# Presentation: 658972

##      Physics Opportunitiesin a NuMI Offaxis Experiment      

- Stanley Wojcicki
- Stanford University
- September 16, 2002
- London, England

##              Outline

- Introductory Comments
- Advantages of an Off-axis Beam
- Important Physics Issues
- NuMI Capabilities

- Stan Wojcicki,  Physics at Off-axis

- September 16, 2002

## Introduction

- Stan Wojcicki,  Physics at Off-axis

- September 16, 2002

## Introductory Comments

- The current generation of long and medium baseline terrestial  oscillation experiments is designed to:

- Confirm SuperK results with accelerator ’s (K2K)
- Demonstrate oscillatory behavior of ’s (MINOS)
- Make precise measurement of oscillation parameters (MINOS)
- 4.    Demonstrate explicitly  oscillation mode by
-       detecting ’s (OPERA, ICARUS)
- 5.   Improve limits on e subdominant oscillation
-       mode, or detect it (MINOS, ICARUS)
- Resolve the LSND puzzle (MiniBooNE)
- Confirm indications of LMA solution (KamLAND)

- Many issues in neutrino physics will then still remain unresolved. Next generation experiments will try to address them.

- Stan Wojcicki,  Physics at Off-axis

- September 16, 2002

## The Physics Goals

- Observation of the transition e
- Measurement of 13
- Determination of mass hierarchy (sign of m23)
- Search for CP violation in neutrino sector
- Measurement of CP violation parameters
- Testing CPT with high precision

- Stan Wojcicki,  Physics at Off-axis

- September 16, 2002

## Offaxis Beam 

-  Advantages

- Stan Wojcicki,  Physics at Off-axis

- September 16, 2002

##   The Off-axis Situation

- The physics issues to be investigated are clearly delineated
- The dominant oscillation parameters are known reasonably well
- One wants to maximize flux at the desired energy (near oscillation maximum)
- One wants to minimize flux at other energies
- One wants to have narrow energy spectrum

- Stan Wojcicki,  Physics at Off-axis

- September 16, 2002

##     Kinematics of  Decay

- Lab energy given by length of vector from origin to contour
- Lab angle by angle wrt vertical
- Energy of  is relatively independent of  energy
- Both higher and lower  energies give ’s of somewhat lower energy
- There will be a sharp edge at the high end of the resultant  spectrum
- Energy varies linearly with angle
- Main energy spread is due to beam divergence

- Compare E spectra from 10,15, and 20  GeV ’s

- LAB

- ELAB

- Stan Wojcicki,  Physics at Off-axis

- September 16, 2002

## Kinematics Quantitatively

- Stan Wojcicki,  Physics at Off-axis

- September 16, 2002

## Optimization of off-axis beam

- Choose optimum E (from L and m232)
- This will determine mean E and LAB from the 90o CM decay condition
- Tune the optical system (target position, horns) so as to accept maximum  meson flux around the desired mean E

- Stan Wojcicki,  Physics at Off-axis

- September 16, 2002

## Off-axis ‘magic’ ( D.Beavis at al. BNL Proposal E-889)

- NuMI beam can produce 1-3 GeV intense beams with well defined energy in a cone around the nominal beam direction

- Stan Wojcicki,  Physics at Off-axis

- September 16, 2002

## Medium Energy Beam

- More flux than low energy on-axis (broader spectrum of pions contributing)

- Neutrino event spectra at putative detectors located at different _transverse_ locations

- Neutrinos from K decays

- A. Para, M. Szleper, hep-  ex/0110032

- Stan Wojcicki,  Physics at Off-axis

- September 16, 2002

## Experimental Challenge

- Stan Wojcicki,  Physics at Off-axis

- September 16, 2002

##    Physics

- Stan Wojcicki,  Physics at Off-axis

- September 16, 2002

## 2 Mass Hierarchy Possibilities

- Stan Wojcicki,  Physics at Off-axis

- September 16, 2002

##   e transition equation

- A. Cervera et al., Nuclear Physics B 579 (2000) 17 – 55, expansion to second order in

*P (****** **** ****e**)  =  P**1** + P**2** + P**3** + P**4*

- Stan Wojcicki,  Physics at Off-axis

- September 16, 2002

##     Several Observations

- First 2 terms are independent of the CP violating parameter 
- The last term changes sign between  and 
- If 13 is very small (≤ 1o) the second term (subdominant oscillation) competes with 1st
- For small 13, the CP terms are proportional to 13; the first (non-CP term) to 132
- The CP violating terms grow with decreasing Efor a given L)
- There is a strong correlation between different parameters
- CP violation is observable _only if all_ angles ≠ 0

- Stan Wojcicki,  Physics at Off-axis

- September 16, 2002

## 13 Issue

- The measurement of 13 is made complicated by the fact that oscillation probability is affected by matter effects and possible CP violation
- Because of this, _there is not a unique_ mathematical relationship between oscillation probability and 13
- Especially for low values of 13, sensitivity of an experiment to seeing e _depends very much_ on 
- Several experiments with different conditions and _with both ____ and ___ will be necessary to disentangle these effects
- The focus of next generation oscillation experiments is to _observe_ e transition
- 13 needs to be sufficiently large if one is to have a chance to investigate CP violation in  sector

- Stan Wojcicki,  Physics at Off-axis

- September 16, 2002

##          Matter Effects

- The experiments looking at  disappearance measure m232
- Thus they cannot measure  sign of that quantity ie determine _mass hierarchy_
- The sign can be measured by looking at the rate for e for both  and .
- The rates will be different by virtue of different e-e- CC interaction in matter, independent of whether CP is violated or not
-  At L = 750km and oscillation maximum, the size of the effect is given by A = 2√2 GF ne E / m232 ~ 0.15

- Stan Wojcicki,  Physics at Off-axis

- September 16, 2002

##     Source of Matter Effects

- Stan Wojcicki,  Physics at Off-axis

- September 16, 2002

## Scaling Laws (CP and Matter)

- Both matter and CP violation effects can be best investigated if the dominant oscillation phase  is maximum, ie  = n/2, n odd (1,3,...)
- Thus  E  L / n
- For practical reasons (flux, cross section) relevant values of n are 1 and 3
- Matter effects scale as  132E or  132 L/n
- CP violation effects scale as  13 m122 n

- Stan Wojcicki,  Physics at Off-axis

- September 16, 2002

##      Scaling Laws (2)

- If 13 is small, eg sin2213 < 0.02, then CP violation effects obscure matter effects
- Hence, performing the experiment at 2nd maximum (n=3) might be a best way of resolving the ambiguity
- Good knowledge of m232 becomes then critical
- Several locations (and energies) are required to determine all the parameters

|     Detector |   L(km) | E(GeV) |   Relative
matter effect |   Relative
CP effect |
| --- | --- | --- | --- | --- |
|       JHF |  295 |  0.6  |      1.0 |    1.0 |
| NuMI Phase I |  712 |  1.4 |      2.9 |    1.0 |
| NuMI Phase II |  985 |  0.7 |      1.1 |    3.0 |

- Stan Wojcicki,  Physics at Off-axis

- September 16, 2002

## CP and Matter Effects

- Stan Wojcicki,  Physics at Off-axis

- September 16, 2002

##       NuMI 

- Capabilities

- Stan Wojcicki,  Physics at Off-axis

- September 16, 2002

##      Important Reminder

- Oscillation Probability (or sin22e) is not unambigously related to _fundamental_ parameters, 13 or Ue32
- At low values of sin2213 (~0.01), the uncertainty could be as much as a factor of 4 due to matter and CP effects
- Measurement precision of _fundamental _parameters can be optimized by a judicious choice of running time between  and 

- Stan Wojcicki,  Physics at Off-axis

- September 16, 2002

##   CP/mass hierarchy/13                  ambiguity

- Neutrinos only, L=712 km, E=1.6 GeV, m232 = 2.5

- Stan Wojcicki,  Physics at Off-axis

- September 16, 2002

## Antineutrinos help greatly

- Antineutrinos are crucial to understanding:
- Mass hierarchy
-       CP violation
-    CPT violation
-         High energy  experience: antineutrinos are ‘expensive’.

- For the same number of POT

- Ingredients: (+)~3(-) (large x)

- NuMI ME beam energies:
- (+)~1.15(-) (charge conservation!)
- Neutrino/antineutrino events/proton ~ 3

- (no Pauli exclusion)

- Stan Wojcicki,  Physics at Off-axis

- September 16, 2002

##   How antineutrinos can help resolve the  CP/mass hierarchy/13 ambiguity

- L=712 km, E=1.6 GeV, m232 = 2.5

- Neutrino range

- Antineutrino range

- Stan Wojcicki,  Physics at Off-axis

- September 16, 2002

##    Optimum Run Strategy

- Start the experiment with neutrinos
- Run in that mode until either:
- A definite signal is seen, or
- Potential sensitivity with antineutrinos could be significantly higher (x 2?) than with neutrinos
- Switch to antineutrinos and run in that mode until either:
- A definite signal is seen
- Potential sensitivity improvement from additional running would be better with neutrinos

- Stan Wojcicki,  Physics at Off-axis

- September 16, 2002

## Sensitivy for Phases I and II    (for different run scenarios)

- We take the
- Phase II to have
- 25 times higher
- POT x Detector
- mass
- Neutrino energy
- and detector
- distance remain
- the same

- Stan Wojcicki,  Physics at Off-axis

- September 16, 2002

##       Concluding Remarks

- Neutrino Physics appears to be an exciting field for many years to come
- Most likely several experiments with different running conditions will be required
- Off-axis detectors offer a promising avenue to pursue this physics
- NuMI beam is excellently matched to this physics in terms of beam intensity, flexibility,  beam energy, and potential source-to-detector distances that could be available
- We have great interest in forming a Collaboration that could work on these opportunities

- Stan Wojcicki,  Physics at Off-axis

- September 16, 2002