Vertex Tracker Research Articles

LHCb potential to discover long-lived new physics particles with lifetimes above 100 ps

For years, it has been believed that the main LHC detectors can play only a limited role of a lifetime frontier experiment exploring the parameter space of long-lived particles (LLPs)—hypothetical particles with tiny couplings to the Standard Model. This paper demonstrates that the LHCb experiment may become a powerful lifetime frontier experiment if it uses the new Downstream algorithm reconstructing tracks that do not allow hits in the LHCb vertex tracker. In particular, for many LLP scenarios, LHCb may be as sensitive as the proposed experiments beyond the main LHC detectors for various LLP models, including heavy neutral leptons, dark scalars, dark photons, and axion-like particles.

ALICE ITS 3: the first truly cylindrical inner tracker

The high integration density of MAPS, with silicon sensor and readout electronics implemented in the same device, allows very thin structures with a greatly reduced material budget. Thicknesses of (50 μm), values at which silicon chips become flexible, are readily used in many applications. In addition, MAPS can be produced in sensors of wafer size by a process known as stitching. This in turn allows to build detector elements that are large enough to cover full tracker half-layers with single bent sensors. The ALICE ITS 3 project is planning to build a new vertex tracker based on truly cylindrical wafer-scale sensors, with <0.05% X/X0 per layer and located as close as 18 mm to the interaction point. R&D on all project aspects (including mechanics for bent wafer-scale devices, test beams of bent MAPS, design of stitched sensors) is rapidly progressing with the aim for installation during LHC long shutdown 3 (2025–2027). This contribution summarises the project motivation, its R&D schedule, and will show selected highlights of recently accomplished project milestones, including full-scale engineering prototypes with dummy chips and small-scale, fully functional assemblies of functional, bent MAPS.

Incremental Graph Computation: Anchored Vertex Tracking in Dynamic Social Networks

User engagement has recently received significant attention in understanding the decay and expansion of communities in many online social networking platforms. When a user chooses to leave a social networking platform, it may cause a cascading dropping out among her friends. In many scenarios, it would be a good idea to persuade critical users to stay active in the network and prevent such a cascade because critical users can have significant influence on user engagement of the whole network. Many user engagement studies have been conducted to find a set of critical <i>(anchored)</i> users in the static social network. However, social networks are highly dynamic and their structures are continuously evolving. In order to fully utilize the power of anchored users in evolving networks, existing studies have to mine multiple sets of anchored users at different times, which incurs an expensive computational cost. To better understand user engagement in evolving network, we target a new research problem called <i>Anchored Vertex Tracking</i> (AVT) in this paper, aiming to track the anchored users at each timestamp of evolving networks. Nonetheless, it is nontrivial to handle the AVT problem which we have proved to be NP-hard. To address the challenge, we develop a greedy algorithm inspired by the previous anchored <inline-formula><tex-math notation="LaTeX">$k$</tex-math></inline-formula>-core study in the static networks. Furthermore, we design an incremental algorithm to efficiently solve the AVT problem by utilizing the smoothness of the network structure&#x0027;s evolution. The extensive experiments conducted on real and synthetic datasets demonstrate the performance of our proposed algorithms and the effectiveness in solving the AVT problem.

Numerical study of droplet thermocapillary migration behavior on wettability-confined tracks using a three-dimensional color-gradient lattice Boltzmann model

Thermocapillary migration describes the phenomenon whereby liquid droplets move from warm to cold regions on a nonuniformly heated hydrophilic surface. Surface modifications can be applied to manipulate this migration process. In the present study, a three-dimensional color-gradient lattice Boltzmann model is used to investigate the droplet migration behavior on a series of wettability-confined tracks subject to a uniform temperature gradient. The model is validated by simulating the thermocapillary-driven flow with two superimposed planar fluids in a heated microchannel and the capillary penetration of a wetting fluid in a capillary tube. An in-depth study of the wettability-confined tracks confirms the capacity to manipulate the droplet migration process, that is, the wettability-confined tracks can accelerate thermocapillary migration compared with a smooth surface. The effects of changes in the viscosity ratio and interfacial tension are investigated, and it is found that a lower viscosity ratio and larger interfacial tension cause the droplet to migrate faster. Moreover, a systematic study of the track vertex angle is conducted, and the mechanism through which this parameter influences the droplet migration is analyzed. Then the effect of the track wettability on droplet migration is explored and analyzed. Finally, a serial wettability-confined track is designed to realize long-distance droplet migration, and the narrow side width of the connection region is found to play a key role in determining whether the droplets can migrate over long distances. The results provide some guidance for designing tracks that enable precise droplet migration control.

Heavy flavor physics with the sPHENIX MAPS vertex tracker upgrade

The sPHENIX detector at the Relativistic Heavy Ion Collider will measure a suite of unique jet and Upsilon observables with unprecedented statistics and kinematic reach. A MAPS-based vertex detector upgrade to sPHENIX, the MVTX, will provide a precise determination of the impact parameter of tracks relative to the collision vertex in high multiplicity heavy ion collisions. The MVTX utilizes the latest generation of MAPS technology to provide precision tracking with high tracking efficiency over a broad momentum range in the high luminosity RHIC environment. These new capabilities will enable precision measurements of open heavy flavor observables, covering an unexplored kinematic regime at RHIC. The physics program, its potential impact, and recent detector development of the MVTX will be discussed.

Online Track Vertex Reconstruction Method Based on an Artificial Neural Network for MPGD

In this paper, an online vertex reconstruction algorithm based on an artificial neural network (ANN) was proposed for the micro-pattern gaseous detector (MPGD). A simulation based on Geant4 was performed to generate the training and testing samples for the two cascade neural networks. Compared with a center-of-mass reconstruction, the proposed method shows better precision and much higher efficiency. Furthermore, a scheme for implementing the proposed algorithm on a Field-Programmable Gate Array (FPGA) chip is also presented to demonstrate that the algorithm could be integrated in a modern data acquisition (DAQ) system for online imaging techniques.

Real-time reconstruction of long-lived particles at LHCb using FPGAs

Finding tracks downstream of the magnet at the earliest LHCb trigger level is not part of the baseline plan of the upgrade trigger, on account of the significant CPU time required to execute the search. Many long-lived particles, such as KS 0 and strange baryons, decay after the vertex track detector, so that their reconstruction efficiency is limited. We present a study of the performance of a future innovative real-time tracking system based on FPGAs, developed within a R&D effort in the context of the LHCb Upgrade Ib (LHC Run 4), dedicated to the reconstruction of the particles downstream of the magnet in the forward tracking detector (Scintillating Fibre Tracker), that is capable of processing events at the full LHC collision rate of 30 MHz.

The CLAS12 Silicon Vertex Tracker

For the 12 GeV upgrade of Jefferson Laboratory, a Silicon Vertex Tracker (SVT) has been designed for the CLAS12 spectrometer using single-sided microstrip sensors fabricated by Hamamatsu Photonics. The sensors have a graded angle design to minimize dead areas and a readout pitch of 156μm, with intermediate strips. Each double-sided SVT module hosts three daisy-chained sensors on each side with a full strip length of 33 cm. There are 512 channels per module, read out by four Fermilab Silicon Strip Readout (FSSR2) chips, featuring data-driven architecture, mounted on a rigid–flex hybrid board. The modules are assembled in a barrel configuration using a unique cantilevered geometry to minimize the amount of material in the tracking volume. This paper is focused on the design, qualification of the performance, and experience in operating and commissioning the tracker during the first year of the data taking.

The CLAS12 Spectrometer at Jefferson Laboratory

The CEBAF Large Acceptance Spectrometer for operation at 12 GeV beam energy (CLAS12) in Hall B at Jefferson Laboratory is used to study electro-induced nuclear and hadronic reactions. This spectrometer provides efficient detection of charged and neutral particles over a large fraction of the full solid angle. CLAS12 has been part of the energy-doubling project of Jefferson Lab’s Continuous Electron Beam Accelerator Facility, funded by the United States Department of Energy. An international collaboration of 48 institutions contributed to the design and construction of detector hardware, developed the software packages for the simulation of complex event patterns, and commissioned the detector systems. CLAS12 is based on a dual-magnet system with a superconducting torus magnet that provides a largely azimuthal field distribution that covers the forward polar angle range up to 35∘, and a solenoid magnet and detector covering the polar angles from 35° to 125° with full azimuthal coverage. Trajectory reconstruction in the forward direction using drift chambers and in the central direction using a vertex tracker results in momentum resolutions of <1% and <3%, respectively. Cherenkov counters, time-of-flight scintillators, and electromagnetic calorimeters provide good particle identification. Fast triggering and high data-acquisition rates allow operation at a luminosity of 1035 cm−2s−1. These capabilities are being used in a broad program to study the structure and interactions of nucleons, nuclei, and mesons, using polarized and unpolarized electron beams and targets for beam energies up to 11 GeV. This paper gives a general description of the design, construction, and performance of CLAS12.

The CLAS12 Micromegas Vertex Tracker

The Micromegas Vertex Tracker was designed to improve upon the tracking capabilities of the baseline design of the CLAS12 spectrometer in Hall B at Jefferson Laboratory. A Barrel Micromegas Tracker made with six concentric cylinders, each made of three 120∘-sector tiles, surrounds the Silicon Vertex Tracker, and a Forward Micromegas Tracker composed of 6 disks is placed 30 cm downstream of the liquid-hydrogen target. Both trackers sit in a 5 T solenoid magnetic field. All Micromegas elements are based on resistive technology to withstand luminosities up to 1035 cm−2 s−1, as well as on bulk technology to enforce gain uniformity and mechanical robustness. Due to the high magnetic field, dedicated electronics have been designed and displaced ∼2 m away from the detectors. The electronics readout is based on the DREAM ASICs that allow sustained operation up to 20 kHz trigger rate at the maximum luminosity.

Restoration of the natural E(1/2[formula omitted]) - E(3/2[formula omitted]) energy splitting in odd-K isotopes towards N = 40

We report on the first γ-ray spectroscopy of 51,53K produced via the 52,54Ca(p,2p) reactions at ∼250 MeV/nucleon. Unambiguous final-state angular-momentum assignments were achieved for beam intensities down to few particles per second by using a new technique based on reaction vertex tracking combined with a thick liquid-hydrogen target. Through γ-ray spectroscopy and exclusive parallel momentum distribution analysis, 3/2+ ground states and 1/2+ first excited states in 51,53K were established quantifying the natural ordering of the 1d3/2 and 2s1/2 proton-hole states that are restored at N = 32 and 34. State-of-the-art ab initio calculations and shell-model calculations with improved phenomenological effective interactions reproduce the present data and predict consistently the increase of the E(1/21+) - E(3/21+) energy differences towards N = 40.

Bubbly Cell Tracking Velocimetry – An algorithm for cell vertex and cell shape tracking

Bubbly Cell Tracking Velocimetry – An algorithm for cell vertex and cell shape tracking

Direct photon measurements in He+Au collisions at 200 GeV

The PHENIX experiment has published direct photon yields from different collisions at RHIC energies and discovered a large excess of low-pT direct photons in Au+Au collisions at GeV compared to reference p+p collisions, which has been attributed to thermal radiation from the hot and dense medium. PHENIX has also developed a new technique to identify conversion photons without assuming the radius where the conversion happened. This method greatly increases the available statistics and reduces systematic uncertainties. This paper presents the results obtained from real photons in the electromagnetic calorimeter and photons converted at the layers of Silicon Vertex Tracker (VTX).

Geometry Processing Problems Using the Total Variation of the Normal Vector Field

AbstractThis paper presents a novel approach to the formulation and solution of discrete geometry processing problems including mesh denoising. The main quantity of interest is the piecewise constant unit normal vector field, which we consider on piecewise flat, triangulated surfaces. In a similar fashion as one does for images defined on ‘flat’ domains, our goal is to remove noise while preserving shape features such as sharp edges. To this end, we model a denoising problem via a quadratic vertex tracking term and a regularizer based on the total variation of the normal vector field. Since the latter has values on the unit sphere, its total variation reduces to a finite sum of the geodesic distances of neighboring normals. We solve the model numerically by applying split‐Bregmann iterations and provide results for the ‘fandisk’ benchmark.

Comparison of Silicon, Germanium, Gallium Nitride, and Diamond for using as a detector material in experimental high energy physics

Abstract Semiconductor detectors with Silicon as the sensor material are widely used in High Energy Physics (HEP) experiments for high precision tracking and determination of primary and secondary vertices with good spatial resolution. They are close to the interaction point, so they are prone radiation damage due to the high fluence of produced particles. The choice of semiconductor material is based on the signal to noise ratio, multiple scattering, pulse timing and radiation hardness. In this paper, we compare the suitability of Silicon (Si), Germanium (Ge), Gallium Nitride (GaN), and Diamond for high energy and high luminosity experiments. In addition, we also show the results on the growth of diamond films and their characterizations.

SPHENIX - a new jet detector at RHIC

sPHENIX is a new state-of-the-art detector optimized for measurements of jets and heavy flavor which will take advantage of increased luminosity available at the Relativistic Heavy Ion Collider (RHIC). It comprises vertex tracking and hadronic and electromagnetic calorimetry. This enables studies of jet structure, heavy flavor jets, open heavy flavor, and quarkonia, the pillars of the sPHENIX physics program. These measurements will complement measurements at the LHC and enable determination of the properties of the medium created in heavy ion collisions to high precision, including its temperature dependence. This talk will discuss the detector design and key measurements enabled by the new detector, as well as the status of the project itself.

Tracking with the MINOS Time Projection Chamber

We report on the performance of the MINOS Time Projection Chamber developed as a vertex tracker to study exotic nuclei produced from hydrogen-induced knockout via in-beam γ-ray and invariant-mass spectroscopy. In-beam measurements with 4He and 20Ne beams at 200 and 350 MeV/nucleon, respectively, were performed at the HIMAC facility. The tracking algorithm for protons after quasi-free scattering is described. Realistic simulations and physics experiments are compared and show a good agreement. The vertex position resolution reaches 5 mm FWHM, mostly from re-scattering with the target and the Aluminum reaction chamber. The overall efficiency of vertex reconstruction is also benchmarked with the first experimental campaign data performed at the RIBF, confirming an overall efficiency better than 90% for physics experiments.

Highlights from PHENIX at RHIC

Hadrons conveying strange quarks or heavy quarks are essential probes of the hot and dense medium created in relativistic heavy-ion collisions. With hidden strangeness, ϕ meson production and its transport in the nuclear medium have attracted high interest since its discovery. Heavy quark-antiquark pairs, like charmonium and bottomonium mesons, are mainly produced in initial hard scattering processes of partons. While some of the produced pairs form bound quarkonia, the vast majority hadronize into particles carrying open heavy flavor. In this context, the PHENIX collaboration carries out a comprehensive physics program which studies the ϕ meson production, and heavy flavor production in relativistic heavy-ion collisions at RHIC. In recent years, the PHENIX experiment upgraded the detector in installing silicon vertex tracker (VTX) at mid-rapidity region and forward silicon vertex tracker (FVTX) at the forward rapidity region. With these new upgrades, the experiment has collected large data samples, and enhanced the capability of heavy flavor measurements via precision tracking. This paper summarizes the latest PHENIX results concerning ϕ meson, open and closed charm and beauty heavy quark production in relativistic heavy-ion collisions. These results are presented as a function of rapidity, energy and system size, and their interpretation with respect to the current theoretical understanding.

Operational Experience With the Readout System of the MINOS Vertex Tracker

The magic numbers off stability (MINOS) vertex tracker is a compact instrument built for in-beam spectroscopy of exotic nuclei. Its main component is a ~30–cm-long hollow cylinder shape time projection chamber (TPC) surrounding a liquid hydrogen target. The anode of the TPC is read out by a Micromegas detector segmented in 18 concentric rings of 2 mm $\times2$ mm pads totaling 3604 channels. A dedicated system based on the AFTER and AGET chips was designed to read out this TPC, and the required software to configure, monitor, and acquire data was developed. After a construction period of two years and the validation in a test beam, four nuclear physics experiments exploiting MINOS have successfully been conducted at RIKEN, Japan. We describe the prominent aspects of the readout system of MINOS and we report on lessons learned during the three years of exploitation.

Studies for an upgrade of ALICE Inner Tracking System: Pixel chip characterization

Inner Tracking System (ITS) of ALICE is used for vertex determination and tracking. Future heavy-ion program at the LHC aims to run with high luminosity. To address this challenge, upgrade program of ITS is underway, which aims at better position resolution (factor of 3), high detection efficiency (>99%), high-rate readout capabilities (100 kHz for Pb-Pb) and moderate radiation hardness (> 700 krad). The new ITS will be composed with 7 layers of silicon pixel chip based on Monolithic Active Pixel Sensor (MAPS) technology. The characterization test of various version of prototype chips at different phases of development has been performed. This contribution will provide the main characterization results obtained from the measurements performed at laboratories and using test beam for finalizing the pixel chip specification.