Is It the Era of Racing for Colliders’ Physics?

Particle Accelerators have a long story which started since the beginnings of the twentieth century.

This question may be brought to mind after China's announcement in 2014 that they plan to build a super collider. This announcement came after decades of European and American leadership in the field of high-energy particle colliders.

The particles collider planned by the scientists at the Institute of High Energy Physics in Beijing, working with international collaborators is a 'Higgs factory' - a 52-kilometer underground ring that would smash together electrons and positrons. It’s supposed to be built by 2028.

It’s worth mentioning that there is a difference between hadron colliders such as the famous European Large Hadron Collider (LHC) and the e^-−e⁺ colliders. A Hadrons collider smash proton-proton or proton-anitproton beams together, while e^-−e⁺colliders can have a lower energy and give cleaner data that are easier to analyze, because they are already smashing together fundamental particles which are smaller than both protons and antiprotons.

Particle Accelerators have a long story which started since the beginnings of the twentieth century. By around 1932, Synchrotrons were one of the initial models of accelerators that dealt with single beams of particles like Protons and Deuterons for research proposes. A few years later in 1956, the Norwegian physicist Rolf Widerøe published the first concept of particles collider in Germany.

The idea grew up until 1960, when the European Council for Nuclear Research (CERN) set up a study focused on a Proton-proton Collider, meanwhile, CERN's Proton Synchrotron (PS) was already under construction.

Bringing the first particles collider into action, its design was based on the so-called Intersecting Storage Rings (ISR), which involved two interlaced proton-synchrotron rings that crossed at eight points.

Comparative Infograph for the sizes of CERN and the future particles smashers.

The advantage of these rings was to obtain sufficient beams current (particles flux).

In October 1970, after around ten years of planning, the first proton beam was injected and immediately circulated in Ring 1.

Once Ring 2 was available, the first collisions occurred on June 1971 at a beam momentum of 15 GigaElectronVolt (GeV).

Comparing by nowadays facilities, that project can be considered a simpler one. Yet at the same time it was an important layout for a larger collider launched after that at CERN, the Electron-Positron (LEP) collider with a 27-kilometer circumference.

The main aim of LEP collider was studying carefully the Z Boson and its charged partner the W Boson. Both particles were discovered at CERN in 1983 and appeared to be responsible for the Weak Force which drives the radioactive decays.

The first beam circulated in LEP occurred in July 1989. The collider's initial energy was around the Z boson’s mass ~91 GeV, so that Z bosons could be produced.

There were four detectors at LEP built around four collision points within underground halls named ALEPH, DELPHI, OPAL, and L3.

During its operation period near 100 GeV, LEP was capable of producing around 17 million Z bosons. Observing the creation and decay of such short-lived particles was a real window to test the electroweak sector of the Standard Model Theory (SM).

ISR consisted of two interlaced proton synchrotron rings, both 300 m in diameter, which received protons from the PS.

Additionally, one of the most interesting discoveries at LEP was to prove that there are three-and only three-generations of particles of matter (for example, leptons, there are only electrons, muons, and tau particles, which almost have identical properties except for their masses).

LEP was closed down on November 2, 2000 to make way for the construction of the LHC in the same tunnel.

US's Most Famous Particles Accelerators

Meanwhile, on the other side of the globe, there were wide discussions between 1973 and 1981 to build a Proton-antiproton Accelerator at Fermi National Accelerator Laboratory (Fermilab) in the United States.

The Tevatron was designed to accelerate two beams of protons and antiprotons to 99.999954 percent of the speed of light around a six-km circumference.

After the collisions of the two beams, conditions similar to those in the early universe get reproduced, allowing us to probe the structure of matter, space and time at a very small scale.

Scientists at Fermilab also studied particle collisions by directing beams into stationary targets to produce neutrino beams (Fixed Target program). The main Tevatron experiments were CDF and DZero which are located on opposite sides along the Tevatron's beam pipe.

Tevatron’s first run was in 1983, it accelerated protons up to energy of 512 GeV, the energy then increased gradually until it reached 1.9 TeraElectronvolt (TeVU center of mass energy).

During its run, the most important discoveries of the Tevatron were the detection of the Top Quark in 1977, and the discovery of the Tau Neutrino at the Direct Observation of the NU Tau Experiment (DONUT) in 2000.

Although Tevatron was shutdown in September 30, 2011, the scientists continue to make analysis on the previous collected data and in 2012 they presented constrains on the mass regions of the Higgs boson consistent with those from LHC.

A 1974 photo of the part named Intersection 5 (I5) of the ISR of CERN's old PS, clearly shows the layout of the magnets and the crossing of the two beams pipes.

Also one of the other famous particle physics experiments in the US is the BaBar Experiment at SLAC National Accelerator Laboratory.

The aim of BaBar was to understand the inequality between the matter and antimatter content in the observable universe (so that, we still exist and were not annihilated) by studying the interactions of the meson system and its antiparticle B̅ (B bar).

If nature doesn’t distinguish between both systems, the decay rate of B mesons and their antiparticles should be equal, but as found, that was not the case.

The BaBar detector consists of two rings, one for electron beam and another for positron beam. These beams get accelerated to collide to each other to have B and B̅ (B bar) mesons among the collision products.

The data recorded in BaBar from October 1999 till April 2008 may have suggested possible flaws in SM Theory as the results were a potential sign of something amiss in particle physics and are likely to impact existing theories we widely accept, including those attempting to deduce the properties of Higgs bosons.

East Asian Contributions

On the other hand, Japan has paid a bigger attention for the neutrino researches. The beginning was when the Super-Kamiokande Observatory- a neutrino detector located under Mount Kamioka in Japan- indicated that atmospheric neutrinos, coming from the sun and other cosmic sources undergo oscillations between different flavors. 

Following these observations, Japan tended to operate a new experiment at the High Energy Accelerator Research Organization (KEK Laboratory) to verify these results.

The experiment was called the neutrino oscillation experiment K2K, it worked from 1999 to November 2004. A well-controlled beam of muon neutrinos was sent to long distances to detect the neutrinos behavior. K2K was able to introduce the first positive measurement of neutrino oscillations which consisted with the previous results.

However, according to the SM the neutrino is a massless particle, meaning that it can't have different flavors. Hence, the observation of the neutrino oscillations is so far considered as one of the strongest contradictions to the SM.

Belle Experiment was another study started in the same year with K2K Experiment at KEK laboratory. Similar to BaBar Experiment, Belle was a B-factory which got constructed to study rare decays, search for exotic particles, and to conduct precision measurements of the processes of B mesons and D mesons.

Future of Understanding How the Universe Started

The former LEP tunnel at CERN being filled with magnets for the LHC.

It's worth mentioning that there are promising plans set up for the future. The International Linear Collider (ILC) which is planned to be an electron-positron linear accelerator is designed to operate at much higher energies than China's proposed 52-kilometer electron-positron ring.

So, as we saw, for around 100 years scientists from all over the world worked out on enhancing and developing the machines called particles colliders to introduce clues for the secrets of the universe around us, and searches are just going on.

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