L. Ludhova

Proton Structure from the Measurement of 2S-2P Transition Frequencies of Muonic Hydrogen

Proton Still Too Small Despite a protons tiny size, it is possible to measure its radius based on its charge or magnetization distributions. Traditional measurements of proton radius were based on the scattering between protons and electrons. Recently, a precision measurement of a line in the spectrum of muonium—an atom consisting of a proton and a muon, instead of an electron—revealed a radius inconsistent with that deduced from scattering studies. Antognini et al. (p. 417; see the Perspective by Margolis) examined a different spectral line of muonium, with results less dependent on theoretical analyses, yet still inconsistent with the scattering result; in fact, the discrepancy increased. A precision spectroscopic measurement of the proton radius indicates a growing discrepancy with respect to scattering results. [Also see Perspective by Margolis] Accurate knowledge of the charge and Zemach radii of the proton is essential, not only for understanding its structure but also as input for tests of bound-state quantum electrodynamics and its predictions for the energy levels of hydrogen. These radii may be extracted from the laser spectroscopy of muonic hydrogen (μp, that is, a proton orbited by a muon). We measured the 2S1/2F=0-2P3/2F=1 transition frequency in μp to be 54611.16(1.05) gigahertz (numbers in parentheses indicate one standard deviation of uncertainty) and reevaluated the 2S1/2F=1-2P3/2F=2 transition frequency, yielding 49881.35(65) gigahertz. From the measurements, we determined the Zemach radius, rZ = 1.082(37) femtometers, and the magnetic radius, rM = 0.87(6) femtometer, of the proton. We also extracted the charge radius, rE = 0.84087(39) femtometer, with an order of magnitude more precision than the 2010-CODATA value and at 7σ variance with respect to it, thus reinforcing the proton radius puzzle.

Thin-Disk Yb:YAG Oscillator-Amplifier Laser, ASE, and Effective Yb:YAG Lifetime

We report on a thin-disk Yb:YAG laser made from a Q-switched oscillator and a multipass amplifier delivering pulses of 48 mJ at 1030 nm. The peculiar requirements for this laser are the short delay time (< 500 ns) between electronic trigger and optical output pulse and the time randomness with which these triggers occur (with trigger to next trigger delay ges 1.5 ms). Details concerning the oscillator dynamics (-switching cycle, intensity stabilization), and the peculiar amplifier layout are given. Simulations of the beam propagation in the amplifier based on the Collins integral and the measured aspherical components of the disk reproduce well the measured beam intensity profiles (with higher order intensity moments) and gains. Measurements of the thermal lens and ASE effects of the disk are also presented. A novel method to deduce the effective Yb:YAG upper state lifetime (under real laser operation and including ASE effects) is presented. That knowledge is necessary to determine gain and stored energy in the active medium and to understand the limiting factors for energy scaling of thin-disk lasers.

Laser spectroscopy of muonic deuterium

The deuteron is too small, too The radius of the proton has remained a point of debate ever since the spectroscopy of muonic hydrogen indicated a large discrepancy from the previously accepted value. Pohl et al. add an important clue for solving this so-called proton radius puzzle. They determined the charge radius of the deuteron, a nucleus consisting of a proton and a neutron, from the transition frequencies in muonic deuterium. Mirroring the proton radius puzzle, the radius of the deuteron was several standard deviations smaller than the value inferred from previous spectroscopic measurements of electronic deuterium. This independent discrepancy points to experimental or theoretical error or even to physics beyond the standard model. Science, this issue p. 669 The charge radius of the deuteron is several standard deviations smaller than the previously accepted value. The deuteron is the simplest compound nucleus, composed of one proton and one neutron. Deuteron properties such as the root-mean-square charge radius rd and the polarizability serve as important benchmarks for understanding the nuclear forces and structure. Muonic deuterium μd is the exotic atom formed by a deuteron and a negative muon μ–. We measured three 2S-2P transitions in μd and obtain rd = 2.12562(78) fm, which is 2.7 times more accurate but 7.5σ smaller than the CODATA-2010 value rd = 2.1424(21) fm. The μd value is also 3.5σ smaller than the rd value from electronic deuterium spectroscopy. The smaller rd, when combined with the electronic isotope shift, yields a “small” proton radius rp, similar to the one from muonic hydrogen, amplifying the proton radius puzzle.

Behaviour of large-area avalanche photodiodes under intense magnetic fields for VUV- visible- and X-ray photon detection

The behaviour of large-area avalanche photodiodes for X-rays, visible and vacuum-ultra-violet (VUV) light detection in magnetic fields up to 5 T is described. For X-rays and visible light detection, the photodiode pulse amplitude and energy resolution were unaffected from 0 to 5 T, demonstrating the insensitivity of this type of detector to strong magnetic fields. For VUV light detection, however, the photodiode relative pulse amplitude decreases with increasing magnetic field intensity reaching a reduction of about 24% at 5 T, and the energy resolution degrades noticeably with increasing magnetic field. r 2002 Elsevier Science B.V. All rights reserved. PACS: 07.85.F; 29.40.M; 85.60.D

Characterization of large area avalanche photodiodes in X-ray and VUV-light detection

The present manuscript reviews our RD this may be compromised by the non-linearity between gains measured for X-rays and VUV-light. The gain was found to be lower for X-rays than for VUV light, especially at higher bias voltages. For 5.9 keV X-rays, gain variations of 10% and 6% were measured relative to VUV light produced in argon ( ~ 128 nm) and xenon ( ~ 172 nm) for gains of about 200. The effect of temperature on the LAAPD performance was investigated for X-ray and VUV-light detection. Gain variations of more than -4% per oC were measured for 5.9 keV X-rays for gains above 200, while for VUV light variations are larger than -5% per oC. The energy resolution was found to improve with decreasing temperature, what is mainly attributed to dark current. The excess noise factor, another contribution to the energy resolution, was experimentally determined and found to be independent of temperature, increasing linearly with gain, from 1.8 to 2.3 for a 50-300 gain range. The LAAPD response under intense magnetic fields up to 5 Tesla was investigated. While for X-ray detection the APD response practically does not vary with the magnetic field, for 172 nm VUV light a significant amplitude reduction of more than 20% was observed.

LAAPD low temperature performance in X-ray and visible-light detection

The performance of a large area avalanche photodiode (LAAPD) has been investigated for X-ray and visible-light detection as a function of temperature. Energy resolution improves significantly with decreasing temperature down to 0/spl deg/C and, below that value, at a much slower rate, achieving 9.6% for 5.9 keV X-rays at 0/spl deg/C and for a gain of 60. The gain drift with temperature increases with the reverse bias voltage and is almost constant for temperatures above -15/spl deg/C, reaching rates higher than -5% per degrees Celsius, for a bias voltage of 1770 V. Similar results were obtained for X-ray and visible-light detection. LAAPD nonlinearity between X-ray and light gains is less than 2%, even for gains around 300, and decreases with temperature, being less than 0.5% at 0/spl deg/C, for gains up to 200. For X-rays, the minimum detectable energy is about 0.7 keV at operation temperatures around 16/spl deg/C, for gains above 100, decreasing to about 0.3 keV at temperatures less than 0/spl deg/C, for gains above 200.

A new method to obtain a precise value of the mass of the charged kaon

Abstract The results of a feasibility study performed by measuring, with a test setup at the collider DAΦNE of Frascati, two previously unobserved transitions of kaonic nitrogen, demonstrated the possibility to make a precision measurement of the mass of the charged kaon.

Status of the muonic hydrogen Lamb-shift experiment

The Lamb-shift experiment in muonic hydrogen (μ– p) aims to measure the energy difference between the atomic levels to a precision of 30u2002ppm. This would allow the r.m.s. proton charge radius rp to be deduced to a precision of 10–3 and open a way to check bound-state quantum electrodynamics (QED) to a level of 10–7. The poor knowledge of the proton charge radius restricts tests of bound-state QED to the precision level of about 6u2002×u200210–6, although the experimental data themselves (Lamb-shift in hydrogen) have reached a precision of u2002×u200210–6. Values for rp not depending on bound-state QED results from electron scattering experiments have a surprisingly large uncertainty of 2%. In our Lamb-shift experiment, low-energy negative muons are stopped in low-density hydrogen gas, where, following the μ– atomic capture and cascade, 1% of the muonic hydrogen atoms form the metastable 2S state with a lifetime of about 1 μs. A laser pulse at λu2002≈u20026u2002μm is used to drive the 2S → 2P transition. Following the laser excitation...

Muonic hydrogen cascade time and lifetime of the short-lived 2S state

Metastable

Large area APDs for low energy X-ray detection in intense magnetic fields

{2S}