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Richard Ruiz | Univ. of Pittsburgh | U.S.A.

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Neutrino 2012: Day 2

When it comes to neutrino experiments, they were all there Day 2: T2K, MINOS, OPERA, ICARUS, and NOνA, and LBNE!

Hi All,

Here is a run down of what happened Tuesday. I will try to post Day 3 things this afternoon, which should be Wednesday morning for the US. An update on the LBNE is at the bottom of the post.

Happy Colliding

- richard (@bravelittlemuon)


Figure 1: Update of T2K experiment after March 11, 2011 earthquake that struct Japan. Credit: NAKAYA, Tsuyoshi.

The Tokai to Kamoika Experiment, or T2K for short, is a one impressive behemoth of an experiment. Much like MINOS Experiment at Fermilab, you shoot protons into a target to make pions. The pions then decay into neutrinos, and the neutrinos travel 183 mi (295 km) through the Earth to the (Super-, Hyper-) Kamiokande detector in Kamioka, Japan.

When the March 2011 earthquake struck Japan, the proton accelerator at the J-PARC physics lab was heavily damaged, and power throughout the country was effectively shut off. Due to immense leadership of J-PARC’s director, Shoji Nagamiya, the accelerator was back online December 9, 2011, and by December 24, 2011, neutrinos were being observed in Kamioka. It is baffling that despite all this, the experiment still marched on and announced the herculean result it had observed 10 events where a muon-neutrino had converted into electron-neutrino. The predicted results were 9.07±0.93 event assuming sin213=0.1, and 2.73±0.37 events assuming sin213=0.0. Consequently, the experiment was able to measure θ13 itself and found sin213=0.104 +0.060-0.045

Figure 2: Schematic of T2K (Tokai To Kamioka) Experiment. Image: http://www2.warwick.ac.uk/newsandevents/news/t2k


The MINOS Experiment at Fermilab is most simply described at the US version of T2K. It is unfair and a disservice to both MINOS and T2K to make that comparison because of the unique features of the experiments, but I have a lot to write. In 2010, MINOS caused a bit of a stir when it measured the mass difference between two of the three anti-neutrinos. The measurement itself was not at all controversial. The issue was that this result differed from the well measured mass difference for regular neutrinos. Here the Fermilab presser that can tell you all about it. On Day 2, MINOS announced that the discrepancy between neutrinos and anti-neutrinos has completely disappeared and that the previous disagreement is believed to have been a statistical fluctuation. It appears that Fermilab has released a new press release this morning explaining things in more detail. Below are the main plots. Oh, and MINOS data also slightly favors inverted hierarchy for anyone interested in that. Fun fact: In its seven years of running, MINOS has used over 1.5 sextillion protons to produce all of its neutrinos.

Figure 3: Preliminary results from the MINOS detector showing best fit value for neutrino mass splitting and mixing angle. Credit: NICHOL, Ryan


Figure 4: Preliminary results from the MINOS detector showing best fit value for anti-neutrino mass splitting and mixing angle. Credit: NICHOL, Ryan

Figure 5: Preliminary results from the MINOS detector showing best fit value for neutrino and anti-neutrino mass splitting and mixing angle. Credit: NICHOL, Ryan


The OPERA Experiment, or Oscillation Project with Emulsion-tRacking Apparatus, is a fine and mighty experiment capable of one of the most time-consuming tasks in neutrino physics that even tests the patience of sleeping mountains: observing the conversion of tau-neutrinos into muon-neutrinos. Like T2K and MINOS, OPERA gets its neutrinos from pions, which are produced when protons strike a fixed target. Specifically, the experiment uses CERN protons in its first four years of running has used about 14.2 x 1019 protons!

Figure 6: A breakdown, by year, of how many protons the OPERA experiment has observed. Credit: NAKAMURA, Mitsuhiro

OPERA’s defining characteristic is how well it is able to extract out a signal from everything else. Below is an example of a real event in which a neutrino has collided with a nucleus, producing a charge lepton and nucleus somewhat fragments.

Figure 7: An example of a real neutrino event being extracted from the data. Credit: NAKAMURA, Mitsuhiro

The big news from OPERA on Day 2 was the second observation of a muon-neutrino converting into a tau-neutrino! 2 events in over four years; I told you this thing required patience. Here is how the event works.

Figure 8: The OPERA Experiment's second candidate event of a muon-neutrino converting into a tau-neutrino. Credit: NAKAMURA, Mitsuhiro

Here is an explanation of the event.

Figure 9: A breakdown of OPERA's second tau-neutrino candidate. Credit: NAKAMURA, Mitsuhiro

Finally, here is a summary of the status of OPERA’s search tau-neutrinos. It is worth mentioning that the experiment also announced it has observed 19 instances where a muon-neutrino has converted into an electron-neutrino!

Figure 10: A summary of the current status of the OPERA Experiment's search for appearances of tau-neutrinos. Credit: NAKAMURA, Mitsuhiro

A Few Words on ICARUS and NOνA

Due to the lack of time, I will simply say that one can expect big things from ICARUS and NOνA when they both have results. ICARUS has already started running and the gigantic, LHC-Detector-sized NOνA will start running next year when Fermilab flips on its proton beam again. NOνA will be capable of determining whether neutrinos have normal mass hierarchy or inverted mass hierarchy.



Interesting things happen at conferences, like an impromptu talk added the morning of the second day of events. Long Baseline Neutrino Experiment co-spokesperson Robert Svoboda surprisingly gave an update of the LBNE, the first since its budget was gravely slashed. Much is still being kept internally for another few weeks when the final proposal will be submitted, so I will limit what I say. In summary, there are three options being considered for the experiment for phase 1 construction. Beyond that, it is up to the Funding Lords.

Figure 11: Update of the Long Baseline Neutrino Experiment. Credit: SVOBODA, Robert

Figure 12: Update of the Long Baseline Neutrino Experiment. Credit: SVOBODA, Robert



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  • Elaine Jek

    Greatly appreciate the update!