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  • richardmitnick 6:44 pm on January 4, 2016 Permalink | Reply
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    From FNAL- “Neutrinos: telling the whole story” 

    FNAL II photo

    Fermilab is an enduring source of strength for the US contribution to scientific research world wide.

    January 4, 2016
    Dipak Rimal

    1
    This plot shows the total probability of neutrinos (top) or antineutrinos (bottom) interacting on a plastic scintillator target as a function of energy. Black points are new results from MINERvA and the colored points are the results from earlier experiments. The solid line is the expected value from simulation.

    2
    Jeff Nelson of the College of William and Mary is seen here in the process of making a plane of scintillator for the MINERvA detector. He will present these results in the Jan. 8 Wine and Cheese Seminar.

    Neutrinos are the most abundant yet most elusive massive particles in the universe. They rarely interact with matter and oscillate into different identities over time. In order to understand these ghostly particles in greater detail, understanding and modeling their feeble interaction with various detector materials used in giant detectors is critical. Neutrino oscillation experiments seek to improve and constrain models used in their simulations to match the reality as closely as possible.

    The MINERvA experiment continues to provide measurements relevant to these experiments to help scientists better model these interactions and implement in their simulation.

    FNAL Minerva
    MINERvA experiment

    This week’s Wine and Cheese Seminar at Fermilab features a talk from MINERvA collaboration, presenting its measurement of the total probability that a muon type neutrino (or antineutrino) interacts with the protons and neutrons inside the MINERvA detector via something called charged-current interaction.

    The signature of the charged-current interaction is the neutrino changing into a charged muon (a heavier cousin of electron) by the exchange of a charged W boson. In the process, the neutrino transfers some of its energy and momentum to the recoil proton or neutron. Depending on the energy and momentum transfer, the recoiled particle can experience one of the following processes: It remains intact; becomes what is called an excited state and decays into other particles; or breaks up into individual constituents and coalesces immediately to form other particles. A measurement of the probability of the interaction happening by any of these channels is what is known as the inclusive cross section.

    When only a small amount of energy is transferred from the neutrino to the proton or neutron, the probability for this charged-current interaction is largely independent of the initial neutrino energy. This provides an alternative method to estimate the number of neutrinos per unit area through the detector, referred to by physicists as neutrino flux, as a function of neutrino energy. This method also provides a valuable tool to complement other methods for determining neutrino flux. The new MINERvA measurement employed this method to extract the neutrino flux and used the extracted flux to measure the inclusive scattering cross sections as the function of initial neutrino energy.

    See the full article here .

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    Fermilab Campus

    Fermi National Accelerator Laboratory (Fermilab), located just outside Batavia, Illinois, near Chicago, is a US Department of Energy national laboratory specializing in high-energy particle physics. Fermilab is America’s premier laboratory for particle physics and accelerator research, funded by the U.S. Department of Energy. Thousands of scientists from universities and laboratories around the world
    collaborate at Fermilab on experiments at the frontiers of discovery.

     
  • richardmitnick 10:59 am on September 18, 2015 Permalink | Reply
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    From FNAL- “Frontier Science Result: MINERvA The one-percenters and those who fake it” 

    FNAL II photo

    Fermilab is an enduring source of strength for the US contribution to scientific research world wide.

    Sept. 18, 2015
    Chris Marshall, University of Rochester

    Temp 1
    This is an event from the MINERvA data that shows the signal when an electron neutrino hits a neutron in MINERvA’s plastic scintillator, becomes an electron and changes the neutron into a proton. The color in each triangle represents how much energy is deposited in each of MINERvA’s triangular scintillator bars.

    In today’s Wine and Cheese seminar, MINERvA will present a measurement of the probability that an electron neutrino interacts with a nucleus inside the MINERvA detector and produces an electron and no other particles besides protons and neutrons.

    FNAL Minerva
    MINERvA

    This new result is the first high-statistics measurement of this process at energies comparable to a few times the proton mass.

    Neutrino beams made by accelerators produce mostly muon neutrinos, not electron neutrinos. This makes it very difficult to study electron neutrino interactions. The NuMI beam at Fermilab, which is used by MINERvA, MINOS+ and NOvA, is made up of 99 percent muon neutrinos and only 1 percent electron neutrinos. (However, it is so intense that MINERvA still records thousands of electron neutrino interactions each year.)

    FNAL NuMI upgrade
    From NUMI

    FNAL MINOS
    MINOS

    FNAL NOvA experiment
    NOvA

    Because of the relative lack of electron neutrino data, simulation programs assume that the only difference in the interaction probability between muon and electron neutrinos is due to the mass of the muon or electron that is produced. Today’s result is the most in-depth look at electron neutrino interaction probabilities ever, and an important check on that assumption.

    When we compare our electron neutrino result to the analogous measurement for muon neutrinos that was published in 2013, we find that they are consistent with one another.

    This measurement is a very important input for experiments such as NOvA, which measures the probability for muon neutrinos to change into electron neutrinos as they travel from Fermilab to Ash River, Minnesota. To do that, they need to know how many muon neutrinos are produced at Fermilab and how many electron neutrinos reach their detector in Ash River.

    The number of neutrinos that reach the NOvA detector is equal to the number of interactions they see divided by the probability that the neutrino will interact. The probability for a neutrino interaction is really tiny and difficult to measure accurately. To get around that, oscillation experiments like NOvA use two detectors, one near where the beam is produced and another far away to give the neutrinos a chance to change flavor. If you take the ratio of interactions at the near and far detectors, the interaction probability cancels out as long as it is the same in both detectors.

    Neutrino interactions must be the same in Illinois and in Minnesota, right? The problem is that the neutrinos detected at Fermilab are muon-type, while the far detector sees mostly electron-type neutrino interactions. This means it is important to understand any differences in the interactions between the two types of neutrino.

    In the course of searching for electron neutrino interactions, we found an unexpected background of events that look more like photons than electrons but were otherwise consistent with our signal. MINERvA can separate photons and electrons well, so this background has a tiny effect on our electron neutrino measurement. This kind of event is important for oscillation experiments because muon neutrinos that produce photons can be mistaken for electron neutrinos. We have characterized these background events, and believe they are similar to what we would expect from a process called diffractive scattering, where a single neutral pion is produced by a soft collision with the hydrogen in our scintillator target. Our observation and characterization is a first step towards development of a model to predict this process in other experiments.

    See the full article here .

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    Fermilab Campus

    Fermi National Accelerator Laboratory (Fermilab), located just outside Batavia, Illinois, near Chicago, is a US Department of Energy national laboratory specializing in high-energy particle physics. Fermilab is America’s premier laboratory for particle physics and accelerator research, funded by the U.S. Department of Energy. Thousands of scientists from universities and laboratories around the world
    collaborate at Fermilab on experiments at the frontiers of discovery.

     
  • richardmitnick 11:51 am on July 17, 2015 Permalink | Reply
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    From FNAL- “Frontier Science Result: MINERvA Neutrinos in nuclei: studying group effects of interactions” 

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    Fermilab is an enduring source of strength for the US contribution to scientific research world wide.

    July 17, 2015

    1
    Joel Mousseau, University of Florida

    These results were presented by the author at a recent Joint Experimental-Theoretical Physics Seminar. Mousseau’s presentation is available online.

    2
    This plot shows the ratio for iron (top) and lead (bottom) for neutrino deep inelastic scattering cross sections versus the fractional momentum of the struck quarks (Bjorken-x) for MINERvA data (black points) and the prediction (red line).

    Physics is a holistic science in which we consider not only the individual parts but also how these parts combine into groups. Nucleons, or protons and neutrons, combine in groups to form atomic nuclei. The differences between how free nucleons behave and how nucleons inside a nucleus (bound nucleons) behave are called nuclear effects.

    In the past, scientists have measured nuclear effects using beams of high-energy electrons. These high-energy beams allow electrons to interact with the quarks contained inside nucleons and nuclei, an interaction called deep inelastic scattering, or DIS. Scientists can now also bombard nuclei with neutrinos, which can also induce deep inelastic scattering. Studying these interactions can help us understand the behavior of quarks.

    Using a beam of neutrinos, MINERvA has performed the first neutrino DIS analysis in the energy range of 5 to 50 GeV.

    FNAL MINERvA
    MINERvA

    Neutrinos and electrons interact with quarks within the nucleus differently; we do not expect nuclear effects in neutrino DIS will be the same as electron DIS.

    MINERvA observes DIS interactions by measuring the cross section, or probability, of a neutrino interacting with quarks inside bound nucleons as a function of a property called Bjorken-x. Bjorken-x is proportional to the momentum of the quark that was stuck inside the nucleon.

    MINERvA took data on neutrino interactions with carbon, iron and lead nuclei. We compared these data to a theoretical model that assumes the nuclear effects for both neutrino and electron interactions are the same.

    We found that the data did not agree with the assumption in the lowest Bjorken-x values (0.1 to 0.2 — see figures) for lead. Further, the cross section for lead at those values differs significantly from those for carbon or iron. We say that the nuclear effect is enhanced in that region for lead.

    This enhancement was seen in a previous MINERvA inclusive analysis that considered all kinds of interactions together — without singling out deep inelastic scattering.

    In contrast, the model in the largest Bjorken-x range (0.4 to 0.75) agrees very well with data. This is intriguing, since the cause of nuclear effects in this region is not well understood. Whatever underlying physics governs behavior in this region, it appears to be the same for neutrinos and electrons.

    This information is very valuable in building new models of this mysterious effect. Understanding these effects are a priority for MINERvA and will be studied more extensively using data we are currently collecting, taken at higher energies and higher statistics. This data will be invaluable in resolving the theoretical puzzles at large and small Bjorken-x.

    See the full article here.

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    Fermilab Campus

    Fermi National Accelerator Laboratory (Fermilab), located just outside Batavia, Illinois, near Chicago, is a US Department of Energy national laboratory specializing in high-energy particle physics. Fermilab is America’s premier laboratory for particle physics and accelerator research, funded by the U.S. Department of Energy. Thousands of scientists from universities and laboratories around the world
    collaborate at Fermilab on experiments at the frontiers of discovery.

     
  • richardmitnick 9:24 am on March 20, 2015 Permalink | Reply
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    From FNAL- “Frontier Science Result: MINERvA – The MINERvA test beam program: trust but verify” 

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    Fermilab is an enduring source of strength for the US contribution to scientific research world wide.

    Friday, March 20, 2015
    Rik Gran, University of Minnesota – Duluth

    1
    This plot shows the energy deposited in the MINERVA test beam detector divided by the incoming kinetic energy of the pion as a function of the kinetic energy of the pion. No image credit

    All particle physics experiments rely on computer simulations of their detectors to make measurements, but neutrino experiments struggle to test these simulations using particles that are created from the neutrino beam itself.

    Neutrino interactions often produce charged particles such as muons or electrons, and they knock one or more protons or neutrons out of the nucleus. Neutrino interactions also produce quark-antiquark pairs called pions (see earlier MINERvA results from February, August and January). Each of these different particles gives us a view inside the nucleus, but to make these precise measurements, MINERvA needs to understand what these particles do once they exit the nucleus and enter the rest of the detector.

    We could simply trust a computer package (called Geant4) that simulates particle interactions, but to be rigorous, we verify that package. To do this we use a well-calibrated low-energy beam of pions, protons, muons and electrons from the Fermilab Test Beam Facility and a scaled-down version of the full MINERvA detector that is made of planes of scintillator, lead and steel. This smaller detector, which can be configured to replicate the downstream third of the neutrino detector, uses the same materials, electronics and calibration strategy.

    FNAL Minerva
    MINERvA

    We took data for six weeks in the summer of 2010 using the scaled-down detector and have been poring over this data ever since to measure many different aspects of the way the detector performs.

    With these data we were able to address, for one, how the kinetic energy of a pion entering our detector is translated into an energy measurement. When we use a popular Geant4 model for low-energy pions interacting in the simulated detector, the prediction is a good, though not perfect, description of the data. The experiment was designed to test the simulation, and the systematic uncertainties are small enough that we can assign a small uncertainty on how well Geant4 predicts the pion’s energy.

    We also used the test beam data to measure details about the scintillator material itself to improve the model of the detector geometry and electronics. We also improved how we calibrate both the test beam and the neutrino detector.

    We have continually fed back all of these improvements into the neutrino analysis since the test beam program started. This has been a benefit to other programs too. For example, the low-energy beamline design and hardware is now being used in MCenter for the LArIAT experiment.

    The results have been recommended for publication in Nuclear Instruments and Methods A. MINERvA has also started a second round of higher-energy test beam measurements to match the new higher-energy neutrino beam to understand still more about the way this detector performs.

    2
    Josh Devan of the College of William and Mary in 2010 helps assemble the low-energy test beam run detector. No image credit

    3
    Pictured here is part of the test beam crew. From left: Anne Norrick (College of William and Mary), Rob Fine (University of Rochester), Carrie McGivern (University of Pittsburgh), Leo Bellantoni, (Fermilab, front), Dan Ruterbories (University of Rochester, in red), Aaron Bercellie (University of Rochester), Manuel Alejandro Ramirez (University of Guanajuato), Geoff Savage (Fermilab).No image credit

    See the full article here.

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    Fermi National Accelerator Laboratory (Fermilab), located just outside Batavia, Illinois, near Chicago, is a US Department of Energy national laboratory specializing in high-energy particle physics. Fermilab is America’s premier laboratory for particle physics and accelerator research, funded by the U.S. Department of Energy. Thousands of scientists from universities and laboratories around the world
    collaborate at Fermilab on experiments at the frontiers of discovery.

     
  • richardmitnick 5:28 am on December 31, 2014 Permalink | Reply
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    From U Rochester: “Researchers show neutrinos can deliver not only full-on hits but also ‘glancing blows’” 

    U Rochester bloc

    University of Rochester

    December 30, 2014
    Leonor Sierra and Peter Iglinski
    585-276-6264
    lsierra@ur.rochester.edu
    @leonor_sierra

    In what they call a “weird little corner” of the already weird world of neutrinos, physicists have found evidence that these tiny particles might be involved in a surprising reaction.

    Neutrinos are famous for almost never interacting. As an example, ten trillion neutrinos pass through your hand every second, and fewer than one actually interacts with any of the atoms that make up your hand. However, when neutrinos do interact with another particle, it happens at very close distances and involves a high-momentum transfer.

    And yet a new paper, published in Physical Review Letters this week, shows that neutrinos sometimes can also interact with a nucleus but leave it basically untouched – inflicting no more than a “glancing blow” – resulting in a particle being created out of a vacuum.

    Professor Kevin McFarland is a scientific co-spokesperson with the international MINERvA collaboration, which carries out neutrino scattering experiments at Fermilab. McFarland, who also heads up the Rochester team that was primarily responsible for the analysis of the results, compares neutrino interactions to the firing of a bullet at a bubble, only to find the bubble was left intact.

    f
    from Fermilab Today: This MINERvA event display shows a coherent pion production candidate interaction. The neutrino enters the detector from the left and interacts with a nucleus, producing a muon and a pion. The colors indicate the amount of energy deposited at that point.

    “The bubble – a carbon nucleus in the experiment – deflects the neutrino ‘bullet’ by creating a particle from the vacuum,” McFarland explains. “This effectively shields the bubble from getting blasted apart and instead the bullet only delivers a gentle bump to the bubble.”

    Producing an entirely new particle – in this case a charged pion – requires much more energy than it would take to blast the nucleus apart – which is why the physicists are always surprised that the reaction happens as often as it does. McFarland adds that even painstakingly detailed theoretical calculations for this reaction “have been all over the map.”

    “The production of pions from this reaction had not been observed consistently in other experiments,” McFarland said. By using a new technique, they were able to measure how much momentum and energy were transferred to the carbon nucleus – showing that it remained undisturbed – and the distribution of the pions that were created.

    “After analyzing the results, we now have overwhelming evidence for the process,” McFarland says.

    The two members of the collaboration who were primarily responsible for analyzing the results were Aaron Higuera, at the time a postdoc at Rochester and now at the University of Houston, and Aaron Mislivec, one of McFarland’s doctoral students.

    Working with Higuera, Mislivec wrote the computer code that allowed them to sift through the results and get a picture of the reaction. “Our detector gave us access to the full information of exactly what was happening in this reaction,” Mislivec explains. “Our data was consistent with the unique fingerprint of this reaction and determined how these interactions happen and how often.” The key to identifying the reaction was finding undisturbed carbon nuclei and then studying the two resulting particles – the pion, which is responsible for shielding the nucleus, and the muon.

    Understanding this reaction, McFarland states, “is not going to make a better mousetrap, but it is exciting to learn that this weird reaction really does take place.”

    Researchers in the MINERvA collaboration measure low energy neutrino interactions both to support neutrino oscillation experiments and study the strong dynamics of the nucleon and nucleus that affect the interactions.

    The work is funded by the Department of Energy, the National Science Foundation, and partnering scientific agencies in Brazil, Chile, Mexico, Switzerland, Peru and Russia.

    See the full article here.

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    The University of Rochester is one of the country’s top-tier research universities. Our 158 buildings house more than 200 academic majors, more than 2,000 faculty and instructional staff, and some 10,500 students—approximately half of whom are women.

    Learning at the University of Rochester is also on a very personal scale. Rochester remains one of the smallest and most collegiate among top research universities, with smaller classes, a low 10:1 student to teacher ratio, and increased interactions with faculty.

     
  • richardmitnick 2:13 pm on August 5, 2014 Permalink | Reply
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    From Symmetry: “Neutrino researchers pull double duty” 

    Symmetry

    August 05, 2014
    Hanae Armitage

    Neutrino researchers work collaboratively, sharing and comparing results to help advance the field of neutrino physics.

    For Philip Rodrigues, a postdoc at the University of Rochester, receiving a new dataset from the MINERvA neutrino experiment means two things: that one of the neutrino experiments in which he participates has met a milestone and that the other can verify some of its predictions.

    Rodrigues, who is a member of both MINERvA in the US and the T2K experiment in Japan, is not the only neutrino physicist to double dip like this. More than 50 percent of neutrino researchers work on multiple projects simultaneously.

    minerva
    Scientists stand with the Minerva neutrino detector, located 330 feet underground at Fermi National Accelerator Laboratory.

    t2k
    T2K experiment passes five-sigma threshold

    “You want the scientists designing future generations of experiments to have a broad experience in current neutrino research,” says Fermilab physicist Debbie Harris, co-leader of the MINERvA neutrino experiment. “So it’s great to have people on multiple projects.”

    Unlike collaborative neutrino researchers like Rodrigues, the neutrino is extremely anti-social. We can’t see it, we can’t feel it, and we don’t entirely understand it. But it may be important for understanding the formation of the universe.

    The elusive nature of neutrinos makes working together even more appealing. Scientists who share Fermilab’s neutrino beamline meet regularly to discuss neutrino flux, the quantity of neutrinos per unit area observed in the detectors, and how that information can inform their respective projects.

    “It’s impossible to have one detector that can measure every little last thing about the interaction at every neutrino energy that’s important,” Harris said. “So that’s why we need to have a lot of different experiments to help each other make these measurements.”

    Neutrino experiments are usually in one of two categories: interaction experiments and oscillation experiments. The primary goal of interaction experiments is to observe the way neutrinos interact with different materials. The primary goal of oscillation experiments is to observe the way neutrinos, which come in three types, change from one type to the next. Both types of experiments can give researchers insight into neutrino characteristics such as their masses and how the different types of neutrinos relate to each other.

    Both kinds of experiments shoot extremely intense beams of neutrinos at particle detectors, but the placement of the detector depends on the type of experiment. Detectors for oscillation experiments are located much farther away, miles from the neutrino source, to give the particles time to change.

    Data from interaction experiments is critical for scientists at oscillation experiments to understand how the particles will interact in their detectors.

    “Neutrinos are neutrinos, and we can measure how they interact with different nuclei, and those results can help us constrain models,” Harris says. “Then those models can be used for experiments that use the same type of target for their far detector.”

    In addition, data from similar experiments can be used to double-check one another.

    “I think the more data we can get, and the more measurements we can take, the more input we have to help us understand what’s going on in terms of the physics,” Rodrigues says. “It’s very useful, both for the individual experiment, as well as the advancement of the field as a whole.”

    See the full article here.

    Symmetry is a joint Fermilab/SLAC publication.


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  • richardmitnick 11:23 am on August 1, 2014 Permalink | Reply
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    From Fermilab- “Frontier Science Result: MINERvA Pion on the break shot” 


    Fermilab is an enduring source of strength for the US contribution to scientific research world wide.

    Friday, Aug. 1, 2014
    Aaron Mislivec, University of Rochester

    graph
    This shows what an event in the MINERvA detector looks like when a neutrino comes in from the left and interacts with a proton in the detector, creating a pion that goes backwards, in addition to a proton and a muon.

    In February, the MINERvA experiment at Fermilab reported its findings of what happens when a neutrino produces a pion (a particle made of a quark and an antiquark)

    pion
    Pion

    by interacting with a proton

    prot
    Proton

    or neutron

    neut
    Neutron

    inside the nucleus. In today’s wine and cheese seminar, MINERvA will release its measurement of what happens when a neutrino or antineutrino produces a pion outside a nucleus by interacting with the nucleus as a whole but leaving the nucleus intact. Neutrino physicists refer to this reaction as coherent pion production.

    A neutrino interaction with a nucleus is like the break shot at the beginning of a billiards game where the cue ball is shot into a tightly packed group of target balls to break up the group. If coherent pion production were to happen in billiards, the target balls would remain tightly packed after being struck and an additional ball (the pion) would emerge from the collision.

    Coherent pion production can be a background to neutrino oscillation experiments that measure how neutrinos change from one type of neutrino to another as they travel through space. Predictions for coherent pion production disagree in how much background the reaction should produce in oscillation experiments. In addition, recent experiments that looked for coherent pion production at neutrino energies important to oscillation experiments came up empty — until now, that is.

    MINERvA has measured coherent pion production on carbon atoms where the interaction changes the neutrino (or antineutrino) into a muon (a heavier cousin of the electron). MINERvA searches for coherent pion production using its defining characteristic — that the interaction does not breakup the nucleus.

    MINERvA can see whether or not breakup of the nucleus occurs in two ways. First, it can detect the particles ejected from the nucleus when it is broken up and can require that only a muon and a pion are detected at the interaction point. Second, MINERvA can measure the momentum transferred to the nucleus by measuring the muon and pion momentum and can require it be consistent with not breaking the nucleus apart.

    These two signatures together greatly reduce the background and allow MINERvA to measure, for the first time, the details of coherent pion production to understand how it produces background for oscillation experiments.

    See the full article here.

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  • richardmitnick 2:58 pm on February 7, 2014 Permalink | Reply
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    From Fermilab- “Frontier Science Result: MINERvA What happens in hydrocarbon stays in hydrocarbon (sometimes)” 


    Fermilab is an enduring source of strength for the US contribution to scientific research world wide.

    Friday, Feb. 7, 2014
    Carrie McGivern, University of Pittsburgh

    When a neutrino enters the nucleus of an atom, it can interact with the protons and neutrons inside and impart enough energy to create completely new particles. Often a pion (a particle made of a quark and an antiquark) is produced. However, the nucleus is such a dense place that sometimes the pions never make it out of the atom!

    Figuring out how many pions are produced and how many exit the nucleus is very important in the field of neutrino physics because it determines how well the energy of the incoming neutrino can be measured. Experiments such as LBNE will measure how neutrinos oscillate as a function of neutrino energy, but they will need to understand what those pions are doing in order to get the neutrino energies right.

    Particle physicists have been measuring pions and constructing models of how they interact for a long time, but the neutrino interactions that produce these pions and what happens to them as they exit the nucleus is not nearly as well modeled. The interactions felt by the pions on their way out of the nucleus are called final-state interactions, and they are difficult to calculate because there are so many moving parts — all the protons and neutrons in the nucleus. We do have a few models, but it is important to verify them with experimental data from neutrino experiments. When the MiniBooNE measurement of pion production was first released, it was clear that the most complete models of what happens inside the nucleus were not describing the data. MINERvA now has a sample of several thousand events where a pion, proton and muon are produced when a neutrino interacts with a neutron or proton in the detector’s plastic scintillator, which is made of hydrocarbons (see top figure).

    graph
    This shows what an event in the MINERvA detector looks like when a neutrino comes in from the left and interacts with a proton in the detector, creating a pion that goes backwards, in addition to a proton and a muon.

    By studying the energy distribution of the pions that make it out of the nucleus, MINERvA can determine how big an effect the nucleus has on those pions. The better we understand (and then model) that effect, the better the whole field will be able to measure neutrino energies.

    See the full article here.

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  • richardmitnick 11:12 am on May 10, 2013 Permalink | Reply
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    From Fermilab- “Frontier Science Result: MINERvA Scouting the party: neutrinos and nuclei” 

    Fermilab is an enduring source of strength for the US contribution to scientific research world wide.

    Friday, May 10, 2013
    Philip Rodrigues

    Neutrinos are notoriously difficult particles to study: For every 50 billion neutrinos that pass through the MINERvA detector at Fermilab, only about one will interact leaving a trace in our detector, producing particles that we can observe directly.

    tracker
    The likelihood of a neutrino undergoing a quasi-elastic interaction for different values of the momentum transferred to the proton or neutron (Q2) compared to several theoretical models. The data agree best with a model in which the neutrino can interact with multiple protons or neutrons at a time.

    In spite of this, we are starting to use neutrinos to learn more about protons and neutrons and how they behave when they’re together inside an atomic nucleus. We already understand a lot about the nucleus: We know that it’s made of protons and neutrons, and we know the number of protons and the number of neutrons in the nucleus for every chemical element. But there is much we still don’t fully understand, especially about what those protons and neutrons are doing inside the nucleus.

    We can study the protons’ and neutrons’ behavior in the nucleus the way we might study how people act at a party. Do the party-goers mingle according to the general spirit of the party, or do they break off into pairs? We could determine the party’s nature by sending in very shy folks and observing how quickly they leave and whether they leave through the same door they entered.

    In a nucleus, does each proton and neutron react to just the average effect of the others, or do they occasionally pair up? One way to answer this question is to fire neutrinos at nuclei and measure the particles produced when neutrinos do interact with the nuclei of atoms in our detector. By studying those particles, we can try to infer the behavior of the protons and neutrons.”

    graph
    The energy near the neutrino interaction point in neutrino quasi-elastic events. The data points, in black, are at higher energies on average than the prediction, in red, suggesting that the neutrino really is interacting with multiple protons or neutrons, which are kicked out of the nucleus.

    See the full article here.

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  • richardmitnick 12:41 pm on June 7, 2012 Permalink | Reply
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    From Fermilab Today: “Special Result of the Week – Fingerprinting the neutrino” 

    Fermilab continues to be a great source of strength in the U.S. Basic Research Community.

    Thursday, June 7, 2012
    Laura Fields, Northwestern University

    Neutrino scientists are currently trying to answer some exciting questions. How much do neutrinos weigh and why are they so light? How much do neutrinos change from one kind to another (called mixing) and why are their transformations so different from quark mixing? Do neutrinos mix differently from anti-neutrinos? To answer these questions, neutrino physicists must study how neutrinos and anti-neutrinos mix over time, which means using neutrino interactions to measure their energies and the distances they travel.

    neut
    This plot shows the likelihood of an anti-neutrino colliding with a proton to produce a muon and a neutron as a function of the square of the four-momentum (a property that is proportional to the energy) given to the neutron (Q2). The red lines show theoretical predictions that include (dashed) and exclude (solid) a model in which the anti-neutrino can collide with several particles in the nucleus rather than just one.

    “…if future experiments see a difference between neutrino and anti-neutrino mixing, it will be hard to determine the reason. On one hand, it could be caused by the neutrino and anti-neutrino actually mixing differently. On the other, it could be a difference between their interactions in the detector, which by definition is made only of matter (no antimatter).

    The MINERvA collaboration has recently measured one of the most important interactions for mixing measurements. In this interaction, an anti-neutrino meets a proton, producing a muon and a neutron. This interaction is special because the energy of the anti-neutrino can be estimated simply by measuring the muon energy and direction. However, this isn’t as straightforward as it seems, and that may hamper our ability to infer neutrino energy.”

    minerva
    MINERvA

    See the full article here.

     
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