Live feed of MiniBoone results seminar today! April 11, 2007Posted by dorigo in internet, news, physics, science.
MiniBoone is an experiment at Fermilab which is investigating neutrino oscillations and has the explicit purpose of clarifying the reality of an earlier controversial signal found by the LSND collaboration.
The MiniBoone detector is a 12-meter sphere filled with 800 tons of mineral oil; its inner surface is lined with 1280 photomultiplier tubes which can detect the faint light signal produced by neutrino interactions. 240 additional tubes provide a veto to cosmic rays entering the active volume as charged tracks. The layout of the detector is shown below.
Located 500 meters downstream of the 8 GeV proton beam coming from the Fermilab Booster (a machine which is part of the Tevatron accelerating chain), MiniBoone collects a neutrino interaction every 20 seconds on average. The neutrinos are produced when the 8 GeV protons hit a beryllium target (a light material, which minimizes the divergence of the secondary beam). The kaons and pions produced in the high-intensity collisions decay to muons and muon neutrinos, and the latter travel to the tank in large numbers.
MiniBoone is looking for a signal of electron neutrinos: that would allow to determine the oscillation parameters of the conversion of muon to electron neutrinos in the range measured by LSND. Electron neutrinos interacting with the mineral oil will produce an electron, which leaves a distinctly fuzzy cone of light around its trajectory by the Cherenkov effect. On the contrary, muons materialized by muon neutrino interactions will produce a better focused ring of light. The light is observed by photomultipliers, and offline analysis of the signals, allows a clean discrimination.
Readers familiar with the concept that neutrinos “oscillate” – that is, change their flavor periodically – might be confused to know that a whole experiment is dedicated to the task of confirming a past result by another collaboration. And it is easy to get lost while studying neutrino oscillation experiments: each of them is sensitive to different ranges of a few among many parameters describing the oscillation frequency and amplitude of processes changing each of the three neutrino flavors into any other.
That neutrinos could convert from one kind to another was something physicists had suspected for many years, due to several results dating as much as thirty years back which had shown a deficit of solar and atmospheric neutrinos. After the definitive confirmation of SuperKamiokande, everybody now believes neutrinos oscillate, but things appear only marginally better understood. How many neutrino species are there ? What is their mass ? What is the frequency of oscillation from one kind to another ? These are only a few of the many open questions that present-day neutrino experiments try to address.
Eyes will be wide open today at the MiniBoone seminar. And in fact, there is a lot at stake: the oscillation signal found by LSND is important to confirm or exclude, because if found true beyond doubt it would imply some startling new physics: the existence of a fourth family of neutrinos, or the inequality of neutrino and antineutrino masses.
The graphs below show what LSND measured, in the plane of two parameters: the square of the mass difference between electron and muon neutrino on the y axis, and the squared sine of twice the angle theta describing the oscillation amplitude on the x axis. In blue is highlighted the region corresponding to the LSND signal. The wavy lines in the plot on the left show the area which MiniBoone will be able to investigate (left to right: exclusion region, 3-sigma, and 5-sigma discovery contours – meaning that if the parameters have a value on the right of the lines, they will be measured, while if they lie on the left of the leftmost line, MiniBoone will be useless to determine them, while excluding the LSND result). The ellipses in the plot on the right instead show how well MiniBoone expects to measure the parameters, if these have a value within the LSND preferred region.
The live stream of the seminar will be available at this link from 11.00 to 12.30 CDT (16.00 GMT). I am very interested in the results, since I read in one of the pages of the Boone collaboration’s web site that
“MiniBooNE is the first phase of the Booster Neutrino Experiment (BooNE); in this phase, neutrino oscillation measurements will be made with a single detector. If oscillations are observed, then MiniBooNE will be upgraded to stage two (BooNE) with a two-detector configuration. “
A few lines down, they make it even more clear:
“If MiniBooNE verifies the LSND signal, then BooNE will proceed to its next stage: a second detector built at the appropriate neutrino source-detector distance. This distance will be determined so that the two-detector configuration can precisely measure the oscillation parameters, and search for CP and CPT violation.“
That is to say: if today we see no signal of oscillations, forget the upgrade! Hmmm. Let me guess. I bet a dime they will not exclude the oscillation signal of LSND today, but show inconclusive but intriguing hints that muon neutrinos disappear into electron neutrinos or other ones. This, despite rumours around… Anybody here who wants to take my dime bet?
UPDATE: I would have lost my bet… Although there is something in the disclosed results that does not fit with the model (and which might indeed represent an open door to more investigations and another detector). See a thorough explanation at the cosmic variance site .
UPDATE 2: The video of the seminar is available at http://vmsstreamer1.fnal.gov/VMS_Site_03/Lectures/MiniBooNE/070411Live/index.htm