124991249
Particle astrophysics in antarctica
35843308
Spectropolarimetry of the massive post -Red Supergiants IRC +10420 and HD 179821
We present medium resolution spectropolarimetry and long term photo-polarimetry of two massive post-red supergiants, IRC +10420 and HD 179821. The data provide new information on their circumstellar material as well as their evolution. 
In IRC +10420, the polarization of the Ha line is different to that of the continuum, which indicates that the electron-scattering region is not spherically symmetric. The observed long term changes in the polarimetry can be associated with an axi-symmetric structure, along the short axis of the extended reflection nebulosity. Long term photometry reveals that the star increased in temperature until the mid-nineties, after which the photospheric flux in the optical levelled off. As the photometric changes are mostly probed in the red, they do not trace high stellar temperatures sensitively. And so, it is not obvious whether the star has halted its increase in temperature or not. For HD 179821 we find no polarization effects across any absorption or emission lines, but observe very large polarization changes of order 5% over 15 years. During the same period, the optical photometry displayed modest variability at the 0.2 magnitude level. This is unexpected, because large polarization changes are generally accompanied by 
strong photometric changes. Several explanations for this puzzling fact are discussed. Most of which, involving asymmetries in the circumstellar material, seem to fail as there is no evidence for the presence of hot, dusty material close to the star. A caveat is that the sparsely available near-infrared photometry could have missed periods of strong polarization activity. Alternatively, the variations can be explained by the presence of a non-radially pulsating photosphere. Changes in the photometry hint at an 
increase in temperature corresponding to a change through two spectral subclasses over the past ten years.
15505534
On the difference between Herbig Ae and Herbig Be stars
We present linear spectropolarimetric data for eight Herbig Be and four Herbig Ae stars at Hα ,H β and Hγ . Changes in the linear polarization are detected across all Balmer lines for a large fraction of the observed objects, confirming that the small-scale regions surrounding these objects are flattened (i.e. disc-like). Furthermore, all objects with detections show similar characteristics at the three spectral lines, despite differences in transition probability and optical depth going from Hα to Hγ . A large fraction of early Herbig Be stars (B0‐B3) observed show line-depolarization effects. However, the early Herbig Ae stars (A0‐A2), observed for comparison, show intrinsic line-polarization signatures. Our data suggest that the popular magnetic accretion scenario for T Tauri objects may be extended to Herbig Ae stars, but that it may not be extended to early Herbig Be stars, for which the available data are consistent with disc accretion.
73520646
PLASTEX: the palermo-leeds air shower tracking experiment
SummaryAn experiment is described in which air shower measurement are carried out by means of a «track detector» placed in a test location near the center of a conventional array telescope currently in use for gamma-ray astronomy. This array, consisting of scintillators (GREX, operated at Haverah Park (U.K.) by the Department of Physics of the University of Leeds), provides, in the usual way, for each shower it selects, its own estimates of shower direction and shower particle density at the test location. Estimates of the muon density at the test location are provided by a large muon detector in operation nearby. The scintillator array triggers this muon detector and it is able to provide flexibly tailored trigger signals for the track detector. This detector named PLASTEX (acronym for Palermo Leeds Air Shower Tracking Experiment), consisting of tracking chambers above and below a thin sheet of lead, designed to provide data on charged particles incident from the air, on the stopping, scattering and multiplication of these particles in the lead sheet and on charged particles created in the lead sheet by shower photons. From these data estimates are derived of the densities and directional properties of the electrons, photons and muons striking the track detector. These results are to be compared with those given by the conventional detectors and with theoretical predictions given by simulations that are being carried out. The objective is to develop and assess optimal procedures for employing clusters of PLASTEX-type detectors as telescopes for the observation of UHE cosmic rays, including cosmic gammarays, over a very wide energy range.RiassuntoIn questo articolo viene descritto un esperimento (PLASTEX) in cui venogo effettuate misure di sciami cosmici per mezzo di un rivelatore posto al centrol di un telescopio convenzionale per gamma-astronomia alle alte energie (GREX, Haverah Park, Leeds, Gran Bretagna). Il telescopio, costituito da unarray di scintillatori, fornisce, per ogni sciame rivelato, le stime della direzione di arrivo e della densità di particelle in corrispondenza alla posizione del rivelatore di PLAXTEX. La stima del contenuto muonico dello sciame in tale posizione è invece data da un rivelatore di muoni posto nelle vicinanze. L'array di scintillatori pilota tale rivelatore di muoni e fornisce gli opportuni segnali ditrigger al rivelatore di PLASTEX. Quest'ultimo consiste in due camere a tracciamento di muoni separate da un sottile strato di piombo, che possono fornire dati sulle particelle cariche incidenti, sull'arresto, la dispersione e la moltiplicazione di tali particelle nello strato di piombo, e sulle particelle cariche create nel piombo dai fotoni appartenenti allo sciame incidente. Da questi dati vengono derivate le stime delle densità e delle proprietà direzionali degli elettroni, dei fotoni e dei muoni che colpiscono il rivelatore che sono poi confrontate con quelle ottenute dagli scintillatori di GREX e con le predizioni teoriche ricavate da simulazioni attualmente in corso. L'obiettivo è di studiare la possibilità dell'impiego di unarray di rivelatori tipo PLASTEX come telescopi per l'osservazione di radiazione cosmica di energia molto alta.РезюмеОписывается эксперимент в котором измерения атмосферных ливней проводятся с помощью «трекового детектора», помещенного в близи центра обычной антенной решетки, используемой для целей гамма-астрономии. Эта антенная решетка, состоящая из сцинтилляторов, обеспечивает для каждого ливбя его селекцию, оценку направления лицня и определение плотности чстиш в ливне. Определение плотности мюонов в месте регистрации обеспечивается большим мюонным детектором. Система сцинтилляторов запускает этот мюонный детектор и обеспечивает триггерные сигналы для трекового детектора. Этот детектор, называемый PLATEX (Палермо-Лидс трековый эксперимент по детектироцанию атмосферных ливней), котортй состоит из трекоцых камер, расположенных выше и ниже тонкого листа свинца, предназначен для сбора данных о заряженных частицах, падающих из атмосферы, о торможении, рассеянии и мультипликации этих частицв листе свинца, и о заряженных частишах, образованных в листе свинца фотонами ливня. Из полученных выводятся плотности и определяются направления электронов, фотонов, мюонов, попадающих в трекоцый детектор. Эти результаты сравниваются с данными, полученными с помощью обычных детекторов, и с теоретическими предсказаниями, полученными с помощью моделироцания. Цель этих исследоцаний—развить и определить оптимальнню прошедуру для использования детекторов типа PLATEX как телескоппв для наблюдения космическиы лучей сцерхцысоких энергий, включая гамма-лучи в широой огласти энергий.
120390470
STAR CLUSTER: a tracking array for gamma-ray astronomy
SummaryA new type of extensive air shower array-telescope is being constructed, close to the GREX scintillator array at Haverah Park. The design of the new instrument is based on identification and measurement of individual shower particles by means of pattern recognition techniques applied to data from LST chambers above and below a thin sheet of high-Z material. Air showers will be detected in the range from 1014 eV to 1018 eV. The directions of the shower primaries will be reconstructed with an accuracy of a few tenths of a degree using triangulation between tracks of detected shower particles: >1 GeV electrons, photons and muons. Particle densities measured at the detector locations will be used to calculate shower sizes and core locations. Information about the height of production of the high-energy secondaries will be obtained for each shower. This information will be taken into account in calculating the primary energies. It will be used together with the observed muon content (ratio of muons to all particles), to draw conclusions about the nature of the primary particles.
178365536
Tracking Chamber Data from PLASTEX: Instrumental Performance for Single Particles
119418934
ANALYSIS OF TEST-BEAM DATA FROM A PROTOTYPE LHCB RICH DETECTOR
118055934
Summary of the CKM 2010 Working Group on Rare Decays
Rare decays were essential in the discovery of the CKM mechanism of flavour and CP violation and are highly sensitive probes of physics beyond the Standard Model. In this summary the current status and future prospects of experimental measurements and the Standard Model theory predictions of various rare B, D and K decay observables are discussed. The specific new physics sensitivities of each mode are also briefly reviewed.