Accelerator Neutrino Programme at Fermilab ∗

FERMILAB-CONF-10-099-T

Stephen J. Parke

Theoretical Physics Department, Fermi National Accelerator Laboratory P.O.Box 500, Batavia, IL 60510, USA [email protected]

The accelerator neutrino programme in the USA consists primarily of the Fermilab neutrino programme. Currently, Fermilab operates two neutrino beamlines, the Booster neutrino beamline and the NuMI neutrino beamline and is the planning stages for a third neutrino beam to send neutrinos to DUSEL. The experiments in the Booster neutrino beamline are miniBooNE, SciBooNE and in the future microBooNE, whereas in the NuMI beamline we have MINOS, ArgoNut, MINERVA and coming soon NOνA. The major experiment in the beamline to DUSEL will be LBNE.

1. Neutrino Standard Model

The ﬂavor content of the three neutrino mass eigenstates is given in Fig. 1. The current questions in this model are what is the size of

2 2 1 2 1 2 sin θ13, (sin θ23 ), (sin θ12 ), sign(δm ) and sin δCP (1) − 2 − 3 31

It is possible that the ﬁrst three of these are related to some small parameter 2 2 like δm21/δm31 0.03 raised to some power, n. From current experiments the size of this power≈ is constrained to be larger than one, n > 1, except for 2 1 (sin θ23 ) where the lower bound is weaker, approximately n > 1/2. − 2 This could be due to some broken Tri-Bi-Maximal symmetry which would be very interesting and exciting. Another possibility is that it is coincidental which would be much less interesting from a theorists perspec- tive.

∗ Presented at Cracow Ephiphany Conference, January 5-8, 2010, Krakow, Poland.

(1) 2 krakow˙nus printed on April 9, 2010 Solar Sector: 12 { } 2 Νe ΝΜ ΝΤ Uαj | | cos ∆ $ cos ∆ $ 2 2 sinΘ sin Θ23 sin Θ12 13 2 5 2 3 1 2 1 "1 δmsol"1 = +7.6 10− eV Squared 2 2 2 5 2 sin Θ13 (msol × 2 δm 1= +7.6 10− eV (m 1 ! ! sol atm "1

Mass sinΘ13 × 2 2 3 2 sin Θ sinΘ13 12 1 2 δm = 2.4 10− eV 2 (matm 2atm 3 2 2 "1 |δm |= 2.4 ×10− eV (msol 2 atm sin Θ23 ! ! ! ! 1 1 Neutrino 1 3 | | × " Reactor/Acc2ele" rator 2Sector: 13 sinΘ 1 2 1 13 sin Θ13 δm2 / δm 2 0.03 NORMAL INVERTEDδm sol 30atmδm { } CPT invariant δ δ|| atm| ≈| ∗ | | ≈sol| ! ! ⇒ ↔ − 2 6 ∆ δm2 = 0.05 eV < m < 0.5 eV = 106 m Fractional Flavor Content varying cos δm atm= 0.05 eV < m <νi 0.5 eV = 10− −m e atm νi ∗ e∗ !22 " 2 Fig. 1. The ﬂavor content5 2 of the neutrino mass eigenstates[1]. Thesin!sin widthθθ12 of12 the 11/3/3 " δmsol = +7.6 10− eV lines is used× to show how these fractions change as cos δCP varies from -1 to +1.∼∼ Of course, this ﬁgure must be the same for neutrinos and anti-neutrinos2 if CPT is 2 2 5 2 3 2 2 δm δm= +7.6conserved.=102−.4eV 10− eV sinsin θθ2323 11/2/2 sol| atm|× × ∼∼ 2 3 2 δmatm =2 2.4 102− eV2. Current Neutrino Program at Fermilab 22 | δm| sol / ×δmatm 0.03 sinsin θθ1313<<3%3% |2 | | 2 | ≈ δmatm 30 Currentlyδmsol there are two operating neutrino beamlines at Fermilab with | δ|m≈ 2 another∗ |= 0 being.05| eV proposed.< Thesem are< 0.5 eV = 10 6 m 2 atm νi 6 − 0e δ < 2π δmatm = 0.05 eV < mνi < 0.5 eV = 10− me ∗ 0 δ < 2π The Booster Neutrino Beamline∗ which uses 8 GeV protons≤≤ from the ! 2 • Booster. Currently only miniBooNE is taking data in this beamline ! msinν =θ12 1/3 " " i ∼ since SciBooNE has completed it’s data taking and mircoBooNE is 2 f"1 cos2 θ 68%still in the approval process. ∼sin θ23" ≈ 1/2 2 ∼ NuMI (Neutrinos from the Main Injector) which uses 120 GeV protons f2 sin θ 32%• ∼sin2 θ" ≈< 3%from the main injector. This beamline sends neutrinos to the MINOS 13 near and far detectors. Also in the near detector hall is ArgoNut and MINERVA. ArgoNut is taking data and MINERVA will start 0 δ < 2πdata taking in 2010. The NOνA near and far detectors will also use ≤ neutrinos from this beamline.– Typeset by FoilTEX – 4 In addition there is a proposal to build a third neutrino beamline to • send a neutrino beam from Fermilab to DUSEL in the Homestake mine. This beamline will initially be powered by protons from the main injector but will eventually be powered by a– veryTypeset highby intensityFoilTEX – 1 proton beam (>2MW) from Project X. – Typeset by FoilTEX – 1

– Typeset by FoilTEX – 1

– Typeset by FoilTEX – 1 – Typeset by FoilTEX – 1 krakow˙nus printed on April 9, 2010 3 2&&34"5)6"7%3+) •! 83+93:#;)3(9'%+"5):;%+7)) !"&5$'+<83:;%+;)9"=>+%?:",) %+=&:5%+7);.;9"$'@=;) •! A:&&)3;=%&&'@3+)>.B39>";%;) "C=&:5"5)'9)11D) •! 8EF)=3+;"#G%+7)B3%+9)H#3$) 9>")-IAJ*)+":9#%+3)'+'&.;%;) %;)4%9>%+)10D)=3+93:#)

•! KL)(";9)M9)%;)'9)>%7>)G'&:",) CPT 5:")93)5"M=%9)'9)>%7>)"+"#7.) •! N+;>'5"5)#"7%3+)'#3:+5) $'C%$'&)$%C%+7)%;)"C=&:5"5) '9)11OPD)8OQO) more Anti-neutrino running NOW ! !"#$%&'()*"$%+'#,)-'.)/01) R"S)T'#9+"&&)<)N+%G"#;%9.)3H)*:;;"C)2 2 UV) Fig. 2. The δm32 v sin 2θ23 allowed region obtained using the anti-neutrinos in the neutrino beam. The CPT conserving point is within the 90% contour. MINOS has now ﬁnished a dedicated run with anti-neutrinos to tighten the contours on this plot.

MINOS uses 120 GeV protons from the main injector with a nominal beam power of 300kW and currently has the world’s best measurement of ∆m2 using the neutrino beam [2], | 32| ∆m2 = 2.43 0.13 10−3 eV2, (2) | 32| ± × and is currently running in anti-neutrino mode to check whether or not CPT is violated in the neutrino sector, see Fig.2. 4 krakow˙nus printed on April 9, 2010

MiniBooNE and SciBooNE are measuring neutrino cross sections rele- vant for future neutrino experiments. Also, MiniBooNE is also looking for deviations from the three active neutrino Standard Model that has been assembled in the last ten years and in particular to conﬁrming or refuting the LSND anomaly. No evidence in support of LSND has been found but a unexplained low energy excess in the 200 to 475 MeV was observed [3],

Excess Events (200 to 475MeV ) = 128.8 20.4 38.3. (3) ± ± MiniBooNE appearance data show a low-energy excess While in the anti-neutrino !e channel the evidence for an excess is inconclusive. A.A. Aguilar-Arevalo et al., PRL 102, 101802 (2009)

Excess from 200-475 MeV = 128.8+-20.4+-38.3 events

6.46E20 POT

Excess Fig. 3. The excess events as seen in neutrino running at MiniBooNE. Between 200 and 475 MeV, a clear excess is seen.

2.1. NOνA The NOνA project consists of increasing the beam power in NuMI (Neu- trinos from the Main Injector) from 300 kW to 700 kW and to build the 15 kton liquid scintillator NOνA detector in Ash River, 810 km from Fermilab, so as to explore both P (νµ νe) and P (¯νµ ν¯e) at the sub 1% level. This 2 → → will put a limit on sin 2θ13 at the 0.01 level, see Fig. 4. This experiment will also give us the ﬁrst glimpse of the neutrino mass hierarchy and/or the ﬁrst restrictions of the range of the CP violating phase δCP , see Fig. 5. krakow˙nus printed on April 9,2 2010 5 Sensitivity to sin (213) ! 0

Gary Feldman P5 Meeting 2 25 Fig. 4. The 90% sensitivity to sin 2θ13 for NOνA [4] assuming equal running time for neutrinos and anti-neutrinos. The blue (red) curves is for the normal (inverted) hierarchy. The three lines from right to left are for 0.7, 1,2 and 2.3 MW of protons on target respectively. These curves correspond to P (ν ν ) and P (¯ν ν¯ ) at µ → e µ → e the sub 1% level.

Also the MINERvA experiment operating in the NuMI near detector hall will perform precision measurements of neutrino cross sections above 1 GeV on various nuclear targets. The information obtained from this experiment will be invaluable for future very long baseline neutrino oscillations.

2.2. The Physics of Long Baseline: νµ → νe The amplitude for νµ νe can be simple written a sum of three amplitudes, one associated with→ each neutrino mass eigenstate,

2 2 2 im1L/2E im2L/2E im3L/2E Uµ∗1e− Ue1 + Uµ∗2e− Ue2 + Uµ∗3e− Ue3. The ﬁrst term can be eliminated using the unitarity of the MNS matrix and thus the appearance probability can be written as follows[6]

2 −i(∆32+δ) P (νµ νe) Patme + Psol . (4) → ≈

p p

Off-Axis Beams: BNL 1994 95% CL Resolution of the Mass 6 krakow˙nus printed on April 9, 2010 Neutrino v Anti-Neutrino One Expt. Ordering NO!A Alone Proposed Experiments: NOvA 2 T2K sin 2θ13 sin δ + sin δ = 2 θ /θcrit 1.4 Narrow Beams! - Cou" −nting! Expts":− ! " ≈ ! 0.05 L=295 km and Energy at Vac. Osc. Max. (vom) 2 δm32 Evom = 0.6 GeV 3 2 2 2.5 10− eV sin 2θ Proposed Experiments: × 13 sin δ +! sin δ " = 2 θ /θcrit 0.47 ! " − ! "− ! " ≈ ! 0.05 2 Narrow Beams - Counting Expts: sin 2θ13 sin δ sin δ = 2 θ /θ 1.4 L=700 - 1000 km and + crit L=295 km and 2 ! " − ! "− ! " ≈ ! 0.05 Energyi.e. sinnear22θcrGeitV= 0.10 in the overlap region 2 Energy at Vac. Osc. Max. (vom) δm32 Normal Ordering Inverted Ordering 2 E(vρomL)=fo1.r8 NOvAGeV 2.three5 10 3timeeV 2 s larger than (ρL) than T2K.2 δm32 − sin 2θ13 Evom = 0.6 GeV 3 2 L × 2.5 10− eV sin δ + sin δ = 2 θ /θcrFig.it 5. The1 left.4 panel is the bi-probability plot, ν ν versesν ¯ ν¯ for the 26 × 8202 km ! 2 " µ e µ e ! ×" π− !sin 2θ12"−δm21 ! " ≈ ! 0.05 →2 2 → ! " θcrit = 2 /(aL) 1/NO6 νA experiment showing the critical value of θ13 (sinsin2θ132θ= 0.11) as well as two 0.75 upgrade to 4 MW 0.4 upgrade# 8 ta$n toθ23 2δm MW 13 exact along diagonal --- appr31osinximatelδ y+ true∼ thrsin(outoughoutδ of four) the = ofoverla the2p ellipses rθegion!!!/θ whichcrit pass through0.47 the data point (large cross) with 2 − 2 !2 " 2 −2 !sin 2θ" = 0.05 [1] .! The" right panel≈ shows the parameters! 0.05 in sin 2θ v δ plane π2 sin 2θ δm 4∆ /π 13 13 sparkE – 19 April 2004 θ = 12 21 15 /(aL) 1/6 crit 8 tan θ δm2 1 ∆ cot ∆ that NOνA [4] determines the hierarchy assuming it is normal. L=700 - 1000 km and 23 31 − ∼ 2 sinO2. θMena13 + SP sin δ + sin δ =2 "2 θ /θcri#t 0.47 Energy near 2 GeV − hep-ph/0408070 2 2 ! " − ! i.e." sin 2θcr!it"= 0.10∆jk≈is used as! a shorthand0.05 for the the kinematic phase, δmjkL/4E. As the δm32 Evom = 1.8 GeV 3 2 2 2.5 10− eV notation suggests the amplitude √Patm only depends on δm31 and √Psol L × (ρL) for sinNOvAδ +three timesins laδ rger than2 (ρL) than T2K. ! " ! " −only! depends"− on δm21. For propagation in the matter, these amplitudes are × 820 km (ρL) for NOvA three times larger2 than (ρL)simpletha2 n T2K. given by – Typeset by FoilTEX – π sin 2θ12 δm21 2 3 # $ θcrit = 2 /(aL) sin1/62θ13 2 2 8 tan θ23 δm sin(∆31 aL) π sin 2θ12 δm21 31 ∼ θ = /(aL) 1/6 0.47 Patm = sin θ23 sin 2θ13 − ∆31 crit 8 tan θ δm2 23 31 ∼ ≈ ! 0.05 (∆31 aL) sparkE – 19 April 2004 15 − p sin(aL) Psol = cos θ23 sin 2θ12 ∆21. (5) sin δ sin δ (aL) + p sin δ + sin δ ! " − ! "− −1 ! " − ! "The− matter potential is given by a = GF Ne/√2 (4000 km) and the sign of ∆ (and ∆ ) determines2 the hierarchy; normal≈ ∆ > 0 whereas 2 31 32 sin 2θ13 31 sin 2θ13 0.5 inverted ∆31 < 0. When0.5 a is set to zero one recovers the vacuum result. ≈ ! See0. Fig.605 [7]. ≈ ! 0.05 – Typeset by FoilTEX – 3 For anti-neutrinos a a and δ δ. Thus the phase between √Patm → − → − and √Psol changes from (∆32 +δ) to (∆32 δ). This changes the interference – Typeset by FoilTEX – term from 3 −

2 Patm Psol cos(∆32 + δ) 2 Patm Psol cos(∆32 δ). (6) ⇒ − sin δ + sin δ ! " − ! "Expanding− p cos(∆p32 δ), one has a CP conservingp p part ± 2 Patm Psol cos ∆32 cos δ (7) p p krakow˙nus printed on April 9, 2010 7 and the CP violating part

2 Patm Psol sin ∆32 sin δ. (8) ∓ p p π Therefore CP violation is maximum when ∆32 = (2n + 1) 2 and grows as n grows. Notice also, that for this term to be non-zero the kinematical phase ∆32 cannot be nπ. The first person who emails me having noticed this statement will get a prize. I’m checking to see if anybody reads these things. This is the neutrino counter part to the non-zero strong phase requirement for CP violation in the quark sector. The asymmetry between P (νµ νe) and P (¯νµ ν¯e) is a maximum → → when √Patm = √Psol. At the first oscillation maximum, ∆31 = π/2, this 2 2 occurs when sin 2θ13 = 0.002 in vacuum. For values of sin 2θ13 < 0.002 the oscillation probabilities are dominated by Psol and thus observing the 2 effects of non-zero sin 2θ13 become increasing more challenging.

Fig. 6. The left panel shows the two components Patm and Psol in matter for the 2 normal and inverted hierarchies for sin 2θ13 = 0.04 and a baseline of 1200 km. The37 right panel shows the total probability including the interference term between the two components for various values of the CP phase δ for the neutrino. Notice that the coherent sum of two amplitudes shows a rich structure depending on the hierarchy and value of CP phase. These curves can also be interpreted as anti- neutrino probabilities if one interchanges the hierarchy AND the values of the CP phase.

2.3. DUSEL and LBNE 2 Even if sin 2θ13 > 0.01, a further experiment will be needed to determine the precise value of the CP violating phase, δCP . Fermilab has 8 krakow˙nus printed on April 9, 2010 proposed to build a new neutrino beamline to DUSEL and to build a large neutrino detector there. This experiment is called the Long Baseline Neu- trino Experiment (LBNE). The detector would consist of 300 ktons of water Cerenkov detectors or 50 ktons of Liquid Argon detectors or some combination of both. The new neutrino beamline would be initially powered by the main injector but then by Project X which would deliver 2.2 MW of protons at 50-120 GeV. Project X in addition could provide up to 2 MW of protons at 2-3 GeV for Kaon, Muon and other experiments. The detector technology would be either water cerenkov similar to Su- perK or a LAr TPC or a combination of both. The water cerenkov detector could be built with little R&D but would have to be larger than LAr due to it’s lower efficiency. Whereas substantial R&D is required for a large LAr TPC but this technology has a higher efficiency than water cervenkov due to it’s better discrimination of electron and gamma (π0) events. LAr also has a enhanced sensitivity to proton decay in the K+ν channel over water Cerenkov which also makes it an attractive alternative assuming a successful R&D program. For both detector technology a modular design is probably necessary to get the very large fiducial volumes required. If affordable, a combination of both detectors would be very powerful. For a possible evolution of this R&D see Fig.7. 2 The reach for sin 2θ13, the mass hierarchy and CP violating for the 2 Fermilab Project X program is given in Fig.8. If sin 2θ13 is significantly smaller than 10−3 or precision measurements of the oscillation parameters are required then protons from Project X could be used for a neutrino factory with detector(s) at DUSEL. With further technical developments these facilities could also be used for a future multi-TeV muon collider. A brief outline of Project X is given and a possible neutrino program that could be performed. At this stage many options need to be studied in detail especially with regard to various funding profiles. However, it is clear that an intense neutrino source combined with very massive detectors is required to explore the size of θ13, the neutrino mass hierarchy and the CP violation in the neutrino sector.

2.4. Project X Summary Project X with it’s multi-megawatt high energy beams for neutrino physics and it’s multi-megawatt low energy beams for rare Kaon physics, Muon physics and possibly other projects is a true Intensity Frontier Ma- chine. The neutrino experiments have a clear goal to determine CP violation in the neutrino sector and determine the neutrino mass hierarchy. The Kaon program would look for 1000 events in both K+ π+νν¯ and K0 π0νν¯. → → krakow˙nus printed on April 9, 2010 9

Evolution of the Liquid Argon Physics Program

R&D Purity, electronics development Yale TPC Luke & Bo “phased R&D program” Underground safety, cryo operation, R&D Physics TPC performance, reconstruction ArgoNeuT Cold electronics, evacuation microBooNE R&D Physics requirement, tank construction, insulation LAr5 R&D Physics near Large Mass operation, far Technical & cost scaling

M x N = 100 kT Physics !!!

Fig. 7. Possible evolution of a Liquid Argon detector program[5] in North America.

The Muon program would look for µ + N e + N at unprecedented sensi- → tivity as well as to push for a more precise measurement of (g-2)µ. Further in time is the possibility to use Project X to power a neutrino factory and then to regain the energy frontier with a multi-TeV muon collider.

3. Acknowledgements I would like to thank the Organizing Committee and especially Ag- nieszka Zalewska for the wonderful opportunity to attend this conference.

REFERENCES

[1] O. Mena and S. J. Parke, Phys. Rev. D 70, 093011 (2004) [arXiv:hep- ph/0408070]. [2] P. Adamson et al. [MINOS Collaboration], Phys. Rev. Lett. 101, 131802 (2008) [arXiv:0806.2237 [hep-ex]]. 10 krakow˙nus printed on April 9, 2010

The 3 Reach of the Successive Phases

2 sin 213 Mass Ordering CP Violation

101 101

102 102

3 10"3 10"

4 4 ! 10" ! 10

N. Saoulidou 39 !

2 Fig. 8. The evolution of the reach for sin 2θ13, the mass hierarchy and CP violating for the Fermilab Project X program [8] .

[3] A. A. Aguilar-Arevalo et al. [MiniBooNE Collaboration], Phys. Rev. Lett. 102, 101802 (2009) [arXiv:0812.2243 [hep-ex]]. [4] D. S. Ayres et al. [NOvA Collaboration], arXiv:hep-ex/0503053. [5] From the ”Project X workshop Series”, FNAL, 2007-2008. [6] A. Cervera, A. Donini, M. B. Gavela, J. J. Gomez Cadenas, P. Hernandez, O. Mena and S. Rigolin, Nucl. Phys. B 579, 17 (2000) [Erratum-ibid. B 593, 731 (2001)] [arXiv:hep-ph/0002108]. [7] H. Nunokawa, S. J. Parke and J. W. F. Valle, Prog. Part. Nucl. Phys. 60, 338 (2008) [arXiv:0710.0554 [hep-ph]]. [8] “Fermilab Steering Group Report,” CITATION = FERMILAB-PUB-07-672- DO;