# IDS Mumbai

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```					Near detectors and systematics

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

Walter Winter
Universität Würzburg
Contents
   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)
   Systematics requirements (for simulation)
   Summary of new physics requirements

2
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?

3
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

2xLxq
 We use two
beam angles:
 Beam opening
angle:

Beam divergence

 Beam
divergence:
contains 90% of
total flux                              (arXiv:0903.3039)
5
Geometry of the detectors?
What are the
physics
requirements for
the geometry of the
detectors?

(ISS detector WG report)
6
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
7
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)

8
Different ND versions?
 Near detectors described in GLoBES by
 Some ND versions:
Near detector limit

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

Nearest point

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

Averaged

(Tang, Winter,
arXiv:0903.3039)
9
Extreme cases: Spectra
 Some spectra:

~ND limit            ~FD limit

(Tang, Winter, arXiv:0903.3039)
10
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%)
11
Systematics, qualitatively
(arXiv:0903.3039)

 Near detectors important for
 Flux monitoring (by NDs or other means) important
for CPV measurement
 Almost no impact for q13 and MH discovery
(background limited)
12
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
matters!
13
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)
14
CP violation measurement

3s

IDS-NF systematics
too conservative?

(Tang, Winter, arXiv:0903.3039)

15
Low-E NuFact
 „High statistics“ setup from
(Bross, Ellis, Geer, Mena, Pascoli,
arXiv:0709.3889)
 Em=4.12 GeV, L=1290 km
 5 1020 useful decays per
polarity and year, 10
years, 20 kt mass x
efficiency
 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)
16
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)
17
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)
18
SBL systematics
 Systematics similar to reactor experiments:
Use two detectors to cancel X-Sec errors

10%
shape
error

arXiv:0907.3145

(Giunti, Laveder, Winter, arXiv:0907.5487)

19

 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?
20
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
Bay!)
 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“?

21
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
 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)

What we need to understand
(for new physics)

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

 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.
http://www-off-axis.fnal.gov/MINSIS/
23

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