# ![](media/image1.wmf){width="6.896527777777778in" height="9.204166666666667in"} 

# Super Neutrino Beam (Proton Driver)

######## M. Diwan, T. Kirk, W.T. Weng -- BNL

**February 7, 2003**

**Executive Summary**

Dr. Ray Davis of BNL and Prof. Masatoshi Koshiba of Japan shared the
2002 Nobel Prize in Physics for their path-breaking measurements of the
terrestrial fluxes of solar and atmospheric neutrinos. Their research
established that neutrinos have mass and oscillate among three flavor
states as they propagate through space and time. The remaining basic
properties of neutrinos are now ripe for measurement and the results
will have profound implications for our understanding of the fundamental
properties of matter and for the evolution of the early universe. The
neutrino physics advocated in this paper offers a ***bold and exciting
vision* *for the next twenty years* *of neutrino experimentation*** and
delineates a compelling path forward that is uniquely empowered to lead
to the complete unraveling of the remaining mysteries of neutrino
physics. This exciting neutrino physics vision is closely related to a
frontier program of astrophysical neutrino flux measurements and a
search for nucleon decay of greatly expanded sensitivity. Together,
these coupled programs enable us to take giant steps forward in neutrino
physics, astrophysics and nucleon decay. They comprise a truly rich and
productive direction for re-emergence of the U.S. as a world leader in
fundamental particle physics.

The new facilities required for this program are: 1) a **1 MW "Super
Neutrino Beam"** provided by an upgraded AGS proton driver accelerator
at Brookhaven National Laboratory \[1\]; 2) a **half-megaton water
Cerenkov detector**, such as the "UNO" detector \[2\] or the "3M"
concept \[3\], located deep underground in the former Homestake Mine in
Lead, South Dakota (or in a comparable location). This paper will
delineate the neutrino physics that can be achieved and describes the
needed accelerator upgrades to realize the 1 MW, wide-band neutrino beam
at BNL. A companion paper, "Proton Decay Detector" relates the
astrophysics and nucleon decay discovery potential of the half-megaton
UNO Detector. The value to U.S. physics and the importance of these
neutrino program elements were confirmed in a recent report commissioned
from the National Research Council by Dr. John H. Marburger III, Head of
the OSTP and President Bush's Science Advisor \[4\].

The complete set of neutrino oscillation parameters will be measured (or
definitive upper limits set) in the proposed ***Very Long Baseline
Neutrino Beam*** (VLBNB) as noted here:

*precise determination of the oscillation parameters m~32~^2^ and
sin^2^2~23~ (see Figs. 3, 4);*

*detection of the oscillation of ~e~ and measurement of sin^2^2~13~ (see
Figs.5, 6, 7, 8);*

*measurement of m~21~^2^ sin^2^2~12~ in a ~e~ appearance mode,
independent of the value of ~13~ (see Fig.9)*

*verification of matter enhancement and the sign of m~32~^2^ (i.e.,
which neutrino is heavier);*

*determination of the CP-violation parameter ~CP~ in the neutrino sector
(see Figs. 6, 7, 8).*

The enabling neutrino beam facility to realize this vision is available
with a modest intensity upgrade of the Alternating Gradient Synchrotron
(AGS) accelerator at BNL and the addition of a new 1 MW, wide-band,
few-GeV neutrino beam of a kind well documented in previous experiments.
Critical to the success of the entire neutrino oscillation program are
two key conditions: 1) the very long baseline (over 2500 km) that is
possible in the U.S. and naturally realized in the BNL-Homestake venue
discussed in this paper; 2) the specific few-GeV energy band of the
neutrino beam in which the cross sections and background parameters are
critical to success. No other neutrino oscillation program, worldwide,
has put forward a practical plan for achieving these ***critical***
***geographical baseline and beam energy conditions for success***.

All the enabling technologies required to realize this program have been
demonstrated in existing facilities and both projects are ***ready to
enter the engineering design phase*** as soon as funding is made
available.

#### Importance of the Science

Measurements of solar and atmospheric neutrinos have provided strong
evidence for non-zero neutrino masses and mixing \[5,6\]. Atmospheric
results have been further strengthened by the K2K collaboration\'s
accelerator based results \[7\]. The Solar neutrino results have been
confirmed by the KamLAND collaboration in a reactor based experiment
that has shown that the large mixing angle (LMA) solution is most likely
the correct one \[8\]. Interpretation of the experimental results is
based on oscillations of one neutrino flavor state, ~e~or , into the
others, and described quantum mechanically in terms of neutrino mass
eigenstates, and . The energies involved in the transitions are measured
to be approximately *m~21~^2^* *m*(~2~)^2^-*m*( = (5-10)10^-5^ eV^2^ for
the solar neutrinos and *m~32~^2^* *m*(~3~)^2^-*m*(= (1.6--4.0)10^-3^
eV^2^ for the atmospheric neutrinos, with large mixing strengths,
*sin^2^2* and *sin^2^2* in both cases. These parameters will be measured
with better accuracy in the experiments that are now either under
construction or taking data (MINOS, K2K, and KamLAND). Nevertheless, the
parameters are now sufficiently well-known that they open the
possibility for an accelerator based very long baseline experiment that
can explore the complete set of neutrino oscillation parameters in a
single experiment, complete measurement of the mixing parameters, and
search for new physics.

In this paper we describe how these measurements could be carried out
with good precision in a single accelerator based experiment, making use
of the already measured oscillation parameters and under reasonable
assumptions for as yet unmeasured ones. The experiment will require an
intense source of neutrinos based on a high energy proton accelerator
with total power of order 1 megawatt. The experiment will also require a
large detector with fiducial mass of about 500 kT located at least 2000
km away from the neutrino source.

The project we have outlined below is unique in many respects. The
existing data on neutrino oscillations and the prospect of searching for
CP-violation make clear that the next generation of oscillation
experiments must be significantly more ambitious than before. In
particular, the source of neutrinos needs to be accelerator-based so
that both the neutrino flavor content and the energy spectrum of the
initial state can be selected. Several alternatives have been explored
in the literature. These involve either a narrow band beam produced
"off-axis" with a conventional magnetic focusing system or a neutrino
factory based on a muon storage ring. We show that for the currently
favored oscillation parameters a few-GeV, wide-band super beam and a
very long baseline experiment can address all measurements of interest.
Other proposed facilities do not have the multiple node characteristics
described below, and do not have the wide reach in parameter space with
neutrino-only running.

###### The Experimental Strategy

For the experiment proposed here, the high-energy proton accelerator to
be used for making the neutrino beam must be intense ( 1 MW) to provide
a sufficient neutrino-induced event rate in a massive detector very
distant from it. Such a long baseline experimental arrangement can be
realized with a neutrino beam from the upgraded 28 GeV proton beam of
the Alternating Gradient Synchrotron (AGS) at Brookhaven National
Laboratory (BNL) with a water Cerenkov detector of 0.5 megaton fiducial
mass located at the Homestake mine in South Dakota (2540 km) or,
possibly, at the Waste Isolation Pilot Plant in New Mexico (2900 km).

We have performed detailed simulations of a wide-band, horn-focused
neutrino beam using 1 MW of 28 GeV protons on a graphite target. The
neutrino spectrum obtained in these simulations and used for the results
in this paper is shown in Figure 1. We calculate that with such a beam
we will obtain about 60000 charged current and 20000 neutral current
events in an exposure lasting 5 10^7^ seconds in a 0.5 megaton water
Cerenkov detector located at the Homestake mine 2540 km away from BNL.
The improved AGS will realize the needed flux with 5 months of running
each year for 5 years. We use the spectra obtained by making various
cuts appropriate for a water Cerenkov detector to select single muon or
electron events for the results reported below. Events with multiple
particles could be used to further enhance the statistical significance
of the effects. The event rate for an anti-neutrino beam running for the
same period of time is about 19000 charged current and 6000 neutral
current events. We will discuss the anti-neutrino beam in a separate
paper; here we wish to focus on the physics reach of running neutrinos
only. This strategy will achieve the results shown in the page 1 physics
bullets.

**Disappearance**

For precise and definitive measurement of oscillations we must observe
multiple oscillation nodes in the spectrum of reconstructed charged
current events. The multiple node signature is also necessary in order
to distinguish between oscillations and other explanations such as
neutrino decay or extra dimensions for the muon neutrino deficit in
atmospheric neutrinos. Since the cross-section, Fermi motion, and
nuclear effects limit the statistics and the energy resolution (for
reconstructed neutrino energy) of low energy charged current events, we
must utilize neutrinos with energies greater than few hundred MeV and
use clean events, with a single visible

![](media/image2.jpeg){width="2.4930555555555554in"
height="2.4194444444444443in"}

![](media/image3.wmf){width="2.433333333333333in"
height="2.433333333333333in"}

FIG. 1: The simulated wide band neutrino flux for 28 GeV protons on a
graphite target used for the calculations in this paper. (POT = protons
on target).

FIG. 2: Nodes of neutrino oscillations for disappearance (Not affected
by matter effects) as a function of oscillation length and energy for
*m~32~^2^* = 0.0025 eV^2^. The distances from FNAL to Soudan and from
BNL to Homestake are shown by the vertical lines.

muon or electron, dominated by quasi-elastic scattering for analysis.
Figure 2 shows that the distance needed to observe at least 3 nodes is
greater than 2000 km for *m~32~^2^* = 0.0025 eV^2^, the currently
favored value from Super-Kamiokande atmospheric data. A baseline of
greater than 2000 km coupled with a wide band beam with high flux from
0.5 to 7 GeV will provide a nodal pattern in the disappearance channel
and good sensitivity over a broad range of *m~32~^2^*.

![](media/image4.wmf){width="2.4694444444444446in"
height="2.5409722222222224in"}

FIG. 3: Spectrum of expected single muon events in a 0.5 MT water
Cerenkov detector. The top histogram is without oscillations; the middle
histogram with error bars is with oscillations. Both histograms include
the dominant single pion charged current background. The bottom
histogram shows this background contribution to the oscillated spectrum.

An advantage of the very long baseline is that the multiple node pattern
is detectable over a broad range of *m*^2^. At energies lower than
\~1GeV the energy resolution will be dominated by Fermi motion and
nuclear effects as shown in Figure 2. The contribution to the resolution
from water Cerenkov track reconstruction depends in first

approximation on the photomultiplier tube coverage. With fractional
coverage greater than 10%, reconstruction resolution of better than
\~10% can be achieved; 10% resolution was assumed in our simulations.

The simulated spectrum of the expected disappearance signal including
backgrounds is shown in Figure 3 for *m~32~^2^* = 0.0025 eV^2^ as a
function of reconstructed neutrino energy. The background, which will be
primarily charged current events, will also oscillate and slightly
broaden the dips in the nodal pattern. The determination of *m~32~^2^*
will have a statistical uncertainty of approximately 0.7% at *m~32~^2^*
= 0.0025 eV^2^ and *sin*^2^ 2 ~23~= 1. The experiment can determine
*sin^2\ ^*2~23~ \> 0.99 at 90% confidence level. The precision of the
experiment is compared in Figure 4 with the precision expected from the
MINOS experiment and Super Kamiokande. The large event rate in this
experiment will allow us to measure *m~32~^2^* precisely in a short
period of time; this measurement will be very important to predict the
shape of the appearance signal that we will now discuss.

![](media/image5.png){width="2.995833333333333in"
height="2.917361111111111in"}

![](media/image6.wmf){width="2.779861111111111in"
height="2.779861111111111in"}

FIG. 4: Resolution including statistical and systematic effects at 90%
confidence level on *m~32~^2^* and *sin*^2^2~23~ for the 2540 baseline
experiment; assuming 1 MW, 0.5 MT, and 510^7^sec of exposure. We have
included a 5% bin-to-bin systematic uncertainty in the energy
calibration as well as a 5% systematic uncertainty in the normalization.
We have not included a systematic uncertainty on the global energy
scale; this should be added in quadrature to the expected resolution on
*m~32~^2^*. The expected resolution of the MINOS experiment at Fermilab
and the allowed region of Super Kamiokande are indicated.

FIG. 5: Probability of *~e~* oscillations at 2540 km. The calculation
includes the effects of matter. The dotted (*~CP~* = 45^o^) and solid
(*~CP~* = 0^o^) curves are for *NO* and the lower dot-dashed (*~CP~* =
0^o^) curves is for *UO*. The parameters used for the figure are
*sin*^2^2*~12~* = 0.8, *sin*^2^= 1.0, and *sin* = 0.04 and *m*~21~^2^ =
6.010 ^--5^ eV^2^, *m*~32~^2^ = 0.0025 eV^2^.

***~e~* Appearance**

The low energy wide band beam and the very long distance present a
number of important advantages for the appearance channel *~e~*. These
advantages can be summarized using Figure 5 which shows the probability
of ~e~ oscillation as afunction of neutrino energy for the distance of
2540 km. The oscillation parameters that we have assumed are indicated
in the figure and the caption. We define the natural mass ordering
(*NO*) of neutrinos to be *m*~3~ \> *m*~2~ \> *m*~1~, and the unnatural
mass (*UO*) ordering to be *m*~2~ \> *m*~1~ \> *m*~3~. The third
possibility of reversed ordering (*RO*), *m*~1~ \> *m*~2~ \> *m*~3~, is
disfavored by the LMA solution. The effects of *UO* and *RO* are
approximately the same. Since neutrinos from an accelerator beam must
pass through the Earth to arrive at a detector located 2540 km away, the
probability in Figure 5 includes the effects of matter that enhance
(suppress) the probability above 3.0 GeV for *NO* (*UO*). Therefore the
appearance probability above 3.0 GeV is sensitive to both the mass
ordering and the parameter *sin*^2^ 2~13~. The probability in the region
1.0 to 3.0 GeV is less sensitive to matter but much more sensitive to
the CP phase ~CP~. The increase in the probability below 1.5 GeV is due
to the presence of terms involving the solar oscillation parameters,
*m*~21~^2^ and *sin*^2^ 2~12~. Therefore, the spectrum of electron
neutrino events, measured with a wide band beam over 2500 km with
sufficiently low background, has the potential to determine
*sin*^2^2~13~, ~CP~, *m*~21~^2^ and *sin*^2^ 2~12~, as well as the mass
ordering of the neutrinos, *because these parameters affect different
ranges of the energy spectrum*.

We have examined how well the parameters can be determined and the
implications for the detector performance and background. A conventional
horn focused beam can be run in either the neutrino or the anti-neutrino
mode. We have shown that most of the physics program can be carried out
by taking data in the neutrino mode alone. If the value of *sin*^2^2~13~
turns out to be too small or the true mass ordering is *UO*, then a
switch to antineutrino data-taking will be indicated. This will emerge
during the early neutrino running.

While the disappearance result will be affected principally by
systematic errors, the *~e~* appearance result will be affected mainly
by the backgrounds. The *~e~* signal will consist of clean, single
electron events (single showering rings in a water Cerenkov detector)
that result mostly from the quasi-elastic reaction *~e~* + *n* *e^-^* +
*p*. The main backgrounds will be from the electron neutrino
contamination in the beam and reactions that have a ^0^ in the final
state. The ^0^ background will depend on how well the detector can
distinguish events with single electron induced electromagnetic (e.m.)
showers and two photon induced e.m. showers.

Because of the rapid fall in the proposed neutrino spectrum beyond 4
GeV, the largest contribution to the ^0^ background will come from
neutral current events with a single ^0^ in the final state. It is well
known that resonant single pion production in neutrino reactions has a
rapidly falling cross section as a function of momentum transfer,
*q*^2^, up to the kinematically allowed value. This characteristic alone
suppresses this background by more than 2 orders of magnitude for ^0^
(or shower) energies above 2 GeV. Therefore, the modest ^0^ background
suppression (factor of \<20 below 2 GeV and by a factor of \~2 above 2
GeV) that can be obtained with a Water Cerenkov detector is sufficient
to reduce the ^0^ background to manageable level over the entire
spectrum. The electron neutrino contamination in the beam, from decays
of muons and kaons, is well understood to be approximately 0.7% of the
muon neutrino flux with a similar spectrum (Figure 1). The
experimentally observed electron neutrino spectrum will therefore have
three components: the rapidly falling shape of the ^0^ background, the
spectral shape of the *~e~* beam contamination slightly modified by
oscillation, and the oscillatory shape of the appearance signature. The
shape of the appearance spectrum will be very well known because of the
precise knowledge of *m*~32~^2^ from the disappearance measurement as
well as the improved knowledge of *m*~21~^2^ from KamLAND. These
distinguishing spectra will allow experimental detection of *~e~* with
good confidence. Figure 6 shows a simulation of the expected spectrum of
reconstructed electron neutrino energy after 510^7^ sec of running. The
parameters assumed are listed in the figure as well as the caption.

Figure 6 further illustrates the previously described three regions of
the appearance spectrum: 1) the high energy region (\> 3 GeV) with a
matter enhanced (for *NO*) appearance has the main contribution to the
background from *~e~* contamination in the beam; 2) the intermediate
region (1 3 GeV) with high sensitivity to the CP phase, but little
dependence on mass ordering, has approximately equal contribution from
both background sources; 3) and the low energy region (\<1.5 GeV), where
the effects of the CP phase and *m*~21~^2^ dominate, will have the main
background from the ^0^ events unless larger background suppression can
be obtained in the detector. Matter enhancement of the oscillations has
been postulated for a long time without experimental confirmation.
Detection of such an effect by observing a matter enhanced peak around 3
GeV will be very important. However, in the case of *UO* mass ordering,
this enhanced peak will be missing, but the effect (depending on ~CP~)
on the rest of the electron neutrino spectrum will be small.

In Figure 7 we show the 90 and 99.7% C.L. sensitivity of the proposed
experiment in the variables *sin*^2^2~13~ versus ~CP~. The actual limit
obtained in the case of a lack of signal will depend on various
ambiguities. Here we show the 99.7% C.L. lines for *NO* and *UO*, on the
right hand of which the experiment will observe an electron appearance
signal with greater than 3 sigma significance and thus determine the
corresponding mass ordering. The sign uncertainty of ~23~ = /4
introduces an additional ambiguity onto Figure 7 of ~CP~ ~CP~ +. For
this plot we have assumed that the other parameters are well known,
either from other experiments or by our disappearance measurement, to
be: *m*~21~^2^ = 6 10^-5^ eV^2^; *m*~32~^2^ = 0.0025 eV^2^. The values
of *sin*^2^2~12~ and *sin*^2^2~23~ are set to 0.8, 1.0, respectively.
The sensitivity to *sin*^2^2~13~ is somewhat better (worse) if
*m*~32~^2^ is smaller (larger). However, it does not diminish rapidly
within the range allowed by Super Kamiokande. The value of *m*~21~^2^
mainly affects the modulation of the *sin*^2^2~13~ sensitivity with
respect to ~CP~. If there is no excess electron appearance signal other
than the expected signal due to *m*~21~^2^, then a switch to
anti-neutrino running would be made to validate the *UO* hypothesis with
parameters on the left hand side of Figure 7.

**Sensitivity to the CP-violation Parameter**

If a signal in the *~e~* appearance mode with the *NO* ordering is
observed then a measurement of both *sin*^2^2~13~ and ~CP~ can be made
with the neutrino data alone. Since both *sin*^2^2~13~ and ~CP~ affect
the appearance probability, the measurement of the two parameters is
correlated. This correlation is much reduced, however, in the case of
the wide-band beam and the very long baseline because the effect of ~CP~
has an energy dependence opposite to that of *sin*^2^2~13~. Figure 8
shows the expected resolution on *sin*^2^2~13~ versus ~CP~ at
*sin*^2^2~13~ = 0.04 and ~CP~ = /4 with all other parameters fixed
(assuming they will be known before this measurement), as indicated

![](media/image7.wmf){width="2.4881944444444444in"
height="2.4881944444444444in"}

![](media/image8.wmf){width="2.4881944444444444in"
height="2.4881944444444444in"}

FIG 6: The expected reconstructed electron neutrino spectrum for 3
different values of the CP parameter ~CP~ including background
contamination. The error bars are for ~CP~ = 135^0^; the error bars
indicate the statistical error on each bin. The histogram directly below
the error bars is for ~CP~ = 45^0^ and the third histogram is for ~CP~ =
-45^0^. The hatched histogram shows the total background. This plot is
for *m*~32~^2^ = 0.0025 eV^2^. We have assumed *sin*^2^2~13~ = 0.04 and
*m*~21~^2^ = 6 10^-5^ eV^2^. The values of *sin*^2^2~12~ and
*sin*^2^2~23~ are set to 0.8, 1.0, respectively. Running conditions are
as in Figure 4.

FIG. 7: 90 and 99.7% C.L. contours of the proposed experiment in the
variables *sin*^2^2~13~ versus ~CP~ for the natural (*NO*) and unnatural
ordering of parameters (*UO*). The solid lines are for *NO*, the left
line for 90% and right line for 99.7% C.L. The dashed and dotted lines
are for 90 and 99.7% C.L. for *UO*.

in the figure and caption. A number of other ambiguities must be
considered to fully understand this measurement. These ambiguities and
correlations, however, do not significantly reduce the ability of the
experiment to determine whether the neutrino mixing contains a non-zero
complex phase, hence a CP-violating term. This is seen if we consider
the resolution on the quantity *m*~21~^2^ *J*~CP~ which is CP violating.
Note, the following important point: if ~13~ is large enough to give
observable ~e~ oscillations, the determination of ~CP~ is very
insensitive to the specific value of ~13~. A forthcoming paper will
discuss this in detail.

![](media/image9.wmf){width="2.4881944444444444in"
height="2.4881944444444444in"}

FIG. 8: 68% and 90% confidence level error contours in *sin*^2^2~13~
versus ~CP~ for statistical and systematic errors. The test point used
here is *sin*^2^2~13~=0.04 and ~CP~=45^0^. *m*~32~^2^ = 0.0025 eV^2^,
and *m*~21~^2^ = 610^-5^ eV^2^. The values of *sin*^2^2~12~ and
*sin*^2^2~23~ are set to 0.8, 1.0, respectively.

Finally, we remark that the very long baseline combined with the low
energy spectrum make it possible to observe *~e~* conversion even if
*sin*^2^2~13~ = 0 because of the contribution from *m*~21~^2^ if the
Solar neutrino large mixing angle solution (LMA) holds. The expected
appearance spectrum (Figure 9) for *m*~21~^2^ = 610^-5^ eV^2^ and
*sin*^2^2~12~=0.8 should have about 60 excess events above

background. If *m*~21~^2^ = 1010^-5^ eV^2^ (a higher value for the LMA)
then an excess of 230 events will result. Nevertheless, this measurement
will be sensitive to the magnitude and knowledge of the background
because there will be no oscillating behavior to distinguish the signal.
We estimate that the statistical and systematic errors in this
measurement will allow us to determine *sin^2^2~12~ x sin^2^(m~21~^2^
L/4E)* to about 12%; this corresponds to a measurement of *m*~21~^2^ to
a precision of 10% if *sin^2^2~12\ ~*from the LMA-solar best-fit
measurement is used. This is competitive with the expected measurement
from KamLAND. However, this will be in appearance mode and qualitatively
different from results in the SNO and KamLAND experiments.

![](media/image10.wmf){width="2.4881944444444444in"
height="2.4881944444444444in"}

FIG.9: The expected spectrum of electron neutrino events for
*sin*^2^2~13~ = 0. The other important parameters in this figure are
*m*~21~^2^ = 6 10^-5^ eV^2^ and *sin*^2^2~12~ = 0.8. Other parameters
and running conditions as in Figure 6.

######### The Accelerator and Beam Complex

The required performance upgrades to the AGS proton driver complex for
the 1 MW Super Neutrino Beam are summarized in Table I. A layout of the
upgraded AGS is shown in Figure 10. Three upgrade elements are
needed: 1) a superconducting addition to the existing 200 MeV Linac to
reach a total energy of 1.2 GeV for direct H^-^ injection

###### 

into the AGS; 2) upgrade of the AGS magnet power supply to a 2.5 Hz
cycling rate; 3) a power upgrade of the AGS rf system. The detailed
upgrade descriptions can be found in \[9\]. The neutrino beam target and
pion decay channel design will be described in the next section.

Table I - AGS Proton Driver Parameters

  -------------------------------------------- --------------------------
  Total beam power                             1 MW

  Protons per bunch                            0.410^13^

  Beam energy                                  28 GeV

  Injection turns                              230

  Average beam current                         38 A

  Repetition rate                              2.5 Hz

  Cycle time                                   400 ms

  Pulse length                                 0.72 ms

  Number of protons per fill                   9.6 10^13^

  Chopping rate                                0.75

  Number of bunches per fill                   24

  Linac average/peak current                   20/30 mA
  -------------------------------------------- --------------------------

![](media/image11.wmf){width="3.1104166666666666in"
height="1.8534722222222222in"}

FIG. 10: AGS Proton Driver Layout.

**Superconducting Linac**

Three superconducting linac (SCL) sections accelerate the proton beam
from 200 MeV to 1.2 GeV. All three are built up from a sequence of
identical periods. The major parameters of the three sections of the SCL
are given in Table II. The low energy section operates at 805 MHz and
accelerates proton from 200 to 400 MeV. The following two sections,
accelerating to 800 MeV and 1.2 GeV, operate at 1.61 GHz. A higher
frequency is desirable for obtaining a larger accelerating gradient with
a more compact structure and reduced cost. The SCL will be operated at 2
^0^K in order to reach the desired gradient.

Table II - Superconducting Linac Parameters

  -------------------------------------- ---------- ---------- ----------
  **Linac Section**                      **LE**     **ME**     **HE**

  Average Beam Power, kW                 7.14       14.0       14.0

  Average Beam Current, A                35.7       35.7       35.7

  Kinetic Energy Gain, MeV               200        400        400

  Frequency, MHz                         805        1610       1610

  Total Length, m                        37.82      41.40      38.32

  Accel. Gradient, MeV/m                 10.8       23.5       23.4

  Norm. rms Em, mm-mrad                  2.0        2.0        2.0
  -------------------------------------- ---------- ---------- ----------

**Target Station and Neutrino Beam**

The neutrino beam will be derived from the decay of pions produced in a
target embedded in a focusing horn. This technology has been widely used
since the 1970s. To achieve the needed 1 MW capability, however, serious
consideration must be given to the target materials and to the
target/horn configuration.

To accomplish these objectives, the following concerns were addressed by
BNL engineers and physicists:

*Optimization of neutrino flu Survivability of the target*

*Heat removal from the target and horn Irradiation and integration*

The design of the target/horn configuration is shown in Fig. 11. The
material selected for the proton target is a Carbon-Carbon composite. It
is a 3-dimensional woven material that exhibits extremely low thermal
expansion for temperatures up to 1000^0^C; for higher temperatures it
responds like graphite. This property is important for greatly reducing
the thermo-elastic stresses induced by the beam, thereby extending the
life of the target.

![](media/image12.jpeg){width="2.9972222222222222in"
height="2.0493055555555557in"}

FIG.11: Graphite target and horn configuration.

The target consists of an 80-cm long cylindrical rod of 12 mm diameter.
The target intercepts a 2 mm rms proton beam of 10^14^ protons/pulse.
The total energy deposited as heat in the target is 7.3 kJ with peak
temperature rise of about 280^0^C. Heat will be removed from the target
through forced convection of helium gas across its outside surface.

The extracted proton beam uses an existing beamline at the AGS, but is
then directed to a target station atop a constructed earthen hill. The
target is followed by a downward sloping pion decay channel. This
vertical arrangement keeps the target

and decay pipe well above the water table in this area. The 11-degree
slope aims the neutrino beam to the water Cerenkov detector located in
the Homestake mine of South Dakota. A plan view of the AGS facility is
shown in Figure 12. A 3-dimensional view of the neutrino beam is
provided in Figure 13.

![](media/image13.jpeg){width="2.3631944444444444in"
height="2.6743055555555557in"}

FIG. 12: A plan view of the neutrino beam facility at the AGS. The 1 MW
proton beam will be taken from the existing fast extraction line (the
U-line) and continued on the up-slope of the hill. The vertical and
horizontal bending magnets are separate in this plan. The beam will be
bent downwards at the top of the hill to aim it towards Homestake at
11^0^.

![](media/image14.jpeg){width="2.8006944444444444in"
height="2.3027777777777776in"}

FIG. 13: 3-dimensional view of the neutrino beamline. The beamline is
shown without shielding on top of the beam-line magnets and the decay
tunnel.

#######   {#section-2 .unnumbered}

####### Cost Estimates for the AGS Upgrade and Neutrino Beam

A preliminary cost for upgrading the accelerator complex to 1 MW is
shown in Table III. Details of this estimate are given in Ref \[1\]. The
upgrade could be done in phases if required by the project funding plan.

Table - III Estimated AGS Upgrade Cost

  ----------------------------------------------- -----------------------
  **1.2 GeV SC Linac:**                           **Cost**

  Front End                                       \$ 2.2 M

  LE SC Linac                                     \$38.3 M

  ME SC Linac                                     \$30.7 M

  HE SC Linac                                     \$28.1 M

  **AGS upgrades:**                               

  AGS Power Supply                                \$32.0 M

  AGS RF upgrade                                  \$ 8.6 M

  AGS injection channel                           \$ 3.7 M

  Full turn extraction                            \$ 5.5 M

  Shielding                                       \$ 3.5 M

  Installation                                    \$ 4.2 M

  **Total Direct Cost**                           **\$156.8 M**
  ----------------------------------------------- -----------------------

Table IV -- Estimated Neutrino Beam Cost

+------------------------------+----------------------+----------------+
| **Item**                     | **Basis**            | **Cost**       |
+------------------------------+----------------------+----------------+
| Proton transport             | RHIC injector        | \$14.8 M       |
+------------------------------+----------------------+----------------+
| Target/horn                  | E889                 | \$ 5.5 M       |
+------------------------------+----------------------+----------------+
| Shielding/Dump               | New                  | \$ 5.8 M       |
+------------------------------+----------------------+----------------+
| Decay Tunnel                 | E889                 | \$ 0.4 M       |
+------------------------------+----------------------+----------------+
| Hill. const.                 | New                  | \$ 8.0 M       |
+------------------------------+----------------------+----------------+
| Near Detector vault          | E889                 | \$ 8.5 M       |
+------------------------------+----------------------+----------------+
| Conventional Facil.          | RHIC                 | \$ 7.5 M       |
+------------------------------+----------------------+----------------+
| Other const.                 | E889                 | \$ 6.0 M       |
+------------------------------+----------------------+----------------+
| Installation                 |                      | \$ 5.2 M       |
+------------------------------+----------------------+----------------+
| ######## Total Direct Cost   |                      | **\$61.7 M**   |
+------------------------------+----------------------+----------------+

A preliminary estimate of the direct costs for the neutrino beamline
without burdens is shown in Table IV. Costs are scaled from the RHIC
injection line, as well as the E889 proposal and the Neutrino Factory
study \[9\]. The conventional construction costs are dominated by the
size of the hill at 54 m. In our cost estimate we assume that the beam
dump is underground to reduce the height of the hill. The target station
shielding will be provided from existing BNL shielding inventory. A
preliminary estimate of the total cost of the AGS upgrade and super
neutrino beam includes: EDIA @ 15%; contingency @ 30%; BNL project
overhead @ 13%. The total estimated cost (TEC) is \$369 M in FY03
dollars. Escalation cannot be estimated without a project start year.

###### The Detector

The conversion of the Homestake Gold Mine in Lead, South Dakota into the
National Underground Science and Engineering Laboratory (NUSEL) is
anticipated to take place in the next few years and offers a unique
opportunity for a program of very long baseline neutrino oscillation
experiments. As noted above, these experiments are achievable only with
the very long baseline (2540 km) from BNL to Lead, SD. It is proposed
that NUSEL will accommodate either a single monolithic detector (or an
array of modules) with fiducial mass of one-half megaton. The leading
technology is a water Cerenkov detector that can observe neutrino
interactions in the desired energy range with appropriate energy and
time resolution. A possible alternative to Homestake also exists at
DOE's Waste Isolation Pilot Plant (WIPP) located in an ancient salt bed
at a depth of \~700 meters near Carlsbad, New Mexico. The distance from
BNL to WIPP is about 2880 km.

In this report we do not address the detailed issues of detector design
and cost. More detailed studies of very large water Cerenkov detectors,
appropriate for this experiment, have been done by the UNO collaboration
\[2\] and by physicists from the University of Pennsylvania \[3\]. The
UNO proton decay detector version for this detector will be presented to
the HEPAP review of the DOE Office of Science facilities opportunities
and will address the issues of how to build and operate such a detector.

**Readiness for Construction**

The concept for this project has been studied in a neutrino working
group at Brookhaven National Laboratory for over 1 year. The accelerator
upgrade is well understood and preliminary costs have been prepared. New
targeting systems for the neutrino beam have been designed and the flux
yields are well understood. Preliminary engineering studies indicate
that this design will satisfy all mechanical and radiation shielding
requirements for the 1 MW beam. The AGS is already the world's highest
intensity proton synchrotron and is clearly able to achieve the 1 MW
performance needed for the neutrino program. An additional power upgrade
to 2 MW could be realized later by extending this design.

The feasibility of the large water Cerenkov detector is addressed in
references \[2\] and \[3\]. The designs described there will be refined
as we understand the mine requirements more completely. Water Cerenkov
detector technology is already very well understood from the Super
Kamiokande Experiment and we are confident that a successful working
detector can be constructed. Since the technology of both the neutrino
source and the detector are well understood, this project is "***ready
to initiate detailed engineering design followed by facility
construction***".

**References**

\[1\] D. Beavis et al., Report of the BNL neutrino working group,

BNL-69395, hep-ex/0211001. <http://nwg.phy.bnl.gov/preprints.php>

\[2\] Physics Potential and Feasibility of UNO, UNO collaboration, June
2001. SBHEP01-3.

\[3\] 3M Collaboration: Proposal titled, "Megaton Modular Multi-Purpose
Neutrino Detector, Nov. 26, 2001".

\[4\] "Neutrino Facilities Assessment Committee," National Research
Council project no. BPAX-L-02-01-A,

\[5\] PDG, Phys. Rev. **D66**, 010001 (2002), p. 281. Y.Fukuda et al.,
Phys. Rev. Lett. **81**, 1562 (1998),

S. Fukuda et al., Phys. Rev. Lett. **86** 5656, 2001; E.W. Beier, Phys.
Lett. **B283**, 446 (1992);

T. Kajita and Y. Totsuka, Rev. Mod. Phys. **73**, 85 (2001).

\[6\] Q. R. Ahmad et al., Phys. Rev. Lett. **87** 071301 (2001); S.
Fukuda et al., Phys. Rev. Lett., **86** 5651 (2001).

\[7\] S. H. Ahn et al., Phys. Lett. **B 511** 178 (2001);

\[8\] K. Eguchi, *et. al*, Phys. Ref. Lett. **90**, 021802 (2003).
hep-ex/0212021.

\[9\] S. Ozaki et al., Neutrino Factory Feasibility Study II,
<http://server.cap.bnl.gov/mumu/studyii/>;

M. Zisman, Status of Neutrino Factory and Muon Collider R&D, PAC2001,
WOAB008