# Presentation: 132818

## NuMI Off-axisBeam,  Systematics, Background

- Outline:
- 1)      Brief description of NuMI beamline, construction status, on-axis beam to MINOS
- Kinematics that lead to off-axis beam
-  e beam background
- Prediction of far off-axis spectrum from near detector measurement
- Anti-neutrino running
- Is another near detector useful ?
- Further optimization of beamline ?

##  Two Detector NeutrinoOscillation Experiment(Start Dec 2004)

- Near Detector: 980 tons

- Far Detector: 5400 tons

- MINOS Experiment

**735 km**

## How  beam is produced

## Underground Excavation Complete !To do: outfit, surface bldg., install

- 677 m decay pipe

-    Near
- Detector

- Target

##     Status of NuMI Tunnel

- MARCH 2002

- Decay pipe is
- finished and
- encased in
- concrete

## Magnetic Horns focused by toroidal field between conductors

- Large toroidal magnetic field
- Requires large current,   200 kAmp
- Thin inner conductor, to minimize  absorption
- Water spray cooling on inner conductor
- Most challenging devices in beam design
- Prototype test 1999-2000 to check design

- Focus  toward detector

- Outer Conductor

- Inner Conductor

- Stripline

- Drain

- Insulating Ring

- Spray Nozzle

- 

- 

- 

- Precision control of field -
-     Achieved ~ 0.1 mm horn tolerance after weld

##          NuMI Horn1

-  1st Horn under test

-      1 year worth of pulses

## Horn 2 nearing completion 

-  Initial weld samples                 Final horn being welded

## + Production, Focusing, Decay

- p

- ~

- 

- to detector

- 

- 

- Pt() ~ 300 MeV

- 

- 300 MeV

- ~

- P()

- 0.43 E

- 1 + 22

- Flux~

- 2

- (1 + 22) 2

-  Without focusing, flux to detector is only ~1/25 of flux in pion direction
-  With a parabolic shaped horn inner conductor,
- 	B dL (i.e. pt kick) is linear with radius  ->  lens
- The focal length is proportional to p:
-  	choice of target to horn distance selects momentum
-   focused parallel by horn 1 go through hole in horn 2;
- 	somewhat under or overfocused  are focused by horn 2

- 

- f p

## Different  spectra obtainedby moving target and 2nd horn

- MINOS on-axis:

##       Likely NuMI Schedule

- The Underground (tunnel, caverns, and shafts) contractor will finish mid-November of this year (2002)
- Surface buildings, outfitting take about 1 year
- Installation of beam technical components and Near Detector  take about 1 year
- 					First beam on NuMI target ~ 11/04

## Advantages of off-axis beam

- NuMI-MINOS is designed as broad band oscillation  disappearance search facility,
- 	has much higher reach in E for its L than current knowledge would require
- 		(for M2=0.003 eV2, 1st osc. node at 735 km is at 2 GeV)
- @2GeV, (off-axis ME / on-axis LE):
- gives twice the  beam flux
- e beam background /  beam reduced by factor 2-3 at source
- 		        (and much of   oscillate away, reducing mis-ID b.g.)
-  High energy tail in spectrum greatly reduced
- 	NC feed-down background greatly reduced
- 	Events above  CC threshold, and thus  -> *e* b.g., greatly reduced
-  e beam background mostly from muon decay
- 	(easier to predict than kaon decay background)

## Decay kinematicsof perfectly focused pions

## Two body decay kinematicsof perfectly focused pions

- ‘On axis’: E=0.43E

- At this angle, 15 mrad, energy of produced neutrinos is 1.5-2 GeV for all pion energies  very intense, narrow band beam

## What are Pt scales?Does this magic really work?

- Pt max for  from pi decay is 30 MeV/c
- Hadronic production of pions peaks around Pt of 200 – 300 MeV/c
- 	Horn focus reduces this to ~ 10 MeV/c over some momentum range,
- 	   so that this off-axis “magic” can help, and Pt (pion) < Pt (decay).
- 	 Does induce significant smearing, need full M.C. to understand beam
- At other momentum ranges, pion Pt dominates decay Pt
- (multiple scattering ~  few MeV/c)
- For reference, Beamline geometry aperture ~ 10 mr at low momentum
- 	effective aperture becomes smaller at high momentum

##  spectra moving off-axis( unoscillated, GEANT M.C. )

## What parent pionsare actually contributing? 

- L.E. tune

- Understand from pi production, focus, flux fact.

## Quantitatively 

- Solid angle for off-axis ~ 2/(1 + ()2)2/L2
- E (and hence x-section) ~  / (1 + 22)
- Compare with 2 / L2 and  for 0o
- For optimum, ~ 1
- For NuMI, advantages are energy compression and shift to better match to L and m2
- But per pion , neutrino event yield is 8 times smaller
- Once you choose your location, you no longer have much flexibility to change beam parameters

## e rates moving off-axis (L.E.)

## Sources of the e background

- At low energies the dominant background is from +e++e+ decay, hence
- K production spectrum is not a major source of systematics
******e** background directly related to the ********** **spectrum at the near detector

- All

- K decays

## N.C. rates off-axis (M.E.)

- Detector will require
-   good NC rejection

## N.C. rates off-axis (L.E.)

- M.E. off-axis
-   looked a little better
-     than this L.E. off-axis beam

##  oscillated spectrum

-  Mis-ID from  CC
-   can get really small,
-     since most of 
-        may have oscillated away

- Event spectra at far detectors located at different positions derived from  the  single near detector spectrum using _different particle production models._
- Four different histograms superimposed

-      Far Detector spectra from
-  Near Detector measurements

- Total flux
-    is predictable
-            to 2 %

## How does prediction of off-axis spectrum work?

- Input the Measured Near Detector Spectrum
-     (for now, other hadron production models)

-         Output the
- Far Off-axis Spectrum

- Weight matrix from M.C.
-        of pion decay locations
-              L.E. tune

## Raw production model  prediction.Then near detector constrained !

## A first attempt to extrapolateoff-axis far e from near flux

## What about systematics frompoorly known neutrino cross sections ?

- With well understood near detector, and above flux predictions,
- 	will measure neutrino cross sections to a few %
- -> want near detector of same material as far, but location of near detector may not be important

- MIPP will run at FNAL in 2003
-  Measure 120 GeV proton-carbon -> , K, ...
-  Good precision, ~ 2%
-  NOT single arm spectrometer
-  *	**-  get all P**t**, P*
* **	**-  acceptance correction easier*
-  Use actual NuMI target
- With NuMI precision horns and above MIPP
-   hadron production measurements, will make
-   very good prediction of  flux in near detector
-  *	**- have already measured excellent *
*	**magnetic field quality in 1**st** horn*

## Anti-neutrino beamby reversing horn current

- Slightly less flux,   bigger hit in anti-neutrino cross section,  ~ 1/3 as many events !

## Anti-neutrino running backgrounds

##  Near Detector location options

- Distance from  present MINOS Near Detector to FNAL site boundary is 2 km.
- Thus distant Near Detector at the appropriate angle is possible.
- There appears to be _no requirement_ for such a distant near detector.
- Probably put N.D. in present cavern (on axis), or present transfer tunnel (off axis)

##      Near Detector Issues

- Off-axis Near Detector may not be necessary for e background estimate:
-     pion flux (and hence muon flux) measured in on-axis ND
-     muon flux checked directly in muon monitors
-     K decays are minor contribution
-      decays don’t contribute in this energy range
-     MINOS Near Detector can perform the required measurements
- NC background estimate is more difficult
-     the level of understanding required depends on its size
-     off-axis Near Detector of same technology can measure this background
-     the Far Detector spectrum does not have to be reproduced exactly
- Both these backgrounds have much broader spectrum in far detector than the e oscillation signal

## Further Beam Optimization ?(just some of my thoughts for discussion)

- Optimum with existing horns is probably close to ME focus,
-  has not been fine tuned
- Probably want longer, narrower target; not studied yet
- Change in horn shape not investigated, may give modest improvement
- E907 MIPP experiment will measure target hadron production,
-  will allow more precise optimization studies
- Extrapolation of beam *e* background deserves more detailed study
- How cross section factors into extrapolation also needs study