Thursday, July 2, 2015
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From symmetry

How do you solve a problem like neutrinos?

When it comes to studying particles that zip through matter as though it weren't even there, you use every method you can think of. Image: Sandbox Studio with Ana Kova

Sam Zeller sounds borderline embarrassed by scientists' lack of understanding of neutrinos — particularly how much mass they have.

"I think it's a pretty sad thing that we don't know," she says. "We know the masses of all the particles except for neutrinos." And that's true even for the Higgs, which scientists only discovered in 2012.

Ghostly neutrinos, staggeringly abundant and ridiculously aloof, have held onto their secrets long past when they were theorized in the 1930s and detected in the 1950s. Scientists have learned a few things about them:

  • They come in three flavors associated with three other fundamental particles (the electron, muon and tau).
  • They change, or oscillate, from one type to another.
  • They rarely interact with anything, and trillions upon trillions stream through us every minute.
  • They have a very small mass.

But right now, there are still more questions than answers.

Zeller, one of thousands of neutrino researchers around the world and co-spokesperson for the neutrino experiment MicroBooNE based at Fermilab, says the questions about neutrinos don't stop at mass. She writes down a shopping list of things physicists want to find out.

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Lauren Biron

In Brief

Thirteen-week accelerator shutdown for upgrades and maintenance begins July 4

Fermilab's accelerator complex will enter a 13-week shutdown on Saturday, July 4.

During the shutdown, employees from across the lab will help install a new beamline, which will allow them to send 8-GeV protons from the Recycler to the Muon Campus; remove old Main Ring components to allow more efficient beam delivery to the Muon Campus; add radio-frequency accelerating cavities to the Booster; upgrade the Recycler vacuum for future high-intensity running; replace NuMI Horn 1; and install a laser notching system in the Linac.

The accelerator complex is planned to come back online by Oct. 5.

Photo of the Day

Accelerator shutdown plans come into focus

The Accelerator Division's Dan Johnson discusses accelerator shutdown plans, which come into focus through the eyes of Jim Hylen, AD. Elliott McCrory took this photo at a recent All-Experimenters' Meeting. Photo: Elliott McCrory, AD
In Brief

Friday, July 3, is Independence Day observed

Julie Kurnat created this chalk drawing for Independence Day. Photo: Julie Kurnat, TD

Happy Independence Day. Enjoy a safe and happy holiday.

In the News

Recreating the beginning of time

From Cosmos, June 29, 2015

The Big Bang theory, despite being a popular television show, is misunderstood. It is not a hand-wavy concept of a great cosmic "boom". The theory describes in exquisite detail the baby Universe that grew up to be our vast, varied and beautiful cosmos. And it's not only a set of equations. The early Universe described by the theory has been verified, photographed, and, in part, recreated in the lab.

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Frontier Science Result: CDF

The rest of the story

This plot shows CDF data at 1.96, 0.9 and 0.3 TeV on the charged-particle density in the transMIN region as defined by the leading charged particle as a function of the transverse momentum of the leading charge particle, PTmax.

Almost all scientific publications on research at the Tevatron or the LHC focus on the physics of what happens when a postcollision particle, in particular a quark or gluon, shoots well away from the path of the incoming colliding beams. However, the collision process is complicated, and we must understand the rest of the story — what happens to the other particles that are part of the collision. We call this remaining part the underlying event.

An outgoing particle that travels considerably away from the incoming beam path is said to have a high transverse momentum or, put another way, to experience hard scattering. It is the star of the collision event, but its supporting players in the underlying event are numerous. There are the outgoing particles whose paths remain relatively close to those of the incoming beams (soft scattering). There are also the particles that accompany the hard-scattering event, not to mention the additional particles they radiate.

In this analysis, CDF scientists looked at events for which the hard-scattering particle was above a certain energy. They compared underlying event components from three different regions of the detector, defined by where they were in relation to the hard-scattering particle: in the same part of the detector, in the opposite part of the detector and in between.

They repeated this analysis for runs from three different collision energies: 0.3, 0.9 and 1.96 TeV. The 0.3 and 0.9 TeV data were part of special runs taken near the end of the Tevatron in which beam was collided at lower energy in order to study the energy dependence of certain reactions. This analysis is the first to use the data taken at 0.3 TeV.

CDF simulated the collisions using computer programs, such as PYTHIA, that use the theory of strong interactions for the hard-scattering parts of the interaction and that could also model the soft components of the collisions. The soft-component models contain adjustable parameters; a particular set of the adjustable parameters is called a tune. Previous CDF analyses have resulted in two tunes, Z1 and Z2*. The data in the upper figure shows that the charged-particle density of the detector's in-between regions increases by a factor of 2.8 in going from 0.3 TeV to 1.96 TeV. This is just one plot of many that are studied in this analysis.

For the first time, because of the use of data at three different energies, we are able to see directly the energy behavior of the different components of the underlying energy. The occurrence of events that accompany the hard-scattering event increases exponentially relative to the center-of-mass collision energy. The radiated particles increase logarithmically.

The data presented in this analysis can be used to constrain and improve PYTHIA simulations, resulting in more precise predictions for the upcoming LHC run at 13 TeV.

Rick Field and Andy Beretvas

Learn more

These scientists are the primary analysts for this result. From left: Rick Field (University of Florida) and Craig Group (University of Virginia and Fermilab).
In the News

Why the Big Bang's light may have a tilt

From Quanta Magazine, June 30, 2015

Half a century ago, astronomers got their first look at the infant universe: a haze of soft light that suffused the entire sky. This cosmic microwave background (CMB) radiation seemed to indicate that the early cosmos was remarkably uniform — a hot, dense fireball that expanded and cooled over the next 14 billion years. It was the world's first beacon from the Big Bang.

Like a slowly developing Polaroid, our understanding of this radiation has come into focus gradually. In 1990, NASA's Cosmic Background Explorer (COBE) satellite found that light from the CMB had the telltale spectrum of a system in equilibrium, known as a blackbody — exactly what was expected if the universe began as a dense, scalding soup of particles and photons that all interacted with one other. In addition, another instrument on COBE revealed slight hot and cold spots in the light.

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