Precision Neutrino Precision Neutrino Oscillation Measurements & Oscillation Measurements &

the Neutrino Factorythe Neutrino Factory

Scoping Study for a Future Accelerator Neutrino Complex – Discussion Meeting

Steve Geer, 6 May 2005

Fermilab

22

IntroductionIntroduction

Neutrino physics is exciting

The main accelerator-based neutrino physicsquestions we want to address are:

What is the rough value of sin22?Is the Mass Hierarchy Normal or Inverted ?What is the value of (Is there CPV in the sector) ?What is the precise value of (Is sin =1) ?Is three-flavor mixing the whole story ?

Answering these questions will be challenging

33

Neutrino Factory Beam PropertiesNeutrino Factory Beam Properties

Precisely known neutrino fluxes & spectraPrecise comparison between neutrino & antineutrino properties possible

e and beams (a wealth of measurements)

e e 50% e , 50%

- e- e 50% e , 50%

_

_

_

_

Muon decay kinematics very well known:

44

Low BackgroundsLow BackgroundsNeutrino factories provide electron neutrinos (antineutrinos)

in addition to muon anti-neutrinos (neutrinos).

Backgrounds to the detection of a wrong-sign muon are expected

to be at the 10-4 level background-free e oscillations with amplitudes as small as O(10-4) can be measured !

e oscillations at a neutrino factory result in the appearance of a “wrong-sign” muon … one with opposite charge to those stored in the ring:

e e CC

-

CC

55

RatesRatesMany groups have calculated signal & background rates. Example: Hubner, Lindner & Winter; hep-ph/0204352

JPARC-SK: Beam = 0.75 MW, Mfid = 22.5 kt, T = 5 yrsJPARC-HK: Beam = 4 MW, Mfid = 1000 kt, T = 8 yrsNUFACT: Beam = 2.6 1020 decays/yr, Mfid = 100 kt, T = 8 yrs

m322 = 0.003 eV2 , m21

2 = 3.710-5 eV2 , sin2 223 = 1, sin2 213

= 0.1, sin2 212 = 0.8, = 0

Superbeams Neutrino Factory JPARC-SK JPARC-HK

Signal 140 13000 65000 Background 23 2200 180S/B 6 360

66

MeasurementsMeasurements

There is a wealth of information that can be used at a neutrino factory. Oscillation parameters can be extracted using events tagged by:

a) right-sign muonsb) wrong-sign muonsc) electrons/

positronsd) positive -leptonse) negative -

leptonsf) no leptons2 (+ stored and - stored)

Bu

en

o,

Cam

pan

elli

, R

ub

bia

; h

ep

-ph

/00

05

00

07

10 kt LAr detector, L = 7400 km,

30 GeV nu-factory with 1021 + decays.

77

The ChallengeThe Challenge

88

Neutrino Factory SensitivityNeutrino Factory Sensitivity

The Neutrino Factory provides hope that the full program (measuring 13, determining the mass hierarchy, & searching for CPV) can be accomplished if sin2213 > O(10-4) !

Huber, Winter; Phys. Rev. D68, 2003

10-5 10-4 10-3 10-2 10-1

sin2213

7500 km + 3000 km

sin2213

Mass Hierarchy

CP Violation

As 13 0, P(e) 0

If sin2213 < O(10-4) a NF would make the first observation of e appearance important test of three-flavor mixing.

99

ee and Other Channels and Other Channels

If sin2213 > O(10-3) the e channel enables elimination

of false solutions for combined NF + SB scenarios (Donini et al; hep-ph/020940, and others).

The e channel is unique to NFs the only direct test

of e mixing.

To analyze the full NF potential the e channel must be

analyzed together with right-sign & wrong-sign muons, and the two NC rates or the two e rates.

1010

“Short-Term” Program

YEAR

sin

sin22 22

13

13

R

each

(3

Rea

ch

(3 )

)

Ability to observe non-zero 13

versus time

Calculations ofW. Winter

Within bands varies

Substantial uncertainties on time-axis … but thetrend is clear

1111

“Longer-Term” Program ?

Calculations ofW. Winter

Even greater uncertainties on time-axis

Need to develop a clearer picture:

NF timescale ?

Branching point(s) ?

Alternative paths and basis for choice ?

YEAR

sin

sin22 22

13

13

R

each

(3

Rea

ch

(3 )

)

1212

Mass Hierarchy Sensitivity

Figures like thiscan help us developthe neutrino physics“road map”

It would be good to develop an agreed on list of figures and experiments to beplotted, and timelinesto be used.

YEAR

sin

sin22 22

1313

1313

Wish-List for StudyWish-List for Study

There have been a series of neutrino physics studies in Europe, Japan and the US, aimed at understanding future needs and options. Lots has been done, but there are still some questions to be nailed … for example:

Is a NF needed if sin22 is large ? What is the minimum NF energy that will deliver the physics (cost issue) ? How do we best test the three-flavor frameworkand how do we quantify the test? How can we best articulate the physics case for precision measurements of the neutrino parameters if sin22 > O(0.01), & continuing the program if sin22 < O(0.01) ?

1414

Final RemarksFinal Remarks

Neutrino Factories offer great physics potential

If, within our lifetimes, we want answers to the basic neutrino questions then, beyond the foreseen programwe will need to make a big step in detectors and facilities.We must continue to work on articulating the physicscase for this big step plots, numbers, road-map.

We also need to work on consensus within the neutrinocommunity (proton drivers, beta beams, neutrino factories).The physics drives us (not the facility).

Cost is an issue for all our desired future facilities. For NFs muon acceleration is a cost driver. The NF energy needed must be considered carefully.