Low Energy Neutrino Cross Sections: Past, Present, and Future Sam Zeller Columbia University APS/DPF 2003 Philadelphia, PA April 8, 2003 Outline ffl W

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1 Low Energy Neutrino Cross Sections: Past, Present, and Future Sam Zeller Columbia University APS/DPF 2003 Philadelphia, PA April 8, 2003 Outline ffl Why is it important to know low energy ν ff's? ffl Past measurements,! knowledge from bubble chamber experiments? how well have we measured low E ff ν? various Monte Carlo models ffl Present experiments,! K2K near detector,! MiniBooNE ffl Prospects for the future,! FINeSE, NuMI initiatives

2 Sam Zeller, Low Energy Neutrino Cross Sections, 04/08/03 2 Motivation ffl Last 5 years have given us compelling indications that neutrinos are oscillating ffl Evidence for ν mass has sparked intense interest in ν experiments ffl CHOOZ ffl ICARUS ffl KamLAND ffl K2K ffl MINOS ffl OPERA ffl Palo Verde ffl BUGEY ffl CHORUS ffl Karmen ffl LSND ffl MiniBooNE ffl NOMAD ffl Kamiokande ffl MACRO ffl Super K ffl BOREXINO ffl GALLEX Neutrinos in the literature ο 50% increase in 5 years! ffl SNO

3 Sam Zeller, Low Energy Neutrino Cross Sections, 04/08/03 3 Where Do Cross Sections Matter? Why do we need to know low energy ν cross sections? ffl Atmospheric Neutrinos,! m 2 23, 23 limited by systematics on flux, ff ν,! ν μ! ν fi or ν μ! ν s limited by ff ν uncertainties ffl Proton Decay Searches,! good knowledge of ff ν required to reliably evaluate expected backgrounds ffl Appearance Experiments (ν μ! ν e ), 13,! limited by stat and syst uncertainty of background subtraction,! ν e component in the beam,! misidentified NC ß 0 production (important to not only understand rate but contributions from different channels)? resonant single ß 0 production? coherent ß 0 production? feed down from inelastic channels (where nuclear absorption of add'l hadrons plays a role) Systematics are already beginning to dominate these measurements

4 Sam Zeller, Low Energy Neutrino Cross Sections, 04/08/03 4 Status of Low E ν Cross Sections Knowledge of ν differential and total cross sections in low energy region is limited: No consensus on best way to combine channels at fixed E ν ffl DIS limited to W > W 0 to avoid double counting ffl modeling DIS at low E (Bodek P13 session) Bodek, Yang hep-ex/ Principal reactions: ffl quasi elastic scattering ffl resonance production ffl deep inelastic scattering

5 Sam Zeller, Low Energy Neutrino Cross Sections, 04/08/03 5 Modeling Low E ν Cross Sections ffl Recent neutrino experiments using a variety of Monte Carlos (many have long histories),! NUANCE Λ (IMB, K2K, SuperK, MiniBooNE),! NEUT (Kamiokande, K2K, Super K),! NEUGEN Λ (Soudan 2, MINOS),! NUX, GENEVE (Icarus, NOMAD),! JETTA, RESQUE (CHORUS, OPERA) ffl Generally these Monte Carlos are proprietary" (many are not well documented publically)! exceptions Λ ffl Share common theoretical inputs,! Llewellyn Smith for free nucleon QE cross section,! Rein Sehgal resonance cross sections,! standard DIS formula for high W, Q 2 ffl But nontrivial differences,! implementation of Fermi gas model for QE,! joining of resonance and DIS regions,! treatment of nuclear effects (final state interactions of ß; K; n; p)

6 Sam Zeller, Low Energy Neutrino Cross Sections, 04/08/03 6 Nuclear Effects Oscillation experiments measure ν reactions on nuclear targets (O 16 ;C 12 ;Ar 40 ;Fe 56 ;Pb 207 ) ) vastly complicates description of ν reactions ffl Pauli suppression (relatively straight forward) ffl Fermi motion of target nucleons ffl Final state interactions (much larger and have not been disentangled experimentally),! nuclear reinteractions,! ß absorption,! charge exchange ffl Impacts kinematics/rates and observed final states ffl Nuclear effects studied extensively in DIS using μ; e beams, but have only been glanced at in low statistics ν experiments,! Gargamelle, SKAT (C 3 H 8 CF 3 Br),! FNAL (Ne),! Serpukov (Al spark chamber),! CHARM, CHARM II (marble, glass) ffl but they typically publish free nucleon ff

Sam Zeller, Low Energy Neutrino Cross Sections, 04/08/03 7 Early ff ν Measurements ffl Low E ff ν measurements come from early experiments at ANL, BNL, CERN, and FNAL ffl bubble chamber experiments

7 Sam Zeller, Low Energy Neutrino Cross Sections, 04/08/03 7 Early ff ν Measurements ffl Low E ff ν measurements come from early experiments at ANL, BNL, CERN, and FNAL ffl bubble chamber experiments Gargamelle at CERN ffl simplest exclusive states measured ffl considerable errors due to:,! low statistics,! imprecise knowledge of incoming ν flux ffl in addition to large errors, results are often conflicting ffl even ignored by PDG (ff ν removed after 1996)

8 Sam Zeller, Low Energy Neutrino Cross Sections, 04/08/03 8 Past ff ν Measurements ffl How well have we measured low energy neutrino cross sections? ffl Along the way, point out how good our current theoretical understanding is. ffl Review the status of past measurements of ff ν at E ν ο 1 GeV:,! Quasi elastic scattering,! Resonance production (CC and NC single ß),! Coherent ß production,! Multi ß production (small ff but can feed down),! ν production of strange

9 Sam Zeller, Low Energy Neutrino Cross Sections, 04/08/03 9 Quasi Elastic Scattering ν μ n! μ p ffl Most well known cross section at low energies ffl These processes have been studied with low energy (100 MeV 10 GeV) bubble chambers experiments; most on light targets: Experiment Target Type Reference ANL bubble chamber, D 2 Barish, PRD 16, 3103 (1977) GGM bubble chamber, propane freon Pohl, Nuovo Cimento 26, 332 (1979) BNL bubble chamber, D 2 Baker, PRD 23, 2499 (1981) FNAL bubble chamber, D 2 Kitagaki, PRD 28, 436 (1983) Serpukhov spark chamber, Al Belikov, Z. Phys. A320, 625 (1985) BEBC bubble chamber, D 2 Allasia, Nucl. Phys. B343, 285 (1990) SKAT bubble chamber, CF 3 Br Ammosov, Sov.J.P.Nuc. 23, 283 (1992) ffl Theoretical calculations for free nucleons all based on C.H. Llewellyn Smith, Phys. Rep. 3C, 261 (1972) < N 0 jj μ jn > = u(n 0 ) F V (q 2 ) ο 2 6 4fl μ F 0 V (q2 )+ iff μνq ν οf 2 V (q2 ) 2M 1 (1 q 2 =M 2 V )2 F A (q 2 ) = F A (0) (1 q 2 =M 2 A )2 ffl Form factors depend on M V ; F A (0); M A + fl 5 fl μ F A (q 2 ) 5 u(n) 3 7

10 Sam Zeller, Low Energy Neutrino Cross Sections, 04/08/03 10 Quasi-Elastic Cross Section Existing QE ff measurements were made ο 20 years ago and have limited precision: ffl largest contrib to exp'l error 15 20% flux uncertainties ffl considerable spread in the QE ff data for any given E ν ffl apart from nuclear effects, theoretical uncertainty dominated by M A = 1:026 ± 0:021 GeV (world average) ffl Monte Carlo predictions agree (w/ consistent pars) ffl but from spread in exp'l data =) realistic QE ff uncertainty is more like 20%

11 Sam Zeller, Low Energy Neutrino Cross Sections, 04/08/03 11 Quasi-Elastic Cross Section Is there room for improvement? ffl Work by Bodek, Budd, Arrington (P13 session) ffl input updated form factors G n;p E (Q2 ), G n;p M (Q2 ) from e scattering ffl largest effect G n E (Q2 ) 6= 0 ffl with latest values, re analyze ν data for M A Argonne (1969) Argonne (1973) CERN (1977) Argonne (1977) CERN (1979) BNL (1980) BNL (1981) Argonne (1982) Fermilab (1983) BNL (1986) BNL (1987) BNL (1990) Average M A [GeV] ν data not yet updated from Bernard et al. hep-ph/

12 Sam Zeller, Low Energy Neutrino Cross Sections, 04/08/03 12 Neutrino Resonance Production ffl In addition, there are excitation of resonances and their subsequent decays: νn! l N Λ N Λ! ßN 0 ffl 7 possible channels (3 CC, 4 NC): ν μ p! μ pß + ν μ n! μ nß + ν μ n! μ pß 0 ffl Main contribution is from (1232) (but others can contribute) ν μ p! ν μ nß + ν μ p! ν μ pß 0 ν μ n! ν μ nß 0 ν μ n! ν μ pß ffl ν Monte Carlos covering this kinematic region have been using early theoretical predictions by Rein Sehgal Rein and Sehgal, Annals Phys 133, 79 (1981) ffl Feynman, Kislinger, Ravndal model of baryon resonances (to account for higher mass resonant states) Feynman, Kislinger, Ravndal, Phys. Rev. D3, 2706 (1971) ffl Contributions from baryonic resonances (N Λ, ) ffl Recent calcs on nuclear effects (ß absorption, CE) Paschos, Nucl. Phys. B588, 263 (2000) Quality and quantity of data varies...

13 Sam Zeller, Low Energy Neutrino Cross Sections, 04/08/03 13 CC Single Pion Production ν μ p! μ pß + ν μ n!μ pß 0 ν μ n!μ nß +

14 Sam Zeller, Low Energy Neutrino Cross Sections, 04/08/03 14 NC Single Pion Production ffl NC amplitudes obtained by simply rescaling form factors by terms depending on sin 2 W ffl Most of available data on NC single ß production exists in the form of NC/CC cross section ratios ffl NC single ß data more sketchy than CC case In some cases, measurements can differ by factors 2 3 (experiments needed to understand neutron backgrounds)

15 Sam Zeller, Low Energy Neutrino Cross Sections, 04/08/03 15 Absolute NC 1ß Cross Sections ffl re analysis of Gargamelle 1970's bubble chamber data mostly propane (C 2 H 8 ), 10% heavy freon (CF 3 Br) ffl using published Φ, ff at < E ν >= 2:2 GeV (E. Hawker with help from Morfin, Pohl - shown at NuInt02) ν μ p! ν μ n ß + ν μ n! ν μ p ß ν μ p! ν μ p ß 0 ν μ n! ν μ n ß 0

16 Sam Zeller, Low Energy Neutrino Cross Sections, 04/08/03 16 Coherent Pion Production ffl Scatter from entire nucleus rather than from its ν individual constituents ν,µ ffl Both NC and CC processes possible: ν μ A! ν μ Aß 0 ν μ A!μ Aß + A W,Z A 1 P π A ffl Distinct kinematics,! negligible energy transfer to the target (low Q 2 ),! forward scattered ß ffl Kinematics well known, but overall rate less certain (exps typically assign a 100% uncertainty) ffl Theoretical model based on Adler's PCAC theorem ff(νa) / ff(ßa) as Q 2! 0 d 3 ff dq 2 dνdt (νa;q2 = 0) = ffl Extrapolation to Q 2 Rein-Sehgal, Nucl. Phys. B223, 29 (1983) d 3 ff dq 2 dνdt 0 M 2 A M 2 A + Q2 G2 F 2ß 2 ν Eμ E ν f 2 ß dff dt (ßA) 6= 0 through propagator term: 1 C A 2 ; M A ο 1 1:35 GeV

17 Sam Zeller, Low Energy Neutrino Cross Sections, 04/08/03 17 Coherent Pion Production ffl Shown are NC, CC data off variety of nuclear targets (to allow comparison between exps, assume A 1 3 scaling) ffl Lowest energy data is at 2 GeV off Al target ffl Possible to measure at K2K 1kton and at MiniBooNE < E ν >ο 1 GeV,! important since ο 20% of single ß 0 rate,! impacts limits on osc of standard ν's to sterile states

18 Sam Zeller, Low Energy Neutrino Cross Sections, 04/08/03 18 Multi Pion Production Large 40%-ish uncertainties on dipion production data at E ν ο 1 GeV: ν μ n! μ pß + ß ν μ p!μ pß + ß 0 ν μ p!μ nß + ß +

19 Sam Zeller, Low Energy Neutrino Cross Sections, 04/08/03 19 Single Kaon Production ffl Important background for nucleon decay searches p! K + ν (preferred in SUSY GUTs) ffl Finite probability that a ν int can mimic a proton decay event, since > 800 MeV ν production of strange: CC NC ν μ n! μ K + Λ 0 ν μ p! ν μ K + Λ 0 ν μ n! ν μ K 0 Λ 0 ν μ p! μ K + p ν μ n! μ K 0 p ν μ n! μ K + n ν μ p! μ K + ± + ν μ p! ν μ K + ± 0 ν μ n! μ K + ± 0 ν μ p! ν μ K 0 ± + ν μ n! μ K 0 ± + ν μ n! ν μ K 0 ± 0 ν μ n! ν μ K + ± ) important to reliably estimate this background ffl Little experimental data - most from bubble chambers where strange particle decays easily observed: ffl Few theoretical models:,! R. Shrock, Phys. Rev. D12, 2049 (1975),! A. A. Amer, Phys. Rev. D18, 2290 (1978) ν μ n! μ K + Λ 0 dominant channel at low energies (and hence the limiting background)

20 Sam Zeller, Low Energy Neutrino Cross Sections, 04/08/03 20 CC Associated Production of K + Λ ν μ n! μ K + Λ Experimental measurements based on handfuls of events ffl BNL 7ft, D 2, 8 evts ffl FNAL 15ft, D 2, 21 evts Data on these reactions is scarce particularly at E's near threshold which are relevant for proton decay searches ffl Models use same framework as single ß (Rein Sehgal) (add additional resonance decays other than Nß) ffl Ability to measure strange production rates in ν ints will play important role in helping p decay exps reach their ultimate sensitivity,! Measure at MiniBooNE (expect 1,000's of events) (K. Datchev talk in P13 session),! Plans to measure using K2K new near detector,! And in the future at FINeSE, NuMI near detectors

21 Sam Zeller, Low Energy Neutrino Cross Sections, 04/08/03 21 Present Experimental Handles on Low E Neutrino Cross Sections ffl K2K near detector,! started taking data in June 1999,! < E ν >ο 1:3 GeV ffl MiniBooNE,! started taking data in late August 2002,! < E ν >ο 1 GeV MiniBooNE Detector Signal Region Veto Region both primarily ν μ beam

detector ffl near detector ο 300 m from ß production target ffl set of detectors with

22 Sam Zeller, Low Energy Neutrino Cross Sections, 04/08/03 22 K2K Near Detector Goal is to measure beam profile and physics cross sections to aid in interpreting results from SuperK detector ffl near detector ο 300 m from ß production target ffl set of detectors with complementary abilities MRD SciFi 1kton H 2 O Cerenkov» 330 ton fid. 6 ton fid. 25 ton fid. 124k evt 8k evt 36k evt

Sam Zeller, Low Energy Neutrino Cross Sections, 04/08/03 23 K2K: 1kton H 2 O»Cerenkov Detector ffl 25 ton

technology as SuperK 680 20" PMTS w/ 70 cm spacing R ß 0 = (ß0 =μ) data (ß 0 =μ) MC = 1:03 ± 0:02 (stat) ± 0:09

112 (2002) observed ο 4; 000 ß 0 and 16; 000 μ ffl primary method for estimating NC ß 0 background has been from

23 Sam Zeller, Low Energy Neutrino Cross Sections, 04/08/03 23 K2K: 1kton H 2 O»Cerenkov Detector ffl 25 ton fiducial ffl scaled down replica of SuperK (1/50) 1 ring FC μ like event ffl uses same analysis algo and technology as SuperK " PMTS w/ 70 cm spacing R ß 0 = (ß0 =μ) data (ß 0 =μ) MC = 1:03 ± 0:02 (stat) ± 0:09 (syst) C. Mauger, Nucl. Proc. Suppl. 112 (2002) observed ο 4; 000 ß 0 and 16; 000 μ ffl primary method for estimating NC ß 0 background has been from Monte Carlo ffl w/ 1kton measurement, uncertainty in predicted NC ß 0 yield reduced by factor 2 ffl applications to ν μ! ν fi vs. ν μ! ν s discrimination in SuperK atmospheric analysis (consistent w/ ν μ! ν fi )

FGD event (CC QE candidate) ffl allows one to more cleanly separate QE from inelastic (60% pure

24 Sam Zeller, Low Energy Neutrino Cross Sections, 04/08/03 24 K2K: Fine Grain Detector (FGD) ffl SciFi: tracker scintillating fiber ffl MRD: large steel plates and drift tubes (E μ, μ ) typica FGD event (CC QE candidate) ffl allows one to more cleanly separate QE from inelastic (60% pure QE, 86% pure non QE) ffl using this technique, K2K measures non QE/QE ratio to < 10% total ο 8; 000 events

Sam Zeller, Low Energy Neutrino Cross Sections, 04/08/03 25 MiniBooNE ffl 40 ft diameter sphere ffl 800 tons undoped mineral oil MiniBooNE Detector Signal Region Veto Region ffl light tight inner

25 Sam Zeller, Low Energy Neutrino Cross Sections, 04/08/03 25 MiniBooNE ffl 40 ft diameter sphere ffl 800 tons undoped mineral oil MiniBooNE Detector Signal Region Veto Region ffl light tight inner region lined with " PMTS ffl ν interactions in oil,! prompt» Cerenkov light,! delayed scintillation light ffl since P osc small =) treat MBooNE as a near detector ffl Measure QE, NC elastic (ν μ p! ν μ p), ß 0 (resonant + coherent), strange particle production ffl Study production ff and kinematics (ß 0 ~p, angle) with high statistics ffl Advantages:,! Unlike H 2 O» C detectors, are not blind to sub» C p's since can make use of scintillation light,! expect order of magnitude more events than K2K

Sam Zeller, Low Energy Neutrino Cross Sections, 04/08/03 26 MiniBooNE Events So far, have collected 50,000 ν ints... (ο 5% of our goal) already comparable to K2K data set ß 0!

26 Sam Zeller, Low Energy Neutrino Cross Sections, 04/08/03 26 MiniBooNE Events So far, have collected 50,000 ν ints... (ο 5% of our goal) already comparable to K2K data set ß 0! flfl candidate: Currently calibrating the detector ) can reconstruct ß 0 events: Events Preliminary 2 χ /NDF / 142 Prob Exp ± 2.80 Mass ± 1.95 Width ± 2.13 clear ß 0 peak ο 135 MeV π 0 candidate mass (MeV/c )

Tayloe) ffl ο 10 ton fiducial detector 100 m from ν source ffl active target - highly segmented ffl strange spin of nucleon ( s)

27 Sam Zeller, Low Energy Neutrino Cross Sections, 04/08/03 27 FINeSE ffl Fermilab Intense Neutrino Scattering Experiment ffl Use same ν source as MiniBooNE (FNAL Booster) < E ν >ο 1 GeV ffl EOI submitted to FNAL PAC in Nov 2002 (B. Fleming, R. Tayloe) ffl ο 10 ton fiducial detector 100 m from ν source ffl active target - highly segmented ffl strange spin of nucleon ( s) from R ν μ p! ν μ p ν μ n! μp ffl precision measurements of NC,CC ν cross sections (10 100k event samples) ffl talk by B. Fleming in P13 session 1 A

Sam Zeller, Low Energy Neutrino Cross Sections, 04/08/03 28 NuMI Initiatives ffl plans for a near detector using NuMI beam ffl EOI submitted to FNAL PAC in Nov

Morfin) ffl fully active fine grained neutrino near detector ffl solid scintillator strips (interspersed w/ variable A target) expect ο 200; 000 CC events/yr/ton

28 Sam Zeller, Low Energy Neutrino Cross Sections, 04/08/03 28 NuMI Initiatives ffl plans for a near detector using NuMI beam ffl EOI submitted to FNAL PAC in Nov 2002 (J. Morfin) ffl fully active fine grained neutrino near detector ffl solid scintillator strips (interspersed w/ variable A target) expect ο 200; 000 CC events/yr/ton in low E configuration (peak E ν = 3 GeV) at startup in 2005 ffl precision ff measurements: (high stats, ο 3% flux syst),! QE form factors,! resonance prod region,! s from ν elastic,! strange particle prod ffl study of nuclear effects (selection of nuclear targets installed in Sci based detector) 11.5 GeV CC ν interaction

29 Sam Zeller, Low Energy Neutrino Cross Sections, 04/08/03 29 Testing ν Cross Section Models ffl compare against previous ν measurements,! re analyze old ν data (NC ß, M A from QE) ffl ν nucleus models can be tested against (more precise) e scattering data,! can gain valuable information from (e; e 0 ) scattering,! high statistics e data exists on a variety of relevant targets (C 12, O 16, etc.),! can gain insight into meeting of QE and resonance regions,! checks Fermi gas model parameters (E B, p F ) Electron -Carbon Scattering Data r r ry n s CE C Energy Loss [MeV] O'Connell, PRL 53, 1627 (1984), 730 MeV e on 12 C, 37.1 ffi ffl provided nuclear effects are the same for e, ν

30 Sam Zeller, Low Energy Neutrino Cross Sections, 04/08/03 30 Where We've Been and Where We're Headed Past Measurements (bubble chambers) low E 15 20% low statistics σ flux uncertainties ν?? Neutrino Factories? JHF? Superbeams?? DIS larger, denser targets high E higher statistics probe nucleon structure Future σ ν Present Experiments ν Oscillations more intense low E beams high granularity detectors NuMI σν K2K FINeSE MiniBooNE p storage rings? (FNAL debuncher, CERN decelerator)

31 Sam Zeller, Low Energy Neutrino Cross Sections, 04/08/03 31 Conclusions ffl Interest in low E ν processes has increased following compelling indications of neutrino oscillations ffl Several new experiments are now being planned or under construction aimed at determining oscillation parameters with high precision,! will be even more sensitive to sources of systematic uncertainties,! among them: ff ν, nuclear effects, FSI ffl Although we have been using accelerator based ν beams for over 30 years there is still a surprisingly large amount we don't know about ν interactions at low energy,! lack of high statistics low energy ν data? results often conflicting? little ν data on nuclear targets? still valuable, but situation could be improved ffl Lack of understanding may haunt the next generation of experiments ffl Look forward to improved ff ν measurements (K2K, MiniBooNE,... FINeSE, NuMI,...)... to help oscillation experiments reach their maximum discovery potential...

Neutrino Physics at MiniBooNE

Neutrino Physics at MiniBooNE G. P. Zeller Columbia University Department of Physics 538 W. 120th St., New York, NY 10027, USA for the MiniBooNE Collaboration As its primary design goal, the MiniBooNE