A Near Detector for the BNL Very Long Baseline Facility

1. A Near Detector for the BNL Very Long Baseline Facility Steve Kahn BNL Review AGS Upgrade and Super Neutrino Beam Facility June 11, 2004 S. Kahn -- Near Detector Facility

2. The Purpose of a Near Detector • The main purpose of the near detector is to provide knowledge of the composition of the neutrino beam: • The energy spectrum of the dominant  flux. • The energy spectrum of the contaminant neutrino species in the beam: , e, ande. • The integrated neutrino flux for overall normalization. • Neutrino direction information for extrapolation to far detector. • e elastic scattering • Statistically from Quasi-elastic interactions. • Alignment monitoring information from neutrino data during a run. • Also it should hopefully have its own physics program. S. Kahn -- Near Detector Facility

3. Near Detector Location • The near detector facility is planned to be located at 285 m from the target. • It would be desirable to have the near detector further from the target, so that the neutrinos appear to come from a point source. • The steep 11.3° incline limits the choice of location. • At this position the near detector hall is 21 m below the ground level. S. Kahn -- Near Detector Facility

4. Near Detector Location (cont.) • The near detector hall is behind a 10 meter iron 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. • There should be essentially no muon punch through. • A study of how to relate the flux distribution at 285 m to that expected at 2540 km will be necessary. • This will have to be done for J-PARC’s near detector also. S. Kahn -- Near Detector Facility

5. Comparison of the  Flux Distribution at the Near and Far Detectors • Figure shows the flux distribution at the near location (red) and the flux distribution at the far detector (blue) scaled to the near detector position. • The near flux peaks at a lower energy than the flux at the far detector. • Because of the large statistics that will be present at the near detector the flux can be measured as a function of position to provide information for the extrapolation to the far detector. S. Kahn -- Near Detector Facility

6. Flux Contamination Seen at the Near Detector • Flux distributions can be obtained from a simulation of the target and horn system using both GEANT and MARS programs • MARS gives the , K± and ± produced on the carbon target. • GEANT tracks these particles through the horn system and allows them to decay to channels that produce neutrinos. • At the near detector the flux has: • 3%  component • 1% e component S. Kahn -- Near Detector Facility

7. Expected Event Rates at the Near Detector • The number of events of each neutrino species produced in the detector can be obtained by integrating the flux with the appropriate cross section. • The table below shows the expected number of events for a 200 ton detector during a 5107 second running period. • 200 tons was chosen to be large enough to contain the entire event, but small enough to be affordable. • For this 5107 second period we expect a total of 4109 events in a 200 ton detector. • That is 32 events per pulse! S. Kahn -- Near Detector Facility

8. Desired Attributes of a Near Detector • The technology chosen should be able to handle the high event rate. • It should be able to distinguish events from different neutrino species. • Distinguish electrons from muons. • Determine the sign of the lepton, particularly the muon. • Do we need a magnetic field? • It should be able to distinguish the lepton from hadrons • Muons from pions • Electrons from  • It would be desirable that the interactions be on a similar nucleus as the far detector so that uncertainties about  re-absorption will cancel. • The near detector should have its own physics program to take advantage of the large statistics available. S. Kahn -- Near Detector Facility

9. The Choice of Near Detector Technology • It is certainly not my intention to choose the Near Detector technology. • This should be done by a group of physicists who are proposing the experiment and should be reviewed by the usual committees. S. Kahn -- Near Detector Facility

10. Intermediate Distance Water Cherenkov proposed for JPARC What about Water Cherenkov? • High event rate at 285 m may limit the usefulness of a water Cherenkov detector. • The Super-K guidelines requires 2 m from the surface of the fiducial volume to the PMTs. In addition to measure  energy up to 1 GeV requires 4 m down stream region. • This says that 100 ton fiducial volume requires 1kton size water Cherenkov detector. • The water Cherenkov detector would be better suited at a distance of 1.5-2 km. Intermediate Distance Water Cherenkov proposed for JPARC S. Kahn -- Near Detector Facility

11. Schematic of a Liquid Argon TPC Near Detector 100 ton active liquid argon volume 14 ton fiducial volume Magnetized Iron-scintillator Detector for muon identification S. Kahn -- Near Detector Facility

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15. Typical Shower from a 2.5 GeV Electron in a 1 T Transverse Field S. Kahn -- Near Detector Facility

16. Events in Liquid Argon • Events are clean in liquid argon. • Separation of electrons from muons should be easy. • Separation of 0 from electrons should be possible. • Expect ~16 events in 100 ton active region or ~2 events in fiducial volume. • A typical event should occupy about 6 m3. (The fiducial volume is about 10 m3) S. Kahn -- Near Detector Facility

17. Cost Estimate Guess • Liquid Argon TPC • Based on A. Rubbia’s numbers for the actual cost of the Icarus prototype module: M$ 20/kiloton. • Estimate that 200 ton Liquid Argon TPC would be ~M$5 • 0.5 T magnetic field on Liquid Argon would be additional. • Magnetized Iron Scintillator. • MINOS near detector was estimated at M$5 in the design report. This would escalate to M$6.2 today. • I am using a smaller iron-scintillator detector behind the Liq-Ar cryostat. Estimate about 1/3 the cost: ~M$2.1 • Expect the Near Detector to cost M$ 7-9 S. Kahn -- Near Detector Facility

18. S. Kahn -- Near Detector Facility

19. Summary • The near detector will provide the necessary understanding of the neutrino flux and its contamination. • The detector will be challenging because of its location and its high event rate. • Extrapolating to the flux at the far detector will require some analysis. • A liquid argon TPC may be a reasonable technology for this detector. • The cost of this detector should be of the order of 10 million dollars. S. Kahn -- Near Detector Facility