New Ideas in Neutrino Detection. Mark Vagins University of California, Irvine. WHEPP 9 – Bhubaneswar, India January 6, 2006. So, what’s new and exciting in the world of neutrino detection?. Solar 7 Be neutrinos will be quite popular in 2006-7:.
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University of California, Irvine
WHEPP 9 – Bhubaneswar, India
January 6, 2006
So, what’s new and exciting in the
world of neutrino detection?
Solar 7Be neutrinos will be quite popular in 2006-7:
SNO will drain their heavy water at the end of 2006,
possibly replacing it with liquid scintillator (SNO++).
KamLAND is currently purifying their scintillator in
order to focus on looking for the 7Be solar neutrinos.
Borexino looks like it will finally turn on this year.
Going even lower in energy…
CLEAN - 10 tons fiducial LNe needed for pp solar neutrinos
Mini-CLEAN (600 kg LNe) in SNOLAB in 2007? – R&D plus WIMP search
Another new super low energy project: XMASS
Multi purpose low-background experiment with liquid Xe
Meanwhile, on the other end of the n energy scale:
My own beloved Super-Kamiokande has been
taking data, with an occasional interruption,
for over nine years now…
But what does the future hold?
On July 30th, 2002, at ICHEP2002 in Amsterdam,
Yoichiro Suzuki, then the newly appointed head of SK,
said to me,
“We must find a way to get the new physics.”
This partnership of theory and experiment has proven quite productive.
Now, galactic supernovas may be somewhat rare on a human timescale, but supernovas are not.
On average, there is one supernova
explosion somewhere in our universe every second!
After traveling an average distance of
six billion light years, about 100,000 of these genuine supernova neutrinos pass through our bodies every second.
In 2003, Super-Kamiokande published the world’s best limits on this so-far unseen flux [M.Malek et al., Phys. Rev. Lett.90 061101 (2003)].
Unfortunately, the search was strongly limited by backgrounds, and no clear event excess was seen.
So, experimental DSNB limits are approaching theoretical predictions. Clearly, reducing the remaining backgrounds and going lower in energy would be extremely valuable. But how?
Well, all of the events in the present SK analysis are singles in time and space.
And this rate is actually very low… just
three events per cubic meter per year.
Since the reaction we are looking for is
ne + p e+ + n
what if we could reliably identify the
neutron and look for coincident signals?
Plus, plain old NaCl isn’t going to work…
We’d need to add 3 kilotons of salt to SK just to
get 50% of the neutrons to capture on the chlorine!
NaCl Saturation Point
Man, that’s one tasty lanthanide!
In 1984: $4000/kg -> $400,000,000
In 1993: $485/kg -> $48,500,000
In 1999: $115/kg -> $11,500,000
In 2005: $4/kg -> $400,000
So, perhaps Super-K can be turned into a great big antineutrino detector… it would then steadily collect a handful of DSNB events every year with greatly reduced backgrounds and threshold. Also, imagine a next generation, megaton-scale water Cherenkov detector collecting 100+ per year!
This is the only neutron detection technique which is extensible to such scales, and at minimal expense, too:
~1% of the detector construction costs
Here’s our proposed name for this water Cherenkov upgrade:
first 22 months of data
GADZOOKS! will collect this much reactor neutrino data in two weeks.
Hyper-K with GdCl3 will collect six KamLAND years of data in one day!
Beacom and I finally got our first GADZOOKS! paper written up as hep-ph/0309300 and sent it off to Physical Review Letters.
After a long wait due largely to one
of the world’s slowest referees,
our paper was finally
published in Physical Review Letters as
Phys. Rev. Lett., 93:171101, 2004
Within a year it was “topcited” on SPIRES!
Choubey and Petcov consider the reactor signal of GADZOOKS!
Here are their main results…
Choubey and Petcov consider the reactor signal of GADZOOKS!
Therefore, we could very well be just a few years away from the world’s first true precision measurement (<1 % uncertainty) of a fundamental neutrino parameter!
So, adding 100 tons of GdCl3 to Super-K would provide
us with at least two brand-new, guaranteed signals:
2) Discovery of the diffuse supernova
neutrino background [DSNB],
also known as the
“relic” supernova neutrinos
(~5 events per year)
In addition to our two guaranteed new signals,
it is likely that adding GdCl3 to SK-III will
provide a variety of other interesting
(and not yet fully explored) possibilities:
For example, Odrzywodek et al. note that late-stage Si burning in very large, very close stars could provide a two day early warning of a core collapse supernova if neutron detection is possible.
In SK with GdCl3 this would mean an increase in the low energy singles rate… a factor of 10 increase in the case of Betelgeuse.
[Odrzywodek, Misiaszek, and Kutschera,
Astropart.Phys. 21:303-313, 2004]
[SK with Gd is the only detector which can do this]
One other thing you can do with this technology…
Two months ago I co-authored a modest (~$2,000,000)
proposal to use GdCl3-based neutron detection as
part of the Office of Nonproliferation Research’s
Active Interrogation Program.
At NNN05, before I had even
given my talk, John Ellis suddenly
stood up and demanded of
the SK people in attendance:
you guys put gadolinium in
Our GADZOOKS! proposal has definitely
been getting a lot of attention recently:
As I told him, studies
are under way…
Now, suggesting a major modification of one of the world’s leading neutrino detectors may not be the easiest route…
Work immediately got under way at UC Irvine [UCI] building a small version of the SK water filtration system, while at Louisiana State University [LSU] a materials aging study was put together under the supervision of Bob Svoboda.
Tank Weld Joint:
soak in 2% GdCl3
We will inspect surface
every three months via
SEM, optical, and XRD
Now at 30 years of
These bench tests have been very encouraging.
In a single pass through our UCI water filtering system
we can remove ~99.99% of the Gd and return
it to our 500 liter holding tank.
But can this be scaled
up to kilotons of
With the help of this big
detector at KEK
(and a new 2005-6 DoE ADR grant)
we’re in the process of finding out!
After two years of small-scale testing at UCI and LSU, in order
to study the GdCl3 concept in a “real world” setting it was
suggested that we use a beautiful piece of equipment –
the old one kiloton [1KT] detector from the K2K experiment.
This 2% model of Super-K and Super-K itself are quite similar, but they are not completely identical…
K2K’s 1 kiloton tank is being used for “real world” studies of
This September, 4,000 kg of GdCl3 (enough for two fills)
was shipped from Shanghai to Yokohama.
Bringing thousands of kilos of mysterious, high-purity
white powder into the country from China
was not entirely trivial…
…but at least this time I managed
to avoid being arrested!
4,000 kg of GdCl3 at KEK...
…contained in 80 barrels.
On November 10th, 2005, after 3.5 years of work on the idea, the
first scoop of GdCl3 goes into our 500 liter pre-treatment tank.
After a few hours of filtering the solution, 200 kg (0.02% by mass)
of dissolved GdCl3 was injected into the main 1KT tank.
Proposed SK Level
Initial 1KT level
So, what did we see?
The Gd filtering system worked perfectly, producing
four tons/hour of Gd-free water while at the same
time returning the gadolinium to the main tank.
Two days after being injected
from the bottom,
the GdCl3 had reached
the top of the tank.
Collected light from
downward muons had
dropped by less than 1%.
So now we know -
the filtering works,
and the GdCl3 will not
significantly degrade SK’s water transparency!
However, something unexpected
eventually did appear in the water…
…some of the rust layer on the inside of the iron
1KT tank, which had accumulated during six years
in contact with pure water,
had been released into solution.
We know that our normal filters remove all of the rust while
passing all of the gadolinium, so I am confident that in the coming weeks it will be removed as the water is recirculated.
N.B.: This will NOT be an issue in Super-K!
Here are SK tank samples after 8000X the GdCl3
exposure of the 1KT – no rust!
So, what have we learned so far?
There’s still lots to do,
but perhaps our goal of
showing that this whole
thing will really work in SK
could soon be within reach…
2003 2004 2005 2006 2007 2008
Bench Tests @
UCI & LSU
1 kton trial run @ KEK
GADZOOKS! @ Super-K
A few months ago at NuInt05 in Okayama, Japan,
Kenzo Nakamura suggested that (at least) one
“tube” of Hyper-Kamiokande should be designed,
from the beginning, for GdCl3-enriched water.
We clearly have our colleagues’ attention and interest.
Now we simply have to make it all work!