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Level-1 pixel-based trigger for LHC experiments

In 2015, the Large Hadron Collider (LHC) started to smash protons at the unprecedented energy of 13 tera-electron-volts. To expand the Physics exploration potential at LHC, EU-funded scientists, developed algorithms and tools, based on a novel real time event-filtering trigger, using the pixel detector information.
Level-1 pixel-based trigger for LHC experiments
The discovery of the Higgs boson in 2012 completed the set of particles predicted by the standard model. The operation of the LHC at higher energy will allow the study of Higgs boson properties. In the highest-energy particle collisions ever achieved, physicists will search for hints of new particles that defy the known laws of physics.

To meet the experimental challenges of colliding protons at nearly twice the energy of the previous run, the ability of the Compact Muon Solenoid (CMS) to isolate and precisely measure the products will need to be improved. EU-funded scientists had a significant contribution in the efforts to ensure that CMS can efficiently increase its performances on triggering events from yet unknown physics processes.

The scientists, working on the EU-funded project TAUKITFORNEWPHYSICS (Tau toolkit for opening the new physics window at LHC and possible spin off effects), played a leading role in the development of a level-1 pixel trigger for CMS. The PiXTRK algorithm is the first attempt to achieve real-time track reconstruction using pattern recognition based on the pixel hits.

To do so, PiXTRK relies on pixel hits, seeded by the level-1 electromagnetic calorimeter trigger system of the CMS detector. In other words, cluster of hits at the pixel detector are matched with clusters identified at the level-1 calorimeter level. Pattern recognition proceeds by defining windows in the transverse and longitudinal planes to the beam axis and then moves backwards to the beam spot.

When applying the algorithm to the level-1 trigger on electrons case, it proved able to reconstruct the particle trajectories from the pixel clusters with an overall efficiency above 95 %, keeping the electron momentum threshold as low as 20 GeV/c, a rate reduction of 5, over large angular acceptance coverage and for high pile-ups rates. This was a very encouraging indication of the performance potential of this trigger.

The scientists also contributed to the design of an innovative sensor to detect and measure with high precision coordinates of impinging charged particles. The avalanche pixel sensor (APiX) is derived from the Silicon PM technology and based on the 3D vertical integration of multiple avalanche pixels, implemented in fully digital readout electronics on the same structure.

When TAUKITFORNEWPHYSICS ended in 2014, the technology to produce this new type of ionising radiation detector was under development. Once manufactured, the APiX operation will feature low noise and low-power consumption as well as high radiation tolerance. The outcome of this research is expected to have applications in fields ranging from research instrumentation to electron microscopy and medical imaging.

Related information


LHC, standard model, physics, Compact Muon Solenoid, TAUKITFORNEWPHYSICS
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