arXiv subjects

C. Fan

Publications and source records attributed to C. Fan.

At least 19 recordsLinked to original sources

arXiv2026

Production and installation of wavelength-shifting reflective light enhancers for the Short-Baseline Near Detector

We report on the design, production, and installation of a wavelength-shifting reflective system on the cathode of the Short-Baseline Near Detector (SBND), a liquid argon time projection chamber located along the Fermilab Booster Neutrino Beam. To increase and homogenize scintillation-light collection, 64 double-sided plates were fabricated from FR4, laminated with specular reflector film and coated with 300 $\mu$g/cm$^2$ of tetraphenyl butadiene (TPB) wavelength shifter using controlled physical vapor deposition. The coating uniformity was validated through dedicated measurements of deposited mass and profilometry studies. Because exposure to ambient blue/UV light could degrade the TPB, protective filtering and controlled storage conditions were implemented during handling and installation. The coated plates were assembled between conductive meshes for high-voltage compatibility and installed in situ during detector integration. This system constitutes the largest TPB-coated area deployed in a neutrino detector. It operates in conjunction with SBND's photon detection system, which consists of photomultiplier tubes and X-ARAPUCAs. Early light-collection measurements show high uniformity and light response across the detector, supporting improved triggering, calorimetry, and position reconstruction in SBND.

physics.ins-det↗

arXiv2025

Sampling Off-Axis Neutrino Fluxes with the Short-Baseline Near Detector

The Short-Baseline Near Detector (SBND), the near detector in the Short-Baseline Neutrino Program at Fermi National Accelerator Laboratory, is located just 110 m from the Booster Neutrino Beam target. Thanks to this close proximity, relative to its 4 m $\times$ 4 m front face, neutrinos enter SBND over a range of angles from $0^{\circ}$ to approximately $1.6^{\circ}$, enabling the detector to sample variations in the neutrino flux as a function of angle-a technique known as PRISM, referred to here as SBND-PRISM. In this paper, we show how muon- and electron-neutrino fluxes vary as a function of the neutrino beam axis angle and how this can be exploited to expand the physics potential of SBND. We make use of a model that predicts an angle-dependent electron-neutrino excess signal to illustrate this effect, such as $\nu_\mu \to \nu_e$ oscillations. We present how SBND-PRISM provides a method to add robustness against uncertainties in cross-section modeling and, more generally, uncertainties that do not depend on the spatial position of neutrino interaction inside the detector. The fluxes, along with their associated covariance matrices, are made publicly available with this publication.

hep-ex↗

arXiv2025

The Short-Baseline Near Detector at Fermilab

SBND is a 112 ton liquid argon time projection chamber (LArTPC) neutrino detector located 110 meters from the Booster Neutrino Beam (BNB) target at Fermilab. Its main goals include searches for eV-scale sterile neutrinos as part of the Short-Baseline Neutrino (SBN) program, other searches for physics beyond the Standard Model, and precision studies of neutrino-argon interactions. In addition, SBND is providing a platform for LArTPC neutrino detector technology development and is an excellent training ground for the international group of scientists and engineers working towards the upcoming flagship Deep Underground Neutrino Experiment (DUNE). SBND began operation in July 2024, and started collecting stable neutrino beam data in December 2024 with an unprecedented rate of ~7,000 neutrino events per day. During its currently approved operation plans (2024-2027), SBND is expected to accumulate nearly 10 million neutrino interactions. The near detector dataset will be instrumental in testing the sterile neutrino hypothesis with unprecedented sensitivity in SBN and in probing signals of beyond the Standard Model physics. It will also be used to significantly advance our understanding of the physics of neutrino-argon interactions ahead of DUNE. After the planned accelerator restart at Fermilab (2029+), opportunities are being explored to operate SBND in antineutrino mode in order to address the scarcity of antineutrino-argon scattering data, or in a dedicated beam-dump mode to significantly enhance sensitivity to searches for new physics. SBND is an international effort, with approximately 40% of institutions from Europe, contributing to detector construction, commissioning, software development, and data analysis. Continued European involvement and leadership are essential during SBND's operations and analysis phase for both the success of SBND, SBN and its role leading up to DUNE.

hep-ex↗

arXiv2024

Scintillation Light in SBND: Simulation, Reconstruction, and Expected Performance of the Photon Detection System

SBND is the near detector of the Short-Baseline Neutrino program at Fermilab. Its location near to the Booster Neutrino Beam source and relatively large mass will allow the study of neutrino interactions on argon with unprecedented statistics. This paper describes the expected performance of the SBND photon detection system, using a simulated sample of beam neutrinos and cosmogenic particles. Its design is a dual readout concept combining a system of 120 photomultiplier tubes, used for triggering, with a system of 192 X-ARAPUCA devices, located behind the anode wire planes. Furthermore, covering the cathode plane with highly-reflective panels coated with a wavelength-shifting compound recovers part of the light emitted towards the cathode, where no optical detectors exist. We show how this new design provides a high light yield and a more uniform detection efficiency, an excellent timing resolution and an independent 3D-position reconstruction using only the scintillation light. Finally, the whole reconstruction chain is applied to recover the temporal structure of the beam spill, which is resolved with a resolution on the order of nanoseconds.

physics.ins-det↗

arXiv2024

Score-CDM: Score-Weighted Convolutional Diffusion Model for Multivariate Time Series Imputation

Multivariant time series (MTS) data are usually incomplete in real scenarios, and imputing the incomplete MTS is practically important to facilitate various time series mining tasks. Recently, diffusion model-based MTS imputation methods have achieved promising results by utilizing CNN or attention mechanisms for temporal feature learning. However, it is hard to adaptively trade off the diverse effects of local and global temporal features by simply combining CNN and attention. To address this issue, we propose a Score-weighted Convolutional Diffusion Model (Score-CDM for short), whose backbone consists of a Score-weighted Convolution Module (SCM) and an Adaptive Reception Module (ARM). SCM adopts a score map to capture the global temporal features in the time domain, while ARM uses a Spectral2Time Window Block (S2TWB) to convolve the local time series data in the spectral domain. Benefiting from the time convolution properties of Fast Fourier Transformation, ARM can adaptively change the receptive field of the score map, and thus effectively balance the local and global temporal features. We conduct extensive evaluations on three real MTS datasets of different domains, and the result verifies the effectiveness of the proposed Score-CDM.

cs.LG↗

arXiv2022

Acceleration of 60 MeV proton beams in the commissioning experiment of SULF-10 PW laser

We report the experimental results of the commissioning phase in the 10 PW laser beamline of Shanghai Superintense Ultrafast Laser Facility (SULF). The peak power reaches 2.4 PW on target without the last amplifying during the experiment. The laser energy of 72\pm 9 J is directed to a focal spot of ~6 {\mu}m diameter (FWHM) in 30 fs pulse duration, yielding a focused peak intensity around 2.0 \times 10^{21} W/cm^2. First laser-proton acceleration experiment is performed using plain copper and plastic targets. High-energy proton beams with maximum cut-off energy up to 62.5 MeV are achieved using copper foils at the optimum target thickness of 4 {\mu}m via target normal sheath acceleration (TNSA). For plastic targets of tens of nanometers thick, the proton cut-off energy is approximately 20 MeV, showing ring-like or filamented density distributions. These experimental results reflect the capabilities of the SULF-10 PW beamline, e.g., both ultrahigh intensity and relatively good beam contrast. Further optimization for these key parameters is underway, where peak laser intensities of 10^{22}-10^{23} W/cm^2 are anticipated to support various experiments on extreme field physics.

physics.plasm-ph↗

arXiv2015

Low-temperature thermal conductivity of Dy_2Ti_2O_7 and Yb_2Ti_2O_7 single crystals

We study the low-temperature thermal conductivity (\kappa) of Dy_2Ti_2O_7 and Yb_2Ti_2O_7 single crystals in magnetic fields up to 14 T along the [111], [100] and [110] directions. The main experimental findings for Dy_2Ti_2O_7 are: (i) the low-T \kappa(H) isotherms exhibit not only the step-like decreases at the low-field (< 2 T) magnetic transitions but also obvious field dependencies in high fields (> 7 T); (ii) at T \le 0.5 K, the \kappa(H) curves show anisotropic irreversibility in low fields, that is, the \kappa(H) hysteresis locates at the first-order transition with H \parallel [100] and [110], while it locates between two successive transitions with H \parallel [111]; (iii) the \kappa in the hysteresis loops for H \parallel [100] and [110] show an extremely slow relaxation with the time constant of \sim 1000 min. The main experimental findings for Yb_2Ti_2O_7 are: (i) the zero-field \kappa(T) show a kink-like decrease at the first-order transition (\sim 200 mK) with decreasing temperature; (ii) the low-T \kappa(H) isotherms show a decrease in low field and a large enhancement in high fields; (iii) the low-T \kappa(H) curves show a sharp minimum at 0.5 T for H \parallel [110] and [111]. The roles of monopole excitations, field-induced transitions, spin fluctuations and magnetoelastic coupling are discussed.

cond-mat.str-el↗

arXiv2014

Ground state and magnetic phase transitions of orthoferrite DyFeO_3

Low-temperature thermal conductivity (κ), as well as magnetization (M) and electric polarization (P), of multiferroic orthoferrite DyFeO_3 single crystals are studied with H \parallel c. When the crystal is cooled in zero field, M, P, and κall consistently exhibit irreversible magnetic-field dependencies. In particular, with 500 mK < T \le 2 K, all these properties show two transitions at the first run of increasing field but only the higher-field transition is present in the subsequent field sweepings. Moreover, the ultra-low-T (T < 500 mK) κ(H) shows a different irreversibility and there is only one transition when the field is swept both up and down. All the results indicate a complex low-T H-T phase diagram involving successive magnetic phase transitions of the Fe^{3+} spins. In particular, the ground state, obtained with cooling to subKelvin temperatures in zero field, is found to be an unexplored phase.

cond-mat.str-el↗

arXiv2014

Low-temperature heat transport of the geometrically frustrated antiferromagnets R_2Ti_2O_7 (R = Gd and Er)

We report a systematic study on the low-temperature thermal conductivity (κ) of R_2Ti_2O_7 (R = Gd and Er) single crystals with different directions of magnetic field and heat current. It is found that the magnetic excitations mainly act as phonon scatterers rather than heat carriers, although these two materials have long-range magnetic orders at low temperatures. The low-T κ(H) isotherms of both compounds show rather complicated behaviors and have good correspondences with the magnetic transitions, where the κ(H) curves show drastic dip- or step-like changes. In comparison, the field dependencies of κare more complicated in Gd_2Ti_2O_7, due to the complexity of its low-T phase diagram and field-induced magnetic transitions. These results demonstrate the significant coupling between spins and phonons in these materials and the ability of heat-transport properties probing the magnetic transitions.

cond-mat.str-el↗

arXiv2013

Growth of (CH$_3$)$_2$NH$_2$CuCl$_3$ single crystals using evaporation method with different temperatures and solvents

The bulk single crystals of of low-dimensional magnet (CH$_3$)$_2$NH$_2$CuCl$_3$ (DMACuCl$_3$ or MCCL) are grown by a slow evaporation method with different kinds of solvents, different degrees of super-saturation of solution and different temperatures of solution, respectively. Among three kinds of solvent, methanol, alcohol and water, alcohol is found to be the best one for growing MCCL crystals because of its structural similarity to the raw materials and suitable evaporation rate. The best growth temperature is in the vicinity of 35 $^{\circ}$C. The problem of the crystals deliquescing in air has been solved through recrystallization process. The crystals are characterized by means of x-ray diffraction, specific heat and magnetic susceptibility.

cond-mat.str-el↗

arXiv2013

Crystal growth and characterization of Haldane chain compound Ni(C$_3$H$_{10}$N$_2$)$_2$NO$_2$ClO$_4$

The bulk single crystals of $S = 1$ chain compound Ni(C$_3$H$_{10}$N$_2$)$_2$NO$_2$ClO$_4$ are grown by using a slow evaporation method at a constant temperature and a slow cooling method. It is found that the optimum condition of growing large crystals is via slow evaporation at 25 $^\circ$C using 0.015 mol Ni(ClO$_4$)$_2$$\cdot$6H$_2$O, 0.015 mol NaNO$_2$, and 0.03 mol 1,3-propanediamine liquid dissolved into 30 ml aqueous solvent. High-quality crystals with size up to $18 \times 7.5 \times 5$ mm$^3$ are obtained. The single crystals are characterized by measurements of x-ray diffraction, magnetic susceptibility, specific heat and thermal conductivity. The susceptibilities along three crystallographic axes are found to exhibit broad peaks at $\sim 55$ K, and then decrease abruptly to zero at lower temperatures, which is characteristic of a Haldane chain system. The specific heat and the thermal conductivity along the $c$ axis can be attributed to the simple phononic contribution and are analyzed using the Debye approximation.

cond-mat.str-el↗

arXiv2013

Single crystal growth of the pyrochlores $R_2$Ti$_2$O$_7$ ($R$ = rare earth) by the optical floating-zone method

We report a systematic study on the crystal growth of the rare-earth titanates $R_2$Ti$_2$O$_7$ ($R$ = Gd, Tb, Dy, Ho, Y, Er, Yb and Lu) and Y-doped Tb$_{2-x}$Y$_x$Ti$_2$O$_7$ ($x$ = 0.2 and 1) using an optical floating-zone method. High-quality single crystals were successfully obtained and the growth conditions were carefully optimized. The oxygen pressure was found to be the most important parameter and the appropriate ones are 0.1--0.4 MPa, depending on the radius of rare-earth ions. The growth rate is another parameter and was found to be 2.5--4 mm/h for different rare-earth ions. X-ray diffraction data demonstrated the good crystallinity of these crystals. The basic physical properties of these crystals were characterized by the magnetic susceptibility and specific heat measurements.

cond-mat.str-el↗

arXiv2013

Single crystal growth of the hexagonal manganites $R$MnO$_3$ ($R$ = rare earth) by the optical floating-zone method

We report a study on the crystal growth of the hexagonal manganites $R$MnO$_3$ ($R$ = Y, Lu, Ho, Er, and Tm) by using an optical floating-zone method. It was found that high-quality single crystals of $R$ = Y, Lu, and Ho could be easily grown with essentially the same conditions as those reported in literature, that is, with an atmosphere of normal pressure Ar and oxygen mixture and a growth rate of 2--4 mm/h. However, these conditions were not feasible for growing good crystals of $R$ = Er and Tm. The chemical analysis indicated that it was due to an off-stoichiometric phenomenon in the formed single crystals. We used an effective and simple way to resolve this problem by adjusting the nominal compositions of the polycrystal feed rods to be 1--$2\%$ rare-earth excess. The structures and physical properties were characterized by X-ray diffraction, magnetic susceptibility, specific heat, resistivity, and dielectric constant measurements.

cond-mat.str-el↗

arXiv2013

Magnetically originated phonon-glass-like behavior in Tb_2Ti_2O_7 single crystal

We report a study on the thermal conductivity (κ) of Tb_2Ti_2O_7 single crystals at low temperatures. It is found that in zero field this material has an extremely low phonon thermal conductivity in a broad temperature range. The mean free path of phonons is even smaller than that of amorphous materials and is 3--4 orders of magnitude smaller than the sample size at 0.3 K. The strong spin fluctuation of the spin-liquid state is discussed to be the reason of the strong phonon scattering. The magnetic-field dependence of κand comparison with Y_2Ti_2O_7 and TbYTi_2O_7 confirm the magnetic origin of this phonon-glass-like behavior.

cond-mat.str-el↗

arXiv2013

An irreversible magnetic-field dependence of low-temperature heat transport of spin-ice compound Dy_2Ti_2O_7 in a [111] field

We study the low-temperature thermal conductivity (κ) of Dy_2Ti_2O_7 along and perpendicular to the (111) plane and under the magnetic field along the [111] direction. Besides the step-like decreases of κat the field-induced transitions from the spin-ice state to the kagomé-ice state and then to the polarized state, an abnormal phenomenon is that the κ(H) isotherms show a clear irreversibility at very low temperatures upon sweeping magnetic field up and down. This phenomenon surprisingly has no correspondence with the well-known magnetization hysteresis. Possible origins for this irreversibility are discussed; in particular, a pinning effect of magnetic monopoles in spin ice compound by the weak disorders is proposed.

cond-mat.str-el↗

arXiv2012

Low-temperature heat transport and magnetic-structure transition of the hexagonal TmMnO_3 single crystals

We study the low-temperature heat transport, as well as the magnetization and the specific heat, of TmMnO_3 single crystals to probe the transitions of magnetic structure induced by magnetic field. It is found that the low-T thermal conductivity (κ) shows strong magnetic-field dependence and the overall behaviors can be understood in the scenario of magnetic scattering on phonons. In addition, a strong "dip"-like feature shows up in κ(H) isotherms at 3.5--4 T for H \parallel c, which is related to a known spin re-orientation of Mn^{3+} moments. The absence of this phenomenon for H \parallel a indicates that the magnetic-structure transition of TmMnO_3 cannot be driven by the in-plane field. In comparison, the magnetothermal conductivity of TmMnO_3 is much larger than that of YMnO_3 but smaller than that of HoMnO_3, indicating that the magnetisms of rare-earth ions are playing the key role in the spin-phonon coupling of the hexagonal manganites.

cond-mat.str-el↗

arXiv2012

Paramagnetic ground state with field-induced partial order in Nd_3Ga_5SiO_{14} probed by low-temperature heat transport

We study the low-temperature heat transport of Nd_3Ga_5SiO_{14}, which is a spin-liquid candidate, to probe the nature of ground state and the effect of magnetic field on the magnetic properties. The thermal conductivity (κ) shows a purely phononic transport in zero field. The external magnetic field along the c axis induces a dip-like behavior of κ(H), which can be attributed to a simple paramagnetic scattering on phonons. However, the magnetic field along the ab plane induces another step-like decrease of κ. This kind of κ(H) behavior is discussed to be related to a field-induced partial order, which yields low-energy magnetic excitations that significantly scatter phonons. These results point to a paramagnetic ground state that partial magnetic order can be induced by magnetic field along the ab plane, which is also signified by the low-T specific heat data.

cond-mat.str-el↗

arXiv2012

Heat transport of quasi-one-dimensional Ising-like antiferromagnet BaCo_2V_2O_8 in the longitudinal and transverse fields

The very-low-temperature thermal conductivity (κ) is studied for BaCo_2V_2O_8, a quasi-one-dimensional Ising-like antiferromagnet exhibiting an unusual magnetic-field-induced order-to-disorder transition. The nearly isotropic transport in the longitudinal field indicates that the magnetic excitations scatter phonons rather than conduct heat. The field dependence of κshows a sudden drop at \sim 4 T, where the system unndergoes the transition from the Néel order to the incommensurate state. Another dip at lower field of \sim 3 T indicates an unknown magnetic transition, which is likely due to the spin-flop transition. Moreover, the κ(H) in the transverse field shows a very deep valley-like feature, which moves slightly to higher field and becomes sharper upon lowering the temperature. This indicates a magnetic transition induced by the transverse field, which however is not predicted by the present theories for this low-dimensional spin system.

cond-mat.str-el↗