Massive neutrinos solve a cosmological conundrum

Scientists have solved a major problem with the current standard model of cosmology identified by combining results from the Planck spacecraft and measurements of gravitational lensing in order to deduce the mass of ghostly sub-atomic particles called neutrinos.

The team, from the universities of Manchester and Nottingham, used observations of the Big Bang and the curvature of space-time to accurately measure the mass of these elementary particles for the first time.

The recent Planck spacecraft observations of the Cosmic Microwave Background (CMB) – the fading glow of the Big Bang – highlighted a discrepancy between these cosmological results and the predictions from other types of observations.

The CMB is the oldest light in the Universe, and its study has allowed scientists to accurately measure cosmological parameters, such as the amount of matter in the Universe and its age. But an inconsistency arises when large-scale structures of the Universe, such as the distribution of galaxies, are observed.

Professor Richard Battye, from the University of Manchester’s School of Physics and Astronomy, said: “We observe fewer galaxy clusters than we would expect from the Planck results and there is a weaker signal from gravitational lensing of galaxies than the CMB would suggest.

“A possible way of resolving this discrepancy is for neutrinos to have mass. The effect of these massive neutrinos would be to suppress the growth of dense structures that lead to the formation of clusters of galaxies.”

Neutrinos interact very weakly with matter and so are extremely hard to study. They were originally thought to be massless but particle physics experiments have shown that neutrinos do indeed have mass and that there are several types, known as flavours by particle physicists. The sum of the masses of these different types has previously been suggested to lie above 0.06 eV (much less than a billionth of the mass of a proton).

In this paper, Professor Battye and co-author Dr Adam Moss, from the University of Nottingham, have combined the data from Planck with gravitational lensing observations in which images of galaxies are warped by the curvature of space-time. They conclude that the current discrepancies can be resolved if massive neutrinos are included in the standard cosmological model. They estimate that the sum of masses of neutrinos is 0.320 +/- 0.081 eV (assuming active neutrinos with three flavours).

Dr Moss said: “If this result is borne out by further analysis, it not only adds significantly to our understanding of the sub-atomic world studied by particle physicists, but it would also be an important extension to the standard model of cosmology which has been developed over the last decade.”

The paper is published in Physical Review Letters on 7 February and has been selected as an Editor’s choice.

Ends

Notes for editors

A copy of the paper is available from http://arxiv.org/abs/1308.5870 orhttp://prl.aps.org/abstract/PRL/v112/i5/e051303

Jodrell Bank's role in Planck

This paper makes use of CMB data from the European Space Agency’s Planck spacecraft -http://www.esa.int/Our_Activities/Space_Science/Planck - and from the South Pole Telescope -http://pole.uchicago.edu/.

Jodrell Bank Centre for Astrophysics (JBCA - http://www.jodrellbank.manchester.ac.uk/) is directly involved with the two lowest frequencies of the Low Frequency Instrument on board Planck, the 30 and 44 GHz radiometers. These have four and six detectors respectively, operating at 20Kelvin (-253.15°C or -423.67°F). The resolution on the sky is 33 and 27 arc minutes, and the sensitivity 1.6 and 2.4 micro K (over 12 months). The cryogenic low noise amplifiers which are the heart of the radiometers were developed at Jodrell Bank, with help from the National Radio Astronomy Observatory in Virginia, USA.

Dr B Maffei and Dr G Pisano are involved in the other focal instrument, the HFI. First at Cardiff University and now at The University of Manchester, they have played a major role in the design, development and calibration of the Focal Plane Unit, in particular the cold optics, in collaboration with the Institut d'Astrophysique Spatiale, France, Maynooth University, Ireland and JPL/Caltech, USA.

The work to understand the Galactic emission seen by Planck is being co-led from Jodrell Bank by Emeritus Professor Rod Davies and Dr Clive Dickinson. A number of projects are led by Jodrell Bank scientists, including Professor Richard Davis and Dr Clive Dickinson. Each of the 14 projects focuses on one aspect of the Galaxy as seen by Planck, including the electrons that gyrate in the Galactic magnetic field, the ionized gas that pervades the interstellar medium and the dust grains that emit across the entire frequency range that Planck is sensitive to. Jodrell Bank is also leading the calibration and identifying systematics in the LFI data.

Jodrell Bank and Gravitational Lensing

This work uses gravitational lensing data from the Canada-France-Hawaii Telescope Lensing Survey (CFHTLenS - http://www.cfhtlens.org/).

The first gravitational lens to be discovered, the Double Quasar, was found by Dr Denis Walsh of The University of Manchester during a radio survey of the northern sky using telescopes at Jodrell Bank. Follow-up work by Walsh and collaborators using an optical telescope at Kitt Peak in the USA, led to its identification as the first gravitational lens (see Walsh et al 1979, Nature 279, 381). The quasar is at a redshift of 1.41 (a co-moving distance of about 13.7 billion light years) and is lensed by a bright galaxy (and associated cluster of galaxies) at a redshift of 0.355 (a co-moving distance of about 4.54 billion light years) forming a second image of the quasar core and inner jet.

One of the major current e-MERLIN  - http://www.e-merlin.ac.uk/ - legacy programmes (led by Neal Jackson of The University of Manchester and Stephen Serjeant of The Open University) will take advantage of its unique combination of sharpness of view and sensitivity to faint emission to map the multiple images in gravitational lenses and thereby study the evolution of the distribution of mass in distant galaxies.

For further information contact:

Aeron Haworth
Media Relations
Faculty of Engineering and Physical Sciences
The University of Manchester

Tel: 0161 275 8387
Mob: 07717 881563
Email: aeron.haworth@manchester.ac.uk

Source: http://www.manchester.ac.uk/aboutus/news/display/?id=11555

High-energy physicists predict new family of four-quark objects

An international team of high-energy physicists says the discovery of an electrically charged subatomic particle called Z_c(4020) is a sign that they have begun to unveil a whole new family of four-quark objects.

The Beijing Spectrometer (BESIII) collaboration, which includes scientists from UH Mānoa, previously announced the discovery of a mysterious four-quark particle called Z_c(3900) in April 2013.

“While quarks have long been known to bind together in groups of twos or threes, these new results seem to be quickly opening the door to a previously elusive type of four-quark matter,” said Frederick Harris, a professor of physics and astronomy at UH Mānoa, and a spokesman for the BESIII experiment.  “The unique data sample collected by the BESIII collaboration has continued to yield a stream of clues about the nature of multi-quark objects.”

The recent breakthroughs by the BESIII collaboration have come about through a dedicated study of the byproducts of the anomalous Y(4260) particle.

Using the Beijing Electron Positron Collider (BEPCII) in China, scientists tuned the energy at which electrons and positrons annihilate matter to 4260 MeV, which corresponds to the mass of the Y(4260) particle. The BESIII Collaboration used this method to directly produce and collect large samples of the particle’s byproducts, or decays.

This experimental method allowed the BESIII collaboration to first observe the Z_c(3900) and then the Z_c(4020).  Also recently spotted in the decays is the electrically neutral X(3872), a particle that has been experimentally established for more than 10 years, and has long been suspected to be a four-quark object.

“The year 2013 has so far been an exciting one for the BESIII experiment,” Harris said. “Using decays of the Y(4260), a family of four-quark objects has begun to appear. While the theoretical picture remains to be finalized, more and more clues are suggesting that we are witnessing new forms of matter. And while a new ‘zoo’ of mysterious particles is emerging, it seems a new classification system may soon be at hand to understand it.”

About the BESIII Experiment:

The Beijing Spectrometer (BESIII) experiment at the Beijing Electron Positron Collider is composed of about 350 physicists from 50 institutions in 11 countries. U.S. groups include Carnegie Mellon University, Indiana University, The University of Minnesota, The University of Rochester, as well as physicists in the High Energy Physics Group, in the Department of Physics and Astronomy at the University of Hawai‘i at Mānoa.

The scientists have reported their findings to the scientific journal Physical Review Letters, including:

Observation of Z_c(4040) in e+e- --> D*D*- pi+ process at 4.26 GeV
arXiv:1308.2760

Observation of a charged charmoniumlike structure Z_c(4020) and search for the Z_c(3900) in e+e- to pi+pi-h_c
arXiv:1309.1896

Observation of a charged (DD*bar)- mass peak in e+e- --> pi+(DD*bar)-at Ecm=4.26 GeV
arXiv:1310.1163

Observation of the X(3872) in e+e- --> gamma pi+pi- J/psi at sqrt(s) around 4.26 GeV
arXiv:1310.4101

For more information, visit: http://www.phys.hawaii.edu/newsEvents/docs/bes-pr-11-2013.pdf

New Results from Daya Bay: Tracking the Disappearance of Ghostlike Neutrinos

Daya Bay neutrino experiment releases high-precision measurement of subatomic shape shifting and new result on differences among neutrino masses

The international Daya Bay Collaboration has announced new results about the transformations of neutrinos - elusive, ghostlike particles that carry invaluable clues about the makeup of the early universe.  The latest findings include the collaboration's first data on how neutrino oscillation – in which neutrinos mix and change into other "flavors," or types, as they travel – varies with neutrino energy, allowing the measurement of a key difference in neutrino masses known as "mass splitting."  

"Understanding the subtle details of neutrino oscillations and other properties of these shape-shifting particles may help resolve some of the deepest mysteries of our universe," said Jim Siegrist, Associate Director of Science for High Energy Physics at the U.S. Department of Energy (DOE), the primary funder of U.S. participation in Daya Bay. 

U.S. scientists have played essential roles in planning and running of the Daya Bay experiment, which is aimed at filling in the details of neutrino oscillations and mass hierarchy that will give scientists new ways to test for violations of fundamental symmetries. For example, if scientists detect differences in the way neutrinos and antineutrinos oscillate that are beyond expectations, it would be a sign of charge-parity (CP) violation, one of the necessary conditions that resulted in the predominance of matter over antimatter in the early universe.  The new results from the Daya Bay experiment about mass-splitting represent an important step towards understanding how neutrinos relate to the structure of our universe today.  

"Mass splitting represents the frequency of neutrino oscillation," says Kam-Biu Luk of the U.S. Department of Energy's Lawrence Berkeley National Laboratory (Berkeley Lab), the Daya Bay Collaboration's Co-spokesperson, who identified the ideal site for the experiment. "Mixing angles, another measure of oscillation, represent the amplitude. Both are crucial for understanding the nature of neutrinos." Luk is a senior scientist in Berkeley Lab's Physics Division and a professor of physics at the University of California (UC)  Berkeley.  

The Daya Bay Collaboration, which includes more than 200 scientists from six regions and countries, is led in the U.S. by DOE's  Berkeley Lab and Brookhaven National Laboratory (BNL). The Daya Bay Experiment is located close to the Daya Bay and Ling Ao nuclear power plants in China, 55 kilometers northeast of Hong Kong.  The latest results from the Daya Bay Collaboration will be announced at the XVth International Workshop on Neutrino Factories, Super Beams and Beta Beams in Beijing, China. 

"These new precision measurements are a great indication that our efforts will pay off with a deeper understanding of the structure of matter and the evolution of the universe – including why we have a universe made of matter at all," says Steve Kettell, a Senior Scientist at BNL and U.S. Daya Bay Chief Scientist. 

U.S. contributions to the Daya Bay experiment include coordinating detector engineering; perfecting the recipe for the liquid used to track neutrinos in the Daya Bay detectors; overseeing the photo-detector systems used to observe neutrino interactions and muons; building the liquid-holding acrylic vessels and the detector-filling and automated calibration systems; constructing the muon veto system; developing essential software and data analysis techniques; and managing the overall project. 

Measuring neutrino mass and flavors 

Neutrinos come in three "flavors" (electron, muon, and tau) and each of these exists as a mixture of three masses. Measuring oscillations of neutrinos from one flavor to another gives scientists information on the probability of each flavor occupying each mass state (the mixing angles) and the differences between these masses (mass splitting). 

Daya Bay measures neutrino oscillation with electron neutrinos – actually antineutrinos, essentially the same as neutrinos for the purpose of these kinds of measurements. Millions of quadrillions of them are created every second by six powerful reactors. As they travel up to two kilometers to underground detectors, some seem to disappear.  

The missing neutrinos don't vanish; instead they have transformed, changing flavors and becoming invisible to the detectors. The rate at which they transform is the basis for measuring the mixing angle, and the mass splitting is determined by studying how the rate of transformation depends on the neutrino energy. 

Daya Bay's first results were announced in March 2012 and established the unexpectedly large value of the mixing angle theta one-three, the last of three long-sought neutrino mixing angles. The new results from Daya Bay put the precise number for that mixing angle at sin22θ13=0.090 plus or minus 0.009. The improvement in precision is a result of having more data to analyze and having the additional measurements of how the oscillation process varies with neutrino energy. 

The energy-dependence measurements also open a window to the new analysis that will help scientists tease out the miniscule differences among the three masses. From the KamLAND experiment in Japan, they already know that the difference, or "split," between two of the three mass states is small. They believe, based on the MINOS experiment at Fermilab, that the third state is at least five times smaller or five times larger.  Daya Bay scientists have now measured the magnitude of that mass splitting,  |Δm2ee|, to be (2.54±0.20)x10-3 eV2.

The result establishes that the electron neutrino has all three mass states and is consistent with that from muon neutrinos measured by MINOS. Precision measurement of the energy dependence should further the goal of establishing a "hierarchy," or ranking, of the three mass states for each neutrino flavor.

MINOS, and the Super-K and T2K experiments in Japan, have previously determined the complementary effective mass splitting (Δm2μμ) using muon neutrinos. Precise measurement of these two effective mass splittings would allow calculations of the two mass-squared differences (Δm232 and Δm231) among the three mass states. KamLAND and solar neutrino experiments have previously measured the mass-squared difference Δm221 by observing the disappearance of electron antineutrinos from reactors about 100 miles from the detector and the disappearance of neutrinos from the sun. 

UC Berkeley and Berkeley Lab's Bill Edwards, Daya Bay's U.S. Project and Operations Manager, says, "The ability to measure these subtle effects with greater and greater precision is a testament to the scientific and engineering team that designed and built this exceptional experiment." 

U.S. scientists are also laying the groundwork for a future neutrino project, the Long-Baseline Neutrino Experiment (LBNE). This experiment would use high intensity accelerators at Fermi National Accelerator Laboratory to produce high-energy muon neutrinos and aim them at detectors 1,300 kilometers away in South Dakota, a distance from neutrino source to detector needed to observe the transformations of high-energy muon neutrinos. LBNE would detect the appearance of the other two flavors at the far-away detector in addition to the disappearance of one flavor of neutrino as evidence of oscillation.  The combined results from LBNE and other global neutrino experiments will give scientists new ways to test for violations of fundamental symmetries, and open other avenues to understanding the structure of the universe today.  

http://www.bnl.gov/newsroom/news.php?a=11568