K2K Cross Section Measurements

1. NC single p0/(All CC) in 1KT Cherenkov detector

2. CC-Coherent Pion Production in SciBar detector

3. MA-QE from shape fit to SciFi detector data

(4. Final results from mu-disappearance and e-appearance)

Rik Gran

U. Minnesota Duluth, U. Washington

For the K2K collaboration

Cross Sections and Nuclear Effects

are important for extracting

oscillation parameters from

nu-mu disappearance

nu-e appearance experiments.

Motivations

Improve

knowledge of

Cross Sections

(Lipari 1995)

En (GeV)

K2K oscillation result

Neutrino Cross Sections

SciFi Water Target

E (GeV)

K2K beam and near detectors

98% pure nm beam target materials: H2O, HC, Fe

nm energies

at the K2K

near detectors

NC single p0 in the water Cherenkov detector

n + N n + N + p0

Neutral Current (no muon),

recoil proton below 1 GeV/c threshold (no proton)

Typical p0 candidate

has two electron-like rings

with the right invariant mass

Reconstructed invariant mass (MeV)

NC single p0 signal and backgrounds

Signal (70%) is from NC resonant and NC coherent pizero production

AFTER pion-nucleus reinteractions such as charge exchange

(and includes a small amount from non-resonant “DIS” pion production)

Background from multiple (below threshold) pion production

And from Charged Current pion product with muon below threshold

# of FC 2ring 0 events

( MC is normalized

by area )

# of FC 2ring 0 events

preliminary

preliminary

Direction cosqp

p0 momentum (MeV/c)

NC single p0 fraction result

signal in 25 ton fiducial volume

(3.61 0.07 stat 0.36 syst) x 103

all muon-like in 25t fiducial volume

(5.65 0.03 stat 0.26 syst) x 104

S. Nakayama, et al., Phys. Lett. B 619 (2005)

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NC1p0/m ratio at <En> ~ 1.3 GeV

= 0.064 0.001 stat 0.007 syst.

(Prediction from our MC = 0.065)

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After efficiency

and background

corrections

Create ratio with

single-ring

muon-like events

as the reference.

Major sources of systematic error:

DIS model dependence 5.6%	NC/CC cross section 3.2%

Ring counting 5.4%	e-like ring particle ID 4.2%

(In mu-like denominator only: vertex reconstruction 4%)

CC coherent pion in SciBar detector



Extruded

scintillator

(15t)

Multi-anode

PMT (64 ch.)

Wave-length

shifting fiber

EM calorimeter

1.7m

3m

3m

Fully active

scintillator detector

(neutrino target HC)

Low thresholds

for protons and pions

and proton vs pion

particle ID via dE/dx

CC coherent pion selection

Resonant pion production

is scattering from nucleon

Coherent pion scatters

from entire nucleus.

No recoil nucleon (see only m- and p+)

Very low momentum transfer (low Q2, low angle).

Several recent experiments see disagreement

between data and expectation in very low Q2 region.

Does CC coherent pion contribute to disagreement?

m

n

p

n

p

m

proton

Reconstruct Q2 from the muon in CC samples

1. Assume CCQE kinematics,

get En and Q2 from pm and qm

get the “wrong answer” (too low)

for non quasi-elastic events

but this treat data and MC same

2. Still using CCQE kinematics

Divide into QE enhanced

and nonQE enhanced subsamples

3. Apply SciBar PID ability

to the non muon track to

separate protons and pions



p



CCQE candidate in SciBar



p





p

expected

CC coherent pion results

2trk CC QE

as a control sample.

Reconstructed Q2 for four sub-samples

Further purify expected CC coherent pion

reject events with a lot of vertex activity

Normalized by

total CC events

2-track nonQE pion-like

CC coherent pion results

Select the 113 events

with Q2rec < 0.1 (GeV/c)2

Coherent Pion content expected

21.1% efficiency 47.1% purity

Mesurement

relative to

all CC events

sCCcohp

sAll CC

= (0.04 0.29 stat syst) x 10-2

Compute

upper bound

< 0.60 x 10-2 (at 90% CL)

+0.32

-0.35

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sCCcohp

sAll CC

This is ~30% of Rein-Sehgal model

Largest systematics: sResonant Pion and pion reinteractions in carbon

M. Hasegawa, et al.,

Phys. Rev. Lett. 95 (2005)

Scintillating Fiber (SciFi) detector

To Muon Range

Detector

~1 degree angle resolution

Require muon in the

muon range detector

Pm > 600 MeV

Recoil proton threshold

is three layers in SciFi

Pp > 600 MeV

(so proton not always seen)

Neutrino interaction

Target is Water

in Aluminum tanks

(70% H2O, 22% Al, 8% HC)

ddq2(10-38cm2/(GeV/c)2)

Absolute

Quasi-elastic

Cross section

(includes normalization)

M

MA=1.2 GeV

MA=1.1 GeV

MA=1.0 GeV

MA=1.0 GeV

MA=1.1 GeV

MA=1.2 GeV

Q2(GeV/c)2

This analysis: Shape Only

Q2(GeV/c)2

Axial mass and shape of Q2 distribution

Measure Q2 for each event

still assuming QE interaction

Other model effects that change the shape

Free neutron (no Pauli Blocking)

210

kf = 225

235

MeV/c

Cut here

Pauli Blocking in (Fermi Gas) model

And CC Coherent Pion uncertainty

contribute at low Q2.

We exclude this region from the fit.

Ratio of sQE

new/dipole

form factors

QE cross section calculation also

depends on vector form factors.

We use updated form factors from

fits to electron scattering data.

These, plus a second axial mass

parameter (we take MA1p=1.1 GeV)

affect the nonQE background

Reconstructed Q2 for subsamples (after fitting)

~85% nonQE

(mostly single-pion)

Constrains relative size

of nonQE background

Fit shape of signal

Subsample division

(as in slides 9 and 10 but no PID)

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p





p

expected

60% QE

60% QE

One-track events

Two-track QE

Results for effective Quasi-elastic MA on Oxygen

MA = 1.20 0.12 GeV (c2 = 261/235 dof) shape only

Can be compared with Deuterium bubble chamber results

(primarily also shape fits) with older vector form factors

K2K result MA = 1.23 0.12 Deuterium MA ~ 1.03 0.03

Most significant errors:

Muon momentum scale	0.07

Relative flux and normalization	0.06

MA 1p	0.03

relative nonQE fraction	0.03

Nuclear rescattering	0.03

Statistics only	0.03

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Our data has a

flatter Q2 spectrum

than MC prediction

K2K default MC

uses MA=1.1 GeV

dipole vector form factors

RG, Jeon, et al., submitted to PRD, hep-ex/0603034

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Final neutrino oscillation results

using the K2K data

HARP hadron measurements

for new far/near extrapolation

Updated Super-Kamiokande reconstruction

Electron neutrino appearance analysis

now uses entire data set.

(Other smaller refinements)

Final electron appearance result

limit

sensitivity

one event observed

expected background 1.7 events

background consists of

1.32 from muon neutrinos

0.38 from beam electron neutrinos

Yamamoto, Zalipska, et al., PRL 96 (2006)

Upper limit (90%CL) sin22qme<0.13 at Dm2 = 2.8x10-3 eV2

(Two-flavor analysis)

Final nm disappearance result

All neutrino events in SuperK

Observed 112, expected 158

+9.2

-8.6

58 events

fully-contained

single-ring

muon-like

- no osc. shape

- best fit shape

Ahn, et al. sub. to PRD hep-ex/0606032

Final nm disappearance result

Ahn, et al. sub. to PRD hep-ex/0606032

All neutrino events in SuperK

Observed 112, expected 158

+9.2

-8.6

58 events

fully-contained

single-ring

muon-like

- no osc. shape

- best fit shape

(zoom in from previous slide)

Maximal mixing 90% CL

1.9 x 10-3 < Dm2 < 3.5 x 10-3 eV2

Best fit in physical region 2.8 x 10-3

Conclusions

Several cross section measurements:

Neutral Current single-pizero

Charged Current coherent pion

Shape of Quasi-elastic Q2 spectrum

Still some ongoing cross section work

Oscillation analyses are final,

papers available now.

2006-05-25T14:08:14