ALICE first collision data demonstrates success of Wright Lab detector upgrade

data visualization.
November 12, 2021

Wright Lab’s Relativistic Heavy Ion Group (RHIG), led by professor of physics Helen Caines and D. Allan Bromley Professor Emeritus of Physics John Harris,  has been taking advantage of the extended 3-year shutdown of the Large Hadron Collider (LHC)–the world’s largest and most powerful particle accelerator located at the Center for European Nuclear Research (CERN) in Geneva, Switzerland–to contribute to the upgrade of one of the LHC’s detectors, called A Large Ion Collider Experiment (ALICE).

ALICE uses collisions of heavy nuclei, as well as proton-proton and proton-nucleus collisions, to study the physics of strongly interacting matter at the highest energy densities reached so far in the laboratory. The primary goal of the experiment is to re-create the quark-gluon plasma (QGP) state of matter, which is predicted by the Standard Model of particle physics to have existed ten millionths of a second after the Big Bang.  

After several years of construction and then installation during the LHC shutdown, the upgraded LHC started delivering stable beams in collision for detectors on October 27, 2021. ALICE immediately started taking data to test its new detector systems—including a completely new silicon inner tracking system (10 m2 of active silicon area and nearly 13 billion pixels) and new Time Projection Chamber (TPC) endcap readout–as well as its online and offline software.

Wright Lab research scientist Nikolai Smirnov and the late Richard Majka, also a research scientist in Wright Lab’s RHIG, were in charge of the assembly and testing of ALICE’s inner Gas Electron Multiplier (GEM) TPC chambers in Wright Lab. Majka also served as the U.S. Project Leader for the U.S. Department of Energy (DOE) supported GEM-TPC construction project effort. Graduate students from RHIG also played an important role in the R&D for this new type of TPC readout prior to its construction.

The GEM-TPC (cylindrical tracking detector 5 meters in diameter, 5 meters long) and its new readout electronics feature a continuous readout mode that allows ALICE to record the thousands of tracks produced in Pb-Pb collisions at event rates of 50 kHz leading to a staggering data rate of 3.5 TB/s.

Seen in the online display (see snapshot pictured, above) is the real-time sequence of the continuous TPC data stream in 11 millisecond slices. Tracks from individual proton-proton collision events can be seen as they curve through the magnetic field along the cylindrical axis. Given the continuously streaming, real-time data readout and the new detector systems, ALICE expects to accumulate 50 times more heavy-ion collision data in the upcoming LHC Run 3 than in Runs 1 and 2 combined.

In addition to leading construction of the inner sectors of the ALICE TPC upgrade, RHIG at Yale has been engaged with the ALICE Collaboration since its beginning.  The Wright Lab group has contributed significantly to ALICE analyses and papers, as well as the original design of the detector.  The Wright Lab group assembled, tested, calibrated, and installed the electromagnetic calorimeter (EMCal) in ALICE.  Harris is a past chair of the ALICE Collaboration Board. Furthermore, the group engages in simulations, R&D, design and prototyping of future detectors.