Sunday, 1 November 2015
The Large Hadron Collider (LHC)
The
Large Hadron Collider (LHC) is the world's largest and most
powerful particle collider, the largest, most complex experimental facility
ever built, and the largest single machine in the world. It was built by the European Organization for Nuclear Research
(CERN) between 1998 and 2008 in collaboration with over 10,000 scientists
and engineers from over 100 countries, as well as hundreds of universities and
laboratories. It lies in a tunnel 27 kilometres (17 mi) in circumference, as
deep as 175 metres (574 ft) beneath the France–Switzerland border near Geneva,
Switzerland. Its first research run took place from 30 March 2010 to 13
February 2013 at an initial energy of 3.5 tera electronvolts (TeV) per beam (7
TeV total), almost 4 times more than the previous world record for a collider,
rising to 4 TeV per beam (8 TeV total) from 2012. On 13 February 2013 the LHC's
first run officially ended, and it was shut down for planned upgrades. 'Test'
collisions restarted in the upgraded collider on 5 April 2015, reaching 6.5 TeV
per beam on 20 May 2015 (13 TeV total, the current world record for particle
collisions). Its second research run commenced on schedule, on 3 June 2015.
The LHC's aim is to
allow physicists to test the predictions of different theories of particle
physics, high-energy physics and in particular, to prove or disprove the
existence of the theorized Higgs boson and the large family of new particles
predicted by super symmetric theories, and other unsolved questions of physics,
advancing human understanding of physical laws. It contains seven detectors,
each designed for certain kinds of research. The proton-proton collision is the
primary operation method, but the LHC has also collided protons with lead
nuclei for two months in 2013 and used lead–lead collisions for about one month
each in 2010, 2011, and 2013 for other investigations.
The LHC's computing
grid was (and currently is) a world record holder. Data from collisions was
anticipated to be produced at an unprecedented rate for the time, of tens of
petabytes per year, a major challenge at the time, to be analysed by a
grid-based computer network infrastructure connecting 140 computing centres in
35 countries – by 2012 the Worldwide LHC Computing Grid was also the world's
largest distributed computing grid, comprising over 170 computing facilities in
a worldwide network across 36 countries.
Purpose
Physicists hope that
the LHC will help answer some of the fundamental open questions in physics,
concerning the basic laws governing the interactions and forces among the
elementary objects, the deep structure of space and time, and in particular the
interrelation between quantum mechanics and general relativity, where current
theories and knowledge are unclear or break down altogether. Data is also
needed from high energy particle experiments to suggest which versions of
current scientific models are more likely to be correct – in particular to
choose between the Standard Model and Higgsless models and to validate their
predictions and allow further theoretical development. Many theorists expect
new physics beyond the Standard Model to emerge at the TeV energy level, as the
Standard Model appears to be unsatisfactory. Issues possibly to be explored by
LHC collisions include:
- Are the masses of elementary particles actually generated by the Higgs mechanism via electroweak symmetry breaking?] It is expected that the collider will either demonstrate or rule out the existence of the elusive Higgs boson, thereby allowing physicists to consider whether the Standard Model or its Higgs less alternatives are more likely to be correct.
- Is supersymmetry, an extension of the Standard Model and Poincaré symmetry, realized in nature, implying that all known particles have supersymmetric partners?
- Are there extra dimensions, as predicted by various models based on string theory, and can we detect them?
- What is the nature of the dark matter that appears to account for 27% of the mass-energy of the universe?
- It is already known that electromagnetism and the weak nuclear force are different manifestations of a single force called the electroweak force. The LHC may clarify whether the electroweak force and the strong nuclear force are similarly just different manifestations of one universal unified force, as predicted by various Grand Unification Theories.
- Why is the fourth fundamental force (gravity) so many orders of magnitude weaker than the other three fundamental forces? See also Hierarchy problem.
- Are there additional sources of quark flavour mixing, beyond those already present within the Standard Model?
- Why are there apparent violations of the symmetry between matter and antimatter? See also CP violation.
- What are the nature and properties of quark–gluon plasma, thought to have existed in the early universe and in certain compact and strange astronomical objects today? This will be investigated by heavy ion collisions, mainly in ALICE, but also in CMS and ATLAS. Findings published in 2012 confirmed the phenomenon of jet quenching in heavy-ion collisions, and was first observed in 2010
Detectors
Seven detectors have
been constructed at the LHC, located underground in large caverns excavated at
the LHC's intersection points. Two of them, the ATLAS experiment and the
Compact Muon Solenoid (CMS), are large, general purpose particle
detectors.ALICE and LHCb have more specific roles and the last three, TOTEM,
MoEDAL and LHCf, are very much smaller and are for very specialized research.
The BBC's summary of the main detectors is
Timeline of Operations
Findings
and discoveries
An initial focus of
research was to investigate the possible existence of the Higgs boson, a key
part of the Standard Model of physics which was predicted by theory but had not
yet been observed or proven to exist due to its elusive nature and exceedingly
brief lifespan. CERN scientists estimated that, if the Standard Model were
correct, the LHC would produce several Higgs bosons every minute, allowing
physicists to finally confirm or disprove the Higgs bosons existence. In
addition, the LHC allowed to search for supersymmetric particles and other
hypothetical particles as possible unknown areas of physics. Some extensions of
the Standard Model predict additional particles, such as the heavy W' and Z'
gauge bosons, which were also estimated to be within reach of the LHC to
discover.
First
run (data taken 2009–2013)
The first physics
results from the LHC, involving 284 collisions which took place in the ALICE
detector, were reported on 15 December 2009. The results of the first
proton–proton collisions at energies higher than Fermilab's Tevatron
proton–antiproton collisions were published by the CMS collaboration in early
February 2010, yielding greater-than-predicted charged-hadron production.
After the first year of
data collection, the LHC experimental collaborations started to release their
preliminary results concerning searches for new physics beyond the Standard
Model in proton-proton collisions. No evidence of new particles was detected in
the 2010 data. As a result, bounds were set on the allowed parameter space of
various extensions of the Standard Model, such as models with large extra
dimensions, constrained versions of the Minimal Supersymmetric Standard Model,
and others.
On 24 May 2011, it was
reported that quark–gluon plasma (the densest matter thought to exist besides
black holes) had been created in the LHC.
Between July and August
2011, results of searches for the Higgs boson and for exotic particles, based
on the data collected during the first half of the 2011 run, were presented in
conferences in Grenoble and Mumbai. In the latter conference it was reported that,
despite hints of a Higgs signal in earlier data, ATLAS and CMS exclude with 95%
confidence level (using the CLs method) the existence of a Higgs boson with the
properties predicted by the Standard Model over most of the mass region between
145 and 466 GeV. The searches for new particles did not yield signals either,
allowing to further constrain the parameter space of various extensions of the
Standard Model, including its supersymmetric extensions
On 13 December 2011,
CERN reported that the Standard Model Higgs boson, if it exists, is most likely
to have a mass constrained to the range 115–130 GeV. Both the CMS and ATLAS
detectors have also shown intensity peaks in the 124–125 GeV range, consistent
with either background noise or the observation of the Higgs boson.
On 22 December 2011, it
was reported that a new particle had been observed, the χb (3P) bottomonium
state. On 4 July 2012, both the CMS and ATLAS teams announced the discovery of
a boson in the mass region around 125–126 GeV, with a statistical significance
at the level of 5sigma. This meets the formal level required to announce a new
particle which is consistent with the Higgs boson, but scientists were cautious
as to whether it is formally identified as actually being the Higgs boson,
pending further analysis
On 8 November 2012, the
LHCb team reported on an experiment seen as a "golden" test of
supersymmetry theories in physics,by measuring the very rare decay of the
Bsmeson into two muons (Bs0 → μ+μ−).
The results, which match those predicted by the non-supersymmetrical Standard
Model rather than the predictions of many branches of supersymmetry, show the
decays are less common than some forms of supersymmetry predict, though could
still match the predictions of other versions of supersymmetry theory. The results
as initially drafted are stated to be short of proof but at a relatively high
3.5 sigma level of significance. The result was later confirmed by the CMS
collaboration.
In August 2013 the LHCb
team revealed an anomaly in the angular distribution of B meson decay products
which could not be predicted by the Standard Model; this anomaly had a
statistical certainty of 4.5 sigma, just short of the 5 sigma needed to be
officially recognized as a discovery. It is unknown what the cause of this
anomaly would be, although the Z' boson has been suggested as a possible
candidate.
On 19 November 2014,
the LHCb experiment announced the discovery of two new heavy subatomic
particles, Ξ′−b and Ξ∗−b.
Both of them are baryons that are composed of one bottom, one down, and one
strange quark. They are excited states of the bottom Xi baryon.
On 13 July 2015, the
LHCb collaboration at CERN reported results consistent with pentaquark states
in the decay of bottom Lambda baryons
Second
run (2015 onwards)
At the conference EPS-HEP
2015 in July, the collaborations presented first cross-section measurements of
several particles at the higher collision energy.
How will the Universe end? The Big Freeze..!
If there’s one thing scientists love discussing more than the beginning of the universe, it’s the end. There are literally hundreds of known stellar events that could obliterate the life on our planet before we even knew what hit us. However, the chances of Earth suffering a life-ending global catastrophe are actually rather slim.
But we know that it is coming. At the very least, it
will happen when the sun transitions into a red giant.
The end of everything else though, is a little bit
more difficult to predict; however, that won’t stop scientists from speculating
and theorizing. With this in mind, there are four popular theories on how the
universe might end. BIG FREEZE is the latest theory on the end of universe.
The Big Freeze
It is one theory on how the universe will end: the
‘Heat Death’ – also known as the ‘Big Freeze’ or the ‘Big Chill’ – has been
suggested as one of the ways in which the cosmos could come to an end,
especially since it’s ever expanding.
The idea of heat death actually originates from the
second law of thermodynamics – that’s that idea that entropy increases in an
isolated system (this system being the universe). Entropy, which is the number
of ways in which a system can be arranged, should never decrease, evolving to a
state of maximum disorder (or thermodynamic equilibrium). When this happens,
all energy will be evenly distributed throughout the cosmos, leaving no room
for any reusable energy or heat to burst into existence. Processes that consume
energy, which includes our very living on Earth, would cease.
You might think that Heat Death implies some
astronomically high temperature that snubs everything out. However British
physicist Lord Kelvin, who proposed the idea in the 1850s, referred to the loss
of mechanical energy as the theory of heat. In fact, it has been suggested that
the more the Universe expands, the cooler it gets.
We’re looking at a continual expansion of the
universe, according to readings of the Cosmic Microwave Background, but at a
decreasing rate and it look likely that the cosmos will end in a Heat Death.
Not to worry though; our universe will continue to produce entropy for a while
yet!
Many astronomers and physicists alike believe this may be one of the most probable scenarios thought up at the present moment.
Furthermore, such an event might have already happened before. Some scientists have theorized that the universe we see is the result of a cyclic repetition of the Big Bang, where the first cosmological event came about after the collapse of a previous universe. This is something called Conformal Cyclic Cosmology.
Four theories on end of the universe
There are four important theories which describes the end of the universe. They are,
- The Big Rip
- The Big Freeze
- The Big Crunch
- The Big Slurp
THE BIG RIP:
The Big Rip is a cosmological hypothesis first published in 2003, about the ultimate fate of the universe, in which the matter of the universe, from stars and galaxies to atoms and subatomic particles, is progressively torn apart by the expansion of the universe at a certain time in the future. According to the hypothesis, the scale factor of the universe and with it all distances in the universe will become infinite at a finite time in the future.
THE BIG CRUNCH:
In physical cosmology, the Big Crunch is one possible scenario for the ultimate fate of the universe, in which the metric expansion of space eventually reverses and the universe re-collapses, ultimately ending as a black hole singularity or causing a reformation of the universe starting with another big bang.
THE BIG SLURP:
The doomsday scenario that's been refined by the Danish researchers is known as "The Big Slurp." The Big Slurp would occur when there is a radical shift in the forces that govern the Universe. This violent process is called a phase transition and is very similar to what happens when, for example, water turns to steam
Subscribe to:
Posts (Atom)