arXiv subjects

X. Qian

Publications and source records attributed to X. Qian.

At least 91 records · Page 5Linked to original sources

arXiv2013

Measurement of pretzelosity asymmetry of charged pion production in Semi-Inclusive Deep Inelastic Scattering on a polarized $^3$He target

An experiment to measure single-spin asymmetries in semi-inclusive production of charged pions in deep-inelastic scattering on a transversely polarized $^3$He target was performed at Jefferson Lab in the kinematic region of $0.16<x<0.35$ and $1.4<Q^2<2.7$ ${\rm GeV^2}$. The pretzelosity asymmetries on $^3$He, which can be expressed as the convolution of the $h^\perp_{1T}$ transverse momentum dependent distribution functions and the Collins fragmentation functions in the leading order, were measured for the first time. Using the effective polarization approximation, we extracted the corresponding neutron asymmetries from the measured $^3$He asymmetries and cross-section ratios between the proton and $^3$He. Our results show that for both $π^{\pm}$ on $^3$He and on the neutron the pretzelosity asymmetries are consistent with zero within experimental uncertainties.

nucl-ex↗

arXiv2013

LAr1-ND: Testing Neutrino Anomalies with Multiple LArTPC Detectors at Fermilab

This white paper describes LAr1-ND and the compelling physics it brings first in Phase 1 and next towards the full LAr1 program. In addition, LAr1-ND serves as a key step in the development toward large-scale LArTPC detectors. Its development goals will encompass testing existing and possibly innovative designs for LBNE while at the same time providing a training ground for teams working towards LBNE combining timely neutrino physics with experience in detector development.

physics.ins-det↗

arXiv2013

Neutrino mass hierarchy determination and other physics potential of medium-baseline reactor neutrino oscillation experiments

Medium-baseline reactor neutrino oscillation experiments (MBRO) have been proposed to determine the neutrino mass hierarchy (MH) and to make precise measurements of the neutrino oscillation parameters. With sufficient statistics, better than ~3%/\sqrt{E} energy resolution and well understood energy non-linearity, MH can be determined by analyzing oscillation signals driven by the atmospheric mass-squared difference in the survival spectrum of reactor antineutrinos. With such high performance MBRO detectors, oscillation parameters, such as \sin^22θ_{12}, Δm^2_{21}, and Δm^2_{32}, can be measured to sub-percent level, which enables a future test of the PMNS matrix unitarity to ~1% level and helps the forthcoming neutrinoless double beta decay experiments to constrain the allowed values. Combined with results from the next generation long-baseline beam neutrino and atmospheric neutrino oscillation experiments, the MH determination sensitivity can reach higher levels. In addition to the neutrino oscillation physics, MBRO detectors can also be utilized to study geoneutrinos, astrophysical neutrinos and proton decay. We propose to start a U.S. R&D program to identify, quantify and fulfill the key challenges essential for the success of MBRO experiments.

hep-ex↗

arXiv2013

JLab Measurement of the $^4$He Charge Form Factor at Large Momentum Transfers

The charge form factor of $^$4He has been extracted in the range 29 fm$^{-2}$ $\le Q^2 \le 77$ fm$^{-2}$ from elastic electron scattering, detecting $^4$He nuclei and electrons in coincidence with the High Resolution Spectrometers of the Hall A Facility of Jefferson Lab. The results are in qualitative agreement with realistic meson-nucleon theoretical calculations. The data have uncovered a second diffraction minimum, which was predicted in the $Q^2$ range of this experiment, and rule out conclusively long-standing predictions of dimensional scaling of high-energy amplitudes using quark counting.

nucl-ex↗

arXiv2013

Assembly and Installation of the Daya Bay Antineutrino Detectors

The Daya Bay reactor antineutrino experiment is designed to make a precision measurement of the neutrino mixing angle theta13, and recently made the definitive discovery of its nonzero value. It utilizes a set of eight, functionally identical antineutrino detectors to measure the reactor flux and spectrum at baselines of 300 - 2000m from the Daya Bay and Ling Ao Nuclear Power Plants. The Daya Bay antineutrino detectors were built in an above-ground facility and deployed side-by-side at three underground experimental sites near and far from the nuclear reactors. This configuration allows the experiment to make a precision measurement of reactor antineutrino disappearance over km-long baselines and reduces relative systematic uncertainties between detectors and nuclear reactors. This paper describes the assembly and installation of the Daya Bay antineutrino detectors.

physics.ins-det↗

arXiv2013

Unitarity Tests of the Neutrino Mixing Matrix

We discuss unitarity tests of the neutrino mixing (PMNS) matrix. We show that the combination of solar neutrino experiments, medium-baseline and short-baseline reactor antineutrino experiments make it possible to perform the first direct unitarity test of the PMNS matrix. In particular, the measurements of Daya Bay and JUNO (a next generation medium-baseline reactor experiment) will lay the foundation of a precise unitarity test of $|U_{e1}|^2 + |U_{e2}|^2 + |U_{e3}|^2 = 1 $. Furthermore, the precision measurement of $\sin^22θ_{13}$ in both the $\barν_e$ disappearance and the $ν_e$ appearance (from a $ν_μ$ beam) channels will provide an indirect unitarity test of the PMNS matrix. Together with the search for appearance/disappearance at very short distances, these tests could provide important information about the possible new physics beyond the three-neutrino model.

hep-ex↗

arXiv2013

Measurement of the Parity-Violating Asymmetry in Electron-Deuteron Scattering in the Nucleon Resonance Region

We report on parity-violating asymmetries in the nucleon resonance region measured using $5 - 6$ GeV longitudinally polarized electrons scattering off an unpolarized deuterium target. These results are the first parity-violating asymmetry data in the resonance region beyond the $Δ(1232)$, and provide a verification of quark-hadron duality in the nucleon electroweak $γZ$ interference structure functions at the (10-15)% level. The results are of particular interest to models relevant for calculating the $γZ$ box-diagram corrections to elastic parity-violating electron scattering measurements.

nucl-ex↗

arXiv2013

A Second Detector Focusing on the Second Oscillation Maximum at an Off-axis Location to Enhance the Mass Hierarchy Discovery Potential in LBNE10

The Long Baseline Neutrino Oscillation Experiment (LBNE) is proposed to determine the neutrino mass hierarchy and measure the CP phase in the leptonic sector. The current design of LBNE Phase I consists of a 10 kt liquid argon time projection chamber (LBNE10). The neutrino-antineutrino asymmetry in the electron-neutrino appearance probability has contributions from both the CP phase and the matter effect. For this reason, experimental sensitivity to the mass hierarchy depends both on the true value of the CP phase and the true mass hierarchy; LBNE10 will determine the mass hierarchy at high levels of significance for half of CP phase space. We propose placing a second detector at an off-axis location. Such a detector will share the same beamline as the primary LBNE detector. The detector location is chosen such that this detector focuses on a measurement of electron (anti-)neutrino appearance at the second oscillation maximum. We will show that this configuration will enhance the ability of LBNE to determine the mass hierarchy and to discover CP violation in the leptonic sector.

hep-ex↗

arXiv2013

Automated Calibration System for a High-Precision Measurement of Neutrino Mixing Angle $θ_{13}$ with the Daya Bay Antineutrino Detectors

We describe the automated calibration system for the antineutrino detectors in the Daya Bay Neutrino Experiment. This system consists of 24 identical units instrumented on 8 identical 20-ton liquid scintillator detectors. Each unit is a fully automated robotic system capable of deploying an LED and various radioactive sources into the detector along given vertical axes. Selected results from performance studies of the calibration system are reported.

physics.ins-det↗

arXiv2013

First Measurements of Spin-Dependent Double-Differential Cross Sections and the GDH Integrand from \vec{^3He}(\vecγ,n)pp at Incident Photon Energies of 12.8 and 14.7 MeV

The first measurement of the three-body photodisintegration of longitudinally-polarized ^3He with a circularly-polarized γ-ray beam was carried out at the High Intensity γ-ray Source (HIγS) facility located at Triangle Universities Nuclear Laboratory (TUNL). The spin-dependent double-differential cross sections and the contributions from the three-body photodisintegration to the ^3He GDH integrand are presented and compared with state-of-the-art three-body calculations at the incident photon energies of 12.8 and 14.7 MeV. The data reveal the importance of including the Coulomb interaction between protons in three-body calculations.

nucl-ex↗

arXiv2013

Reactor Antineutrino Anomaly with known θ_{13}

We revisit the reactor antineutrino anomaly using the recent reactor flux independent determination of sizable theta?13 by considering the full set of the absolute reactor electron antineutrino flux measurements. When normalized to the predicted flux of Mueller et al. [1], the new world average, after including results from Palo Verde, Chooz, and Double Chooz, is 0.959 +- 0.009 (experiment uncertainty) +- 0.027 (flux systematics). Including the data with kilometer baseline, the new world average is only about 1.4 sigma lower than the unity, weakening the significance of the reactor antineutrino anomaly. The upcoming results from Daya Bay, RENO, and the Double Chooz will provide further information about this issue.

nucl-ex↗

arXiv2013

Mass Hierarchy Resolution in Reactor Anti-neutrino Experiments: Parameter Degeneracies and Detector Energy Response

Determination of the neutrino mass hierarchy using a reactor neutrino experiment at $\sim$60 km is analyzed. Such a measurement is challenging due to the finite detector resolution, the absolute energy scale calibration, as well as the degeneracies caused by current experimental uncertainty of $|Δm^2_{32}|$. The standard $χ^2$ method is compared with a proposed Fourier transformation method. In addition, we show that for such a measurement to succeed, one must understand the non-linearity of the detector energy scale at the level of a few tenths of percent.

physics.ins-det↗

arXiv2012

Statistical Evaluation of Experimental Determinations of Neutrino Mass Hierarchy

Statistical methods of presenting experimental results in constraining the neutrino mass hierarchy (MH) are discussed. Two problems are considered and are related to each other: how to report the findings for observed experimental data, and how to evaluate the ability of a future experiment to determine the neutrino mass hierarchy, namely, sensitivity of the experiment. For the first problem where experimental data have already been observed, the classical statistical analysis involves constructing confidence intervals for the parameter Δm^2_{32}. These intervals are deduced from the parent distribution of the estimation of Δm^2_{32} based on experimental data. Due to existing experimental constraints on |Δm^2_{32}|, the estimation of Δm^2_{32} is better approximated by a Bernoulli distribution (a Binomial distribution with 1 trial) rather than a Gaussian distribution. Therefore, the Feldman-Cousins approach needs to be used instead of the Gaussian approximation in constructing confidence intervals. Furthermore, as a result of the definition of confidence intervals, even if it is correctly constructed, its confidence level does not directly reflect how much one hypothesis of the MH is supported by the data rather than the other hypothesis. We thus describe a Bayesian approach that quantifies the evidence provided by the observed experimental data through the (posterior) probability that either one hypothesis of MH is true. This Bayesian presentation of observed experimental results is then used to develop several metrics to assess the sensitivity of future experiments. Illustrations are made using a simple example with a confined parameter space, which approximates the MH determination problem with experimental constraints on the |Δm^2_{32}|.

hep-ph↗

arXiv2012

Methods for Optical Calibration of the BigBite Hadron Spectrometer

The techniques for optical calibration of Jefferson Lab's large-acceptance magnetic hadron spectrometer, BigBite, have been examined. The most consistent and stable results were obtained by using a method based on singular value decomposition. In spite of the complexity of the optics, the particles' positions and momenta at the target have been precisely reconstructed from the coordinates measured in the detectors by means of a single back-tracing matrix. The technique is applicable to any similar magnetic spectrometer and any particle type. For 0.55 GeV/c protons, we have established the vertex resolution of 1.2 cm, angular resolutions of 7 mrad and 16 mrad (in-plane and out-of-plane, respectively), and a relative momentum resolution of 1.6%.

nucl-ex↗

arXiv2012

Beam-Target Double Spin Asymmetry A_LT in Charged Pion Production from Deep Inelastic Scattering on a Transversely Polarized He-3 Target at 1.4<Q^2<2.7 GeV^2

We report the first measurement of the double-spin asymmetry $A_{LT}$ for charged pion electroproduction in semi\nobreakdash-inclusive deep\nobreakdash-inelastic electron scattering on a transversely polarized $^{3}$He target. The kinematics focused on the valence quark region, $0.16<x<0.35$ with $1.4<Q^{2}<2.7\,\textrm{GeV}^{2}$. The corresponding neutron $A_{LT}$ asymmetries were extracted from the measured $^{3}$He asymmetries and proton over $^{3}$He cross section ratios using the effective polarization approximation. These new data probe the transverse momentum dependent parton distribution function $g_{1T}^{q}$ and therefore provide access to quark spin-orbit correlations. Our results indicate a positive azimuthal asymmetry for $π^{-}$ production on $^{3}$He and the neutron, while our $π^{+}$ asymmetries are consistent with zero.

nucl-ex↗

arXiv2012

New measurements of high-momentum nucleons and short-range structures in nuclei

We present new measurements of electron scattering from high-momentum nucleons in nuclei. These data allow an improved determination of the strength of two-nucleon correlations for several nuclei, including light nuclei where clustering effects can, for the first time, be examined. The data also include the kinematic region where three-nucleon correlations are expected to dominate.

nucl-ex↗

arXiv2011

High Precision Measurement of the Proton Elastic Form Factor Ratio $μ_pG_E/G_M$ at low $Q^2$

We report a new, high-precision measurement of the proton elastic form factor ratio μ_p G_E/G_M for the four-momentum transfer squared Q^2 = 0.3-0.7 (GeV/c)^2. The measurement was performed at Jefferson Lab (JLab) in Hall A using recoil polarimetry. With a total uncertainty of approximately 1%, the new data clearly show that the deviation of the ratio μ_p G_E/G_M from unity observed in previous polarization measurements at high Q^2 continues down to the lowest Q^2 value of this measurement. The updated global fit that includes the new results yields an electric (magnetic) form factor roughly 2% smaller (1% larger) than the previous global fit in this Q^2 range. We obtain new extractions of the proton electric and magnetic radii, which are ^(1/2)=0.875+/-0.010 fm and ^(1/2)=0.867+/-0.020 fm. The charge radius is consistent with other recent extractions based on the electron-proton interaction, including the atomic hydrogen Lamb shift measurements, which suggests a missing correction in the comparison of measurements of the proton charge radius using electron probes and the recent extraction from the muonic hydrogen Lamb shift.

nucl-ex↗

arXiv2011

Low Q^2 measurements of the proton form factor ratio $mu_p G_E / G_M$

We present an updated extraction of the proton electromagnetic form factor ratio, mu_p G_E/G_M, at low Q^2. The form factors are sensitive to the spatial distribution of the proton, and precise measurements can be used to constrain models of the proton. An improved selection of the elastic events and reduced background contributions yielded a small systematic reduction in the ratio mu_p G_E/G_M compared to the original analysis.

nucl-ex↗