MUON STORAGE RING MUON STORAGE RING MUON STORAGE RING MUON STORAGE RING MUON STORAGE RING MUON STORAGE RING MUON STORAGE RING MUON STORAGE RING MUON

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1 Prospecting for Neutrino Physics at a Muon Storage Ring Kevin McFarland University of Rochester LNS Journal Club 3 March 2000

2 K. McFarland, Prospecting for Neutrino Physics at a Muon Storage Ring 2 Outline 1. Why Muons as a Source? 2. Anatomy of a Neutrino Factory" 3. Capabilities: ffl Long-baseline neutrino oscillations ffl High rate neutrino experiments 4. Conclusions

3 K. McFarland, Prospecting for Neutrino Physics at a Muon Storage Ring 3 Why Muon Decays? Protons secondary/teritiary charged beam ν Detector manipulate (e.g. focus) decay Shield/ Baseline Conventional" ν beams are produced by ß +! μ + ν μ fi ß ± ο 25 ns Muon decays μ +! e + ν e ν μ fi μ ο 2 μs ß +! μ + ν μ Can focus, but large emittance Q ο 34 MeV ν μ, ν μ only μ +! e + ν e ν μ Time to cool and focus Q ο 105 MeV ν μ, ν μ, ν e, ν e

4 K. McFarland, Prospecting for Neutrino Physics at a Muon Storage Ring 4 Neutrino Detection Rates Neutrino event rates depend on a relatively small number of factors Protons secondary/teritiary charged beam manipulate (e.g. focus) decay ν Shield/ Baseline Detector ffl Parent decays ffl Neutrino beam divergence ( spot size" at the detector) From parent decay kinematics, ffl Neutrino energy N ν / ο 1 h ν i 2; h νi = ß 4fl parent ff(νn! `±X) / G F s ffl Baseline", i.e. distance to detector (may be determined by physics goals) N ν / 1 L2; L large Muons as a source potentially win in decays, divergence and energy due to long lifetime!

5 K. McFarland, Prospecting for Neutrino Physics at a Muon Storage Ring 5 Beam Divergence Key difference between conventional and muon source is optimization of parent production rates vs. beam divergence Conventional (ß ± ) Beam Economics ffl Production rates fall steeply with increasing E ß (production cross-section, proton acceleration) ffl N ν / ο Nß E ß 3 (neutrino cross-section, divergence) μ Beam Economics ffl Produce and capture at low energies (large cross-section, higher p power) ffl Accelerate parent beam after cooling N ν / ο Nμ E 3 μ

6 K. McFarland, Prospecting for Neutrino Physics at a Muon Storage Ring 6 Beam Divergence Benefits are great......so can it be done?

7 K. McFarland, Prospecting for Neutrino Physics at a Muon Storage Ring 7 A Resounding Maybe" Requirements ffl Very intense proton source O(10 14 ) protons, 15 Hz, 1 ns bunches (S.D.Holmes et al., FERMILAB-TM-2021) ffl Pion Capture. Collection efficiency: 0.6 ß + per proton. p z ο p t ο 200 MeV. ff( E=E) ß and then it decays to muons ffl Left with a very large muon beam

8 K. McFarland, Prospecting for Neutrino Physics at a Muon Storage Ring 8 A Resounding Maybe" (cont'd) Hot muon beam! storable muon beam ffl Cool via multiple scattering alternating with longitudinal acceleration Ionization Cooling" (Skirnsky and Parkhomchuk, 1981) ffl Strong focusing needed ffl Transverse emittance! longitudinal emittance MUCOOL R& D program: collider/cool.html

9 K. McFarland, Prospecting for Neutrino Physics at a Muon Storage Ring p/s A generic neutrino factory design Proton Driver Target Phase Rotate #1 (42 m rf) Mini Cooling (3.5 m H2) Drift (160m) Phase Rotate #2 (10m rf) Cooling (80m) Linac (2 GeV) Recirc. Linac #1 (2-8 GeV) Recirc. Linac #2 (8-50GeV) Storage Ring (50GeV 900m circ) µ/yr Neutrino Beam µ/p

10 K. McFarland, Prospecting for Neutrino Physics at a Muon Storage Ring 10 Neutrino Factory" Design (cont'd) ffl Active Accelerator, Detector and Physics working groups at FNAL and CERN ffl All contributions to working groups welcomed!

11 K. McFarland, Prospecting for Neutrino Physics at a Muon Storage Ring 11 Expected Neutrino Rates Assumed Parameters (FNAL study group) ffl /yr μ decays in the green straight section ) 800 m 50 GeV c.f.: Competing facilities Beam he ν i [GeV] ν per year NuTeV/CCFR (Fermilab) 100 ο =m 2 CHORUS/NOMAD (CERN) 30 ο =m 2 MINOS Near (Fermilab) 15 ο =m 2 Neutrino Factory Near 30 5 ο =m 2 Highly intense beams can... ffl Contend with 1=L 2. Long-baseline neutrino oscillations ffl Or defeat small G F s.. High rate neutrino experiments

12 K. McFarland, Prospecting for Neutrino Physics at a Muon Storage Ring 12 A Field Guide to Neutrino Oscillations Neutrino oscillations may be observed if: ffl Neutrino flavor eigenstates mix mass eigenstates jν`i = X m U`m jν m i ffl Mass eigenstates are non-degenerate A(ν`! ν`0) = X hν`jν m i e im2 m L 2E m fi νm jν`0fl ffl For two neutrino species mixing A(ν`! ν`06=l ) = sin2 2 mix sin :27ffiM 2 L E GeV km ev LEP I tells us there are three active" light neutrino species, so can parameterize mixing matrix in terms of 12 ; 13 ; 23 ; ffi as U`m ß 0 C 12 C 13 S 12 C 13 S 13 e iffi S 12 C 23 C 12 S 23 S 13 e iffi C 12 C 23 S 12 S 23 S 13 e iffi S 23 C 13 S 12 S 23 C 12 C 23 S 13 e iffi C 12 S 23 S 12 C 23 S 13 e iffi C 23 C 13 1 C A

13 K. McFarland, Prospecting for Neutrino Physics at a Muon Storage Ring 13 Field Guide to ν Oscillations (cont'd) Coherent Forward Scattering ) Matter Effects e- - e- ν e ν e - e W + ν e - e W - ν e ffl ν e has W ± exchange interaction ffl Energy-level crossing when r p2 + M 2 = r p 2 + M 2 νx ν e + p 2G F N e ffl Changes ν e oscillation probability: where x = 2 p sin 2 2 sin 2 2 M (x)! sin (±x cos 2 ) r 2 L! L sin (±x cos 2 ) 2 2G F N e E ν ffim 2 ; ± for ν, ν ffl Implies P (ν e! ν μ ) 6= P (ν e! ν μ ) ffl Solar ν e : ffim 2 ν e ;ν X ο 10 5 ev 2 Wolfenstein, Phys. Rev. D17 (1978) ffl Smaller Z exchange effect also for ν e, ν μ, ν fi

14 K. McFarland, Prospecting for Neutrino Physics at a Muon Storage Ring 14 Field Guide to ν Oscillations (cont'd) Neutrinos from the Sun: ffl Fusion: pp! de + ν e ν e (10 11 cm 2 sec 1 )

15 K. McFarland, Prospecting for Neutrino Physics at a Muon Storage Ring 15 Field Guide to ν Oscillations (cont'd) Discovering Mass The farther neutrinos travel, the more time they have to oscillate. By comparing the ratio of flavors of neutrinos coming "up" through the Earth to those coming from overhead, physicists determined that neutrinos oscillate, which neutrinos can only do if they have mass. Neutrinos from the Atmosphere: 2 SUPER KAMIOKANDE DETECTOR Neutrinos continue on the trajectory and begin to oscillate as they pass through the earth Oscillating neutrinos 3 A cosmic ray (usually a proton) from space A neutrino strikes another elementary particle in the detector tank. The interaction is recorded and analyzed by scientists to identify both the flavor of the neutrino and its flight path. Cosmic ray Earth s atmosphere 1 The cosmic ray hits the earth's atmosphere, making a spray of secondary particles, some of which decay into neutrinos One cycle of an oscillating neutrino as it passes through earth University of Hawai'i media graphic (U-D)/(U+D) µ-like event counts Momentum (GeV/c) ffl ν μ! ν e strongly disfavored by data ffl μ μ! ν fi weakly favored over disappearance by observed matter effects

16 K. McFarland, Prospecting for Neutrino Physics at a Muon Storage Ring 16 Field Guide to ν Oscillations (cont'd) Neutrinos from... New Mexico(?): ffl LSND experiment: ß +! μ + ν μ, μ +! e + ν e ν μ ffl Observe ν e and ν e above muon kinematic limit

17 K. McFarland, Prospecting for Neutrino Physics at a Muon Storage Ring 17 Field Guide to ν Oscillations (cont'd)

18 K. McFarland, Prospecting for Neutrino Physics at a Muon Storage Ring 18 What Will We Know? ffl LSND will be confirmed/refuted. If confirmed, suggests 4 light neutrinos Mass (ev) HDM ν 2 ν 3 δμ (ν ο. ) δμ (ν Atmos ) ν 0 ν 1 δμ 2 1 (LSND) Will know oscillation parameters ffim 12, sin to 10% or better. If refuted, Mass (ev) ν ν 1 ν 2 δμ (ν ο ). δm 2 ~ 4x10-3 (ν Atmos )

19 K. McFarland, Prospecting for Neutrino Physics at a Muon Storage Ring 19 What Will We Know? ffl K2K, MINOS, ICANOE will (likely) confirm atmospheric oscillations. ν μ! ν fi, ν μ! ν sterile?. ffim 2 23 known to 30%, sin to 20% ffl SNO, Borexino, KAMLAND, SuperK will determine correct solar solution. ν e! ν sterile?. MSW (ffim 2 ο 10 5 ) or vacuum (ffim 2 ο )?. Maximal or small mixing? Remaining Questions: ffl Mass hierarchy: how many light, how many heavy? ffl Unitarity of 3-generation mixing matrix ffl CP violation? ffl Observation of Matter Effects in accelerator beam? ffl Sterile neutrinos: how many and mixings?

20 K. McFarland, Prospecting for Neutrino Physics at a Muon Storage Ring 20 Muon Storage Ring Capabilities ν e ν e ν µ ν µ And their CP conjugates... ν τ ν τ Ideas for Neutrino Oscillation Experiments 30 GeV Neutrino Beams Baselines of few or many thousand kilometers International Collaboration

21 K. McFarland, Prospecting for Neutrino Physics at a Muon Storage Ring 21 What is the Neutrino Factory Killer App"? Scenario 1: MiniBooNE does not confirm the LSND oscillation result > the world attention grabbing channel is: ν e > νµ CC µ + > ν e + ν µ + e + µ + ν µ CC µ Wrong sign muons and long baselines Scenario 2: MiniBooNE confirms the LSND oscillation result > the world attention grabbing channel is probably : ν e > ντ τ appearance and shorter baselines Assume Scenario 1 for now (Scenario 2 is assumed to be more exciting, easier)

22 K. McFarland, Prospecting for Neutrino Physics at a Muon Storage Ring 22 Rates For a 20 GeV ring and a 50 kt detector, can calculate the total CC rate versus baseline: If the back ground / total CC rate is ~10 4 then L > 2000 km preferred > >1 background for 1019 decays Note that for L = 2800 km the total CC rate is ~5000 events / 1019 decays / 50 kt ffl Long-baseline rates / E3 μ L 2 ffl For appearance experiment with L(km) E(GeV) < 1 ffim 2 (ev 2 ), appearance rate is constant with L! ffl Backgrounds (/ 1 L 2 ) set baseline ffl Baseline sets detector size

23 K. McFarland, Prospecting for Neutrino Physics at a Muon Storage Ring 23 ν e! ν μ Appearance Measurements Three-Stage Program: ffl Discover ν e! ν μ P (ν e! ν μ ) ß S 2 23 sin sin 2 (ffim 2 23 L=4E) Gives a first measurement of sin ffl Use matter effects to determine sign of ffim 23. Compare μ + and μ appearance rate and spectrum. Resolve mass hierarchy ffl Discover CP violation in lepton sector?. Compare μ + and μ appearance rate and spectrum. Requires matter effects to be understood!. Multiple baselines may be important for above. Only viable if Solar mixing maximal, and mass difference from MSW

24 K. McFarland, Prospecting for Neutrino Physics at a Muon Storage Ring 24 How many muon decays/year are needed to make contact with the world attention grabbing neutrino oscillation physics if the muon energy is 20 GeV? Suppose the "entry level" physics goal is to make the first observation of ν e > ν µ at the 10 event level and make the first measurement of sin 2 2θ 13 V. Barger, S. Geer, R.Raja, K. Whisnant Conclude that ~1019 decays/yr would enable the goal to be met provided sin 2 2θ 13 is > 0.01

25 With more data we could determine the sign of δm 2 K. McFarland, Prospecting for Neutrino Physics at a Muon Storage Ring 25 L = 2800 km, Eµ = 30 GeV, 2 x Decays Barger, Geer, Raja, Whisnant Fermilab Pub T µ Appearance µ+ Appearance } Three Flavor Mixing m 2 21 = 5 x 10 5 ev 2 /c 4 sin 2 2θ 23 = 1 sin 2 2θ 12 = 0.8 sin 2 2θ 31 = 0.04 δ = 0 µ Appearance +tve m 2 32 gives larger rate & softer spectrum than tve m 2 32 µ+ Appearance +tve m 2 32 gives smaller rate & harder spectrum than tve m 2 32 Data with stored µ + and stored µ would enable sign of m 2 32 to be determined!

26 K. McFarland, Prospecting for Neutrino Physics at a Muon Storage Ring 26 How many muon decays/year are needed for a "beyond the entry level" neutrino factory if the muon energy is 20 GeV? V. Barger, S. Geer, R.Raja, K. Whisnant Suppose the "upgrade" goal is to make the first measurement of matter effects & determine the sign of δm 2 at 3σ. Recipe: 1) Calculate ratio of wrong sign µ rates when µ+stored c.f. µ stored. 2) Compare ratios for δm2 32 >0 with δm2 32 < 0. 3) Identify sin22θ13 that yields 3σ difference in measured ratios. Conclude that ~1020 decays/yr would enable the goals to be met provided sin 2 2θ 13 > 0.01

27 K. McFarland, Prospecting for Neutrino Physics at a Muon Storage Ring 27 How many muon decays/year are needed to begin to make contact with CP violation in the neutrino sector? Suppose we want to distinguish between δ = +90o and δ = 90o. What is needed to produce a 3σ change in the measured ratio of wrong sign muon rates (µ + stored cf µ stored)? V. Barger, S. Geer, R.Raja, K. Whisnant Recipe: 1) Calculate ratio of wrong sign µ rates when µ+stored c.f. µ stored. 2) Compare ratios for δ= +90o with δ= 90o. 3) Identify sin22θ13 that yields 3σ difference in measured ratios.

28 K. McFarland, Prospecting for Neutrino Physics at a Muon Storage Ring 28 V. Barger, S. Geer, R.Raja, K. Whisnant Maximal MSW: With a 20 GeV ring, 5x1020 decays/yr would yield a 3σ difference in the ratio of rates if δ = +90o is changed to δ = 90o, provided sin 2 2θ 13 > 0.01

29 K. McFarland, Prospecting for Neutrino Physics at a Muon Storage Ring 29 V. Barger, S. Geer, R.Raja, K. Whisnant

30 K. McFarland, Prospecting for Neutrino Physics at a Muon Storage Ring 30 What about this ο 50 kton Detector? Possible Technologies: ffl Magnetized Steel / Scintillator Calorimeter (MINOS,CCFR/NuTeV,CDHS) ffl Liquid Argon TPC plus Spectrometer (ICANOE) ffl Water Cerenkov Detector plus Spectrometer (SuperK+...) Requirements: ffl Outgoing Muon Charge ID at least ffl Neutrino Energy Measurement ffl Angular Discrimination for Background Suppression

31 K. McFarland, Prospecting for Neutrino Physics at a Muon Storage Ring 31 Default" Technology: Steel Tracker/Calorimeter Magnetized steel: _ tracking and calorimetry NC and CC ν e, ν µ ν e ν ν Z q q ν e q W q e CC ν µ CC _ ν e _ ν µ ν µ µ - W q q _ ν + µ µ W q q Wrong-sign muon appearance is distinctive signature

32 K. McFarland, Prospecting for Neutrino Physics at a Muon Storage Ring 32 &KDUJHDQG0RPHQWXP 0HDVXUHPHQWZLWK%ILHOG February 18, 2000 D. Casper, University of California Irvine 21

33 K. McFarland, Prospecting for Neutrino Physics at a Muon Storage Ring 33 enu,x,y=49.2,.28, m 3 H 2 O, downstream spectrometer

34 K. McFarland, Prospecting for Neutrino Physics at a Muon Storage Ring 34 High Rate Neutrino Experiments /yr μ decays in the green straight section ) ffl 5 8% of all interactions within r < 10 cm ffl 40 50% of all interactions within r < 50 cm ffl 1: E μ /kg/yr at beam center 50 GeV 800 m 50 GeV 30m Near Detector Hall Magnetized Fe Shield 70m (multi-purpose detector design of B. King) Small targets open up new possibilities in ffl Target material ffl Final state detection =) New physics opportunities

35 K. McFarland, Prospecting for Neutrino Physics at a Muon Storage Ring 35 Nucleon Structure at a Neutrino Factory Why use neutrinos to probe nucleon structure? ffl xf 3 : separate sea and valence ffl Flavor tagging. νs! μ c, c! X`ν tags strange quarks. νd! μ u but νu! dμ +. νc! ν c, c! X`ν (? hard... ) ffl High rate means we can wean νn from its addiction to heavy isoscalar targets. Polarized Targets? 1m 4 He Evaporator 4 He phase separator 3 He Condenser Target cells 3 He/ 4 He Distiller Sintered Heat Exchanger Mixing chamber Dilution refrigerator Solenoid magnet Trim coils Dipole magnet Superconducting magnets. Solid Butanol, dilution factor of 0.1 (SMC)

36 K. McFarland, Prospecting for Neutrino Physics at a Muon Storage Ring 36 Example: Polarized Target Experiment (D. Harris, KSM) Goal: Flavor-Separated Spin νu! ` d νd! ` u νd! `+u νu! `+d νs! `+c νs! ` c ffl q and q from the inelasticity distributions ffl ν/ν from lepton flavor ν(ν)s(s)! μ ± c(c) separated from c! `νx final states (ο 1% of cross-section at 50 GeV) ) Measure strange sea polarization to ο 1% precision (one year) ffl Vastly superior flavor separation compared to hadronbased separation in HERMES

37 K. McFarland, Prospecting for Neutrino Physics at a Muon Storage Ring 37 Neutrino Charm Factory: By-Products ff charm ff CC ff bottom ff CC ffl Charm Production averages ß 3% of cross-section ffl Bottom Production not accessible at 50 GeV. precise measure of jv ub j at high E ν? (B. King)

38 K. McFarland, Prospecting for Neutrino Physics at a Muon Storage Ring 38 Neutrino Charm Factory II ffl Charm spectrum is soft by fixed target standards ffl Still, 10 5 /kg-yr charmed hadrons above 10 GeV ffl Rate is high; non-charm backgrounds relatively low ffl Tagging. ν s! ` c. ν s! `+c. Tagging backgrounds are typically very low Λ Most common mistag from c! `+Xν (benign since charm is misreconstructed also) ffl So what to do with ο 10 8 tagged charm?

39 K. McFarland, Prospecting for Neutrino Physics at a Muon Storage Ring 39 D 0 D 0 Mixing ffl D 0 D 0 is a clean signature of new physics if seen above 10 6 level ffl e + e and Fixed Target currently at few 10 3 level (BaBar estimates few10 4 sensitivity with years at design luminosity). Stuck on systematics/backgrounds. Reconstructed flavor from D 0! K ß + (but D 0! K + ß is 1% of this rate). Proper lifetime analysis required to get below 10 2 One idea for D 0 D 0 Mixing in a Neutrino Factory Beam: ffl High momentum lepton is tag ffl Measure (inclusive) second lepton charge. about 30% from neutral D mesons. 10% efficient, assuming only e ± useful Λ There is a few 10 2 background from light meson decays in showers for the case of muons. probe D 0 decays ffl D 0 D 0 mixing gives `±tag`charm ±. vs dominant `±tag` charm

40 K. McFarland, Prospecting for Neutrino Physics at a Muon Storage Ring 40 νe Scattering ν l e l ν μ e! ν μ e NC only ν μ e! ν e μ CC only ( inverse muon decay") ν μ e! ν μ e NC only ν e e! ν e e NC and CC ν e e! ν e e NC and CC ν e e! ν μ μ ; ν fi fi ; ud : : : s-channel annihilation Why are these interesting? ffl Target is a point particle: well-predicted cross-section ffl NC processes sensitive to new physics (ννee coupling)

41 K. McFarland, Prospecting for Neutrino Physics at a Muon Storage Ring 41 νe Scattering: Cross-Sections ff(e ν =1 GeV ) ffl μ + beam, ν e e! ν e e varies by 0:1% for ffisin 2 W 0:0005 ffl μ beam: partial neutrino flavors summed less sensitive than flavor-separate case ο

42 K. McFarland, Prospecting for Neutrino Physics at a Muon Storage Ring 42 νe Scattering: Experiment ν ν e Z e ν ν e in lab frame ffl Signal is single high-e electron ffl CC-only process in μ beam (IMD) easy to normalize. Part per mil normalization available for 400 ffl Quasi-elastic backgrounds: νn! `N 0 ψ! 50GeV E μ kg-yr. ff QE =ff νe ο 4000 GeV E ν. Signal p 2 t ο m e E ν Φ m 2 μ (reaction Φ beam). Background p 2 t ο m N E ν. But background very well measured (high p t )

43 K. McFarland, Prospecting for Neutrino Physics at a Muon Storage Ring 43 νe Scattering: (sin 2 W ) (B. King, KSM, H. Schellman, J. Yu) For 1 GeV neutrinos, (10 46 cm 2 is 20 kg of material in beam) ffl Reasonable to imagine ffisin 2 W (stat)ο 0: :00004 ( GeV E μ kg-yr) ffl μ beam easy to normalize (IMD) but less sensitive

44 K. McFarland, Prospecting for Neutrino Physics at a Muon Storage Ring 44 Direct Probes of Neutrino Properties Some of the laundry list: ffl Electric/Magnetic moments as an elastic form-factor or radiative emission ffl Decays of heavy neutrinos with m L 0 ο 50 MeV m L 0! e + e ν ffl... Why persue these at a muon storage ring neutrino source? ffl Roughly 10 4 increase in available neutrino fluxes over small areas

45 K. McFarland, Prospecting for Neutrino Physics at a Muon Storage Ring 45 Conclusions 1. Exciting Times! Accelerator R&D efforts are suggesting the possibility of high intensity, accelerated beams of muons ffl Collimated, high rate ν μ and ν e beams 2. Long Baseline Oscillation Capabilities ffl Measurement of 13 (ν e! ν μ rate) ffl Matter effects and mass hierarchy (ν e! ν μ vs ν e! ν μ ) ffl CP violation is possible ffl If LSND correct, whole menu of possibilities Many high rate experiments supported by such a facility as well ffl Interesting and diverse physics menu ffl Surprises here? ffl May attract a large experimental community