arXiv subjects

S. Cao

Publications and source records attributed to S. Cao.

At least 91 records · Page 5Linked to original sources

arXiv2022

Probing the multi-scale dynamical interaction between heavy quarks and the QGP using JETSCAPE

The dynamics of shower development for a jet traveling through the QGP involves a variety of scales, one of them being the heavy quark mass. Even though the mass of the heavy quarks plays a subdominant role during the high virtuality portion of the jet evolution, it does affect longitudinal drag and diffusion, stimulating additional radiation from heavy quarks. These emissions partially compensate the reduction in radiation from the dead cone effect. In the lower virtuality part of the shower, when the mass is comparable to the transverse momenta of the partons, scattering and radiation processes off heavy quarks differ from those off light quarks. All these factors result in a different nuclear modification factor for heavy versus light flavors and thus for heavy-flavor tagged jets. In this study, the heavy quark shower evolution and the fluid dynamical medium are modeled on an event by event basis using the JETSCAPE Framework. We present a multi-stage calculation that explores the differences between various heavy quark energy-loss mechanisms within a realistically expanding quark-gluon plasma (QGP). Inside the QGP, the highly virtual and energetic portion of the shower is modeled using the MATTER generator, while the LBT generator models the showers induced by energetic and close-to-on-shell heavy quarks. Energy-momentum exchange with the medium, essential for the study of jet modification, proceeds using a weak coupling recoil approach. The JETSCAPE framework allows for transitions, on the level of individual partons, from one energy-loss prescription to the other depending on the parton's energy and virtuality and the local density. This allows us to explore the effect and interplay between the different regimes of energy loss on the propagation and radiation from hard heavy quarks in a dense medium.

nucl-th↗

arXiv2022

Scintillator ageing of the T2K near detectors from 2010 to 2021

The T2K experiment widely uses plastic scintillator as a target for neutrino interactions and an active medium for the measurement of charged particles produced in neutrino interactions at its near detector complex. Over 10 years of operation the measured light yield recorded by the scintillator based subsystems has been observed to degrade by 0.9--2.2\% per year. Extrapolation of the degradation rate through to 2040 indicates the recorded light yield should remain above the lower threshold used by the current reconstruction algorithms for all subsystems. This will allow the near detectors to continue contributing to important physics measurements during the T2K-II and Hyper-Kamiokande eras. Additionally, work to disentangle the degradation of the plastic scintillator and wavelength shifting fibres shows that the reduction in light yield can be attributed to the ageing of the plastic scintillator.

physics.ins-det↗

arXiv2022

Testing Non-Standard Interactions Between Solar Neutrinos and Quarks with Super-Kamiokande

Non-Standard Interactions (NSI) between neutrinos and matter affect the neutrino flavor oscillations. Due to the high matter density in the core of the Sun, solar neutrinos are suited to probe these interactions. Using the $277$ kton-yr exposure of Super-Kamiokande to $^{8}$B solar neutrinos, we search for the presence of NSI. Our data favors the presence of NSI with down quarks at 1.8$σ$, and with up quarks at 1.6$σ$, with the best fit NSI parameters being ($ε_{11}^{d},ε_{12}^{d}$) = (-3.3, -3.1) for $d$-quarks and ($ε_{11}^{u},ε_{12}^{u}$) = (-2.5, -3.1) for $u$-quarks. After combining with data from the Sudbury Neutrino Observatory and Borexino, the significance increases by 0.1$σ$.

hep-ex↗

arXiv2022

Search for solar electron anti-neutrinos due to spin-flavor precession in the Sun with Super-Kamiokande-IV

Due to a very low production rate of electron anti-neutrinos ($\barν_e$) via nuclear fusion in the Sun, a flux of solar $\barν_e$ is unexpected. An appearance of $\barν_e$ in solar neutrino flux opens a new window for the new physics beyond the standard model. In particular, a spin-flavor precession process is expected to convert an electron neutrino into an electron anti-neutrino (${ν_e\to\barν_e}$) when neutrino has a finite magnetic moment. In this work, we have searched for solar $\barν_e$ in the Super-Kamiokande experiment, using neutron tagging to identify their inverse beta decay signature. We identified 78 $\barν_e$ candidates for neutrino energies of 9.3 to 17.3 MeV in 2970.1 live days with a fiducial volume of 22.5 kiloton water (183.0 kton$\cdot$year exposure). The energy spectrum has been consistent with background predictions and we thus derived a 90% confidence level upper limit of ${4.7\times10^{-4}}$ on the $ν_e\to\barν_e$ conversion probability in the Sun. We used this result to evaluate the sensitivity of future experiments, notably the Super-Kamiokande Gadolinium (SK-Gd) upgrade.

hep-ex↗

arXiv2022

Role of bulk viscosity in deuteron production in ultrarelativistic nuclear collisions

We use a Bayesian-calibrated multistage viscous hydrodynamic model to explore deuteron yield, mean transverse momentum and flow observables in LHC Pb-Pb collisions. We explore theoretical uncertainty in the production of deuterons, including (i) the contribution of thermal deuterons, (ii) models for the subsequent formation of deuterons (hadronic transport vs coalescence) and (iii) the overall sensitivity of the results to the hydrodynamic model -- in particular to bulk viscosity, which is often neglected in studies of deuteron production. Using physical parameters set by a comparison to only light hadron observables, we find good agreement with measurements of the mean transverse momentum $\langle p_T \rangle$ and elliptic flow $v_2$ of deuterons; however, tension is observed with experimental data for the deuteron multiplicity in central collisions. The results are found to be sensitive to each of the mentioned theoretical uncertainties, with a particular sensitivity to bulk viscosity, indicating that the latter is an important ingredient for an accurate treatment of deuteron production.

hep-ph↗

arXiv2021

First Gadolinium Loading to Super-Kamiokande

In order to improve Super-Kamiokande's neutron detection efficiency and to thereby increase its sensitivity to the diffuse supernova neutrino background flux, 13 tons of $\rm Gd_2(\rm SO_4)_3\cdot \rm 8H_2O$ (gadolinium sulfate octahydrate) was dissolved into the detector's otherwise ultrapure water from July 14 to August 17, 2020, marking the start of the SK-Gd phase of operations. During the loading, water was continuously recirculated at a rate of 60 m$^3$/h, extracting water from the top of the detector and mixing it with concentrated $\rm Gd_2(\rm SO_4)_3\cdot \rm 8H_2O$ solution to create a 0.02% solution of the Gd compound before injecting it into the bottom of the detector. A clear boundary between the Gd-loaded and pure water was maintained through the loading, enabling monitoring of the loading itself and the spatial uniformity of the Gd concentration over the 35 days it took to reach the top of the detector. During the subsequent commissioning the recirculation rate was increased to 120 m$^3$/h, resulting in a constant and uniform distribution of Gd throughout the detector and water transparency equivalent to that of previous pure-water operation periods. Using an Am-Be neutron calibration source the mean neutron capture time was measured to be $115\pm1$ $μ$s, which corresponds to a Gd concentration of $111\pm2$ ppm, as expected for this level of Gd loading. This paper describes changes made to the water circulation system for this detector upgrade, the Gd loading procedure, detector commissioning, and the first neutron calibration measurements in SK-Gd.

physics.ins-det↗

arXiv2021

New Methods and Simulations for Cosmogenic Induced Spallation Removal in Super-Kamiokande-IV

Radioactivity induced by cosmic muon spallation is a dominant source of backgrounds for $\mathcal{O}(10)~$MeV neutrino interactions in water Cherenkov detectors. In particular, it is crucial to reduce backgrounds to measure the solar neutrino spectrum and find neutrino interactions from distant supernovae. In this paper we introduce new techniques to locate muon-induced hadronic showers and efficiently reject spallation backgrounds. Applying these techniques to the solar neutrino analysis with an exposure of $2790\times22.5$~kton.day increases the signal efficiency by $12.6\%$, approximately corresponding to an additional year of detector running. Furthermore, we present the first spallation simulation at SK, where we model hadronic interactions using FLUKA. The agreement between the isotope yields and shower pattern in this simulation and in the data gives confidence in the accuracy of this simulation, and thus opens the door to use it to optimize muon spallation removal in new data with gadolinium-enhanced neutron capture detection.

hep-ex↗

arXiv2021

Diffuse Supernova Neutrino Background Search at Super-Kamiokande

A new search for the diffuse supernova neutrino background (DSNB) flux has been conducted at Super-Kamiokande (SK), with a $22.5\times2970$-kton$\cdot$day exposure from its fourth operational phase IV. The new analysis improves on the existing background reduction techniques and systematic uncertainties and takes advantage of an improved neutron tagging algorithm to lower the energy threshold compared to the previous phases of SK. This allows for setting the world's most stringent upper limit on the extraterrestrial $\barν_e$ flux, for neutrino energies below 31.3 MeV. The SK-IV results are combined with the ones from the first three phases of SK to perform a joint analysis using $22.5\times5823$ kton$\cdot$days of data. This analysis has the world's best sensitivity to the DSNB $\barν_e$ flux, comparable to the predictions from various models. For neutrino energies larger than 17.3 MeV, the new combined $90\%$ C.L. upper limits on the DSNB $\barν_e$ flux lie around $2.7$ cm$^{-2}$$\cdot$$\text{sec}^{-1}$, strongly disfavoring the most optimistic predictions. Finally, potentialities of the gadolinium phase of SK and the future Hyper-Kamiokande experiment are discussed.

astro-ph.HE↗

arXiv2021

Search for neutrinos in coincidence with gravitational wave events from the LIGO-Virgo O3a Observing Run with the Super-Kamiokande detector

The Super-Kamiokande detector can be used to search for neutrinos in time coincidence with gravitational waves detected by the LIGO-Virgo Collaboration (LVC). Both low-energy ($7-100$ MeV) and high-energy ($0.1-10^5$ GeV) samples were analyzed in order to cover a very wide neutrino spectrum. Follow-ups of 36 (out of 39) gravitational waves reported in the GWTC-2 catalog were examined; no significant excess above the background was observed, with 10 (24) observed neutrinos compared with 4.8 (25.0) expected events in the high-energy (low-energy) samples. A statistical approach was used to compute the significance of potential coincidences. For each observation, p-values were estimated using neutrino direction and LVC sky map ; the most significant event (GW190602_175927) is associated with a post-trial p-value of $7.8\%$ ($1.4σ$). Additionally, flux limits were computed independently for each sample and by combining the samples. The energy emitted as neutrinos by the identified gravitational wave sources was constrained, both for given flavors and for all-flavors assuming equipartition between the different flavors, independently for each trigger and by combining sources of the same nature.

astro-ph.HE↗

arXiv2021

Characterisation of spatial charge sensitivity in a multi-mode superconducting qubit

Understanding and suppressing sources of decoherence is a leading challenge in building practical quantum computers. In superconducting qubits, low frequency charge noise is a well-known decoherence mechanism that is effectively suppressed in the transmon qubit. Devices with multiple charge-sensitive modes can exhibit more complex behaviours, which can be exploited to study charge fluctuations in superconducting qubits. Here we characterise charge-sensitivity in a superconducting qubit with two transmon-like modes, each of which is sensitive to multiple charge-parity configurations and charge-offset biases. Using Ramsey interferometry, we observe sensitivity to four charge-parity configurations and track two independent charge-offset drifts over hour timescales. We provide a predictive theory for charge sensitivity in such multi-mode qubits which agrees with our results. Finally, we demonstrate the utility of a multi-mode qubit as a charge detector by spatially tracking local-charge drift.

quant-ph↗

arXiv2021

Determining the jet transport coefficient $\hat{q}$ from inclusive hadron suppression measurements using Bayesian parameter estimation

We report a new determination of $\hat{q}$, the jet transport coefficient of the Quark-Gluon Plasma. We use the JETSCAPE framework, which incorporates a novel multi-stage theoretical approach to in-medium jet evolution and Bayesian inference for parameter extraction. The calculations, based on the MATTER and LBT jet quenching models, are compared to experimental measurements of inclusive hadron suppression in Au+Au collisions at RHIC and Pb+Pb collisions at the LHC. The correlation of experimental systematic uncertainties is accounted for in the parameter extraction. The functional dependence of $\hat{q}$ on jet energy or virtuality and medium temperature is based on a perturbative picture of in-medium scattering, with components reflecting the different regimes of applicability of MATTER and LBT. In the multi-stage approach, the switch between MATTER and LBT is governed by a virtuality scale $Q_0$. Comparison of the posterior model predictions to the RHIC and LHC hadron suppression data shows reasonable agreement, with moderate tension in limited regions of phase space. The distribution of $\hat{q}/T^3$ extracted from the posterior distributions exhibits weak dependence on jet momentum and medium temperature $T$, with 90\% Credible Region (CR) depending on the specific choice of model configuration. The choice of MATTER+LBT, with switching at virtuality $Q_0$, has 90\% CR of $2<\hat{q}/T^3<4$ for $p_\mathrm{T}^\mathrm{jet}>40$ GeV/c. The value of $Q_0$, determined here for the first time, is in the range 2.0-2.7 GeV.

nucl-th↗

arXiv2021

Supernova Model Discrimination with Hyper-Kamiokande

Core-collapse supernovae are among the most magnificent events in the observable universe. They produce many of the chemical elements necessary for life to exist and their remnants -- neutron stars and black holes -- are interesting astrophysical objects in their own right. However, despite millennia of observations and almost a century of astrophysical study, the explosion mechanism of core-collapse supernovae is not yet well understood. Hyper-Kamiokande is a next-generation neutrino detector that will be able to observe the neutrino flux from the next galactic core-collapse supernova in unprecedented detail. We focus on the first 500 ms of the neutrino burst, corresponding to the accretion phase, and use a newly-developed, high-precision supernova event generator to simulate Hyper-Kamiokande's response to five different supernova models. We show that Hyper-Kamiokande will be able to distinguish between these models with high accuracy for a supernova at a distance of up to 100 kpc. Once the next galactic supernova happens, this ability will be a powerful tool for guiding simulations towards a precise reproduction of the explosion mechanism observed in nature.

astro-ph.IM↗

arXiv2021

Physics potentials with a combined sensitivity of T2K-II, NO$ν$A extension and JUNO

Leptonic \textit{CP} violation search, neutrino mass hierarchy determination, and the precision measurement of oscillation parameters for a unitary test of the leptonic mixing matrix are among the major targets of the ongoing and future neutrino oscillation experiments. The work explores the physics reach for these targets by around 2027, when the third generation of the neutrino experiments starts operation, with a combined sensitivity of three experiments: T2K-II, NO$ν$A extension, and JUNO. It is shown that a joint analysis of these three experiments can conclusively determine the neutrino mass hierarchy. Also, at certain values of \emph{true} \dcp, it provides closely around a $5σ$ confidence level (C.L.) to exclude \textit{CP}-conserving values and more than a $50\%$ fractional region of \emph{true} $δ_{\text{CP}}$ values can be explored with a statistic significance of at least a $3σ$ C.L. Besides, the joint analysis can provide unprecedented precision measurements of the atmospheric neutrino oscillation parameters and a great offer to solve the $θ_{23}$ octant degeneracy in the case of nonmaximal mixing.

hep-ph↗

arXiv2021

Search for Tens of MeV Neutrinos associated with Gamma-Ray Bursts in Super-Kamiokande

A search for neutrinos produced in coincidence with Gamma-Ray Bursts(GRB) was conducted with the Super-Kamiokande (SK) detector. Between December 2008 and March 2017, the Gamma-ray Coordinates Network recorded 2208 GRBs that occurred during normal SK operation. Several time windows around each GRB were used to search for coincident neutrino events. No statistically significant signal in excess of the estimated backgrounds was detected. The $\barν_e$ fluence in the range from 8 MeV to 100 MeV in positron total energy for $\barν_e+p\rightarrow e^{+}+n$ was found to be less than $\rm 5.07\times10^5$ cm$^{-2}$ per GRB in 90\% C.L. Upper bounds on the fluence as a function of neutrino energy were also obtained.

astro-ph.HE↗

arXiv2021

Determining the jet transport coefficient $\hat{q}$ of the quark-gluon plasma using Bayesian parameter estimation

We present a new determination of $\hat{q}$, the jet transport coefficient of the quark-gluon plasma. Using the JETSCAPE framework, we use Bayesian parameter estimation to constrain the dependence of $\hat{q}$ on the jet energy, virtuality, and medium temperature from experimental measurements of inclusive hadron suppression in Au-Au collisions at RHIC and Pb-Pb collisions at the LHC. These results are based on a multi-stage theoretical approach to in-medium jet evolution with the MATTER and LBT jet quenching models. The functional dependence of $\hat{q}$ on jet energy, virtuality, and medium temperature is based on a perturbative picture of in-medium scattering, with components reflecting the different regimes of applicability of MATTER and LBT. The correlation of experimental systematic uncertainties is accounted for in the parameter extraction. These results provide state-of-the-art constraints on $\hat{q}$ and lay the groundwork to extract additional properties of the quark-gluon plasma from jet measurements in heavy-ion collisions.

nucl-th↗

arXiv2021

Improved constraints on neutrino mixing from the T2K experiment with $\mathbf{3.13\times10^{21}}$ protons on target

The T2K experiment reports updated measurements of neutrino and antineutrino oscillations using both appearance and disappearance channels. This result comes from an exposure of $14.9~(16.4) \times 10^{20}$ protons on target in neutrino (antineutrino) mode. Significant improvements have been made to the neutrino interaction model and far detector reconstruction. An extensive set of simulated data studies have also been performed to quantify the effect interaction model uncertainties have on the T2K oscillation parameter sensitivity. T2K performs multiple oscillation analyses that present both frequentist and Bayesian intervals for the PMNS parameters. For fits including a constraint on \ssqthonethree from reactor data and assuming normal mass ordering T2K measures $\sin^2θ_{23} = 0.53^{+0.03}_{-0.04}$ and $Δm^2_{32} = (2.45 \pm 0.07) \times 10^{-3}$ eV$^{2}$c$^{-4}$. The Bayesian analyses show a weak preference for normal mass ordering (89% posterior probability) and the upper $\sin^2θ_{23}$ octant (80% posterior probability), with a uniform prior probability assumed in both cases. The T2K data exclude CP conservation in neutrino oscillations at the $2σ$ level.

hep-ex↗

arXiv2021

First T2K measurement of transverse kinematic imbalance in the muon-neutrino charged-current single-$π^+$ production channel containing at least one proton

This paper reports the first T2K measurement of the transverse kinematic imbalance in the single-$π^+$ production channel of neutrino interactions. We measure the differential cross sections in the muon-neutrino charged-current interaction on hydrocarbon with a single $π^+$ and at least one proton in the final state, at the ND280 off-axis near detector of the T2K experiment. The extracted cross sections are compared to the predictions from different neutrino-nucleus interaction event generators. Overall, the results show a preference for models which have a more realistic treatment of nuclear medium effects including the initial nuclear state and final-state interactions.

hep-ex↗

arXiv2021

Constraint on the Matter-Antimatter Symmetry-Violating Phase in Neutrino Oscillations

The current laws of physics do not explain the observed imbalance of matter and antimatter in the universe. Sakharov proposed that an explanation would require the violation of CP symmetry between matter and antimatter. The only CP violation observed so far is in the weak interactions of quarks, and it is too small to explain the matter-antimatter imbalance of the universe. It has been shown that CP violation in the lepton sector could generate the matter-antimatter disparity through the process called leptogenesis. The quantum mixing of neutrinos, the neutral leptons in the Standard Model, provides a potential source of CP violation through a complex phase dCP, which may have consequences for theoretical models of leptogenesis. This CP violation can be measured in muon neutrino to electron neutrino oscillations and the corresponding antineutrino oscillations, which are experimentally accessible with accelerator-produced beams as established by the T2K experiment. Until now, the value of dCP has not been significantly constrained by neutrino oscillation experiments. Here the T2K collaboration reports a measurement that favors large enhancement of the neutrino oscillation probability, excluding values of dCP which result in a large enhancement of the observed anti-neutrino oscillation probability at three standard deviations (3 sigma). The 3 sigma confidence level interval for dCP, which is cyclic and repeats every 2pi, is [-3.41,-0.03] for the so-called normal mass ordering, and [-2.54,-0.32] for the inverted mass ordering. Our results show an indication of CP violation in the lepton sector. Herein we establish methods for sensitive searches for matter-antimatter asymmetry in neutrino oscillations using accelerator-produced neutrino beams. Future measurements with larger data samples will determine whether the leptonic CP violation is larger than the quark sector CP violation.

hep-ex↗