K2K Cross Section Studies

0. K2K experiment and NEUT interaction code

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

Rik Gran

U. Minnesota Duluth

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

K2K neutrino oscillation experiment

200m

fast extraction

every 2.2sec

beam spill width

1.1s ( 9 bunches )

~6x1012 protons/spill

Al target

12 GeV PS

K2K beamline at KEK in Tsukuba, Japan

Operated from 1999 to 2004

SciFi Water Target

K2K beam and near detectors

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

nm energies

at the K2K

near detectors

En (GeV)

The NEUT neutrino interaction model

Charged current quasi-elastic	n + N -> l + N'

Neutral current elastic	n + N -> n + N

CC/NC single p (h,K) resonance	n + N -> l(n) + N' + p

NC coherent pion (not CC !)	n + A -> n + A + p0

CC/NC deep inelastic scattering	n + q -> l(n) + had

/E (10-38cm2/GeV)

Total (NC+CC)

CC Total

CC quasi-elastic

DIS

CC single 

NC single 0

E (GeV)

Cross-sections

n	= neutrino (e, m or t)

l	= lepton (e, m or t)

From 100 MeV to 10 TeV

(cosmic ray induced neutrinos too!)

More about the interaction models

Quasi-elastic follows Llewelyn-Smith

using dipole form factors and MAQE = 1.1 GeV

(For neutrino beam, target is always neutron)

Resonance production from Rein and Sehgal

18 resonances, MA1p = 1.1 GeV

(Coherent pion production also from Rein and Sehgal)

Deep inelastic Scattering from GRV94

PYTHIA/JETSET for hadron final states

Bodek-Yang correction in Resonance-DIS overlap region

Nuclear Effects in the NEUT model

Fermi-gas model for interaction target C, O, Fe

nucleon momentum, Pauli blocked final states

Rescattering as hadrons leave interaction target

Pion rescattering, charge exchange, absorption

Proton rescattering

Hadron STARTS in the nucleus

not identical to hadron scattering experiments

use cascade model of Bertini, et al.

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.

Model issues related to the analysis

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

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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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%)

Coherent p+ production and very low Q2

Q2 < 0.1 (GeV/c)2

Plots below from SciBar detector

Seen also in SciFi detectors

2track

QE-like

2track

non-QE-like

1track

q2rec

q2rec

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

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

Still CCQE kinematics

Take events with

two tracks

Predict where the

recoil proton should be

Divide into

QE enhanced

nonQE enhanced

subsamples





CCQE candidate in SciBar





Produce enhanced non-QE subsamples

p

p

qp

qexpected

qm

Pion vs proton via dE/dx

 enriched

Proton

enriched

Proton

Pion

Others

103

102

10

Likelihood

Average dE/dx

from data

(muon and

proton)

Apply SciBar PID ability

to the non-muon track to

separate protons and pions

CC coherent pion subsamples

Reconstructed Q2 for four sub-samples

Normalized by

total CC events

2trk CC QE

as a control sample.

Further purify expected CC coherent pion

reject events with a lot of vertex activity

2-track nonQE pion-like

Vertex activity cut

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)

Progress since then

Two recent examples

(not the only work on the topic)

Lalakulich and Paschos, hep-ph/0501109

Rein and Sehgal, hep-ph/0606185

Muon mass must be included in

Charged current p+ interactions.

Gives rise to some cancellation

at low Q2 for these energies

Quasi-elastic Axial Form Factor studies

and quasielastic axial mass parameter

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)

Some basic distributions from SciFi

No MA fitting yet

Uses best fit flux from

fits to all K2K

near detector data

hep-ex/0606032

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

Subsample division



p





p

expected

Muon angle again, divide into subsamples

No MA fitting yet...

One-track events

Two-track QE

Two-track non-QE

60% QE

60% QE

Reconstructed Q2 for subsamples (after fitting)

~85% nonQE

(mostly single-pion)

Constrains relative size

of nonQE background

Fit shape of signal

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

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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K2K default MC

uses MA=1.1 GeV

dipole vector form factors

Our data has a

flatter Q2 spectrum

than MC prediction

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

Compare with results on Deuterium

Reslts from bubble chamber experiments

(Primarily also shape fits)

Deuterium MA ~ 1.03 0.03

But they use “Olsson, et al.” vector form form factors

Rerun the K2K-SciFi analysis with their assumptions

in order to make comparison

K2K result MA = 1.23 0.12

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In agreement at the 2-sigma level

More about the relevant Q2 region

Calculation by

Nakamura + Seki

Compare 1 GeV QE

for free neutron

and in oxygen

(Fermi gas model)

Ratio Fermi gas/free

Slope here

affects MA extraction

My list of interesting questions

Should nuclear effects modify the Q2 distribution?

At what level?

(or is the 2-sigma discrepancy due to experiment?)

This result is from a shape fit.

What if normalization information is available?

Can we extract information about very-low Q2?

We should not expect a dipole axial form factor?

Compare cross sections for Iron and Water

Muon Range Detector is made of iron

The Cerenkov detector is made of water

Compare these two high-rate detectors

to learn about the iron/water cross section

Muon Range Det. (Data/MC)

Water Cerenkov (Data/MC)

=1.04

+0.08

-0.11

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0.003

stat.

Beam and spectrum systematics partially cancel.

Fiducial mass errors are significant (-6%)

Because of different energy thresholds

neutrino model errors do NOT cancel perfectly ~5%

In M.H. Ahn, et al., hep-ex/0606032

Conclusions

K2K neutrino interaction results

with modest precision.

Systematic errors are dominating.

Mix of model errors and detector errors

depending on the study

The models we use

do not produce great agreement with these data

there is a need for improvement

E (MeV)

NC elastic

MC is normalized

by area

Data

MC

Neutral Current Elastic Scattering

in the 1kT Water Cerenkov detector

n+p -> n+p

recoil proton not seen if below Cerenkov threshold

Look for 6.32 MeV de-excitation gamma from 16O

Important for oscillation experiments

elastic scattering separates nt from ns hypothesis

Also of interest for proton decay experiments

Other topics

Gammas from de-excitation of target nuclei is

simulated.

In K2K experiments, Carbon target & Fe target

interaction are also simulated.

Fermi momentum

(225MeV250MeV for Fe, no change for C)

proton/neutron ratio is tuned.

Cross section for coherent p production depend

Atomic number, and it is taken into account.

Nuclear effects are not modified for C and Fe.

We checked the systematics from this

approximation is small for K2K FD detectors.

Final kinematics for DIS is determined by

JETSET 7.4 package. (W> 2GeV/c2)

For low W region (1.3GeV/c2 < W < 2.0 GeV/c2),

our original codes is used.

pion multiplicity is determined from

experimental results and KNO scaling.

5. Deep Inelastic scattering

ν + N  l + hadrons

Cross section is calculated by GRV94(DIS) PDF.

Correction for small q2 region is taken into account.

(for K2K experiment, (A.Bodek et al., Nucl Phys.Proc.. Suppl. 112.70-76.2002) )

νμ + N  μ- + X

νμ + N  μ+ + X

4. Coherent pion production

Based on J.Marteau, et al. (Nucl. Inst. Meth. A451,76(2000))

ν + 16O ν + 16O + π0

+

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ν + 16O l + 16O + π±

( )

( )

( )

Eν (GeV)

ν + 16O ν + 16O + π0

ν + 16O μ- + 16O + π^

CC QE

CC 1

CC coherent

Scattered angle of the outgoing

Lepton is small for

coherent  production

 between  and l (deg.)

E = 1GeV

Pionless decay of the resonances is taken into account.

Δ(N*)+ N  N’ + N’’

20% of delta resonances in oxygen are killed.

( M.Hirata et al., Ann.Phys. 108(1977) )

Pion,K,interactions in nuclear are considred.

The pion’s cross section is calculated by a model by L.Salcedo et al. .

(Nucl. Phys. A484(1998) 79)

Scattering, absorption, charge exchange, pion productions are considered.

ex0 survives about

40% at p= 300 MeV/c

Nuclear effects are important

for0 production rate, which

is the background source for

e appearance search .

3. Single meson production via resonances

Based on

D.Rein, and L.M.Sehgal,

Ann. of Phys. 133(1981)

Resonant production

amplitude is calculated

by FKR model.

(Phys.Rev.D3 2706(1971))

Up to W = 2GeV/c2

Resonances are taken

Into account.

(18 resonances)

ν + N  l + N’ + π(K、η)

νμ + ｎ  μ- + p + π+

νμ + ｎ  μ- + Δ++

νμ + ｎ  μ- + p + π+

νμ + ｎ  μ- + p + π+

EGeV)

EGeV)

Angular correlation

Angular correlation between

neutrino and outgoing lepton

become better as Ebecome

higher

ldegree at 1GeV

l



l

Free nucleon

Bound nucleon

+ p + + n

e+ p e+ + n

Fermi momentum of target nucleon

(fermi gas model with Pf = 225 MeV/c )

Pauli blocking effects (Pf = 225 MeV/c)

Nuclear potential (V= -26MeV ,fixed potential)

are taken into account.

Cross sections

are suppressed

~ 20% at 1GeV.

2. Charged Current Quasi elastic scattering

ν + N  l + N’

Based on

C.H.L. Smith,

(Phys. Rep. 3,261(1972))

For bound nucleon effects,

R.A.Smith et al.,

(Nucl.Phys.B43 605(1972)

Axial vector mass (MA) =1.1GeV2

Dominant interaction

at Eν<1GeV region.

Important interaction

to measure neutrino energy in

long baseline experiments.

νμ + n  μ- + p

νμ + p  μ+ + n

(+ n - + p)

Charged Current Quasi-Elastic scattering

is very useful to measure the neutrino energy spectrum.

Importance of neutrino interaction studies

To search for the e appearance in the  oscillation experiments,

0 productions will be one of the major backgrounds.

It is important to understand

the neutrino induced  productions

and  interactions in nucleus.

However,  interacts in nucleus.

Asymmetric 0 decay event looks like e appearance signal.

(Energetic  looks like

e from e charged current interaction.)

Because of this, some of the single  production events

looks like CC quasi-elastic events.

2006-05-25T14:08:14