After the Higgs-boson-like particle, what's next?

This article, as written by me, appeared in print in The Hindu on July 5, 2012.

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The ATLAS (A Toroidal LHC Apparatus) collaboration at CERN has announced the sighting of a Higgs boson-like particle in the energy window of 125.3 ± 0.6 GeV. The observation has been made with a statistical significance of 5 sigma. This means the chances of error in their measurements are 1 in 3.5 million, sufficient to claim a discovery and publish papers detailing the efforts in the hunt.

Rolf-Dieter Heuer, Director General of CERN since 2009, said at the special conference called by CERN in Geneva, “It was a global effort, it is a global effort. It is a global success.” He expressed great optimism and concluded the conference saying this was “only the beginning.”

With this result, collaborations at the Large Hadron Collider (LHC), the atom-smashing machine, have vastly improved on their previous announcement on December 13, 2011, where the chance of an error was 1-in-50 for similar sightings.

[caption id="attachment_23590" align="aligncenter" width="600"] A screenshot from the Dec 13, 2011, presentation by Fabiola Gianotti, leader of the ATLAS collaboration, that shows a global statistical significance of 2.3 sigma, which translates to a 1-in-50 chance of the result being erroneous.[/caption]

Another collaboration, called CMS (Compact Muon Solenoid), announced the mass of the Higgs-like particle with a 4.9 sigma result. While insufficient to claim a discovery, it does indicate only a one-in-two-million chance of error.

Joe Incandela, CMS spokesman, added, “We’re reaching into the fabric of the universe at a level we’ve never done before.”

The LHC will continue to run its experiments so that results revealed on Wednesday can be revalidated before it shuts down at the end of the year for maintenance. Even so, by 2013, scientists, such as Dr. Rahul Sinha, a participant of the Belle Collaboration in Japan, are confident that a conclusive result will be out.

“The LHC has the highest beam energy in the world now. The experiment was designed to yield quick results. With its high luminosity, it quickly narrowed down the energy-ranges. I’m sure that by the end of the year, we will have a definite word on the Higgs boson’s properties,” he said.

However, even though the Standard Model, the framework of all fundamental particles and the dominating explanatory model in physics today, predicted the particle’s existence, slight deviations have been observed in terms of the particle’s predicted mass. Even more: zeroing in on the mass of the Higgs-like particle doesn’t mean the model is complete when, in fact, it is far from.

While an answer to the question of mass formation took 50 years to be reached, physicists are yet to understand many phenomena. For instance, why aren’t the four fundamental forces of nature equally strong?

The weak, nuclear, electromagnetic, and gravitational forces were born in the first few moments succeeding the Big Bang 13.75 billion years ago. Of these, the weak force is, for some reason, almost 1 billion, trillion, trillion times stronger than the gravitational force! Called the hierarchy problem, it evades a Standard Model explanation.

In response, many theories were proposed. One, called supersymmetry (SUSY), proposed that all fermions, which are particles with half-integer spin, were paired with a corresponding boson, or particles with integer spin. Particle spin is the term quantum mechanics attributes to the particle’s rotation around an axis.

Technicolor was the second framework. It rejects the Higgs mechanism, a process through which the Higgs boson couples stronger with some particles and weaker with others, making them heavier and lighter, respectively.

Instead, it proposes a new form of interaction with initially-massless fermions. The short-lived particles required to certify this framework are accessible at the LHC. Now, with a Higgs-like particle having been spotted with a significant confidence level, the future of Technicolor seems uncertain.

However, “significant constraints” have been imposed on the validity of these and such theories, labeled New Physics, according to Prof. M.V.N. Murthy of the Institute of Mathematical Sciences (IMS), whose current research focuses on high-energy physics.

Some other important questions include why there is more matter than antimatter in this universe, why fundamental particles manifest in three generations and not more or fewer, and the masses of the weakly-interacting neutrinos. State-of-the-art technology worldwide has helped physicists design experiments to study each of these problems better.

For example, the India-based Neutrino Observatory (INO), under construction in Theni, will house the world’s largest static particle detector to study atmospheric neutrinos. Equipped with its giant iron-calorimeter (ICAL) detector, physicists aim to discover which neutrinos are heavier and which lighter.

The LHC currently operates at the Energy Frontier, with high-energy being the defining constraint on experiments. Two other frontiers, Intensity and Cosmic, are also seeing progress. Project X, a proposed proton accelerator at Fermilab in Chicago, Illinois, will push the boundaries of the Intensity Frontier by trying to look for ultra-rare process. On the Cosmic Frontier, dark matter holds the greatest focus.

Understanding accelerator luminosity

Advanced physics is essentially a study in precision, and the particle accelerators of today that are located at the cutting-edge Intensity and Energy Frontiers work against approximations everyday. The particles they synthesize, track and study are so small, quick and short-lived that they might as well have simply popped in and out of existence and nothing would've changed. However, fortunately, that's not the point of studying these things at all: understanding why the "popping" happens at all is what is key.

[caption id="attachment_21639" align="aligncenter" width="346" caption="Some famous accelerators: (clockwise from top-left) Kō Enerugī Kasokuki Kenkyū Kikō (KEK), Japan; Tevatron at FERMILAB; CERN's Large Hadron Collider; and LINAC at Stanford Linear Accelerator Centre."][/caption]

At the world's most powerful collider, the LHC at CERN, two proton beams are shot around 27-km long rings. These are not continuous beams but ones intermittently segregated into bunches, like a pulse. Each of these bunches contains 2,808 protons (which are the hadrons in question) and there are 1,000 bunches per beam. It is ensured that the bunches from the rings don't cross each other - "collide" - more than once every 25 nanoseconds. At this rate, 112.32 billion protons - 56.16 billion from each side - meet each other every second. This is what every particle accelerator makes possible: a rendezvous.

Once this is done, the detectors take over, and they are the real measure of an accelerator's performance. The accelerator will have ensured that enough collisions occur so that the detector can record at least one (even though I'm understating the ratio, it is really quite small). Ergo, to measure a detector's performance as either being good or bad, or perhaps even as somewhere in between in the rare case, how much it is capable of seeing is what makes the difference. This is where luminosity comes in.

The generic definition of luminosity is that it is a measure of the quantity of light that passes through an area each second, and so its units are per metre-squared per second. Accelerator physics adopted this definition and modified it a little: accelerator luminosity is a measure of the number of particles that pass through a given area each second multiplied by the opacity of the detector. This final parameter is necessary because it also accounts for the tendency of some particles to escape detection by passing right through the target: if the target's opacity is high, most particles will be "seen", and if it is low, most particles will be invisible to the cameras' eyes.

(Even though the definition of luminosity indicates the number of particles that pass through an area per second, its meaning in the confines of an accelerator changes: it is the number particles that are seen by a detector irrespective of how many particles there are in total.)

Inside the accelerator and in the presence of the detector, the following differential equation dictates the machine's luminosity:



Here, σ is the total cross section of the detector - the area that is exposed to and receives the stream of particles, N the number of particles, L the instantaneous luminosity, and t the duration over which the detector remains in operation. The opacity affects σ. (The 'd' denotes that the value of the parameter is being considered for an infinitesimal period of time, as indicated by the dt in the denominator. If it was dx or dy instead of dt, it would mean the value of N is being considered over a very small distance in the x or y direction.)

If Ω (omega) were the solid angle through which the detector's cross section was exposed, its differential cross section is computed as



 

This formula gives the luminosity with respect to the angular cross section (as opposed to a planar surface) as the number of particles per degree per second, and from here, the number of particles per volume of space can be easily computed. The formula also shows that the greater the detecting cross section per degree of solid angle, the greater the luminosity per degree of the same angle (or, "particle-seeability"). And for the detector to be useful at all, the instantaneous luminosity has to be high enough to detect particles so small that... well, they're incredibly small. Therefore, the smaller the particle being studied, the larger the detector will be.

There is no better way to illustrate this conclusion than to point, again, to the LHC, where the Higgs boson particle, one of the smallest particles conceivable, a veritable building block of nature, is being hunted by the world's largest detector (which also has a misleading name): the Compact Muon Solenoid (CMS). The CMS, weighing 12,500 tons, has been able to achieve an astounding integrated (as in not instantaneous) luminosity of 1 per femtobarn: 1 barn is one-hundred-billion-billion-billionth of a squared metre; 1 femtobarn is one-million-billionth of that!

[caption id="attachment_21633" align="aligncenter" width="461" caption="The total integrated luminosity delivered to and collected by CMS until 17th June, 2011."][/caption]

Another detector at the site, the much more prolific A Toroidal LHC Apparatus (ATLAS) weighs 7,000 tons and has a luminosity of 50 per femtobarn. The under-construction iron-calorimeter (ICAL) detector at the India-based Neutrino Observatory (INO) in Theni, Tamil Nadu, will weigh 50,000 tons after being completed in 2015 and will be used to track and study neutrinos exclusively. Neutrinos are particles more elusive than the Higgs, and, though the luminosity of ICAL hasn't been disclosed, we can expect the device to be one of the pioneers in detector technology simply because its luminosity must be that low for the project to be a success.

This much and more can be said of accelerator luminosity. While the media goes gaga over the energies at which the beams are being accelerated, there is a silent revolution in detector technology happening in the background, a revolution that is spawning brilliant techniques to spot the fastest, smallest and most volatile particles. These detectors also consume the greater part of accelerator budgets to build and the greater part of total maintenance time. Some of the most advanced detectors in existence include hadronic calorimeters (HCAL), ring-imaging Cherenkov detectors (RICH detectors) and muon spectrometers.

Star of the Orient

India’s first particle physics observatory is to be constructed in the district of Theni in Tamil Nadu at an expense of Rs. 1,200 crore (USD 250 million). Called the India-based Neutrino Observatory (INO), the entire experiment will be situated 1.3 km under a hill to keep other radiations and cosmic rays from interfering with the study. This is because the neutrinos that the detector will be studying rarely interact with matter and pass through it at the rate of three or four interactions per nearly 85 trillion trillion trillion. The gouging of a tunnel 7m wide and 1.9km long for accessing the cavern that will house the systems was commenced on October 14, Friday, and is expected to take a year.

Twenty-seven days ago, a startling discovery set off tremors across the scientific community when the Gran Sasso National Laboratory inItalyreported that certain fundamental particles called neutrinos had been observed moving faster than light. The reason this observation caused such dissonance and a flurry of excitement is that, according to the physics megagiant Albert Einstein, the Universe would allow nothing to travel faster than light.

Then again, conclusive proof was not presented by the physicists at the lab—at least, not anything that was within the infamous six-sigma accuracy tolerance limit: 99.99999 per cent. It was little surprise, then, that within a week of the report, engineers were working in full-swing atJapan's Kamioka reactor, at theUSA's dreaded Fermilab, at the Sudbury Neutrino Observatory inCanada, to recreate the conditions at Gran Sasso. Far away, in India, a country that had until then been the principle centre for processing second-hand information, a 22-year old plan was finally being mobilized.

With just a 29-year old history, the energy frontier of physics research was supposed to last at least until 2018—the year of the Super Large Hadron Collider. With such unprecedented discoveries, however, a shift away from high-energy research and toward ultra-rare processes has become conspicuous. For the INO, the timing couldn’t have been better.

The decision to locate the observatory at Theni was finalized after evaluating the local topography, seismic stability, environmental disturbance, rock quality, availability of electricity and water, and rain patterns. In order to further minimize the impact of the project’s logistical and infrastructural operations, an extant but little-used road is being re-laid for the trucks and earthmovers to use, instead of having them move through five villages.

Funded by the government of India and the Tata Institute of Fundamental Research (TIFR), and coordinated by the Institute of Mathematical Sciences (IMS), the INO will host a supersensitive static detector called the Iron Calorimeter (ICAL), incorporating a magnet exactly four times as large as the one in use at the Large Hadron Collider. Such an effort will involve the INO-industry interface in a big way, drawing heavily on available industrial infrastructure, in issues related to mechanical structure, electronics and detector-related technology.

The detector will consist of a stack of alternating plates of iron and borosilicate glass, each totally numbering 30,000 and measuring 12m to a side. The glass plates, in turn, will consist of glass sheets with a noble gas sandwiched in between—an arrangement referred to collectively as a resistive plate chamber (RPC). When a neutrino interacts with iron, it will knock out an electron from its orbit around an atom and send it into the RPC. Once there, the electron will be picked up by positively charged electrodes sewn into the glass, translated into a signal, and sent to the data processors.

The source of the neutrinos will be the sun, supernovae, cosmic rays and other intergalactic phenomena, and the output will correspond to the particle’s mass, position of interaction, velocity, type, degree of oscillation and charge.

There are two reasons the INO stands out from its peers: the first is that the ICAL is going to be devoted to studying neutrinos and neutrinos only, and the second is that the ICAL will study them continuously without stopping (except for scheduled maintenance). Because of such principled and technical dedication, physicists expect the detector to shine light on some of the more elusive characteristics of neutrinos, such as flavour oscillations and neutrino-neutrino interactions.

These are boom times for Indian science. The national spending on science and technology has gone up in the last five years and is inching towards two per cent ofIndia's GDP. Hordes of new institutes are coming up in the nook and corner of the country—30 new central universities, 5 new Indian Institutes of Science Education and Research, 8 new Indian Institutes of Technology and 20 new Indian Institutes of Information Technology are in various stages of conception and completion.

However, simply increasing the number of institutes will not lead to better scientific prowess. The education system needs a complete rethink in order to attract more students to science and produce world class scientists (the last home-grown scientist to win a Nobel Prize was Sir C. V. Raman in 1930). In this direction, the INO is a giant leap forward because of its capacity to sustain research in subjects at the energy and cosmic frontiers, because of the special and exotic experimentation environments it will support, and because of the invaluable access it will provide to the Indian scientific community to cutting-edge information.

Star of the Orient

India’s first particle physics observatory is to be constructed in the district of Theni in Tamil Nadu at an expense of Rs. 1,200 crore (USD 250 million). Called the India-based Neutrino Observatory (INO), the entire experiment will be situated 1.3 km under a hill to keep other radiations and cosmic rays from interfering with the study. This is because the neutrinos that the detector will be studying rarely interact with matter and pass through it at the rate of three or four interactions per nearly 85 trillion trillion trillion. The gouging of a tunnel 7m wide and 1.9km long for accessing the cavern that will house the systems was commenced on October 14, Friday, and is expected to take a year.

Twenty-seven days ago, a startling discovery set off tremors across the scientific community when the Gran Sasso National Laboratory inItalyreported that certain fundamental particles called neutrinos had been observed moving faster than light. The reason this observation caused such dissonance and a flurry of excitement is that, according to the physics megagiant Albert Einstein, the Universe would allow nothing to travel faster than light.

Then again, conclusive proof was not presented by the physicists at the lab—at least, not anything that was within the infamous six-sigma accuracy tolerance limit: 99.99999 per cent. It was little surprise, then, that within a week of the report, engineers were working in full-swing atJapan's Kamioka reactor, at theUSA's dreaded Fermilab, at the Sudbury Neutrino Observatory inCanada, to recreate the conditions at Gran Sasso. Far away, in India, a country that had until then been the principle centre for processing second-hand information, a 22-year old plan was finally being mobilized.

With just a 29-year old history, the energy frontier of physics research was supposed to last at least until 2018—the year of the Super Large Hadron Collider. With such unprecedented discoveries, however, a shift away from high-energy research and toward ultra-rare processes has become conspicuous. For the INO, the timing couldn’t have been better.

The decision to locate the observatory at Theni was finalized after evaluating the local topography, seismic stability, environmental disturbance, rock quality, availability of electricity and water, and rain patterns. In order to further minimize the impact of the project’s logistical and infrastructural operations, an extant but little-used road is being re-laid for the trucks and earthmovers to use, instead of having them move through five villages.

Funded by the government of India and the Tata Institute of Fundamental Research (TIFR), and coordinated by the Institute of Mathematical Sciences (IMS), the INO will host a supersensitive static detector called the Iron Calorimeter (ICAL), incorporating a magnet exactly four times as large as the one in use at the Large Hadron Collider. Such an effort will involve the INO-industry interface in a big way, drawing heavily on available industrial infrastructure, in issues related to mechanical structure, electronics and detector-related technology.

The detector will consist of a stack of alternating plates of iron and borosilicate glass, each totally numbering 30,000 and measuring 12m to a side. The glass plates, in turn, will consist of glass sheets with a noble gas sandwiched in between—an arrangement referred to collectively as a resistive plate chamber (RPC). When a neutrino interacts with iron, it will knock out an electron from its orbit around an atom and send it into the RPC. Once there, the electron will be picked up by positively charged electrodes sewn into the glass, translated into a signal, and sent to the data processors.

The source of the neutrinos will be the sun, supernovae, cosmic rays and other intergalactic phenomena, and the output will correspond to the particle’s mass, position of interaction, velocity, type, degree of oscillation and charge.

There are two reasons the INO stands out from its peers: the first is that the ICAL is going to be devoted to studying neutrinos and neutrinos only, and the second is that the ICAL will study them continuously without stopping (except for scheduled maintenance). Because of such principled and technical dedication, physicists expect the detector to shine light on some of the more elusive characteristics of neutrinos, such as flavour oscillations and neutrino-neutrino interactions.

These are boom times for Indian science. The national spending on science and technology has gone up in the last five years and is inching towards two per cent ofIndia's GDP. Hordes of new institutes are coming up in the nook and corner of the country—30 new central universities, 5 new Indian Institutes of Science Education and Research, 8 new Indian Institutes of Technology and 20 new Indian Institutes of Information Technology are in various stages of conception and completion.

However, simply increasing the number of institutes will not lead to better scientific prowess. The education system needs a complete rethink in order to attract more students to science and produce world class scientists (the last home-grown scientist to win a Nobel Prize was Sir C. V. Raman in 1930). In this direction, the INO is a giant leap forward because of its capacity to sustain research in subjects at the energy and cosmic frontiers, because of the special and exotic experimentation environments it will support, and because of the invaluable access it will provide to the Indian scientific community to cutting-edge information.