The Study of ν-nucleus Scattering Physics Interplay of Cross sections and Nuclear Effects

Transcription

1 The Study of ν-nucleus Scattering Physics Interplay of Cross sections and Nuclear Effects Jorge G. Morfín Fermilab University of Pittsburgh, 8 December

2 ν H / D Scattering Life was simpler when our targets were nucleons as opposed to nuclei. Contemporary neutrino (oscillation) experiments demand high statistics massive nuclei as targets. Jorge G, Morfín - Fermilab 2

3 Neutrino Nucleus Scattering What do we observe in our detectors? 3

4 Neutrino Nucleus Scattering What do we observe in our detectors? appearance of ν e distance = 1300km Jorge G, Morfín - Fermilab 4

5 Neutrino Nucleus Scattering What do we observe in our detectors? Neutrino Anti-neutrino J.A. Formaggio and G.P. Zeller, Rev. Mod. Phys., Jorge G, Morfín - Fermilab 5

6 Neutrino Nucleus Scattering What do we observe in our detectors? Jorge G, Morfín - Fermilab 6

7 What are these Nuclear Effects Nuc c,d,e.. c (Ε Ε) in Neutrino Nucleus Interactions? Target nucleon in motion classical Fermi gas model or the superior spectral functions (Benhar et al.) Certain reactions prohibited - Pauli suppression Meson exchange currents: multi-nucleon initial states Form factors are modified within the nuclear environment. (Butkevich / Kulagin, Tsushima et al.) Produced topologies are modified by final-state interactions modifying topologies and possibly reducing detected energy. Convolution of δσ(nπ) x formation zone uncertainties x π-charge-exchage/ absorption Cross sections and structure functions are modified and parton distribution functions within a nucleus are different than in an isolated nucleon. Important for DIS AND Transition region events! 7

8 Target Nucleon in Motion Classical Fermi Gas Model or the Superior Spectral Functions Impulse Approximation (IA) nucleus treated as a collection of independent nucleons no collective excitations breaks down as Q decreases with spatial resolution decreasing as 1/Q In the IA the nucleus is fully described by its spectral function The spectral function gives the distribution of momenta and energies of the nucleons inside the nucleus The original model to describe this distribution is the Fermi Gas model Jorge G, Morfín - Fermilab 8

9 Spectral Function Approach Superior Particularly as Q Decreases Artur Ankowski NuInt09 Jorge G, Morfín - Fermilab 9

10 Final State Interactions (FSI) Components of the initial hadron shower interact within the nucleus changing the apparent final state configuration and even the detected energy. For example, an initial pion can charge exchange or be absorbed on a pair of nucleons and an initial nucleon can scatter producing a pion Example numbers Final µ p Final µ p π Initial µ p 90% 10% Initial µ p π 25% 75% Jorge G, Morfín - Fermilab 10

11 Attempt to Remove Resonance Background MiniBooNE Experiment example Event generator a particular model - is used to remove QE-like background (pion absorption) from QE-like Xsect (blue) yielding an extracted QE Xsect (red) large pion absorption model dependence of QE result. Jorge G, Morfín - Fermilab 11

12 Nuclear Effects can Change the Energy Reconstruction for QE Events In pure QE scattering on nucleon at rest, the outgoing lepton can determine the neutrino energy: Since all modern experiments contain nuclei as targets. NUFACT 2012 Reconstructed energy shifted to lower energies for all processes other than true QE U. Mosel GiBUU Jorge G, Morfín - Fermilab 12

13 Experimental Studies of (Parton-level) Nuclear Effects with Neutrinos: until recently - essentially NON-EXISTENT EMC NMC E139 E665 Fermi motion 0.8 shadowing EMC effect sea quark x valence quark F 2 / nucleon changes as a function of A. Specifically measured in µ/e - A not in ν Α Good reason to consider nuclear effects are DIFFERENT in ν - A. Presence of axial-vector current. SPECULATION: Stronger shadowing for ν -A but somewhat weaker EMC effect. Different nuclear effects for valance and sea --> different shadowing for xf 3 13 compared to F 2.

14 F 2 Structure Function Ratios: ν-iron ncteq Collaboration F 2 (ν + Fe) F 2 (ν + [n+p]) 14

15 What do we observe in our detectors? effective σ cα (Ε) 15

16 Range of Existing Model (MC) Predictions off C NuInt09 Steve Dytman Jorge G, Morfín - Fermilab 16

17 Significant Implications for Oscillation Experiments Can not simply plug in effective σ π0 C from experiments in a significantly different beam. In a two-detector oscillation experiment the neutrino flux entering the far detector is altered from the neutrino flux at the near detector due to oscillations. The σ c Α (E) effective that should be applied to expectations (Monte Carlo) at the far detector is NOT the same as that which we would measure at the near detector. The convoluted σ(ε) X Nuc(E E) effects do not simply cancel near and far. However, the near detector results give us an excellent starting point for calculating the difference. Jorge G, Morfín - Fermilab 17

18 Don t Forget ν e and ν e Cross Sections M.Day: S. Zeller: What do we know about σ νe (Ε)? Mostly very low energy results. Reactor neutrinos studying Inverse Beta Decay Solar neutrino off deuterium (SNO) Stopping π/µ decay neutrinos off higher A targets See Formaggio and Zeller Rev. Mod. Phys. 84, (2012). One of few measurements of spectral shape of σ reflects the upper limit of most existing measurements, E 50 MeV. Jorge G, Morfín - Fermilab 18

19 What do we know about σ νe (Ε)? Need to measure the σ e (E) of multiple channels to predict spectrum at the far detector. Want an intense source of ν e events. Would like to know the flux of ν e (and ν µ, by the way) to order 1%. σ µ (E) 19

20 What do we know about σ νe (Ε)? Need to measure the σ e (E) of multiple channels to predict spectrum at the far detector. Want an intense source of ν e events. Would like to know the flux of ν e (and ν µ, by the way) to order 1%. σ µ (E) σ e (E) 20 20

21 What are the Differences σ νµ (Ε) and σ νe (Ε)? Quasi-elastic Scattering Day-McFarland study: Phys.Rev. D86 (2012) QE scattering dominates at low energies (2 nd oscillation maxima) Sources of possible differences and uncertainties - obvious: Kinematic limits from µ / e mass difference. Radiative Corrections. This may be an overestimate. Need full calculation. ν e (σ µ -σ e )/σ e radiative corrections ν µ (M. Day, K. McFarland, arxiv: ) 21

22 What are the Differences? Mainly QE Scattering Due to Nuclear Effects For standard models, 5% differences on ν e /ν µ ratio E < 200 MeV 22 (spectral function/fermi Gas) (superscaling/fermi Gas) ν e /ν µ ratio ν e /ν µ ratio stay tuned! S. Zeller: νstorm Workshop 22

23 What are the Differences? Mainly QE Scattering Meson-exchange Current Contributions Marco Martini via S. Zeller Hadronic part (nuclear response functions) is the same for ν e or ν µ cross section. However, the lepton tensor changes the relative weight of the nuclear responses in the several channels may change. The double ratio suggests the effect on the ν e /ν µ cross section ratio is 5% (S. Zeller) 23

24 What are the Differences? Δ Production Paschos Schalla: arxiv: Manny and his student have investigated ν µ and ν µ differences in Δ production in the low-q region where PCAC dominates the axial contribution. At E = 1-2 GeV, V part and V/A interference same size cancel for ν Use the Adler-Nussinov-Paschos model for nuclear corrections. 24

25 What are the Differences? Δ Production Paschos Schalla: arxiv: Paschos-Schalla predicts the following differences in cross sections where only the lepton mass term contributions are shown and any differences in form factors are not yet included. ν e solid ν µ dashed 25

26 Can we Actually MEASURE these Differences in the GeV region νstorm Neutrinos from Stored Muons High-Precision ν interaction physics program. The νstorm beam will provide a very well-known (δ φ(e) 1%) beam of ν and ν. ν e and ν e cross-section measurements. ν µ and ν µ cross-section measurements Address the large Δm 2 oscillation regime, make a major contribution to the study of sterile neutrinos. Either allow for precision study (in many channels), if they exist in this regime. Or greatly expand the dis-allowed region. Provide a µ decay ring test demonstration and µ beam diagnostics test bed. Provide a precisely understood ν beam for detector studies. Change the conception of the neutrino factory. 26

27 The νstorm Neutrino Beam µ + ν µ + ν e + e + µ - ν µ + ν e + e - A high-intensity source of ν e events for experiments. ν e ν µ µ + µ GeV µ + stored, 150m straight, flux at 100m (thanks to Sam Zeller and Chris Tunnell!) event rates per 1E21 POT tons at 50m 27

28 ν e Event Fractions in νstorm ν e produced by 3.8 GeV µ + beam. total CC ν e CC events QE RES DIS out of the CC modes: * 56% resonant * 32% QE * 12% DIS true E ν (GeV) For ν e sample, 52% resonant, 40% QE, 8% DIS) 28

29 Summary and Conclusions Nuclear effects, present in the data of all contemporary neutrino oscillation experiments, mixes channels and changes energy between produced and final states (observed). Observed results for a specific channel from one detector does not transfer to another detector unless they are using the same neutrino beam. What is a standard candle? Need to study these effects on a variety of nuclear targets and with a variety of incoming neutrino energy distributions. A significant step forward would be a high-statistics neutrinohydrogen /deuterium experiment to untangle these effects. ν e Cross sections are also important for future oscillation studies. Best would be a neutrino beam with a flux that we know to 1% Combine the needs A high precision cross section experiment both 29 for ν µ & ν e. nustorm

30 Backup Jorge G, Morfín - Fermilab 30

31 What could MINERνA Contribute? Preliminary Predictions for MINERνA Targets Preliminary l ± -A Preliminary Combined (poor) fit ν A Preliminary Careful! Based on analysis of NuTeV ν-fe results and scaled in A as charged lepton nucleus scattering results! (Karol Kovarik Katlsruhe) 31

32 A More-Detailed Look at Differences NLO QCD calculation of in the ACOT-VFN scheme charge lepton fit undershoots low-x data & overshoots mid-x data low-q 2 and low-x data cause tension with the shadowing observed in charged lepton data 32

33 A More-Detailed Look at Differences NLO QCD calculation of in the ACOT-VFN scheme charge lepton fit undershoots low-x data & overshoots mid-x data low-q 2 and low-x data cause tension with the shadowing observed in charged lepton data 33

34 Muon Tracking x Matching Why not 100%? * big shower * pileup * deadtime data MC ν µ CC overlaid with data Jorge G, Morfín - Fermilab 34

35 Fermi Gas vs. Spectral Function p Distribution Bodek Ritchie adds high p tail to FG due to SRC Artur Ankowski NuInt09 Jorge G, Morfín - Fermilab 35

36 F 2 Structure Function Ratios: ν-iron F 2 (ν + Fe) F 2 (ν + [n+p]) 36

37 Final State Interactions can mimic a QE event Define a class of events as QE-like that have the apparent topology but can have been produced as something other than QE. Jorge G, Morfín - Fermilab 37

38 MiniBooNE Measurement of M A : Much Higher Jorge G, Morfín - Fermilab 38

39 QE and QE-like events M.Martini NuFact09 Jorge G, Morfín - Fermilab 39

40 Meson Exchange Currents 2p2h Effects CCQE and CCQE-like Jorge G, Morfín - Fermilab 40

41 Why are ν e Cross Sections Important? ν e A scattering results are interesting on their own. Recent determination of large θ 13 has opened up possibilities of Determining ν mass ordering. Searching for CP-violation in the ν sector. To be sensitive to these effects, current/near-future long-baseline experiments will be looking for ν µ to ν e and ν µ to ν e oscillations over a range of energies. These will no longer be only counting experiments but rather will depend on observing distortions in the far detectors neutrino energy spectrum in both neutrino appearance of ν e distance = 1300km CP effect largest MH effect largest and anti-neutrino samples. 41 S. Parke

42 Large θ 13 means we could have reasonable statistics. However, as the now-well-known plot at right suggests, the asymmetry between ν and ν will be small and the goal of constraining the range of δ will demand minimal systematic errors. One of these systematics will be our knowledge of ν e and ν e cross Why are ν e and ν e Cross Sections Important? we re here (not including matter effects & backgrounds) (S. Parke) sections in the relevant energy range. 42

43 What are the Differences σ νµ (Ε) and σ νe (Ε)? Quasi-elastic Scattering Day-McFarland study: Phys.Rev. D86 (2012) Sources of possible differences: form factor uncertainties entering through lepton mass alterations - much more subtle: Form factor contributions both Axial and Pseudoscalar Second class current contributions to vector and axial-vector form factors Possible contribution to CP uncertainties: effect on the FF could be different for ν and ν (σ µ -σ e )/σ e (ν ν difference) pseudo-scalar form factor and second class currents 10% 1% (M. Day, K. McFarland, arxiv: ) stay tuned! 43