# Presentation: 700454

## A Close-In Detector for the BNL Long Baseline Experiment

- Steve Kahn
- 10 Jan 2003

- Jan 10, 2003

## 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.

- Jan 10, 2003

## 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.

- Jan 10, 2003

## 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.

- Jan 10, 2003

## 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 pp can look like np 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.

- Jan 10, 2003

## Cartoon Design of the Close-In Detector

- 3 meters

- 1.5 m

- Jan 10, 2003

## 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:
- 0.70.73.0 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.

- Jan 10, 2003

## Slide 8

- Jan 10, 2003

## Slide 9

- Jan 10, 2003

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

- Jan 10, 2003

## 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.

- Jan 10, 2003

## Muon Magnet

- Liquid Argon has interaction84 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.

- Jan 10, 2003

## Estimates of Events Seen in this Detector.

|  | n–p | ene–p | N–X | eNeX |
| --- | --- | --- | --- | --- |
| Liquid Argon | 9.75106 | 1.2105 | 3.05107 | 3.94105 |
| ICE Target | 1.07106 | 1.33104 | 3.39106 | 4.38104 |
| Homestake
0.5 Mtons | 13300 | 116 | 53853 | 476 |

- Estimates are for 5107 sec and don’t include fiducial volume cuts

- Jan 10, 2003

## 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.

- Jan 10, 2003