quarta-feira, 24 de abril de 2013

Brazilian Researchers Seek Signs of a "New Physics"

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It follows one article published on the day (04/24) in the website of the ”Agência FAPESP” noting that Brazilian Researchers seek signs of a "New Physics".

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Articles

Researchers Seek Signs of a "New Physics"

By Elton Alisson
April 24, 2013

Group from Universidade de
São Paulo's Physics Institute
initiates projects to forecast
phenomena that should be
observed in LHC experiments
starting in 2015. 
Agência FAPESP – After concluding the first phase of experimental tests to find elementary particles in December, the Large Hadron Collider (LHC) at the European Organization for Nuclear Research (CERN) in Switzerland will not resume these types of experiments until 2015, when the intensity of proton beams and energy at the world’s largest particle accelerator will be increased.

During the two-year interval, however, the international community of theoretical physicists will develop a series of numerical models and simulations to predict the types of phenomena that should be observed experimentally in the LHC particle detectors beginning in 2015.

A group of researchers from Universidade de São Paulo’s Physics Institute (IF-USP), for example, has begun a FAPESP-funded Thematic Project to look for signs of a “new physics” in a new round of experiments at the LHC. Such physics should supplement the so-called “Standard Model” of particle physics established over the past 50 years, which describes the strong, weak and electromagnetic interactions of fundamental particles that make up all matter.

“The next two years will be very intense, both in theory as well as in simulation, so that in 2015 when the LHC resumes with proton experiments with higher intensity and energy, we will already have our forecasts concluded. That way the physics experiments can look for a new Physics beyond the Standard Model,” commented Gustavo Alberto Burdman, professor at IF-USP and coordinator of the project, in an interview with Agência FAPESP.

Burdman was one of the speakers at the USP Conference on Cosmology, Large Scale Structures and First Objects held from February 4 to 7, 2013 in São Paulo.

According to the researcher, with the discovery of the Higgs boson (a hypothetical subatomic particle proposed in 1964 by the British physicist Peter Higgs) at CERN in early July, it was presumed that the Standard Model of particle physics would be completely validated.

The Standard Model and the Higgs boson, however, have some gaps, according to Burdman, which have led theoretical and experimental physicists to consider the possibility that there is physics beyond these models.

“The fact that the Higgs boson has severe stability problems and the Standard Model does not include certain particles that we have observed has led us to believe that there is new physics on the scale that is being studied by the LHC,” commented Burdman.

“The increase in the intensity of proton beams and energy in the tests that will be conducted starting in 2015 at the collider will allow us to look for this physics beyond the Standard Model,” he affirmed.

Dark Matter

Throughout the Thematic Project, Burdman and IF-USP researchers Renata Funchal and Oscar José Pinto Eboli will build theories and simulations to predict the existence of some particles not described by the Standard Model, such as those constituting dark matter.

Hypothesized to be responsible for 30% of the Universe’s energy density, the matter, which received the name “dark” because it does not emit light, is not on the Standard Model’s radar.

“The Standard Model does not have any type of particle that could be dark matter. That’s why we need to construct theories to explain the problems presented by the Standard Model relating to dark matter,” affirmed Burdman.

One of the main questions to be answered about the hypothetical particles, according to the researcher, is what they really are. What we know is that dark matter is not composed of particles that interact electromagnetically, like neutrons and protons, detectable by conventional measurement instruments.

“We don’t have the faintest idea of what dark matter is. That’s why we need to extend the Standard Model to have theoretical models that predict it,” summed up Burdman.

Theory As a Guide

According to researchers, during experimental tests with protons conducted at the LHC, scientists observed signs of particles described by the Standard Model.

But the signs of particles observed in models developed by theoretical physicists, which can be produced on the scale of experiments at CERN’s LHC – like the Higgs boson and dark matter particles — are, however, unstable and decay (split) immediately after being produced.  Furthermore, they are hidden beneath several sources of noise produced by the Standard Model, which prevent them from being visualized.

As a way of illustrating how these indications of new particles can be extracted from experiments, the identity models of particle physics and corresponding simulations conducted by theoretical physicists should indicate which particles outside of the Standard Model can be detected in these collisions, into what particles they will decay, with what probability and in which direction, in addition to other information.

“In order to search for a specific particle in the type of experiments conducted at the LHC, one must have a guide to know where and how to look for it. This guide is the theory,” explained Burdman.

Once the signs and the frequency with which they occur are identified in experiments, theoretical physicists can reconstruct their models as a means of certifying that the phenomena can really be observed in the experiments and go beyond the Standard Model.

“We, theoretical physicists, say what should be sought after in experiments, and experimental physicists, on the other hand, tell us what should be observed so that we can adjust our theories,” commented Burdman.

“It was based on this dialogue between theoretical and experimental physicists that the Standard Model of particle physics was built over the last 50 years, and we expect to repeat it now in the quest for the new physics beyond the Standard Model,” he evaluated.

Updating the Cluster of Computers

To test and translate the models developed by theoretical physicists in highly detailed predictions of the events that can be observed experimentally in LHC detectors, scientists must use high-performance computer tools to perform numerical simulations, explained Burdman.

The simulations conducted by the group of IF-USP researchers – both for the LHC as well as for experiments with neutrinos (subatomic particles without electric charge) and dark matter – are performed in a cluster of computers located in the Department of Mathematical Physics.

The processing equipment, however, is old and should be updated through a Thematic Project conducted with FAPESP funding. “The thematic project should give us significant power to conduct computer simulations compatible both with the first LHC data, which began to be released now, as well as with data that will be generated beginning in 2015 with the high-energy collisions,” estimates Burdman.

During the first stage of tests with protons in 2010, scientists at the LHC observed data on the collisions of protons at up to 8 teraelectronvolts (TeV), instead of the 14 TeV per nucleon initially forecast. Thus, in Burdman’s assessment, only now has the highest energy particle accelerator in the world begun to do the work it was conceived to do.

“The new stage of the LHC, with greater energy and proton beam intensity, will allow us to both test particles with greater mass than previously measured and measure the interaction of the Higgs boson with other known particles,” commented Burdman.

For now, according to the researcher, what is known is that there are strong indications that the particle detected at CERN in July is the Higgs boson postulated by the Standard Model.

Because the data are very preliminary, however, the measurements of the particle’s interactions with other known particles present very large margins of error, according to researchers.

“There is still much room for the interaction of the Higgs boson to not be standard, which would signal a new physics. But in order to prove this, more precise measurements must be made, such as the ones that the LHC should allow in the next round of experimental tests,” Burdman indicated.

“Our expectation is that some of the theories that we develop, or some others that we have not pondered, could be built based on the data generated by the LHC in the next few years”.


Source: WebSite Agência FAPESP -  http://agencia.fapesp.br/en/

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