TAU researchers further understanding of 'God particle' at CERN
Scientists found that the decay of the Higgs boson into "charm" quarks doesn't deviate from the Standard Model of particle physics.
ATLAS experiment at the Large Hadron Collider (LHC) at CERN, (photo credit: TEL AVIV UNIVERSITY)
Researchers from Tel Aviv University have found new insights into the behavior of the Higgs boson particle (commonly known as the "God Particle") in a new study, the university announced on Sunday.
The
Higgs boson is a particle that is theorized to be responsible for
allowing particles to clump together to form stars, planets and other
bodies. The researchers are investigating the decay of the Higgs boson
into a pair of elementary particles called charm quarks.
The
study was conducted as part of the ATLAS experiment at the Large Hadron
Collider (LHC) at the CERN research center by Prof. Erez Etzion and
doctoral students Guy Koren, Hadar Cohen and David Reikher from the
Raymond and Beverly Sackler School of Physics and Astronomy, Raymond and
Beverly Sackler Faculty of Exact Sciences, at Tel Aviv University.
Prof. Eilam Gross from the Weizmann Institute of Science collaborated
with the research team.
The Moment: CERN Scientist Announces Higgs Boson 'God Particle' Discovery, 4 Jul 2012
The
"charm" is one of the six "flavors" or types of quarks in the Standard
Model of particle physics. Quarks are split into three different
"generations." The first generation contains quarks with the smallest
masses: "up" and "down." The second generation, with greater masses,
contains the "charm" and "strange" quarks. The third generation contains
the heaviest ones, the "top" (truth) and "bottom" (beauty) quarks.
The
Higgs boson is a relatively heavy elementary particle and can be
created in collisions between protons, as long as the accelerator's
energy is high enough. “It is interesting to investigate into which
types of particles the Higgs decays, and with what frequency it decays
into each type of particle,” said Koren in a press release. “To help
answer that question, our group is trying to measure the rate at which
the Higgs boson decays into particles called ‘charm quarks.’”
Koren
stressed that this isn't a simple mission. “It is a very rare process –
only one out of billions of collisions end with the creation of Higgs
bosons, and only three percent of the Higgs bosons that do emerge will
decay into charm quarks," said Koren. "Moreover, there are five other
types of quarks, and the problem is that all of them leave similar
signatures in our detectors. So that even when this process does indeed
take place, it is very difficult for us to identify it.”
The
researchers have not yet identified enough decays of the Higgs bosons
into charm quarks to measure the rate of the process with the required
statistical accuracy, but have found sufficient data to state what the
maximal rate of the process is with respect to the theoretical
predictions.
The
gold standard of particle physics is five standard deviations, also
known as five sigma, meaning there is about a 1 in 3.5 million chance
that the measurement is a statistical coincidence.
If
the rate of decay is found to be higher than the predicted rate, it
could constitute an important indicator for "new" physics or expansions
of the Standard Model. The researchers have concluded with a
well-defined statistical certainty that there is "no chance" that the
rate of decay is higher than 8.5 times the theoretical predictions, as
enough such decays would have been observed to measure it if this was
the case.
“This
might not sound like such an exciting declaration, but this is the first
time that anyone has ever succeeded in saying something important about
the rate of this specific decay based on a direct measurement of it,
therefore it is a very important and significant statement in our
field,” said Koren.
Higgs Hunters at CERN, 11 Oct 2019
Etzion
explained in the press release that the Higgs boson's rate of decay is
predicted to be proportional to the mass (squared) of the particles into
which it decays. "Therefore, we expect that in most cases it will decay
into the heavier particles (lighter than the Higgs boson), and only
rarely will it decay into the light ones."
The
results the team found confirm this prediction, according to Etzion,
with enough Higgs decays into the heavy third-generation quarks observed
in order to verify their existence and measure their rate.
"The
rate does indeed correspond to the theoretical predictions, but the
game is not over, as Higgs decays into second (or first) generation
quarks have not yet been observed. And therefore we cannot yet be sure
that the same ‘rules’ apply to quarks from those generations,” added
Etzion.
“If we
suddenly discover that the Higgs boson decays into them at a rate that
is not proportional to the square of their mass, there could be
far-reaching implications for our understating of the universe, and in
particular about the way in which elementary particles get their mass,"
said Etzion. "This is also the reason why we are investing such great
efforts to characterize the decay of Higgs bosons into charm quarks –
this is the heaviest quark into which the rate of decay has not yet been
measured.”
The new study is the latest in a series of groundbreaking research which has been published at CERN in recent months.
In
July, the Large Hadron Collider beauty (LHCb) experiment at CERN
presented the discovery of a new particle which is the longest-lived
exotic matter ever discovered, labeled as Tcc+, a tetraquark, an exotic
hadron containing two quarks and two antiquarks. The particle is also
the first to contain two heavy quarks and two light antiquarks.
Hadrons
are formed from quarks. Tcc+ contains two charm quarks and an up and a
down antiquark. Charm quarks (second-generation quarks) are heavier than
up and down quarks (first generation quarks). This is called "double
open charm." While particles with a charm quark and a charm antiquark
have a charm quantum number that adds up to zero (known as "hidden
charm), this particle has a charm quantum number that adds up to two.
The
discovery of the new particle paves the way for the search for heavier
particles of the same type, with one or two charm quarks replaced by
bottom quarks, which could have a much longer lifetime than any
previously observed exotic hadron.
In
March, physicists from the Universities of Cambridge, Bristol, and
Imperial College London taking part in the LHCb experiment at CERN
published a paper stating that data from the LHC suggested a violation of the Standard Model, which may point to the existence of new particles or a new force of nature. The paper has not yet been peer-reviewed.
The scientists found evidence that "beauty" quarks do not decay in the way they should following the Standard Model.
Beauty
quarks, particles similar to but heavier than electrons, interact with
all forces in the same way, so they should decay into muons and
electrons at the same rate.
However,
the data collected by the LHCb seems to show that these quarks are
decaying into muons less often than they decay into electrons, which
should only be possible if unknown particles are interfering and making
them more likely to decay into electrons.
While
the Standard Model doesn't explain about 95% of what the universe is
made of, it is the current central theory of particle physics. If the
results are confirmed further, it could open a whole new area of physics
to discover.
The
LHC is the world's largest and most powerful particle accelerator,
measuring 27-kilometers long. Two high-energy particle beams travel at
close to the speed of light inside the accelerator until they collide,
forming new particles and allowing physicists to study particles that
are unstable and cannot be directly observed.
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