2,903 research outputs found
VELO Module Production - Laser Test and Noise Analysis
This note describes the algorithms used to detect problems by analyzing datasets taken at different stages of module production using the hybrid readout systems
Radiation damage in the LHCb vertex locator
The LHCb Vertex Locator (VELO) is a silicon strip detector designed to reconstruct charged particle trajectories and vertices produced at the LHCb interaction region. During the first two years of data collection, the 84 VELO sensors have been exposed to a range of fluences up to a maximum value of approximately 45 × 1012 1 MeV neutron equivalent (1 MeV neq). At the operational sensor temperature of approximately −7 °C, the average rate of sensor current increase is 18 μA per fb−1, in excellent agreement with predictions. The silicon effective bandgap has been determined using current versus temperature scan data after irradiation, with an average value of Eg = 1.16±0.03±0.04 eV obtained. The first observation of n+-on-n sensor type inversion at the LHC has been made, occurring at a fluence of around 15 × 1012 of 1 MeV neq. The only n+-on-p sensors in use at the LHC have also been studied. With an initial fluence of approximately 3 × 1012 1 MeV neq, a decrease in the Effective Depletion Voltage (EDV) of around 25 V is observed. Following this initial decrease, the EDV increases at a comparable rate to the type inverted n+-on-n type sensors, with rates of (1.43±0.16) × 10−12 V/ 1 MeV neq and (1.35±0.25) × 10−12 V/ 1 MeV neq measured for n+-on-p and n+-on-n type sensors, respectively. A reduction in the charge collection efficiency due to an unexpected effect involving the second metal layer readout lines is observed
Performance of the LHCb vertex locator
The Vertex Locator (VELO) is a silicon microstrip detector that surrounds the proton-proton interaction region in the LHCb experiment. The performance of the detector during the first years of its physics operation is reviewed. The system is operated in vacuum, uses a bi-phase CO2 cooling system, and the sensors are moved to 7 mm from the LHC beam for physics data taking. The performance and stability of these characteristic features of the detector are described, and details of the material budget are given. The calibration of the timing and the data processing algorithms that are implemented in FPGAs are described. The system performance is fully characterised. The sensors have a signal to noise ratio of approximately 20 and a best hit resolution of 4 μm is achieved at the optimal track angle. The typical detector occupancy for minimum bias events in standard operating conditions in 2011 is around 0.5%, and the detector has less than 1% of faulty strips. The proximity of the detector to the beam means that the inner regions of the n+-on-n sensors have undergone space-charge sign inversion due to radiation damage. The VELO performance parameters that drive the experiment's physics sensitivity are also given. The track finding efficiency of the VELO is typically above 98% and the modules have been aligned to a precision of 1 μm for translations in the plane transverse to the beam. A primary vertex resolution of 13 μm in the transverse plane and 71 μm along the beam axis is achieved for vertices with 25 tracks. An impact parameter resolution of less than 35 μm is achieved for particles with transverse momentum greater than 1 GeV/c
Precision luminosity measurements at LHCb
Measuring cross-sections at the LHC requires the luminosity to be determined accurately at each centre-of-mass energy √s. In this paper results are reported from the luminosity calibrations carried out at the LHC interaction point 8 with the LHCb detector for √s = 2.76, 7 and 8 TeV (proton-proton collisions) and for √sNN = 5 TeV (proton-lead collisions). Both the "van der Meer scan" and "beam-gas imaging" luminosity calibration methods were employed. It is observed that the beam density profile cannot always be described by a function that is factorizable in the two transverse coordinates. The introduction of a two-dimensional description of the beams improves significantly the consistency of the results. For proton-proton interactions at √s = 8 TeV a relative precision of the luminosity calibration of 1.47% is obtained using van der Meer scans and 1.43% using beam-gas imaging, resulting in a combined precision of 1.12%. Applying the calibration to the full data set determines the luminosity with a precision of 1.16%. This represents the most precise luminosity measurement achieved so far at a bunched-beam hadron collider
Measurement of the Lifetime Difference Between B_s Mass Eigenstates
We present measurements of the lifetimes and polarization amplitudes for B_s
--> J/psi phi and B_d --> J/psi K*0 decays. Lifetimes of the heavy (H) and
light (L) mass eigenstates in the B_s system are separately measured for the
first time by determining the relative contributions of amplitudes with
definite CP as a function of the decay time. Using 203 +/- 15 B_s decays, we
obtain tau_L = (1.05 +{0.16}/-{0.13} +/- 0.02) ps and tau_H = (2.07
+{0.58}/-{0.46} +/- 0.03) ps. Expressed in terms of the difference DeltaGamma_s
and average Gamma_s, of the decay rates of the two eigenstates, the results are
DeltaGamma_s/Gamma_s = (65 +{25}/-{33} +/- 1)%, and DeltaGamma_s = (0.47
+{0.19}/-{0.24} +/- 0.01) inverse ps.Comment: 8 pages, 3 figures, 2 tables; as published in Physical Review Letters
on 16 March 2005; revisions are for length and typesetting only, no changes
in results or conclusion
Measurement of and Production in Collisions at = 1.96 TeV
The Standard Model predictions for and production are
tested using an integrated luminosity of 200 pb of \ppbar collision data
collected at the Collider Detector at Fermilab. The cross sections are measured
selecting leptonic decays of the and bosons, and photons with
transverse energy GeV that are well separated from leptons. The
production cross sections and kinematic distributions for the and
are compared to SM predictions.Comment: 7 pages, 4 figures, submitted to PR
Evidence for the exclusive decay Bc+- to J/psi pi+- and measurement of the mass of the Bc meson
We report first evidence for a fully reconstructed decay mode of the
B_c^{\pm} meson in the channel B_c^{\pm} \to J/psi \pi^{\pm}, with J/psi \to
mu^+mu^-. The analysis is based on an integrated luminosity of 360 pb$^{-1} in
p\bar{p} collisions at 1.96 TeV center of mass energy collected by the Collider
Detector at Fermilab. We observe 14.6 \pm 4.6 signal events with a background
of 7.1 \pm 0.9 events, and a fit to the J/psi pi^{\pm} mass spectrum yields a
B_c^{\pm} mass of 6285.7 \pm 5.3(stat) \pm 1.2(syst) MeV/c^2. The probability
of a peak of this magnitude occurring by random fluctuation in the search
region is estimated as 0.012%.Comment: 7 pages, 3 figures. Version 3, accepted by PR
Top quark mass measurement using the template method at CDF
We present a measurement of the top quark mass in the lepton+jets and
dilepton channels of decays using the template method. The data
sample corresponds to an integrated luminosity of 5.6 fb of
collisions at Tevatron with TeV, collected with the CDF II
detector. The measurement is performed by constructing templates of three
kinematic variables in the lepton+jets and two kinematic variables in the
dilepton channel. The variables are two reconstructed top quark masses from
different jets-to-quarks combinations and the invariant mass of two jets from
the decay in the lepton+jets channel, and a reconstructed top quark mass
and , a variable related to the transverse mass in events with two
missing particles, in the dilepton channel. The simultaneous fit of the
templates from signal and background events in the lepton+jets and dilepton
channels to the data yields a measured top quark mass of Comment: submitted to Phys. Rev.
Measurement of the ttbar Production Cross Section in ppbar Collisions at sqrt{s}=1.96 TeV using Lepton + Jets Events with Secondary Vertex b-tagging
We present a measurement of the ttbar production cross section using events
with one charged lepton and jets from ppbar collisions at a center-of-mass
energy of 1.96 TeV. In these events, heavy flavor quarks from top quark decay
are identified with a secondary vertex tagging algorithm. From 162 pb-1 of data
collected by the Collider Detector at Fermilab, a total of 48 candidate events
are selected, where 13.5 +- 1.8 events are expected from background
contributions. We measure a ttbar production cross section of 5.6^{+1.2}_{-1.1}
(stat.) ^{+0.9}_{0.6} (syst.) pb.Comment: 28 pages, 20 figures. Published in Physical Review
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