Prospects for NUMI Off-axis Initiative Kwong Lau University of Houston November 28, 2003

11/28/03Kwong Laup.2 Outline Introductory Comments Advantages of an Off-axis Beam Important Physics Issues NuMI Capabilities Detector issues Present schedule

11/28/03Kwong Laup.3 Introductory Comments The current generation of long and medium baseline terrestial oscillation experiments is designed to: 1.Confirm SuperK results with accelerator ’s (K2K) 2.Demonstrate oscillatory behavior of  ’s (MINOS) 3.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) 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.

11/28/03Kwong Laup.4 The Physics Goals Observation of the transition   e Measurement of  13 Determination of mass hierarchy (sign of  m 23 ) Search for CP violation in neutrino sector Measurement of CP violation parameters Testing CPT with high precision

11/28/03Kwong Laup.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 E LAB

11/28/03Kwong Laup.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

11/28/03Kwong Laup.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

11/28/03Kwong Laup.8 Optimization of off-axis beam Choose optimum E (from L and  m 23 2 ) This will determine mean E  and  LAB from the 90 o CM decay condition Tune the optical system (target position, horns) so as to accept maximum  meson flux around the desired mean E 

11/28/03Kwong Laup.9   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

11/28/03Kwong Laup.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 (≤ 1 o ) the second term (subdominant oscillation) competes with 1st For small  13, the CP terms are proportional to  13 ; the first (non-CP term) to  13 2 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

11/28/03Kwong Laup.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

11/28/03Kwong Laup.12 Matter Effects The experiments looking at  disappearance measure  m 23 2 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 G F n e E /  m 23 2 ~ 0.15

11/28/03Kwong Laup.13 Source of Matter Effects

11/28/03Kwong Laup.14 CP and Matter Effects

11/28/03Kwong Laup.15 Experimental Challenge

11/28/03Kwong Laup.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

11/28/03Kwong Laup.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

11/28/03Kwong Laup.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,  m 2 = eV 2 Below the tau threshold! (BR(  ->e)=17%)

11/28/03Kwong Laup.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$

11/28/03Kwong Laup.20 The off-axis detector: Stacks 28.8 m

11/28/03Kwong Laup.21 The absorbers

11/28/03Kwong Laup.22 The active detectors: scintillators

11/28/03Kwong Laup.23 The active detectors: WLS fibers

11/28/03Kwong Laup.24 The DAQ system

11/28/03Kwong Laup.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

11/28/03Kwong Laup.26 A ‘typical’ signal event Fuzzy track = electron

11/28/03Kwong Laup.27 A ‘typical’ background event

11/28/03Kwong Laup.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%

11/28/03Kwong Laup.29 Sensitivity dependence on e efficiency 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

11/28/03Kwong Laup.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’ |U e3 | 2 at the level (phase I) and (phase II)

11/28/03Kwong Laup.31 Off-axis potential

11/28/03Kwong Laup.32 Numerology: My perspective A 20-kton detector 712 km from Fermilab, 9 km off axis will have order N CC =10,000 muon-type charged-current interactions in 5 years of running There will be order N NC =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 N CC =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

11/28/03Kwong Laup.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

11/28/03Kwong Laup.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 Michael Witherell

11/28/03Kwong Laup.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

11/28/03Kwong Laup.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

11/28/03Kwong Laup.37 Scaling Laws (2) If  13 is small, eg sin 2 2  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  m 23 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 NuMI Phase I NuMI Phase II

11/28/03Kwong Laup.38 Important Reminder Oscillation Probability (or sin 2 2   e ) is not unambigously related to fundamental parameters,  13 or U e3 2 At low values of sin 2 2  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

11/28/03Kwong Laup.39 Sensitivity 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

11/28/03Kwong Laup.40 An example of a possible detector Low Z tracking calorimeter Issues: absorber material (plastic? Water? Particle board?) longitudinal sampling (  X 0 )? 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

11/28/03Kwong Laup.41 Background rejection: beam + detector issue e background NC (visible energy), no rejection spectrum Spectrum 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

11/28/03Kwong Laup.42 Fighting NC background:the Energy Resolution M. Messier, Harvard U. Cut around the expected signal region to improve signal/background ratio

11/28/03Kwong Laup.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 2 E  or  13 2 L/n CP violation effects scale as  13  m 12 2 n

11/28/03Kwong Laup.44 CP/mass hierarchy/  13 ambiguity Neutrinos only, L=712 km, E =1.6 GeV,  m 23 2 = 2.5

11/28/03Kwong Laup.45 Kinematics Quantitatively

11/28/03Kwong Laup.46 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)

11/28/03Kwong Laup.47 2 Mass Hierarchy Possibilities

11/28/03Kwong Laup.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

11/28/03Kwong Laup.49 Location of Canadian Sites Stewart Lodge Beam Gravel Pit

11/28/03Kwong Laup.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/

11/28/03Kwong Laup.51 How antineutrinos can help resolve the CP/mass hierarchy/  13 ambiguity L=712 km, E =1.6 GeV,  m 23 2 = 2.5 Neutrino range Antineutrino range

11/28/03Kwong Laup.52 Det. 2 NuMI Beam: on and off-axis Det. 1 " Selection of sites, baselines, beam energies Physics/results driven experiment optimization