Jan 10, 2003 1

A Close-In Detector for the BNL Long Baseline Experiment

Steve Kahn10 Jan 2003

Steve KahnJan 10, 2003 Close-In Detector Page 2

Requirements for a Close-in Detector for the Long Baseline Neutrino Experiment This detector should provide flux distributions as a

function of E. It should provide flux distributions for all

components: e e A magnetic field is desired to distinguish the sign of the

leptons. The detector should provide a flux that can be

extrapolated to the far detector. The most desirable case would be to position the

close detector such that the neutrino source position looks like a point.

This would suggest that the close-in detection should be placed greater than 2 km from the target. This is not easily achievable for a beam inclined 11.3o.

Steve KahnJan 10, 2003 Close-In Detector Page 3

Requirements, continued. A realistic position for the close in detector is 275 meters

from the target. This is behind a 10 meter beam stop at the end of the

decay tunnel and benefits from the additional 60 meters of soil between the beam stop and the detector enclosure.

A study of how to relate the flux distribution at 275 m to that at 2540 km will be necessary.

This will have to be done for J-PARC also. In order to avoid relying heavily on a Monte Carlo description

of the beam-line one would need either: Two close detectors with some separation between them A single detector at a distance greater than ~2 km, so

that the neutrino source (pion decay position) appears as a point.

Steve KahnJan 10, 2003 Close-In Detector Page 4

Neutrino Fluxes at Detector Locations

e fluxes are scaled by 20 in order to be visible.

Off-axis

Note the different shapes at 250 m and 2540 km.

Steve KahnJan 10, 2003 Close-In Detector Page 5

Technology to be used for the Close Detector

It would be desirable to have neutrino interactions off the same nuclei at the near and far detector.

There are nuclear effects such as pion reabsorption. A resonance event pp can look like np in an Ar

detector but not in a H2O detector.

There are Fermi Motion effects that would be different with different nuclear targets.

There different resolutions with different detectors. One needs to evaluate the size of these effects. There

are likely to cause ~10% errors in the knowledge of the beam flux at the far detector.

We might be able to live with it.

Steve KahnJan 10, 2003 Close-In Detector Page 6

Cartoon Design of the Close-In Detector

3 meters 1.5 m

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Liquid Argon Detector

The major component of this detector is a magnetized liquid argon TPC detector modeled after that proposed in the -LANNDD experiment.

I have chosen as a start the dimensions of -LANNDD: 0.70.73.0 m3

These dimensions may have to change to enclose the lateral growth of a shower.

A detector of this size could fit into 120D36 dipole magnet which could give a 1 T field.

This detector would have 2 tons of liquid argon.

Steve KahnJan 10, 2003 Close-In Detector Page 8

Steve KahnJan 10, 2003 Close-In Detector Page 9

Steve KahnJan 10, 2003 Close-In Detector Page 10

Typical Shower from a 2.5 GeV Electron in a 1 T Transverse Field

Steve KahnJan 10, 2003 Close-In Detector Page 11

Ice Target

In order to address the criticism that the near detector has a different target than the far detector, a supplementary target made of ice could be put in front of the liquid argon to provide a sample of events that interacted on water.

The ice would not have active detection. Events would observed as tracks from an interaction upstream.

An upstream veto detector would be necessary to verify that the interaction occurred in the ice.

I have assumed about 0.5 meters of ice which would give 0.22 tons of target.

Steve KahnJan 10, 2003 Close-In Detector Page 12

Muon Magnet

Liquid Argon has interaction84 cm. This would provide on average ~2 interaction lengths to distinguish pions from muons. An external magnetized iron-scintillator detector could verify muons and provide a measurement of the muon momentum. The field in the iron is sort of torroidal, à la

Minos. The magnet in the liquid argon only provides

the momentum projected in a plane.

Steve KahnJan 10, 2003 Close-In Detector Page 13

Estimates of Events Seen in this Detector.

n–p ene–p N–X eNeX

Liquid Argon

9.75106

1.2105 3.05107

3.94105

ICE Target

1.07106

1.33104

3.39106

4.38104

Homestake0.5 Mtons

13300 116 53853 476

Estimates are for 5107

sec and don’t

include fiducial volume

cuts

Steve KahnJan 10, 2003 Close-In Detector Page 14

What Next?

I am in the process of setting up this detector system in a Geant4 simulation. This should give insight on whether this

system will work. Also we need to study how to use the flux

measured at the close-in detector to determine the flux at the far detector.