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L. Nguyen

Publications and source records attributed to L. Nguyen.

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Picosecond Timing-Planes for Future Collider Detectors

We report experimental test-beam results on dielectric-loaded waveguide detectors that utilize microwave Cherenkov signals to time and characterize high energy particle showers. These results are used to validate models and produce high-fidelity simulations of timing plane systems which yield picosecond time tags and millimeter spatial coordinates for the shower centroid. These timing planes, based on the Askaryan effect in solid dielectrics, are most effective at the high center-of-momentum energies planned for the Future Circular Collider (FCC-hh), and are of particular interest in the forward region due to their high radiation immunity. We use our beam test results and GEANT4 simulations to validate a hybrid microwave detector model, which is used to simulate a reference timing plane design for the FCC forward calorimeters. Our results indicate that 0.5-3 ps particle timing is possible for a wide range of collision products in the reference FCC hadron collider detector, even with current technology.

physics.ins-det

BES3 time of flight monitoring system

A Time of Flight monitoring system has been developed for BES3. The light source is a 442-443 nm laser diode, which is stable and provides a pulse width as narrow as 50 ps and a peak power as large as 2.6 W. Two optical-fiber bundles with a total of 512 optical fibers, including spares, are used to distribute the light pulses to the Time of Flight counters. The design, operation, and performance of the system are described.

physics.ins-det

Spectroscopic evidence for polarons in partially occupied spin-orbit states of YBa2Cu3O7

The spin-orbit split white line, synchrotron X-ray spectra at the respective Cu and Ba L2,3 and Ba M4,5 edges in YBa2Cu3O7 crystal, powders, films and derivatives are compared to those for standard BaBr2 and CuO powders. The white line absorption integrated intensity, I ratios: r3,2 = I(L3)/I(L2) and r5,4 = I(M5)/I(M4) for BaBr2 are equal to the ratio of core states degeneracy, but r3,2(Ba in YBCO powder) < 2 < r3,2(Cu in CuO and YBCO film) and r5,4(Ba in YBCO film) < 1.5 (Table I) indicate an apparent overpopulation of the Cu:3d3/2 final states relative to the 3d5/2, and the Ba:5d5/2 over the 5d3/2, and the 4f7/2 over the 4f5/2 at room temperature. The difference spectrum DEL=A(YBCO)-A(CuO) with a leading sharp peak, (HWHH of 0.2 eV) at E0+0.5, and the temperature changes in the atomic X-ray absorption fine structure A-XAFS observed at 0.08 to 0.07 nm near the heaviest atom, Ba suggest that charge polarization contributes to the final state band occupancy in YBCO.

cond-mat.supr-con