1. Fine-Grained Near Detector(s) at JHF: Purpose and Thoughts
Kevin McFarland
University of Rochester
31 October 2002

2. Precision P(nm→ne) and P(nm→nm)
Conventional “superbeams” will be our only windows into nm→ne for a long time…
Analogous to |Vub| in quark sector
Long time before m sources or “b beams”
Studying in neutrinos and anti-neutrinos gives us magnitude and phase information on |Ue3|
Comparing two precise n measurements at different E or L/E does same
P(nm→nm) is mixing maximal? Precise dm23
Sign of dm23
|Ue3| d
31 October 2002
Kevin McFarland

3. Where do Cross-Sections matter?
1ring FC m-like
Reconstructed En (MeV)
Oscillation with
Dm2=3×10-3
sin22q=1.0
No oscillation
Non-QE
nm→nm, dm223, q23
Signal is suppression in MeV bin
Dominated by non-QE background
20% uncertainty in non-QE is comparable to statistical error
Non-QE background feeds down from En>Epeak
31 October 2002
Kevin McFarland

4. Where do Cross-Sections matter?
nm→ne, q13
Shown at right is most optimistic q13; we may instead be fighting against background
Equal parts NC p0 and beam ne background
NC p0 cross-section poorly known
We can calculate sCC(ne)/sCC(nm). Is it right?
We must prove to the world we are right with S/N of 1:1
Precision measurement is the endgame
sin22qme=0.05
(sin22qme  0.5sin22q13)
31 October 2002
Kevin McFarland

5. Where do Cross-Sections matter?
nm→ne vs nm→ne, d
Cross-sections very different in two modes
“Wrong sign” background only relevant in anti-neutrino
Crucial systematic in comparison
Need sCC(n)/sCC(n) at high precision in sub- to few-GeV region nm nm
31 October 2002
Kevin McFarland

6. Status of Cross-Sections
Not well-known at 1-few GeV
Backgrounds for JHFn
Signal and Background at NUMI 0.70 off-axis proposal
n–p0
nn+
31 October 2002
Kevin McFarland

7. Low Energy Neutrino cross-sections
Neutrino interactions
Quasi-Elastic / Elastic , nmn→m-p (x =1, W=Mp)
well measured and described by form factors
BUT, need to account for Fermi Motion/binding effects in nucleus, e.g. Bodek-Ritchie prescription
Resonance, nmp→m-pp (low Q2, W)
Poorly measured and only 1st resonance described by Rein and Seghal
Deep Inelastic, nmp→m-X (high Q2, W)
well measured by high energy experiments
well described by quark-parton model (pQCD with NLO PDFs)
but doesn’t work well at low Q2 region.
at x = 1
(quasi)elastic
F2 integral=0.43
(e.g. SLAC data at Q2=0.22)
Issues at few GeV :
Resonance production and low Q2 DIS contribution meet.
The challenge is to describe ALL THREE processes at ALL neutrino (or electron) energies
HOW CAN THIS BE DONE?
QPM model with proper scaling behavior above 1st resonance using ideas from quark-hadron duality
31 October 2002
Kevin McFarland

8. Does model work? Can test in electron scattering
Ref: Bodek and Yang hep-ex/
Q2= 0.22 GeV2
Can test in electron scattering
Data at right predicted by fit
More complicated in neutrino charged-current
Isospin selection, e.g., np→mD++
EOI considered by FNAL PAC
Collaboration (FNAL, Hampton, Jefferson Lab, Rochester) being formed
Note that this project requires a JHF 280m type detector
Is NUMI our test beam?
Q2= 0.07 GeV2
Q2= 1. 4 GeV2
Q2= 9 GeV2
Q2= 3 GeV2
Q2= 15 GeV2
Q2= 25 GeV2
31 October 2002
Kevin McFarland

9. Fine-Grained Detector Goals
Observe recoil protons
Important for n–p, n–p0
Investigate n capture layers?
0 , – reconstruction
Adds a lot of mass. Muon charge needed for n
Oxygen-rich Target
Water miscible scintillator layers
Exists. Commercially available. Need detailed study of properties
Light output problematic? VLPC readout?
Sampling water + plastic scint?
Acrylic? Is it stable? Lowish oxygen content
31 October 2002
Kevin McFarland

10. Fine Grained Location: Off-Axis
Narrow band beam, similar to far detector
NBB crucial for study of cross-sections, particularly for neutral current
Event cannot be fully reconstructed without knowing En
En can be varied by varying position
Bonus: can check beam spectrum, particularly backgrounds for nm→ne
Not clean as in case of “2km” detector
31 October 2002
Kevin McFarland

11. Event Spectra in Near Off-Axis, Near On-Axis and Far Detectors at NUMI
Far 0.7o OA
Far 0.7o OA
Near 0.7o OA (LE)
Near On-Axis (LE)
Near 0.7o OA (ME)
Near On-Axis (ME)
31 October 2002
Kevin McFarland

12. NUMI EOI (technology test?)
Ideal locations in NUMI tunnel complex exist for 2.5 GeV beam
1.5 GeV possible. 1 GeV tough.
Locate in access drift
31 October 2002
Kevin McFarland

13. Conceptual NUMI Near Detector
Active/passive frame around target
Active scintillator strip target
31 October 2002
Kevin McFarland