- Email: [email protected]
KARMEN νe → νx disappearance search in a 3 neutrino flavor analysis
Progress in Particle and Nuclear Physics PERGAMON
Progressin Particle and Nuclear
The 56 ton scintillation
ealcrimeter
Physics 40 (199X) 203 -204
KARMEN
at the beam stop neutrinosource
ISIS haa been used to search for neutrino oscillations in the disappearance channel v,*v..
The v, emitted in G+ decay at rest (DAR) are detected with spectro-
scopic quality via the exclusive charged current (CC) reaction “C ( uc ,e- ) “N,.,.. Analyi
of the spectralshape of e- from the v. induced reaction as well (UIa me+
aurement of the absolute v. flux allow to investigate oscillations of the type vc+ v, and v,-+ v,,. The flux independent ratio Rccl~c to NC events “C ( Y,
of CC events ‘*C (v, , e- ) “N,...
u’) lac’ provides additional information. All three methods
show no evidence for oscillations. data with respect to v.o
A complete 3 flavor analysis of the experimental
v, and v,tr v,, mixing is presented.
The KARMEN experiment is performed at the neutron spalIation facility ISIS. The neutrinos are produced by stopping 800 MeV protons in a heavy beam stop target, where they emerge from the DAR sequence 7r+-+ p++ Y,, and p+ --) e+ + v, + ij,,. The energy spectra of the v’s are well defined due to the DAR of both the ?r+ and $,
with I+ energies up to 52.8 MeV. Two parabolic proton pulses of
100 ns basis width and a gap of 225 ns are produced with a repetition frequency of 50 Hz. The different lifetimes of pions (T = 26 ns) and muons (r = 2.2 ps) ensure clear separation in time of the u,,-burst from the following v,‘s and fi,,‘s. The neutrinos are used to investigate neutrino-nucleus interactions and to search for neutrino oscillations [2]. For this purpose, a 56 t liquid scintillation
calorimeter
is
situated at a distance of 17.7m to the v production target. Electron neutrinos v. from p+ DAR are detected via the exclusive CC reaction 12C( I+ , e- ) 12Ng.a.. The Nitrogen decays (T = 15.9ms) at its production point: “N,...
+
12C + e+ + v,. The almost
background-free detection signature therefore consists of a prompt electron within a few ps after beam-on-target followed by a spatially correlated
positron.
The extracted e-e+ sequences from
data
taken in 1990-1995 are shown in [2]. Oscillations v.+ vz would result in a lower number of sequences than expected, since CC reactions on “C
cannot be induced by v, or u, due to the low neutrino
energies. In addition, the characteristic dependance in energy and distance of flavor oscillations would lead to a distortion of the electron energy and production point. The comparison of the number of CC sequences with the expectation from theoretical calculations is done on the basis of the extracted flux averaged cross section (u) for v,‘s from cc+ DAR. The I+ disappekrance oscillation probability Pv,+ v, can be written in terms of cross sections (~10~~~ cm2):
Py,+u, 0146-6410:98:%19.00 + 0.00 0 Ptl: SOl46-6410(98)00026-X
=l-
(“L (fl)t*
=I_
9.3 f 0.89 9.2f0.5
<
o 16g
*
1998 Elsevier Science BV. All rights reserved.
Printed
(1)
(90% CL) in Great
Britain
204
K. Eitelj bog.
Parr. Nzd. Pkys. 40 (1998) 203-204
Figure 1: limits to the mixing angles Cpand Q deduced from various oscillation channels of this experiment in comparison with other experiments: Bugey, FNAL I%31 and LSND (shaded). where the statistical and systematical errors of the experimental value [2] have been C&US: The
added
qua&a&
theoretical value represents the mean value of different calculations with a realistic estimate
of the systematic error.
In a 3 flavor ‘one mass scale dominance’ scheme of v oscillations in the
KARMEN ‘short baseline’ configuration, the oscillation probability is [I] Py, -+ u, = Pv,-+u,
+Pv,+u,
= 4(ain20cos2’%co&’
+ sin%cos2@sin2+).
~in~(1.27T,
(2)
The detection efficiency for I+-+ u, and u,+ u,, is different due to the experimental situation: In the case of uee, uI1mixing, e+e- sequences from “C ( & , e+ ) 12B arise from ii,,+ & oscillation of ii,, which are simultaneously produced in the ISIS target. These sequences mostly compensate the loss due to u,+ u,. However, applying a maximum likelihood (MLHD) analysis, tic-induced CC sequences can be separated from the usual 12C ( u, , e- ) 12Ng.#.events and from lacking sequences by u.+ u, due to the differences in energy and detection point of the prompt as well as energy and time difference of the sequential event. In such a shape analysis, the oscillation amplitudes in (2) are independent and free parameters of the MLHD fit. The combined analysis results in limits on ip and e for Am2 > 0.5eV2/c4. In figure 1 the obtained 90% CL limits are shown in comparison with other experimental results for a fixed value of Am2 = 2eV2/c4. The oscillation evidence by LSND has been recompiled in a combined fit [I] including negative results of other oscillation search experiments. A detailed description of this vc+ u, search is given in 13)with references therein.
References [l] G. Fogli et al., Phys. Rev. D 52 (1995) 5334 G. Fogli et al., Phys. Rev. D 56 (1997) 3081 (21 R. Maschuw, B. Zeitnitz, these proceedings [3] B. Armbruster et. al. (KARMEN Collaboration), to be published in Phys. Rev. C
Progressin Particle and Nuclear
The 56 ton scintillation
ealcrimeter
Physics 40 (199X) 203 -204
KARMEN
at the beam stop neutrinosource
ISIS haa been used to search for neutrino oscillations in the disappearance channel v,*v..
The v, emitted in G+ decay at rest (DAR) are detected with spectro-
scopic quality via the exclusive charged current (CC) reaction “C ( uc ,e- ) “N,.,.. Analyi
of the spectralshape of e- from the v. induced reaction as well (UIa me+
aurement of the absolute v. flux allow to investigate oscillations of the type vc+ v, and v,-+ v,,. The flux independent ratio Rccl~c to NC events “C ( Y,
of CC events ‘*C (v, , e- ) “N,...
u’) lac’ provides additional information. All three methods
show no evidence for oscillations. data with respect to v.o
A complete 3 flavor analysis of the experimental
v, and v,tr v,, mixing is presented.
The KARMEN experiment is performed at the neutron spalIation facility ISIS. The neutrinos are produced by stopping 800 MeV protons in a heavy beam stop target, where they emerge from the DAR sequence 7r+-+ p++ Y,, and p+ --) e+ + v, + ij,,. The energy spectra of the v’s are well defined due to the DAR of both the ?r+ and $,
with I+ energies up to 52.8 MeV. Two parabolic proton pulses of
100 ns basis width and a gap of 225 ns are produced with a repetition frequency of 50 Hz. The different lifetimes of pions (T = 26 ns) and muons (r = 2.2 ps) ensure clear separation in time of the u,,-burst from the following v,‘s and fi,,‘s. The neutrinos are used to investigate neutrino-nucleus interactions and to search for neutrino oscillations [2]. For this purpose, a 56 t liquid scintillation
calorimeter
is
situated at a distance of 17.7m to the v production target. Electron neutrinos v. from p+ DAR are detected via the exclusive CC reaction 12C( I+ , e- ) 12Ng.a.. The Nitrogen decays (T = 15.9ms) at its production point: “N,...
+
12C + e+ + v,. The almost
background-free detection signature therefore consists of a prompt electron within a few ps after beam-on-target followed by a spatially correlated
positron.
The extracted e-e+ sequences from
data
taken in 1990-1995 are shown in [2]. Oscillations v.+ vz would result in a lower number of sequences than expected, since CC reactions on “C
cannot be induced by v, or u, due to the low neutrino
energies. In addition, the characteristic dependance in energy and distance of flavor oscillations would lead to a distortion of the electron energy and production point. The comparison of the number of CC sequences with the expectation from theoretical calculations is done on the basis of the extracted flux averaged cross section (u) for v,‘s from cc+ DAR. The I+ disappekrance oscillation probability Pv,+ v, can be written in terms of cross sections (~10~~~ cm2):
Py,+u, 0146-6410:98:%19.00 + 0.00 0 Ptl: SOl46-6410(98)00026-X
=l-
(“L (fl)t*
=I_
9.3 f 0.89 9.2f0.5
<
o 16g
*
1998 Elsevier Science BV. All rights reserved.
Printed
(1)
(90% CL) in Great
Britain
204
K. Eitelj bog.
Parr. Nzd. Pkys. 40 (1998) 203-204
Figure 1: limits to the mixing angles Cpand Q deduced from various oscillation channels of this experiment in comparison with other experiments: Bugey, FNAL I%31 and LSND (shaded). where the statistical and systematical errors of the experimental value [2] have been C&US: The
added
qua&a&
theoretical value represents the mean value of different calculations with a realistic estimate
of the systematic error.
In a 3 flavor ‘one mass scale dominance’ scheme of v oscillations in the
KARMEN ‘short baseline’ configuration, the oscillation probability is [I] Py, -+ u, = Pv,-+u,
+Pv,+u,
= 4(ain20cos2’%co&’
+ sin%cos2@sin2+).
~in~(1.27T,
(2)
The detection efficiency for I+-+ u, and u,+ u,, is different due to the experimental situation: In the case of uee, uI1mixing, e+e- sequences from “C ( & , e+ ) 12B arise from ii,,+ & oscillation of ii,, which are simultaneously produced in the ISIS target. These sequences mostly compensate the loss due to u,+ u,. However, applying a maximum likelihood (MLHD) analysis, tic-induced CC sequences can be separated from the usual 12C ( u, , e- ) 12Ng.#.events and from lacking sequences by u.+ u, due to the differences in energy and detection point of the prompt as well as energy and time difference of the sequential event. In such a shape analysis, the oscillation amplitudes in (2) are independent and free parameters of the MLHD fit. The combined analysis results in limits on ip and e for Am2 > 0.5eV2/c4. In figure 1 the obtained 90% CL limits are shown in comparison with other experimental results for a fixed value of Am2 = 2eV2/c4. The oscillation evidence by LSND has been recompiled in a combined fit [I] including negative results of other oscillation search experiments. A detailed description of this vc+ u, search is given in 13)with references therein.
References [l] G. Fogli et al., Phys. Rev. D 52 (1995) 5334 G. Fogli et al., Phys. Rev. D 56 (1997) 3081 (21 R. Maschuw, B. Zeitnitz, these proceedings [3] B. Armbruster et. al. (KARMEN Collaboration), to be published in Phys. Rev. C