INTRODUCTION
The Large Hadron Collider (LHC) is the world's largest and highest-energy particle accelerator. The LHC lies near
The Large Hadron Collider was built by the European Organization for Nuclear Research (CERN). with the intention of testing various predictions of high-energy physics, including the existence of the hypothesized Higgs boson and of the large family of new particles predicted by supersymmetry. Physicists will use the LHC to recreate the conditions just after the Big Bang, by colliding the two beams at very high energy. It is funded by and built in collaboration with over 10,000 scientists and engineers from over 100 countries as well as hundreds of universities and laboratories.
Two beams of subatomic particles called 'hadrons' – either protons or lead ions – will travel in opposite directions inside the circular accelerator, gaining energy with every lap. Physicists will use the LHC to recreate the conditions just after the Big Bang, by colliding the two beams head-on at very high energy. Teams of physicists from around the world will analyse the particles created in the collisions using special detectors in a number of experiments dedicated to the LHC.
There are many theories as to what will result from these collisions, but what's for sure is that a brave new world of physics will emerge from the new accelerator, as knowledge in particle physics goes on to describe the workings of the Universe. For decades, the Standard Model of particle physics has served physicists well as a means of understanding the fundamental laws of Nature, but it does not tell the whole story. Only experimental data using the higher energies reached by the LHC can push knowledge forward, challenging those who seek confirmation of established knowledge, and those who dare to dream beyond the paradigm.
Tunnelling to the beginning of time
DESIGN
The LHC is the world's largest and highest-energy particle accelerator. The collider is contained in a circular tunnel, with a circumference of 27 kilometres (17 mi), at a depth ranging from 50 to 175 metres (160 to 574 ft) underground.
The 3.8-metre (12 ft) wide concrete-lined tunnel, constructed between 1983 and 1988, was formerly used to house the Large Electron–Positron Collider. It crosses the border between
Superconducting quadrupole electromagnets are used to direct the beams to four intersection points, where interactions between accelerated protons will take place.
The collider tunnel contains two adjacent parallel beam pipes that intersect at four points, each containing a proton beam, which travel in opposite directions around the ring. Some 1,232 dipole magnets keep the beams on their circular path, while an additional 392 quadrupole magnets are used to keep the beams focused, in order to maximize the chances of interaction between the particles in the four intersection points, where the two beams will cross. In total, over 1,600 superconducting magnets are installed, with most weighing over 27 tonnes. Approximately 96 tonnes of liquid helium is needed to keep the magnets at their operating temperature of 1.9 K (−271.25 °C), making the LHC the largest cryogenic facility in the world at liquid helium temperature.
Once or twice a day, as the protons are accelerated from 450 GeV to 7 TeV, the field of the superconducting dipole magnets will be increased from 0.54 to 8.3 teslas (T). The protons will each have an energy of 7 TeV, giving a total collision energy of 14 TeV. At this energy the protons have a Lorentz factor of about 7,500 and move at about 0.999999991 c, or about 3 metres per second slower than of the speed of light (c). It will take less than 90 microseconds (μs) for a proton to travel once around the main ring – a speed of about 11,000 revolutions per second. Rather than continuous beams, the protons will be bunched together, into 2,808 bunches, so that interactions between the two beams will take place at discrete intervals never shorter than 25 nanoseconds (ns) apart. However it will be operated with fewer bunches when it is first commissioned, giving it a bunch crossing interval of 75 ns.
Prior to being injected into the main accelerator, the particles are prepared by a series of systems that successively increase their energy. The first system is the linear particle accelerator LINAC 2 generating 50-MeV protons, which feeds the Proton Synchrotron Booster (PSB). There the protons are accelerated to 1.4 GeV and injected into the Proton Synchrotron (PS), where they are accelerated to 26 GeV. Finally the Super Proton Synchrotron (SPS) is used to further increase their energy to 450 GeV before they are at last injected (over a period of 20 minutes) into the main ring. Here the proton bunches are accumulated, accelerated (over a period of 20 minutes) to their peak 7-TeV energy, and finally circulated for 10 to 24 hours while collisions occur at the four intersection points.
The LHC physics program is mainly based on proton–proton collisions. However, shorter running periods, typically one month per year, with heavy-ion collisions are included in the program. While lighter ions are considered as well, the baseline scheme deals with lead ions[30] (see A Large Ion Collider Experiment). The lead ions will be first accelerated by the linear accelerator LINAC 3, and the Low-Energy Ion Ring (LEIR) will be used as an ion storage and cooler unit. The ions will then be further accelerated by the PS and SPS before being injected into LHC ring, where they will reach an energy of 2.76 TeV per nucleon (or 575 TeV per ion), higher than the energies reached by the Relativistic Heavy Ion Collider. The aim of the heavy-ion program is to investigate quark–gluon plasma, which existed in the early universe.
EXPECTED RESULT
This gigantic scientific instrument is intended to collide opposing particle beams of either protons at an energy of 7 teraelectronvolts per particle, or lead nuclei at an energy of 574 TeV per nucleus. The term hadron refers to particles composed of quarks. It is expected that it will help us to know about the deepest laws of nature.
CURRENT RESULT
On 10 September 2008, the proton beams were successfully circulated in the main ring of the LHC for the first time, but nine days later, operations were halted due to a serious fault between two superconducting bending magnets. Repairing the resulting damage and installing additional safety features took over a year.
On 20 November 2009, the proton beams were successfully circulated again, with the first proton–proton collisions being recorded three days later at the injection energy of 450 GeV per beam. The LHC became the world's highest-energy particle accelerator on 30 November 2009, achieving a world record 1.18 TeV per beam and surpassing the record previously held by the Tevatron at Fermilab in
After the 2009 winter shutdown, the LHC was restarted and the beam was ramped up to 3.5 TeV per beam, half its designed energy, which is planned for after its 2012 shutdown. On 30 March 2010, the first planned collisions took place between two 3.5 TeV beams, which set a new world record for the highest-energy man-made particle collisions.
TEST TIMELINE
Date Event
10 Sep 2008 CERN successfully fired the first protons around the entire tunnel circuit in stages.
30 Sep 2008 First "modest" high-energy collisions planned but postponed due to accident.
16 Oct 2008 CERN released a preliminary analysis of the incident.
21 Oct 2008 Official inauguration.
05 Dec 2008 CERN released detailed analysis.
20 Nov 2009 Low-energy beams circulated in the tunnel for the first time since the incident.
23 Nov 2009 First particle collisions in all four detectors at 450 GeV.
30 Nov 2009 LHC becomes the world's highest-energy particle accelerator achieving 1.18 TeV per beam, beating the Tevatron's previous record of 0.98 TeV per beam held for eight years.
28 Feb 2010 The LHC continues operations ramping energies to run at 3.5 TeV for 18 months to two years, after which it will be shut down to prepare for the 14 TeV collisions (7 TeV per beam).
30 Mar 2010 The two beams collided at 7 TeV in the LHC at 13:06 CEST, marking the start of the LHC research programme.
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