Publications (345)23.3 Total impact
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Article: The LHCb Detector at the LHC
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ABSTRACT: The LHCb experiment is dedicated to precision measurements of CP violation and rare decays of B hadrons at the Large Hadron Collider (LHC) at CERN (Geneva). The initial configuration and expected performance of the detector and associated systems, as established by test beam measurements and simulation studies, is described.Journal of Instrumentation 08/2008; 3(08):S08005. · 1.87 Impact Factor -
Article: The LHCb Detector at the LHC
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ABSTRACT: The LHCb experiment is dedicated to precision measurements of CP violation and rare decays of B hadrons at the Large Hadron Collider (LHC) at CERN (Geneva). The initial configuration and expected performance of the detector and associated systems, as established by test beam measurements and simulation studies, is described.Journal of Instrumentation 08/2008; 3(08):S08005. · 1.87 Impact Factor -
Article: The LHCb VELO: status and upgrade developments
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ABSTRACT: The VErtex LOcator (VELO) is the silicon microstrip vertexing and triggering sub-detector of the LHCb experiment. It consists of a series of forward disks with the active region extending to just 8 mm from the LHC beams. The current status of the VELO is presented. Due to the high radiation environment, the VELO may have to be replaced after some years, possibly with new materials. A candidate material is Czochralski silicon. We present here promising new results on the first test beam of a large, high resistivity Czochralski microstrip silicon detector read out with LHC speed electronics. The performance was studied before and after irradiation with high energy protons. A signal to noise of over 20:1 was obtained from the detector and significant charge collection efficiencies were measured at relatively modest voltages after a fluence of 4.3×10<sup>14</sup> 1 MeV neutron equivalents (n<sub>eq</sub>) per cm<sup>2</sup>. Studies using the Transient Current Technique probed the electric field within MCz test detectors and proved that MCz silicon does not type invert up until a radiation level of at least 5×10<sup>14</sup> 24GeV/c p/cm<sup>2</sup>. This would mean the VELO could possibly replace, in a potential upgrade, n<sup>+</sup>-on-n DOFZ sensors and the complicated processing involved, for standard p<sup>+</sup>-on-n processing with MCz.IEEE Transactions on Nuclear Science 07/2006; · 1.45 Impact Factor -
Article: Radiation-hard semiconductor detectors for SuperLHC
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ABSTRACT: An option of increasing the luminosity of the Large Hadron Collider (LHC) at CERN to 1035 cm-2 s-1 has been envisaged to extend the physics reach of the machine. An efficient tracking down to a few centimetres from the interaction point will be required to exploit the physics potential of the upgraded LHC. As a consequence, the semiconductor detectors close to the interaction region will receive severe doses of fast hadron irradiation and the inner tracker detectors will need to survive fast hadron fluences of up to above 1016cm-2. The CERN-RD50 project "Development of Radiation Hard Semiconductor Devices for Very High Luminosity Colliders" has been established in 2002 to explore detector materials and technologies that will allow to operate devices up to, or beyond, this limit. The strategies followed by RD50 to enhance the radiation tolerance include the development of new or defect engineered detector materials (SiC, GaN, Czochralski and epitaxial silicon, oxygen enriched Float Zone silicon), the improvement of present detector designs and the understanding of the microscopic defects causing the degradation of the irradiated detectors. The latest advancements within the RD50 collaboration on radiation hard semiconductor detectors will be reviewed and discussed in this work. 2005 Published by Elsevier B.V.Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment 05/2005; 541:189-201. · 1.21 Impact Factor -
Article: Low- and high-energy proton irradiations of standard and oxygenated silicon diodes
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ABSTRACT: Oxygenated and standard (not oxygenated) silicon diodes processed by two different manufacturers (ST Microelectronics and Micron Semiconductor) have been irradiated by low (27 MeV) and high- (24 GeV) energy protons. The leakage current density increase rate (α) and its annealing do not show any significant dependence on oxygenation and are the same for both manufacturers. Oxygenation improves the radiation hardness by decreasing the acceptor introduction rate (β) and mitigating the depletion voltage (V<sub>dep</sub>) increase. Nevertheless, standard ST diodes present β values lower than Micron standard devices and close to oxygenated devices, whose βs are similar for both manufacturers. The amplitude of the V<sub>dep</sub> reverse annealing is reduced by oxygenation, which in addition delays the electrically active defect increase, at least for high-energy protons. Oxygenation is consequently the best approach for silicon substrate radiation hardeningIEEE Transactions on Nuclear Science 01/2002; · 1.45 Impact Factor -
Article: Test results on heavily irradiated silicon detectors for the CMS experiment at LHC
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ABSTRACT: We report selected results of laboratory measurements and beam tests of heavily irradiated microstrip silicon detectors. The detectors were single-sided devices, produced by different manufacturers and irradiated with different sources, for several total ionizing doses and fluences up to 4 ×10<sup>14</sup> 1-MeV-equivalent neutrons per cm <sup>2</sup>. Strip resistance and capacitance, detector leakage currents and breakdown performance were measured before and after irradiations. Signal-to-noise ratio and detector efficiency were studied in beam tests, for different values of the detector temperature and of the read-out pitch, as a function of the detector bias voltage. The goal of these test is to optimise the design of the final prototypes for the Silicon Strip Tracker of the CMS experiment at the CERN LHC colliderIEEE Transactions on Nuclear Science 01/2001; · 1.45 Impact Factor -
Article: Charge Collection Eciency and Resolution of an Irradiated Double Sided Silicon Microstrip Detector Operated at Cryogenic Temperatures
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ABSTRACT: This paper presents results on the measurement of the cluster shapes, resolution and charge collection e#ciency of a double sided silicon microstrip detector after irradiation with 24 GeV protons to a fluence of 3.5 10 14 p/cm 2 and operated at cryogenic temperatures. An empirical model is presented which describes the expected cluster shapes as a function of depletion depth, and is shown to agree with the data. It is observed that the clusters on the p-side broaden if the detector is under-depleted, leading to a degradation of resolution and e#ciency. The model is used to make predictions for detector types envisaged for the LHC experiments. The results also show that at cryogenic temperature the charge collection e#ciency varies depending on the operating conditions of the detector and can reach values of 100% at unexpectedly low bias voltage. By analysing the cluster shapes it is shown that these variations are due to changes in depletion depth. This phenomenon, kno...08/1999; -
Article: Tracking with heavily irradiated silicon detectors operated at cryogenic temperatures
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ABSTRACT: In this work we show that a heavily irradiated double-sided silicon microstrip detector recovers its performance when operated at cryogenic temperatures. A DELPHI microstrip detector, irradiated to a fluence of ~4×10<sup>14</sup> p/cm<sup>2</sup>, no longer operational at room temperature, cannot be distinguished from a non-irradiated one when operated at T<120 K. Besides confirming the previously observed `Lazarus effect' in single diodes, these results establish, for the first time, the possibility of using standard silicon detectors for tracking applications in extremely demanding radiation environmentsIEEE Transactions on Nuclear Science 07/1999; · 1.45 Impact Factor -
Article: Comparative study of (111) and (100) crystals and capacitance measurements on Si strip detectors in CMS
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ABSTRACT: For the construction of the silicon microstrip detectors for the Tracker of the CMS experiment, two different substrate choices were investigated: A high-resistivity (6 k cm) substrate with (111) crystalorientation and a low-resistivity (2k cm) one with (100) crystalorientation. The interstrip and backplane capacitances were measured before and after the exposure to radiation in a range of strip pitches from 60 μm to 240 μm and for values of the width-over-pitch ratio between 0.1 and 0.5. PACS 29.40.GxTracking and position-sensitive detectors PACS 29.40.WkSolid-state detectors PACS 61.82.FkSemiconductors PACS 01.30.CcConference proceedingsIl Nuovo Cimento A 04/1999; 112(11):1261-1269. -
Article: High-voltage breakdown studies on Si microstrip detectors
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ABSTRACT: The breakdown performance of CMS barrelmodule prototype detectors and test devices with single and multi-guard structures were studied before and after neutron irradiation up to 2·1014 1 MeV equivalent neutrons. Before irradiation avalanche breakdown occurred at the guard ring implant edges. We measured 100–300 V higher breakdown voltage values for the devices with multi-guard than for devices with single-guard ring. After irradiation and type inversion the breakdown was smoother than before irradiation and the breakdown voltage value increased to 500–600 V for most of the devices. PACS 29.40.WkSolid-state detectors PACS 01.30.CcConference ProceedingsIl Nuovo Cimento A 04/1999; 112(11):1271-1283. -
Article: The silicon microstrip tracker for CMS
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ABSTRACT: This paper describes the silicon microstrip tracker of the CMS experiment at the future LHC. The silicon tracker consists of a barrel part with 5 layers and two endcaps with 10 disks each. About 6500 modules will have to be built, each one carrying two daisy-chained silicon sensors and their front-end electronics. The modules have been designed to be as simple and robust as possible. Radiation damage in the silicon sensors is minimized by cooling the whole system down to -10°C. Safe operation after heavy irradiation will be possible due to the high-voltage capability of the sensors. We expect the sensors to have a signal-to-noise ratio of 10 at the end of 10years of LHC running, which still gives an efficiency of almost 100%. PACS 29.40.GxTracking and position-sensitive detectors PACS 29.40.WkSolid-state detectors PACS 01.30.CcConference proceedingsIl Nuovo Cimento A 04/1999; 112(11):1307-1316. -
Conference Proceeding: Test results on heavily irradiated silicon detectors for the CMS experiment at LHC
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ABSTRACT: The R&D of silicon micro-strip detectors for CMS able to survive a radiation environment with fluxes above 10<sup>14</sup> particles per cm<sup>2</sup> has started since few years. Micro-strip detectors have been studied before and after irradiation performed with different sources and doses. The analysis of the experimental data helps to optimise the design of detectors which can be operated efficiently during LHC lifetimeNuclear Science Symposium, 1998. Conference Record. 1998 IEEE; 02/1998 -
Article: Search for B0s-
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ABSTRACT: Oscillations of B0s mesons were studied in events with a large transverse momentum lepton selected from 3.2 million hadronic Z0 decays registered by DELPHI between 1991 and 1994. A limit on the mass difference between the physical B0s stateswas obtained by combining the results obtained in three channels.Physics Letters B 10/1997; 414:382-400. · 3.95 Impact Factor -
Article: Measurement of the spin density matrix for the ρ0, K*0 (892) and φ produced in Z0 decays
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ABSTRACT: The spin density matrix elements for the ρ0, K*0(892) and φ produced in hadronic Z0 decays are measured in the DELPHI detector. There is no evidence for spin alignment of the K*0(892) and φ in the region xp <= 0.3 (xp = p/pbeam), where ρ00 = 0.33 +/- 0.05 and ρ00 = 0.30 +/- 0.04, respectively. In the fragmentation region, xp >= 0.4, there is some indication for spin alignment of the ρ0 and K*0(892), since ρ00 = 0.43 +/- 0.05 and ρ00 = 0.46 +/- 0.08, respectively. These values are compared with those found in meson-induced hadronic reactions. For the φ, ρ00 = 0.30 +/- 0.04 for xp >= 0.4 and 0.55 +/- 0.10 for xp >= 0.7. The off-diagonal spin density matrix element ρ1-1 is consistent with zero in all cases.Physics Letters B 01/1997; 406:271-286. · 3.95 Impact Factor -
Article: Search for high mass γγ resonances ine^ + e^ - to ell ^ + ell ^ - γ γ ,ν bar ν γ γ andqbar qγ γ at LEP Iat LEP I
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ABSTRACT: A search for high mass photon pairs from the processese^ + e^ - to ell ^ + ell ^ - γ γ ,e^ + e^ - to qbar qγ γ ande^ + e^ - to ν bar ν γ γ with the DELPHI detector at LEP I is reported. From a data sample containing 3.5 million hadronic Z0 decays, collected by DELPHI during the years 1991 to 1994, 79 events with two charged leptons and two isolated photons were selected with photon pair masses above 10 GeV/c2, where 76±6 events were predicted from standard sources. In the same data sample, noν bar ν γ γ candidates were found and no accumulation of events was visible for γγ masses above 10 GeV/c2 in theqbar qγ γ channel. Upper limits at 95% confidence level on the Z0 branching ratios for the three different channels were extracted from the data. In the mass region m γγ >30 GeV/c2 the limits obtained are between 3×10-6 and 4×10-6.Zeitschrift für Physik C 05/1996; 72:179-190. -
Article: Search for high massγγ resonances in , and at LEP Iat LEP I
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ABSTRACT: A search for high mass photon pairs from the processes$e^ + e^ - \to \ell ^ + \ell ^ - \gamma \gamma $e^ + e^ - \to \ell ^ + \ell ^ - \gamma \gamma ,$e^ + e^ - \to q\bar q\gamma \gamma $e^ + e^ - \to q\bar q\gamma \gamma and$e^ + e^ - \to \nu \bar \nu \gamma \gamma $e^ + e^ - \to \nu \bar \nu \gamma \gamma with the DELPHI detector at LEP I is reported. From a data sample containing 3.5 million hadronic Z0 decays, collected by DELPHI during the years 1991 to 1994, 79 events with two charged leptons and two isolated photons were selected with photon pair masses above 10 GeV/c2, where 76±6 events were predicted from standard sources. In the same data sample, no$\nu \bar \nu \gamma \gamma $\nu \bar \nu \gamma \gamma candidates were found and no accumulation of events was visible forγγ masses above 10 GeV/c2 in the$q\bar q\gamma \gamma $q\bar q\gamma \gamma channel. Upper limits at 95% confidence level on the Z0 branching ratios for the three different channels were extracted from the data. In the mass regionm γγ >30 GeV/c2 the limits obtained are between 3×10−6 and 4×10−6.Zeitschrift für Physik C 04/1996; 72(2):179-190. -
Article: Mean lifetime of theBs0 meson
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ABSTRACT: This paper presents an update of the measurement of the mean lifetime of theB s 0 meson. CombiningD s−ℓ,D s−h,φ−ℓ and inclusiveD s final states from the 3.2 million hadronic Z decays collected by DELPHI between 1991 and 1994, theB s 0 mean lifetime was measured to be:τ(B s 0)=1.67±0.14 ps.Zeitschrift für Physik C 04/1996; 71(1):11-30. -
Article: Measurement of the B d0 oscillation frequency using kaons, leptons and jet charge
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ABSTRACT: A measurement of the mass difference,Δm d , between the two physical B d 0 states has been obtained from the analysis of the impact parameter distribution of a lepton emitted at large transverse momentum (p t ) relative to the jet axis and from the analysis of the flight distance distribution of secondary vertices tagged by either a highp t lepton or an identified kaon. In the opposite hemisphere of the event, the charge of the initial quark has been evaluated using a highp t lepton, a charged kaon or the mean jet charge. With 1.7 million hadronic Z0 decays recorded by DELPHI between 1991 and 1993,Δm d is found to be: Dmd = 0.531 - 0.046 + 0.050 (stat.) ±0.078 (syst.) ps - 1 .\Delta m_d = 0.531_{ - 0.046}^{ + 0.050} (stat.) \pm 0.078 (syst.) ps^{ - 1} . .Zeitschrift für Physik C 04/1996; 72(1):17-30. -
Article: Study of rareb decays with the DELPHI detector at LEP
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ABSTRACT: Rare decays of beauty particles were studied in several charmless modes using the data collected with the DELPHI detector at LEP from 1991 to 1994. These decays are mediated by both tree levelb→u and one-loop penguinb→s, d transitions. Evidence for charmlessB decays was obtained in two body hadronic modes. The branching ratios ofB d,s 0 toπ + π − orK + π − andB u − toρ 0 π − orK*0 π − were found to be (2.8−1.0+1.5±0.2)×10−5 and (1.7−0.8+1.2±0.2)×10−4 respectively. The fraction of these decays with a charged kaon in the final state that is not from the spectators quark, was measured to be 0.58±0.18. Upper limits were set at 90% confidence level on the branching ratios for three and four body charmless hadronic decays in the range of (1–3)×10−4, for inclusive radiativeb→sγ decays at 5.4×10−4, for the exclusive radiative decaysB d 0→K*(892)0 γ andB s 0→φ(1020)γ at 2.1×10−4 and 7.0×10−4 respectively, and for dineutrino decaysb ® sn[`(n)]b \to s\nu \bar \nu , in the exclusive channelsBd0 ® K* (892)0 n[`(n)]B_d^0 \to K^* (892)^0 \nu \bar \nu andBs0 ® f(1020)n[`(n)]B_s^0 \to \phi (1020)\nu \bar \nu at 1.0×10−3 and 5.4×10−3 respectively. The limits on dineutrino decays constrain theories with a newU(1) gauge boson coupling predominantly to the third family of fermions.Zeitschrift für Physik C 04/1996; 72(2):207-220. -
Article: First study of the interference between initial and final state radiation at the Z resonance
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ABSTRACT: The interference between initial and final state radiation in the processe + e −→μ + μ − at √s≈MZ has been studied by measuring the forward-backward asymmetry as a function of the acoplanarity angle between the final state muons. The interference is expected to be sensitive to the space-time separation of the initial and final state radiation. The measured asymmetry distribution has been compared to theoretical predictions using thekoralz generator, with and withoutO(a){\mathcal{O}}(\alpha ) interference. The magnitude of the interference between initial and final state radiation was found to be of the order predicted and to follow the expected distribution. Using the theoretical predictions, a value of GZ = 2.50 ±0.21 (stat.) ±0.06 (syst.) GeV.\Gamma _{\rm Z} = 2.50 \pm 0.21 (stat.) \pm 0.06 (syst.) GeV. has been extracted. The interpretation of this result is discussed. There is an additional uncertainty in the estimate ofΓ Z from as yet uncalculated higher order interference terms. By assuming a value ofΓ Z consistent with the world average, the data were used to estimate the size of these uncalculated corrections.Zeitschrift für Physik C 04/1996; 72(1):31-38.
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Institutions
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2001
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Università di Pisa
Pisa, Tuscany, Italy
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1999
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University of Padua
Padova, Veneto, Italy
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