The Level 0 Pixel Trigger System for the ALICE experiment

The ALICE Silicon Pixel Detector contains 1200 readout chips. Fast-OR signals indicate the presence of at least one hit in the 8192 pixel matrix of each chip. The 1200 bits are transmitted every 100 ns on 120 data readout optical links using the G-Link protocol. The Pixel Trigger System extracts and processes them to deliver an input signal to the Level 0 trigger processor targeting a latency of 800 ns. The system is modular and based on FPGA devices. The architecture allows the user to define and implement various trigger algorithms. The system uses advanced 12-channel parallel optical fiber modules operating at 1310 nm as optical receivers. Multi-channel G-Link receivers were realized in programmable hardware and tested. The design of the system and the progress of the ALICE Pixel Trigger project are described in this paper

The Magnetic Distortion Calibration System of the LHCb RICH1 Detector

The LHCb RICH1 detector uses hybrid photon detectors (HPDs) as its optical sensors. A calibration system has been constructed to provide corrections for distortions that are primarily due to external magnetic fields. We describe here the system design, construction, operation and performance.Comment: 9 pages, 14 figure

The pixel Fast-OR signal for the ALICE trigger in p-p collisions

The silicon pixel detector of the ALICE experiment at LHC comprises the two innermost layers of the inner tracking system of the apparatus. It contains 1200 readout chips, each of them corresponding to a 8192 pixel matrix. The single chip outputs a digital Fast-OR signal which is active whenever at least one of the pixels in the matrix records a hit. The 1200 Fast-OR output signals can be used to implement a unique triggering capability: few details on the pixel trigger system and some of the possible applications for p-p collisions are presented

Multiparametric advanced research tool for meteo satellites data interfacing with space observation of ultra high energy cosmic rays

To approach the study of the cosmic rays in the energy range E > 1020 eV, the upper end of the spectrum observed to date, with a large statistical significance (103 events/year), and hence address the solution of several astrophysical and cosmological problems related to their existence and behaviour, a new generation of experiments will probably have to be conceived and realised. They will be based on the observation and measurements of cosmic rays from space. The extremely low rate of these events (∼ 1 event/(century × km2 × sr)) imposes a very large effective area to be monitored, of the order of 105 km2, as an observational requirement to meet the target statistics. The Extreme Universe Space Observatory (EUSO)mission has been proposed as the precursor of this new generation of experiments. Its approach consists in fact in looking downwards to the Earth atmosphere by means of a large field-of-view telescope accommodated aboard an orbiting satellite. The fluorescence strike produced by a cosmic ray through the atmosphere will be recorded by the detector, which will reconstruct the kinematical and dynamical features of the primary cosmic ray. The atmosphere acts therefore as an active target for the detectable event. A strategic tool for the success of EUSO as well as for all the experiments of its category will be a correct and detailed atmospheric sounding system, in order to monitor the atmospheric parameters within the field-of-view of the telescope. Beside an on-board measurement by means of dedicated devices such an infrared camera (IR)and possibly a LIDAR (LIght Detection And Ranging)coupled to the main instrument, the Atmosphere Sounding will take advantage from the continuous observation of the atmospheric parameters given by the orbiting meteorological satellites. Their databases have thus to be interfaced to the experimental data and used picking-up the relevant data according to the space and time coordinates corresponding to each triggered event. The present work outlines a software module (MARVIN-Multiparametric Advanced Research tool for Visualisation In the Network) able to build-up such an interface, and shows a preliminary implementation of it, using a sample of existing satellites and ISCCP meteorological data collection. It has been developed during the phase A study of the EUSO mission but is general enough to be adapted to different missions observing the Earth atmosphere from space

Suppression of high transverse momentum D mesons in central Pb-Pb collisions at √sNN= 2.76 TeV

The production of the prompt charm mesons D0, D+, D∗+, and their antiparticles, was measured with the ALICE detector in Pb-Pb collisions at the LHC, at a centre-of-mass energy √sNN = 2.76 TeV per nucleon-nucleon collision. The pt-differential production yields in the range 2 < pt < 16 GeV/c at central rapidity, |y| < 0.5, were used to calculate the nuclear modification factor RAA with respect to a proton-proton reference obtained from the cross section measured at √s = 7 TeV and scaled to √s = 2.76 TeV. For the three meson species, RAA shows a suppression by a factor 3–4, for transverse momenta larger than 5 GeV/c in the 20% most central collisions. The suppression is reduced for peripheral collisions

The ALICE silicon pixel detector read-out electronics

The ALICE silicon pixel detector (SPD) constitutes the two innermost layers of the ALICE inner tracker system. The SPD contains 10 million pixels segmented in 120 detector modules (half staves), which are connected to the offdetector electronics with bidirectional optical links. Raw data from the on-detector electronics are sent to 20 FPGA-based processor cards (Routers) each carrying three 2-channel linkreceiver daughter-cards. The routers process the data and send them to the ALICE DAQ system via the ALICE detector data link (DDL). The SPD control, configuration and data monitoring is performed via the VME interface of the routers. This paper describes the detector readout and control via the off-detector electronics

First measurement of Ξc0\Xi_{\rm c}^0 production in pp collisions at s\mathbf{\sqrt{s}} = 7 TeV

The production of the charm-strange baryon $\Xi_{\rm c}^0$ is measured for the first time at the LHC via its semileptonic decay into e$^+\Xi^-\nu_{\rm e}$ in pp collisions at $\sqrt{s}=7$ TeV with the ALICE detector. The transverse momentum ($p_{\rm T}$) differential cross section multiplied by the branching ratio is presented in the interval 1 $<$ $p_{\rm T}$ $<$ 8 GeV/$c$ at mid-rapidity, $|y|$ $<$ 0.5. The transverse momentum dependence of the $\Xi_{\rm c}^0$ baryon production relative to the D$^0$ meson production is compared to predictions of event generators with various tunes of the hadronisation mechanism, which are found to underestimate the measured cross-section ratio.Comment: 22 pages, 6 captioned figures, 1 table, authors from page 17, published version, figures at http://aliceinfo.cern.ch/ArtSubmission/node/412

Constraining the magnitude of the Chiral Magnetic Effect with Event Shape Engineering in Pb-Pb collisions at sNN\sqrt{s_{\rm NN}} = 2.76$ TeV

In ultrarelativistic heavy-ion collisions, the event-by-event variation of the elliptic flow $v_2$ reflects fluctuations in the shape of the initial state of the system. This allows to select events with the same centrality but different initial geometry. This selection technique, Event Shape Engineering, has been used in the analysis of charge-dependent two- and three-particle correlations in Pb-Pb collisions at $\sqrt{s_{_{\rm NN}}} =2.76$ TeV. The two-particle correlator $\langle \cos(\varphi_\alpha - \varphi_\beta) \rangle$, calculated for different combinations of charges $\alpha$ and $\beta$, is almost independent of $v_2$ (for a given centrality), while the three-particle correlator $\langle \cos(\varphi_\alpha + \varphi_\beta - 2\Psi_2) \rangle$ scales almost linearly both with the event $v_2$ and charged-particle pseudorapidity density. The charge dependence of the three-particle correlator is often interpreted as evidence for the Chiral Magnetic Effect (CME), a parity violating effect of the strong interaction. However, its measured dependence on $v_2$ points to a large non-CME contribution to the correlator. Comparing the results with Monte Carlo calculations including a magnetic field due to the spectators, the upper limit of the CME signal contribution to the three-particle correlator in the 10-50% centrality interval is found to be 26-33% at 95% confidence level.Comment: 20 pages, 6 captioned figures, 1 tables, authors from page 15, published version, figures at http://aliceinfo.cern.ch/ArtSubmission/node/382

Energy dependence of exclusive J/ψJ/\psi photoproduction off protons in ultra-peripheral p-Pb collisions at sNN\sqrt{s_{\rm{NN}}} = 5.02 TeV

The ALICE Collaboration has measured the energy dependence of exclusive photoproduction of $J/\psi$ vector mesons off proton targets in ultra-peripheral p-Pb collisions at a centre-of-mass energy per nucleon pair $\sqrt{s_{\rm NN}} = 5.02$ TeV. The e$^+$e$^-$ and $\mu^+\mu^-$ decay channels are used to measure the cross section as a function of the rapidity of the $J/\psi$ in the range $-2.5 < y < 2.7$, corresponding to an energy in the $\gamma$p centre-of-mass in the interval $40 < W_{\gamma\mathrm{p}}<550$ GeV. The measurements, which are consistent with a power law dependence of the exclusive $J/\psi$ photoproduction cross section, are compared to previous results from HERA and the LHC and to several theoretical models. They are found to be compatible with previous measurements.Comment: 25 pages, 3 captioned figures, 3 tables, authors from page 19, published version, figures at http://alice-publications.web.cern.ch/node/455

Measurement of the production of charm jets tagged with D0^{0} mesons in pp collisions at s\sqrt{s}= 7 TeV

The production of charm jets in proton-proton collisions at a center-of-mass energy of $\sqrt{s}=7$ TeV was measured with the ALICE detector at the CERN Large Hadron Collider. The measurement is based on a data sample corresponding to a total integrated luminosity of $6.23$ ${\rm nb}^{-1}$, collected using a minimum-bias trigger. Charm jets are identified by the presence of a D$^0$ meson among their constituents. The D$^0$ mesons are reconstructed from their hadronic decay D$^0\rightarrow$K$^{-}\pi^{+}$. The D$^0$-meson tagged jets are reconstructed using tracks of charged particles (track-based jets) with the anti-$k_{\mathrm{T}}$ algorithm in the jet transverse momentum range $5<p_{\rm{T,jet}}^{\mathrm{ch}}<30$ ${\rm GeV/}c$ and pseudorapidity $|\eta_{\rm jet}|<0.5$. The fraction of charged jets containing a D$^0$-meson increases with $p_{\rm{T,jet}}^{\rm{ch}}$ from $0.042 \pm 0.004\, \mathrm{(stat)} \pm 0.006\, \mathrm{(syst)}$ to $0.080 \pm 0.009\, \rm{(stat)} \pm 0.008\, \rm{(syst)}$. The distribution of D$^0$-meson tagged jets as a function of the jet momentum fraction carried by the D$^0$ meson in the direction of the jet axis ($z_{||}^{\mathrm{ch}}$) is reported for two ranges of jet transverse momenta, $5<p_{\rm{T,jet}}^{\rm{ch}}<15$ ${\rm GeV/}c$ and $15<p_{\rm{T,jet}}^{\rm{ch}}<30$ ${\rm GeV/}c$ in the intervals $0.2<z_{||}^{\rm{ch}}<1.0$ and $0.4<z_{||}^{\rm{ch}}<1.0$, respectively. The data are compared with results from Monte Carlo event generators (PYTHIA 6, PYTHIA 8 and Herwig 7) and with a Next-to-Leading-Order perturbative Quantum Chromodynamics calculation, obtained with the POWHEG method and interfaced with PYTHIA 6 for the generation of the parton shower, fragmentation, hadronisation and underlying event.Comment: 29 pages, 8 captioned figures, 3 tables, authors from page 24, published version, figures at http://alice-publications.web.cern.ch/node/525