- Email: [email protected]
The Fermilab Neutrino Program
Nuclear Physics B (Proc. Suppl.) 155 (2006) 18–22 www.elsevierphysics.com
The Fermilab Neutrino Program R. Plunkett, Fermilab
1. Introduction The Fermi National Accelerator Laboratory (Fermilab) is currently home to many of the most important accelerator-based particle physics efforts in the United States. At the energy frontier, the Tevatron program will continue to explore the physics of the top quark and search for new phenomena without competition until the turnon of the LHC. In addition, Fermilab is home to an active and growing program in neutrino physics, where studies of the phenomenon of neutrino mixing as discovered by atmospheric neutrino experiments such as super-Kamionkande [1] are being pursued (by MINOS and the proposed NOvA experiments) along with an experiment (MiniBoone) aiming at clarification of the oscillation effects reported by LSND[2]. Improved understanding of these phenomena, which typically occur at lower neutrino energies than recent experiments which have concentrated on neutrino deep inelastic scattering[3], requires better knowledge than currently available of the neutrino scattering process. This is the goal of the MINERVA experiment . This paper concentrates on the Fermilab program using conventional neutrino beam facilities, including , in some cases, a proposed Proton Driver upgrade to the Fermilab complex. The Proton Driver possiblility is discussed by Apollinari in his contribution to these proceedings[4].
The Fermilab Booster neutrino beam began operation in late 2002 and utilizes 8 GeV primary protons on a Be target. The secondary, horn-focused beam decays in a 50 m decay region to provide a neutrino beam with an average neutrino energy of approximately 600 MeV. The Booster has achieved a peak intensity of more than 7.0 x 1016/hr., and has delivered a total intensity to the experiment of more than 6.0 x 1020 protons. The principal reaction sought by MiniBoone is the quasi-elastic scattering of electron neutrinos on carbon, νeC −> e-N. The detector consists of a tank of 950 kliters of pure mineral oil in a 12m diameter spherical tank. Prompt Cerenkov light and delayed scintillation light are read out by an array of 1280 large (8 inch) photomultimplier tubes, with an outer veto region of 240 PMT’s. Electrons, muons and o π ’s give distinctive topological and timing signatures which allow systematic comparisons of the data with the expected components of the MiniBoone beam, including νμ CC quasi-elastic o events and NC π production (see figure 1).
2. MiniBoone – Testing LSND at Fermilab The goal of the MiniBoone experiment is to explore the region of neutrino oscillation parameters from which the reported LSND signal originates, e.g L/E = 1 km/GeV. If confirmed, oscillations with Δm2 = 0.1 – 10 eV2 would require fundamental theoretical innovations to accommodate the overall picture of solar, atmospheric, and an additional oscillation region, together with the LEP measurement of 3 active, light neutrinos. MiniBoone provides an experiment which can verify the LSND result with different systematics and higher statistics, using a neutrino beam from the Fermilab Booster. 0920-5632/$ – see front matter © 2006 Published by Elsevier B.V. doi:10.1016/j.nuclphysbps.2006.02.003
Figure 1. Comparison of MiniBoone data for NC πo production with signal and background Monte Carlo simulation. A clear 2-ring Cerenkov signal is required in the detector, with each photon energy being > 40 MeV.
Models of the lepton sector which accommodate the LSND result often include CP violation and one
R. Plunkett / Nuclear Physics B (Proc. Suppl.) 155 (2006) 18–22
or more sterile neutrinos[5]. Such models can produce a significant difference in oscillation probability for neutrinos and antineutrinos, often enhancing the antineutrino mode. It is important to note therefore that the Booster neutrino beam is capable of producing antineutrinos by reversal of the horn current. Running with antineutrinos would also produce a sample of data relevant for studying a number of poorly known cross-sections. The MiniBoone collaboration intends to decide if antineutrino running is warrented based upon the results of their initial results obtained with neutrinos.
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The long-baseline MINOS far detector is located at an underground depth of 715 m at Soudan, Minnesota, providing a baseline of 735 km. Detector construction consists of 5.4 kT of toroidally magnetized steel planes equipped with scintillator strip (4.1cm width) readout. Two orthogonal views of the interactions are provided by alternating the direction of the scintillator strips. Light proceeds along optical fibers to Hamamatsu M16 multi-pixel photomultipliers, after which the signals are digitized and read out.
3. The MINOS Long Baseline Experiment On January 21, 2005, the MINOS experiment at Fermilab recorded its first neutrino events produced by the recently completed NuMI beamline. The beamline operates by extraction of 120 GeV protons from the Main Injector onto a graphite target, forming a secondary beam which decays to neutrinos in a 675 m evacuated beampipe. The beam enegy is adjustable by motion of the target with respect to the focussing horns, providing valuable systematic checks of the beam composition. Details of the beam operation and instrumentation are found in the contribution of Marchionni to these Proceedings [6]. The primary goal of MINOS is a precision measurment of the atmospheric Δm2, using a wellunderstood source of artificially produced neutrinos (see Fig. 2). In addition, the experiment expects to perform a search for νμ -> νe oscillations for θ13 within a factor of 2 of the CHOOZ [7] limit, to rule out non-oscillation hypotheses for νμ disappearance, and to directly separate the contributions to atmospheric oscillations of neutrinos and antineutrinos using a magnetic field.
Figure 2. MINOS physics sensitivities for an exposure of 16 x 1020 protons. The left plot shows the expected shape difference and errors for the spectrum with and without oscillation, and for alternative hypotheses. The right plot shows the expected precision achievable on Δm2.
Figure 3. The MINOS far detector showing magnet coil.
The lowest energy beam configuration (peaking at 3 GeV) is used to provide the strongest oscillation signal. However, a period of higher energy running (9-10 GeV peak) was used in the spring of 2005 to increase the far detector neutrino rate for checkout purposes. Some results of this running are shown in Fig. 4.
Figure 4. Neutrino candidates (preliminary) in the MINOS far detector form a clearly separated central band compared to a large sample of cosmic rays when plotted as a function of the angle in degrees of the reconstructed muon track with respect to the horizontal and vertical (yaxis). Events were obtained by a visual scan of <100 events occuring in-time with the NuMI beam spill.
20
R. Plunkett / Nuclear Physics B (Proc. Suppl.) 155 (2006) 18–22
The approximately 1 kT MINOS near detector is located in the NuMI neutrino beam at Fermilab, approximately 300 m downstream of the decay pipe and hadron absorber. It provides a high-statistics sample of neutrino interactions in a detector which is highly similar to the far detector, allowing an excellent measurement of the unoscillated spectrum. Because of the high neutrino occupancy of the near detector (up to 20 events per 10 μs spill) , the near detector electronics differ somewhat from the far detector, employing timing to separate events. Figure 4 shows a distribution of events from the near detector.
Figure 4. Preliminary distribution of reconstructed track angles in degrees, with respect to the vertical axis, of neutrino candidates observed in the MINOS near detector. Data points are compared to the results of the Monte Carlo simulation (histogram). The mean angle is pointed slightly downward, as required to point to the MINOS far detector.
4. Off-axis Beams and NOVA MINOS and continuing atmospheric neutrino experiments, will greatly improve our knowledge of the fundamental parameters of neutrino mixing at the scale of (L/E) of order 500 km/GeV. At the same time, there will remain a need for a better understanding of the fundamental and interesting question of the role of the electron neutrino in these flavor transitions (parameterized by the mixing matrix angle θ13). Situating a long-baseline neutrino detector off the axis of a conventional muon neutrino beam provides the kinematics of a narrow band beam with little background from intrinsic νe from K decay, at the same time giving increased flux at 2 GeV. The narrow band energy spectrum for a detector in the medium energy NuMI beam at an angle of 14 mrad peaks around 2 GeV with a FWHM of 800 MeV. This feature allows the identification of νe appearing in the oscillation
process without contamination from misidentified higher-energy neutral currents. Since the NuMI beam exists, what is needed is a large detector sensitive to low rates of νe appearance; this requirement is addressed by the proposed NovA experiment. This large experiment will be constructed of approximately 24,000 PVC extrusions of 15.7 m length, filled with liquid scintillator. The extrusions are arranged in alternating vertical and horizontal planes, giving a detector length of 132 m and a total detector mass of 30 kton. The detector will be read out using 32 pixel avlanche photodiodes after the scintillation light is captured with an imbedded wavelength-shifting fiber. At the expected location of 12 km (approx. 15 mrad) off the NuMI beam axis, this detector configuration gives approximately 2000 νμ CC events for each 7.0 x 1020 protons on the NuMI target. As an appearance experiment, NovA will benefit from the maximum achievable number of protons which can be delivered by the NuMI complex. In this context, currently anticipated improvements in beam intensity will be agumented by additional factors coming from the expected end of the Fermilab Collider program. In particular, a factor of about 1.4 should be gained by eliminating the cycle time associated with antiproton production and use of the Recycler ring as a proton accumulator should produce a factor of 1.5. All factors taken together allow an estimated rate of 6.5 x 1020 protons annually to be used to estimate the sensitivity of NOvA. If a Proton Driver is constructed, the flux would increase to 25 x 1020 annually. The physics goals of the NovA experiment include, in addition to the measurement of θ13, resolution of the mass hierarchy in oscillations at the atmospheric scale. The oscillation phenomenon in vacuum is sensitive only the difference in masses between neutrino eigenstates, typically entering in 2 the combination Δm23 . This leaves unresolved the question of the mass hierarchy, specifically whether ν3 is the eigenstate with highest or lowest mass. Experiments with long baselines through the earth can distinguish the mass hierarchy by making use of the fact that electron neutrinos differ in their interactions with matter from antineutrinos. These additional contributions depend on the mass hierarchy and the CP-violating phase δ, and allow separation of the two hierarchies for large enough values of sin22θ13. Figure 5 shows the ranges in sin22θ13 and δ for which NOvA gives separation of the mass hierarchies, for a variety of future
R. Plunkett / Nuclear Physics B (Proc. Suppl.) 155 (2006) 18–22
scenarios. Some increase in range is gained by combination of information with the T2K experiment. Note that, in many cases of the parameters, information on the correlation of the CP phase and the mass hierarchy can be gained even if the hierarchy is not separately resolved.
Figure 5. Allowed regions for 95% confidence level separation of normal and inverted mass hierarchies with NOvA, as a fraction of the range of CP-violating δ . Solid lines indicate NOvA alone for both mass hierachies and dotted lines indicate the allowed regions if NOvA is combined with other experiments as noted. Here “PD” means a Fermilab Proton Driver, “HK” means HyperKamiokande, “T2K PD” means T2K with an upgraded proton source, and “2nd Det” means a detector at the second NuMI oscillation maximum. Beam assumptions are 19.5 x 1020 protons for both neutrinos and antineutrinos (without a Proton Driver) and 75 x 1020 for both (with a Proton Driver). The “2nd Det” curves assume an additonal 6 years of running with a Proton Driver. [8] To summarize, the NOvA experiment provides a rich means of accessing important goals of the new neutrino physics: - Measurement of sin22θ13, without a Proton Driver, to better than 0.02 for all δ and to approx. 0.008 for some δ. A proton driver improves this measurement to better than 0.01 for all δ. - Resolution of the mass hierarchy for a large fraction of δ. - Greatly improved measurements of sin22θ23 and Δm223. - With a Proton Driver, sensitivity to the CPviolating phase δ over part of its range.
21
5. Neutrino Scattering – MINERVA Experiments with conventional neutrino beams eventually rely on knowledge of the mechanism of neutrino interactions in material. The proposed MINERvA experiment at Fermilab will address our limited knowledge of neutrino interactions in the energy range of 2-20 GeV. The detector is to be located immediately upstream of the MINOS near detector . It is a high-granularity active target design of approximately 6 T which also incorporates an additiona 1 T of nuclear targets in the first detector section as an integral part of its construction. The active target consists of wedge-shaped overlapping scintillator strips which utilize charge sharing to improve position resolution. In the nuclear target section, a plane of target material (C, Fe, or Pb) is followed by several planes of scintillator. The detector is surrounded by electromagnetic and hadronic calorimeters The outermost steel section of the detector is magnetized. Muons exiting the detector will be correlated with events appearing in the MINOS near detector to provide a muon catcher. The readout of the detector consists of 31,000 channels in 503 Hamamatsu M64 photomultipliers. Fig. 6 shows a conceptual drawing of the MINERvA detector.
Figure 6. Conceptual drawing of MINERvA, showing upsteam veto shield counters in cutaway. The lightcolored upstream section of the calorimeter contains nuclear targets of varying A.
Among the many MINERvA physics goals, some of the most important measurements include: - The axial vector form factor of the nucleon at high Q2. - Coherent cross-section vs. energy - Differential distributions of exclusive final states.
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R. Plunkett / Nuclear Physics B (Proc. Suppl.) 155 (2006) 18–22
- Dependence on A of various processes, including low Q2 quasi-elastic scattering, deep inelastic scattering, and exclusive final states (probing nuclear reinteractions). Figure 7 shows the remarkable improvement in one typical area, the A-dependence of coherent pion production, that can be expected from MINERvA.
- A test exposure of emulsion bricks for the OPERA experiment [9] in the MINOS near hall (named PEANUT). 7. Summary The Fermilab neutrino program combines a major running experimental program with an active program for the future. The breadth of the program addresses many of the current issues of neutrino physics. Interesting results can be expected on a short timescale. The next generation of experiments and beam upgrades are powerful in and of themselves. In addition, Fermilab is also continuing R&D into a Proton Driver and other further beam upgrades. More will be known about developments in this area when the schedule for ILC activities becomes more mature.
References
Figure 7. Expected results from MINERvA for coherent charged-current pion production, compared to existing data. Note that MiniBoone and K2K measurements will improve our knowledge of the region below 2.5 GeV. Simulated data are for 4 years of running at 2.5 x 1020 per year.
6. Additional Efforts at Fermilab In addition to the major experiments described in this paper, there are a number of ongoing Fermilab research and development efforts which contribute to the future of the field of neutrino physics. These include: - Investigations into large liquid Ar TPC’s. The aim of this effort is to learn about the viability of multi-kton detectors with excellent electron resolution, probably based on commercial technology of large tank construction. - Consultation and liaison with efforts to build a large underground laboratory. Optimizations of neutrino measurements at such a facillity (named DUSEL) may have impacts on layouts of Fermilab Proton Driver plans which need to be addressed at an early stage. Fermilab is helping develop site conceptual designs during the ongoing selection process.
[1] Y. Ashie et al., Phys. Rev. D71, 112005 (2005). [2] C. Athanassopoulos et al., Phys. Rev. Lett. 75, 2650 (1995); C. Athanassopoulos et al., Phys. Rev. Lett. 77, 3082 (1996). [3] M. Goncharov et al., Phys. Rev. D64, 112006 (2001), hep-ex/0102049.; M. Tzanov et al., hepex/0509010. [4] G. Apollinari, contribution to these proceedings. [5] M. Sorel, J.M. Conrad, and M. Shaevitz, Phys. Rev. D70, 73004 (2004), hep-ph/0305255. [6] A.Marchionni, contribution to these proceedings. [7] M. Apollonio, et al., Phys. Lett. B420, 397 (1998); M. Apollonio et al., Phys. Lett. B466, 415 (1999). [8]http://wwwnova.fnal.gov/NOvA_Proposal/NOvA _P929_March21_2005.pdf [9] CERN/SPSC 2000-028, SPSC/P318, LNGS P25/2000
The Fermilab Neutrino Program R. Plunkett, Fermilab
1. Introduction The Fermi National Accelerator Laboratory (Fermilab) is currently home to many of the most important accelerator-based particle physics efforts in the United States. At the energy frontier, the Tevatron program will continue to explore the physics of the top quark and search for new phenomena without competition until the turnon of the LHC. In addition, Fermilab is home to an active and growing program in neutrino physics, where studies of the phenomenon of neutrino mixing as discovered by atmospheric neutrino experiments such as super-Kamionkande [1] are being pursued (by MINOS and the proposed NOvA experiments) along with an experiment (MiniBoone) aiming at clarification of the oscillation effects reported by LSND[2]. Improved understanding of these phenomena, which typically occur at lower neutrino energies than recent experiments which have concentrated on neutrino deep inelastic scattering[3], requires better knowledge than currently available of the neutrino scattering process. This is the goal of the MINERVA experiment . This paper concentrates on the Fermilab program using conventional neutrino beam facilities, including , in some cases, a proposed Proton Driver upgrade to the Fermilab complex. The Proton Driver possiblility is discussed by Apollinari in his contribution to these proceedings[4].
The Fermilab Booster neutrino beam began operation in late 2002 and utilizes 8 GeV primary protons on a Be target. The secondary, horn-focused beam decays in a 50 m decay region to provide a neutrino beam with an average neutrino energy of approximately 600 MeV. The Booster has achieved a peak intensity of more than 7.0 x 1016/hr., and has delivered a total intensity to the experiment of more than 6.0 x 1020 protons. The principal reaction sought by MiniBoone is the quasi-elastic scattering of electron neutrinos on carbon, νeC −> e-N. The detector consists of a tank of 950 kliters of pure mineral oil in a 12m diameter spherical tank. Prompt Cerenkov light and delayed scintillation light are read out by an array of 1280 large (8 inch) photomultimplier tubes, with an outer veto region of 240 PMT’s. Electrons, muons and o π ’s give distinctive topological and timing signatures which allow systematic comparisons of the data with the expected components of the MiniBoone beam, including νμ CC quasi-elastic o events and NC π production (see figure 1).
2. MiniBoone – Testing LSND at Fermilab The goal of the MiniBoone experiment is to explore the region of neutrino oscillation parameters from which the reported LSND signal originates, e.g L/E = 1 km/GeV. If confirmed, oscillations with Δm2 = 0.1 – 10 eV2 would require fundamental theoretical innovations to accommodate the overall picture of solar, atmospheric, and an additional oscillation region, together with the LEP measurement of 3 active, light neutrinos. MiniBoone provides an experiment which can verify the LSND result with different systematics and higher statistics, using a neutrino beam from the Fermilab Booster. 0920-5632/$ – see front matter © 2006 Published by Elsevier B.V. doi:10.1016/j.nuclphysbps.2006.02.003
Figure 1. Comparison of MiniBoone data for NC πo production with signal and background Monte Carlo simulation. A clear 2-ring Cerenkov signal is required in the detector, with each photon energy being > 40 MeV.
Models of the lepton sector which accommodate the LSND result often include CP violation and one
R. Plunkett / Nuclear Physics B (Proc. Suppl.) 155 (2006) 18–22
or more sterile neutrinos[5]. Such models can produce a significant difference in oscillation probability for neutrinos and antineutrinos, often enhancing the antineutrino mode. It is important to note therefore that the Booster neutrino beam is capable of producing antineutrinos by reversal of the horn current. Running with antineutrinos would also produce a sample of data relevant for studying a number of poorly known cross-sections. The MiniBoone collaboration intends to decide if antineutrino running is warrented based upon the results of their initial results obtained with neutrinos.
19
The long-baseline MINOS far detector is located at an underground depth of 715 m at Soudan, Minnesota, providing a baseline of 735 km. Detector construction consists of 5.4 kT of toroidally magnetized steel planes equipped with scintillator strip (4.1cm width) readout. Two orthogonal views of the interactions are provided by alternating the direction of the scintillator strips. Light proceeds along optical fibers to Hamamatsu M16 multi-pixel photomultipliers, after which the signals are digitized and read out.
3. The MINOS Long Baseline Experiment On January 21, 2005, the MINOS experiment at Fermilab recorded its first neutrino events produced by the recently completed NuMI beamline. The beamline operates by extraction of 120 GeV protons from the Main Injector onto a graphite target, forming a secondary beam which decays to neutrinos in a 675 m evacuated beampipe. The beam enegy is adjustable by motion of the target with respect to the focussing horns, providing valuable systematic checks of the beam composition. Details of the beam operation and instrumentation are found in the contribution of Marchionni to these Proceedings [6]. The primary goal of MINOS is a precision measurment of the atmospheric Δm2, using a wellunderstood source of artificially produced neutrinos (see Fig. 2). In addition, the experiment expects to perform a search for νμ -> νe oscillations for θ13 within a factor of 2 of the CHOOZ [7] limit, to rule out non-oscillation hypotheses for νμ disappearance, and to directly separate the contributions to atmospheric oscillations of neutrinos and antineutrinos using a magnetic field.
Figure 2. MINOS physics sensitivities for an exposure of 16 x 1020 protons. The left plot shows the expected shape difference and errors for the spectrum with and without oscillation, and for alternative hypotheses. The right plot shows the expected precision achievable on Δm2.
Figure 3. The MINOS far detector showing magnet coil.
The lowest energy beam configuration (peaking at 3 GeV) is used to provide the strongest oscillation signal. However, a period of higher energy running (9-10 GeV peak) was used in the spring of 2005 to increase the far detector neutrino rate for checkout purposes. Some results of this running are shown in Fig. 4.
Figure 4. Neutrino candidates (preliminary) in the MINOS far detector form a clearly separated central band compared to a large sample of cosmic rays when plotted as a function of the angle in degrees of the reconstructed muon track with respect to the horizontal and vertical (yaxis). Events were obtained by a visual scan of <100 events occuring in-time with the NuMI beam spill.
20
R. Plunkett / Nuclear Physics B (Proc. Suppl.) 155 (2006) 18–22
The approximately 1 kT MINOS near detector is located in the NuMI neutrino beam at Fermilab, approximately 300 m downstream of the decay pipe and hadron absorber. It provides a high-statistics sample of neutrino interactions in a detector which is highly similar to the far detector, allowing an excellent measurement of the unoscillated spectrum. Because of the high neutrino occupancy of the near detector (up to 20 events per 10 μs spill) , the near detector electronics differ somewhat from the far detector, employing timing to separate events. Figure 4 shows a distribution of events from the near detector.
Figure 4. Preliminary distribution of reconstructed track angles in degrees, with respect to the vertical axis, of neutrino candidates observed in the MINOS near detector. Data points are compared to the results of the Monte Carlo simulation (histogram). The mean angle is pointed slightly downward, as required to point to the MINOS far detector.
4. Off-axis Beams and NOVA MINOS and continuing atmospheric neutrino experiments, will greatly improve our knowledge of the fundamental parameters of neutrino mixing at the scale of (L/E) of order 500 km/GeV. At the same time, there will remain a need for a better understanding of the fundamental and interesting question of the role of the electron neutrino in these flavor transitions (parameterized by the mixing matrix angle θ13). Situating a long-baseline neutrino detector off the axis of a conventional muon neutrino beam provides the kinematics of a narrow band beam with little background from intrinsic νe from K decay, at the same time giving increased flux at 2 GeV. The narrow band energy spectrum for a detector in the medium energy NuMI beam at an angle of 14 mrad peaks around 2 GeV with a FWHM of 800 MeV. This feature allows the identification of νe appearing in the oscillation
process without contamination from misidentified higher-energy neutral currents. Since the NuMI beam exists, what is needed is a large detector sensitive to low rates of νe appearance; this requirement is addressed by the proposed NovA experiment. This large experiment will be constructed of approximately 24,000 PVC extrusions of 15.7 m length, filled with liquid scintillator. The extrusions are arranged in alternating vertical and horizontal planes, giving a detector length of 132 m and a total detector mass of 30 kton. The detector will be read out using 32 pixel avlanche photodiodes after the scintillation light is captured with an imbedded wavelength-shifting fiber. At the expected location of 12 km (approx. 15 mrad) off the NuMI beam axis, this detector configuration gives approximately 2000 νμ CC events for each 7.0 x 1020 protons on the NuMI target. As an appearance experiment, NovA will benefit from the maximum achievable number of protons which can be delivered by the NuMI complex. In this context, currently anticipated improvements in beam intensity will be agumented by additional factors coming from the expected end of the Fermilab Collider program. In particular, a factor of about 1.4 should be gained by eliminating the cycle time associated with antiproton production and use of the Recycler ring as a proton accumulator should produce a factor of 1.5. All factors taken together allow an estimated rate of 6.5 x 1020 protons annually to be used to estimate the sensitivity of NOvA. If a Proton Driver is constructed, the flux would increase to 25 x 1020 annually. The physics goals of the NovA experiment include, in addition to the measurement of θ13, resolution of the mass hierarchy in oscillations at the atmospheric scale. The oscillation phenomenon in vacuum is sensitive only the difference in masses between neutrino eigenstates, typically entering in 2 the combination Δm23 . This leaves unresolved the question of the mass hierarchy, specifically whether ν3 is the eigenstate with highest or lowest mass. Experiments with long baselines through the earth can distinguish the mass hierarchy by making use of the fact that electron neutrinos differ in their interactions with matter from antineutrinos. These additional contributions depend on the mass hierarchy and the CP-violating phase δ, and allow separation of the two hierarchies for large enough values of sin22θ13. Figure 5 shows the ranges in sin22θ13 and δ for which NOvA gives separation of the mass hierarchies, for a variety of future
R. Plunkett / Nuclear Physics B (Proc. Suppl.) 155 (2006) 18–22
scenarios. Some increase in range is gained by combination of information with the T2K experiment. Note that, in many cases of the parameters, information on the correlation of the CP phase and the mass hierarchy can be gained even if the hierarchy is not separately resolved.
Figure 5. Allowed regions for 95% confidence level separation of normal and inverted mass hierarchies with NOvA, as a fraction of the range of CP-violating δ . Solid lines indicate NOvA alone for both mass hierachies and dotted lines indicate the allowed regions if NOvA is combined with other experiments as noted. Here “PD” means a Fermilab Proton Driver, “HK” means HyperKamiokande, “T2K PD” means T2K with an upgraded proton source, and “2nd Det” means a detector at the second NuMI oscillation maximum. Beam assumptions are 19.5 x 1020 protons for both neutrinos and antineutrinos (without a Proton Driver) and 75 x 1020 for both (with a Proton Driver). The “2nd Det” curves assume an additonal 6 years of running with a Proton Driver. [8] To summarize, the NOvA experiment provides a rich means of accessing important goals of the new neutrino physics: - Measurement of sin22θ13, without a Proton Driver, to better than 0.02 for all δ and to approx. 0.008 for some δ. A proton driver improves this measurement to better than 0.01 for all δ. - Resolution of the mass hierarchy for a large fraction of δ. - Greatly improved measurements of sin22θ23 and Δm223. - With a Proton Driver, sensitivity to the CPviolating phase δ over part of its range.
21
5. Neutrino Scattering – MINERVA Experiments with conventional neutrino beams eventually rely on knowledge of the mechanism of neutrino interactions in material. The proposed MINERvA experiment at Fermilab will address our limited knowledge of neutrino interactions in the energy range of 2-20 GeV. The detector is to be located immediately upstream of the MINOS near detector . It is a high-granularity active target design of approximately 6 T which also incorporates an additiona 1 T of nuclear targets in the first detector section as an integral part of its construction. The active target consists of wedge-shaped overlapping scintillator strips which utilize charge sharing to improve position resolution. In the nuclear target section, a plane of target material (C, Fe, or Pb) is followed by several planes of scintillator. The detector is surrounded by electromagnetic and hadronic calorimeters The outermost steel section of the detector is magnetized. Muons exiting the detector will be correlated with events appearing in the MINOS near detector to provide a muon catcher. The readout of the detector consists of 31,000 channels in 503 Hamamatsu M64 photomultipliers. Fig. 6 shows a conceptual drawing of the MINERvA detector.
Figure 6. Conceptual drawing of MINERvA, showing upsteam veto shield counters in cutaway. The lightcolored upstream section of the calorimeter contains nuclear targets of varying A.
Among the many MINERvA physics goals, some of the most important measurements include: - The axial vector form factor of the nucleon at high Q2. - Coherent cross-section vs. energy - Differential distributions of exclusive final states.
22
R. Plunkett / Nuclear Physics B (Proc. Suppl.) 155 (2006) 18–22
- Dependence on A of various processes, including low Q2 quasi-elastic scattering, deep inelastic scattering, and exclusive final states (probing nuclear reinteractions). Figure 7 shows the remarkable improvement in one typical area, the A-dependence of coherent pion production, that can be expected from MINERvA.
- A test exposure of emulsion bricks for the OPERA experiment [9] in the MINOS near hall (named PEANUT). 7. Summary The Fermilab neutrino program combines a major running experimental program with an active program for the future. The breadth of the program addresses many of the current issues of neutrino physics. Interesting results can be expected on a short timescale. The next generation of experiments and beam upgrades are powerful in and of themselves. In addition, Fermilab is also continuing R&D into a Proton Driver and other further beam upgrades. More will be known about developments in this area when the schedule for ILC activities becomes more mature.
References
Figure 7. Expected results from MINERvA for coherent charged-current pion production, compared to existing data. Note that MiniBoone and K2K measurements will improve our knowledge of the region below 2.5 GeV. Simulated data are for 4 years of running at 2.5 x 1020 per year.
6. Additional Efforts at Fermilab In addition to the major experiments described in this paper, there are a number of ongoing Fermilab research and development efforts which contribute to the future of the field of neutrino physics. These include: - Investigations into large liquid Ar TPC’s. The aim of this effort is to learn about the viability of multi-kton detectors with excellent electron resolution, probably based on commercial technology of large tank construction. - Consultation and liaison with efforts to build a large underground laboratory. Optimizations of neutrino measurements at such a facillity (named DUSEL) may have impacts on layouts of Fermilab Proton Driver plans which need to be addressed at an early stage. Fermilab is helping develop site conceptual designs during the ongoing selection process.
[1] Y. Ashie et al., Phys. Rev. D71, 112005 (2005). [2] C. Athanassopoulos et al., Phys. Rev. Lett. 75, 2650 (1995); C. Athanassopoulos et al., Phys. Rev. Lett. 77, 3082 (1996). [3] M. Goncharov et al., Phys. Rev. D64, 112006 (2001), hep-ex/0102049.; M. Tzanov et al., hepex/0509010. [4] G. Apollinari, contribution to these proceedings. [5] M. Sorel, J.M. Conrad, and M. Shaevitz, Phys. Rev. D70, 73004 (2004), hep-ph/0305255. [6] A.Marchionni, contribution to these proceedings. [7] M. Apollonio, et al., Phys. Lett. B420, 397 (1998); M. Apollonio et al., Phys. Lett. B466, 415 (1999). [8]http://wwwnova.fnal.gov/NOvA_Proposal/NOvA _P929_March21_2005.pdf [9] CERN/SPSC 2000-028, SPSC/P318, LNGS P25/2000