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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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new ideas in neutrino detection
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 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


Solar neutrino

Another new super low energy project: XMASS

Multi purpose low-background experiment with liquid Xe

  • Xenon MASSive detector for solar neutrino (pp/7Be)
  • Xenon neutrino MASS detector (bb decay)
  • Xenon detector for Weakly Interacting MASSive Particles (DM search)

Dark matter

Double beta




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.”

Taking this as our mandate, theorist John Beacom and I focused on finding some way to get new physics out of Super-Kamiokande.

This partnership of theory and experiment has proven quite productive.

supernova neutrinos are certainly interesting but how could we be sure of seeing some in sk
Supernova neutrinos are certainly interesting… but how could we be sure of seeing some in SK?

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!

These constitute the diffuse supernova neutrino background [DSNB], also known as the “relic” supernova neutrinos [SRN].

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.

wouldn t it be great we thought if there was a way to tag every dsnb event in super k
“Wouldn’t it be great,” we thought, “if there was a way to tag every DSNB event in Super-K?”

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?

but we re going to have to compete with hydrogen p n d 2 2 mev g in capturing the neutrons
But we’re going to have to compete with hydrogen (p + n  d + 2.2 MeV g)in capturing the neutrons!

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

so we eventually turned to the best neutron capture nucleus known gadolinium
So, we eventually turned to the best neutron capture nucleus known – gadolinium.
  • GdCl3 , unlike metallic Gd, is highly water soluble
  • Neutron capture on Gd emits a 8.0 MeV g cascade
  • 100 tons of GdCl3 in SK (0.2% by mass) would yield >90% neutron captures on Gd
  • Plus, it’s not even toxic!

Man, that’s one tasty lanthanide!

but um didn t you just say 100 tons what s that going to cost
But, um, didn’t you just say 100 tons?What’s that going to cost?

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

if we can do relics we can do a great job with a galactic supernova
If we can do relics, we can do a great job with a galactic supernova:
  • The copious inverse betas get individually tagged and can be subtracted away from
  • the directional elastic scatter events, doubling SK’s SN pointing accuracy.
  • The 16O NC events no longer sit on a large background and are hence individually identifiable, as are
  • the backwards-peaked 16O CC events.

Here’s our proposed name for this water Cherenkov upgrade:











oh and as long as we re collecting n e s
Oh, and as long as we’re collecting ne’s…


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!

Here’s what the coincident signals in Super-K-III with GdCl3 will look like (energy resolution is applied):

Most modern

DSNB range

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!

from phys lett b594 333 2004

Choubey and Petcov consider the reactor signal of GADZOOKS!

From Phys. Lett. B594: 333, 2004:
  • “The upper limit on Dm221 is determined solely by the SK-Gd data.”
  • “The lower limit on sin2q12 is determined by the SK-Gd data.”
  • “The results of our analysis show that the SK-Gd experiment has a remarkable potential in reducing the uncertainties in the values of Dm221and sin2q12.”
  • “We find that the SK-Gd experiment could provide one of the most precise (if not the most precise) determinations of the solar neutrino oscillation parameters Dm221and sin2q12.”

Here are their main results…


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:

  • Precision measurements of the
  • neutrinos from all of
  • Japan’s power reactors
  • (~5,000 events per year)

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:

  • Solar antineutrino flux limit improvements (X100)
  • Full de-convolution of a galactic supernova’s n signals
  • Early warning of an approaching SN n burst
  • (Free) proton decay background reduction
  • New long-baseline flux normalization for T2K
  • Matter- vs. antimatter-enhanced atmospheric n samples(?)

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:

Why haven’t

you guys put gadolinium in

Super-K yet?

Our GADZOOKS! proposal has definitely

been getting a lot of attention recently:

As I told him, studies

are under way…

you see beacom and i never wanted to merely propose a new technique we wanted to make it work
You see, Beacom and I never wanted to merely propose a new technique – we wanted to make it work!

Now, suggesting a major modification of one of the world’s leading neutrino detectors may not be the easiest route…

and so to avoid wiping out some careful hardware studies would be needed
…and so to avoid wiping out, some careful hardware studies would be needed.
  • What does GdCl3 do the Super-K tank materials?
  • Will the resulting water transparency be acceptable?
  • Any strange Gd chemistry we need to know about?
  • How will we filter the SK water but retain GdCl3?
As a matter of fact, early on I made two discoveries regarding GdCl3 while carrying a sample from Los Angeles to Tokyo:
  • GdCl3 is quite opaque to X-rays
  • Airport personnel get very upset when they find a kilogram of white powder in your luggage
Two years ago I was awarded a U.S. DoE Advanced Detector Research Program grant to support the study of key gadolinium R&D issues.

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.

example of soak sample
Example of Soak Sample

Tank Weld Joint:

Room temperature

soak in 2% GdCl3

We will inspect surface

every three months via

SEM, optical, and XRD

Now at 30 years of

equivalent exposure!


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…

  • Three key differences:
  • the SK tank is high grade stainless steel
  • while the 1KT tank is iron
  • the SK water is degasified but the 1KT’s is not
  • surface/volume ratio 6X higher for 1KT
So, starting two months ago, I have begun using K2K’s old one kiloton water Cherenkov detector to study the GdCl3 technique:

K2K’s 1 kiloton tank is being used for “real world” studies of

  • Gd Water Filtering – UCI built and maintains this water system
  • Gd Light Attenuation – using real 20” PMTs
  • Gd Materials Effects – many similar detector elements as in Super-K

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!


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?

  • We have now demonstrated:
  • Choice of high-quality detector materials is important
  • That GdCl3 itself does not impair water transparency
  • Our PMT’s work properly in conductive water
  • Gd filtering works well at large scales and flows
  • GdCl3 does not affect SK steel (or other components)
  • One micron filters remove dissolved rust but pass Gd

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…

a gdcl 3 timeline
A GdCl3 Timeline:

2003 2004 2005 2006 2007 2008

Bench Tests @


1 kton trial run @ KEK



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!