JPARC beam profile and asymmetries

A.Meregaglia, A.Rubbia (ETH Zürich)

¸ Study of neutrino fluxes in Korea at different off-axis angles and locations.

¸ Study of the JPARC beam profile.

¸ Study of beam asymmetries including possibility to monitor them with different

detectors.

Outline

Korea fluxes

¸ Using the jnubeam simulation of the

JPARC beam, neutrino fluxes have been

calculated at different locations in Korea.

¸ Assume 2.5 deg off-axis @ SK (3 deg no

more possible)

¸ Ntuples were produced for neutrino and

antineutrino polarity of horn.

¸ Data can be found at:

http://neutrino.ethz.ch/GLACIER/internal/

ntuples/

Chosen tentative locations

¸ Neutrino fluxes and events have been calculatedand used in some sensitivities studies carriedout (see A.Rubbia’s talk).

¸ Events with energy below 4 GeV at variouslocations for a 100 kton LAr detector, for 1E+21p.o.t.

Event rates¸ More events for smaller off-axis angles (as

expected)

¸ !e/!µ ratio improves at smaller off-axis angles

¸ Antineutrino run has !2.5:1 contamination of

wrong helicity neutrinos

Spectra (flux)

Spectra (events)

Beam profile: how precisely can

the beam be determined at far

location?

Take SK & 2km as example

¸ The shape of the decay tunnel is expected to break circular symmetry but not Left-Right symmetry.

¸ The vertical opening angle is 2.41 degrees and the horizontal one is 1.32 degrees. These angles are

not negligible compared to the off-axis angle of 2.5 degrees. Important issue for high energy tail i.e.

neutrinos coming from pions going “towards” the detector.

T2K decay tunnel shape

3m

5.48m

!

Beam profile

130m

Decay tunnel

( Original dimensions,

now shorter but same shape ) Positions with the

same off axis angle

but different flux.

y

x

Detectors used to study asymmetry

SK2km

“2kmSX”

Beam centre

y

x

Beam

axis

SK295 km

2km2 km

target

"

"

FRONT VIEW TOP VIEW

“2kmSX”

Left/right symmetry

±10%

Flux(_/cm2/50MeV/1021p.o.t.)

(2km - SK)*100/SK (%)

2km

SK

¸ The beam is left/right symmetric as it can

be seen by the ratio between the fluxes at

2km detector and SK.

¸ This symmetry was expected since the

decay tunnel is left/right symmetric.

Circular symmetry

±10%

¸ The evidence that the beam does not have

a circular symmetry comes from the ratio

between the flux seen at two detectors

located at 2km (1839m), 2.5 degrees off-axis but at a different _ (not symmetric

respect to the vertical axis).

¸ The problem is mainly related to high

energy neutrinos (i.e. neutrinos above peak)

coming from pions going “towards” the

detector.

Flux(_/cm2/50MeV/1021p.o.t.)

(2km - “2kmSX”)*100/ “2kmSX” (%)

2km

“2kmSX”

Detection of beam asymmetries

¸ The 280m on axis detector (NGRID) is a

cross 10 m large and 10 m high; each

module (7 in a row) has a 1m x 1m area

and a mass of 5 ton.

¸ The beam monitors are located at 11.61

m in Y direction (level of SK) and 3.05 m

(- 3.05 m) in X direction (position of ND5).

The mass is 5 ton (in the simulation).

Beam centre (0,0) Y

X

Beam monitors (3.05 m,11.61 m)

1 m 1 m

1 m1 m

Detectors to monitor asymmetry

Expected events

CROSSmodule 1

(1m x 1m, 5 ton)

module 2

(1m x 1m, 5 ton)

module 3

(1m x 1m, 5 ton)

module 4

(1m x 1m, 5 ton)

X direction

(from centre

outward)

411000 380000 302000 212000

Y direction

( from centre

outward )

411000 386000 317000 233000

1E+20 proton on target.

Considered only events with energy less than 5 GeV.

BEAM MONITOR (1m x 1m, 5 ton) 41000

About 8 times less with respect

to the 280m on axis detectors.

¸ The Left/Right asymmetry has been studied for a shift of the protons on target

and for a shift of the horn number 2, as a function of the position of the beam

monitor detectors.

¸ The X position was fixed (i.e. ±3.05 m which is the same value of 280m off axis

detector).

¸ The Y position spanned from 0 m (beam centre level) to 13 m.

¸ NOTE: Only for this study the mass of the detectors was set to 1 ton and the

p.o.t. used was 1E+21.

Asymmetry as a function of position

HEIGHTANGLE

(deg)LEFT RIGHT L-R/R(%)

0 cm 3.637 577312 628997 -8.2

100 cm 3.432 561269 608693 -7.8

200 cm 3.228 516417 558876 -7.6

300 cm 3.023 451046 488588 -7.7

400 cm 2.819 378654 407893 -7.2

500 cm 2.614 307295 333043 -7.7

600 cm 2.409 248373 266026 -6.6

700 cm 2.205 198908 210370 -5.4

800 cm 2.000 160777 166148 -3.2

900 cm 1.796 130273 135107 -3.6

1000 cm 1.592 106043 109149 -2.8

1100 cm 1.387 89041 91377 -2.5

1200 cm 1.183 74278 76412 -2.8

1300 cm 0.979 63444 64455 -1.6

Test beam monitor at different heights

Shift protons 3mm left

On axis detector Beam monitors

Effect about 3 times

less with respect to

the on axis detectors.

Test beam monitor at different heights

Shift horn2 3mm left

On axis detector Beam monitors

HEIGHTANGLE

(deg)LEFT RIGHT L-R/R(%)

0 cm 3.637 603047 587743 2.7

100 cm 3.432 585755 570246 2.7

200 cm 3.228 538785 524597 2.7

300 cm 3.023 472141 459467 2.8

400 cm 2.819 397316 386675 2.8

500 cm 2.614 322595 313539 2.9

600 cm 2.409 258130 251286 2.7

700 cm 2.205 205475 202006 1.7

800 cm 2.000 165173 162417 1.7

900 cm 1.796 133728 131858 1.4

1000 cm 1.592 109643 108034 1.5

1100 cm 1.387 91281 89873 1.6

1200 cm 1.183 76539 75837 0.9

1300 cm 0.979 64468 64160 0.5

Effect about 3 times

less with respect to

the on axis detectors.

¸ Both in case of shift of the protons on target and shift of the horn, there is a

“definite” trend of the L/R asymmetry as a function of the height.

¸ At the height of the beam monitor the asymmetry is less visible and there is

about a factor 3 on the effect both for shifting of the protons and of the horns.

¸ The effect is smaller at larger values of Y since it depends on the difference on

the radial distance from the beam centre between L and R position. This

difference gets smaller the bigger the vertical Y coordinate is.

Remarks

¸ The possibility to detect beam asymmetries using the on axis detector (cross) andthe beam monitors has been investigated.

¸ In the measurement using the on axis detector, the beam profile on the X axis ismeasured with 7 detectors. The number of events in each one is measured and the 7points are fitted with a Gaussian function.

¸ The error on the number of events measured in each detector is a sum of the realstatistical one, the MC statistical one and 10% systematics due to intercalibration ofthe modules.

¸ In the measurement using the beam monitors, the Left/Right asymmetry between thetwo detectors is measured.

¸ The error on the number of events measured in each detector is a sum of the realstatistical one and the MC statistical one. No systematics has been included(Possibility to use one detector and slide it from left to right position?).

Detection of beam asymmetries

Asymmetry = 0.03 %

Systematics = 10% # error = 18.6 cm

Systematics = 5% # error = 9.7 cm

Systematics = 2% # error = 3.9 cm

Beam Centred

On axis detector Beam monitor

The sensitivity on beam asymmetries is strongly

dependent on the systematics due to the

intercalibration between the different modules.

Asymmetry = -3.0 %

Given the error on the mean as a function of the

systematics and a mean of about 18 cm for a shift

of the beam of 3mm, the error on the

intercalibration must be smaller than 10%.

Beam Shifted 3mm left

On axis detector Beam monitor

Asymmetry = 1.7 %

Given the error on the mean as a function of the

systematics and a mean of about 30 cm for a shift of

the horn1 of 3mm, there is not a strict constraint on

the error on the intercalibration. However, it should

be smaller than 15%.

Horn1 shifted 3mm left

On axis detector Beam monitor

Asymmetry = 1.3 %

Given the error on the mean as a function of the

systematics and a mean of about 6 cm for a shift

of the horn2 of 3mm, the error on the

intercalibration must be smaller than 5%.

Horn2 shifted 3mm left

On axis detector Beam monitor

Asymmetry = 1.2 %

Given the error on the mean as a function of the

systematics and a mean of about 4 cm for a shift

of the horn3 of 3mm, the error on the

intercalibration must be smaller than 5%.

Horn3 shifted 3mm left

On axis detector Beam monitor

¸ The intercalibration of the different modules of the 280 m on axis detector plays animportant role on the beam shifts sensitivity.

¸ In order to appreciate the difference given by a shift of the beam of 3mm the systematicon the intercalibration must be less than 10%, for a shift of the horn2 and 3 by 3mm itmust be less than 5%.

¸ As far as the beam monitors are concerned, no systematic on intercalibration has beenincluded, but it must be below 2% to appreciate a shift of the beam of 3mm and below 1%to detect a shift of the horns by 3mm.

¸ Since at the height of the BM the changes due to proton shifts on target are about 3%,the change of the ratio between fluxes at 2km and SK detector should not be too large(see next slide).

¸ Since at the height of the BM the changes due to horns shifts are about 1.5%, thechange of the ratio between fluxes at 2km and SK detector should be negligible (see nextslide).

Remarks

±10%

Fluctuations related to low MC statistics

Beam Centred Beam shifted 3mm right

2km

SK

2km

SK

2km

SK

Horn2 shifted 3mm right

Flux ratio comparisons

¸ The expected fluxes and rates in Korea for various tentative locations at different off-axis angleshave been calculated.

¸ Neutrino and antineutrino horn polarities have been calculated.

¸ Ntuples are available on the web.

¸ Neutrino(antineutrino) polarity provide !3%(!40%) contamination from wrong-helicity.

¸ Electron neutrino contamination increases for increasing off-axis angle.

¸ Given the non-circular shape of the decay tunnel, the fluxes at a “given off-axis angle” dependon the actual chosen location (“around the ellipse”). Hence, being at the same off-axis anglein SK and Korea does not imply same neutrino flux!

¸ In order to precisely (<<±10%) predict flux in Korea, beam properties in Tokai must be carefullymonitored with e.g. NGRID and L/R monitors at 280m and 2km detectors.

Conclusions