Leonello Servoli - Academia.edu (original) (raw)

Papers by Leonello Servoli

2008 IEEE Nuclear Science Symposium Conference Record, 2008

The recent developments in the domain of the standard CMOS imagers for visible light, mainly in t... more The recent developments in the domain of the standard CMOS imagers for visible light, mainly in the reduction of the pixel size, has led us to investigate the suitability of some of these devices as ionizing radiation detectors. A standard 640x480 imager with 5.6x5.6 micrometer pixel size (Micron product type MT9V011) has been characterized with both photons (55 Fe and 8 keV X-ray tube) than charged particles sources (500 MeV electrons). The main results obtained are: a small pixel multiplicity (4-5), for the detection of either X-ray or charged particles; a good linearity of the response; a S/N ratio > 30 for a Minimum Ionizing Particle and an estimated sensitivity down to about 2 keV.

Journal of Instrumentation, 2010

The CMS Level-1 trigger was used to select cosmic ray muons and LHC beam events during data-takin... more The CMS Level-1 trigger was used to select cosmic ray muons and LHC beam events during data-taking runs in 2008, and to estimate the level of detector noise. This paper describes the trigger components used, the algorithms that were executed, and the trigger synchronisation. Using data from extended cosmic ray runs, the muon, electron/photon, and jet triggers have been validated, and their performance evaluated. Efficiencies were found to be high, resolutions were found to be good, and rates as expected.

Journal of Instrumentation, 2010

The CMS silicon tracker, consisting of 1440 silicon pixel and 15 148 silicon strip detector modul... more The CMS silicon tracker, consisting of 1440 silicon pixel and 15 148 silicon strip detector modules, has been aligned using more than three million cosmic ray charged particles, with additional information from optical surveys. The positions of the modules were determined with respect to cosmic ray trajectories to an average precision of 3-4 microns RMS in the barrel and 3-14 microns RMS in the endcap in the most sensitive coordinate. The results have been validated by several studies, including laser beam cross-checks, track fit self-consistency, track residuals in overlapping module regions, and track parameter resolution, and are compared with predictions obtained from simulation. Correlated systematic effects have been investigated. The track parameter resolutions obtained with this alignment are close to the design performance.

Journal of Instrumentation, 2008

The European Physical Journal C, 2010

2006 IEEE Nuclear Science Symposium Conference Record, 2006

The suitability of standard CMOS technology featuring no epitaxial layer for particle detection h... more The suitability of standard CMOS technology featuring no epitaxial layer for particle detection has been investigated through extensive experimental characterization. Different pixel layout and read-out schemes have been devised and implemented, as well as different test strategies. In this work test results are reported concerning the response of the detector to IR laser, beta-particles and X-rays stimuli, thus confirming the suitability of the proposed approach for high energy physics applications.

Journal of Physics G: Nuclear and Particle Physics, 2007

Abstract CMS is a general purpose experiment, designed to study the physics of pp collisions at 1... more Abstract CMS is a general purpose experiment, designed to study the physics of pp collisions at 14 TeV at the Large Hadron Collider (LHC). It currently involves more than 2000 physicists from more than 150 institutes and 37 countries. The LHC will provide extraordinary opportunities for particle physics based on its unprecedented collision energy and luminosity when it begins operation in 2007. The principal aim of this report is to present the strategy of CMS to explore the rich physics programme offered by the LHC. This ...

To measure the intrinsic spatial resolution of silicon pixel sensor is usually a non-trivial task... more To measure the intrinsic spatial resolution of silicon pixel sensor is usually a non-trivial task, particularly for small pixel sizes where the multiple scattering may be the limiting factor. In this work, we present a new measurement technique to obtain the intrinsic spatial resolution of silicon active pixel sensors. The method relies on the capability of the device to record the passage of a charged particle, incoming at a grazing angle, over several tens or hundreds of pixels, acting as a solid state ionization chamber and thus defining a track. The track will then be fitted by a line and the intrinsic spatial resolution will be obtained using two methods: i) extracted by the σ of the fit; ii) defining a telescope-on-chip configuration to find a residual distribution. Comparison with a more traditional measurement (telescope configuration) and a discussion on the limit of this technique, when the pixel size shrinks, will also be presented.

Journal of Instrumentation, 2012

In this work we present the results of full Geant4 and FLUKA simulations and comparison with dosi... more In this work we present the results of full Geant4 and FLUKA simulations and comparison with dosimetry data of an electron LINAC of St. Maria Hospital located in Terni, Italy. The facility is being used primarily for radiotherapy and the goal of the present study is the detailed investigation of electron beam parameters to evaluate the possibility to use the e−LINAC (during time slots when it is not used for radiotherapy) to test the performance of detector systems, in particular those designed to operate in space. The critical beam parameters are electron energy, profile and flux available at the surface of device to be tested. The present work aims to extract these parameters from dosimetry calibration data available at the e−LINAC. The electron energy ranges from 4 MeV to 20 MeV. The dose measurements have been performed by using an Advanced Markus Chamber which has a small sensitive volume.

Nuclear Physics B-proceedings Supplements, 2008

Starting from 2007 the CMS experiment will produce several Pbytes of data each year, to be distri... more Starting from 2007 the CMS experiment will produce several Pbytes of data each year, to be distributed over many computing centers located in many different countries. The CMS computing model defines how the data are to be distributed such that CMS physicists can access them in an efficient manner in order to perform their physics analysis. CRAB (CMS Remote Analysis

The CMS experiment will produce several Pbytes of data every year, to be distributed over many co... more The CMS experiment will produce several Pbytes of data every year, to be distributed over many computing centers geographically distributed in different countries. Analysis of this data will be also performed in a distributed way, using grid infrastructure. CRAB (CMS Remote Analysis Builder) is a specific tool, designed and developed by the CMS collaboration, that allows a transparent access to distributed data to end physicist. Very limited knowledge of underlying technicalities are required to the user. CRAB interacts with the local user environment, the CMS Data Management services and with the Grid middleware. It is able to use WLCG, gLite and OSG middleware. CRAB has been in production and in routine use by end-users since Spring 2004. It has been extensively used in studies to prepare the Physics Technical Design Report (PTDR) and in the analysis of reconstructed event samples generated during the Computing Software and Analysis Challenge (CSA06). This involved generating thousands of jobs per day at peak rates. In this paper we discuss the current implementation of CRAB, the experience with using it in production and the plans to improve it in the immediate future.

Journal of Instrumentation, 2008

The Compact Muon Solenoid (CMS) detector is described. The detector operates at the Large Hadron ... more The Compact Muon Solenoid (CMS) detector is described. The detector operates at the Large Hadron Collider (LHC) at CERN. It was conceived to study proton-proton (and leadlead) collisions at a centre-of-mass energy of 14 TeV (5.5 TeV nucleon-nucleon) and at luminosities up to 10 34 cm −2 s −1 (10 27 cm −2 s −1 ). At the core of the CMS detector sits a high-magneticfield and large-bore superconducting solenoid surrounding an all-silicon pixel and strip tracker, a lead-tungstate scintillating-crystals electromagnetic calorimeter, and a brass-scintillator sampling hadron calorimeter. The iron yoke of the flux-return is instrumented with four stations of muon detectors covering most of the 4π solid angle. Forward sampling calorimeters extend the pseudorapidity coverage to high values (|η| ≤ 5) assuring very good hermeticity. The overall dimensions of the CMS detector are a length of 21.6 m, a diameter of 14.6 m and a total weight of 12500 t.

European Physical Journal C, 2006

The four LEP collaborations, ALEPH, DELPHI, L3 and OPAL, have searched for the neutral Higgs boso... more The four LEP collaborations, ALEPH, DELPHI, L3 and OPAL, have searched for the neutral Higgs bosons which are predicted by the Minimal Supersymmetric standard model (MSSM). The data of the four collaborations are statistically combined and examined for their consistency with the background hypothesis and with a possible Higgs boson signal. The combined LEP data show no significant excess of events which would indicate the production of Higgs bosons. The search results are used to set upper bounds on the cross-sections of various Higgs-like event topologies. The results are interpreted within the MSSM in a number of “benchmark” models, including CP-conserving and CP-violating scenarios. These interpretations lead in all cases to large exclusions in the MSSM parameter space. Absolute limits are set on the parameter cosβ and, in some scenarios, on the masses of neutral Higgs bosons.

Physics Letters B, 2010

We present a measurement of the ratio of positive to negative muon fluxes from cosmic ray interac... more We present a measurement of the ratio of positive to negative muon fluxes from cosmic ray interactions in the atmosphere, using data collected by the CMS detector both at ground level and in the underground experimental cavern at the CERN LHC. Muons were detected in the momentum range from 5 GeV/c to 1 TeV/c. The surface flux ratio is measured to be 1.2766 ± 0.0032 (stat.) ± 0.0032 (syst.), independent of the muon momentum, below 100 GeV/c. This is the most precise measurement to date. At higher momenta the data are consistent with an increase of the charge ratio, in agreement with cosmic ray shower models and compatible with previous measurements by deep-underground experiments.

Physics Letters B, 2003

Exclusive ρ 0 ρ 0 production in two-photon collisions involving a single highly virtual photon is... more Exclusive ρ 0 ρ 0 production in two-photon collisions involving a single highly virtual photon is studied with data collected at LEP at centre-of-mass energies 89 GeV < √ s < 209 GeV with a total integrated luminosity of 854.7 pb −1 . The cross section of the process γ γ * → ρ 0 ρ 0 is determined as a function of the photon virtuality, Q 2 , and the two-photon centre-of-mass energy, W γ γ , in the kinematic region: 1.2 GeV 2 < Q 2 < 30 GeV 2 and 1.1 GeV < W γ γ < 3 GeV.

Astroparticle Physics, 2005

Physical Review Letters, 2010

Bose-Einstein correlations have been measured using samples of proton-proton collisions at 0.9 an... more Bose-Einstein correlations have been measured using samples of proton-proton collisions at 0.9 and 2.36 TeV center-of-mass energies, recorded by the CMS experiment at the CERN Large Hadron Collider. The signal is observed in the form of an enhancement of pairs of same-sign charged particles with small relative four-momentum. The size of the correlated particle emission region is seen to increase significantly with the particle multiplicity of the event.

Physics Letters B, 1999

We report on measurements of the mass and total decay width of the W boson with the L3 detector a... more We report on measurements of the mass and total decay width of the W boson with the L3 detector at LEP. W-pair events produced in e + e − interactions between 161 GeV and 183 GeV centre-of-mass energy are selected in a data sample corresponding to a total luminosity of 76.7 pb −1 . Combining all final states in W-pair production, the mass and total decay width of the W boson are determined to be M W = 80.61 ± 0.15 GeV and Γ W = 1.97 ± 0.38 GeV, respectively.

2008 IEEE Nuclear Science Symposium Conference Record, 2008

The recent developments in the domain of the standard CMOS imagers for visible light, mainly in t... more The recent developments in the domain of the standard CMOS imagers for visible light, mainly in the reduction of the pixel size, has led us to investigate the suitability of some of these devices as ionizing radiation detectors. A standard 640x480 imager with 5.6x5.6 micrometer pixel size (Micron product type MT9V011) has been characterized with both photons (55 Fe and 8 keV X-ray tube) than charged particles sources (500 MeV electrons). The main results obtained are: a small pixel multiplicity (4-5), for the detection of either X-ray or charged particles; a good linearity of the response; a S/N ratio > 30 for a Minimum Ionizing Particle and an estimated sensitivity down to about 2 keV.

Journal of Instrumentation, 2010

The CMS Level-1 trigger was used to select cosmic ray muons and LHC beam events during data-takin... more The CMS Level-1 trigger was used to select cosmic ray muons and LHC beam events during data-taking runs in 2008, and to estimate the level of detector noise. This paper describes the trigger components used, the algorithms that were executed, and the trigger synchronisation. Using data from extended cosmic ray runs, the muon, electron/photon, and jet triggers have been validated, and their performance evaluated. Efficiencies were found to be high, resolutions were found to be good, and rates as expected.

Journal of Instrumentation, 2010

The CMS silicon tracker, consisting of 1440 silicon pixel and 15 148 silicon strip detector modul... more The CMS silicon tracker, consisting of 1440 silicon pixel and 15 148 silicon strip detector modules, has been aligned using more than three million cosmic ray charged particles, with additional information from optical surveys. The positions of the modules were determined with respect to cosmic ray trajectories to an average precision of 3-4 microns RMS in the barrel and 3-14 microns RMS in the endcap in the most sensitive coordinate. The results have been validated by several studies, including laser beam cross-checks, track fit self-consistency, track residuals in overlapping module regions, and track parameter resolution, and are compared with predictions obtained from simulation. Correlated systematic effects have been investigated. The track parameter resolutions obtained with this alignment are close to the design performance.

Journal of Instrumentation, 2008

The European Physical Journal C, 2010

2006 IEEE Nuclear Science Symposium Conference Record, 2006

The suitability of standard CMOS technology featuring no epitaxial layer for particle detection h... more The suitability of standard CMOS technology featuring no epitaxial layer for particle detection has been investigated through extensive experimental characterization. Different pixel layout and read-out schemes have been devised and implemented, as well as different test strategies. In this work test results are reported concerning the response of the detector to IR laser, beta-particles and X-rays stimuli, thus confirming the suitability of the proposed approach for high energy physics applications.

Journal of Physics G: Nuclear and Particle Physics, 2007

Abstract CMS is a general purpose experiment, designed to study the physics of pp collisions at 1... more Abstract CMS is a general purpose experiment, designed to study the physics of pp collisions at 14 TeV at the Large Hadron Collider (LHC). It currently involves more than 2000 physicists from more than 150 institutes and 37 countries. The LHC will provide extraordinary opportunities for particle physics based on its unprecedented collision energy and luminosity when it begins operation in 2007. The principal aim of this report is to present the strategy of CMS to explore the rich physics programme offered by the LHC. This ...

To measure the intrinsic spatial resolution of silicon pixel sensor is usually a non-trivial task... more To measure the intrinsic spatial resolution of silicon pixel sensor is usually a non-trivial task, particularly for small pixel sizes where the multiple scattering may be the limiting factor. In this work, we present a new measurement technique to obtain the intrinsic spatial resolution of silicon active pixel sensors. The method relies on the capability of the device to record the passage of a charged particle, incoming at a grazing angle, over several tens or hundreds of pixels, acting as a solid state ionization chamber and thus defining a track. The track will then be fitted by a line and the intrinsic spatial resolution will be obtained using two methods: i) extracted by the σ of the fit; ii) defining a telescope-on-chip configuration to find a residual distribution. Comparison with a more traditional measurement (telescope configuration) and a discussion on the limit of this technique, when the pixel size shrinks, will also be presented.

Journal of Instrumentation, 2012

In this work we present the results of full Geant4 and FLUKA simulations and comparison with dosi... more In this work we present the results of full Geant4 and FLUKA simulations and comparison with dosimetry data of an electron LINAC of St. Maria Hospital located in Terni, Italy. The facility is being used primarily for radiotherapy and the goal of the present study is the detailed investigation of electron beam parameters to evaluate the possibility to use the e−LINAC (during time slots when it is not used for radiotherapy) to test the performance of detector systems, in particular those designed to operate in space. The critical beam parameters are electron energy, profile and flux available at the surface of device to be tested. The present work aims to extract these parameters from dosimetry calibration data available at the e−LINAC. The electron energy ranges from 4 MeV to 20 MeV. The dose measurements have been performed by using an Advanced Markus Chamber which has a small sensitive volume.

Nuclear Physics B-proceedings Supplements, 2008

Starting from 2007 the CMS experiment will produce several Pbytes of data each year, to be distri... more Starting from 2007 the CMS experiment will produce several Pbytes of data each year, to be distributed over many computing centers located in many different countries. The CMS computing model defines how the data are to be distributed such that CMS physicists can access them in an efficient manner in order to perform their physics analysis. CRAB (CMS Remote Analysis

The CMS experiment will produce several Pbytes of data every year, to be distributed over many co... more The CMS experiment will produce several Pbytes of data every year, to be distributed over many computing centers geographically distributed in different countries. Analysis of this data will be also performed in a distributed way, using grid infrastructure. CRAB (CMS Remote Analysis Builder) is a specific tool, designed and developed by the CMS collaboration, that allows a transparent access to distributed data to end physicist. Very limited knowledge of underlying technicalities are required to the user. CRAB interacts with the local user environment, the CMS Data Management services and with the Grid middleware. It is able to use WLCG, gLite and OSG middleware. CRAB has been in production and in routine use by end-users since Spring 2004. It has been extensively used in studies to prepare the Physics Technical Design Report (PTDR) and in the analysis of reconstructed event samples generated during the Computing Software and Analysis Challenge (CSA06). This involved generating thousands of jobs per day at peak rates. In this paper we discuss the current implementation of CRAB, the experience with using it in production and the plans to improve it in the immediate future.

Journal of Instrumentation, 2008

The Compact Muon Solenoid (CMS) detector is described. The detector operates at the Large Hadron ... more The Compact Muon Solenoid (CMS) detector is described. The detector operates at the Large Hadron Collider (LHC) at CERN. It was conceived to study proton-proton (and leadlead) collisions at a centre-of-mass energy of 14 TeV (5.5 TeV nucleon-nucleon) and at luminosities up to 10 34 cm −2 s −1 (10 27 cm −2 s −1 ). At the core of the CMS detector sits a high-magneticfield and large-bore superconducting solenoid surrounding an all-silicon pixel and strip tracker, a lead-tungstate scintillating-crystals electromagnetic calorimeter, and a brass-scintillator sampling hadron calorimeter. The iron yoke of the flux-return is instrumented with four stations of muon detectors covering most of the 4π solid angle. Forward sampling calorimeters extend the pseudorapidity coverage to high values (|η| ≤ 5) assuring very good hermeticity. The overall dimensions of the CMS detector are a length of 21.6 m, a diameter of 14.6 m and a total weight of 12500 t.

European Physical Journal C, 2006

The four LEP collaborations, ALEPH, DELPHI, L3 and OPAL, have searched for the neutral Higgs boso... more The four LEP collaborations, ALEPH, DELPHI, L3 and OPAL, have searched for the neutral Higgs bosons which are predicted by the Minimal Supersymmetric standard model (MSSM). The data of the four collaborations are statistically combined and examined for their consistency with the background hypothesis and with a possible Higgs boson signal. The combined LEP data show no significant excess of events which would indicate the production of Higgs bosons. The search results are used to set upper bounds on the cross-sections of various Higgs-like event topologies. The results are interpreted within the MSSM in a number of “benchmark” models, including CP-conserving and CP-violating scenarios. These interpretations lead in all cases to large exclusions in the MSSM parameter space. Absolute limits are set on the parameter cosβ and, in some scenarios, on the masses of neutral Higgs bosons.

Physics Letters B, 2010

We present a measurement of the ratio of positive to negative muon fluxes from cosmic ray interac... more We present a measurement of the ratio of positive to negative muon fluxes from cosmic ray interactions in the atmosphere, using data collected by the CMS detector both at ground level and in the underground experimental cavern at the CERN LHC. Muons were detected in the momentum range from 5 GeV/c to 1 TeV/c. The surface flux ratio is measured to be 1.2766 ± 0.0032 (stat.) ± 0.0032 (syst.), independent of the muon momentum, below 100 GeV/c. This is the most precise measurement to date. At higher momenta the data are consistent with an increase of the charge ratio, in agreement with cosmic ray shower models and compatible with previous measurements by deep-underground experiments.

Physics Letters B, 2003

Exclusive ρ 0 ρ 0 production in two-photon collisions involving a single highly virtual photon is... more Exclusive ρ 0 ρ 0 production in two-photon collisions involving a single highly virtual photon is studied with data collected at LEP at centre-of-mass energies 89 GeV < √ s < 209 GeV with a total integrated luminosity of 854.7 pb −1 . The cross section of the process γ γ * → ρ 0 ρ 0 is determined as a function of the photon virtuality, Q 2 , and the two-photon centre-of-mass energy, W γ γ , in the kinematic region: 1.2 GeV 2 < Q 2 < 30 GeV 2 and 1.1 GeV < W γ γ < 3 GeV.

Astroparticle Physics, 2005

Physical Review Letters, 2010

Bose-Einstein correlations have been measured using samples of proton-proton collisions at 0.9 an... more Bose-Einstein correlations have been measured using samples of proton-proton collisions at 0.9 and 2.36 TeV center-of-mass energies, recorded by the CMS experiment at the CERN Large Hadron Collider. The signal is observed in the form of an enhancement of pairs of same-sign charged particles with small relative four-momentum. The size of the correlated particle emission region is seen to increase significantly with the particle multiplicity of the event.

Physics Letters B, 1999

We report on measurements of the mass and total decay width of the W boson with the L3 detector a... more We report on measurements of the mass and total decay width of the W boson with the L3 detector at LEP. W-pair events produced in e + e − interactions between 161 GeV and 183 GeV centre-of-mass energy are selected in a data sample corresponding to a total luminosity of 76.7 pb −1 . Combining all final states in W-pair production, the mass and total decay width of the W boson are determined to be M W = 80.61 ± 0.15 GeV and Γ W = 1.97 ± 0.38 GeV, respectively.