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					Near detectors and systematics

    IDS-NF plenary meeting
    at TIFR, Mumbai
    October 13, 2009

    Walter Winter
    Universität Würzburg
   Initial IDS-NF questions
   Beam and detector geometry
   Systematics
   Results for high energy NuFact
   Results for low energy NuFact
   Near detectors for new physics (examples)
   Answers to initial questions
   Systematics requirements (for simulation)
   Summary of new physics requirements

              Introduction: Initial questions

 What is the potential of near detectors to
  cancel systematical errors?
 (implies: need to address what kind of systematics …)
 When do we need a near detector for
  standard oscillation physics?
 What (minimal) characteristics do we
  require? (technology, number, sites, etc.)
 What properties do near detectors need for
  new physics searches?

              Geometry of decay ring
 Need two near detectors, because m+/m- circulate
  in different directions
 For the same reason: if only std. oscillations, no
  CID required, only excellent flavor-ID; caveat:
  background extrapolation

                                             (Tang, Winter,
                                           arXiv:0903.3039)   4
              Geometry of the beam
 Beam diameter ~     Beam opening angle

 We use two
  beam angles:
   Beam opening

                          Beam divergence

   Beam
    contains 90% of
    total flux                              (arXiv:0903.3039)
Geometry of the detectors?
                    What are the
                    requirements for
                    the geometry of the

               (ISS detector WG report)
               Geometry: Extreme cases
 Far detector limit:
  The spectrum is the same as the on-axis spectrum,
  i.e., the detector diameter
  D < 2 x L x q, where q is the beam opening angle,
  for any point of the decay straight
  NB: Point source approximation d >> s (size of
  source) not required for this limit. The extension of
  the source can be desribed by
 Near detector limit:
  The detector catches almost the whole flux, i.e., the
  detector diameter D > 2 x L x q, where q is the beam
  divergence, for any point of the decay straight
                  Assumptions for NDs
 Only muon neutrino+antineutrino inclusive CC
  event rates measured (other flavors not needed
  in far detectors for IDS-NF baseline)
 No charge identification
 At least same characteristics/quality (energy
  resolution etc.) as far detectors
 No explicit BG extrapolation
 Fiducial volume cylindrical
 No systematical errors considered, which are
  potentially uncorrelated among ND and FD
  (they are present, but they cannot be improved on with the NDs)

                   Different ND versions?
 Near detectors described in GLoBES by
  e(E)=Aeff/Adet x on-axis flux and
 Some ND versions:
     Near detector limit

     Far detector limit                     Hypothetical   SciBar-size   Silicon-   OPERA-
                                                                         vertex      size

                           Nearest point

                                                             e=1: FD limit
                                                             Dashed: ND limit
                           Farthest point


                                                                      (Tang, Winter,
           Extreme cases: Spectra
 Some spectra:

      ~ND limit            ~FD limit

                       (Tang, Winter, arXiv:0903.3039)
              Systematics treatment
 Cross section errors: Fully correlated
  among all channels, detectors etc.
  measuring the same cross section, fully
  uncorrelated among bins and neutrinos-
  antineutrinos (30% cons. estimate)
 Flux errors: Fully correlated among all
  detectors in the same straight and all bins,
  but uncorrelated among polarities, storage
  rings (2.5% for no flux monitoring to 0.1%)
 Background normalization errors: as
  IDS-NF baseline (20%)
              Systematics, qualitatively

 Near detectors important for
  Leading atmospheric and CPV measurements
 Flux monitoring (by NDs or other means) important
  for CPV measurement
 Almost no impact for q13 and MH discovery
  (background limited)
                Relevance of statistics
 Event rates (10 years) extremely large   (arXiv:0903.3039)

   Physics is limited by
    statistics in FD, not
    spectrum in ND

   Near detector location
    and size not relevant
    (caveat: elastic scattering
    for flux monitoring)

 However, for new physics
  searches, such as
  ne -> nt (emts, eets), size
                     Atmospheric parameters
 Atmospheric parameters measured at L=4000km:

      sin22q13 = 0.08, dCP=0     Unfilled: 30% XSec-errors, no ND
                                 Filled: Near detectors

 At L=4000km+7500km no impact of NDs!
                                 (Tang, Winter, arXiv:0903.3039)
     CP violation measurement


                          IDS-NF systematics
                           too conservative?

                 (Tang, Winter, arXiv:0903.3039)

                          Low-E NuFact
 „High statistics“ setup from
  (Bross, Ellis, Geer, Mena, Pascoli,
 Em=4.12 GeV, L=1290 km
 5 1020 useful decays per
  polarity and year, 10
  years, 20 kt mass x
 Reference: 2% system.
 Our ND3 with IDS-NF-like
  storage ring
 PROBLEM: We need
  decay ring geometry for
  some applications!
                                        (Tang, Winter, arXiv:0903.3039)
                  Low-E versus high-E NuFact

 Low-E NuFact: Systematics estimate seems quite accurate
  Near detectors mandatory!
 High-E NuFact: Qualitatively different, since two far detectors
  Need something like Double Chooz/Daya Bay systematics?

                                         (Tang, Winter, arXiv:0903.3039)
                  NDs for new physics
                  Example: SBL ne disappearance

 Two flavor short-baseline
  searches useful to constrain
  sterile neutrinos etc.
 ne disppearance:

 Also some interest in CPT-
  invariance test (neutrino
  factory ideal!)
 Averaging over straight         90% CL, 2 d.o.f.,
  important (dashed versus        No systematics,
  solid curves)                         m=200 kg
 Pecularity: Baseline
  matters, depends on Dm312
 Magnetic field if
                                  (Giunti, Laveder, Winter, arXiv:0907.5487)
                SBL systematics
 Systematics similar to reactor experiments:
  Use two detectors to cancel X-Sec errors



                                     (Giunti, Laveder, Winter, arXiv:0907.5487)

                     Summary: Answers to initial questions

 What is the potential of near detectors to cancel
  systematical errors?
 Cancels X-section errors; possibly useful for flux monitoring etc.
 When do we need a near detector to cancel cross
  section errors?
 If we only operate one baseline for sure! Mainly needed for leading
  atmospheric and CP violation searches.
 What (minimal) characteristics do we require?
  (technology, number, sites, etc.)
 Two near detectors; at least as good as far detectors for nm; not
  necessarily magnetic field, site and size hardly important (statistics high)
 What properties do near detectors need for new
  physics searches?
 Also ne, nt detection; as large as possible (statistics matters!); magnetic
  field; site application-dependent; maybe more sites
 Near detector characteristics driven by new physics requirements?
                  Systematics requirements
 For a more accurate simulation, PPEG needs to know
  systematics treatment
 The simulation results depend not only on the numbers
  for some systematical errors, but also the
  implementation of systematics (cf., Double Chooz, Daya
 What systematical errors (and how large) are there
  correlated/uncorrelated among
      Bins
      Detectors
      Storage rings
      Channels at the same detector
      Channels measuring the same X-secs
      …
 Possible alternative (discussed via mailing list some time
  ago): Show also curve with „no systematics“?

                  Summary of (new) physics requirements

 Number of sites
  At least two (neutrinos and antineutrinos), for some applications four
  (systematics cancellation)
 Exact baselines
  Not relevant for source NSI, NU, important for oscillatory effects
  (sterile neutrinos etc.)
 Flavors
  All flavors should be measured
 Charge identification
  Is needed for some applications (such as particular source NSI); the
  sensitivity is limited by the CID capabilities
 Energy resolution
  Probably of secondary importance (as long as as good as FD); one
  reason: extension of straight leads already to averaging
 Detector size
  In principle, as large as possible. In practice, limitations by beam
  geometry or systematics.
 Detector geometry
  As long (and cylindrical) as possible (active volume)

                        Aeff < Adet                      Aeff ~ Adet       22
              What we need to understand
              (for new physics)

 How long can the baseline be for geometric
  reasons (maybe:
  use „alternative

 What is the impact of systematics (such as X-Sec
  errors) on new physics parameters
 What other kind of potentially interesting physics
  with oscillatory SBL behavior is there?
 How complementary or competitive is a nt near
  detector to a superbeam version, see e.g.

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