Detectors on the drawing board

Linear collider detector developers inside and outside CERN are tackling the next generation of detector technology. While their focus has centred on high-energy linear collider detectors, their innovative concepts and designs will be applicable to any future detector.


A simulated event display in one of the new generation detectors.

“While the LHC experiments remain the pinnacle of detector technology, you may be surprised to realise that the design and expertise behind them is well over 10 years old,” says Lucie Linssen, CERN’s Linear Collider Detector (LCD) project manager whose group is pushing the envelope of detector design. “The next generation of detectors will have to surpass the achievements of the LHC experiments. It’s not an easy task but, by observing detectors currently in operation and exploiting a decade’s worth of technological advancements, we’ve made meaningful progress.”

The LCD team is currently working on detectors for the CLIC experiment. “Electron-positron colliders like CLIC demand detectors with significantly more precision than those at the LHC,” explains Lucie. “We’ve studied a variety of techniques to cope with this precision and other CLIC-specific issues. Many of these were pioneered for earlier linear colliders, but have since been adapted to fit CLIC’s unique parameters.” The team's work has culminated in two detector designs, published in the CLIC Conceptual Design Report.

At a glance, one could easily mistake the Linear Collider experiments for CMS. But while very similar, they incorporate a number of new elements to improve the efficiency and precision of the detectors. These include:

More Precise Vertex Detectors: The pixel detector at the heart of the linear collider detector designs will have up to 40 times more readout channels and a much smaller pixel size (approximately 20 x 20 μm2, compared to CMS’s 100 x 150 μm2).

Particle Flow Analysis: This technique combines information from different parts of the detector in order to extract the maximum knowledge from individual particles – including particles inside jets. To fully exploit this technique, the linear collider experiments are developing calorimeters with ultra-fine granularity. 

Tungsten Calorimeters: The sizeable CLIC collision energy (up to 3 TeV) means that the calorimeters designed by the LCD team need to be both deep and dense in order to avoid energy leaks. To accomplish this, they have designed the hadronic calorimeter to use tungsten absorbers instead of the traditional steel. As tungsten is extremely dense, it can provide the required depth without dramatically increasing the size of the detector. Read more about CLIC’s tungsten calorimeters here.

Calorimeters with ultra-fine granularity allow particle recognition inside jets.

The LCD team performed 6 physics analyses to study the potential for discoveries and precision physics of their detector designs at CLIC. These analyses took simulated physics events and simulated background events, and overlaid them to create a “real” electron-positron collision environment. These data were then sent through a computer model of the detector to create a realistic readout. Finally, using highly specialised software, the physics signals were extracted from the detector readout.

By comparing the input physics event with the extracted physics signals, the LCD team was able, for example, to calculate Higgs boson properties and study whether it is an elementary particle or a composite particle. The LCD analyses have found the sensitivity to the Higgs compositeness scale to be significantly superior to what is possible at the LHC.

“While we need to continue to develop the detector technology, the analyses have shown that our detector concepts are feasible,” concludes Lucie. “In fact, they are not just feasible – they can provide an unprecedented level of precision measurements for interactions that have only ever been theorised.”

No matter what new detector makes it off the drawing board and into production, its design is likely to incorporate these linear collider concepts.

by Katarina Anthony