is produced via initial hard scatterings. No suppression of $D^0$ $R_{AA}$ in Au+Au 0-80% minbias collisions is observed at $p_T$ below 3 GeV/$c$. Blast-wave predictions with light-quark hadron parameters are different from data, which may indicate that $D^0$ decouples earlier from the medium than the light-quark hadrons.

nucl-ex↗

arXiv2008

Measurement of charm production cross-section and leptons from its semileptonic decay at RHIC

In this thesis, we present the measurements of $D^{0}\to Kπ$ at low $p_T$ ($p_T\leq2$ GeV/$c$) and non-photonic electron spectra ($0.9\leq p_T\leq5$ GeV/$c$) from $D^0$ semi-leptonic decay. In addition, we use a newly proposed technique to identify muons from charm decays at low $p_T$. The combination of all these three measurements stringently constrains the total charm production cross-section at mid-rapidity at RHIC. They also allow the extraction of the charmed hadron spectral shape and a study of possible charm radial flow in Au+Au collisions.

nucl-ex↗

arXiv2008

Overview of charm production at RHIC

We present an overview of the recent abundant measurements for charm production at RHIC. The significant information of charm cross sections in different collision system at 200 GeV and charmed hadron freeze-out and flow properties extracted from these measurements are presented. The heavy flavor energy loss in the medium and heavy flavor related azimuthal correlations in heavy ion collisions are also discussed.

nucl-ex↗

arXiv2008

Identification of Bottom Contribution in Non-photonic Electron Spectra and $v_2$ at RHIC

We present a study on the spectra for heavy flavor (charm and bottom) decayed electrons in 200 GeV $p+p$ collisions and provide the relative contributions of charm and bottom hadrons from the PYTHIA calculations. The results suggest that the crossing point of the electron spectra from charm and bottom decays is above 7 GeV/$c$ and bottom contribution is not dominant for electron $p_{T}<3$ GeV/$c$. The upper limit of the relative cross section ratio is reported as $σ_{b\bar{b}}/σ_{c\bar{c}}\leq(0.49\pm0.09\pm0.09)%$. We also compare the $v_2$ distribution from simulation to the experimental data in 200 GeV $Au+Au$ collisions and estimate the possible charm $v_2$.

hep-ph↗

arXiv2006

Open charm production in $\sqrt{s_{NN}}$=200 GeV Au+Au collisions

We report on the measurement of D meson production from the analysis of their hadronic ($D^0\to Kπ$) and semileptonic ($D\to μ+X$, $D\to e+X$) decays in $\sqrt{s_{NN}}$=200 GeV Au+Au collisions. The transverse momentum ($p_T$) spectra and the nuclear modification factors for $D^0$ and for electron/muon from charm semileptonic decays will be presented. The differential cross section $dσ/dy$ is found to be consistent with the number of binary scaling. The blast-wave fit suggests that the charm hadron freeze out earlier than other light flavor hadrons.

nucl-ex↗

arXiv2006

Extracting the charm cross section from semileptonic decays into muons

We propose a sensitive measurement of the charm total cross-section at RHIC through muon identification from charm semileptonic decay at low transverse momentum ($p_T$). This can test the binary-collision scaling ($N_{bin}$) properties of the charm total cross-section and be used to study whether heavy-flavor quarks, which are used as a probe, are produced exclusively at the initial impact in hadron-hadron collisions. The effect of the charm semileptonic decay form factor on extracting the total charm cross section and on the shape of the lepton spectra are also discussed in detail. We conclude that lepton spectra from charmed hadron decays at transverse momentum $p_T\simeq1.0$ GeV/$c$ are sensitive to the charmed hadron spectrum shape. Therefore, the interactions of heavy quarks with the medium created in relativistic heavy-ion collisions, especially the flow effects, can be extracted from the lepton spectra from charmed hadron decays at low $p_T$.

nucl-ex↗