Narrow Results

We present results from luminosity, energy and polarization studies at a future Linear Collider. We compare e⁺e^- and e^-e^- modes of operation and consider both NLC and TESLA beam parameter specifications at a center-of-mass energy of 500 GeV. Realistic colliding beam distributions are used, which include dynamic effects of the beam transport from the Damping Rings to the Interaction Point. Beam-beam deflections scans and their impact for beam-based feedbacks are considered. A transverse kink instability is studied, including its impact on determining the luminosity-weighted center-of-mass energy. Polarimetry in the extraction line from the IP is presented, including results on beam distributions at the Compton IP and at the Compton detector.

In this paper, we present a new design of the interferometer, intended for high-precision measurements of electric fields. We combined both arms of the interferometer in one segment of the fiber and the electric field sensor. The interferometer made using this scheme has a high resistance to mechanical and thermal fluctuations.

Radio source observations play important roles in polarimetric cosmological studies. On the one hand, they constitute the main foregrounds for cosmic microwave background (CMB) radiation on scales smaller than 30 arcmin up to 100 GHz, on the other they can be used as targets for validation of products of polarimetric experiments dedicated to cosmology. Furthermore, extragalactic high-redshift sources have been used for cosmic polarization rotation (CPR) investigation. In this paper, we will discuss the support to cosmological studies from ground-based polarimetric observations in the radio and millimetric wavelength bands. Most of the limits to accuracy improvements arise from systematic effects and low calibration quality. We will discuss some details of interferometric calibration procedures and show some of the perspectives that the Atacama large millimeter array (ALMA) could offer for CPR studies.

Polarimetry encompasses a collection of optical techniques broadly used in a variety of fields. Nowadays, such techniques have provided their suitability in the biomedical field through the study of the polarimetric response of biological samples (retardance, dichroism and depolarization) by measuring certain polarimetric observables. One of these features, depolarization, is mainly produced by scattering on samples, which is a predominant effect in turbid media as biological tissues. In turn, retardance and dichroic effects are produced by tissue anisotropies and can lead to depolarization too. Since depolarization is a predominant effect in tissue samples, we focus on studying different depolarization metrics for biomedical applications. We report the suitability of a set of depolarizing observables, the indices of polarimetric purity (IPPs), for biological tissue inspection. We review some results where we demonstrate that IPPs lead to better performance than the depolarization index, which is a well-established and commonly used depolarization observable in the literature. We also provide how IPPs are able to significantly enhance contrast between different tissue structures and even to reveal structures hidden by using standard intensity images. Finally, we also explore the classificatory potential of IPPs and other depolarizing observables for the discrimination of different tissues obtained from ex vivo chicken samples (muscle, tendon, myotendinous junction and bone), reaching accurate models for tissue classification.

Polarimetry is a powerful optical tool in the biomedical field, providing more comprehensive information on the sub-wavelength micro-physical structure of a sample than traditional light intensity measurement techniques. This review summarizes the concepts and techniques of polarization and its biomedical applications. Specifically, we first briefly describe the basic principles of polarized light and the Mueller matrix (MM) decomposition method, followed by some research progress of polarimetric measurement techniques in recent years. Finally, we introduce some studies on biological tissues and cells, and then illustrate the application value of polarization optical method.

Electrostatic accelerators have played a glorious role in physics, especially for low energy atomic and nuclear physics and electron microscopy. But circular accelerators have depended almost exclusively on the far greater bending force possible with static magnetic, rather than electric, fields. There is a potential exception to this magnetic bending monopoly for experimental high energy elementary particle physics — it is the possibility of measuring the electric dipole moments (EDMs) of charged elementary particles, such as proton, deuteron, or electron, using an electrostatic storage ring. Any such non-zero EDM would demonstrate violation of both parity (P) and time-reversal (T) invariance. One way of understanding the preponderance of matter over anti-matter in the present-day universe pre-supposes the existence of violations of P and T substantially greater than are allowed by the “standard model” of elementary particle physics. This provides the leading motivation for measuring EDMs. Currently, only upper limits are known for these EDMs. The very same smallness that makes it important to determine them makes their measurement difficult. Accepting as obvious the particle physics motivation, this paper concentrates on the accelerator physics of the (not very) high energy electrostatic accelerators needed for EDM measurements. Developments already completed are emphasized. Impressive advances have been made in the diagnostic tools, spin control and polarimetry that will make EDM measurement possible. Ring design for minimizing spin decoherence and limiting systematic EDM errors is presented. There have, however, been worrisome indications from low energy rings, concerning beam current limitations. A prototype ring design is proposed for investigating and addressing this concern.

We have developed a software-based polarization spectrometer, PolariS, to acquire full-Stokes spectra with a very high spectral resolution of 61 Hz. The primary aim of PolariS is to measure the magnetic fields in dense star-forming cores by detecting the Zeeman splitting of molecular emission lines. The spectrometer consists of a commercially available digital sampler and a Linux computer. The computer is equipped with a graphics processing unit (GPU) to process FFT and cross-correlation using the Compute Unified Device Architecture (CUDA) library developed by NVIDIA. Thanks to a high degree of precision in quantization of the analog-to-digital converter and arithmetic in the GPU, PolariS offers excellent performances in linearity, dynamic range, sensitivity, bandpass flatness and stability. The software has been released under the MIT License and is available to the public. In this paper, we report the design of PolariS and its performance verified through engineering tests and commissioning observations.

The Canarias InfraRed Camera Experiment (CIRCE) is a near-infrared (1–2.5$\mu$m) imager, polarimeter and low-resolution spectrograph operating as a visitor instrument for the Gran Telescopio Canarias (GTC) 10.4-m telescope. It was designed and built largely by graduate students and postdocs, with help from the University of Florida (UF) astronomy engineering group, and is funded by the UF and the US National Science Foundation. CIRCE is intended to help fill the gap in near-infrared capabilities prior to the arrival of Especrografo Multiobjecto Infra-Rojo (EMIR) to the GTC and will also provide the following scientific capabilities to compliment EMIR after its arrival: high-resolution imaging, narrowband imaging, high-time-resolution photometry, imaging polarimetry, and low resolution spectroscopy. In this paper, we review the design, fabrication, integration, lab testing, and on-sky performance results for CIRCE. These include a novel approach to the opto-mechanical design, fabrication, and alignment.

Electrostatic accelerators have played a glorious role in physics, especially for low energy atomic and nuclear physics and electron microscopy. But circular accelerators have depended almost exclusively on the far greater bending force possible with static magnetic, rather than electric, fields. There is a potential exception to this magnetic bending monopoly for experimental high energy elementary particle physics — it is the possibility of measuring the electric dipole moments (EDMs) of charged elementary particles, such as proton, deuteron, or electron, using an electrostatic storage ring. Any such non-zero EDM would demonstrate violation of both parity (P) and time-reversal (T) invariance. One way of understanding the preponderance of matter over anti-matter in the present-day universe pre-supposes the existence of violations of P and T substantially greater than are allowed by the “standard model” of elementary particle physics. This provides the leading motivation for measuring EDMs. Currently, only upper limits are known for these EDMs. The very same smallness that makes it important to determine them makes their measurement difficult. Accepting as obvious the particle physics motivation, this paper concentrates on the accelerator physics of the (not very) high energy electrostatic accelerators needed for EDM measurements. Developments already completed are emphasized. Impressive advances have been made in the diagnostic tools, spin control and polarimetry that will make EDM measurement possible. Ring design for minimizing spin decoherence and limiting systematic EDM errors is presented. There have, however, been worrisome indications from low energy rings, concerning beam current limitations. A prototype ring design is proposed for investigating and addressing this concern.

Gamma-ray bursts (GRBs) are bright extragalactic flashes of gamma-ray radiation and briefly the most energetic explosions in the Universe. Their catastrophic origin —the merger of compact objects or the collapse of massive stars— drives the formation of a newborn compact remnant (black hole or magnetar) that powers two highly relativistic jets. As these jets continue to travel outwards, they collide with the external material surrounding the dying star, producing a long-lasting afterglow that can be seen across the entire electromagnetic spectrum, from the most energetic gamma-ray emission to radio wavelengths. But how can such material be accelerated and focused into narrow beams? The internal shock model proposes that repeated collisions between material blasted out during the explosion can produce the gamma-ray flash. The competing magnetic model credits primordial large-scale ordered magnetic fields that collimate and accelerate the relativistic outflows. To distinguish between these models and ultimately determine the power source for these energetic explosions, our team studies the polarization of the light during the first minutes after the explosion (using novel instruments on fully autonomous telescopes around the globe) to directly probe the magnetic field properties in these extragalactic jets. This technology allowed the detection of highly polarized optical light in GRB 120308A and confirmed the presence of mildly magnetized jets with large-scale primordial magnetic fields in a reduced sample of GRBs (e.g. GRB 090102, GRB 110205A, GRB 101112A, GRB 160625B). Here we discuss the observations of the most energetic and first GRB detected at very high TeV energies, GRB 190114C, which opens a new frontier in GRB magnetic field studies suggesting that some jets can be launched highly magnetized and that the collapse and destruction of these magnetic fields at very early times may have powered the explosion itself. Additionally, our most recent polarimetric observations of the jet of GRB 141220A indicate that, when the jetted ejected material is decelerated by the surrounding environment, the magnetic field amplification mechanisms at the front shock —needed to generate the observed synchrotron emission— produce small magnetic domains. These measurements validate theoretical expectations and contrast with previous observations that suggest large magnetic domains in collisionless shocks (i.e. GRB 091208B).

The measurement of the polarization of the high-energy photons from cosmic sources has now become a key observational parameter for understanding the emission mechanisms and the geometry of the active regions involved. Therefore, a mandatory requirement for new instrumentation in this energy regime will provide high sensitivity for polarimetric measurements associated with spectroscopy and imaging.

In this perspective, the Advanced Surveyor of Transient Events and Nuclear Astrophysics (ASTENA) mission, which includes two main instruments: the Wide field monitor (WFM-IS), with a large effective area and a wide energy passband (2 keV – 20 MeV); and the Narrow Field Telescope (NFT), with a broad energy passband (50–600 keV) with focusing capabilities based on the use of an advanced Laue lens; will both provide high sensitivity for polarimetric measurements. Furthermore, both instruments will include spectometers with a good 3D spatial resolution allowing to perform 3D Compton polarimetry, increasing the possibilities to optimize the event selection. Herein, we report on the results of a Monte Carlo study devoted to optimize the configuration of both instruments, in particular, the modulation factor (Q), the events detection efficiency (Eff) and the Minimum Detectable Polarization (MDP).

PoGOLite is a balloon-borne experiment that will measure the polarization of soft gamma-rays between 25 keV and 80 keV through detection of coincident Compton scattering and absorption in a close-packed array of 217 well-type phoswich detector cells. The potential observation targets include pulsars, accreting compact objects and astrophysical jets. The polarization properties of such radiation can reveal important new information on the geometry, magnetic fields and emission mechanisms of these sources.

The polarized beam for RHIC is produced in the optically-pumped polarized H^- ion source and then accelerated in LINAC to 200 MeV for strip-injection to booster and further accelerated 24.3 GeV in AGS for injection in RHIC. In 2009 run polarized protons was successfully accelerated to 250 GeV beam energy. The beam polarization of about 60 % at 100 GeV beam energy and 36-42 % at 250 GeV energy was measured with the H-jet and p-carbon CNI polarimeters. The gluon contribution to the proton spin was studied in collisions of longitudinally polarized proton beams at 100×100 GeV. At 250×250 GeV an intermediate boson W production with the longitudinally polarized beams was studied for the first time.

Longitudinal polarisation of the lepton beam is a key ingredient in the success of the world's unique e^±p ring collider HERA. This article aims at providing a brief introduction to the physics motivation for deep-inelastic scattering of polarised electrons or positrons off protons, the basic mechanisms to establish lepton polarisation in the high-energy storage ring and to describe briefly the three different polarimeters, which measured both the transverse and the longitudinal polarisation.

This article provides an overview of the conceptual design of the ILC polarimeters, the analysing power calibration and data-driven polarisation measurement. A Cherenkov detector prototype for Compton polarimetry is presented.

Low energy (E_k ~ 100 keV) Mott scattering polarimetry is a widely established technique to measure the polarization of an electron beam. We analyze the feasibility of Mott scattering at energies up to 20 MeV. For further studies of the electron spin dynamics in the scattering process a correlation between the linear polarization of bremsstrahlung radiation and the electron beam polarization has been measured for the first time using a planar HPGe Compton polarimeter at the 100 keV source of polarized electrons at TU Darmstadt.

A case for and a characterization of the use of a thin detector such as a TPC as an active target for an excellent angular resolution γ-ray telescope for cosmic sources in the [MeV - GeV] energy range, with sensitivity to the fraction of linear polarization of the radiation.