arXiv subjects

Paola Ferrario

Publications and source records attributed to Paola Ferrario.

14 recordsLinked to original sources

arXiv2022

Status and perspectives of the PETALO project

PETALO (Positron Emission Tof Apparatus with Liquid xenOn) is a novel concept for positron emission tomography scanners, which uses liquid xenon as a scintillation medium and silicon photomultipliers as a readout. The large scintillation yield and the fast scintillation time of liquid xenon, as well as its scalability, makes it an excellent candidate for PET scanners with Time-of-Flight measurements, especially for total-body machines. A first prototype of PETALO is fully operating, devoted to demonstrate the potential of the concept, measuring the energy and time resolution and to test technical solutions for a complete ring. The prototype consists of an aluminum box filled with liquid xenon, with two arrays of SiPMs on opposite sides facing the xenon. A $β$+ emitter source generating 511-keV pairs of gammas is placed in a central port and the SiPMs record the scintillation light produced by the gamma interactions, allowing for the reconstruction of the position, the energy and the time of the interactions.

physics.ins-det↗

arXiv2019

PETALO: Time-of-Flight PET with liquid xenon

The fast scintillation decay time and the high scintillation yield of liquid xenon makes it an appropriate material for nuclear medicine. Moreover, being a continuous medium with a uniform response, liquid xenon allows one to avoid most of the geometrical distortions of conventional detectors based on scintillating crystals. In this paper, we describe how these properties have motivated the development of a novel concept for positron emission tomography scanners with Time-Of-Flight measurement, which uses liquid xenon as a scintillating material and silicon photomultipliers as sensors. Monte Carlo studies have indicated that this technology would provide a very good intrinsic time resolution, of around 70 ps. Moreover, being liquid xenon transparent to UV and blue wavelengths, both scintillation and Cherenkov light can be exploited. While the former can be used for energy measurements, the latter is a prompt signal (of a few picoseconds), which provides a very precise time measurement. Monte Carlo simulations point to a time resolution of 30-50 ps obtained using Cherenkov light. A first prototype is being built to demonstrate the high energy, spatial and time resolution of this concept, using a ring of around 30 cm of internal diameter and a depth of 3 cm instrumented with VUV--sensitive silicon photomultipliers.

physics.ins-det↗

arXiv2017

Liquid xenon in nuclear medicine: state-of-the-art and the PETALO approach

Liquid xenon has several attractive features, which make it suitable for applications to nuclear medicine, such as high scintillation yield and fast scintillation decay time, better than currently used crystals. Since the '90s, several attempts has been made to build Positron Emission Tomography scanners based on liquid xenon, which can be divided into two different approaches: on one hand, the detection of the ionization charge in TPCs, and, on the other one, the detection of scintillation light with photomultipliers. PETALO (Positron Emission Tof Apparatus with Liquid xenOn) is a novel concept, which combines liquid xenon scintillating cells and silicon photomultipliers for the readout. A first Monte Carlo investigation has pointed out that this technology would provide an excellent intrinsic time resolution, which makes it possible to measure the Time-Of-Flight with high efficiency. Also, the transparency of liquid xenon to UV and blue wavelengths opens the possibility of exploiting both scintillation and Cherenkov light for a high-sensitivity TOF-PET.

physics.ins-det↗

arXiv2017

The NEXT double beta decay experiment

NEXT (Neutrino Experiment with a Xenon TPC) aims to observe the neutrinoless double beta decay of \ensuremath{{}^{136}\rm Xe} in a high-pressure gas xenon Time Projection Chamber using electroluminescence to amplify the signal from ionization. The two main advantages of this technology are a high energy resolution and the possibility of reconstructing electron tracks. NEXT-100 is an electroluminescent, asymmetric TPC which will host 100 kg of the \ensuremath{{}^{136}\rm Xe} isotope at 15 bar of pressure. On one side, a sparse array of photomultipliers records both the primary scintillation signal, which gives the starting time of the event, and electroluminescence, which gives a precise measurement of the total deposited energy. On the other side, a dense grid of silicon photomultipliers provides the reconstruction of the electron tracks. Being able to reconstruct the position of a track is doubly useful: on the one hand, it allows the correction of the energy of the event, which varies according to position, and on the other hand it provides an extra handle for background rejection, since a two-electron track shows higher energy density at both ends, while a single-electron track only at one end. After a prototyping period (2009-2014) NEXT has completed the construction and started the operation of its first phase (NEW) in the Laboratorio Subterráneo de Canfranc, in the Spanish Pyrenees, with the objectives of measuring the NEXT background model and the two-neutrino mode of the double beta decay.

physics.ins-det↗

arXiv2017

Monte Carlo study of the Coincidence Resolving Time of a liquid xenon PET scanner, using Cherenkov radiation

In this paper we use detailed Monte Carlo simulations to demonstrate that liquid xenon (LXe) can be used to build a Cherenkov-based TOF-PET, with an intrinsic coincidence resolving time (CRT) in the vicinity of 10 ps. This extraordinary performance is due to three facts: a) the abundant emission of Cherenkov photons by liquid xenon; b) the fact that LXe is transparent to Cherenkov light; and c) the fact that the fastest photons in LXe have wavelengths higher than 300 nm, therefore making it possible to separate the detection of scintillation and Cherenkov light. The CRT in a Cherenkov LXe TOF-PET detector is, therefore, dominated by the resolution (time jitter) introduced by the photosensors and the electronics. However, we show that for sufficiently fast photosensors (e.g, an overall 40 ps jitter, which can be achieved by current micro-channel plate photomultipliers) the overall CRT varies between 30 and 55 ps, depending of the detection efficiency. This is still one order of magnitude better than commercial CRT devices and improves by a factor 3 the best CRT obtained with small laboratory prototypes.

physics.ins-det↗

arXiv2016

Topological signature in the NEXT high pressure xenon TPC

The NEXT experiment aims to observe the neutrinoless double beta decay of Xe-136 in a high-pressure xenon gas TPC using electroluminescence to amplify the signal from ionization. One of the main advantages of this technology is the possibility to use the topology of events with energies close to Qbb as an extra tool to reject background. In these proceedings we show with data from prototypes that an extra background rejection factor of 24.3 +- 1.4 (stat.)% can be achieved, while maintaining an efficiency of 66.7 +- 1.% for signal events. The performance expected in NEW, the next stage of the experiment, is to improve to 12.9% +- 0.6% background acceptance for 66.9% +- 0.6% signal efficiency.

physics.ins-det↗

arXiv2012

NEXT-DEMO: a prototype for the NEXT experiment

NEXT is a high-pressure (10-15 bar) xenon Time Projection Chamber dedicated to neutrinoless double beta decay searches. NEXT-DEMO is a large prototype of the NEXT experiment, constructed to demonstrate the feasibility of the NEXT detector concept, in particular the capability of the TPC to achieve an optimal energy resolution at the Xe Qbb energy (2.458 MeV). It has been operating at IFIC, in Valencia, for one year and a half and a number of results has been achieved. Recently, the reflector panels of the prototype have been coated with a wavelength shifter (TPB), in order to improve light collection. We have obtained an energy resolution of 2.3% FWHM at 511 keV, using Na-22 radioactive sources, corresponding to 1% FWHM once extrapolated to Qbb.

physics.ins-det↗

arXiv2010

Charge asymmetry: a theory appraisal

The most recent measurements at Tevatron of the charge asymmetry in top-antitop quark pair production reduce the discrepancy with the Standard Model from 2sigma to 1.7sigma, and open a little window, at 95% C.L., for negative contributions to the charge asymmetry beyond the SM. We update our analysis for colour octet gauge bosons or axigluons in flavour universal and flavour non universal scenarios. We review other possible models and make an educated guess on their parameter space allowed by the new measurements. Finally, we comment on the prospects to measure the charge asymmetry at the LHC.

hep-ph↗

arXiv2010

Charge asymmetry of top quarks

The LHC is a promising machine to discover new physics in the top sector. There are several models that predict the existence of heavy colored resonances decaying to top quarks in the TeV energy range. The production of such resonances might generate a sizable charge asymmetry of top versus antitop quarks. At the Tevatron, a 2 sigma discrepancy with the SM prediction for the forward--backward asymmetry has been found, boosting a renewed interest for this kind of models. We consider a toy model with general flavour dependent couplings of the resonance to quarks, of both vector and axial-vector kind and investigate the possible constraints on the coupling space from the measurement of the asymmetry and the invariant mass distribution at the Tevatron. Then, we define a central asymmetry in a specific kinematic region and investigate its signature at the LHC as well as its statistical significance, for exclusive processes.

hep-ph↗

arXiv2009

Heavy colored resonances in top-antitop + jet at the LHC

The LHC is the perfect environment for the study of new physics in the top quark sector. We study the possibility of detecting signals of heavy color-octet vector resonances, through the charge asymmetry, in top-antitop+jet events. Besides contributions with the top-antitop pair in a color-singlet state, the asymmetry gets also contributions which are proportional to the color factor f_{abc}^2. This process is particularly interesting for extra-dimensional models, where the inclusive charge asymmetry generated by Kaluza-Klein excitations of the gluon vanishes at the tree level. We find that the statistical significance for the measurement of such an asymmetry is sizable for different values of the coupling constants and already at low energies.

hep-ph↗

arXiv2009

Constraining heavy colored resonances from top-antitop quark events

Recent measurements of the top quark charge asymmetry at Tevatron disfavor the existence of flavor universal axigluons and colorons at 2 sigmas. In this letter we explore the possibility to reconcile the data with these models and use the charge asymmetry and the invariant mass distribution of top-antitop quark pair events to constrain the mass and couplings of massive color-octet gauge bosons decaying to top quarks.

hep-ph↗

arXiv2009

Charge asymmetries of top quarks: a window to new physics at hadron colliders

With the next start of LHC, a huge production of top quarks is expected. There are several models that predict the existence of heavy colored resonances decaying to top quarks in the TeV energy range. A peak in the differential cross section could reveal the existence of such a resonance, but this is experimentally challenging, because it requires selecting data samples where top and antitop quarks are highly boosted. Nonetheless, the production of such resonances might generate a sizable charge asymmetry of top versus antitop quarks. We consider a toy model with general flavour independent couplings of the resonance to quarks, of both vector and axial-vector kind. The charge asymmetry turns out to be a more powerful observable to detect new physics than the differential cross section, because its highest statistical significance is achieved with data samples of top-antitop quark pairs of low invariant masses.

hep-ph↗

arXiv2008

Massive color-octet bosons and the charge asymmetries of top quarks at hadron colliders

Several models predict the existence of heavy colored resonances decaying to top quarks in the TeV energy range that might be discovered at the LHC. In some of those models, moreover, a sizable charge asymmetry of top versus antitop quarks might be generated. The detection of these exotic resonances, however, requires selecting data samples where the top and the antitop quarks are highly boosted, which is experimentally very challenging. We asses that the measurement of the top quark charge asymmetry at the LHC is very sensitive to the existence of excited states of the gluon with axial-vector couplings to quarks. We use a toy model with general flavour independent couplings, and show that a signal can be detected with relatively not too energetic top and antitop quarks. We also compare the results with the asymmetry predicted by QCD, and show that its highest statistical significance is achieved with data samples of top-antitop quark pairs of low invariant masses.

hep-ph↗

arXiv2006

Compact multigluonic scattering amplitudes with heavy scalars and fermions

Combining the Berends-Giele and on-shell recursion relations we obtain an extremely compact expression for the scattering amplitude of a complex scalar-antiscalar pair and an arbitrary number of positive helicity gluons. This is one of the basic building blocks for constructing other helicity configurations from recursion relations. We also show explicity that the all positive helicity gluons amplitude for heavy fermions is proportional to the scalar one, confirming in this way the recently advocated SUSY-like Ward identities relating both amplitudes.

hep-th↗