Born – Shandong, China
PhD – Shandong University, China, and Aix-Marseille University, France
Joined University of Liverpool – 2018
Position – Postdoctoral Research Associate, Department of Physics
Group Name – Nuclear Physics Cluster (ALICE group)
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What is your research about?
My research focuses on the R&D and implementation of state-of-the-art silicon pixel detectors, and the related software tools, needed for high-energy nuclear and particle physics experiments. I am currently working on the upgrade of the Inner Tracking System (ITS2) of the ALICE experiment (A Large Ion Collider Experiment) which is one of the four main experiments at the Large Hadron Collider (LHC) at CERN in Geneva, Switzerland.
This newly designed, constructed and installed ITS2 detector offers a significant improvement of the achievable impact-parameter resolution and tracking efficiency, which will enhance the charged-particle vertexing and tracking capabilities of ALICE. In turn this will extend the physics reach of feasible rare-probe measurements with ALICE for the study of the Quark Gluon Plasma (QGP) and strongly interacting matter at extreme energy densities, using nucleus-nucleus, proton-nucleus and proton-proton collisions in the next data-taking runs at the LHC, starting from mid. 2022.
What or who first inspired you to be interested in your research subject?
When I was a child, I was curious about the origin of the universe and read many popular science books - such as One Hundred Thousand Whys, which is a very famous book series in China - trying to find answers. In high school, the news about the Nobel Prize in Physics 2004, awarded to David J. Gross, H. David Politzer and Frank Wilczek, for the discovery of asymptotic freedom in the theory of the strong interaction attracted me. It sounded like a miracle! I thus chose physics as my subject for my undergraduate studies.
In 2007, I by chance read some articles about the LHC and the ATLAS experiment, which described that the silicon pixel detector with a size of 1.9 m2 is like a digital camera but has 80 million pixels with high-speed readout. Being involved in the R&D of such kinds of detectors became one of my dreams from that moment onwards. During my PhD, my supervisor recommended for me a pixel detector research topic in the ATLAS experiment and that is how I started my research career on what I was keen to do.
What are you most proud of achieving during your research career so far?
One of my most proud achievements has been coordinating the operation of the new Inner Tracking System of the ALICE experiment at CERN and the successful data taking with first stable beams from the LHC in October 2021. I am currently the System Run Coordinator for this new ITS2 detector since July 2021, for one year. It is the largest all-pixel silicon tracker ever built, covering about 10 m2. It was commissioned with proton beams for the first time and a uniform response over about 13 billion pixels was achieved. The first physics signals associated to light-flavour particles have also been reconstructed already from this brand-new detector, which is a great achievement.
What techniques and equipment do you use to conduct your research?
I use various techniques and instruments for different research tasks that are conducted at different points in the detector R&D timeline. The new ALICE ITS2 detector is the first in the world to be entirely built using Monolithic Active Pixel Sensors (MAPS). MAPS are a state-of-the-art silicon sensor technology in which the readout electronics is incorporated within each pixel, so that extremely thin and high-resolution vertexing and tracking detectors can be built. To develop new MAPS chips in a commercial CMOS imaging process, we need a set of software packages to design the charge sensing elements, ICs and testing boards, for example the Cadence and Synopsys design kits.
The designs are then sent to the semiconductor manufacturing companies to produce the silicon pixel sensors. The sensors are then inspected and characterized in the laboratory (such as the Liverpool Semiconductor Detector Centre in the Physics Department) by using sophisticated microscopes, oscilloscopes, source meters etc. Dedicated irradiation facilities, for instance X-ray sources and neutron and proton test beams, are also needed to investigate the sensor response and the radiation hardness of the sensors, which ultimately need to operate in a high radiation environment at the LHC. A lot of programming languages (C++, python, etc) and high-performance computing resources are also required to read out and analyse the data from the pixel sensors. So overall in my research field I have had to build up a combination of many hardware and software skills.
Which other subjects are important for your research?
As you can see from what I mentioned above, research and development on silicon pixel detectors for high-energy physics is interdisciplinary. To build a pixel detector, of course we need physicists to set the specifications to do the science it is meant to achieve but we mainly also need the help from electrical, mechanical and software engineers, as well as highly-skilled technicians, to design the tools, both hardware and software, necessary to ultimately handle the data with a high throughput, construct the detector elements with a high precision and maintain the detector running over long periods of time in a safe and reliable state.
What is the key to a successful research group?
First and foremost, good communication between group members is very important. Sharing plans and difficulties with others is helpful to progress research work and solve problems. In my field in particular, collaborating with other local, national and international colleagues/groups/institutes is also very important, as this usually extends the scope of the group and leads to more research opportunities.
What impact is your research having outside of academia?
The original idea of such a pixel detector is for the detection of charged particles in a high-energy physics experiment, especially to reconstruct the tracks in 3D of particles created during the collisions of protons and/or heavy ions travelling in the LHC at close to the speed of light. Sometimes these particles exist for a very short time only (and therefore only travel a very short distance) before they decay into other particles, which in turn need to be tracked. Often the technologies developed within the high-energy physics community can also be developed or adapted for civil/medical applications, such as X-ray imaging and synchrotron light detection. Most of the data simulation software and data processing tools that we develop are open source. They can be reused and adapted for imaging devices.
We also have regularly open days for the public. Visitors, in particular young students, then have a chance to discover our experimental facilities and follow topical seminars. Finding out how we are trying to understand the evolution of our universe and what are the cutting-edge technologies usually inspires people to find out more.
How do you plan to develop your research in the future?
I am currently working on the Inner Tracking System upgrade to improve the ALICE detector performance for the upcoming data taking period at the LHC (Run 3) starting from mid 2022. During 2021 it was installed into the ALICE experiment, in the underground cavern of one of the interaction points of the LHC, and it is being commissioned by myself and by colleagues from around the world. This new detector is foreseen being used for physics data taking that will be starting next year and for many years to come. In the meantime, however, a new central part of this detector is already under study to further enhance its capabilities. In the short term apart from exploring fully its functionalities, I plan to be involved in the related performance and physics studies with this novel instrument. In the medium term I would potentially also plan to extend my research to the field of x-ray imaging.
What problem would you like to solve in the next 10 years through your research?
There will be a couple of further upgrades for the current tracking system of the ALICE experiment as well as a few newly proposed collider-based future experiments to be designed and constructed in the next years or even decades. Building more advanced silicon pixel detectors in terms of resolution and efficiency for instance will likely be my main research topic in the next 10 years or even more. For instance, more R&D is needed to decrease even more the material budget of the detectors.
The technology also needs developing further to be able to sustain higher levels of radiation as well as to achieve high resolution for timing purposes. In a way the ALICE ITS upgrade, being the first of its kind, entirely built from Monolithic Active Pixel Sensors, can be seen as a first ‘prototype’ of this new generation of large-scale silicon pixel detectors.
What advice would you give to someone considering a career in research?
Well, honestly, I would say do what you really want to do. Researching nowadays might not be what you may have thought. Make sure you are interested in your research field so that you can keep going. Otherwise, you might not concentrate enough on what you are doing or not manage to keep your eyes on the bigger picture or ultimate goal as well. Try and understand problems and find out solutions independently. But never be frustrated if you get stuck or encounter failures. Communicating with your colleagues and digging into more documents in the literature would also help you a lot. There are more solutions than difficulties! And finally, all your work will pay off.
Where can readers learn more about your research?
You can find more information via the ALICE Collaboration website as well as by reading a recent article published in CERN Courier.
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