The LHCb experiment at CERN’s Large Hadron Collider yesterday submitted a report to the journal Physical Review Letters detailing observation of the until now only theorised pentaquark particle.
“The pentaquark is not just any new particle,” said LHCb spokesperson Guy Wilkinson. “It represents a way to aggregate quarks, namely the fundamental constituents of ordinary protons and neutrons, in a pattern that has never been observed before in over fifty years of experimental searches. Studying its properties may allow us to understand better how ordinary matter, the protons and neutrons from which we’re all made, is constituted.”
In 1964 American physicist, Murray Gell-Mann, proposed the existence of quarks – subatomic particles. He said the category of particles known as baryons, which includes protons and neutrons, are comprised of three fractionally charged objects – quarks – and that another category, the mesons, are formed of quark-antiquark pairs.
This proposal was revolutionary, garnering Gell-Mann the Nobel Prize for physics in 1969, for it represented, and does to this day, the most fundamental structure of matter known.
The model also allowed for the existence of quark composite states, such as the pentaquark composed of four quarks and an antiquark. The pentaquark therefore represents another piece in the biggest jigsaw puzzle of all.
They were observed in a tunnel, 27km in circumference, 500ft beneath the Franco-Swiss border near Geneva, in the largest machine in the world.
-The LHC accelerates particles, for collision, to 11,000 revolutions per second or three metres per second slower than the speed of light. The aim, to test predictions of different theories of particle and high-energy physics, and to prove or disprove the existence of the theorised Higgs boson, the god particle and believed destroyer of worlds.
The European Organization for Nuclear Research, known as CERN, is the organisation operating the LHC, and there are seven experiments collecting data, of which the LHCb or Large Hadron Collider beauty is one.
The LHCb is a detector set up to explore what happened after the Big Bang that allowed matter to survive and build the Universe. It weighs 5,600 tonnes. It is 21m long, 10m high and 13m wide. It is made up of a forward spectrometer and planar detectors.
The next step for the LHCb collaboration, made up of hundreds of scientists from different institutes and universities, will be to study how the quarks are bound together within pentaquarks. The five quarks might be tightly bonded, as illustrated above left, or in a meson (one quark and one antiquark) and a baryon (three quarks), right. – “In which,” says LHCb physicist Liming Zhang of Tsinghua University, “the meson and baryon feel a residual strong force similar to the one binding protons and neutrons to form nuclei.”
The LHCb will collect new data in LHC run 2, to distinguish between these possibilities and see what else might be learned from pentaquarks.
For further reading see paper on ArXiv, http://arxiv.org/abs/1507.03414, or visit the LHCb collaboration site, http://lhcb-public.web.cern.ch/lhcb-public/Welcome.html#Penta.
By Harrison Drury