Pile up management at the high-luminosity LHC and introduction to the crab-kissing concept

The future High Luminosity LHC (HL-LHC) is expected to deliver about 5 times higher instantaneous luminosity than the present LHC, resulting in pile-up up to 200 interactions per bunch crossing (PU200). As part of the phase-II upgrade program, the CMS collaboration is developing a new endcap calorimeter system, the High Granularity Calorimeter (HGCAL), featuring highly-segmented hexagonal silicon sensors and scintillators with more than 6 million channels. For each event, the HGCAL clustering algorithm needs to group more than 105 hits into clusters. As consequence of both high pile-up and the high granularity, the HGCAL clustering algorithm is confronted with an unprecedented computing load. CLUE (CLUsters of Energy) is a fast fullyparallelizable density-based clustering algorithm, optimized for high pile-up scenarios in high granularity calorimeters. In this paper, we present both CPU and GPU implementations of CLUE in the application of HGCAL clustering in the CMS Software framework (CMSSW). Comparing with the previous HGCAL clustering algorithm, CLUE on CPU (GPU) in CMSSW is 30x (180x) faster in processing PU200 events while outputting almost the same clustering results.

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New techniques for pile-up simulation in ATLAS

EPJ Web of Conferences ◽

10.1051/epjconf/201921402044 ◽

2019 ◽

Vol 214 ◽

pp. 02044

Author(s):

Tadej Novak

Keyword(s):

Real Data ◽

Current Approach ◽

Single Event ◽

High Luminosity ◽

Previous Approach ◽

New Techniques ◽

Proton Proton ◽

Atlas Data ◽

Pile Up ◽

Overlay Approach

The high-luminosity data produced by the LHC leads to many proton-proton interactions per beam crossing in ATLAS, known as pile-up. In order to understand the ATLAS data and extract physics results it is important to model these effects accurately in the simulation. As the pile-up rate continues to grow towards an eventual rate of 200 for the HL-LHC, this puts increasing demands on the computing resources required for the simulation and the current approach of simulating the pile-up interactions along with the hard-scatter for each Monte Carlo production is no longer feasible. The new ATLAS “overlay” approach to pile-up simulation is presented. Here a pre-combined set of minimum bias interactions, either from simulation or from real data, is created once and a single event drawn from this set is overlaid with the hard-scatter event being simulated. This leads to significant improvements in CPU time. This contribution will discuss the technical aspects of the implementation in the ATLAS simulation and production infrastructure and compare the performance, both in terms of computing and physics, to the previous approach.

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Triggering long-lived particles in HL-LHC and the challenges in the first stage of the trigger system

Journal of High Energy Physics ◽

10.1007/jhep08(2020)141 ◽

2020 ◽

Vol 2020 (8) ◽

Cited By ~ 1

Author(s):

Biplob Bhattacherjee ◽

Swagata Mukherjee ◽

Rhitaja Sengupta ◽

Prabhat Solanki

Keyword(s):

Large Hadron Collider ◽

Hadron Collider ◽

High Luminosity ◽

Trigger System ◽

Pile Up ◽

The Future ◽

Level 1

Abstract Triggering long-lived particles (LLPs) at the first stage of the trigger system is very crucial in LLP searches to ensure that we do not miss them at the very beginning. The future High Luminosity runs of the Large Hadron Collider will have increased number of pile-up events per bunch crossing. There will be major upgrades in hardware, firmware and software sides, like tracking at level-1 (L1). The L1 trigger menu will also be modified to cope with pile-up and maintain the sensitivity to physics processes. In our study we found that the usual level-1 triggers, mostly meant for triggering prompt particles, will not be very efficient for LLP searches in the 140 pile-up environment of HL-LHC, thus pointing to the need to include dedicated L1 triggers in the menu for LLPs. We consider the decay of the LLP into jets and develop dedicated jet triggers using the track information at L1 to select LLP events. We show in our work that these triggers give promising results in identifying LLP events with moderate trigger rates.

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Assessment of the performance of High-Luminosity LHC operational scenarios: integrated luminosity and effective pile-up density

Canadian Journal of Physics ◽

10.1139/cjp-2018-0291 ◽

2019 ◽

Vol 97 (5) ◽

pp. 498-508 ◽

Cited By ~ 2

Author(s):

L. Medina ◽

R. Tomás ◽

G. Arduini ◽

M. Napsuciale

Keyword(s):

Hadron Collider ◽

High Luminosity ◽

Reduced Cross Section ◽

Proton Proton ◽

Density Control ◽

Pile Up ◽

Alternative Scenarios ◽

New Perspective ◽

The Impact ◽

Integrated Luminosity

The High-Luminosity Large Hadron Collider (HL-LHC) experiments will operate at unprecedented levels of event pile-up from proton–proton collisions at 14 TeV centre-of-mass energy. In this paper, we study the performance of the baseline and a series of alternative scenarios in terms of the delivered integrated luminosity and its quality (pile-up density). A new figure-of-merit is introduced, the effective pile-up density, a concept that reflects the expected detector efficiency in the reconstruction of event vertices for a given operational scenario, acting as a link between the machine and experimental sides. Alternative scenarios have been proposed either to improve the baseline performance or to provide operational schemes in the case of particular limitations. Simulations of the evolution of their optimum fills with the latest set of parameters of the HL-LHC are performed with β*-levelling, and the results are discussed in terms of both the integrated luminosity and the effective pile-up density. The crab kissing scheme, a proposed scenario for pile-up density control, is re-evaluated under this new perspective with updated beam and optics parameters. Estimates on the expected integrated luminosity due to the impact of crab cavity noise, full crab crossing, and reduced cross section for burn-off, are also presented.

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Upgrade of the ATLAS detectors and trigger for the High Luminosity LHC: Tracking and timing for pile-up suppression

Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment ◽

10.1016/j.nima.2018.10.172 ◽

2019 ◽

Vol 936 ◽

pp. 394-395

Author(s):

M. Testa

Keyword(s):

High Luminosity ◽

Pile Up

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Asteroids pile up

Nature ◽

10.1038/news020408-10 ◽

2002 ◽

Author(s):

Meera Louis

Keyword(s):

Pile Up

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Anisotropy of Nanoindentation – a tool for the determination of nanocrystal orientation ?

MRS Proceedings ◽

10.1557/proc-779-w5.14 ◽

2003 ◽

Vol 779 ◽

Author(s):

David Christopher ◽

Steven Kenny ◽

Roger Smith ◽

Asta Richter ◽

Bodo Wolf ◽

...

Keyword(s):

Crystal Surface ◽

Scanning Force Microscopy ◽

Depth Range ◽

Dislocation Loops ◽

Force Microscopy ◽

Pile Up ◽

Out Of Plane ◽

Scanning Force ◽

Dynamics Simulations

AbstractThe pile up patterns arising in nanoindentation are shown to be indicative of the sample crystal symmetry. To explain and interpret these patterns, complementary molecular dynamics simulations and experiments have been performed to determine the atomistic mechanisms of the nanoindentation process in single crystal Fe{110}. The simulations show that dislocation loops start from the tip and end on the crystal surface propagating outwards along the four in-plane <111> directions. These loops carry material away from the indenter and form bumps on the surface along these directions separated from the piled-up material around the indenter hole. Atoms also move in the two out-of-plane <111> directions causing propagation of subsurface defects and pile-up around the hole. This finding is confirmed by scanning force microscopy mapping of the imprint, the piling-up pattern proving a suitable indicator of the surface crystallography. Experimental force-depth curves over the depth range of a few nanometers do not appear smooth and show distinct pop-ins. On the sub-nanometer scale these pop-ins are also visible in the simulation curves and occur as a result of the initiation of the dislocation loops from the tip.

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