Jet Trigger Research Articles

The ATLAS jet trigger for Run 3 of the LHC

The ATLAS jet trigger is instrumental in selecting events both for Standard Model measurements and Beyond the Standard Model physics searches. Non-standard triggering strategies, such as storing only a small fraction of trigger objects for each event, avoids bandwidth limitations and increases sensitivity to low-mass and low-momentum objects. These events are used by Trigger Level Analyses, which can reach regions of parameter space that would otherwise be inaccessible. To this end, the calibration of trigger-level jets is imperative both to ensure good trigger performance across the ATLAS physics programme and to provide well-measured jets for Trigger Level Analysis. This contribution presents an introduction to the ATLAS jet trigger for Run-3 of the LHC and discusses the performance of the trigger jet calibration. These studies will allow us to commission a Run-3 trigger jet calibration that provides excellent performance across a broad jet transverse momentum range starting from 25 GeV.

Wave propagation of bending jet in electrospinning process

The electrospinning process features bending jets in space and solidified nanofibers on a collector. Although electrospun nanofibers have been widely applied, the wave characteristics, especially the first jet bend and tapered envelope cone profile, of bending jets are not fully comprehended. In this work, a spatial normal mode k− is true to characterize the convective instability of a bending jet. Some real wave variables are measured and calculated. It is observed that the first jet bend occurs at the jet end. The instability grows quickly at the early stage of a wave. Underdeveloped dispersive waves are temporally and spatially unstable. When dispersive waves develop to a mature stage, the instability grows slowly, and developed dispersive waves are only spatially unstable. Furthermore, the energy ratio of electric energy to kinematic energy accounts for the wave characteristics of a bending jet. A high energy ratio may stabilize the jet, and a very low energy ratio destabilizes the jet. The stabilizing effect of the high energy ratio suppresses the growth of dispersive waves at the jet source. Once residual charges within the jet trigger small perturbations to the electric field near the plate owing to the Coulomb repulsive effect of like charges, the destabilizing effect of the low energy ratio causes the rapid development of small perturbation first at the jet end. The inhomogeneous distribution of electric energy contributes to the tapered envelope cone profile of a bending jet. Numerically and experimentally, the wave speed is in the order of 1 m/s, and the growth rate is in the order of 102 m−1. The numerical results are in accordance with the experimental results.

UVIT view of Centaurus A: a detailed study on positive AGN feedback

ABSTRACT Supermassive black holes at the centre of active galactic nuclei (AGNs) produce relativistic jets that can affect the star formation characteristics of the AGN hosts. Observations in the ultraviolet (UV) band can provide an excellent view of the effect of AGN jets on star formation. Here, we present a census of star formation properties in the Northern Star-forming Region (NSR) that spans about 20 kpc of the large radio source Centaurus A hosted by the giant elliptical galaxy NGC 5128. In this region, we identified 352 UV sources associated with Cen A using new observations at an angular resolution of <1.5 arcsec observed with the Ultra-Violet Imaging Telescope (UVIT) onboard AstroSat. These observations were carried out in one far-ultraviolet (FUV; λmean = 1481 Å) and three near-ultraviolet (NUV; with λmean of 2196, 2447, and 2792 Å, respectively) bands. The star-forming sources identified in UV tend to lie in the direction of the jet of Cen A, thereby suggesting jet triggering of star formation. Separating the NSR into Outer and Inner regions, we found the stars in the Inner region to have a relatively younger age than the Outer region, suggesting that the two regions may have different star formation histories. We also provide the UVIT source catalogue in the NSR.

Estimation of the jet inclination angle for the TDE Swift J1644+57

ABSTRACT An estimate of the jet inclination angle relative to the accreting black hole’s spin can be useful to probe the jet triggering mechanism and the disc–jet coupling. A tidal disruption event (TDE) of a star by a supermassive spinning black hole provides an excellent astrophysical laboratory to study the jet direction through the possibility of jet precession. In this work, we report a new method to constrain the jet inclination angle β and apply it to the well-sampled jetted TDE Swift J1644+57. This method involves X-ray data analysis and comparisons of jet models with broad properties of the observed X-ray dips, to estimate the upper limit of the extent of the contribution of a plausible jet precession to these X-ray dips. From this limit, we find that β is very likely to be less than ∼15° for Swift J1644+57. Such a well-constrained jet inclination angle could be useful to probe the jet physics. The main advantage of our method is that it does not need to assume an origin of the observed X-ray dips, and the conclusion does not depend on any particular type of jet precession (e.g. the one due to the Lense–Thirring effect) or any specific value of precession frequency or any particular jet model. These make this method reliable and applicable to other jetted TDEs, as well as to other jetted accreting systems.

Gamma-ray emitting narrow-line Seyfert 1 galaxies: Past, present, and future

This article reviews our current understanding about $\gamma$-ray detected narrow-line Seyfert 1 ($\gamma$-NLSy1) galaxies. The detection with the Large Area Telescope onboard {\it Fermi}~Gamma-ray Space Telescope has provided the strongest evidence for the presence of closely aligned relativistic jet in these intriguing active galactic nuclei (AGN) and opened up a realm to explore the physical conditions needed to launch the jet in a different central engine and host galaxy environment than that is known for blazars. Promising results acquired from various multi-wavelength campaigns are converging to a scenario in which the $\gamma$-NLSy1 galaxies can be considered as `young' blazars. These enigmatic sources hold the key to unravel the jet triggering mechanism and evolution of the AGN phase of a galaxy, in general. As such, $\gamma$-NLSy1s should be considered as one of the top priority targets for next generation observational facilities.

Search for Low-Mass Dijet Resonances Using Trigger-Level Jets with the ATLAS Detector in pp Collisions at sqrt[s]=13 TeV.

Searches for dijet resonances with sub-TeV masses using the ATLAS detector at the Large Hadron Collider can be statistically limited by the bandwidth available to inclusive single-jet triggers, whose data-collection rates at low transverse momentum are much lower than the rate from standard model multijet production. This Letter describes a new search for dijet resonances where this limitation is overcome by recording only the event information calculated by the jet trigger algorithms, thereby allowing much higher event rates with reduced storage needs. The search targets low-mass dijet resonances in the range 450-1800GeV. The analyzed data set has an integrated luminosity of up to 29.3 fb^{-1} and was recorded at a center-of-mass energy of 13TeV. Noexcesses are found; limits are set on Gaussian-shaped contributions to the dijet mass distribution from new particles and on a model of dark-matter particles with axial-vector couplings to quarks.

SPHENIX Calorimeter Design and Jet Performance

The PHENIX collaboration is planning a detector upgrade, sPHENIX, which consists of large acceptance calorimetry and tracking detectors built around the superconducting solenoid recently shipped to Brookhaven from the decommissioned BaBar experiment at SLAC. The sPHENIX calorimeter system includes three radial layers of sampling calorimeters, a tungsten-scintillating fiber electromagnetic calorimeter, and two longitudinally segmented sampling hadron calorimeters that are made of scintillator tiles and steel plates. Together, they provide hermetic coverage in |η|<1 for calorimetry based jet measurements as well as minimal bias jet trigger capability, which coupled with high resolution tracking, enable an extremely rich jet physics program at RHIC.

Delayed triggering of radio active galactic nuclei in gas-rich minor mergers in the local Universe

We examine the processes triggering star formation and Active Galactic Nucleus (AGN) activity in a sample of 25 low redshift ($z<0.13$) gas-rich galaxy mergers observed at milli-arcsecond resolution with Very Long Baseline Interferometry as part of the mJy Imaging VLBA Exploration at 20cm (mJIVE-20) survey. The high ($>10^7$ K) brightness temperature required for an mJIVE-20 detection allows us to unambiguously identify the radio AGN in our sample. We find three such objects. Our VLBI AGN identifications are classified as Seyferts or LINERs in narrow line optical diagnostic plots; mid-infrared colours of our targets and the comparison of H$\alpha$ star formation rates with integrated radio luminosity are also consistent with the VLBI identifications. We reconstruct star formation histories in our galaxies using optical and UV photometry, and find that these radio AGN are not triggered promptly in the merger process, consistent with previous findings for non-VLBI samples of radio AGN. This delay can significantly limit the efficiency of feedback by radio AGN triggered in galaxy mergers. We find that radio AGN hosts have lower star formation rates than non-AGN radio-selected galaxies at the same starburst age. Conventional and VLBI radio imaging shows these AGN to be compact on arcsecond scales. Our modeling suggests that the actual sizes of AGN-inflated radio lobes may be much larger than this, but these are too faint to be detected in existing observations. Deep radio imaging is required to map out the true extent of the AGN, and to determine whether the low star formation rates in radio AGN hosts are a result of the special conditions required for radio jet triggering, or the effect of AGN feedback.

The performance of the jet trigger for the ATLAS detector during 2011 data taking.

The performance of the jet trigger for the ATLAS detector at the LHC during the 2011 data taking period is described. During 2011 the LHC provided proton–proton collisions with a centre-of-mass energy of 7 TeV and heavy ion collisions with a 2.76 TeV per nucleon–nucleon collision energy. The ATLAS trigger is a three level system designed to reduce the rate of events from the 40 MHz nominal maximum bunch crossing rate to the approximate 400 Hz which can be written to offline storage. The ATLAS jet trigger is the primary means for the online selection of events containing jets. Events are accepted by the trigger if they contain one or more jets above some transverse energy threshold. During 2011 data taking the jet trigger was fully efficient for jets with transverse energy above 25 GeV for triggers seeded randomly at Level 1. For triggers which require a jet to be identified at each of the three trigger levels, full efficiency is reached for offline jets with transverse energy above 60 GeV. Jets reconstructed in the final trigger level and corresponding to offline jets with transverse energy greater than 60 GeV, are reconstructed with a resolution in transverse energy with respect to offline jets, of better than 4 % in the central region and better than 2.5 % in the forward direction.

ATLAS jet trigger performance during run1 and preparation for run2

During run 1 the Large Hadron Collider collided proton beams at the centre-of-mass energy of 7 and 8 TeV, as well as heavy ions at the centre-of-mass energy of 2.76 TeV. The ATLAS trigger is designed to reduce the rate of events from the nominal maximum bunch-crossing rate of 40 MHz to approximately 400 Hz, which is then written on disk offline. The online selection of events containing jets uses a set of jet triggers. The rate from jet events is very high, with a steeply falling spectrum in the distribution of the transverse energy. These jet triggers have been designed to keep an approximately constant jet rate of 0.5 Hz in various transverse momentum intervals and account for around 10% of the total ATLAS trigger rate.During run 1 the jet trigger was fully efficient at Level 1 for jets with transverse energies above 25 GeV, whilst at Event Filter full efficiency was reached for jets with transverse energies above 60 GeV.The overall performance of the jet trigger during the 2011 data taking is summarised, together with important updates made during 2012. In addition, the expected performance of the jet trigger in run 2, to start in 2015, is described.

The ATLAS jet trigger performance in LHC Run I and Run II updates

The Large Hadron Collider (LHC) provides proton-proton collisions with a nominal rate of 40 MHz, and the ATLAS trigger performs the first event selections online during data- taking. The ATLAS jet trigger is an important element of the ATLAS trigger system, selecting collision events containing high transverse energy jets, to provide data samples for studies ranging from Standard Model physics to searches for new physics at the LHC. During LHC Run I, the first LHC operation period from 2010 to 2012, the ATLAS jet trigger system improved as experience developed with triggering in a high luminosity and high event pileup environment. For the next LHC operation period, Run II, the system is being updated for further improved performance and stability. In this contribution, performance and improvements of the ATLAS jet trigger in Run I are presented. Updates for Run II are also shown.

The design and performance of the ATLAS jet trigger

The ATLAS jet trigger is an important element of the event selection process, providing data samples for studies of Standard Model physics and searches for new physics at the LHC. The ATLAS jet trigger system has undergone substantial modifications over the past few years of LHC operations, as experience developed with triggering in a high luminosity and high event pileup environment. In particular, the region-of-interest based strategy has been replaced by a full scan of the calorimeter data at the third trigger level, and by a full scan of the level-1 trigger input at level-2 for some specific trigger chains. Hadronic calibration and cleaning techniques are applied in order to provide improved performance and increased stability in high luminosity data taking conditions. In this note we discuss the implementation and operational aspects of the ATLAS jet trigger during 2011 and 2012 data taking periods at the LHC.

Measurement of charged particle RAA at high pT in PbPb collisions at sNN=2.76TeV with CMS

Charged particle transverse momentum (pT) spectra have been measured by CMS for pp and PbPb collisions at the same sqrt(sNN)=2.76 TeV collision energy per nucleon pairs. Calorimeter-based jet triggers are employed to enhance the statistical reach of the high-pT measurements. The nuclear modification factor (R_AA) is obtained in bins of collision centrality for the PbPb data sample dividing by the measured pp reference spectrum. In the range pT = 5-10 GeV/c, the charged particle yield in the most central PbPb collisions is suppressed by up to a factor of 7. At higher pT, this suppression is significantly reduced, approaching a factor of 2 for particles with pT = 40-100 GeV/c.

The Design and Performance of the ATLAS jet trigger

The ATLAS jet trigger, in combination with other triggers, provides an important ingredient to studies of Standard Model physics and searches for new physics at the LHC. The ATLAS jet trigger system has undergone substantial modifications over the past few years of LHC operations, as experience developed with triggering in a high luminosity and high event pileup environment. In particular, the region-of-interest (ROI) based strategy has been replaced by a full scan of the calorimeter data at the third trigger level, and by a full scan of the level-1 trigger input at level-2 for some specific trigger chains. Hadronic calibration and cleaning techniques are applied in order to provide improved performance and increased stability in high luminosity data taking conditions. In this presentation we describe the structure and performance of the jet trigger in recent data taking conditions.

Performance and Improvements of the ATLAS Jet Trigger System

In 2011-2012 the Large Hadron Collider (LHC) provided proton bunch crossings every 50 ns with up to 40 interactions every crossing. These unprecedented conditions posed stringent demands on the trigger system of the ATLAS experiment, which must provide a fast rejection of background events while maintaining a high efficiency for physics signals of interest.This note focuses on the jet trigger system in ATLAS. Jets are the most prevalent high-PT objects produced at the LHC, and are an important component of a wide range of physics analyses. The challenges faced by the jet trigger system, and how its initial limitations were overcome, will be described. Performance results, including jet efficiency and resolution, will be presented.

Performance and improvements of the ATLAS jet trigger system

The ATLAS jet trigger is the primary means for selecting energetic jets produced in LHC collisions. The ATLAS trigger system has a three level structure, and was designed based on the concept of Regions Of Interest (RoI), wherein only areas of the detector around interesting objects identified at the first level are accessed at the higher levels. The first implementation of the ATLAS jet trigger was entirely RoI based. This was changed in 2011 with the addition of the possibility to access information from the full calorimeter at the Event Filter and similarly in 2012 for the second level. This change enhances the flexibility and versatility of the system as well as improving efficiencies in multi-jet events. This paper presents the performance of the jet trigger in 2011 and an overview of the new features available for 2012.

The D0 Run IIb luminosity measurement

An assessment of the recorded integrated luminosity is presented for data collected with the D0 detector at the Fermilab Tevatron Collider from June 2006 to September 2011 (Run IIb). In addition, a measurement of the effective cross-section for inelastic interactions, also referred to as the luminosity constant, is reported. This measurement incorporates new features that lead to a substantial improvement in the precision of the result. A luminosity constant of σLM=48.3±1.9±0.6mb is obtained, where the first uncertainty is due to the accuracy of the inelastic cross-section used by both CDF and D0, and the second uncertainty is due to D0 sources. The recorded luminosity for the highest ET jet trigger is Lrec=9.2±0.4fb−1, with a relative uncertainty of 4.3%.

A novel calorimeter trigger concept: The jet trigger of the H1 experiment at HERA

We report on a novel trigger for the liquid argon calorimeter which was installed in the H1 Experiment at HERA. This trigger, called the “Jet Trigger”, was running at level 1 and implemented a real-time cluster algorithm. Within only 800 ns, the Jet Trigger algorithm found local energy maxima in the calorimeter, summed their immediate neighbors, sorted the resulting jets by energy, and applied topological conditions for the final level 1 trigger decision. The Jet Trigger was in operation from the year 2006 until the end of the HERA running in the summer of 2007. With the Jet Trigger it was possible to substantially reduce the thresholds for triggering on electrons and jets, giving access to a largely extended phase space for physical observables which could not have been reached in H1 before. The concepts of the Jet Trigger may be an interesting upgrade option for the LHC experiments.

Long range correlations and hydrodynamic expansion

Nuclear collision experiments exhibit correlations peaked in relative azimuthal angle with a long range in rapidity. Called the ridge, this peak occurs both with and without a jet trigger. We argue that the energy and projectile-mass dependence of the ridge can be described by an early Glasma stage followed by hydrodynamic flow.

The relationship between the soft and hard ridges

Two particle correlation measurements in relativistic heavy ion collisions show a 'ridge' of correlated particle pairs not seen in proton on proton collisions. The measured two-dimentional correlation landscape resembles a mountain ridge since correlated pairs are focused into a narrow regions of relative azimuthal angle, but can extend to a long range in relative pseudorapidity. Similar ridge structures are observed in correlations of particles associated with and without a jet trigger. Explanations, with and without a jet, are challenged to explain the long range pseudorapidity behavior of correlations where causality limits the influence of transport dynamics. Glasma initial conditions as predicted by the theory of Color Glass Condensate provide a and early stage correlation that naturally extends far in rapidity. We have previously shown that the soft ridge is a consequence of particles forming from an initial Glasma phase that experience a later stage transverse flow. We extend this work to study the ridge dependence on the pt of the correlated pairs and determine the relationship between the triggered and untriggered measurements.