prospects for numi off-axis initiative
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Prospects for NUMI Off-axis Initiative. Kwong Lau University of Houston November 28, 2003. Outline. Introductory Comments Advantages of an Off-axis Beam Important Physics Issues NuMI Capabilities Detector issues Present schedule. Introductory Comments. - PowerPoint PPT PresentationTRANSCRIPT
Prospects for NUMI Off-axis Initiative
Kwong Lau
University of Houston
November 28, 2003
11/28/03 Kwong Lau p.2
Outline
Introductory Comments Advantages of an Off-axis Beam Important Physics Issues NuMI Capabilities Detector issues Present schedule
11/28/03 Kwong Lau p.3
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)• Improve limits on e subdominant oscillation• Demonstrate explicitly oscillation mode by detecting ’s (OPERA, ICARUS) mode, or detect it (MINOS, ICARUS)6. Resolve the LSND puzzle (MiniBooNE)7. Confirm indications of LMA solution (KamLAND)
Many issues in neutrino physics will then still remain unresolved. Next generation experiments will try to address them.
11/28/03 Kwong Lau p.4
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
11/28/03 Kwong Lau p.5
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
ELAB
11/28/03 Kwong Lau p.6
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
2
2
22 412
zA
Fluxγ
γ⎟⎠
⎞⎜⎝
⎛+
=
11/28/03 Kwong Lau p.7
The Off-axis Advantage
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
11/28/03 Kwong Lau p.8
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
11/28/03 Kwong Lau p.9
e transition equation
A. Cervera et al., Nuclear Physics B 579 (2000) 17 – 55,
expansion to second order in 1212131223,,,LA
P ( e) = P1 + P2 + P3 + P4
11/28/03 Kwong Lau p.10
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 Efor a given L)
There is a strong correlation between different parameters CP violation is observable only if all angles ≠ 0
11/28/03 Kwong Lau p.11
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
11/28/03 Kwong Lau p.12
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 / m23
2 ~ 0.15
11/28/03 Kwong Lau p.13
Source of Matter Effects
11/28/03 Kwong Lau p.14
CP and Matter Effects
11/28/03 Kwong Lau p.15
Experimental Challenge
11/28/03 Kwong Lau p.16
e Appearance: Experimental challenges
•Need to know the expected flux•Need to know the beam contamination•Need to know the NC background* rejection power (Note: need to beat it down to the level of e component of the beam only)•Need to know the electron ID efficiency
11/28/03 Kwong Lau p.17
Detector(s) Challenge
Surface (or light overburden) High rate of cosmic ’s Cosmic-induced neutrons
But: Duty cycle 0.5x10-5
Known direction Observed energy > 1 GeV
Principal focus: electron neutrinos identification
• Good sampling (in terms of radiation/Moliere length)
Large mass:
• maximize mass/radiation length
• cheap
11/28/03 Kwong Lau p.18
Receipe for a Better e Appearance Experiment
More neutrinos in a signal region Less background Better detector (improved efficiency, improved
rejection against background) Bigger detector
Lucky coincidences:
• distance to Soudan = 735 km, m2=0.025-0.035 eV2
• Below the tau threshold! (BR(->e)=17%)
11/28/03 Kwong Lau p.19
NuMI Off-axis Detector
The goal is an eventual 50 kt fiducial volume detector
Liquid scintillator strips readout by APDs with particle board absorber is the baseline design
Backup design is glass RPCs Location is 810 km baseline, 12 km off-axis (Ash
River, MN) Present cost is about 150 M$
11/28/03 Kwong Lau p.20
The off-axis detector: Stacks
Liquid scintillator strips
1.2 m × 3 cm × 14.4 m
30-cell extrusions
797 planes
570 k channels
28.8 m
11/28/03 Kwong Lau p.21
The absorbers
11/28/03 Kwong Lau p.22
The active detectors: scintillators
0
200
400
600
800
1000
0 100 200 300 400
Channel number
Performance of BC517L with
Compton edge of 137Cs gammas
Far right: MINOS
Middle: fresh BC517L
Far left: 5-year old BC517L
11/28/03 Kwong Lau p.23
The active detectors: WLS fibers
0
20
40
60
80
100
120
140
0 20 40 60 80
Relative pulse height
0 pe
1 pe
2 pe
3 pe
4 pe
Pulse height spectra
of cosmic ray muons
7.5 m from end
1.0 mm WLS fibers
HPD photodetector
11/28/03 Kwong Lau p.24
The DAQ system
11/28/03 Kwong Lau p.25
CC e vs NC events in a tracking calorimeter: analysis example
Electron candidate: Long track ‘showering’ I.e. multiple
hits in a road around the track
Large fraction of the event energy
‘Small’ angle w.r.t. beam NC background sample
reduced to 0.3% of the final electron neutrino sample (for 100% oscillation probability)
35% efficiency for detection/identification of electron neutrinos
11/28/03 Kwong Lau p.26
A ‘typical’ signal event
Fuzzy track = electron
11/28/03 Kwong Lau p.27
A ‘typical’ background event
11/28/03 Kwong Lau p.28
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
e/ ~0.5%
11/28/03 Kwong Lau p.29
Sensitivity dependence on eefficiency and NC rejection
Major improvement of sensitivity by improving ID efficiency up to ~50%
Factor of ~ 100 rejection (attainable) power against NC sufficient
NC background not a major source of the error, but a near detector probably desirable to measure it
11/28/03 Kwong Lau p.30
Sensitivity dependence on e efficiency and NC rejection
Major improvement of sensitivity by improving ID efficiency up to ~50%
Factor of ~ 100 rejection power against NC sufficient
NC background not a major source of the error, but a near detector probably desirable to measure it
Sensitivity to ‘nominal’ |Ue3|2 at the level 0.001 (phase I) and 0.0001 (phase II)
11/28/03 Kwong Lau p.31
Off-axis potential
11/28/03 Kwong Lau p.32
Numerology: My perspective
A 20-kton detector 712 km from Fermilab, 9 km off axis will have order NCC =10,000 muon-type charged-current interactions in 5 years of running
There will be order NNC =4,000 neutral current interactions in the same exposure.
Software will suppress neutral current interactions with a rejection factor of order R=500 and an efficiency of order 30%.
There will be order 3% x NCC=300 genuine electron-type CC interactions. These events will be reduced to same order as NC fakes due to its broad energy spectrum.
Cosmic background is negligible. The signal to noise (background fluctuation) for P=0.001
SB
≈0.001×10,000×0.3
≈2(4,000/ 500)≈
316
≈11
11/28/03 Kwong Lau p.33
Letter of Intent (LOI)
A Letter of Intent has been submitted to Fermilab in June expressing interest in a new effort using off-axis detector in the NuMI beam
This would most likely be a ~15 year long, 2 phase effort, culminating in study of CP violation
The LOI was considered by the Fermilab PAC at its Aspen July, 2002, meeting
11/28/03 Kwong Lau p.34
Fermilab Official Reaction
Given the exciting recent results, the eagerly anticipated results from the present and near future program, and the worldwide interest in future experiments, it is clear that the field of neutrino physics is rapidly evolving. Fermilab is already well positioned to contribute through its investment in MiniBooNE and NuMI/MINOS. Beyond this, the significant investment made by the Laboratory and NuMI could be further exploited to play an important role in the elucidation of 13 and the exciting possibility of observing CP violation in the neutrino sector. ( June 2002, PAC Recommendation)
We will encourage a series of workshops and discussions, designed to help convergence on strong proposals within the next few years. These should involve as broad a community as possible so that we can accurately guage the interest and chart our course. Understanding the demands on the accelerator complex and the need for possible modest improvements is also a goal. Potentially, an extension of the neutrino program could be a strong addition to the Fermilab program in the medium term. We hope to get started on this early in 2003. Michael Witherell
11/28/03 Kwong Lau p.35
The Next Steps/Schedule
Workshop on detector technology issues planned for January, 2003 (done)
Proposal to DOE/NSF in early 2003 for support of R&D (done) and subsequent construction of a Near Detector in NuMI beam to be taking data by early 2005
Proposal for construction of a 25 kt detector in late 2004
Site selection, experiment approval, and start of construction in late 2005
Start of data taking in the Far Detector in late 2007 Formation of an international collaboration to construct
a 50 kton detector
11/28/03 Kwong Lau p.36
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
11/28/03 Kwong Lau p.37
Scaling Laws (2) If 13 is small, eg sin2213 < 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 m23
2 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
11/28/03 Kwong Lau p.38
Important Reminder
Oscillation Probability (or sin22e) is not unambigously
related to fundamental parameters, 13 or Ue32
At low values of sin2213 (~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
11/28/03 Kwong Lau p.39
Sensitivity for Phases I and II (for different run scenarios)
We take the Phase II to have25 times higher POT x Detectormass
Neutrino energyand detector distance remainthe same
11/28/03 Kwong Lau p.40
An example of a possible detector
Low Z tracking calorimeter
Issues: absorber material (plastic? Water? Particle
board?) longitudinal sampling (X0)? What is the detector technology (RPC?
Scintillator? Drift tubes?) Transverse segmentation (e/0) Surface detector: cosmic ray background?
time resolution?
NuMI off-axis detector workshop: January 2003
11/28/03 Kwong Lau p.41
Background rejection: beam + detector issue
e background
NC (visible energy), no rejection
spectrumSpectrum mismatch: These neutrinos contribute to background, but no signal
e (|Ue3|2 = 0.01)
NuMI low energy beam
NuMI off-axis beam
These neutrinos contribute to background, but not to the signal
11/28/03 Kwong Lau p.42
Fighting NC background:the Energy Resolution
M. Messier, Harvard U.
Cut around the expected signal region to improve signal/background ratio
11/28/03 Kwong Lau p.43
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 13
2E or 132 L/n
CP violation effects scale as 13 m122 n
11/28/03 Kwong Lau p.44
CP/mass hierarchy/13
ambiguity
Neutrinos only, L=712 km, E=1.6 GeV, m232 = 2.5
11/28/03 Kwong Lau p.45
Kinematics Quantitatively
11/28/03 Kwong Lau p.46Antineutrinos 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)
11/28/03 Kwong Lau p.47
2 Mass Hierarchy Possibilities
11/28/03 Kwong Lau p.48
Two Most Attractive Sites
Closer site, in Minnesota About 711 km from Fermilab Close to Soudan Laboratory Unused former mine Utilities available Flexible regarding exact location
Further site, in Canada, along Trans-Canada highway About 985 km from Fermilab There are two possibilities:
About 3 km to the west, south of Stewart Lodge About 2 km to the east, at the gravel pit site, near compressor
station
11/28/03 Kwong Lau p.49
Location of Canadian Sites
Stewart Lodge Beam Gravel Pit
11/28/03 Kwong Lau p.50
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
11/28/03 Kwong Lau p.51
How antineutrinos can help resolve the CP/mass hierarchy/13 ambiguity
L=712 km, E=1.6 GeV, m232 = 2.5
Neutrino rangeAntineutrino range
11/28/03 Kwong Lau p.52
Det. 2
NuMI Beam: on and off-axis
Det. 1
•Selection of sites, baselines, beam energies•Physics/results driven experiment optimization