Primary Vertex Research Articles

FutureDAQ for CBM: on-line event selection

At the upcoming new Facility for Antiproton and Ion Research FAIR at GSI the Compressed Baryonic Matter experiment CBM requires a new architecture of front-end electronics, data acquisition, and event processing. The detector systems of CBM are a Silicon Tracker System (STS), RICH detectors, a TRD, RPCs, and an electromagnetic calorimeter. The envisioned interaction rate of 10 MHz will produce a data rate of up to 1 TByte/s. Because of the complexity and variability of trigger decisions no common trigger will be applied. Instead, the front-end electronics of all detectors will be self-triggered and marked by time stamps. The full data rate must be switched through a high speed network fabric into a computational network with configurable processing resources for event building and filtering. The decision for selecting candidate events requires tracking, primary vertex reconstruction, and secondary vertex finding in the STS at the full interaction rate. The essential performance factor is now computational throughput rather than decision latency, which results in a much better utilization of the processing resources especially in the case of heavy ion collisions with strongly varying multiplicities. The development of key components is supported by the FutureDAQ project of the European Union (FP6 I3HP JRA1).

Measurement of mass and width of the excited charmed meson statesD10andD2*0at CDF

This paper describes a measurement of the mass and of the width of two neutral narrow resonances $D_10$ and $D_2^{0*}$, both composed of a charm quark and an up antiquark. The difference with respect to the well-known resonance $D0$, also neutral and with the same quark composition, is that the two quarks have an orbital momentum 1, which increases their binding energy. Therefore the mass is larger than that of the $D0$. Since the relative orientation of the spin is the same, in the limit of very large charm mass, the masses of these resonances should be the same; their small difference is predicted by theory and therefore important to measurement to distinguish the different models. These states have been observed in their decay into a kaon and three pions; two of these particles are required to originate from a displaced vertex with respect to the primary interaction vertex, to account for the longer lifetime of the charmed mesons. The resonances parameters have been extracted using a fitting procedure accounting for the expected resonance shape, including effects from detector resolution and background, providing a new best single measurement of the $D_10$ and $D_2^{0*}$ masses and a competitive measurement of their widths.

Measurement of $F_2^{c\bar{c}}$ and $F_2^{b\bar{b}}$ at low Q2 and x * using the H1 vertex detector at HERA

Measurements are presented of inclusive charm and beauty cross sections in e^+p collisions at HERA for values of photon virtuality 12 \le Q^2 \le 60 GeV^2 and of the Bjorken scaling variable 0.0002 \le x \le 0.005. The fractions of events containing charm and beauty quarks are determined using a method based on the impact parameter, in the transverse plane, of tracks to the primary vertex, as measured by the H1 vertex detector. Values for the structure functions F_2^{c\bar{c}} and F_2^{b\bar{b}} are obtained. This is the first measurement of F_2^{b\bar{b}} in this kinematic range. The results are found to be compatible with the predictions of perturbative quantum chromodynamics and withprevious measurements of F_2^{c\bar{c}}.

LHCb Vertex Locator prototyping, testing and production

LHCb is the experiment at the Large Hadron Collider (LHC) dedicated to the study of CP violation in the B-system. Its silicon vertex detector, named VELO for VErtex LOcator, will precisely reconstruct the primary pp interaction vertex, the displaced B-decay vertex and tracks originating from them. The use of the VELO in the LHCb trigger together with its operation in a harsh radiation environment puts additional constraints on the design. The project is soon entering the production phase. Recent results on the tests of prototype modules and components are presented with a focus on the sensor and front-end chip performance.

The FEDRA—Framework for emulsion data reconstruction and analysis in the OPERA experiment

OPERA is a massive lead/emulsion target for a long-baseline neutrino oscillation search. More than 90% of the useful experimental data in OPERA will be produced by the scanning of emulsion plates with the automatic microscopes. The main goal of the data processing in OPERA will be the search, analysis and identification of primary and secondary vertices produced by neutrino in lead-emulsion target. The volume of middle- and high-level data to be analysed and stored is expected to be of the order of several Gb per event. The storage, calibration, reconstruction, analysis and visualization of this data is the task of FEDRA system written in C ++ and based on ROOT framework. The system is now actively used for processing of test beams and simulation data. Several interesting algorithmic solutions permits us to make effective code for fast pattern recognition in heavy signal/noise conditions. The system consists of the storage part, intercalibration and segments linking part, track finding and fitting, vertex finding and fitting and kinematical analysis parts. Kalman Filtering technique is used for tracks & vertex fitting. ROOT-based event display is used for interactive analysis of the special events.

Experience with the NA60 silicon pixel vertex tracker in a harsh radiation environment

The NA60 experiment at CERN's Super Proton Synchrotron studies the production of open charm and prompt dimuons in collisions induced by heavy-ion and proton beams on nuclear targets. The experimental setup includes a dimuon spectrometer previously used in the NA50 experiment, and a new silicon vertex tracker: a telescope built from 12 stations of radiation tolerant pixel detectors placed close to the target inside of a 2.5 T dipole field. For the first time under such harsh radiation conditions, the pixel telescope tracks the large number of charged particles produced at the target. Its good spatial and momentum resolution enables the reconstruction of primary and secondary vertices, and the matching of two of the tracks with the two muons that gave the trigger in the muon spectrometer, placed behind the hadron absorber. In Fall 2003, the NA60 experiment performed a five week long physics run with a beam of 158 GeV/nucleon Indium ions colliding with a segmented Indium target. The run yielded data from several hundred million dimuon and minimum bias triggers. The pixel detectors were exposed to high levels of radiation inhomogeneously distributed over its acceptance. The silicon sensors closest to the beam axis underwent type inversion. This article discusses selected aspects of the silicon pixel detector's design and operation. Its performance is illustrated, in particular, by the vastly improved dimuon mass resolution. The last section discusses the re-utilization of the irradiated pixel detectors in a vertex tracker optimized for NA60's proton-nucleus run in 2004.

The performance of the CMS tracking

Track and vertex reconstruction in the CMS detector use the information from the silicon pixel and the silicon strip detectors. The track and vertex fitting algorithms are based on the Kalman filter approach. The performance of the tracking procedure is evaluated in terms of efficiency and parameter resolution. The vertex reconstruction performance is reported in terms of primary vertex resolution. Some results obtained with a partial/conditional track reconstruction, used for High-Level Trigger algorithms are also given.

Differences between somatosensory-evoked potentials recorded from the ventral posterolateral thalamic nucleus, primary somatosensory cortex and vertex in the rat

Somatosensory-evoked potential (SEP) components recorded over the primary somatosensory cortex (SI) and vertex in the rat within the 10–30 ms latency range were characterised with respect to the anatomy and function of the primary somatosensory pathway. To this aim, these components were compared to SEP components in the similar latency range recorded from the ventral posterolateral thalamic (VPL) nucleus, a nucleus known to be part of the subcortical structure of the primary somatosensory pathway and were described with respect to their stimulus-response characteristics and their response to the μ-opioid agonist fentanyl. The VPL positive (P)11–negative (N)18–P22 and SI P13–N18–P22 differed with respect to peak occurrence (P11 versus P13, respectively) and waveform morphology, but did not differ with respect to stimulus-response characteristics and their response to fentanyl. When compared to the vertex P15–N19–P26, the VPL P11–N18–P22 and SI P13–N18–P22 complex follow a relatively fast acquisition in stimulus intensity-response and were affected significantly less to increasing stimulus frequencies and to fentanyl. These results demonstrated that when compared to the VPL-SEP and SI-SEP, the Vx-SEP was modulated differently by the experimental conditions. It is suggested that this may be related to involvement of neural structures within different functional somatosensory pathways.

The performance of the CMS Pixel Detector and the primary-vertex finding

The CMS Pixel Detector layout, the coverage and the hit resolution are presented. Two algorithms of primary vertex finding based on tracks reconstructed with three pixel hits are described. The primary vertex reconstruction based on pixel hits is shown to be particularly suitable for the CMS High Level Trigger.

The LHCb vertex locator

LHCb is an experiment at the Large Hadron Collider (LHC), dedicated to the study of b-hadron physics. The Vertex Locator (VELO) is a sub-detector which reconstructs primary and secondary vertices, which is of importance for the processes under study. It is a silicon micro-strip detector operated in a harsh radiation environment with demands of high read-out speed and the use of minimal material. In this paper, the LHCb VELO is introduced and the technology choices of the detector are motivated. We report on the present status of the project and one possible upgrade technology is presented.

Measurement of $F_2^{c\bar{c}}$ and $F_2^{b\bar{b}}$ at high Q 2 using the H1 vertex detector at HERA

Measurements are presented of inclusive charm and beauty cross sections in e^+p collisions at HERA for values of photon virtuality Q^2 > 150 GeV^2 and of inelasticity 0.1 < y < 0.7. The charm and beauty fractions are determined using a method based on the impact parameter, in the transverse plane, of tracks to the primary vertex, as measured by the H1 vertex detector. The data are divided into four regions in Q^2 and Bjorken x, and values for the structure functions F_2^{c\bar{c}} and F_2^{b\bar{b}} are obtained. The results are found to be compatible with the predictions of perturbative quantum chromodynamics.

Comparison of predictions for nuclear effects in the Marteau model with the NUX+FLUKA scheme

Nuclear effects in neutrino-nucleus reactions simulated by means of the NUX+FLUKA Monte Carlo generator are compared with the theoretical predictions of the Marteau model. Pion absorption in NUX+FLUKA and non-pionic Delta decays in the Marteau model differ by about 30%. The fraction of pions produced due to the re-interactions after primary quasi-elastic vertex is in the NUX+FLUKA scheme much higher then provided by the Marteau model.

Differences between primary somatosensory cortex- and vertex-derived somatosensory-evoked potentials in the rat

The somatosensory-evoked potential (SEP) elicited by high-intensity stimulation potentially provides a reliable indicator of analgesic efficacy since it reflects the level of activation of the nociceptive system. In the present study, components in the 10–30-ms latency range of SEPs recorded over the primary somatosensory cortex (SI-SEPs) and vertex (Vx-SEP) in the rat were characterized and compared. SEPs were elicited by electrical tail-base stimulation, and SI-SEPs and Vx-SEPs were recorded simultaneously. Responses to increasing stimulus intensity and stimulus frequency while awake and responses to bolus injection of fentanyl, thiopental, and ketamine were investigated. The SI-SEP positive component (P) occurring at 12 ms after stimulation (P12) showed a significantly lower intensity threshold and was significantly less affected by increasing stimulus frequency and by administration of the different drugs when compared to the Vx-SEP P15. The fact that a single stimulus modality results in different signal characteristics dependent on the recording site supports the view that different neural mechanisms involved in primary processing of somatosensory information are responsible for the generation of the SI-SEP P12 and Vx-SEP P15, respectively. This differentiation between SI-SEPs and Vx-SEPs potentially has distinct consequences using the SEP to evaluate nociception and analgesia in the rat model.

Sensitivity of robust vertex fitting algorithms

Robust vertex fitting algorithms are expected to improve the knowledge of the vertex position and of its uncertainty in the presence of mismeasured or misassociated tracks. Such contaminations are likely to happen in real data as well as in realistic detector simulations. This paper describes a simulation study of the sensitivity of two types of robust algorithms: a trimmed least squares estimator and an adaptive estimator. The statistical properties of the algorithms are studied as a function of the source and the level of contamination, and compared to the results obtained with classical least squares estimators. Two typical event topologies are studied: one resembling a high multiplicity primary vertex with a possible contamination from a nearby vertex and one resembling a low multiplicity secondary vertex in a jet.

A measurement of the branching fractions of the b-quark into charged and neutral b-hadrons

The production fractions of charged and neutral b-hadrons in b-quark events from Z0 decays have been measured with the DELPHI detector at LEP. An algorithm has been developed, based on a neural network, to estimate the charge of the weakly-decaying b-hadron by distinguishing its decay products from particles produced at the primary vertex. From the data taken in the years 1994 and 1995, the fraction of b̄-quarks fragmenting into positively charged weakly-decaying b-hadrons has been measured to be: f+=42.09±0.82(stat)±0.89(syst)%. Subtracting the rates for charged Ξ̄b+ and Ω̄b+ baryons gives the production fraction of B+ mesons: fBu=40.99±0.82(stat)±1.11(syst)%.

Status of the LHCb VErtex LOcator

LHCb is a single-arm spectrometer at the LHC. It is dedicated to the study of CP violation in the B-hadron system. The VErtex LOcator (VELO) is a silicon microstrip detector providing accurate measurements of event primary and secondary vertices, impact parameters, and tracks. The second-level trigger decision of LHCb is mainly based on information from a full readout of the VELO. This document gives a general introduction to LHCb as a context for a more extensive description of the VELO. The VELO design emphasises the need for precise reconstruction of tracks down to momenta of a few GeV. The VELO operates inside the LHC beam-pipe, and the sensors, the hybrids, and the foil separating the primary and secondary vacuua must be built with the minimum possible material. The R– φ strip layout is optimised for efficient trigger operation and precise measurements at the smallest radii. The performance must be maintained in the harsh radiation environment close to the LHC beams. These issues have led to a choice of n-on-n, double metal technology for the VELO. This document describes the current status of the VELO design, incorporating changes which have been made in the context of the recent overall optimisation of the LHCb detector (“LHCb light”) (Status of the LHCb Detector Reoptimisation, 2003, CERN/LHCC/2003-003), and summarises the underlying R&D for the technology choice. Issues concerning the electronics, the mechanical integration into LHCb and the LHC machine are discussed in detail elsewhere (LHCb Vertex Locator Technical Design Report, 2001, CERN/LHCC/2001-011).

CDF — secondary vertex trigger

At the beginning of 2002 a new data taking with an upgraded trigger system started for the CDF collaboration. One of the major improvements is the track trigger. A fast processor reconstructs tracks in the central drift chamber and the Silicon Vertex Tracker combines these tracks with the silicon vertex detector information to have track parameters with a precision as good as the offline reconstruction. This system allows CDF to trigger on tracks significantly displaced from the primary vertex with high efficiency for signal events like charm and beauty and to keep low background rates. The performances, in terms of resolution and efficiency, of both the processors are illustrated and the firsts physics results are discussed.

New developments in vertex reconstruction for CMS

Abstract Presently, two kinds of least-squares (LS) vertex fits are implemented in the ORCA reconstruction program ( http://cmsdoc.cern.ch/orca ) of the CMS experiment ( http://cmsinfo.cern.ch ): a full Kalman filter, and an iterative fit working with the impact points of the tracks with respect to an expansion point. In this contribution we concentrate on nonlinear, robust estimators which are insensitive to outlying observations. The aim is to improve the recognition of outliers, to lower the bias in the final fit, and to achieve a better separation between primary vertices and secondary vertices. Robust vertex estimates should also be good starting points for more complex algorithms, such as a multivertex fit.

Primary Vertex in the ALICE Experiment in Absence of the Event Reconstruction

ALICE is a general-purpose apparatus for the study of ultra-relativistic heavy-ion collisions at the Large Hadron Collider of the CERN. The study of such reactions demands the determination of the primary vertex in three dimensions with good resolution. We have developed an algorithm for finding the vertex position even in absence of the event reconstruction. The performances of such an algorithm have been studied as a function of the vertex position, particle multiplicity and magnetic field.

Vertex finding in ALICE by the use of silicon pixel layers in the inner tracking system

The performance of the Inner Tracking System of the ALICE detector for primary vertex estimation is discussed. A simulation study of the vertex reconstruction in ALICE through the information given by the two pixel layers is reported. Vertex resolution was studied as a function of the nominal vertex location and of the particle multiplicity.