1,155 research outputs found
A novel dual-mode tracking device for online dose monitoring in hadron therapy
No full textHadron therapy is a technique for cancer treatment that exploits ion beams (mostly protons and carbons). Due to the shape of the hadron energy deposition pattern, dose releases are more localized with respect to radiotherapy. Hadron therapy is thus particularly suitable to treat tumors close to critical organs. A critical issue is the monitoring accuracy of the dose released by the beam to the patient. We present the design of a dual-tracking device capable of on-line dose monitoring through the detection of prompt photons and charged particles produced by the interactions of the beam in the patient tissues whose emission shapes are correlated to spatial dose release and to the Bragg peak. The dosimeter, whose design has been optimized using Monte Carlo simulations, is composed of a tracker made of six scintillating fiber stations followed by a layer of plastic scintillator (electron shield) and a lyso pixellated crystal to detect photons. A first tracker layer has been assembled and is under test. A complete simulation and reconstruction software has been developed to estimate the achievable spatial resolution. Charged particles are reconstructed using the fiber planes and those identified as protons are back-traced to determine the point of origin. Prompt photons are reconstructed exploiting their Compton interactions by combining the spatial and energy measurements from the tracker for the electron and from the lyso for the photon. For a real hadrotherapeutic treatment the achievable resolution is of the order of ten (few) millimeters using the neutral (charged) component
Status and prospects of charged lepton flavor violation searches with the MEG-II experiment
No full textThe MEG experiment took data at the Paul Scherrer Institut (PSI) in the years 2009-2013 and published the most stringent limit on the charged lepton flavor violating decay μ → eγ: BR(μ → eγ) < 4.2 ×10−13 @90% C.L. The MEG detector is currently being upgraded in order to reach a sensitivity of ∼ 4 × 10−14, which corresponds to an improvement of one order of magnitude. The basic idea of MEG-II is to achieve the highest possible sensitivity by making the maximum use (7 × 107 muons/s) of the available muon intensity at PSI with an improved detector, keeping the background at a manageable level. The status of the MEG-II detector and the current schedule will be presented. MEG-II, together with the next generation charged lepton flavor violation experiments Mu3e (μ+ → e+e−e+) at PSI and Mu2e and COMET (μ → e conversion) at Fermilab and J-PARC respectively, will reach very high sensitivities in the next years. Accelerator upgrades are expected that will make muon beams with intensities of the order of 1010 muons/s feasible. At this extremely high beam rates, new detector concepts should be adopted in order to overcome the accidental background. Some future directions will be discussed
Future μ → eγ experiments
No full textExperiments with muons are a unique window to investigate the Standard Model of particle physics and to look for New Physics effects with high sensitivity. The search for the lepton flavor violating μ+ → e+γ decay will reach a sensitivity of few 10-14 within the next three years thanks to the MEG II experiment, presently taking data at the Paul Scherrer Institut, with a beam intensity of 4 × 107 muons/s. On the other hand, there is a world-wide effort to increase the muon beams intensity at present facilities by a factor 100. In order to exploit such intense muon beams a new generation of experiments has to be designed, since the present experimental concept is not adequate to deal with the expected increase in rate, radiation and background. An international study group has been recently set, the Study Group for Future μ → eγ search experiments, to organize this effort. This paper reviews the present main experimental directions identified, the results of simulations and R&D studies made so far
Evidence for a bone marrow B cell transcribing malignant plasma cell VDJ joined to C mu sequence in immunoglobulin (IgG)- and IgA-secreting multiple myelomas
No full textMultiple myeloma is a B cell malignancy characterized by the expansion of plasma cells producing monoclonal immunoglobulins (Ig). It has been regarded as a tumor arising at the B, pre-B lymphocyte, or even stem cell level. Precursor cells are presumed to proliferate and differentiate giving rise to the plasma cell clonal expansion. Antigenic features and specific Ig gene rearrangement shared by B lymphocytes and myeloma cells have supported this hypothesis. However, the existence of such a precursor is based upon indirect evidence and is still an open question. During differentiation, B cells rearrange variable (V) regions of Ig heavy chain genes, providing a specific marker of clonality. Using an anchor polymerase chain reaction assay, these rearranged regions from five patients with multiple myeloma were cloned and sequenced. The switch of the Ig constant (C) region was used to define the B cell differentiation stage: V regions are linked to C mu genes in pre-B and B lymphocytes (pre-switch B cells), but to C gamma or C alpha in post-switch B lymphocytes and plasma cells (post-switch B cells). Analysis of bone marrow cells at diagnosis revealed the presence of pre-switch B cells bearing plasma cell V regions still joined to the C mu gene. These cells were not identified in peripheral blood, where tumor post-switch B cells were detected. These pre-switch B cells may be regarded as potential myeloma cell precursors
The design of the MEG II experiment: MEG II Collaboration
No full textThe MEG experiment, designed to search for the μ+→ e+γ decay, completed data-taking in 2013 reaching a sensitivity level of 5.3 × 10- 13for the branching ratio. In order to increase the sensitivity reach of the experiment by an order of magnitude to the level of 6 × 10- 14, a total upgrade, involving substantial changes to the experiment, has been undertaken, known as MEG II. We present both the motivation for the upgrade and a detailed overview of the design of the experiment and of the expected detector performance
Combined readout of a triple-GEM detector
No full textOptical readout of GEM based devices by means of high granularity and low noise CMOS sensors allows to obtain very interesting tracking performance. Space resolution of the order of tens of μm were measured on the GEM plane along with an energy resolution of 20%÷30%. The main limitation of CMOS sensors is represented by their poor information about time structure of the event. In this paper, the use of a concurrent light readout by means of a suitable photomultiplier and the acquisition of the electric signal induced on the GEM electrode are exploited to provide the necessary timing informations. The analysis of the PMT waveform allows a 3D reconstruction of each single clusters with a resolution on z of 100 μm. Moreover, from the PMT signals it is possible to obtain a fast reconstruction of the energy released within the detector with a resolution of the order of 25% even in the tens of keV range useful, for example, for triggering purpose
The quest for mu to e gamma and its experimental limiting factors at future high intensity muon beams
No full textThe search for the lepton flavor violating decay +→+ will reach an unprecedented level of sensitivity within the next five years thanks to the MEG-II experiment. This experiment will take data at the Paul Scherrer Institut where continuous muon beams are delivered at a rate of about 108 muons per second. On the same time scale, accelerator upgrades are expected in various facilities, making it feasible to have continuous beams with an intensity of 109 or even 1010 muons per second. We investigate the experimental limiting factors that will define the ultimate performances, and hence the sensitivity, in the search for +→+ with a continuous beam at these extremely high rates. We then consider some conceptual detector designs and evaluate the corresponding sensitivity as a function of the beam intensity
High-dose sequential chemoradiotherapy in multiple myeloma: residual tumor cells are detectable in bone marrow and peripheral blood cell harvests and after autografting
No full textBased on preliminary encouraging results in terms of response rate and survival, high-dose chemoradiotherapy has gained considerable interest in the treatment of patients with multiple myeloma (MM). We have evaluated the presence of residual myeloma cells in 15 of 18 patients enrolled in a high-dose sequential (HDS) chemoradiotherapy program followed by autografting. Our analysis has been performed both on bone marrow (BM) and peripheral blood (PB) cell harvests and after autografting. As it has been recently shown that B cells clonally related to malignant plasma cells are detectable in MM patients, we have developed a polymerase chain reaction (PCR)-based strategy to detect both residual B cells and plasma cells using clone-specific sequences derived from the rearrangement of Ig heavy chain (IgH) genes. The complementarity-determining regions (CDR) of IgH genes have been used to generate tumor-specific primers and probes. The constant (C) region usage defined the differentiation stage of residual myeloma cells. We report that plasma cells were detectable in PB and BM cell harvests and after transplantation in all assessable patients, irrespective of disease status. B cells were detectable in a consistent proportion of BM and PB samples at diagnosis, but only in one case at the time of PB and BM cell harvests. These cells became sometimes detectable after transplantation. Whether residual myeloma cells are clonogenic and contribute to relapse is currently unknown, and further investigations are required
Gas distribution and monitoring for the drift chamber of the MEG II experiment
No full textThe reconstruction of the positron trajectory in the MEG II experiment searching for the μ+e+γ decay uses a cylindrical drift chamber operated with a helium-isobutane gas mixture. A stable performance of the detector in terms of its electron drift properties, avalanche multiplication, and with a gas mixture of controlled composition and purity has to be provided and continuously monitored. In this paper we describe the strategies adopted to meet the requirements imposed by the target sensitivity of MEG II, including the construction and commissioning of a small chamber for an online monitoring of the gas quality
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