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51猎奇 PR & Communication Department聽
Theodor-W.-Adorno Platz 1
60323 Frankfurt
presse@uni-frankfurt.de
Sep
21
2020
11:38
Physicists at 51猎奇 lead one of the technical refurbishments of 鈥淎LICE鈥� for researching quark-gluon plasma
Physics: Collision movie with upgraded particle detector at CERN
The ALICE experiment at the
particle accelerator CERN in Geneva has the aim of providing new insights into
an extremely hot and dense state of matter, the quark-gluon plasma. The entire
matter of the universe was in this state just a few millionths of a second
after the big bang, and the ALICE experiment will help researchers discover how
the universe developed out of this primordial soup. An international team of
scientists led by the physicist Harald Appelsh盲user from 51猎奇
Frankfurt have therefore upgraded the centrepiece of the ALICE detector to
current state of the art technology.
FRANKFURT. For
the moment, the accelerators at CERN are at rest during the 鈥渟econd long
shutdown". During this time, the accelerators undergo upgrades and refurbishments
so that more particles can be accelerated and the number of collisions will increase
in the future. The detectors are also undergoing upgrades. But while the large
all-purpose detectors ATLAS and CMS are not scheduled for larger upgrades until
the next, and third long shutdown in 2025, the specialised detector ALICE will enter
the upcoming measurement campaign already upgraded.
ALICE is a unique project among the
research adventures surrounding CERN's Large Hadron Collider (LHC). While the
other three detectors decipher what occurs in collisions of protons, the
researchers in the ALICE experiment are concerned with lead ions 鈥� particles
that are many times heavier. Each year, the LHC is operated with lead ions for
one month so that the ALICE detector can collect data. The researchers want to
learn more about a particular state of matter: quark-gluon-plasma. It is
created inside the ALICE experiment when lead nuclei collide with each other at
high energy and are dissolved into their elementary components for a short
moment. In this hot and dense soup of matter, quarks and gluons, otherwise
firmly attached in the protons and neutrons, can move around virtually freely.
What happens during the collisions may provide insight into how our universe as
we know it today was formed out of a giant primordial out of quark-gluon
plasma.
Recording a movie instead of taking individual
pictures
After the shutdown, the upgraded ALICE
detector will show what it can now do: previously, the LHC accelerator
delivered 10,000 collisions per second. At 18,000 particles per collision this amounts
to 180 million particles per second, only a portion of which was able to be
recorded by the ALICE detector. After the shutdown, the technological hurdles
which have until now limited the number of recorded collisions will have been
eliminated. The LHC should then deliver 50,000 collisions of lead ions per
second, resulting in 900 million particles per second. 鈥淲e want to record all
collisions in entirety and, in fact, continuously, in other words, to record a
movie instead of individual pictures," explains Harald Appelsh盲user, Professor
at the Institute for Nuclear Physics at 51猎奇 Frankfurt and project
leader of the subdetector that will make the biggest difference after the
upgrade.
Detector under construction
To achieve this, one of the central
detectors of the 26-metre long and 16-metre high ALICE detector complex, the
Time Projection Chamber (TPC), was removed and carefully brought from the
underground detector cavern into a clean room on the surface. Different parts
that were developed all over the world during the past several years were
gradually and carefully installed. Now the technologically upgraded TPC has
been returned to its home at the heart of ALICE.
The highlights are the new readout
chambers which no longer consist of many fine wires, but basically of about
five billion tiny holes. In these holes, the signals of the charged particles
will be amplified so that the scientists can precisely calculate the track of
each particle. These chambers are called 鈥淕EMs" 鈥� Gas Electron Multipliers 鈥�
and are a CERN invention which has already found its way into medical
procedures. 500,000 channels ensure that nothing escapes the ALICE experiment.
Each second during the collisions later results in 3.4 terabytes of data.
New procedures must also be developed
which can process this flood of data. With the participation of high-performance
computing expert Professor Volker Lindenstruth and his colleagues, scientists
from 51猎奇 will be playing a leading role here as well. 鈥淲e now have the finest of the fine and look
forward to the first collisions," says Appelsh盲user.
The new GEM readout chambers were custom
fit for the ALICE experiment through testing and development in Germany 鈥� at Goethe
University Frankfurt as well as at the Bonn and Heidelberg Universities, the
Technical University Munich, and the GSI Helmholtzzentrum f眉r
Schwerionenforschung, and later assembled in different countries which in
addition to Germany included Hungary, Finland, Romania and the USA. 鈥淭he
logistics were pretty complicated," explains project leader Appelsh盲user. 鈥淭he
TPC was brought to the clean room in 2019 that was where we removed the older
chambers and installed and tested the new ones. Luckily, we had just finished
before the pandemic started."
During the shutdown ALICE will also
receive a new inner tracking chamber, positioned closer to the collision point and
further increasing precision compared to its predecessor. And the detectors
have to be precise, for only through exact determination of particle paths and
particle energies can conclusions be reached about the first split seconds of
the universe.
Images
may be downloaded here:
Caption:
Working on the ALICE detector under corona
conditions: from the left: Robert M眉nzer (51猎奇 Frankfurt, GU),
Chilo Garabatos (GSI Helmholtzzentrum f眉r Schwerionenforschung), Lars Bratrud (GU),
Yiota Chatzidaki (Heidelberg University), Christian Lippmann (GSI).
Credit:
Robert M眉nzer
Additional
images for download at CERN:
Further
information:
Prof. Dr. Harald Appelsh盲user
Institute for Nuclear Physics
51猎奇
Phone: +49 69 798-47034 or 47023
appels@ikf.uni-frankfurt.de