χϡʔτϦϊ‫ݕ‬ग़‫ث‬ԣࢁ কࢤʢ౦‫ژ‬େֶେֶӃཧֶ‫ڀݚܥ‬Պ෺ཧֶઐ߈ʣ

1δཧ࿦Ͱ‫ه‬ड़͢Δɻ෺࣭ߏ੒ཻࢠͰ͋ΔΫΥʔΫ͸͡Ίʹ೔ຊͰͷχϡʔτϦϊͷ‫ڀݚ‬͸̎౓ͷϊʔϕϧ෺ཧֶ৆ [1, 2] ͕৅௃͢ΔΑ͏ʹ਺ʑͷ੒ՌΛ͓͋͛ͯΓɼ͍·΍೔ຊͷ͓Ոܳͱ‫ݺ‬͹ΕΔ͜ͱ΋͋ΔɻχϡʔτϦϊͷ࣮‫ݧ‬త‫ʹڀݚ‬͸χϡʔτϦϊΛ‫ݕ‬ग़͢Δ૷ஔ͕ඞཁͰ͋Γɼͦ͜ʹ͸࠷ઌ୺ͷٕज़͕࢖ΘΕ͍ͯΔɻͦΕΒΛ঺հ͢Δͷ͕ຊߨٛͷ໨తͰ͋Δɻͨͩɼͻͱͪ͘ʹχϡʔτϦϊ‫ݕ‬ग़‫ث‬ɼͱ‫ͬݴ‬ͯ΋ɼχϡʔτϦϊͷؔΘΔ࣮‫ݧ‬͸෯޿͘ɼͦΕʹରԠͯ͠‫ݕ‬ग़‫ʹث‬΋༷ʑͳछྨ͕͋Δ 1 ɻ͜ͷߨٛͰ͸χϡʔτϦϊ࣮‫ݧ‬ͷུ֓Λ؆୯ʹड़΂ͨ‫ޙ‬ɼχϡʔτϦϊ‫ݕ‬ग़‫ث‬ͷதͰ΋ɼಛʹεʔύʔΧϛΦΧϯσͱ T2K ࣮‫ݧ‬ͷલஔ‫ݕ‬ग़‫ث‬Λத৺ʹઆ໌͢Δ͜ͱʹ͢Δɻ

ͱϨϓτϯ͸εϐϯ 12 Λɼ૬‫༻࡞ޓ‬Λ఻͑Δήʔδཻࢠ͸εϐϯ̍Λ࣋ͭɻ͞Βʹɼૉཻࢠʹ࣭ྔΛ༩͑Δ‫ͯ͠ͱߏػ‬ରশੑͷࣗൃతഁΕʹΑΔώοάε‫͕͋ߏػ‬Δɻώοάε‫ߏػ‬ͷ‫ͯ͠ͱ݁ؼ‬ଘࡏ͕༧‫͞ݴ‬Ε͍ͯͨεϐϯ̌ͷώοάεཻࢠ͕

LHC Ͱͷ࣮‫͞ݟൃͰݧ‬Εͨ͜ͱ͸‫ه‬Աʹ৽͍͠ɻ‫ࡏݱ‬஌ΒΕ͍ͯΔΫΥʔΫͱϨϓτϯΛද 1 ʹ·ͱΊΔɻిՙ΍ɼͲͷ૬‫͢༻࡞͕༻࡞ޓ‬Δ͔ͱ
͍͏෼ྨ΋ࣔͨ͠ɻ‫͍ڧ‬૬‫͕༻࡞ޓ‬ಇཻ͘ࢠΛΫΥʔΫɼಇ͔ͳཻ͍ࢠΛϨϓτϯͱ෼ྨ͢ΔɻχϡʔτϦϊ͸‫͍ڧ‬૬‫͕༻࡞ޓ‬ಇ͔ͳ͍Ϩϓτϯ
Ͱ͋Δ্ʹిՙΛ࣋ͨͳ͍ͨΊి࣓૬‫༻࡞ޓ‬΋ؔ༩ͤͣɼऑ͍૬‫༻࡞ޓ‬ͷΈͰ൓Ԡ͢Δ͜ͱ͕େ͖
ͳಛ௃Ͱ͋ΔɻΫΥʔΫ΋Ϩϓτϯ΋ɼ࣭ྔҎ֎͸ಉ͡ੑ࣭Λཻ࣋ͬͨࢠͷϖΞ͕̏ͭ‫܁‬Γฦͯ͠
ଘࡏ͢Δ͜ͱ͕Θ͔͓ͬͯΓɼ͜ΕΛੈ୅ߏ଄ͱ

2χϡʔτϦϊͱ͸‫Ϳݺ‬ɻͳͥੈ୅͕ଘࡏ͢Δͷ͔͸ɼΘ͔͍ͬͯͳ

2.1

ૉཻࢠ෺ཧʹ͓͚ΔχϡʔτϦϊɼλ΢χϡʔτϦϊʢντ ʣϛϡʔχϡʔτϦϊʢνμ ʣ͍ɻχϡʔτϦϊʹ͸ɼిࢠχϡʔτϦϊʢνe ʣɼ·ͣɼଌఆର৅ͱͳΔχϡʔτϦϊͱ͸Կ͔ɼͷ̏छྨ͕ଘࡏ͢ΔɻχϡʔτϦϊ͸ɼ‫ݩ‬ʑ์ࣹੑಉҐ‫ݩ‬ૉͷϕʔλʹ͍ͭͯ؆୯ʹड़΂Δɻ‫ݱ‬୅ͷૉཻࢠ෺ཧֶͷඪ४໛‫Ͱܕ‬͸ɼཅࢠ΍தੑࢠΛߏ੒͢ΔʮΫΥʔΫʯͱɼిࢠ΍χϡʔτϦϊͷ஥ؒͰ͋ΔʮϨϓτϯʯΛ෺࣭ͷߏ੒ཁૉͱ
ʮऑ͍૬‫ޓ‬͠ɼͦͷؒʹಇ̏͘छྨ 2 ͷ૬‫༻࡞ޓ‬ʢ࡞༻ʯɼʮి࣓૬‫༻࡞ޓ‬ʯɼʮ‫͍ڧ‬૬‫༻࡞ޓ‬ʯʣΛήʔ่յͰΤωϧΪʔอଘଇΛຬͨͨ͢Ίʹ 1930 ೥ʹύ΢ϦʹΑͬͯԾઆͱͯ͠ಋೖ͞Εͨ΋ͷͰ͋Δɻͦͷ౰ॳ͔ΒɼχϡʔτϦϊͷ࣭ྔ͸ඇৗʹখ͍͜͞ͱ͕Θ͔͍ͬͯͨɻ1950 ೥୅ʹχϡʔτϦϊ͕࣮‫ݧ‬తʹ‫؍‬ଌ͞ΕͯҎ߱ɼχϡʔτϦϊͷ࣭ྔΛଌఆ͢ΔࢼΈ͸ଓ͚ΒΕ͍ͯΔ͕ɼ‫ࡏݱ‬1χϡʔτϦϊ࣮‫Ͱݧ‬΋χϡʔτϦϊΛ‫ݕ‬ग़͠ͳ͍‫ݕ‬ग़‫ث‬΋͋Δɻ
2
ॏྗ૬‫༻࡞ޓ‬͸ඇৗʹখ͍ͨ͞Ί௨ৗߟྀ͠ͳ͍͕ɼॏ
ྗΛૉཻࢠͷཧ࿦ʹ૊ΈೖΕΔ͜ͱ͸ΞΠϯγϡλΠϯҎདྷ௕೥ͷ՝୊Ͱ͋Δɻ·Ͱ࣮‫ݧ‬஋͸ଌఆ‫ࠩޡ‬ͷൣғͰ 0 ͱແໃ६Ͱ͋
Γɼ্‫ݶ‬஋͔͠஌ΒΕ͍ͯͳ͍ 3 ɻ͜ͷͨΊɼඪ

㸶㸫 

3

ա‫ʹڈ‬͸͍͔ͭ͘༗‫ݶ‬஋Λใࠂ࣮ͨ͠‫ݧ‬΋͋Δ͕ɼ͍ͣද 1: ૉཻࢠඪ४໛‫ܕ‬ͷϑΣϧϛΦϯͷ෼ྨ
ిՙ

+ 23
− 12
−1
0

ΫΥʔΫ
Ϩϓτϯ

ୈ̍ੈ୅
uʢΞοϓʣ
dʢμ΢ϯʣ
eʢిࢠʣ
νe

ཻࢠ
ୈ̎ੈ୅
cʢνϟʔϜʣsʢετϨϯδʣμʢϛϡʔʣ
νμ࣭ྔ্‫ݶ‬஋ిࢠ‫ܕ‬ϛϡʔ‫ܕ‬
λ΢‫ܕ‬ɹ

2 eV
190 keV18.2 MeVऑ͍૬‫༻࡞ޓ‬
˓˓˓˓ి࣓૬‫༻࡞ޓ‬
˓
˓
˓
ʷ

‫͍ڧ‬
૬‫༻࡞ޓ‬˓˓ʷʷ‫ڀ‬ΛਐΊɼඍখͳχϡʔτϦϊ࣭ྔͷഎ‫͋ʹޙ‬Δ

ද 2: χϡʔτϦϊ࣭ྔͷ্‫ݶ‬஋ [3]ɻछྨୈ̏ੈ୅tʢτοϓʣbʢϘτϜʣτ ʢλ΢ʣ
ντ෺ཧΛղ͖໌͔͢͜ͱ͕χϡʔτϦϊ෺ཧͷେ͖ͳ໨ඪͷͻͱͭͰ͋Δɻ

2.2

χϡʔτϦϊ‫ݯ‬χϡʔτϦϊͷ‫ʹڀݚ‬͸େྔͷχϡʔτϦϊ͕ඞཁͱͳΔͨΊɼ‫ͳྗڧ‬χϡʔτϦϊ‫ݯ‬͸ɼχϡʔ४໛‫Ͱܕ‬͸௕Β͘χϡʔτϦϊͷ࣭ྔ͸ 0 ͱͯ͠τϦϊ‫ݕ‬ग़‫ͱث‬ฒΜͰ‫ʹڀݚ‬ඞਢͷཁૉͰ͋ΔɻѻΘΕ͖ͯͨɻ

Ͱ͸ɼχϡʔτϦϊͷൃੜ‫ʹݯ‬͸ͲͷΑ͏ͳ΋ͷχϡʔτϦϊৼಈͷଘࡏʹΑΓχϡʔτϦϊͷ

͕͋ΔͩΖ͏͔ɻ

࣭ྔ͕θϩͰͳ͍͜ͱ͸Θ͔͕ͬͨɼχϡʔτϦిࢠ΍ཅࢠʹൺ΂ͯ΋Ұൠʹ͸͓ͦΒ͘ͳ͡Έϊ࣭ྔͰଌఆͰ͖Δͷ͸࣭ྔͷ͚ࠩͩͰ͋Γɼઈͷ͏͍͢χϡʔτϦϊͱ͍͏ཻࢠ͕ͩɼӉ஦શମର஋ʹ͍ͭͯ͸ଞͷखஈͰଌఆ͢Δඞཁ͕͋ΔɻͰΈΔͱɼޫࢠʢӉ஦ϚΠΫϩ೾എ‫ࣹ์ܠ‬ɼCMBʣද 2 ʹɼParticle Data Group [3] ʹΑΔ 2015 ೥ʹ͍࣍Ͱଟ͘ଘࡏ͢ΔɻӉ஦ʹ͓͚ΔχϡʔτϦ࣌఺ͷχϡʔτϦϊ࣭ྔͷ্‫ݶ‬஋Λࣔ͢ɻτϦνϊͷ਺͸ɼཅࢠͷ਺ͷ࣮ʹ 109 ഒʹ΋ͳΔɻͦ

΢Ϝͷ่յͰ์ग़͞ΕΔిࢠͷΤωϧΪʔ෼෍ͷͷ΄ͱΜͲ͸Ӊ஦ॳ‫ʹظ‬ੜ੒͞ΕͨχϡʔτϦ୺఺Λਫ਼ີʹଌΔ͜ͱͰಘΒΕͨʢ൓ʣిࢠχϡʔϊͰ͋Δ͕ɼզʑʹΑΓ਎ۙͳχϡʔτϦϊ‫ݯ‬τϦϊͷ࣭ྔ 4 ͷ্‫ݶ‬஋͸ 2 eV Ͱ͋Γɼχϡʔτͱͯ͠͸ɼଠཅ͕͋Δɻଠཅ಺෦Ͱ͸ɼྫ͑͹Ϧϊͷ࣍ʹ࣭ྔͷখ͍͞ిࢠͷ࣭ྔ͕ 511 keV Ͱ

4p → 4 He + 2e+ + 2νe ͷΑ͏ͳ֩༥߹൓Ԡ͕‫ى‬

͋Δ͜ͱΛߟ͑Δͱɼ25 ສഒҎ্ͷ͕ࠩ͋Δ͜ͱ

͓ͬͯ͜Γɼ͜ͷͱ͖ిࢠχϡʔτϦϊ͕ੜ੒͞ʹͳΔɻͳͥɼχϡʔτϦϊͷ࣭ྔ͕ଞͷૉཻࢠ

ΕΔɻଠཅͰ͸ലେͳΤωϧΪʔ͕ੜ੒͞Ε͍ͯʹൺ΂‫ʹ୺ۃ‬খ͍͞ͷ͔ɼ͸େ͖ͳಾͰ͋Δɻଞ

ΔͨΊɼ͔ͦ͜Β߱Γ஫͙χϡʔτϦϊͷ਺͸஍ͷૉཻࢠͷ࣭ྔͷ‫ݯى‬͸ώοάε‫ʹߏػ‬ΑΔ΋ͷ‫Ͱ্ٿ‬΋ 660 ԯ‫ݸ‬/ඵ/cm2 ͱ͍͏๲େͳ਺Ͱ͋

Ͱ͋Δ͜ͱ͕֬ೝ͞Εͭͭ͋Δ͕ɼ΋͔͢͠Δͱ

Δɻ·ͨɼӉ஦ઢͱେ‫ؾ‬ͷিಥͰ΋ઈ͑ͣχϡʔχϡʔτϦϊʹ͸ଞͷ࣭ྔ֫ಘ‫͕ߏػ‬ಇ͍͍ͯΔ

τϦϊ͕࡞ΒΕ͍ͯΔɻͦͷଞʹɼ௒৽੕രൃ౳

ͷͰ͸ͳ͍͔ɼͱ͍͏Ծઆ΋͋Δɻͦͷ୅දతͳͷఱମ‫ݱ‬৅΍์ࣹੑ෺࣭ͷ่յͰ΋χϡʔτϦϊ΋ͷͱͯ͠ɼγʔιʔ‫͕ߏػ‬஌ΒΕ͍ͯΔ [4–7]ɻ

͸ੜ੒͞ΕΔʢਓମ΋์ࣹੑಉҐ‫ݩ‬ૉΛ‫ؚ‬ΉͨΊɼࠓ‫ޙ‬ɼχϡʔτϦϊৼಈ΍μϒϧϕʵλ่յͷ‫ݚ‬͋ͳͨ΋χϡʔτϦϊ‫͋Ͱݯ‬Δͱ‫͑ݴ‬Δʣɻ·ͨɼ‫࢖ʹڀݚ‬ΘΕΔਓ޻తͳχϡʔτϦϊ‫ͯ͠ͱݯ‬୅Ε΋ͦͷ‫ޙ‬ͷ௥ࢼͰ൱ఆ͞Εͨɻ
4ਖ਼֬ʹ͸ɼ࣭ྔ‫ݻ‬༗ঢ়ଶͰ͸ͳ͍ͷͰɼࠞ߹ߦྻཁૉʹΑΔॏΈ͖ͭฏ‫ʹۉ‬૬౰͢Δɻ

දతͳ΋ͷʹɼ‫ࢠݪ‬࿍΍Ճ଎‫͕͋ث‬Δɻ㸶㸫 χϡʔτϦϊͷ൓Ԡ͸ɼऑ͍૬‫༻࡞ޓ‬Λհ͠ℓ–ͯͷΈ‫͜ى‬Δɻऑ͍૬‫ʹ༻࡞ޓ‬͸ɼେ͖͘෼͚ͯ

W ± ཻࢠ͕ഔհ͠ ൓Ԡͷલ‫ిͰޙ‬ՙ͕มΘΔ ՙ

Z

W
荷電カレント(CC)反応

中性カレント(CC)反応ిΧϨϯτ൓Ԡ (Charged Current, CC) ͱɼZ 0ཻࢠ͕ഔհ͠ ൓Ԡͷલ‫ࢠཻͰޙ‬ͷిՙ͕มΘΒͳ͍ தੑΧϨϯτ൓Ԡ (Neutral Current, NC) ͷ̎छྨ͕͋ΔɻՙిΧϨϯτ൓Ԡͷ৔߹ɼχϡʔτϦϊ͕൓Ԡ͢ΔͱରԠ͢ΔՙిϨϓτϯʢిe-e- or νN
N’
標的：核子（クォーク）
標的：電子ࢠχϡʔτϦϊͰ͋Ε͹ిࢠʣʹͳΔ͕ɼதੑΧϨϯτͰ͸χϡʔτϦϊ͸ऴঢ়ଶͰχϡʔτϦ
ϊͷ··Ͱ͋Δɻ͞Βʹɼ൓Ԡͷඪతͱͯ͠ɼ෺

ਤ 1: χϡʔτϦϊ൓Ԡͷ෼ྨ࣭಺ͷిࢠͱ൓Ԡ͢Δ৔߹ͱɼ‫֩ࢠݪ‬ʢ͋Δ͍͸ͦͷ಺෦ͷ֩ࢠ΍ΫΥʔΫʣͱ൓Ԡ͢Δ৔߹͕͋

2.3

Δʢਤ 1ʣɻχϡʔτϦϊ‫ݕ‬ग़‫Ͱث‬͸ɼ͜ΕΒͷχϡʔτϦϊͷ൓Ԡͱ‫ݕ‬ग़͓͓Αͦ͋ΒΏΔཻࢠ‫ݕ‬ग़‫ث‬͸ి࣓૬‫ʹ༻࡞ޓ‬
ΑΔ৴߸Λར༻͢Δ͕ɼχϡʔτϦϊ͸ిՙΛ࣋ͨͳ͍ͨΊ‫ݕ‬ग़‫੻ࠟʹث‬Λ࢒͞ͳ͍ɻͦͷͨΊɼ‫ݕ‬ग़‫Ͱ಺ث‬χϡʔτϦϊΛ൓Ԡͤ͞ɼੜ੒͞ΕΔ
ऴঢ়ଶͷཻࢠΛ‫؍‬ଌ͢Δ͜ͱͰχϡʔτϦϊͷ਺΍ΤωϧΪʔɼछྨͳͲͷ৘ใΛಘΔɻ͜Ε͸ผʹಛघͳख๏Ͱ͸ͳ͘ɼ΍͸Γి‫ؾ‬తʹதੑͳޫࢠ΍தੑࢠͳͲͷ‫ݕ‬ग़΋ಉ༷ͷ‫ݪ‬ཧʹ‫ͮ͘ج‬ɻͨͩ͠ɼχϡʔτϦϊͷ৔߹ʹ͸൓Ԡ཰͕‫୺ۃ‬ʹ௿͍ͨΊɼલड़ͷ‫ͳྗڧ‬χϡʔτϦϊ‫ͱͱݯ‬΋ʹɼ‫ڊ‬େͰߴੑೳͳ‫ݕ‬ग़‫͕ث‬ඞཁͱͳΔɻྫ͑͹ɼ

10 MeV ͷΤωϧΪʔΛ࣋ͬͨిࢠχϡʔτϦϊͱిࢠͷ൓Ԡஅ໘ੵ͸͓Αͦ 10−43 cm2 Ͱ͋Δɻ͜ͷχϡʔτϦϊͷਫதͰͷฏ‫ࣗۉ‬༝ߦఔΛߟ͑
Δͱɼਫ 1 g(=1 cm3 ) ʹ‫·ؚ‬ΕΔిࢠͷ਺͸ΞϘΨυϩ਺͘Β͍ͷܻ (O(1023 )) ͳͷͰɼL

11023 × 10−43൓ԠͰੜ੒͞Εͨՙిཻࢠ΍ޫࢠΛ‫ݕ‬ग़͢Δ͜ͱͰɼ‫ݩ‬ʑͷχϡʔτϦϊͷ৘ใΛҾ͖ग़͢͜ͱʹͳΔɻՙిΧϨϯτ൓ԠͰ͸ɼऴঢ়ଶʹՙిϨϓτϯ͕‫ݱ‬ΕΔɻૉཻࢠͷੈքͰ͸ཻࢠ͕ੜ੒ɾফ໓͠
ͨΓผͷछྨͷཻࢠʹมΘͬͨΓ͢Δ͕ɼͦͷࡍʹʮϨϓτϯ਺ʯ͕ੈ୅͝ͱʹอଘ͢Δ͜ͱ͕஌ΒΕ͍ͯΔɻྫ͑͹ిࢠ΍ిࢠχϡʔτϦϊ͸ʮిࢠ਺ʯ+1 Λ࣋ͪɼཅిࢠ΍൓ిࢠχϡʔτϦϊ͸ిࢠ਺ −1 Λ΋ͭɻʮϛϡʔΦϯ਺ʯ΍ʮλ΢਺ʯʹ͍ͭͯ΋ಉ༷Ͱ͋Γɼ͜ΕΒͷ਺ͷ࿨͸ͦΕͧΕ൓Ԡͷલ‫Ͱޙ‬มΘΒͳ͍ɻ͢ͳΘͪɼ

νe + n → μ− + p ΍ɼ νe + p → e+ + n ͷΑ͏ͳ൓Ԡ͸‫͜ى‬Βͳ͍ 5 ɻैͬͯɼ൓ԠͰͲͷՙిཻࢠ͕ੜ੒͞Ε͔ͨௐ΂Ε͹ɼχϡʔτϦϊͷछྨΛ஌Δ͜ͱ͕Ͱ͖Δɻ
ిࢠɼμɼτ ͸ͦΕͧΕ 511 keV, 106 MeV,

1.78 GeV ͷ࣭ྔΛ΋ͭͨΊɼχϡʔτϦϊͷΤω

= 1020 cm = 1018 mϧΪʔ͕े෼Ͱͳ͍৔߹ʹ͸͜ΕΒͷཻࢠΛ࡞Δ

1 ޫ೥͕໿ 1016 m Ͱ͋Δ͔Βɼ100 ޫ೥ఔ౓ͷฏ͜ͱ͕Ͱ͖ͣɼैͬͯՙిΧϨϯτ൓Ԡ͕‫͜ى‬Β‫ࣗۉ‬༝ߦఔ͕͋Δ͜ͱ͕Θ͔Δɻͻͱͭͷχϡʔͳ͍ɻ૬ର࿦తӡಈֶ͔ΒΤωϧΪʔᮢ஋Λ‫ࢉܭ‬τϦϊ͚ͩΛΈΔͱ‫؍‬ଌΛ͢Δ͜ͱ͸‫࣮ݱ‬తͰ͸͢Δͱɼද 3 ͷΑ͏ʹͳΔɻ࣍ͷઅͰઆ໌͢ΔΑ

ͳ͍͕ɼ1018 ‫ݸ‬ͷχϡʔτϦϊΛ༻ҙͯ͠‫؍‬ଌ͠͏ʹɼχϡʔτϦϊͷछྨ͕มԽ͢ΔχϡʔτϦͯ΍Ε͹ɼฏ‫ ۉ‬1 m ఔ౓Ͱ 1 ճͷ൓Ԡ͕‫ظ‬଴Ͱϊৼಈͱ͍͏‫ݱ‬৅͕஌ΒΕ͍ͯΔɻχϡʔτϦϊ

͖Δɻ
5

㸶㸫 

ͦΕͧΕɼͳͥ‫͜ى‬Βͳ͍͔ɼઆ໌ͯ͠ΈΑ͏ɻνβද 3: ՙిΧϨϯτ൓ԠͷΤωϧΪʔᮢ஋
ඪత
ిࢠ
֩ࢠ

νe
0
∼0.5 MeVνμ11 GeV
110 MeVντ
3.1 TeV
3.5 GeVν2ৼಈͷछྨ͕มԽͨ͠ͱ͖ʹɼΤωϧΪʔ͕ᮢ஋ΑΓ΋௿͍΋ͷ͸ՙిΧϨϯτ൓ԠΛ‫ͣ͜͞ى‬ɼθ͔͋ͨ΋χϡʔτϦϊ͕ফ͑ͯ͠·ͬͨΑ͏ʹΈ͑Δɻ͜ΕΛʢχϡʔτϦϊࣗମ͕ফ͑ͯ͠·͏Θ͚Ͱ͸ͳ͍͕ʣʮফࣦʯ (disappearance) ͱ‫ݺ‬Ϳ͜ͱ͕ଟ͍ɻͨͱ͑͹ɼଠཅ͔ΒͷχϡʔτϦϊ͸࠷େͰ΋໿ 10 MeV ͷΤωϧΪʔ͔࣋ͨ͠ͳ

ναν1ਤ 2: ̎ੈ୅ͷ৔߹ͷχϡʔτϦϊͷࠞ߹ɻ;ͨͭͷ‫ج‬ఈ͕ɼࠞ߹֯ θ ͚ͩͣΕ͍ͯΔ

͍ͨΊɼੜ੒࣌͸ిࢠχϡʔτϦϊͰ͋ͬͨ΋ͷ͕ଞͷछྨʹมΘͬͯ͠·ͬͨ৔߹ɼՙిΧϨϯτ൓ԠΛ‫ͱ͜͢͜ى‬͸Ͱ͖ͳ͘ͳΔɻ͋Δ͍͸ɼͷΑ͏ʹද͞ΕΔɻ͜Ε͸ਤ 2 ʹࣔ͢Α͏ͳɼ;

1 GeV ͷΤωϧΪʔΛ࣋ͬͨϛϡʔχϡʔτϦͨͭͷ‫ج‬ఈʢ࠲ඪ࣠ʣؒͷճసͱߟ͑ΒΕΔɻ‫ج‬ϊ͕λ΢χϡʔτϦϊʹมԽͨ͠৔߹ɼ΍͸ΓՙఈͲ͏͕͠Ͳͷ͘Β͍ͣΕ͍ͯΔ͔Λࣔ͢ճస֯

ిΧϨϯτ൓Ԡ͸‫͜ى‬Βͳ͍͜ͱ͕Θ͔Δɻ͕ θ Ͱ͋Δɻθ = 0◦ ͷͱ͖ʹ͸;ͨͭͷ‫ج‬ఈ͸Ұக͢Δɻద౰ʹ࠲ඪ࣠ͷϥϕϦϯάͱ޲͖Λ࠶

2.4

ఆٛ͢Δ͜ͱ͕ՄೳͳͨΊɼࠞ߹֯ θ ͷ࠷େ஋͸χϡʔτϦϊৼಈ45◦ ͱͳΔɻऑ͍૬‫ʹ༻࡞ޓ‬ΑΔՙిΧϨϯτ൓ԠͰ͸ɼχχϡʔτϦϊ͸ऑ͍૬‫Ͱ༻࡞ޓ‬ੜ੒͞ΕΔͨ

ϡʔτϦϊ͕૬‫͖ͱͨ͠༻࡞ޓ‬ɼిࢠɾμɾτ ͷΊɼੜ੒࣌ʹ͸ऑ͍૬‫༻࡞ޓ‬ͷ‫ݻ‬༗ঢ়ଶͰ͋Δɻ͍ͣΕ͔͕‫ݱ‬ΕΔɻ͜Ε͸ɼχϡʔτϦϊͷ೾ಈ͜ΕΛ࣭ྔͷ‫ج‬ఈͰΈΔͱɼ‫ݻ‬༗ঢ়ଶͷॏͶ߹Θؔ਺ʹର͠ɼऑ͍૬‫༻࡞ޓ‬ͷ‫ݻ‬༗ঢ়ଶ΁ͷࣹӨΛͤͱͯ͠ॻ͘͜ͱ͕Ͱ͖Δɻྫ͑͹ɼੜ੒࣌ʹ͋औ͍ͬͯΔ͜ͱʹ૬౰͢ΔɻҰํͰɼχϡʔτϦΔχϡʔτϦϊ͕ να Ͱ͋ͬͨͱ͢Δɻࣜ 1 ΑΓɼϊ࣭ྔʢ·ͨ͸ΤωϧΪʔʣʹର͢Δ‫ݻ‬༗ঢ়ଶΛ‫ج‬ఈͱͨ͠‫ܥ‬Λߟ͑Δ͜ͱ΋Ͱ͖ΔɻҰൠʹɼऑ|να = cos θ|ν1 + sin θ|ν2͍૬‫༻࡞ޓ‬ͷ‫ݻ‬༗ঢ়ଶͱɼ࣭ྔͷ‫ݻ‬༗ঢ়ଶ͕Ұக

Ͱ͋Δɻࣗ༝ཻࢠͱͯ͠ͷ࣌ؒൃల͸ͦΕͧΕͷ͢Δඞཁ͸ͳ͍ɻ

࣭ྔ‫ݻ‬༗ঢ়ଶͷ࣌ؒൃలΛߟ͑Ε͹Α͘ɼ(2)ҎԼͰ͸͠͹Β͘ɼ؆୯ͷͨΊʹχϡʔτϦϊ|να ; t = e−iE1 t/h̄ cos θ|ν1 + e−iE2 t/h̄ sin θ|ν2ͷੈ୅͕̎ੈ୅͔͠ͳ͍৔߹Λߟ͑Δɻऑ͍૬‫ޓ‬࡞༻ͷ‫ݻ‬༗ঢ়ଶΛ να , νβ ͱ͠ɼ࣭ྔͷ‫ݻ‬༗ঢ়ଶΛ

(3)

ν1 , ν2 ͱ͢Δͱɼ͜ΕΒͷؒͷؔ܎͸ɼࠞ߹֯ θ

ͱͳΔɻ̎छྨͷχϡʔτϦϊͷ࣭ྔ m1 ͱ m2

Λ༻͍ͯ


να

͕ҟͳΔͱ͖ʹ͸ɼ͕࣌ؒ‫ͱͭܦ‬૬ରతʹҐ૬͕

νβ


=

cos θ

sin θ

− sin θ cos θ



ν1
ν2



ͣΕͯ͘ΔͨΊɼऑ͍૬‫༻࡞ޓ‬ͷ‫ج‬ఈͰΈͨͱ͖(1)ʹ͸ผͷछྨͷ੒෼͕ࠞ͡Δ͜ͱʹͳΔɻ͜Ε͕ɼχϡʔτϦϊৼಈͱ‫ݺ‬͹ΕΔ‫ݱ‬৅Ͱ͋Δɻ㸶㸫 ઌ΄Ͳͷੜ੒࣌ʹ να Ͱ͋ͬͨχϡʔτϦϊ͕ɼτϦϊͷੈ୅ؒͷࠞ߹͕ଘࡏ͠ɼ࣭ྔ͕ 0 Ͱͳ

‫ ཭ڑ‬L ඈߦͨ͠ͷͪʹ να (νβ ) ͱͯ͠‫؍‬ଌ͞ΕΔ֬

͍͜ͱͷূ‫͋Ͱڌ‬ΔɻχϡʔτϦϊৼಈΛར༻͠཰ P (να → να )(P (να → νβ )) ͸ɼχϡʔτϦϊͷͯɼχϡʔτϦϊͷछྨ͕มԽ͢Δ֬཰ΛଌΔ͜

ΤωϧΪʔΛ E ɼ࣭ྔͷ̎৐ͷࠩ Δm2 ≡ m22 −m21ͱʹΑΓɼࣜ (4), (5) ͔Βࠞ߹֯ θ ΍࣭ྔೋ৐ࠩͱఆٛ͢Δͱɼ

Δm2 Λଌఆ͢Δ͜ͱ͕ՄೳͰ͋ΔɻP (να → να ) = 1 − sin 2θ · sin22P (να → νβ ) = sin 2θ · sin
2

2

Δm2 L
4E

Δm2 L
4E



࣮ࡍ͸χϡʔτϦϊ͸̏ੈ୅͋ΔͷͰɼࠞ߹ߦ

(4)


(5)

ͱͳΔɻมԽͷ֬཰͕ L/E Λύϥϝʔλͱͯ͠2ྻ΋ 3 × 3 ͷߦྻͰ͋ΓɼҎԼͷΑ͏ʹॻ͚Δɻ
⎛
⎞
⎛
⎞
νe
ν1
⎜
⎟
⎜
⎟
⎜ νμ ⎟ = U ⎜ ν2 ⎟
(6)
⎝
⎠
⎝
⎠
ντ
ν3
͜ͷߦྻ U ͸ΫΥʔΫͷࠞ߹Λද͢খྛ-ӹ઒

sin ͷ‫Ͱܗ‬มಈ͠ɼҟͳΔঢ়ଶΛߦͬͨΓདྷͨΓߦྻͱಉ͡ߏ଄Ͱ͋Γɼ຀-த઒-ࡔా (MNS) ߦ͢Δ͜ͱ͔ΒɼχϡʔτϦϊৼಈ (neutrino oscil-ྻ [8] ͱ‫ݺ‬͹ΕΔɻMNS ߦྻʹಠཱͳύϥϝʔ

lation) ͱ‫ݺ‬͹ΕΔɻ

λ͸ 4 ͭʢճస֯ɿ3ɼҐ૬ɿ1ʣ͋Γɼύϥϝʔ

ࣜ (4), (5) ͔ΒΘ͔ΔΑ͏ʹɼχϡʔτϦϊλͷऔΓํ͸ҰҙͰ͸ͳ͍͕ɼ3 ͭͷࠞ߹֯ θ12 ,ৼಈ͕‫͜ى‬ΔͨΊʹ͸ࠞ߹֯ θ ͕ 0 Ͱͳ͘ɼ͔ͭ

θ23 , θ13 ͱͻͱͭͷෳૉҐ૬ δCP Λ༻͍ͯɼҎΔm2 ͕ 0 Ͱͳ͍ඞཁ͕͋Δɻ‫͑ݴʹٯ‬͹ɼχϡʔԼͷΑ͏ͳද͕ࣜ‫׳‬शతʹΑ͘࢖ΘΕΔ [3]ɻτϦϊৼಈ͕ଘࡏ͢Ε͹ɼͦΕ͸͢ͳΘͪχϡʔ

⎤

⎡
Ue1

U

Ue2

Ue3

⎥
⎢
⎥
(7)
= ⎢
⎣ Uμ1 Uμ2 Uμ3 ⎦Uτ 1 Uτ 2 Uτ 3
⎤⎡
⎡
⎤⎡
⎤⎡
⎤
1
0
0
c12 s12 010
0
0 s13 e−iδCP
c13
⎥⎢
⎢
⎥⎢
⎥⎢
⎥
⎥ ⎢ −s12 c12 0 ⎥ ⎢ 0 ei α21
⎥⎢
= ⎢
0
1
0
0 ⎥
⎦⎣
⎣ 0 c23 s23 ⎦ ⎣
⎦⎣
⎦ (8)
α2
0
0 1
−s13 eiδCP 0
0
0
ei 2
c13
0 −s23 c23⎤⎡⎤⎡
s12 c13s13 e−iδCP100c12 c13
⎥⎢
⎥
⎢
α
i 1
iδCP
⎢
= ⎢
c12 c23 − s12 s23 s13 eiδCPs23 c13 ⎥0 ⎥⎦⎣ 0 e 2⎦ (9)⎣ −s12 c23 − c12 s23 s13 e
α2
0
0
ei 2
s12 s23 − c12 c23 s13 eiδCP −c12 s23 − s12 c23 s13 eiδCP
c23 c13͜͜Ͱɼsij ɼcij ͸ͦΕͧΕ sin θij ɼcos θij ͷུͰ‫ڀݚ‬͸ૉཻࢠͱӉ஦ͷ‫͍͓ͯʹڀݚ‬େ͖ͳ՝୊Ͱ

͋ΔɻෳૉҐ૬ δCP ͸ɼΫΥʔΫͰখྛ-ӹ઒ [9]͋ΔɻΫΥʔΫͷ CP ରশੑ͸ɼ1964 ೥ʹഁΕ͕ͯఏএͨ͠ͷͱಉ͡‫Ͱߏػ‬ɼCP ରশੑʢཻࢠ-൓

͍Δ͜ͱ͕࣮‫ݧ‬తʹൃ‫͞ݟ‬ΕͯҎདྷ௕͘‫͞ڀݚ‬ΕཻࢠͷରশੑʣΛഁΔɻCP ରশੑͷഁΕ͸ɼӉ͓ͯΓɼKEK ͷ Belle ࣮‫ͰͲͳݧ‬খྛ-ӹ઒‫ߏػ‬஦ͷ෺࣭-൓෺࣭ͷඇରশੑΛઆ໌͢ΔͨΊͷα͕ਖ਼͍͜͠ͱ͕֬ೝ͞Εͯɼ2008 ೥ͷϊʔϕϧϋϩϑͷ̏৚݅ [10] ͷͻͱͭͰ͋Γɼͦͷ‫ݯى‬ͷ෺ཧֶ৆ [11] ʹͭͳ͕ͬͨɻҰํͰχϡʔτϦ㸶㸫    !" 

3εʔύʔΧϛΦΧϯσ

3.1

૷ஔ֓ཁ

 

εʔύʔΧϛΦΧϯσ͸ɼ‫ذ‬ෞ‫ݝ‬ඈଭࢢਆԬொ
#   !!

 
ν 


ʹ͋Δେ‫ܕ‬ਫνΣϨϯίϑ‫؍‬ଌ૷ஔͰ͋Δ [13]ɻ
όοΫάϥ΢ϯυͱͳΔӉ஦ઢΛආ͚ΔͨΊɼ஑ͷࢁͷࢁ௖͔Β໿ 1000 m ͷ஍ԼʹେۭಎΛ۷࡟ͯ͠‫ݐ‬ઃ͞Εͨ 6 ɻ‫ݕ‬ग़‫ث‬ຊମ͸ɼ‫ج‬ຊతʹ͸௚‫ ܘ‬39.3 mɼߴ͞ 41.4 m ͷԁ౵‫ܗ‬Λͨ͠εςϯϨε੡λϯΫͱɼ಺ଆʹऔΓ෇͚ΒΕͨଟ਺ͷޫిਤ 3: εʔύʔΧϛΦΧϯσ‫ݕ‬ग़‫ث‬ͷུ֓ਤࢠ૿ഒ؅͔ΒͳΔɻ

ϊͰ CP ରশੑ͕ഁΕ͍ͯΔ͔Ͳ͏͔͸ɼ͜Ε·Ͱ࣮‫ݧ‬తʹ֬ೝ͞Ε͓ͯΒͣɼχϡʔτϦϊৼಈ࣮‫ݧ‬ͷࠓ‫ޙ‬ͷେ͖ͳ໨ඪͱͳ͍ͬͯΔɻࣜ (9) ͷ࠷‫ޙ‬ͷ߲ʹ‫·ؚ‬ΕΔ α1 , α2 ͸ϚϤϥφ
Ґ૬ͱ‫ݺ‬͹ΕɼχϡʔτϦϊ͕ϚϤϥφཻࢠʢཻࢠͱ൓ཻࢠͷ۠ผ͕͔ͭͳ͍ૉཻࢠʣͰ͋ͬͨ৔
߹ʹଘࡏ͢ΔҐ૬Ͱ͋Δ͕ɼχϡʔτϦϊৼಈʹ͸‫د‬༩͠ͳ͍ɻχϡʔτϦϊ͕ϚϤϥφཻࢠ͔Ͳ͏͔͸ඇৗʹॏཁͳ໰୊Ͱ͋ΓɼχϡʔτϦϊΛ൐Θͳ͍̎ॏϕʔλ่յͷ୳ࡧʹΑΓ࣮‫ݧ‬తͳ‫ݕ‬ূ͕ਐΜͰ͍Δɻ೔ຊͰ΋ KamLAND-Zen ࣮‫ݧ‬͕ੈք࠷ߴ‫౓ײ‬ͷ୳ࡧ݁ՌΛग़͓ͯ͠Γ [12]ɼଞ
ʹ΋࣮‫ܭݧ‬ը͕ਐΜͰ͍Δ͕ɼҎԼͰ͸χϡʔτϦϊৼಈʹओ఺Λஔͨ͘Ίɼ͋·Γ৮Εͳ͍ɻχϡʔτϦϊৼಈ͸ɼ௕͍࣮ؒ‫ݧ‬తʹ୳ࡧ͞Ε͖͕ͯͨɼͳ͔ͳ͔࣮֬ͳূ‫ڌ‬͸ಘΒΕͳ͔ͬͨɻ

1960 ೥୅຤͔Βͷ Davis ΒʹΑΔଠཅχϡʔτϦϊͷ‫؍‬ଌʹ୺Λൃ͢ΔଠཅχϡʔτϦϊ໰୊΍ɼ

1980 ೥୅൒͹ʹΧϛΦΧϯσͰͷֿా͞Μͷൃ‫ͨͬ·࢝ʹݟ‬େ‫ؾ‬χϡʔτϦϊҟৗ͕ɼχϡʔτϦϊৼಈͰઆ໌Ͱ͖ΔՄೳੑ͸஌ΒΕ͍͕ͯͨɼ
χϡʔτϦϊৼಈ͕͔֬ʹଘࡏ͢Δͱ୭ͷ໨ʹ΋໌Β͔ͳ֬ূΛಘΔͨΊʹ͸ɼ1996 ೥ʹՔಇΛ։࢝ͨ͠εʔύʔΧϛΦΧϯσʹΑΔ‫؍‬ଌΛ଴ͨͶ͹ͳΒͳ͔ͬͨɻ

ਫλϯΫ͸̎૚ߏ଄ʹͳ͓ͬͯΓɼ಺ਫ૧ͱ֎
ਫ૧ͷؒ͸ޫΛःณ͢Δߏ଄ମͰ࢓੾ΒΕ͍ͯΔɻ
಺ਫ૧ͷน໘ʹ͸ɼ಺޲͖ʹ 50 cm ‫ܘ‬ͷޫిࢠ૿ഒ؅͕ 11,000 ຊҎ্औΓ෇͚ΒΕ͍ͯΔɻ֎ਫ૧͸ɼओʹӉ஦ઢϛϡʔΦϯͳͲ֎෦͔Βೖͬ
ͯ͘ΔཻࢠΛࣝผ͢ΔͨΊʹ࢖ΘΕɼ20 cm ‫ܘ‬ͷޫిࢠ૿ഒ؅͕ 1,800 ຊҎ্֎޲͖ʹऔΓ෇͚ΒΕ͍ͯΔɻ͜ΕΒͷޫిࢠ૿ഒ؅ͰɼਫதͰՙి
ཻࢠ͕ൃ͢ΔνΣϨϯίϑޫͱ‫ݺ‬͹ΕΔඍऑͳޫΛͱΒ͑Δ͜ͱͰχϡʔτϦϊ౳ͷ‫؍‬ଌΛߦ͏ɻλϯΫશମͰ͸໿ 5 ສτϯͷਫ͕࢖༻͞Ε͍ͯΔ
͕ɼͦͷ͏ͪ಺ਫ૧ͷ಺ଆʹ͋Δਫ͸໿ 3.3 ສτϯͰɼଟ͘ͷσʔλղੳͰ͸ɼࣄ৅ͷ൓Ԡ఺͕಺
น͔Β 2 m Ҏ্཭Ε͍ͯΔ͜ͱΛཁ‫͢ٻ‬ΔͨΊɼ༗ޮ࣭ྔ͸໿ 2.25 ສτϯͰ͋Δɻ
λϯΫͷ্෦΍पลʹ͸ɼޫిࢠ૿ഒ؅͔Βͷి‫ؾ‬৴߸Λॲཧ͢ΔͨΊͷిࢠճ࿏΍ֱਖ਼ͷͨΊͷ૷ஔ‫܈‬ɼ௒७ਫΛਫ਼੡͢ΔͨΊͷ૷ஔͳͲ͕ઃ
ஔ͞Ε͍ͯΔɻ૷ஔ͸ 24 ࣌ؒӡ༻Λଓ͚͍ͯΔͨΊɼ‫ڞ‬ಉ‫ ͕ऀڀݚ‬8 ࣌ؒͣͭ 3 ަ୅੍ͷγϑτͰ‫͢ࢹ؂‬Δɻ‫ࡏݱ‬͸ɼ೔தͷγϑτ͸‫ݕ‬ग़‫ث‬ͷ͙ͦ͢͹ͷ޵಺ͷίϯτϩʔϧϧʔϜͰ‫͠ࢹ؂‬ɼ໷ؒ͸ۙ͘ʹ͋ΔࢪઃͰ‫ࢹ؂‬Λߦ͍ͬͯΔɻͳ͓ɼεʔύʔΧϛΦΧϯσͷλϯΫͷ֎पʹ͸ɼ஍࣓‫ؾ‬Λଧͪফͨ͢ΊͷϔϧϜϗϧπίΠϧ
6
1000 m ͷ஍Լͱ͍ͬͯ΋ࢁ௖͔Β 1000 m ͷΤϨϕʔλ͕͋ΔΘ͚Ͱ͸ͳ͘ɼதෲ͔Β΄΅ਫฏʹग़ೖΓ͢Δɻॳ‫ظ‬͸߭ࢁͷτϩοίͰೖ޵͍ͯͨͦ͠͏͕ͩɼ‫ࡏݱ‬͸ࣗಈंͰ௨ߦͰ͖ΔΞΫηετϯωϧ͕੔උ͞Ε͍ͯΔɻ㸶㸫 ද 4: εʔύʔΧϛΦΧϯσͷ‫ݕ‬ग़‫ߏث‬੒ͱ࣮‫ؒظݧ‬ɻΤωϧΪʔᮢ஋͸ɼଠཅχϡʔτϦϊղੳʹ༻͍Δ൓௓ిࢠͷӡಈΤωϧΪʔͷᮢ஋Λࣔ͢ɻ‫ؒظ‬಺ਫ૧ͷޫిඃ෴཰
ಡΈग़͠ճ࿏
ΤωϧΪʔᮢ஋

SK-I
1996/04–2001/07
40%
ATM
4.5 MeV

SK-II
2002/10–2005/10
19%ATM
6.5 MeV͕‫͔ר‬Ε͍ͯΔɻޫిࢠ૿ഒ؅͸ిࢠͷ‫ي‬ಓ͕‫ۂ‬͛ΒΕΔͨΊ࣓৔ͷӨ‫ڹ‬Λड͚΍͍͕͢ɼେ‫ܘޱ‬ͷޫిࢠ૿ഒ؅͸ޫి໘͔ΒμΠϊʔυ·Ͱͷ‫ڑ‬SK-III
2006/07–2008/08
40%
ATM
4.0 MeV

SK-IV
2008/09–‫ࡏݱ‬
40%
QBEE
3.5 MeVද 5: ֤छͷཻࢠʹର͢ΔਫதͰͷνΣϨϯίϑ
ᮢ஋ʹରԠ͢ΔΤωϧΪʔ Eth ͱӡಈྔ pth཭͕௕͘ɼ஍࣓‫ؾ‬ఔ౓Ͱ΋Ө‫͕͋ڹ‬ΔͨΊͰ͋ΔɻཻࢠҎԼͰड़΂ΔΑ͏ʹɼ20 ೥ʹΘͨΔ࣮‫ݧ‬ͷؒEth (MeV)
pth (MeV/c)ʹ࣌‫ʹظ‬Αͬͯ‫ݕ‬ग़‫ث‬ͷߏ੒͕ҟͳΔɻ͜ΕΛ۠

e
0.8
0.6

μ
160
120

π±
210
160

p
1400
1070

ผ͢ΔͨΊɼ͜Ε·Ͱͷ࣮‫ؒظݧ‬Λද 4 ͷΑ͏ʹ̐ͭʹ෼͚ɼSK-I, II, III, IV ͱ‫͕͋ͱ͜Ϳݺ‬Δɻ
ͳΓɼཅࢠ͕νΣϨϯίϑޫΛ์ग़͢ΔͨΊʹ͸

3.2

1 GeV/c Ҏ্ͷӡಈྔ͕ඞཁͱͳΔɻ‫ݕ‬ग़‫ݪ‬ཧՃ଎‫ث‬Λ༻͍ͨૉཻࢠ‫ݧ࣮֩ࢠݪ‬ͷ‫ݕ‬ग़‫Ͱث‬͸ɼཻࢠͷ଎౓͕ਅۭதͷޫ଎ c Λ௒͑Δ͜ͱ͸ͳνΣϨϯίϑޫͷޫྔ΍֯౓ͷ଎౓ґଘੑΛར༻

͍͕ 7 ɼ۶ં཰ n ͷ෺࣭தͰ͸ޫ଎͕ c/n ͱͳͯ͠ɼཻࢠࣝผʹ༻͍Δ͜ͱ͕ଟ͍ɻεʔύʔΧΔɻՙిཻࢠͷ଎౓ v ͕෺࣭தͷޫ଎ c/n Λ௒͑ϛΦΧϯσͰ͸ɼϦϯάঢ়ͷνΣϨϯίϑޫΛ಺ͨͱ͖์ग़͞ΕΔͷ͕νΣϨϯίϑޫ [14] Ͱ͋ਫ૧ͷน໘ʹऔΓ෇͚ΒΕͨޫిࢠ૿ഒ؅Ͱ‫ݕ‬ग़ΔɻνΣϨϯίϑޫ͸ɼՙిཻࢠͷӡಈํ޲ʹର͠ɼͦͷ࣌ؒɾޫྔ෼෍͔Βཻࢠͷൃੜ఺ɾΤω1
͠ cos θ = nβʢβ = v/cʣΛຬͨ֯͢౓ θ ͷ޲͖ϧΪʔɾํ޲ɾछྨͷ৘ใΛಘΔɻࣄ৅ͷ࠶ߏ੒ʹɼϦϯάঢ়ʹ์ग़͞ΕΔɻਫͷ۶ં཰͸ 1.34 ఔʹؔͯ͠͸ɼ‫ུ֓Ͱޙ‬Λड़΂Δɻ౓Ͱ͋Γ 8 ɼβ = 1 ͷཻࢠʹର͢ΔνΣϨϯίϑ
֯ θC ͸໿ 42◦ ͱͳΔɻཻࢠ‫ݕ‬ग़ʹ޿͘࢖ΘΕΔ
γϯνϨʔλͷγϯνϨʔγϣϯޫͱ୯Ґ‫͋཭ڑ‬ͨΓʹ์ग़͞ΕΔޫͷྔΛൺ΂ΔͱɼνΣϨϯί

3.3
3.3.1

ϑޫͷޫྔ͸ܻҧ͍ʹগͳ͍ͨΊɼ‫ݕ‬ग़ʹ͸ޫ‫ݕ‬ग़‫ث‬ͷੑೳ͕ॏཁͱͳΔɻ಺ਫ૧಺ਫ૧ʹ࢖༻͞Ε͍ͯΔͷ͸ɼ50 cmʢ20 Πϯνʣ‫ܘ‬ͷେ‫૿ࢠిޫܘޱ‬ഒ؅Ͱ͋Δɻ΋ͱ΋ͱɼՙిཻࢠ͕νΣϨϯίϑޫΛൃ͢ΔͨΊʹ͸ɼ଎౓ β ͕ 1/n Λ௒͑Δඞཁ͕͋Δɻ֤छͷཻࢠʹର͢ΔਫதͰͷνΣϨϯίϑޫͷᮢ஋Λද 5 ʹࣔ͢ɻ࣭ྔͷେ͖ͳཻࢠ΄Ͳߴ͍ӡಈྔ͕ඞཁʹ7ޫిࢠ૿ഒ؅

ͨͱ͑χϡʔτϦϊͰ΋ʂ
8೾௕ґଘੑ͕͋ΔͨΊɼγϛϡϨʔγϣϯ΍ղੳͰ͸ͦͷޮՌ΋ߟྀ͢Δɻ

খࣲઌੜΒ͕ΧϛΦΧϯσΛઃ‫ࡍͨ͠ܭ‬ɼ‫ݕ‬ग़‫ث‬ͷେ͖͞ͰউΔΞϝϦΧͰͷϥΠόϧ࣮‫ ݧ‬IMB(Irvine-Michigan-Brookheaven) ʹର͠‫ڝ‬૪ྗΛ΋ͭͨΊʹ඿দϗτχΫεʢ౰࣌͸඿দςϨϏʣͱ։ൃͨ͠ͷ͕ 50 cm ‫૿ࢠిޫܘ‬ഒ؅ͷ࢝·ΓͰ͋Γɼͦͷ‫ܦ‬Ң͸͍Ζ͍Ζͳͱ͜ΖͰ‫ޠ‬ΒΕͯ㸶㸫 ද 6: ޫిࢠ૿ഒ؅ R3600 ͷੑೳʢయ‫ܕ‬తͳ஋ʣޫి໘ͷ௚‫ܘ‬ɹ
ޫి໘
ऩूޮ཰
ྔࢠޮ཰
ήΠϯ
μΠʔΫϊΠζ࣌ؒ෼ղೳͰɼ࿈࠯൓ԠΛ‫͍ͳ͜͞ى‬Α͏ʹ͢Δઃ‫͋Ͱܭ‬Δɻ
ޫి໘ଆʹ͚ͭͨΞΫϦϧͷΧόʔʹΑΔޫࢠͷଛࣦ͸ 350 nm Ҏ্ͷ೾௕ʹର͠ 4%ҎԼͰ͋Δɻ

50 cmόΠΞϧΧϦ (Sb-K-Cs)
70%∼21% (360–400 nm)∼107
4.5 kHz2.2 ns (RMS, 1p.e.)

3.3.2

֎ਫ૧

֎ਫ૧͸ɼओͳ໨త͕֎෦͔Βͷཻࢠͷ VETOͰ͋Γ಺ਫ૧΄Ͳͷਫ਼౓͕ඞཁͳ͍ɻ20 cmʢ8 Πϯνʣ‫ܘ‬ͷޫిࢠ૿ഒ؅ʹ 60 cm ֯ͷ೾௕ม‫׵‬ϓϨʔτΛऔΓ෇͚ɼ͞Βʹޫిࢠ૿ഒ؅Ҏ֎ͷ෦෼Λന৭ͷγʔτͰ෴͏͜ͱͰɼޫྔΛՔ͍Ͱ͍͍Δɻ·ͨɼ͜ͷΦϦδφϧ 50 cm ‫૿ࢠిޫܘ‬ഒ

Δɻ֎ਫ૧ͷޫిࢠ૿ഒ؅͸ɼ΋ͱ΋ͱ IMB ࣮؅ R1449 ͸ 2014 ೥ʹ IEEE ϚΠϧετʔϯʹબ‫࢖Ͱݧ‬ΘΕ͍ͯͨ΋ͷΛ࠶ར༻͍ͯ͠Δ͕ɼ2002

͹ΕͨɻεʔύʔΧϛΦΧϯσͰ࢖༻͞Ε͍ͯΔ೥Ҏ߱͸৽ͨʹ੡଄ͨ͠΋ͷ΋࢖ΘΕ͍ͯΔɻ

ͷ͸ɼվྑΛࢪ͠‫౓ײ‬΍࣌ؒ෼ղೳΛ޲্ͤͨ͞

R3600 ͱ͍͏λΠϓͷޫిࢠ૿ഒ؅Ͱ͋Δ [15]ɻ
R3600 ͷओͳੑೳΛද 6 ʹࣔ͢ɻ3.4

σʔλऩूγεςϜ

2001 ೥ɼվम࡞‫ޙۀ‬ͷ஫ਫதʹେྔͷޫిࢠ૿εʔύʔΧϛΦΧϯσͰ͸ɼ߹Θͤͯ 13,000 ຊഒ؅͕ഁଛ͢Δࣄ‫͕ͨͬ͋ނ‬ɻఈ໘ͷޫిࢠ૿ഒ

Ҏ্ͷޫిࢠ૿ഒ؅͔Βͷిՙͱ࣌ؒͷ৘ใΛ‫ه‬؅ͷҰׂ͕ͭΕരॖ͕‫͖ͯى‬ਫ͕ྲྀΕࠐΉ͜ͱͰ

࿥͢Δඞཁ͕͋ΔɻଠཅχϡʔτϦϊͷΑ͏ͳ௿িܸ೾͕‫͖ى‬ɼۙྡͷޫిࢠ૿ഒ؅͕࿈࠯తʹഁΤωϧΪʔࣄ৅ͷ‫؍‬ଌͷͨΊʹ͸̍ޫిࢠϨϕϧյ͞Ε͍ͯͬͨ͜ͱ͕‫ݪ‬ҼͰ͋ͬͨɻ‫ނ‬ɾ‫ށ‬௩༸ͷ৴߸ΛͱΒ͑ͳ͚Ε͹ͳΒͳ͍ɻχϡʔτϦϊೋࢯͷ‫ͳྗڧ‬Ϧʔμʔγοϓͷ΋ͱ [16]ɼ͙͢͞

ͷ൓ԠʹΑΔࣄ৅͸༷ʑͳχϡʔτϦϊΛ߹Θͤ·‫ݪ‬Ҽ‫໌ڀ‬ɼ࠶ൃ๷ࢭରࡦͷཱҊɼ෮‫چ‬γφϦΦͯ΋̍೔͋ͨΓ਺ेࣄ৅ͳͷʹର͠ɼޫిࢠ૿ഒ

ͷࡦఆʹ޲͚ͨ࡞‫ͨͬ·͕࢝ۀ‬ɻ͋Γ͕͍ͨ͜ͱ

؅ʹ͸਺ kHz ͷμʔΫϊΠζ͕͋Δɻσʔλసʹࠃ಺֎͔ΒͷࢧԉΛड͚ɼ̍೥‫૿ࢠిޫʹޙ‬ഒૹͷଳҬɼ‫ه‬࿥ഔମͷ༰ྔɼσʔλղੳͷͨΊͷ؅ͷ਺Λ൒෼ʹ‫ݮ‬Β࣮ͯ͠‫ݧ‬Λ࠶։͢Δ͜ͱ͕ͰϦιʔεͳͲͷ੍‫͔ݶ‬Βɼᮢ஋Λ௒͑Δώοτͷ

͖ͨɻ౰࣌͸ KEK ͷ 12 GeV ཅࢠγϯΫϩτϩ

৘ใΛ͢΂ͯ‫ه‬࿥͢Δ͜ͱ͸Ͱ͖ͳ͍ͨΊɼࣄ৅ϯ͔ΒχϡʔτϦϊϏʔϜΛ 250 km ඈ͹͢ K2K

Λ͏·͘બͼग़͢ඞཁ͕͋ΔɻҰํͰɼߴΤωϧ࣮‫ߦ͕ݧ‬ΘΕ͓ͯΓɼͦͷͨΊʹ΋ૣ‫ظ‬ͷ෮‫͕چ‬Ϊʔͷେ‫ؾ‬χϡʔτϦϊʹΑΔ൓ԠͳͲͰ͸ɼͻ‫ٸ‬຿Ͱ͋ͬͨɻK2K ࣮‫ݧ‬ऴྃ‫ޙ‬ͷ 2005-2006 ೥ͱͭͷޫిࢠ૿ഒ؅ʹେྔͷޫࢠ͕౸ୡ͢Δ৔߹ʹ͸৽ͨʹ࡞Γ଍ͨ͠ޫిࢠ૿ഒ؅ΛऔΓ෇͚ɼ͕͋ΓɼಡΈग़͠ճ࿏͸෯޿͍Ϩϯδͷ৴߸ʹର‫ݕ‬ग़‫ث‬Λ‫׬‬શʹ෮‫͢چ‬Δ࡞‫ߦ͕ۀ‬ΘΕͨɻԠ͢Δඞཁ͕͋Δɻ

2002 ೥Ҏ߱ɼ಺ਫ૧ͷޫిࢠ૿ഒ؅ʹ͸͢΂࣮‫ݧ‬։࢝౰ॳͷσʔλऩूγεςϜ͸ɼATM

ͯ FRP(ﬁber reinforced plastic) ͱΞΫϦϧͰͰͱ໊෇͚ΒΕͨϑϩϯτΤϯυΤϨΫτϩχΫ

͖ͨΧόʔ͕औΓ෇͚ΒΕ͍ͯΔɻ࣌ʑ‫ޡ‬ղ͞ΕεϞδϡʔϧΛ࢖͍ɼෳ਺ͷޫిࢠ૿ഒ؅͕ಉ࣌

Δ͕ɼ͜ͷΧόʔ͸ͦΕࣗମ͕ਫѹʹ଱͑ΔͨΊʹᮢ஋Λ௒͑Δ৴߸Λग़ͨ͜͠ͱΛϋʔυ΢ΣΞͷ΋ͷͰ͸ͳ͘ɼ࣮͸ਫΛ௨͢খ͞ͳ͕͍݀ͭ͘

Ͱ൑ఆͯ͠τϦΨʔΛग़ͯ͠ɼͦͷલ‫ޙ‬ͷ৴߸ͷ͔ۭ͍͍ͯΔɻສҰ಺෦Ͱޫిࢠ૿ഒ؅ׂ͕Εͯ࣌ؒͱిՙ৘ใΛσδλϧԽͯ͠ΦϯϥΠϯίϯ

͠·ͬͨͱ͖ʹɼਫྲྀΛ཈͑িܸ೾ͷੜ੒Λ๷͍ϐϡʔλʹૹ͍ͬͯͨɻ2008 ೥ʹσʔλऩूγ㸶㸫 εςϜΛҰ৽͔ͯ͠Β͸ [17]ɼμʔΫώοτ΋‫ؚ‬Ͱ͋ΔɻΊ͢΂ͯͷ৴߸ΛσδλϧԽͯ͠Ұ౓ΦϯϥΠϯ
ίϯϐϡʔλʹૹΓࠐΈɼιϑτ΢ΣΞͰΠϕϯτબ୒Λ͢ΔΑ͏ʹͳͬͨɻ͜ͷͨΊʹɼQBEE

3.6

७ਫ

ͱ‫ݺ‬͹ΕΔϑϩϯτΤϯυΤϨΫτϩχΫεϞ

ਫνΣϨϯίϑ‫ݕ‬ग़‫͍͓ͯʹث‬ɼඪతͰ΋͋ΓδϡʔϧΛ։ൃͨ͠ɻQBEE Ϙʔυʹ͸ɼిՙΛνΣϨϯίϑޫΛൃ͢ΔͨΊͷഔ࣭Ͱ͋Δਫ͸‫ݕ‬࣌ؒʹม‫͢׵‬Δ QTC νοϓ [18] ͱϚϧνώοτ

ग़‫ث‬ͷੑೳΛܾΊΔத৺తͳཁૉͷҰͭͰ͋Γɼ

TDC [19] ͕ࡌ͓ͬͯΓɼύΠϓϥΠϯॲཧʹΑͦͷ඼࣭Λҡ࣋͢ΔͨΊʹ͸ฒʑͳΒ͵౒ྗ͕෷Γߴ଎Ͱͷσʔλॲཧ͕Մೳͱͳ͍ͬͯΔɻ

ΘΕ͍ͯΔɻෆ७෺͕͋Δͱಁա཰ͷѱԽ΍ޫͷ͜ͷ৽ͨͳσʔλऩूγεςϜͰ͸ɼιϑτࢄཚͷ‫ݪ‬ҼͱͳΓɼνΣϨϯίϑޫͷ఻ൖʹେ͖΢ΣΞͰࣄ৅ΛબͿͨΊɼॊೈͳτϦΨʔΛ࣮‫ݱ‬ͳӨ‫͕͋ڹ‬Δɻ͞ΒʹɼϥυϯͳͲͷ์ࣹੑ෺࣭

͢Δ͜ͱ͕Մೳʹͳͬͨɻྫ͑͹ɼ൓ిࢠχϡʔ͸௿ΤωϧΪʔࣄ৅ͷόοΫάϥ΢ϯυʹͳΔɻ

τϦϊ൓ԠͰੜ੒͞ΕΔதੑࢠ͕ਫૉʹั֫͞ΕεʔύʔΧϛΦΧϯσͰ͸ɼ௒७ਫੜ੒γες

Δͱ͖์ग़͞ΕΔ 2.2 MeV ͷ γ ઢΛ͔ͭ·͑Δ͜ϜΛ௨ͯ͠ਫΛຖ࣌ 60 τϯͷྲྀ଎Ͱ॥‫ͤ͞؀‬Δ͜

ͱ͕Ͱ͖Ε͹௒৽੕എ‫ܠ‬χϡʔτϦϊࣄ৅ͷ‫౓ײ‬ͱͰਫதͷෆ७෺ೱ౓Λ཈͍͑ͯΔɻ७ਫγεςΛ޲্ͤ͞Δ͜ͱ͕Ͱ͖Δ͕ɼैདྷͷϋʔυ΢ΣϜ͸‫ܧ‬ଓతʹվྑΛ‫܁‬Γฦ͓ͯ͠Γɼ֤छͷϑΟΞτϦΨʔͰ͸ᮢ஋Λͦ͜·ͰԼ͛Δ͜ͱ͕Ͱ͖

ϧλʔ΍ࢵ֎ઢরࣹʢόΫςϦΞΛࡴͨ͢Ίʣɼਅͳ͔ͬͨɻιϑτ΢ΣΞʹΑΔτϦΨʔͰ͸ɼۭ͋୤‫ؾ‬ɼਁಁບͳͲɼ༷ʑͳ૷ஔͷ૊Έ߹ΘͤͰ

Δఔ౓ߴ͍ΤωϧΪʔΛ࣋ͭࣄ৅͕τϦΨʔ͞Εߏ੒͞ΕΔɻ७ਫ૷ஔΛ௨աͨ͠‫ޙ‬ͷ௒७ਫ͸ൺͨ‫͠ޙ‬͹Β͘ͷ͚ؒͩᮢ஋ΛԼ͛ͯσʔλΛ‫ه‬࿥఍߅͕͓Αͦ 18.20 MΩ·cm Ͱ͋Γɼϥυϯͷ‫ؚ‬༗͢Δɼͱ͍͏͜ͱ͕༰қʹՄೳͰ͋Δɻ·ͨɼ‫ޙ‬཰͸ 2 mBq/m3 ఔ౓Ͱ͋ΔɻλϯΫʹ͸ෳ਺ͷ

ड़͢Δ T2K ࣮‫͚޲ݧ‬ͷτϦΨʔͰ͸ɼJ-PARCՕॴʹਫͷग़ೖΓ‫ͳͱޱ‬Δ഑؅͕‫͓͕ͯͬܨ‬ΓɼͰχϡʔτϦϊϏʔϜΛੜ੒ͨ࣌͠ࠁΛ GPS ͰΘ͟ͱϥυϯೱ౓ͷߴ͍ਫΛೖΕͯλϯΫதͷਫਖ਼֬ʹଌΓɼͦͷ৘ใΛ͙͢͞·ਆԬʹૹͬͯιྲྀΛ‫؍‬ଌ͢ΔͳͲɼਫͷ੍‫ؔ͢ʹޚ‬Δ৘ใΛूΊϑτ΢ΣΞτϦΨʔͷΠϯϓοτͱ͢Δ͜ͱͰɼ্ͨͰɼ॥‫؀‬ͷํ޲΍ྔΛ࠷దԽ͍ͯ͠Δɻ͞Βώοτͷ͋Δͳ͠ʹؔΘΒͣϏʔϜ͕ਆԬʹ౸ୡʹɼλϯΫʹ஫ೖ͢ΔਫͷԹ౓Λ 0.01◦ C ୯ҐͰͨ࣌ؒ͠ͷલ‫ ޙ‬1 ms ͷ͢΂ͯͷޫిࢠ૿ഒ؅ͷ੍‫͠ޚ‬ɼ্ԼͰ໿ 0.2◦ C ͷඍົͳԹ౓ޯ഑Λอͭ৘ใΛ࢒͢ͱ͍͏ɼόΠΞεͷͳ͍τϦΨʔΛ࣮͜ͱʹΑΓλϯΫதͷਫྲྀΛ੍‫͠ޚ‬ɼத৺෦ͷ์‫͍ͯ͠ݱ‬Δɻ

ࣹੑ෺࣭ೱ౓Λ௿͘อ͍ͬͯΔɻλϯΫதͷޫͷ‫ݮ‬ਰ௕͸ 400 nm ෇ۙͷ೾௕ʹର͠໿ 100 m Ͱ

3.5

͋Δɻ

‫ػࢉܭ‬

޵ಓ಺ͷۭ‫ʹؾ‬͸‫ؠ‬൫͔Β์ग़͞ΕΔϥυϯ͕24 ࣌ؒՔಇ͠ଓ͚ΔεʔύʔΧϛΦΧϯσ͔ߴೱ౓Ͱ‫·ؚ‬ΕΔͨΊɼ࣮‫ݧ‬ΤϦΞʹ͸֎෦͔ΒΒͷσʔλ͸ɼ1 ೔͋ͨΓ໿ 500GB ʹ΋ͳΔɻ͜

ϑΟϧλʔΛ௨ۭͨ͠‫͕ؾ‬ઈ͑ͣૹΓࠐ·ΕΔɻͷσʔλΛ‫ه‬࿥͠ɼֱਖ਼ɾࣄ৅࠶ߏ੒ͷͨΊͷιεʔύʔΧϛΦΧϯσͷλϯΫ࠷্෦ʹ͸ 60 cm

ϑτ΢ΣΞʹ௨ͯ͠෺ཧղੳʹ࢖͑Δ‫͢ʹܗ‬Δͨ΄Ͳͷۭ‫ؾ‬ͷ૚͕͋Γɼ͜͜ʹ͸͞ΒʹಛผͳΊͷ‫ݯࢿػࢉܭ‬΋࣮‫ݧ‬ͷॏཁͳίϯϙʔωϯτͰϑΟϧλʔγεςϜͰϥυϯΛআ‫ૹ͕ؾۭͨ͠ڈ‬͋Δɻ·ͨɼ࣮‫ࢀʹݧ‬Ճ͢Δ‫ऀڀݚ‬͸ੈքதʹࢄΒΕ͍ͯΔɻ

Β͹͍ͬͯΔͨΊɼσʔλΛ΍ΓͱΓͨ͠ΓϏσΦձٞΛߦͬͨΓ͢ΔͨΊͷωοτϫʔΫ΋ॏཁ

㸶㸫 

3.7

౓ͱӡಈྔɼ1–10 GeV/c ͷϛϡʔΦϯͷ‫ݕ‬ग़‫ث‬ֱਖ਼‫ݕ‬ग़‫ث‬ͷੑೳΛ࠷େ‫͢شൃʹݶ‬Δʹ͸ɼਫ਼ີͳֱਖ਼͕ෆՄܽͰ͋ΔɻεʔύʔΧϛΦΧϯσͰ͸෯޿͍ΤωϧΪʔϨϯδͷࣄ৅͕‫ڀݚ‬ର৅ͱͳ಺ͰͷϨϯδͱӡಈྔͷؔ܎ͳͲΛ༻ֱ͍ͯਖ਼͞
ΕΔɻ࣌ؒมಈͷޮՌ΋‫ؚ‬ΊɼΤωϧΪʔεέʔϧͷෆఆੑ͸ 2%ఔ౓Ͱ͋Δɻ

ΔͨΊɼ༷ʑͳํ๏Λ૊Έ߹Θֱͤͯਖ਼Λߦ͏ඞ
ཁ͕͋Δɻ‫ڊ‬େͳ‫ݕ‬ग़‫ث‬Λ 20 ೥Ҏ্ͷ‫ʹؒظ‬Θ

3.8

ͨͬͯӡ༻͢Δ͜ͱ͸ͦΕ͚ͩͰ΋༰қͰ͸ͳ͍͕ɼ‫ݧܦ‬ΛॏͶΔʹैֱ͍ਖ਼ํ๏΋վળ͞Εɼਫ਼౓͸޲্Λଓ͚͍ͯΔ [20]ɻ
Ωηϊϯϥϯϓ΍ϨʔβʔͳͲͷޫ‫ݯ‬ɼ252 Cf58 Ni ͳͲͷ์ࣹઢ‫Ͳͳݯ‬Λ‫ͯ͠࢖ۦ‬ɼޫిࢠ૿

ഒ؅ͷήΠϯ΍λΠϛϯάɼਫதͷޫͷ‫ݮ‬ਰ΍ࢄཚͷֱਖ਼Λߦ͏ɻ·ͨɼӉ஦ઢϛϡʔΦϯ΍ɼ‫ݕ‬ग़‫ث‬தͰࢭ·ͬͨϛϡʔΦϯ͔Βͷ่յిࢠ΋ɼࣄ৅࠶ߏ੒֤ޫిࢠ૿ഒ؅Ͱ‫ه‬࿥͞Εͨ৴߸ͷిՙͱ࣌ؒ
ͷ৘ใ͔ΒνΣϨϯίϑޫΛൃཻͨ͠ࢠͷ৘ใΛ࠶ߏ੒͢Δํ๏ͷུ֓Λड़΂Δɻͳ͓ɼΤωϧΪʔ͕ 1–10MeV ఔ౓ʢଠཅχϡʔτϦϊɼ௒৽੕χϡʔτϦϊͳͲʣͷࣄ৅ͱɼ100MeV Ҏ্ʢେ‫ؾ‬χϡʔτϦϊɼՃ଎‫ث‬χϡʔτϦϊɼཅࢠ่յ
୳ࡧͳͲʣͷࣄ৅Ͱ͸ɼࣄ৅࠶ߏ੒͕ଟগҟͳΔɻ

ਫͷಁա཰΍ΤωϧΪʔεέʔϧΛֱਖ਼͢ΔͨΊʹॏཁͳιʔεͰ͋ΔɻಘΒΕͨ‫ݕ‬ग़‫ث‬ͷԠ౴ͷ

3.8.1

৘ใ͸ɼϞϯςΧϧϩγϛϡϨʔγϣϯʹ൓ө͞ΕΔɻൃੜ఺ (vertex)ࣄ৅ͷൃੜ఺ (vertexʣ͸ɼ֤ޫిࢠ૿ഒ؅Ͱ‫؍‬ଌ͞Εͨ৴߸ͷ࣌ؒ৘ใΛ༻͍ͯ࠶ߏ੒͞ΕΔɻ

௿ΤωϧΪʔͰͷΤωϧΪʔεέʔϧͷઈର

͋ΔҰ఺͔ΒνΣϨϯίϑޫ͕์ग़͞ΕͨͱԾఆ஋΍ࣄ৅࠶ߏ੒ͷਫ਼౓Λֱਖ਼͢ΔͨΊɼεʔύʔ͢Δͱɼ֤ޫిࢠ૿ഒ؅Ͱ‫؍‬ଌ͞Εͨ৴߸ͷ࣌ؒΧϛΦΧϯσͷ্ʹ͸ిࢠՃ଎‫( ث‬LINAC) ͕ઃ͔Βޫ‫͔ݯ‬Β֤ޫిࢠ૿ഒ؅ͷҐஔ·Ͱޫ͕ਫத

ஔ͞Ε͍ͯΔ [21]ɻ্෦ͷ֖ʹෳ਺͋Δֱਖ਼ͷΛ఻ൖ͢Δͷʹ͔͔Δ࣌ؒΛࠩ͠Ҿ͍ͨ΋ͷ͸ɼͨΊͷ݀Λ௨ͯ͠ LINAC ͔ΒͷϏʔϜύΠϓΛ

ཧ૝తʹ͸͢΂ͯͷޫిࢠ૿ഒ؅ͰҰக͢Δ͸ͣ‫ݕ‬ग़‫಺ث‬෦ʹ৳͹͠ɼ͍͔ͭ͘ͷ৔ॴʹΤωϧ

Ͱ͋Δɻͦ͜Ͱɼਫதͷ఻ൖ࣌ؒΛࠩ͠Ҿ͍ͨ࣌Ϊʔͷܾ·ͬͨిࢠΛଧͪࠐΜͰͦͷԠ౴ΛΈؒ෼෍ͷϐʔΫ͕࠷େԽ͞ΕΔ఺Λ୳͢͜ͱͰൃ

Δ͜ͱͰɼֱਖ਼Λߦ͏ɻ͞ΒʹɼൺֱతҐஔΛಈੜ఺Λ࠶ߏ੒͢Δɻ͞Βʹɼ‫ޙ‬ஈͷεςοϓͰ࠶͔͠΍͍͢ॏਫૉ-ࡾॏਫૉʢD-Tʣ൓ԠʹΑΔ

ߏ੒͞Εͨ৘ใΛ༻͍ͯɼϦϯάͷύλʔϯͳͲதੑࢠൃੜ૷ஔΛ࢖ͬͯɼ16 O + n → 16 N + pɼ
16 N → 16 O + e− + νe ͷ൓Ԡ͔Βͷ β ઢʹΑΔ৴

߸Λ༻͍ɼ৔ॴґଘੑ΍ํ޲ґଘੑΛֱਖ਼͢Δɻ

ͷ෇Ճతͳ৘ใΛ༻͍Δ͜ͱͰ͞ΒʹҐஔਫ਼౓͕վળ͞ΕΔɻ·ͨɼ࣌ؒ෼෍͔ΒɼνΣϨϯίϑ
Ϧϯάͷํ޲΋࠶ߏ੒͞ΕΔɻ

͜ΕΒͷΤωϧΪʔઈର஋ͷֱਖ਼͸ɼಛʹଠཅχϡʔτϦϊͷΤωϧΪʔεϖΫτϧଌఆͰ͸ܾఆతʹॏཁͰ͋ΔɻSK-IV Ͱͷ௿ΤωϧΪʔͰͷ

3.8.2

ΤωϧΪʔεέʔϧͷෆఆੑ͸ 0.54%ͱ‫ੵݟ‬΋Β
Ε͍ͯΔɻ

Ϧϯά਺

ෳ਺ͷཻࢠ͕ൃੜ͠͏ΔߴΤωϧΪʔࣄ৅Ͱ͸ɼϦϯάͷ਺ʢʹཻࢠ਺ʣΛܾఆ͢Δඞཁ͕͋ߴΤωϧΪʔͰͷΤωϧΪʔεέʔϧ͸ɼϛ

Δɻ̎ͭ໨Ҏ߱ͷϦϯάͷ୳ࡧʹ͸ɼHough ม‫׵‬ϡʔΦϯ͔Βͷ่յిࢠ΍ɼେ‫ؾ‬χϡʔτϦϊͷΛ࢖͏ɻώοτͷ͋ͬͨޫిࢠ૿ഒ؅ͷҐஔʹର൓ԠͰੜ੒͞ΕΔ π 0 (→ γγ) ͷෆม࣭ྔɼ200–

ͦ͠ΕͧΕൃੜ఺͔Β 42◦ ͷ֯౓Λ࣋ͬͨίʔϯ

400 MeV/c ͷϛϡʔΦϯͷνΣϨϯίϑޫͷ֯Λඳ͖ɼίʔϯ͕ॏͳΔ఺ʢ=νΣϨϯίϑϦϯ㸶㸫 άͷத৺ͷํ޲ʣΛ֯౓্ۭؒͰͷϐʔΫͱͯ͠޲͖΋͋Γɼ1 ΩϩτϯͷਫνΣϨϯίϑ‫ݕ‬ग़‫ث‬୳͢ɻΈ͔ͭͬͨϦϯάީิʹରͯ͠ɼޫྔ෼෍

Λ༻͍ͯ KEK-PS ͔ΒཻࢠΛଧͪࠐΈੑೳΛূʹ‫ ͨ͠ࢉܭ͍ͯͮج‬likelihood Λ৽͍͠ϦϯάΛ໌͢ΔϏʔϜςετ΋ߦΘΕͨ [22]ɻͳ͓ɼ͜ͷ෇͚଍ͨ͠৔߹ͱ෇͚଍͞ͳ͔ͬͨ৔߹ʹ͍࣮ͭͯ‫ݐͰݧ‬ઃͨ͠λϯΫ͸ͦͷ‫ޙ‬ɼK2K ࣮‫ݧ‬ͷલൺֱ͠ɼ·ͨ͞Βʹৄࡉͳޫྔ෼෍ͷൺֱʹΑΔஔ‫ݕ‬ग़‫ث‬ͷͻͱͭɼ1 ΩϩτϯਫνΣϨϯίϑ‫ݕ‬൑ఆؔ਺Λ༻͍ͯɼຊ෺ͷϦϯάΒ͍͔͠Ͳ͏͔

ग़‫࠶ͯ͠ͱث‬ར༻͞ΕͨɻΛ൑அ͢Δɻຊ෺Β͚͠Ε͹ϦϯάΛ෇͚଍͠ɼ

ཻࢠࣝผʹ͸ɼ‫؍‬ଌ͞ΕͨޫྔͷύλʔϯΛͦ͏Ͱͳ͚Ε͹ͦͷީิ͸ࣺͯΔɻ৽͍͠ϦϯάిࢠɾϛϡʔΦϯͦΕͧΕͷԾఆͷ‫ʹݩ‬༧૝͞Εͷީิ͕ͳ͘ͳΔ·Ͱ͜ͷखॱΛ‫܁‬Γฦ͠ɼ࠷ऴ

Δޫྔ෼෍ͱൺ΂ͯ࡞ͬͨ likelihood Λ༻͍Δɻ

తͳϦϯά਺ΛܾΊΔɻ

ਤ 5 ʹେ‫ؾ‬χϡʔτϦϊࣄ৅Ͱͷ log-likelihood෼෍Λࣔ͢ɻԣ࣠͸ࠨଆʢෛʣ͕ e-likeɼӈଆʢਖ਼ʣ3.8.3

͕ μ-like Ͱ͋Δɻe-like ࣄ৅ͱ μ-like ࣄ৅͕ඇৗ

ཻࢠࣝผʹ៉ྷʹ෼཭͞Ε͍ͯΔ͜ͱ͕Θ͔Δɻ‫ࣝޡ‬ผͷχϡʔτϦϊͷछྨʢϑϨʔόʔʣ͸ɼՙిΧ֬཰͸໿ 1%Ͱ͋ΔɻϨϯτ൓ԠͰͲͷՙిϨϓτϯ͕ੜ੒͞Ε͔ͨʹΑͬͯࣝผ͞ΕΔɻಛʹɼେ‫ؾ‬χϡʔτϦϊ΍Ճ଎‫ث‬χϡʔτϦϊʹΑΔχϡʔτϦϊৼಈͷ‫ݚ‬

3.8.4

ΤωϧΪʔ

‫Ͱڀ‬͸ɼిࢠχϡʔτϦϊͱϛϡʔχϡʔτϦϊՙిཻࢠ͕෺࣭தΛ௨ΔͱɼΠΦϯԽ౳ͰΤωͷࣝผ͕ॏཁͰ͋Γɼ͢ͳΘͪిࢠͱϛϡʔΦϯϧΪʔΛࣦͬͯ΍͕ͯࢭ·ΔɻΤωϧΪʔ͕େ͖Λ۠ผ͢Δඞཁ͕͋Δɻ௿ΤωϧΪʔࣄ৅Ͱ͸ɼͳཻࢠ΄Ͳඈఔ͕௕͘ଟ͘ͷνΣϨϯίϑޫΛϛϡʔΦϯ΍λ΢͸ੜ੒͞ΕͣɼχϡʔτϦϊ-

ൃ͢ΔͨΊɼνΣϨϯίϑޫͷྔΛଌΔ͜ͱͰཻిࢠͷ஄ੑࢄཚ͕ओͳ൓ԠͱͳΔͨΊɼऴঢ়ଶͷࢠͷ౰ॳͷΤωϧΪʔΛ஌Δ͜ͱ͕Ͱ͖ΔɻߴΤཻࢠ͸ৗʹిࢠͰ͋Δɻ

ωϧΪʔࣄ৅Ͱ͸ɼϦϯάͷ಺ଆʹ͋Δޫిࢠ૿ϛϡʔΦϯ͸ਫதΛൺֱత·͙ͬ͢ඈΜͰ୺ͷഒ؅Ͱ‫ݕ‬ग़͞Εͨޫྔͷ࿨͔ΒΤωϧΪʔΛ‫ٻ‬ΊγϟʔϓͳϦϯάΛ࡞Δ͕ɼిࢠ͸ి࣓γϟϫʔΔɻͻͱͭͷޫిࢠ૿ഒ؅Ͱ͍͍ͤͥ 1 ޫిࢠΛ‫ͨ͢͜ى‬Ίଟ਺ͷཻࢠ͔ΒͷνΣϨϯίϑޫͷ͔͠‫ݕ‬ग़͞Εͳ͍Α͏ͳ௿ΤωϧΪʔͷࣄ৅ͷ৔ॏͶ߹ΘͤʹͳΓɼ΅΍͚ͨϦϯάͱͯ͠‫؍‬ଌ͞߹ʹ͸ɼޫྔͷ࿨Λ࢖͏ΑΓ΋෼ղೳ͕ྑ͘ͳΔ

ɻ͜ͷύλʔϯͷҧ͍Λ࢖͏͜ͱͰɼ
ΕΔʢਤ 4ʣͨΊ৴߸͕‫ݕ‬ग़͞Εͨޫిࢠ૿ഒ؅ͷ਺ΛΤωϧ֤νΣϨϯίϑϦϯάΛ μ-likeʢnon-showeringʣΪʔͷࢦඪͱͯ͠࢖͏ɻ௿ΤωϧΪʔࣄ৅Ͱ͸ɼ͔ e-likeʢshoweringʣ͔ʹ෼͚Δɻ

1 MeV ʹର͠ฏ‫Ͱۉ‬໿ 6 ຊͷޫిࢠ૿ഒ؅ʹώοిࢠ΍ϛϡʔΦϯҎ֎ͷཻࢠ΋ɼ͜ͷ̎छྨͷτ͕͋ΔɻͲͪΒ͔ʹ൑ผ͞ΕΔ͜ͱʹͳΔɻπ ± ΍ཅࢠ͸ి࣓γϟϫʔΛ‫͍ͳ͜͞ى‬ͷͰɼμ-like ͱ൑ผ͞3.8.5

෼ղೳ·ͱΊ

ΕΔɻͨͩ͠ɼཅࢠ͸લड़ͨ͠Α͏ʹνΣϨϯί
ϑᮢ஋͕ߴ͍ͨΊɼ‫ݕ‬ग़͞Εͳ͍͜ͱ΋ଟ͍ɻޫද 7 ʹɼεʔύʔΧϛΦΧϯσͷ֤छ෼ղೳ

ࢠ͸ి࣓γϟϫʔΛ‫ͨ͢͜ى‬Ίɼe-like ͱ൑ผ͞Λ·ͱΊΔɻͻͱͭͷଌఆ‫Ͱث‬େ͖͞ͱਫ਼ີ͞Λ

ΕΔ͜ͱʹͳΔɻ݉Ͷඋ͓͑ͯΓɼ਺ MeV ͔Β TeV ·Ͱɼ‫ݕ‬ग़ͰΧϛΦΧϯσͷ࣌୅ʹ͸ɼʮେ‫ؾ‬χϡʔτϦϊ

͖Δࣄ৅ͷΤωϧΪʔൣғ͕޿͍͜ͱ͕ಛ௃Ͱ͋

ҟৗʯͷ‫ݪ‬Ҽͱͯ͠ਫνΣϨϯίϑ‫ݕ‬ग़‫Ͱث‬ຊ౰Δɻେ‫ؾ‬χϡʔτϦϊͱଠཅχϡʔτϦϊΛಉ࣌ʹ্‫ه‬ͷΑ͏ͳཻࢠࣝผ͕Մೳͳͷ͔ٙ໰ࢹ͢Δ

ʹ‫͖Ͱڀݚ‬Δ૷ஔ͸ɼଞʹଘࡏ͠ͳ͍ɻ

㸶㸫 

ਤ 4: εʔύʔΧϛΦΧϯσͰ‫؍‬ଌ͞ΕΔϛϡʔΦϯʢࠨʣͱిࢠʢӈʣʹΑΔνΣϨϯίϑϦϯάͷྫʢγϛϡϨʔγϣϯʣɻԁ౵‫ܗ‬ͷ‫ݕ‬ग़‫ث‬ͷల։ਤͰɼ֤఺͕ޫిࢠ૿ഒ؅ͷ৴߸Λࣔ͢ɻ৭ͷҧ͍͸ޫిࢠ૿ഒ؅Ͱ‫ه‬࿥͞ΕͨిՙͷྔΛද͢ɻϛϡʔΦϯ͸͖ͬ͘Γͱͨ͠ϦϯάΛɼిࢠ͸΅΍͚ͨϦϯάΛ࡞Δ͜ͱΛ࢖͍ɼཻࢠࣝผΛߦ͏͜ͱ͕Ͱ͖Δɻද 7: εʔύʔΧϛΦΧϯσ‫ݕ‬ग़‫ث‬ͷ֤छ෼ղೳ

όʔςοΫεҐஔ෼ղೳ֯౓෼ղೳΤωϧΪʔ෼ղೳ

3.9

10 MeV
e
50 cm
23◦
14%

Sub-GeV1-ring e 1-ring μ
31 cm
24 cm
3.0◦
1.9◦
3%
2%

Milti-GeV
1-ring e 1-ring μ
34 cm
24 cm
1.2◦
0.8◦

ϊʹ

੒Ռ

20 ೥ͷؒʹεʔύʔΧϛΦΧϯσͰಘΒΕͨ

π + → μ+ + ν μ ,π − → μ− + ν̄μ(10)੒Ռ͸޿͍෼໺ʹΘͨΔɻҎԼͰ͸ɼͦͷ͏ͪͰಠஅͰબΜͩओͳ੒ՌΛ঺հ͢ΔɻՃ଎‫ث‬Λ༻͍ͱ่յ͠ɼ͞Βʹϛϡʔཻࢠ͸ʢཅʣిࢠɼిࢠ

ͨ௕‫ج‬ઢχϡʔτϦϊৼಈ࣮‫ͯؔ͠ʹݧ‬͸ɼ࣍ͷ‫ܕ‬ʢ൓ʣχϡʔτϦϊɼϛϡʔ‫ܕ‬ʢ൓ʣχϡʔτষͰड़΂Δɻ

Ϧϊʹμ+ → e+ + ν̄μ + νe ,3.9.1

μ− → e− + νμ + ν̄e (11)େ‫ؾ‬χϡʔτϦϊେ‫ؾ‬χϡʔτϦϊ͸ɼӉ஦͔Βඈདྷ͢ΔཅࢠͳͲͷӉ஦ઢ͕஍‫ٿ‬ͷେ‫ͱؾ‬িಥ͢Δͱ͖ʹͰ͖Δ

π தؒࢠͳͲͷ่յʹΑͬͯੜ੒͞ΕΔɻՙి πதؒࢠ͸ϛϡʔཻࢠͱϛϡʔ‫ܕ‬ʢ൓ʣχϡʔτϦͱ่յ͢Δɻ
ΧϛΦΧϯσ΍εʔύʔΧϛΦΧϯσ͸Ӊ஦ઢͷӨ‫ڹ‬Λ‫ݮ‬Βͨ͢Ίʹ஍Լʹ࡞ΒΕ͕ͨɼେ‫ؾ‬χϡʔτϦϊ͸஍‫ٿ‬Λқʑͱ௨Γൈ͚Δ͜ͱ͕Ͱ͖ΔͨΊɼःณ͕ෆՄೳͰ͋ΔɻχϡʔτϦϊ͕‫ͱ֩ࢠݪ‬൓Ԡ͢Δͱཅࢠ่յͷ৴߸ʹࣅͨࣄ৅Λ㸶㸫 Super Kamiokande IV 1294.7 days : Monitoring

૬͕ؔ͋Δ͜ͱΛར༻ͯ͠ɼχϡʔτϦϊͷ౸དྷµ-likeํ޲Λଌఆ͢Δɻେ‫ؾ‬χϡʔτϦϊͰ͸ɼχϡʔ

250

e-likeτϦϊͷํ޲͸ඈߦ‫ʹ཭ڑ‬ରԠ͢Δɻ·ͨɼੜ੒

200

150

͞ΕཻͨࢠͷΤωϧΪʔΛ଍͠߹ΘͤΔ͜ͱͰɼCCQE electronχϡʔτϦϊͷΤωϧΪʔΛ஌Δ͜ͱ͕Ͱ͖Δɻ

CCQE muonχϡʔτϦϊͷํ޲΍ΤωϧΪʔΛ‫׬‬શʹ஌Δ͜ͱ͸Ͱ͖ͳ͍ͷͰɼχϡʔτϦϊ൓Ԡͷৄࡉ΍

100‫ݕ‬ग़‫ث‬ͷԠ౴Λߟྀͨ͠ϞϯςΧϧϩγϛϡϨʔγϣϯͱൺֱ͢Δ͜ͱͰղੳΛߦ͏ɻ

50

0
-10

-8

-6

-4

-2

0

2

4

6

8

χϡʔτϦϊৼಈͷൃ‫ݟ‬

10

PID likelihood sub-GeV 1ring (FC)χϡʔτϦϊৼಈͷ࣮֬ͳূ‫ॳ͕ڌ‬ΊͯಘΒΕͨͷ͸εʔύʔΧϛΦਤ 5: େ‫ؾ‬χϡʔτϦϊࣄ৅ʢSub-GeV, 1ring ࣄ৅ʣʹ͓͚Δཻࢠࣝผͷ log-likelihood ෼෍ɻԣ࣠
͸ࠨଆʢෛʣ͕ e-likeɼӈଆʢਖ਼ʣ͕ μ-likeɻ౷‫ޡܭ‬ࠩͷΤϥʔόʔ͖ͭࠇ఺͸࣮σʔλΛɼώετάϥϜ͸χϡʔτϦϊৼಈͷޮՌΛߟྀͨ͠ MC γ
ϛϡϨʔγϣϯΛࣔ͢ɻMC γϛϡϨʔγϣϯͷ͏ͪɼϋον͖ͭͷ෦෼͸ՙిΧϨϯτ४஄ੑࢄཚʢCharged Current Quasi-Elastic interactionɼχϡʔτϦϊͱ֩ࢠͷ̎ମ൓ԠʣʹΑΔ൓ԠΛද͢ɻΧϯσʹΑΔେ‫ؾ‬χϡʔτϦϊͷ‫؍‬ଌͰ͋Δ͕ɼͦͷൃ୺͸ΧϛΦΧϯσͷ࣌୅ʹ͔͞ͷ΅ΔɻΧϛΦΧϯσͷ໨త͸ɼૉཻࢠͷେ౷Ұཧ࿦Ͱ༧‫ݴ‬͞ΕΔཅࢠ่յΛ୳ࡧ͢Δ͜ͱͰ͋ͬͨɻ౰࣌ͷཧ࿦Ͱ͸ཅࢠͷण໋͸ 1030–32 ೥ఔ౓ͱ༧‫͞ݴ‬Ε͓ͯΓɼ࣮‫ݧ‬Λ࢝ΊΕ͹͙͢Έ͔ͭΔͱࢥΘΕ͍ͯͨɻ͔͠͠ɼ਺೥‫ͯͬܦ‬΋ͳ͔ͳ͔Έ͔ͭΒͳ͍͜ͱ͔Βɼֿా͞Μ͸ཅࢠ่յ୳ࡧͷ‫౓ײ‬Λ্͛ΔͨΊʹෳ਺ͷϦϯά͕͋Δࣄ৅ʹର͠ిࢠͱ
ϛϡʔΦϯΛࣝผ͢ΔϓϩάϥϜΛ։ൃͨ͠ɻ·ͣಈ࡞ΛνΣοΫ͢ΔͨΊʹɼखࠒͳσʔλͱ͠࡞Δ͜ͱ͕͋Γ͏ΔͨΊɼେ‫ؾ‬χϡʔτϦϊ͸΋

ͯ࢖ΘΕͨͷ͕େ‫ؾ‬χϡʔτϦϊͰ͋ͬͨɻ
ࣜ ʢ10ʣɼ
ʢ11ʣ͔ΒɼϛϡʔΦϯ‫ܕࢠిͱܕ‬ͱ΋ͱཅࢠ่յͷόοΫάϥ΢ϯυͱͯ͠अຐͳ

ͷχϡʔτϦϊͷ਺ͷൺ͸͓Αͦ 2 : 1 ͱͳΔ͜ଘࡏͰ͋ͬͨɻ
େ‫ؾ‬χϡʔτϦϊ‫؍‬ଌͷର৅ͱͳΔΤωϧΪʔͱ͕‫ظ‬଴͞ΕΔɻͱ͜Ζ͕ɼ࣮ࡍʹ‫؍‬ଌ͞Εͨ਺ྖҬ͸ 100 MeV ఔ౓Ҏ্Ͱ͋Γɼ‫ͱ֩ࢠݪ‬ͷ൓Ԡͷൺ͸ 1.2 : 1 ఔ౓Ͱ͋ͬͨɻΧϛΦΧϯσʹΑ

ͰͰ͖ͨిࢠ΍ϛϡʔΦϯɼ൓௓֩ࢠ΍ੜ੒͞ΕͨΔ࠷ॳͷେ‫ؾ‬χϡʔτϦϊͷ࿦จ͸ 1988 ೥ʹग़π தؒࢠͳͲͷऴঢ়ଶཻࢠΛ‫؍‬ଌ͢Δɻ‫ݕ‬ग़‫ث‬ͷ൛͞Εͨ [23]ɻ͜ͷ࿦จͷ࠷‫ʹޙ‬ɼχϡʔτϦϊதͰશͯͷཻࢠ͕ࢭ·ͬͨࣄ৅ (Fully Contained,ৼಈ͕‫ݪ‬ҼͰ͋ΔՄೳੑ΋ࢦఠ͞Ε͍ͯΔɻ͔͠FC) ʹՃ͑ɼϛϡʔΦϯͷΤωϧΪʔ͕ߴ͘‫ݕ‬͠ɼ͜ͷ݁ՌΛχϡʔτϦϊৼಈͰઆ໌͢Δʹ͸ɼग़‫΁֎ث‬ൈ͚͍ͯͬͨ΋ͷ (Partially Contained,ࠞ߹͕֯࠷େʹۙ͘ͳ͚Ε͹͍͚ͳ͍ɻ౰࣌͢ͰPC) ΍‫ݕ‬ग़‫ث‬௚Լͷ‫ؠ‬൫Ͱ൓Ԡͨ͠ߴΤωϧΪʔʹଌΒΕ͍ͯͨΫΥʔΫͷࠞ߹֯͸ͲΕ΋͔ͳχϡʔτϦϊʹ‫ى‬Ҽ͢Δ্޲͖ͷϛϡʔΦϯʹΑΓখ͔ͬͨͨ͞ΊɼϨϓτϯͷࠞ߹֯΋ಉ͡Α͏

Δࣄ৅΋࢖༻͢Δ͜ͱͰ‫؍‬ଌͰ͖Δࣄ৅ͷΤωϧʹখ͍͞͸ͣͩͱ͍͏ࢥ͍ࠐΈ͕͋Γɼେ͖ͳࠞ

ΪʔൣғΛ޿͛ɼTeV ఔ౓·ͰͷχϡʔτϦϊΛ߹֯ͷଘࡏ͸ͳ͔ͳ͔ड͚ೖΕΒΕͳ͔ͬͨΑ͏‫؍‬ଌ͢Δ͜ͱ͕Ͱ͖Δɻੜ੒͞ΕΔిࢠ΍ϛϡʔͰ͋Δɻ·࣮ͨ‫ݧ‬ଆͰ΋ɼଞͷ࣮‫͔ݧ‬Β͸ϛϡʔΦϯͷํ޲ʹ͸‫ݩ‬ͷχϡʔτϦϊͷΤωϧΪʔͱχϡʔτϦϊͷ਺͸༧૝ͱҰக͢Δͱ͍͏݁Ռ͕
ग़͖ͯͨΓͨ͠ɻΧϛΦΧϯσͰ΋σʔλΛ૿΍㸶㸫 ຊ౰ʹχϡʔτϦϊৼಈ͔ʁਤ 6 ͷఱ௖֤෼

෍͸ɼ௕͍‫཭ڑ‬Λඈߦ͢ΔͱϛϡʔχϡʔτϦϊͷ਺͕‫ݮ‬Δ͜ͱΛ໌֬ʹ͍ࣔͯ͠Δɻ͔͠͠ɼͦ
ͷഎ‫͋ʹޙ‬Δ෺ཧ͕χϡʔτϦϊৼಈͰ͋Δͱ͸‫ݶ‬ΒͣɼχϡʔτϦϊͷ่յ΍೾ಈؔ਺ͷσίώʔϨϯεͰ΋આ໌͕Ͱ͖ΔͷͰ͸ͳ͍͔ͱ͍
͏Ϟσϧ΋ఏএ͞Εͨɻ‫ݪ‬Ҽ͕χϡʔτϦϊৼಈͰ͋Ε͹ɼχϡʔτϦϊͷछྨ͕มԽ͢Δ֬཰͸ࣜ (4) ʹද͞ΕΔ௨ΓɼχϡʔτϦϊͷඈߦ‫ڑ‬཭ͱΤωϧΪʔͷൺ L/E ͷؔ਺ͱͯ͠ৼಈ͠ɼ
ϛϡʔχϡʔτϦϊͷ‫؍‬ଌ਺͸͋Δ L/E Ͱ‫ۃ‬খ஋Λऔͬͨ͋ͱ૿Ճ͢Δ͸ͣͰ͋ΔɻҰํͰɼଞͷཧ࿦Ͱ͸ϛϡʔχϡʔτϦϊͷ਺͕ L/E ʹର͠୯ௐʹ‫ݮ‬গ͢Δ͜ͱ͕༧૝͞ΕɼχϡʔτϦϊৼಈʹಛ௃తͳ L/E ෼෍ͷσΟοϓߏ଄͸‫ݱ‬Εͳ͍ɻେ‫ؾ‬χϡʔτϦϊࣄ৅ͷதͰ L/E ʹର͢ਤ 6: NEUTRINO98 ͰͷൃදͰ࢖ΘΕͨ OHPͷ̍ຕ [26]
͠ɼ֯౓෼෍ͳͲͷղੳ΋ߦ͕ͬͨɼ౷‫͕ܭ‬গͳܾ͘ఆతͳ݁Ռʹ͸ࢸΒͳ͔ͬͨ [24, 25]ɻͦͯ͠ 1996 ೥ 4 ݄ɼεʔύʔΧϛΦΧϯσ͕ՔಇΛ࢝ΊͨɻΧϛΦΧϯσʹൺ΂ͯ 20 ഒҎ্ͷ༗ޮ࣭ྔΛ࢖ͬͯɼ౷‫ྔܭ‬͸·͞ʹܻҧ͍ʹ૿͑ͨɻ1998 ೥ 6 ݄ʹߴࢁͰ։͔Εͨ 9 χϡʔτϦϊࠃࡍձٞʢִ೥Ͱ։͔ΕΔɼχϡʔτϦϊ෺ཧʹؔ͢Δ࠷େͷձٞʣͰֿా͞Μ͕ྺ࢙తͳൃද
Λߦͬͨ͜ͱ͸Έͳ͞Μ͝ଘ஌ͷ௨ΓͰ͋Δɻ࣮ࡍʹ࢖ΘΕͨϓϨθϯͷ̍ຕʢ౰࣌͸·ͩ OHP
ͷ࣌୅Ͱ͋ΔʣΛਤ 6 ʹࣔ͢ [26]ɻఱ௖֯෼෍
ʹΑΓ஍‫ٿ‬ͷཪଆ͔Β͘ΔϛϡʔχϡʔτϦϊ͕͔֬ʹ‫͓ͯͬݮ‬Γɼ্Լͷඇରশੑ͕͋Δ͜ͱΛ

6.2 σ ͷ༗ҙ౓Ͱࣔͨ͠ɼඒ͍͠σʔλͰ͋Δɻେ‫ؾ‬χϡʔτϦϊͷ‫؍‬ଌσʔλ͔Βʢ‫ޙ‬ͷΑΓਫ਼౓ͷྑ͍ଌఆ݁ՌʹΑΓʣɼΔm232  2.5 ×

10−3 eV2 /c4 Ͱ͋Γɼࠞ߹֯ θ23 ͸࠷େͷ 45◦ ʹ͍ۙ͜ͱ͕Θ͔ͬͨɻΔ‫͕ࠩޡ‬খ͍͞΋ͷΛબͼग़͠ɼL/E ґଘੑΛղੳͨ͠ͱ͜Ζɼ͔֬ʹσΟοϓ͕‫؍‬ଌ͞ΕχϡʔτϦϊৼಈͷ༧૝ͱҰக͢Δ͜ͱ͕Θ͔Γɼଞͷཧ࿦͸‫غ‬٫͞Εͨ [27]ɻ
λ΢χϡʔτϦϊʹͳ͍ͬͯΔͷ͔ʁͰ͸࣍ʹɼχϡʔτϦϊৼಈͰϛϡʔχϡʔτϦϊ͸ͲͷछྨʹมԽͨ͠ͷͩΖ͏͔ɻ࣭ྔ͕ Z Ϙιϯͷ൒෼ҎԼ͔ͭऑ͍૬‫Ͱ༻࡞ޓ‬൓Ԡ͢ΔχϡʔτϦϊ͸̏ੈ୅͔͠ͳ͍͜ͱ͕Θ͔͍ͬͯΔͨ
Ίɼඪ४తͳ࿮૊ΈͰ͸ిࢠχϡʔτϦϊ͔λ΢χϡʔτϦϊʹมԽ͍ͯ͠Δ͜ͱʹͳΔɻਤ 6 ͰిࢠχϡʔτϦϊͷ෼෍͸༧૝ͱҰக͍ͯ͠Δ
͜ͱ͔Βɼλ΢χϡʔτϦϊʹมԽ͍ͯ͠Δ͜ͱ
͕ࣔࠦ͞ΕΔɻ͔͠͠ɼऑ͍૬‫͢༻࡞ޓ‬Βಇ͔ͳ͍ɼʮεςϥΠϧ (sterile)ʯχϡʔτϦϊͳΔ΋ͷ͕ཧ࿦తʹ͸ଘࡏ͠ಘΔɻͻΐͬͱ͢Δͱɼλ΢χϡʔτϦϊͰ͸ͳ͘εςϥΠϧχϡʔτϦϊʹมԽ͍ͯ͠ΔͷͰ͸ͱ͍͏Ծઆ΋͕͋ͬͨɼେ‫ؾ‬χϡʔτϦϊσʔλͷղੳʹΑΓɼ100%εςϥΠϧχϡʔτϦϊ΁มԽ͍ͯ͠Δͱ͍͏Ծఆ͸‫غ‬٫͞Εͨ [28]ɻ

9౰ॳ͸͜ͷ೥ͷձٞ͸ΧφμͰ։࠵ɼ೔ຊ͸ͦͷ̎೥‫ޙ‬ͷ༧ఆͩͬͨͷ͕ɼͦΕͧΕͷ࣮‫ݧ‬ͷਐߦঢ়‫گ‬౳͔Β‫ٸ‬ᬎॱ൪ΛೖΕସ͑ͯ೔ຊͰͷ։࠵ʹͳͬͨΒ͍͠ɻ࠷‫ޙ‬ͷ֬ೝͱͯ͠ɼ࣮ࡍʹλ΢χϡʔτϦϊ͕൓Ԡͯ͠λ΢ཻࢠΛੜ੒ͨ͠ࣄ৅Λ‫؍‬ଌ͢Δ͜ͱ㸶㸫 ͕ॏཁͰ͋Δɻλ΢ཻࢠ͸ 290 fs ͷण໋Ͱ่յ

ଠཅχϡʔτϦϊ໰୊ଠཅχϡʔτϦϊͷ‫؍‬ଌͯ͠͠·͏ͨΊɼεʔύʔΧϛΦΧϯσͰ͸λ΢͸ɼ1960 ೥୅຤͔ΒถࠃͰߦΘΕͨ R. Davis ͷχϡʔτϦϊͷ൓ԠΛࣄ৅͝ͱʹࣝผ͢Δ͜ͱ͸ઌ‫ۦ‬తͳ࣮‫·࢝ʹݧ‬Δ [35, 36]ɻ࢛ԘԽ୸ૉΛ༻ෆՄೳͰ͋Δɻ͔͠͠ɼ‫؍‬ଌ͞Εཻͨࢠͷ਺΍ӡ͍ͯɼ37 Cl + νe → 37 Ar + e− ͱ͍͏൓ԠͰͰ͖ͨ

ಈֶతม਺ͳͲɼࣄ৅ͷʮλ΢Β͠͞ʯΛද͢ࢦඪ

37 Arʢ൒‫ ظݮ‬35 ೔ʣΛճऩ͠ɼΧ΢ϯλʔʹΑΛूΊͯχϡʔϥϧωοτΛ࢖͍ɼ౷‫ܭ‬తʹλ΢Γ‫ࢠݪ‬ͷ਺Λ਺͑Δͱ͍͏ख๏Ͱɼ600 τϯͷ࢛ͷࣄ৅ީิΛूΊͯ͘ΔղੳΛߦͬͨ݁Ռɼ͔֬

ԘԽ୸ૉΛ༻͍ͯ΋ 1 ೔ʹੜ੒͞ΕΔ 37 Ar ͸໿ʹλ΢͕ੜ੒͞Ε͍ͯΔ͜ͱ͕ࣔ͞Εͨ [29,30]ɻ

0.5 ‫͏͍ͱݸ‬೉͍࣮͠‫͋Ͱݧ‬Δ͕ɼDavis ͸प౸λ΢χϡʔτϦϊͷग़‫ݱ‬͸ɼՃ଎‫ث‬χϡʔτϦϊʹ࣮‫ݧ‬Λߦ͍ɼ1990 ೥୅·Ͱ‫ܧ‬ଓͯ͠‫؍‬ଌΛߦͬΛ༻͍ͨ OPERA ࣮‫Ͱݧ‬΋֬ೝ͞Εͨ [31]ɻ

ͨɻͦͷ݁Ռɼ‫؍‬ଌ͞ΕΔχϡʔτϦϊͷྔ͕ཧ࿦త༧૝ͷ໿ 1/3 ͔͠ͳ͍͜ͱ͕Θ͔Γɼଠཅඇඪ४తͳ෺ཧ‫ݱ‬৅ͷ୳ࡧେ‫ؾ‬χϡʔτϦϊͷಛ௃ͷͻͱͭ͸ɼඈߦ‫ ͕཭ڑ‬10 km ͔ΒχϡʔτϦϊ໰୊ͱ‫ݺ‬͹ΕΔಾΛੜΉ͜ͱʹͳͬͨ [37]ɻ

10,000 kmɼΤωϧΪʔ͕ 0.1 GeV ͔Β 1 TeV ·ଠཅχϡʔτϦϊ໰୊ʹؔͯ͠͸ɼଠཅͷϞσͰͷ޿͍ྖҬʹΘͨΔσʔλΛ༩͑ͯ͘ΕΔ͜ͱϧʹ‫ݪ‬Ҽ͕͋Δͷ͔ɼ࣮‫ݧ‬ख๏ʹ໰୊͕͋Δͷ͔ɼ

Ͱ͋Δɻ͜ͷಛ௃Λੜ͔͠ɼεʔύʔΧϛΦΧϯ

ͦΕͱ΋χϡʔτϦϊৼಈ͕‫͍͖ͯى‬Δͷ͔ɼ͍σʹΑΔେ౷‫ܭ‬σʔλΛ࢖͏ͱɼ༷ʑͳඇඪ४త

Ζ͍Ζͳ‫ݪ‬Ҽ͕ߟ͑ΒΕͨɻ΍͕ͯɼΧϛΦΧϯ

ͳ෺ཧ‫ݱ‬৅ͷ୳ࡧ΋ՄೳͰ͋Δɻྫͱͯ͠ɼϩʔσΛ‫ؚ‬Ήख๏ͷҧ͏͍͔ͭ͘ͷ࣮‫Ͱݧ‬΋΍͸ΓϨϯπରশੑͷഁΕ [32] ΍ɼεςϥΠϧχϡʔτχϡʔτϦϊͷྔ͕ଠཅϞσϧΑΓগͳ͍͜ͱ͕

Ϧϊͷଘࡏ [33] ʹର͠‫ݶ੍͍ڧ‬Λ༩͍͑ͯΔɻ֬ೝ͞Εɼ࣮‫ݧ‬ख๏ͷ໰୊Ͱ͸ͳ͍͜ͱ͕Θ͔ͬ
ͨɻ·ͨɼଠཅϞσϧΛվมͯ͠΋͢΂ͯͷ࣮‫ݧ‬େ‫ؾ‬χϡʔτϦϊͷࠓ‫ޙ‬େ‫ؾ‬χϡʔτϦϊ͸ɼͷ݁ՌΛໃ६ͳ͘આ໌͢Δ͜ͱ͸೉͘͠ɼχϡʔͦͷ෯޿͍ΤωϧΪʔͱඈ‫཭ڑ‬Λੜ͔͢͜ͱͰɼ

τϦϊৼಈͷՄೳੑ͕༗ྗࢹ͞ΕΔΑ͏ʹͳͬͨɻࠓ‫ޙ‬΋‫ޙ‬ड़ͷՃ଎‫ث‬χϡʔτϦϊ࣮‫ͱݧ‬૬ิతͳ‫Ͱܗ‬χϡʔτϦϊͷ‫ʹڀݚ‬ॏཁͳ໾ׂΛՌͨ͠ଓଠཅχϡʔτϦϊ໰୊ͷղܾ

͚ΔͱࢥΘΕΔɻಛʹɼχϡʔτϦϊͷ࣭ྔ‫ݻ‬༗ͷ‫ߦͯ͠ͱূݕ‬ΘΕͨΨϦ΢ϜΛ࢖࣮ͬͨ‫Ͱݧ‬ঢ়ଶͷ͏ͪ ν3 ͕ ν1 , ν2 ΑΓ΋ॏ͍͔͍͔ܰʢmass͸ɼχϡʔτϦϊ൓ԠʹΑΔ‫֩ࢠݪ‬ͷมԽΛར༻ordering ͋Δ͍͸ mass hierarchy ͱ‫ݺ‬͹ΕΔʣʹ

͢Δ͕ɼ͋Δఔ౓൓Ԡ਺͕ͨ·Δ·ͰԿ೔΋଴ͬ

ର͢Δ‫ظ͕౓ײ‬଴͞Ε͍ͯΔɻ·ͨɼେ‫ؾ‬χϡʔ͔ͯΒ‫ࢠݪ‬ͷ਺Λ਺͑ΔͨΊɼ֤ࣄ৅ͷ࣌ࠁ΍ΤτϦϊ͕஍‫ٿ‬ͷ಺෦Λ௨աͯ͘͠Δ͜ͱΛར༻͠ωϧΪʔΛ஌Δ͜ͱ͸Ͱ͖ͳ͔ͬͨɻεʔύʔΧͯɼ஍‫಺ٿ‬෦ͷߏ଄ʹؔ͢Δ৘ใΛಘΒΕΔͷͰϛΦΧϯσʹΑΔଠཅχϡʔτϦϊ‫؍‬ଌͰ͸ిࢠ͸ͳ͍͔ͱ͍͏‫ڀݚ‬΋͋Δ [34]ɻ

͕χϡʔτϦϊʹࢄཚ͞ΕΔ൓ԠΛ༻͍͓ͯΓɼ

Davis ͷ࣮‫ݧ‬΍ͦ൓௓ిࢠͷଌఆʹΑΓɼ࣌ؒɼํ޲ɼΤωϧΪʔ

3.9.2

ͷ৘ใΛಘΔ͜ͱ͕Ͱ͖Δɻແ࿦ɼେ࣭ྔΛੜ͔ଠཅχϡʔτϦϊ

ͯ͠େ౷‫ܭ‬ͷσʔλΛಘΒΕΔ͜ͱ΋εʔύʔΧଠཅͷதͰ‫͍͖ͯى‬Δ֩༥߹൓ԠͰ͸େྔͷిϛΦΧϯσͷେ͖ͳར఺Ͱ͋Γɼ2000 ೥ʹ͸ඇࢠχϡʔτϦϊ͕ੜ੒͞Ε͍ͯΔɻੜ੒͞Εͨ࣌ৗʹߴ͍ਫ਼౓ͰిࢠࢄཚʹΑΔଠཅχϡʔτϦϊʹ͸͢΂ͯిࢠχϡʔτϦϊͰ͋ΓɼΤωϧΪʔ‫؍‬ଌͷ݁ՌΛൃදͨ͠ [38]ɻిࢠࢄཚ͸શͯͷछ͸ 1MeV ҎԼ͔Β 10MeV ఔ౓·ͰͷൣғͰ͋Δɻ

ྨͷχϡʔτϦϊ͕‫͖Ͱ͕ͱ͜͢͜ى‬Δ͕ɼిࢠχϡʔτϦϊͷΈʹ W ϘιϯΛհͨ͠ՙిΧϨ㸶㸫 ϯτ൓Ԡͷ‫د‬༩͕͋ΔͨΊʹɼిࢠχϡʔτϦϊ֬཰͕ΤωϧΪʔʹґଘͯ͠มԽ͢Δ༷ࢠ͕ΈΒͷ൓Ԡஅ໘ੵ͕େ͖͘ɼϛϡʔχϡʔτϦϊͱλΕΔ͜ͱʹͳΔɻ΢χϡʔτϦϊͷ൓Ԡஅ໘ੵͷ໿ 6 ഒͱͳΔɻ

Borexino ࣮‫ʹݧ‬ΑΔ௿ΤωϧΪʔଠཅχϡʔ

2001 ೥ʹɼΧφμͰߦΘΕͨ SNO ࣮‫͕ݧ‬ॏਫૉτϦϊͷ‫؍‬ଌ݁Ռ [45] ͱεʔύʔΧϛΦΧϯσ΍

ͱͷՙిΧϨϯτ൓ԠʹΑͬͯଠཅχϡʔτϦϊ

SNO ʹΑΔ‫؍‬ଌ݁Ռ͔Βɼ1MeV ҎԼͱ 5MeV Ҏͷ͏ͪిࢠχϡʔτϦϊ੒෼͚ͩΛଌఆͨ͠ [39]ɻ্ͷྖҬͰ͸ৼಈ֬཰͸༧૝௨Γʹͳ͍ͬͯΔ͜εʔύʔΧϛΦΧϯσͱ SNO ͷ݁ՌΛ߹ΘͤΔͱ͕Θ͔ͬͨɻ͔͠͠ɼৼಈ֬཰͕มԽ͍ͯ͠Δ

͜ͱͰɼଠཅ಺෦ͰͰ͖ͨͱ͖ʹ͸ిࢠχϡʔτΤωϧΪʔྖҬͰͷσʔλ͸े෼Ͱͳ͘ɼMSWϦϊͩͬͨ΋ͷ͕ɼ஍্Ͱ͸ผͷछྨʹมΘͬͯޮՌͰ͸ͳ͍ඇඪ४తͳ‫ݱ‬৅͕‫͍͖ͯى‬ΔՄೳੑ

͍Δɼͭ·ΓχϡʔτϦϊৼಈ͕‫͍͖ͯى‬Δ͜ͱ΋ఏҊ͞Ε͍ͯΔɻ‫ࡏݱ‬εʔύʔΧϛΦΧϯσʹ

͕ࣔ͞Εͨɻ2002 ೥ 4 ݄ʹ͸ SNO ͕ॏਫૉͱ

ΑΔଠཅχϡʔτϦϊ‫؍‬ଌͷΤωϧΪʔᮢ஋͸൓ͷதੑΧϨϯτΛ࢖ͬͯछྨʹΑΒͣଠཅ͔Β͘௓ిࢠͷӡಈΤωϧΪʔͰ 3.5 MeV Ͱ͋Δ͕ɼ͜

ΔશͯͷχϡʔτϦϊͷ਺Λ‫ܭ‬ଌͨ݁͠ՌΛެදΕΛ͞ΒʹԼ͛ɼৼಈ֬཰͕มԽ͍ͯ͠Δͱ‫ظ‬଴͠ɼχϡʔτϦϊͷछྨ͕มԽ͍ͯ͠Δ͜ͱΛ֬͞ΕΔྖҬͷΤωϧΪʔεϖΫτϧΛଌఆ͢Δ࣮͜ͳ΋ͷͱͨ͠ [40]ɻ͞Βʹಉ೥ 12 ݄ʹ͸‫چ‬Χͱ͸ࠓ‫ޙ‬ͷ՝୊Ͱ͋Δɻ

ϛΦΧϯσͷϗʔϧʹ࡞ͬͨ 1 Ωϩτϯͷӷମγ·ͨɼ஍‫ٿ‬Λ௨Γൈ͚Δࡍʹ΋Θ͔ͣͳ͕Β෺ϯνϨʔλ‫ݕ‬ग़‫Ͱث‬ฏ‫ ۉ‬180 km ཭Εͨ‫ࢠݪ‬࿍͔࣭ޮՌΛड͚ΔͨΊɼ೔தʢ஍‫ٿ‬Λ௨Βͳ͍ʣͱΒͷχϡʔτϦϊΛ‫ݕ‬ग़͢Δ KamLAND ࣮‫͕ݧ‬ɼ໷ؒʢ஍‫ٿ‬Λ௨ͬͯ͘ΔʣͱͰɼ‫؍‬ଌ͞ΕΔଠཅ

൓ిࢠχϡʔτϦϊͷফࣦΛ‫؍‬ଌͨ͠ [41]ɻ͜ΕχϡʔτϦϊͷ਺͕Θ͔ͣʹมԽ͢Δ͜ͱ͕༧૝

ʹΑΓɼࠞ߹͕֯େ͖͍ɼ͍ΘΏΔ Large Mixing͞ΕΔɻ͜Ε·ͰʹεʔύʔΧϛΦΧϯσͷσʔAngle(LMA) ղ͕ଠཅχϡʔτϦϊৼಈͷղͰ͋λʹΑΓɼன໷ͷมԽΛ໿ 3 σ ͷ༗ҙ౓Ͱ‫؍‬ଌ͢

Δ͜ͱ͕Θ͔ͬͨɻ

Δ͜ͱʹ੒ޭ͍ͯ͠Δ [46]ɻ

͜͏ͯ͠ɼ30 ೥ʹΘͨΔಾͰ͋ͬͨଠཅχଠཅͷத৺Ͱൃੜͨ͠೤͕ද໘ʹ౸ୡ͢Δʹ͸ϡʔτϦϊ໰୊͕ղܾͨ͠ɻଠཅχϡʔτϦϊ

໿ 10 ສ೥͔͔Δͷʹର͠ɼχϡʔτϦϊ͸΄ͱৼಈʹରԠ͢Δύϥϝʔλ͸ɼΔm221  7.5 ×
10−5 eV2 /c4 ͓Αͼ sin2 θ12  0.3 Ͱ͋ΔɻΜͲ൓Ԡͤͣ΄΅ޫ଎ͰඈͿͷͰɼ஍‫Ͱ·ٿ‬໿ 8෼Ͱ౸ୡ͢ΔɻχϡʔτϦϊ‫؍‬ଌʹΑΓɼଠཅ಺෦ͷঢ়‫گ‬Λ΄΅ϦΞϧλΠϜͰϞχλʔͰ͖Δ΄ଠཅχϡʔτϦϊ‫ڀݚ‬ͷ‫ݱ‬ঢ়ͱࠓ‫ޙ‬χϡʔτϦ͔ɼޫֶʹΑΔ‫؍‬ଌͰ͸ಘΒΕͳ͍಺෦૊੒ʹؔϊ͕෺࣭தΛ఻೻͢Δͱ͖ʹ͸ɼిࢠχϡʔτϦ

͢Δ৘ใͳͲɼଠཅࣗମʹؔ͢Δ‫ڀݚ‬΋ࠓ‫ޙ‬ਐలϊ੒෼ͷΈ͕෺࣭தͷిࢠͱ༨෼ͳ૬‫༻࡞ޓ‬Λ͕‫ظ‬଴͞ΕΔɻ

͢ΔͨΊɼχϡʔτϦϊৼಈͷύϥϝʔλ͕ิਖ਼Λड͚Δɻ͜ͷޮՌΛ෺࣭ޮՌͱ‫Ϳݺ‬ɻଠཅͷத৺෇ۙ͸ߴີ౓Ͱ͋Γɼ໿ 5 MeV Ҏ্ͷΤωϧ

3.9.3

֩ࢠ่յ୳ࡧ

ΪʔΛ࣋ͭχϡʔτϦϊ͸ଠཅத৺͔Βද໘ʹૉཻࢠͷඪ४໛‫Ͱܕ‬͸ɼి࣓૬‫ͱ༻࡞ޓ‬ऑ͍૬

ग़ͯ͘Δؒʹ෺࣭ޮՌʹΑΓ‫ڞ‬໐తʹछྨ͕มԽ

‫͕༻࡞ޓ‬౷Ұ͞ΕΔɻ͜ΕʹՃ͑ͯ‫ྗ͍ڧ‬΋௒ߴ͢ΔʢMikheyev-Smirnov-Wolfenstein, MSW ޮΤωϧΪʔͰ౷Ұ͞ΕΔͱ͢Δେ౷Ұཧ࿦Ͱ͸ɼՌ [42–44]ʣɻҰํͰɼ1 MeV ҎԼͷχϡʔτϦҰൠతͳ‫ͯ͠ͱ݁ؼ‬ཅࢠͷ่յ͕༧‫͞ݴ‬ΕΔɻ֩

ϊʹରͯ͠͸෺࣭ޮՌʹΑΔӨ‫͕ڹ‬গͳ͘ɼਅۭ

ࢠ่յͷ୳ࡧ͸ɼ࣮‫ݧ‬తʹ།ҰՄೳͳେ౷Ұཧ࿦தͷ఻೻ʹΑΔҐ૬ࠩͰͷৼಈͰ‫ه‬ड़Ͱ͖Δɻ݁ͷ௚઀త‫ূݕ‬ͷखஈͰ͋Γɼ΋͠ൃ‫͞ݟ‬ΕΕ͹ͦՌͱͯ͠ɼ3 MeV ෇ۙͰ͸χϡʔτϦϊৼಈͷͷӨ‫ڹ‬͸‫ܭ‬Γ஌Εͳ͍ɻͻͱͭͷ֩ࢠͷण໋͸㸶㸫 ͍Δɻਤ 7 ʹɼۙ೥εʔύʔΧϛΦΧϯσͰ୳ࡧ͞ΕͨόϦΦϯ਺ඇอଘϞʔυʹର͢Δण໋ͷԼ‫ݶ‬஋Λࣔ͢ɻ͜͜ʹࣔ͞Εͨ͢΂ͯͷϞʔυͰɼεʔύʔΧϛΦΧϯσ͕࠷΋‫ݶ੍͍͠ݫ‬Λ༩͑ͯ
͍Δɻ

3.9.4

௒৽੕χϡʔτϦϊ௒৽੕രൃͰ͸ɼΤωϧΪʔͷ 99%Ҏ্ΛχϡʔτϦϊ͕࣋ͪ‫ڈ‬ΔɻେϚθϥϯ੕ӢͰ‫͖ͨى‬௒৽੕ 1987A Ͱ͸ΧϛΦΧϯσͰ໿ 10 ඵؒʹ 11ࣄ৅͕‫؍‬ଌ͞Εͨ [47, 48]ɻͦͷ‫ޙ‬ɼ࢒೦ͳ͕Βզʑ͕χϡʔτϦϊͰ‫؍‬ଌՄೳͳ௒৽੕രൃ͸‫ى‬͖͍ͯͳ͍͕ɼզʑͷۜՏ‫Ͱ಺ܥ‬͸਺े೥ʹҰ౓ͷස౓Ͱ௒৽੕രൃ͕‫͖ى‬Δͱ༧૝͞Ε͍ͯΔɻ΋͠ԾʹۜՏ‫ܥ‬ͷத৺Ͱ௒৽੕രൃ͕‫͖ͨى‬৔߹ɼεʔύʔΧϛΦΧϯσͰ͸໿ 8,000 ࣄ৅Λ‫؍‬ଌͰ͖Δ͸ͣͰ͋ΓɼΤωϧΪʔ΍౸ୡ࣌ؒͷৄࡉͳଌఆ͔Β௒৽੕രൃͷϝΧχζϜʹؔͯ͠ඈਤ 7: ༷ʑͳόϦΦϯ਺ඇอଘϞʔυʹର͢ΔɼεʔύʔΧϛΦΧϯσʹΑΔण໋ͷԼ‫ݶ‬஋ɻ

1030 ೥Ҏ্ͱɼӉ஦ͷ೥ྸ 1.38 × 1010 ೥ʹൺ΂ͯ΋ͣͬͱ௕͍͕ɼ1 g ͷ෺࣭ʹ͸͓͓ΑͦΞϘΨυϩ਺ʢ6 × 1023 ʣͷ֩ࢠ͕‫·ؚ‬ΕΔɻͦ͜Ͱɼ

༂తʹଟ͘ͷ৘ใ͕ಘΒΕΔͱ‫ظ‬଴͞ΕΔɻ
௒৽੕രൃͰ͸χϡʔτϦϊ͕ޫΑΓ΋ૣ͘์ग़͞ΕΔͨΊɼ௒৽੕ͷ৴߸͕‫ݕ‬ग़͞Εͨ৔߹ʹ͸௚ͪʹσʔλΛղੳ̍࣌ؒ͠Ҏ಺ʹੈքதͷఱจ୆΍‫ʹऀڀݚ‬Ξφ΢ϯεΛग़͢ମ੍͕
੔උ͞Ε͍ͯΔ [49]ɻ·ͨɼੈք֤஍ͷχϡʔτͨͱ͑͹ 10 Ωϩτϯʢ1010 gʣͷ෺࣭Λ 1 ೥‫؍‬Ϧϊ‫ݕ‬ग़‫ث‬Λ݁ͼɼૣ‫ʹظ‬ΞϥʔτΛग़ͨ͢Ίͷଌ͢Ε͹ɼ1033 ೥ఔ౓ͷण໋ʹ‫౓ײ‬ͷ͋Δଌఆ͕

SNEWS(Supernova Early Warning System) ͱՄೳͱͳΔɻεʔύʔΧϛΦΧϯσ͸֩ࢠ่յʹ‫ݺ‬͹ΕΔγεςϜ [50, 51] ΋Քಇ͍ͯ͠Δɻ‫౓ײ‬ͷ͋Δ‫ݕ‬ग़‫܈ͯ͠ͱث‬Λൈ͍ͨੑೳΛ࣋ͪɼۜՏ‫Ͱ಺ܥ‬ͷ௒৽੕രൃ͸͍ͭ‫͜ى‬Δ͔༧ଌ࣮‫ݧ‬։࢝Ҏདྷ 20 ೥ʹΘͨΓ΄ͱΜͲͷ֩ࢠ่յͰ͖ͳ͍͕ɼӉ஦શମͰ͸̍ඵʹ̍ճͲ͔͜Ͱ௒

ϞʔυͰ࠷΋‫͍͠ݫ‬ण໋ͷԼ‫ݶ‬Λ༩͍͑ͯΔɻ

৽੕രൃ͕‫͍͖ͯى‬Δͱߟ͑ΒΕΔɻ࠷ॳͷ੕͕ཅࢠ่յͷ୅දతͳ่յϞʔυͱͯ͠ɼp →e+ π 0 ͕͋Δɻ·ͨɼ௒ରশੑΛߟ͑Δͱ p →Ͱ͖͔ͯΒ‫Ͱ·ࡏݱ‬ͷ௒৽੕രൃͰ์ग़͞ΕͨχϡʔτϦϊ͸Ӊ஦தΛඬ͓ͬͯΓɼ͜ΕΒ͸௒ν̄K + ͕༏੎ͳϞʔυͱͳΔ৔߹͕ଟ͍ͱ͞ΕΔɻ

৽੕എ‫ܠ‬χϡʔτϦϊͱ‫ݺ‬͹Ε͍ͯΔɻ௒৽੕എ

‫ࡏݱ‬ͷण໋ͷԼ‫ݶ‬஋͸ͦΕͧΕ 90%ͷ৴པ౓Ͱɼ

‫ܠ‬χϡʔτϦϊͷΤωϧΪʔ΍ϑϥοΫεΛଌఆτ /Br(p → e+ π 0 ) > 1.6 × 1034 ೥ɼτ /Br(p →ν̄K + ) > 6.6 × 1033 ೥Ͱ͋Δɻ͜ͷ΄͔ʹ΋ɼ͢Δ͜ͱͰɼ੕‫ܗ‬੒΍ॏ‫ݩ‬ૉ߹੒ͷྺ࢙ʹ͍ͭͯͷॏཁͳ৘ใΛಘΔ͜ͱ͕Ͱ͖Δɻ௿ΤωϧΪʔ༷ʑͳ่յϞʔυ΍ɼೋͭͷ֩ࢠ͕ಉ࣌ʹ่յͰ͸Ӊ஦ઢʹΑΔ֩ഁࡅͰੜ੒͞ΕΔ์ࣹੑಉ͢ΔϞʔυɼதੑࢠ-൓தੑࢠৼಈͳͲɼ༷ʑͳ

Ґ‫ݩ‬ૉ͕ɼߴΤωϧΪʔͰ͸େ‫ؾ‬χϡʔτϦϊ͕ϞʔυͰόϦΦϯ਺Λอଘ͠ͳ͍‫ݱ‬৅Λ୳ࡧͯ͠όοΫάϥ΢ϯυͱͳΔ͕ɼ16–30 MeV ෇ۙʹ㸶㸫 ‫؍‬ଌՄೳͳ΢Οϯυ΢͕͋Γɼ୳ࡧ͕ߦΘΕ͍ͯΛ෇Ճ͢Δ SK-Gd ‫ܭ‬ը͕͋Δ [55]ɻΨυϦχ΢

Δɻ௒৽੕എ‫ܠ‬χϡʔτϦϊ͸·ͩ‫؍‬ଌ͞Ε͍ͯϜ͸தੑࢠͷั֫அ໘ੵ͕େ͖͘ɼั֫࣌ʹ߹‫ܭ‬ͳ͍͕ɼεʔύʔΧϛΦΧϯσͰಘΒΕͨϑϥο

8 MeV ͷ γ ઢΛग़͢ɻ͜ΕΛ࢖ͬͯதੑࢠΛλΫεͷ্‫ݶ‬஋͸Ϟσϧ͔Β༧૝͞ΕΔ஋ͷ਺ഒͷά͢Δ͜ͱͰɼ௒৽੕എ‫ܠ‬χϡʔτϦϊͷόοΫ

ͱ͜Ζ·Ͱୡ͍ͯ͠Δ [52, 53]ɻ‫ޙ‬ड़͢Δ SK-Gd

άϥ΢ϯυΛআ‫͠ڈ‬৴߸ͷ‫؍‬ଌ͕ՄೳʹͳΔͱ‫ظ‬‫ܭ‬ըʹΑͬͯ‫ٯ‬ϕʔλ่յͷதੑࢠΛଊ͑ɼόο଴͞Ε͍ͯΔɻ·ͨɼχϡʔτϦϊͱ൓χϡʔτΫάϥ΢ϯυΛ࡟‫͖Ͱݮ‬Ε͹ɼ5 ೥ఔ౓ͷσʔλϦϊͰ‫ͱ֩ࢠݪ‬൓Ԡͨ͠ࡍͷதੑࢠͷ์ग़਺͕ҟऩूͰ௒৽੕എ‫ܠ‬χϡʔτϦϊͷ৴߸ΛੈքͰॳͳΔͨΊɼχϡʔτϦϊͱ൓χϡʔτϦϊΛ౷‫ܭ‬Ίͯ‫ݕ‬ग़Ͱ͖Δͱ‫ظ‬଴͞ΕΔɻ

తʹࣝผ͢Δੑೳ͕޲্͢Δ͜ͱ΋‫ظ‬଴Ͱ͖Δɻ࠷৽ͷ৘ใʹ͍ͭͯ͸ɼεʔύʔΧϛΦΧϯσ

3.9.5

ͷϗʔϜϖʔδ [56] ͳͲΛ͝ཡ͍͖͍ͨͩͨɻ

μʔΫϚλʔ୳ࡧ

Ӊ஦‫؍‬ଌ͔ΒɼӉ஦ͷΤωϧΪʔͷ໿ 27%ΛμʔΫϚλʔʢ҉ࠇ෺࣭ʣͱ‫ݺ‬͹ΕΔະ஌ͷཻࢠ

4͕͠Ί͍ͯΔ͜ͱ͕Θ͔͍ͬͯΔɻ΋ۜ͠Տத৺΍ଠཅɼ஍‫ٿ‬౳ͷॏྗϙςϯγϟϧʹμʔΫϚ
λʔ͕ั֫͞Εͯ͋Δఔ౓ͷີ౓ʹͳΔͱɼରফ໓͕‫͖ͯى‬Ұ෦͸χϡʔτϦϊΛ์ग़͢ΔՄೳੑ
͕͋ΔɻͦͷΑ͏ͳχϡʔτϦϊࣄ৅Λ୳ࡧ͢Δ
͜ͱͰɼؒ઀తͳμʔΫϚλʔ୳ࡧΛߦ͏͜ͱ͕
Ͱ͖ΔɻεʔύʔΧϛΦΧϯσ͸ɼଞͷ‫ݕ‬ग़‫ʹث‬ൺ΂ͯൺֱత௿ΤωϧΪʔʹ·Ͱ‫͕͋౓ײ‬Δͷ͕ಛ௃Ͱɼ200 GeV ҎԼͷ࣭ྔͷμʔΫϚλʔʹର͢Δɼεϐϯʹґଘͨ͠൓Ԡஅ໘ੵʹؔͯ͠͸࠷

T2K ࣮‫ݧ‬2009 ೥͔Βɼҵ৓‫ݝ‬౦ւଜͷେ‫౓ڧ‬ཅࢠՃ଎‫ࢪث‬ઃ J-PARC Ͱਓ޻తʹ࡞Γग़ͨ͠χϡʔτϦϊϏʔϜΛ 295 km ཭ΕͨεʔύʔΧϛΦΧϯ
σͰ‫؍‬ଌ͠ɼχϡʔτϦϊৼಈΛਫ਼ີʹଌఆ͢Δ

T2Kʢ౦ւ-to-ਆԬʣ࣮‫ߦ͕ݧ‬ΘΕ͍ͯΔ [57]ɻ͜ͷ࣮‫Ͱݧ‬͸εʔύʔΧϛΦΧϯσʹՃ͑ͯɼJ-

PARC ಺ʹઃஔ͞ΕͨલஔχϡʔτϦϊ‫ݕ‬ग़‫ث‬Ͱ΋χϡʔτϦϊΛଌఆ͍ͯ͠ΔɻҎԼͰ͸ɼए‫ׯ‬ͷಋೖͷ͋ͱ࣮‫ݧ‬શମͷ֓ཁΛઆ໌͠ɼલஔ
χϡʔτϦϊ‫ݕ‬ग़‫͍ͯͭʹث‬ղઆ͢Δɻ΋Α੍͍‫ݶ‬Λ༩͍͑ͯΔ [54]ɻ

3.10

4.1

ࠓ‫ޙ‬ͷల๬

Ճ଎‫ث‬χϡʔτϦϊՃ଎‫ث‬Λ༻͍ͨχϡʔτϦϊ࣮‫ݧ‬͸ɼ1962 ೥ʹεʔύʔΧϛΦΧϯσ͸ɼ࣮‫ݧ‬։͔࢝Β 20 ೥νμ Λൃ‫ ͨ͠ݟ‬BNL-AGS Ͱͷ࣮‫[ ݧ‬58,59] ʹ࢝·‫ࠓͨͬܦ‬΋ੈքͰҰ‫ڃ‬ͷ੒ՌΛग़͠ଓ͚͍ͯΔ‫ڻ‬Γɼऑ͍૬‫༻࡞ޓ‬ͷதੑΧϨϯτͷൃ‫[ ݟ‬60] ΍֩͘΂͖૷ஔͰ͋Δ͕ɼ͞ΒʹੑೳΛ޲্ͤ͞Δ΂ࢠߏ଄ͷ‫ڀݚ‬ɼిऑ૬‫༻࡞ޓ‬ͷ‫Ͳͳڀݚ‬ɼૉཻࢠ͘ɼ౒ྗ͕ଓ͚ΒΕ͍ͯΔɻ

ͷඪ४໛‫ܕ‬ͷཱ֬ʹॏཁͳ໾ׂΛՌͨͨ͠ɻՃ଎

ͦͷͻͱ͕ͭɼࣄ৅࠶ߏ੒ͷΞϧΰϦζϜΛ৽‫ث‬χϡʔτϦϊΛ༻͍ͨχϡʔτϦϊৼಈͷ୳ࡧ

͘͢͠Δ͜ͱʹΑΓɼ࠶ߏ੒ͷਫ਼౓Λ্͛Δ͜ͱ

΋֤஍ͰߦΘΕ͕ͨɼ‫ॴڀݚ‬ͷෑ஍಺ʹ‫ݕ‬ग़‫ث‬ΛͰ͋Δɻ͢ͰʹͦͷҰ෦͸ T2K ࣮‫Ͱݧ‬όοΫάஔͨ͘Ίɼ‫ج‬ઢʢχϡʔτϦϊͷൃੜ఺͔Βଌఆϥ΢ϯυࣄ৅ͷআ‫࢖ʹڈ‬ΘΕ͍ͯΔ͕ɼେ‫ؾ‬χϡʔ఺·Ͱͷ‫཭ڑ‬ʣ͸ 1km ఔ౓ͷΦʔμʔͰ͋ͬͨɻ

τϦϊͷ‫ڀݚ‬΍ཅࢠ่յ୳ࡧʹ΋ద༻͢Δ͜ͱͰՃ଎‫ʹث‬ΑΔχϡʔτϦϊϏʔϜੜ੒ͷ‫ݪ‬ཧ‫্͢޲͕౓ײ‬Δͱ‫ظ‬଴͞Ε͍ͯΔɻ͸ɼ‫ج‬ຊతʹେ‫ؾ‬χϡʔτϦϊͷੜ੒ϓϩηεͱେ‫ن‬໛ͳ‫ݕ‬ग़‫ث‬ͷΞοϓάϨʔυͱͯ͠ɼਫʹಉ͡Ͱ͋ΓɼߴΤωϧΪʔͷཅࢠϏʔϜΛඪతʹΨυϦχ΢ϜΛ༹͔͜͠Έɼதੑࢠͷ‫ݕ‬ग़ೳྗরࣹͨ͠ͱ͖ʹੜ͡Δ π தؒࢠ΍ K தؒࢠͷ่㸶㸫 յͰͰ͖ͨχϡʔτϦϊΛ༻͍ΔɻதͰ΋ओཁͳ

Ceramic insulator ring‫د‬༩Λ͢Δ π ± ͸ 99%Ҏ্ͷ֬཰Ͱ

π + → μ+ + ν μ ,π − → μ− + ν̄μInner conductor(12)

Outer conductor

Current direction

ͱ่յ͢ΔͨΊ10 ɼՃ଎‫ث‬χϡʔτϦϊϏʔϜ

Magnetic field direction͸‫ج‬ຊతʹϛϡʔ‫ܕ‬ͷχϡʔτϦϊ͔ΒͳΔɻK
தؒࢠͷ่յ΍ μ ͷ่յ͔Βੜ·ΕΔిࢠ‫ܕ‬ͷχϡʔτϦϊ΋ए‫·ؚׯ‬ΕΔ͜ͱʹͳΔ͕ɼϏʔਤ 8: T2K ͷୈ̍ϗʔϯͷஅ໘ਤ [64]ϜதʹͲͷ͘Β͍ͷׂ߹͕ࠞೖ͢Δ͔͸ϏʔϜϥΠϯͷઃ‫ʹܭ‬ΑΔɻT2K ࣮‫Ͱݧ‬͸ɼ࠷΋ϑϥοͪɼՃ଎‫࡞Ͱث‬Δ 1 GeV ఔ౓ͷχϡʔτϦϊΛΫεͷଟ͍ 0.6 GeV ෇ۙͰͷిࢠχϡʔτϦϊ਺ඦΩϩඈ͹࣮͢‫͖Ͱ͕ݧ‬Ε͹ɼχϡʔτϦϊৼͷࠞೖ͸ 1%ҎԼͰ͋Δɻಈͷਫ਼ີଌఆ͕ՄೳʹͳΔɻχϡʔτϦϊ͸෺࣭ཅࢠϏʔϜͱඪతͷ൓ԠͰཻࢠ͸޿͍֯౓ʹੜதΛඈΜͰߦͬͯ΋΄ͱΜͲःΒΕΔ͜ͱ͕ͳ͍

੒͞ΕΔ͕ɼ‫ݕ‬ग़‫ʹث‬౸ୡ͢ΔχϡʔτϦϊͷ਺ͨΊɼ਺ඦΩϩඈ͹͢͜ͱ͸ՄೳͰ͋Δɻ͔͠͠Λ૿΍ͨ͢Ίʹ͸ɼͰ͖Δ͚ͩߜͬͨϏʔϜΛ࡞౰વɼ਺ඦΩϩઌͰ͸‫ݕ‬ग़‫ʹ಺ث‬ೖΔχϡʔτϦΓ͍ͨɻχϡʔτϦϊ͸ऑ͍૬‫͍ͳ͔͠͠༻࡞ޓ‬ϊͷ਺͕‫ͨ͏·ͯͬ͠ݮ‬Ίɼ‫ͳྗڧ‬χϡʔτϦϊͨΊ੍‫͢ޚ‬Δ͜ͱ͕Ͱ͖ͳ͍͕ɼ่յલͷ π ± ͸ి‫ڊͱݯ‬େͰߴੑೳͳχϡʔτϦϊ‫ݕ‬ग़‫͕ث‬ඞཁʹՙΛ࣋ͭͨΊి࣓‫ޚ੍Ͱྗؾ‬ՄೳͰ͋Δɻπ ± ΛͳΔɻऩଋ͢ΔͨΊʹ༻͍ΒΕΔͷ͕ి࣓ϗʔϯͱ‫ݺ‬͹ੈքͰॳΊͯͷ௕‫ج‬ઢχϡʔτϦϊৼಈ࣮‫ݧ‬

ΕΔ૷ஔͰ͋Γɼ֬཰ྫྷ٫Ͱ W /Z ͷൃ‫ݙߩʹݟ‬͸ KEK ʹ͋ͬͨ 12 GeV ཅࢠγϯΫϩτϩϯ

͠ϊʔϕϧ৆Λऔͬͨ Simon van der Meer [61]ͰχϡʔτϦϊϏʔϜΛ࡞Γɼ250 km ཭Εͨͷൃ໌඼Ͱ͋Δ [62]ɻT2K ͷୈ̍ϗʔϯͷஅ໘ਤεʔύʔΧϛΦΧϯσʹଧͪࠐΉ K2KʢKEK-Λਤ 8 ʹࣔ͢ɻϏʔϜͷλΠϛϯάʹ߹Θͤ਺ඦ

to-Kamiokaʣ࣮‫ͨͬ͋Ͱݧ‬ɻK2K ࣮‫ݧ‬͸੢઒ެΩϩΞϯϖΞͷύϧεిྲྀΛྲྀ͢͜ͱͰτϩΠμҰ࿠ࢯʹΑͬͯఏҊ͞ΕɼχϡʔτϦϊৼಈൃ‫ݟ‬ϧ࣓৔Λ࡞ΓϏʔϜΛऩଋ͢Δɻిྲྀͷ޲͖ʹΑͷ௚‫ޙ‬ɼ1999 ೥͔Β࣮‫ݧ‬Λߦͬͨɻ࣮‫ʹݧ‬ඞཁΓ࣓৔ͷ޲͖Λ൓సͤ͞Δ͜ͱ͕ՄೳͰ͋Γɼπ +ͳେ‫ن‬໛ͳࢪઃͷ४උ͸਺೥͔͔Δ΋ͷͰɼεʔΛऩଋ͢Ε͹ϏʔϜதͷओͳ੒෼͕χϡʔτϦϊύʔΧϛΦΧϯσͷ݁Ռ͕൑໌͢ΔΑΓ΋લ͔ΒʹͳΓ π − Λऩଋ͢Ε͹൓χϡʔτϦϊʹͳΔɻ

‫ݐ‬ઃ͕࢝ΊΒΕ͍ͯͨɻ͜Ε͸౰࣌ͷੁ‫ߏػݪ‬௕

T2K Ͱ͸ 3 ୆ͷి࣓ϗʔϯΛ࢖༻͍ͯ͠Δ [63]ɻͷӳஅʹΑΔ΋ͷͰ͋ͬͨΑ͏ͩɻK2K ͸ 2004ͦΕͧΕ 320 kA ͷిྲྀ͕ྲྀͤΔΑ͏ઃ‫͞ܭ‬Εͯ೥·Ͱ࣮‫ݧ‬Λߦ͍ɼੈքͰॳΊͯେ‫ؾ‬χϡʔτϦ͍ͯɼ‫Ͱ·ࡏݱ‬ͷͱ͜Ζ 250 kA Ͱӡస͍ͯ͠Δɻϊͷ݁ՌΛਓ޻χϡʔτϦϊͰ֬ೝͨ͠ [65]ɻ

K2K ࣮‫ݧ‬͸ɼGPS ʹΑΔ࣌ؒಉ‫ظ‬΍લஔ‫ݕ‬ग़‫ث‬

4.2

ͷ࢖༻ͳͲ௕‫ج‬ઢ࣮‫ݧ‬ͷ‫ج‬ຊతͳٕज़Λཱ֬͠ɼ௕‫ج‬ઢχϡʔτϦϊৼಈ࣮‫ݧ‬௕‫ج‬ઢχϡʔτϦϊৼಈ࣮‫͕ݧ‬ՄೳͰ͋Δ͹͔Γେ‫ؾ‬χϡʔτϦϊʹΑΓଌΒΕ࣭ͨྔೋ৐ࠩ

Δm232  2.5 × 10−3 ͔ΒɼରԠ͢ΔχϡʔτϦͰͳ͘ɼχϡʔτϦϊৼಈͷ‫ʹڀݚ‬ඇৗʹ༗ޮͳखஈͰ͋Δ͜ͱΛূ໌ͨ͠ɻগ͠஗ΕͯถࠃͰ͸

MINOS ࣮‫͕ݧ‬ɼϤʔϩούͰ͸ OPERA ࣮‫͕ݧ‬500(km)/1(GeV) Ͱ͋Δ͜ͱ͕Θ͔Δɻ͢ͳΘߦΘΕɼ௕‫ج‬ઢχϡʔτϦϊৼಈ࣮‫ݧ‬͸ૉཻࢠ෺ϊৼಈͷޮՌ͕࠷ॳʹ‫ۃ‬େʹͳΔͷ͸ L/E
10

π + → e+ + νe ʹ่յ͠ʹ͍͘ͷ͸ɼϔϦγςΟαϓ
ϨογϣϯʹΑΔɻཧ࣮‫ݧ‬ͷͻͱͭͷ෼໺ͱཱͯ֬ͨ͠͠ɻ

㸶㸫 

4.3

T2K ࣮‫֓ݧ‬ཁτϦϊʹมԽ͍ͯ͠ΔՄೳੑ͸࢒͍ͬͯͨɻి

K2K ࣮‫ݧ‬ͷ‫ݧܦ‬Λ΋ͱʹɼ೔ຊͰͷୈ 2 ੈ୅ͷ௕‫ج‬ઢχϡʔτϦϊৼಈ࣮‫ͨͬ·࢝ͯ͠ͱݧ‬ͷ
͕ T2K ࣮‫͋Ͱݧ‬Δɻཻ̎࣍ࢠͷੜ੒਺͸େ·͔ʹ‫ͯͬݴ‬ཅࢠͷΤωϧΪʔͱ਺ͷੵʹൺྫ͢ΔͨΊɼ୯Ґ࣌ؒ౰ͨΓͷཻࢠੜ੒਺͸ [ΤωϧΪʔ]ʗ [࣌ؒ]ɼͭ·Γϫοτͷ୯ҐͰද͞ΕΔϏʔϜύϫʔʹൺྫ͢ΔɻKEK 12GeV-PS ͷϏʔϜύϫʔ͕໿ 5 kW Ͱ͋ͬͨͷʹର͠ɼJ-PARC ͷઃ‫ܭ‬ϏʔϜύϫʔ͸ 750 kWɼ2016 ೥ 7 ݄‫ࡏݱ‬ͷୡ੒஋͸ 425 kW Ͱ͋Γɼͬ͘͟Γ 100 ഒͷΦʔμʔͷ‫౓ڧ‬ͷϏʔϜ͕ར༻Ͱ͖Δ͜ͱʹͳΔɻ
χϡʔτϦϊৼಈ͕ൃ‫͞ݟ‬ΕͨͷͪɼχϡʔτϦϊৼಈΛ৽ͨͳ‫ڀݚ‬खஈͱͯ͠༻͍Δ͜ͱͰχϡʔτϦϊͷੑ࣭͕໌Β͔ʹͳ͖ͬͯͨɻࠓ‫ޙ‬ͷ࠷΋ॏཁͳ໨ඪ͸ɼχϡʔτϦϊͷ CP ରশੑͷഁΕͷ୳ࡧͰ͋ΔɻC ͸ՙి‫ڞ‬໾ʢిՙ౳ͷූ߸ΛೖΕସ͑ΔʣɼP ͸ύϦςΟʢۭؒ࠲ඪͷූ߸Λม͑ΔʣͰ͋ΓɼCP ม‫׵‬͸ཻࢠͱ൓ཻࢠΛࢠχϡʔτϦϊग़‫ݱ‬ͷ֬཰͸ɼχϡʔτϦϊͷ 3ͭͷࠞ߹֯ʢࣜ (9) ࢀরʣͷ͏ͪ θ13 ͷେ͖͞ʹґଘ͢Δɻେ‫ؾ‬χϡʔτϦϊͱՃ଎‫ث‬χϡʔτϦϊ͔Β θ23 ͕ 45◦ ʹۙ͘ɼଠཅχϡʔτϦϊͱ

KamLAND ͔Β θ12 ͕໿ 34◦ Ͱ͋Δ͜ͱ͕Θ͔͕ͬͨɼୈ 3 ͷࠞ߹֯ θ13 ͷ஋ʹ͍ͭͯ͸ա‫ڈ‬ͷ‫ݪ‬ࢠ࿍࣮‫͔ݧ‬Β໿ 12◦ ΑΓ΋খ͍͜͞ͱ͔͠Θ͔͍ͬͯͳ͔ͬͨɻ
ͦ͜ͰɼT2K ࣮‫ݧ‬ͷ࠷ॳͷେ͖ͳ໨ඪ͸ J-

PARC ͱεʔύʔΧϛΦΧϯσΛ૊Έ߹Θͤͨେ౷‫ܭ‬ɾߴਫ਼౓ͷσʔλͰిࢠχϡʔτϦϊग़‫ݱ‬ͷ୳ࡧΛߦ͏͜ͱͰ͋ͬͨɻ΋͠Έ͔ͭΕ͹ɼ͞ΒʹχϡʔτϦϊͱ൓χϡʔτϦϊͰͷଌఆΛൺֱ͢Δ͜ͱͰ CP ରশੑͷഁΕͷ୳ࡧ΁ͱਐΉઓུͰ͋Δɻ·ͨಉ࣌ʹɼχϡʔτϦϊࠞ߹ͷύϥϝʔλͷਫ਼ີଌఆ΍χϡʔτϦϊ-‫֩ࢠݪ‬൓Ԡஅ໘ੵͷৄࡉͳ‫ڀݚ‬ɼχϡʔτϦϊΛ࢖ͬͨ৽෺ཧ
ͷ୳ࡧͳͲ΋ߦ͏͜ͱ͕Ͱ͖Δɻ

ೖΕସ͑Δ͜ͱʹରԠ͢ΔɻχϡʔτϦϊৼಈͷ֬཰ΛχϡʔτϦϊͱ൓χϡʔτϦϊͰൺ΂Δ͜

4.4ͱͰɼϨϓτϯʹ͓͚Δ CP ରশੑͷഁΕͷ‫؍‬ଌ͕ՄೳͱͳΔɻͱ͜Ζ͕ɼχϡʔτϦϊৼಈͷ‫؍‬ଌํ๏ͷ͏ͪʮফࣦʯϞʔυͰ͸ɼχϡʔτϦϊϏʔϜϥΠϯJ-PARC Ճ଎‫͔ث‬Β‫͞څڙ‬ΕΔେ‫౓ڧ‬ͷཅࢠϏʔϜΛ࢖ͬͯχϡʔτϦϊΛ࡞Γग़͢χϡʔτϦϊϏʔϜϥΠϯ΋ɼ࠷ઌ୺ͷٕज़ͷմͰ͋ΔɻP (να → να ) −−−→ P (ν̄α → ν̄α )Ճ଎‫͔ث‬Βཅࢠ͕औΓग़͞ΕΔՕॴҎ߱ͷϏʔͰ͋ΓɼCPT ରশੑΛԾఆ͢ΔͱχϡʔτϦϊͱΔ͕ɼϏʔϜύϫʔ޲্ͱ҆ఆͳӡ༻͸Ճ଎‫ث‬ά൓χϡʔτϦϊͷৼಈ֬཰ʹҧ͍͸ͳ͍ɻCP ରϧʔϓͱ࣮‫ݧ‬άϧʔϓͷ‫ʹྗڠͳີۓ‬ΑΓ੒ΓশੑͷഁΕͷ୳ࡧʹ͸ɼʮग़‫ݱ‬ʯϞʔυͰ P (να →ཱ͍ͬͯΔɻ

CP T

ϜϥΠϯ͸ T2K ࣮‫ݧ‬άϧʔϓͷઃ‫ܭ‬ɾӡ༻ʹΑνβ ) ͱ P (ν̄α → ν̄β ) Λਫ਼ີʹଌఆͯ͠ൺֱ͢Δ͜

ਤ 9 ʹ J-PARC χϡʔτϦϊϏʔϜϥΠϯͷ

ͱ͕ඞཁͱͳΔɻલड़ͷ௨ΓɼՃ଎‫ث‬ϏʔϜͰ࡞ུ֓Λࣔ͢ɻJ-PARC ϝΠϯϦϯάͰ 30GeV ʹΕΔͷ͸ϛϡʔχϡʔτϦϊͰ͋Δɻλ΢χϡʔՃ଎͞ΕͨཅࢠϏʔϜ͸ 2.48 ඵʹҰ౓ʢ2016 ೥τϦϊ͸‫ݕ‬ग़͕೉͍ͨ͠ΊɼϛϡʔχϡʔτϦϊ‫ࡏݱ‬ʣɼϦϯάͷ಺ଆʹ͋ΔϏʔϜϥΠϯ 11 ʹऔ͔ΒిࢠχϡʔτϦϊ΁ͷมԽ (νμ → νe ɼిࢠΓग़͞ΕɼਆԬͷํ޲΁໿ 80 ౓‫͛ۂ‬ΒΕͨ‫ޙ‬ɼχϡʔτϦϊग़‫ )ݱ‬Λ࢖͏͜ͱ͕Ͱ͖Ε͹ CP ର

ඪత·Ͱ༌ૹ͞ΕΔɻඪతͰൃੜͨ͠ π தؒࢠশੑͷഁΕͷ୳ࡧ͕ՄೳʹͳΔɻେ‫ؾ‬χϡʔτϦ

͸ 3 ୆ͷి࣓ϗʔϯͰऩଋ͞Ε [66]ɼ่յྖҬͰϊ΍ୈ 1 ੈ୅ͷ௕‫ج‬ઢ࣮‫ݧ‬ͷ݁Ռ͔ΒɼϛϡʔχϡʔτϦϊ͸΄ͱΜͲ͕λ΢χϡʔτϦϊʹมԽ͍ͯ͠ΔͱΘ͔͕ͬͨɼ͘͝Ұ෦͕ిࢠχϡʔ11௨ৗ͸ɼϦϯάͷ֎ଆʹऔΓग़͢΋ͷͰ͋Δ͕ɼෑ஍ͷ౎߹Ͱ͜ͷΑ͏ͳઃ‫͍ͯͬͳͱܭ‬ΔɻੈքͰ΋ϢχʔΫͳϏʔϜϥΠϯͱࢥΘΕΔɻ㸶㸫 J-PARCメインリング

νビーム

P(νμ→ νe)

神岡方向

陽子ビーム

P(νμ→ νμ)1
前置ニュートリノ検出器

崩壊領域(→µ+ν)標的
ビームダンプミューオンモニター

sin22θ23 = 1.0
sin22θ13 = 0.1
2
Δm32 = 2.4 × 10-3 eV2

0.5

0.1

NH, δCP = 0
NH, δCP = π/2

0.05

OA 0.0°OA 2.0°OA 2.5°(A.U.)1

Φ29
νμਤ 9: J-PARC χϡʔτϦϊϏʔϜϥΠϯͷུ֓π → μ + νμ ͷ่յʹΑΓχϡʔτϦϊΛੜ੒͢ΔɻχϡʔτϦϊҎ֎ͷ΄ͱΜͲͷཻࢠΛࢭΊΔ
ΔߴΤωϧΪʔͷϛϡʔΦϯΛଌఆ͢Δ͜ͱͰඪతͰੜ੒͞Εͨ 2 ࣍ɾ3 ࣍ϏʔϜͷঢ়‫گ‬ΛϦΞϧλΠϜͰ‫͢ࢹ؂‬ΔϛϡʔΦϯϞχλʔ͕ઃஔ͞Ε͍ͯΔ [67]ɻ

T2K ͷχϡʔτϦϊϏʔϜͷେ͖ͳಛ௃ͱ͠
ͯɼʮΦϑΞΫγε๏ʯ [68] Λ༻͍͍ͯΔ͜ͱ͕‫͛ڍ‬ΒΕΔɻπ தؒࢠΛऩଋ͢Δํ޲ΛΘ͟ͱগ͚ͩ͠εʔύʔΧϛΦΧϯσͷํ޲͔ΒͣΒͯ͠΍ΔͱɼεʔύʔΧϛΦΧϯσͷํ޲ʹඈΜͰ͍͘χϡʔτϦϊͷΤωϧΪʔ͕ӡಈֶత੍໿ʹΑΓ΄΅୯৭ʹͳΔɻ͜ΕʹΑΓɼχϡʔτϦϊͷϑϥοΫε͕࠷େͱͳΔΤωϧΪʔΛৼಈ֬཰͕࠷େͱͳΔ஋ʹ߹Θͤɼ͔͠΋όοΫάϥ΢ϯυ
ͷ‫ݪ‬ҼͱͳΔߴΤωϧΪʔͷχϡʔτϦϊͷ਺Λ‫ݮ‬Βͨ͠ϏʔϜΛ࡞Γग़͢͜ͱ͕ՄೳͱͳΔɻ
ਤ 10 ʹɼT2K Ͱͷ‫ج‬ઢ௕ 295 km ͰͷχϡʔτϦϊৼಈ֬཰ͷΤωϧΪʔґଘੑͱɼΦϑΞΫγ
ε֯ΛมԽͤͨ࣌͞ͷχϡʔτϦϊΤωϧΪʔεϖΫτϧͷ༧૝஋Λࣔ͢ɻT2K Ͱ͸ɼχϡʔτϦϊৼಈ֬཰͕࠷େͱͳΔΤωϧΪʔʹ߹Θͤɼ2.5
౓ͷΦϑΞΫγε֯Λ࠾༻͍ͯ͠ΔɻεʔύʔΧϛΦΧϯσʹ޲͚ͯϏʔϜΛऩଋͨ͠৔߹ʢΦϑΞΫγε 0 ౓ʣʹൺ΂ɼχϡʔτϦϊϑϥοΫε

0.5

0
0

ϏʔϜμϯϓͷഎ‫ʹޙ‬͸ɼμϯϓΛಥ͖ൈ͚ͯ͘

IH, δCP = 0
IH, δCP = π/2

1Eν (GeV)23ਤ 10: ‫ج‬ઢ 295 km ͰͷχϡʔτϦϊৼಈ֬཰ͷΤωϧΪʔґଘੑͱɼΦϑΞΫγε֯ΛมԽͤͨ࣌͞ͷχϡʔτϦϊΤωϧΪʔεϖΫτϧͷ༧૝஋͕ϐʔΫ෦Ͱ͸૿͍͑ͯΔҰํͰɼߴΤωϧΪʔ੒෼͕཈͑ΒΕ͍ͯΔ͜ͱ͕Θ͔Δɻ͜ͷΑ͏ͳΦϑΞΫγε๏Λ࣮ࡍʹ࢖༻࣮ͨ͠‫ݧ‬͸ T2K ͕ੈքͰॳΊͯͰ͋Δʢͦͷ‫ޙ‬ɼถࠃͰͷ NOνA ࣮‫Ͱݧ‬΋࠾༻͞Ε͍ͯΔʣɻ

J-PARC ͷΑ͏ʹେ‫౓ڧ‬ͷཅࢠϏʔϜΛ༻͍Δʹ͸ɼϏʔϜͷঢ়ଶΛߴਫ਼౓Ͱ‫͢ޚ੍͠ࢹ؂‬Δ͜
ͱ͕ܾఆతʹॏཁͱͳΔɻྫ͑͹ϏʔϜϥΠϯதͰཅࢠϏʔϜͷ‫ي‬ಓ͕ͣΕΔͳͲͯ͠ϏʔϜϩε
͕૿͑Δͱɼपғͷ‫ࣹ์͕ثػ‬Խͯ͠อक͕Ͱ͖
ͳ͘ͳΔ‫ڪ‬Ε͕͋Δ 12 ɻ͋Δ͍͸ɼେ‫౓ڧ‬ͷཅࢠϏʔϜ͕ύϧεঢ়ʹরࣹ͞ΕΔඪత͸ઈ͑ͣ೤ি
ܸʹ͞Β͞Ε͍ͯΔͨΊɼϏʔϜͷҐஔ͕ඪతͷத৺͔ΒͣΕͨΓϏʔϜ͕ࡉա͗ͨΓ͢Δͱഁଛ͢Δ‫ڪ‬Ε͕͋Δɻ·ͨɼϏʔϜ͕ඪతʹ౰ͨΔҐ
12ඪతपล෦ͳͲӡ༻্ߴ౓ͷ์ࣹԽ͕ආ͚ΒΕͳ͍৔ॴ͸ɼਓ͕ۙͮ͘͜ͱͳ͘ϦϞʔτͰอकͰ͖Δઃ‫ͬͳͱܭ‬
͍ͯΔɻ

㸶㸫 

2011

2012

27 May 2016
POT total: 1.510×1021

2013

2014

2015

2016

-mode POT: 7.57×1020 (50.14%)
-mode POT: 7.53×1020 (49.86%)

ਤ 11: 2016 ೥Ն·Ͱͷ T2K ࣮‫ݧ‬ͷσʔλऩूঢ়‫گ‬ɻ఺͸֤࣌఺ͰͷϏʔϜύϫʔʢӈ࣠ʣΛɼ࣮ઢ͸ඪతʹ౰ͨͬͨཅࢠͷ਺ (POTʣͷੵࢉ஋ʢࠨ࣠ʣΛද͢ɻ

ਤ 12: INGRID ‫ݕ‬ग़‫ث‬͢ɻ఺͸ϏʔϜύϫʔʢӈ࣠ʣΛɼ࣮ઢ͸ඪతʹ౰ͨͬͨཅࢠͷ਺ (POTʣͷੵࢉ஋ʢࠨ࣠ʣΛද͢ɻ

2016 ೥Ն·Ͱʹඪతʹ౰ͨͬͨཅࢠͷ਺ (protons
ஔ͕ͣΕΔͱχϡʔτϦϊϏʔϜͷํ޲͕ͣΕɼ

on target, POT) ͱͯ͠౰ॳ໨ඪ (7.8 × 1021 ) ͷεʔύʔΧϛΦΧϯσͰ‫؍‬ଌ͞ΕΔχϡʔτϦϊ

໿ 19%ʹ౰ͨΔ 1.5 × 1021 POT ͷσʔλΛऩूͷΤωϧΪʔ͕มΘͬͯ͠·͏ɻ͜ͷͨΊɼӡస͍ͯ͠Δɻ2014 ೥͔Β 2016 ೥͸ओʹ൓χϡʔτதͷϏʔϜύϥϝʔλΛਫ਼֬ʹ஌Δ͜ͱ͸࣮‫ݧ‬ͷϦϊͷϞʔυͰ࣮‫ݧ‬Λߦ͍ɼ͜Ε·Ͱʹχϡʔτ੒ޭʹෆՄܽͰ͋Γɼ͜ΕΒͷཁ੥Λຬͨͨ͢ΊɼϦϊͱ൓χϡʔτϦϊͷσʔλΛ POT ͱ͓ͯ͠ϏʔϜϥΠϯͷશ௕ʹΘͨͬͯཅࢠϏʔϜͷ‫౓ڧ‬͓Αͦ൒ʑͷׂ߹Ͱऩू͍ͯ͠Δɻ΍Ґஔɼ޿͕ΓΛ஌ΔͨΊͷछʑͷϞχλʔ͕ઃஔ͞Ε͍ͯΔ [69]ɻ
χϡʔτϦϊϏʔϜͷϑϥοΫε͸ɼ࣮ଌ͞Ε

4.5

લஔ‫ݕ‬ग़‫ث‬ͨϏʔϜύϥϝʔλΛ΋ͱʹϞϯςΧϧϩγϛϡ

εʔύʔΧϛΦΧϯσͰ‫؍‬ଌͨ͠χϡʔτϦϊϨʔγϣϯͰ‫ٻ‬ΊΒΕΔ [70]ɻෆఆੑͷେ͖ͳ‫ݪ‬ͷ൓Ԡ਺΍ΤωϧΪʔ෼෍ΛɺχϡʔτϦϊৼಈҼͱͳΔ π தؒࢠͷੜ੒அ໘ੵʹؔͯ͠͸ɼCERN

ͷύϥϝʔλΛԾఆͨ͠ͱ͖ͷ༧૝ͱൺֱ͢Δ͜

Ͱߦͬͨ NA61 ࣮‫࣮Ͱݧ‬ଌͨ͠அ໘ੵ [71–74] ΛͱͰɼχϡʔτϦϊৼಈͷύϥϝʔλΛଌఆ͢Δ

࢖ͬͯγϛϡϨʔγϣϯΛνϡʔϯ͢Δ͜ͱͰෆ͜ͱ͕Ͱ͖Δɻ͔͠͠ɼඪతͰͷ π தؒࢠͷੜ੒ఆੑΛ཈͍͑ͯΔɻ

அ໘ੵ΍χϡʔτϦϊͷ൓Ԡஅ໘ੵͷෆఆੑ͕େ

ϏʔϜϥΠϯͷίϛογϣχϯά͸ 2009 ೥ 4͖͍ͨΊɼͦͷ··Ͱ͸ߴਫ਼౓ͷଌఆ͸೉͍͠ɻ݄ʹ࢝·Γɼ2010 ೥ॳ಄͔Βຊ֨తͳ࣮‫ݧ‬Λ࢝Ίͦ͜Ͱɼੜ੒௚‫ޙ‬ͷχϡʔτϦϊΛ௚઀ଌఆͯ͠

ͨɻେ‫౓ڧ‬ϏʔϜϥΠϯͷӡ༻͸Ұ‫ے‬ೄͰ͸͍͔ϏʔϜͷಛੑ΍χϡʔτϦϊ൓Ԡஅ໘ੵΛཧղͣ͢ɼ์ࣹԽ΍‫ثػ‬ͷ‫ނ‬োɼਫ࿙ΕͳͲɼ࣮‫͕ݧ‬ਐ

Δ͜ͱͰɼχϡʔτϦϊৼಈଌఆͷਫ਼౓ͱ৴པ౓

ΉʹͭΕ৽ͨͳ໰୊͕ൃੜͦ͠ͷରԠʹ௥ΘΕͨΛ্͛ΔͨΊͷ૷ஔ͕ɼඪత͔Β໿ 280 m Լྲྀʹ͕ɼ1 ೥໨͸ 50 kW ఔ౓Ͱ͋ͬͨϏʔϜύϫʔ΋ஔ͔Εͨલஔ‫ݕ‬ग़‫͋Ͱث‬Δɻ

425 kW ·Ͱ্͕Γ҆ఆͳσʔλऩूΛୡ੒Ͱ͖

T2K ࣮‫ݧ‬ͷલஔ‫ݕ‬ग़‫ث‬͸ɼେ͖͘෼͚ͯ 2 छྨ

͍ͯΔɻਤ 11 ʹ͜Ε·Ͱͷσʔλऩूঢ়‫گ‬Λࣔͷ‫ݕ‬ग़‫ث‬γεςϜ͔Βߏ੒͞Ε͍ͯΔɻͻͱͭ໨㸶㸫 ϓϥενοΫγϯνϨʔλΛ࢖༻͍ͯ͠Δ [75]ɻ
ͨͩ͠ɼFGD ͸ Fermilab Ͱ։ൃ͞ΕͨॲํʹैͬͯΧφμͰ੡࡞ͨ͠΋ͷΛɼSMRD ͸ϩγΞͰಠࣗʹ੡࡞ͨ͠΋ͷΛ༻͍͍ͯΔɻϙϦενϨϯ
Λϕʔεʹ PPO ͱ POPOP Λ࣭ྔൺͰͦΕͧΕ

1%ͱ 0.03%ͷൺͰࠞͨ΋ͷͰɼԡ͠ग़͠੒‫ʹܗ‬ΑΓ҆ՁʹେྔͷγϯνϨʔλ͕ੜ࢈Ͱ͖Δɻ·ͨɼ੍࡞࣌ʹ೾௕ม‫׵‬ϑΝΠόʔΛ௨ͨ͢Ίͷ݀ͱࢎԽνλϯϕʔεͷ൓ࣹࡐΛ‫ؚ‬Μͩ֎૚͕ಉ࣌
ʹ੒‫͞ܗ‬ΕΔɻγϯνϨʔλ͔Βͷޫ͸೾௕ม‫׵‬ϑΝΠόʔͰूޫ͠ɼޫ‫ݕ‬ग़‫Ͱ·ث‬ಋ͘ɻ೾௕ม
‫׵‬ϑΝΠόʔ͸શͯͷ‫ݕ‬ग़‫Ͱث‬ΫϥϨࣾʹΑΔ௚
‫ ܘ‬1mm ͷ Y-11(200)MS Λ࢖͍ͬͯΔɻਤ 13: ND280 ‫ݕ‬ग़‫ث‬

4.6.2
ͷ‫ݕ‬ग़‫ث‬͸χϡʔτϦϊϏʔϜͷํ޲ɼϓϩϑΝΠϧɼ‫౓ڧ‬ɼ҆ఆੑΛϞχλʔ͢ΔχϡʔτϦϊϞχλʔ INGRIDʢInteractive Neutrino GRIDɼਤ 12ʣͰ͋Δɻ΋͏ͻͱͭ͸ɼεʔύʔΧϛΦΧϯσํ޲ʹ޲͔͏χϡʔτϦϊͷछྨɼϑϥοΫεɼΤωϧΪʔεϖΫτϧɼ൓Ԡஅ໘ੵͷଌఆ͕ओͳ໨తͱ͢ΔχϡʔτϦϊଌఆ‫ ث‬ND280ʢਤ 13ʣ
Ͱ͋Δɻ

R
MPPC

γϯνϨʔλ͔ΒͷޫΛి‫ؾ‬৴߸ʹม͑Δޫ‫ݕ‬ग़‫ͯ͠ͱث‬ɼ඿দϗτχΫεࣾ੡ͷ MultiR) Λ࢖༻ͨ͠ɻ
Pixel Photon Counter (MPPCR
MPPC͸ɼΨΠΨʔϞʔυͰಈ࡞͢ΔඍখͳΞόϥϯγΣϑΥτμΠΦʔυΛଟ਺ฒྻʹͭͳ͍ͩߏ଄Λ͍ͯ͠Δɻ֤μΠΦʔυʢϐΫηϧʣ͸ಠཱʹಈ࡞͠ɼडޫ໘ʹޫࢠ͕ೖࣹͯ͠ੜ੒͞Εͨిࢠ-ਖ਼޸ର͕‫ిٯ‬ѹ͕͔͚ΒΕͨ૿෯ྖҬʹ

ද 8 ʹલஔ‫ݕ‬ग़‫ث‬ͷॾ‫ݩ‬Λ·ͱΊΔɻ౸ୡ͢ΔͱɼΨΠΨʔ์ి͕‫͖ى‬Δɻ͜ͷ์ి͸֤ϐΫηϧʹͭͳ͕ͬͨ఍߅ʹΑͬͯΫΤϯν͢

4.6

લஔ‫ݕ‬ग़‫ث‬ͷ‫ڞ‬௨ٕज़

Δ͕ɼϐΫηϧͷಛੑ͕‫ۉ‬ҰͰ͋Ε͹֤์ిͰ์

લஔ‫ݕ‬ग़‫ث‬ͷ͏ͪɼΨε‫ݕ‬ग़‫͋Ͱث‬Δ TPC(Time Projection Chamber) Λআ͍ͨ‫ݕ‬ग़‫ث‬͸ɼϓϥενοΫγϯνϨʔλ͔ΒͷޫΛ൒ಋମޫ‫ݕ‬RͰಡΈग़͢ͱ͍͏ٕज़Λ‫ڞ‬௨ͯ͠ग़‫ ث‬MPPC༻͍͍ͯΔɻͦͷ૯਺͸໿ 56,000 νϟϯωϧʹ‫ٴ‬Ϳɻ·ͨɼ৴߸Λॲཧ͢ΔಡΈग़͠ճ࿏΋‫ڞ‬௨ͷ΋ͷΛ༻͍͍ͯΔɻ‫ݸ‬ʑͷ‫ݕ‬ग़‫ث‬ͷઆ໌ͷલʹɼ͜ΕΒͷ‫ڞ‬௨ٕज़Λ؆୯ʹ঺հ͢Δɻग़͞ΕΔిՙ Q ͸ҰఆͰ͋ΓɼશϐΫηϧ͔Βͷిՙྔͷ૯࿨͸ Q × (์ిΛ‫ͨ͜͠ى‬ϐΫηϧ਺) ͱͳΔɻͭ·Γɼग़ྗిՙ͸ Q Λ୯ҐʹྔࢠԽ͞Ε͓ͯΓɼ͜ΕΛଌΔ͜ͱͰೖࣹޫࢠ਺Λ਺
͑Δ͜ͱ͕Ͱ͖Δɻਤ 14 ʹࣔ͢Α͏ʹɼඍऑޫΛೖࣹͨ࣌͠ͷిՙ෼෍͸ϐʔΫ͕͸͖ͬΓ෼཭͓ͯ͠ΓɼిՙଌఆʹΑΓೖࣹޫࢠ਺ͷ৘ใΛಘ
Δ͜ͱ͕Ͱ͖Δɻ
R
MPPCͷ։ൃ͸ 2005 ೥ࠒ͔Β࢝·Γଞͷ࣮‫ͱݧ‬΋‫ڞ‬ಉͰਐΊͨ [76, 77] ͕ɼಉ༷ͷ‫ݪ‬ཧʹ‫ج‬

4.6.1

ϓϥενοΫγϯνϨʔλͮ͘ଞࣾͷ੡඼΋‫ؚ‬Ίɼେ‫ن‬໛ͳ࣮༻Խ͸ T2K

γϯνϨʔλ͸ɼถࠃͷϑΣϧϛࠃཱՃ଎‫ݚث‬͕ੈքͰॳΊͯͷྫͰ͋ͬͨɻT2K Ͱ͸ɼਤ 15‫ॴڀ‬ʢFermilabʣͰ։ൃ͞Εͨԡ͠ग़͠੒‫ʹܕ‬ΑΔͷΑ͏ʹ೾௕ม‫׵‬ϑΝΠόʔͷେ͖͞ʹ߹Θͤ㸶㸫 ද 8: T2K લஔ‫ݕ‬ग़‫ث‬ͷ֤αϒ‫ݕ‬ग़‫ͱ·ث‬Ί໊લ

INGRIDछผమ (6.5 cm)+γϯνϨʔλγϯνϨʔλʢϓϩτϯϞδϡʔϧʣ࣓ੴৗ఻ಋμΠϙʔϧ

FGD

̎୆ͷ͏ͪ
্ྲྀଆͷ 1 ୆͸γϯνϨʔλͷΈԼྲྀଆͷ 1 ୆͸γϯνϨʔλ+ਫඪత

TPCTime Projection Chamber

P0D

Ԗ (0.6 mm) +γϯνϨʔλECAL

Ԗ (1.75 mm)+γϯνϨʔλSMRD

మ (48 mm)+γϯνϨʔλʢҐஔ͋Θͤͷਫ਼౓΋ߟྀͯ͠ʣडޫ໘ͷ໘ੵΛ

1.2 × 1.2 × 0.9 m3 × 14 ୆ + 2 ୆
110 τϯ
9,592 νϟϯωϧ
1.42 × 1.42 × 0.96 m3
1,204 νϟϯωϧ
7.6 × 5.6 × 6.1 m3
900 τϯ
0.2 T
2.3 × 2.4 × 0.37 m3 × 2 ୆
1 τϯ × 2
8,448 νϟϯωϧ
2.5 × 2.5 × 0.9 m3 × 3 ୆Ψεɿ95%Ar+2%iso-C4 H10 +3%CF4
Micromegas(36 × 34 cm2 ×72 ຕ) ʹΑΔ૿෯
124,416 νϟϯωϧ
2.1 × 2.2 × 2.4 m3
16 τϯ
10,400 νϟϯωϧ
DS-ECAL, P0D-ECAL, Barrel-ECAL
74 τϯʢ‫ ܭ‬13 Ϟδϡʔϧʣ
22,336 νϟϯωϧ
࣓ੴϤʔΫͷܺؒʹઃஔ
4,016 νϟϯωϧ

4.6.3

1.3×1.3 mm2 ͱ͠ɼ50×50 μm2 ͷϐΫηϧ͕ 667
R‫ݸ‬ฒΜͩૉࢠΛ։ൃ͠࢖༻ͨ͠ [78]ɻMPPC͸ɼޫࢠ‫ݕ‬ग़཰͕ߴ͘ɼ࣓৔ͷӨ‫ڹ‬Λड͚ͳ͍ɼ
ίϯύΫτͰ͋Δɼ70–80V ͷҹՃిѹͰߴ͍૿
෯཰ʢ105 –106 ʣΛ΋ͭɼͳͲɼ਺ʑͷ༏ΕͨಛੑΛ΋ͭɻҰํͰɼT2K Ͱ࢖༻ͨ͠όʔδϣϯʹ͸μʔΫϊΠζϨʔτ͕ߴ͍ɼΞϑλʔύϧε΍ϐΫηϧؒͷΫϩετʔΫ͕͋Δɼੑೳʹ‫͍ڧ‬Թ౓ґଘੑ͕͋ΔͳͲɼվྑ͕๬·ΕΔ఺΋͋ͬͨɻ͜ΕΒ͸ɼͦͷ‫ޙ‬ͷૉࢠͷੑೳ޲্ʹΑΓେ෯ʹվળ͞Εͭͭ͋ΔɻಡΈग़͠ճ࿏

R
FGD Ҏ֎ͷ‫ݕ‬ग़‫Ͱث‬͸ɼMPPCͷ৴߸Λ‫ه‬࿥͢ΔσʔλऩूγεςϜʹ Fermilab Ͱ։ൃ͞Εͨ

Trip-t νοϓͱ͍͏ ASIC Λ࢖͍ͬͯΔ [79, 80]ɻϏʔϜͷλΠϛϯάʹ߹ΘͤͯήʔτΛ։͖ɼ৴߸ͷੵ෼ిՙྔͱ࣌ؒ৘ใΛ‫ه‬࿥͢ΔγεςϜͰ
͋Δɻిՙʹؔͯ͠͸ɼಉ͡৴߸Λ 10 ഒήΠϯͷҧ͏ 2 ͭͷνϟϯωϧͰ‫ه‬࿥͢Δ͜ͱͰμΠφϛοΫϨϯδΛ޿͍͛ͯΔɻ1 ຕͷϘʔυͰ 64
Rνϟϯωϧͷ৴߸Λ‫ه‬࿥Ͱ͖ɼMPPC΁ͷҹՃిѹΛௐ੔͢Δ‫ػ‬ೳ΋උΘ͍ͬͯΔɻόοΫΤϯ
υճ࿏ʹ͸ɼϑϩϯτΤϯυճ࿏ͷίϯτϩʔϧͱλΠϛϯά΍τϦΨʔͷ੍‫ޚ‬Λߦ͏ͨΊͷ਺छ

㸶㸫 

R
ਤ 14: MPPCʹඍऑޫΛೖࣹͨ࣌͠ͷిՙ෼෍ɻΨΠΨʔ์ిΛ‫ͨ͜͠ى‬ϐΫηϧͷ਺ʹ૬౰͢ΔϐʔΫ͕෼཭͍ͯ͠ΔɻR
ਤ 15: T2K ޲͚ MPPCͷडޫ໘֦େਤɻ༗‫ײ‬
2෦ͷ໘ੵ͸ 1.3 × 1.3 mm Ͱ͋Γɼ50 × 50 μm2ͷϐΫηϧ͕ 667 ‫ݸ‬ฒΜͰ͍ΔɻࠨԼͷ 3 × 3 ϐΫηϧ෼ͷྖҬ͸ϫΠϠϘϯσΟϯάͷύου͕ஔ͔Ε͓ͯΓෆ‫͍ͯͬͳʹײ‬ΔɻͷϘʔυ͕͋Δ͕ɼશͯϋʔυ΢ΣΞ͸ಉҰͰɼ

Δଌఆਫ਼౓Λୡ੒͢ΔͨΊʹ͸ϏʔϜํ޲ͷෆఆ

FPGA ͷϑΝʔϜ΢ΣΞΛมߋ͢Δ͜ͱͰछʑ

ੑ͕ 1 mrad Ҏ಺Ͱ͋Δ͜ͱ͕ཁ੥͞Ε͍ͯΔɻͷ‫ػ‬ೳʹରԠ͢ΔΑ͏ઃ‫͞ܭ‬Ε͍ͯΔɻ

·ͨɼඪత΍ి࣓ϗʔϯͷ݈શੑͷ֬ೝΛ‫ؚ‬ΊɼFGD ͱ TPC ͷΤϨΫτϩχΫε͸ T2K ࣮χϡʔτϦϊϏʔϜ‫౓ڧ‬ͷ҆ఆੑΛ୲อ͢Δ͜‫ ʹ༻ݧ‬Saclay ‫Ͱॴڀݚ‬։ൃ͞Εͨ AFTER νͱ΋ॏཁͰ͋ΔɻϏʔϜϥΠϯ࠷ԼྲྀͷϛϡʔΦοϓ [81] Λ࢖༻͍ͯ͠ΔɻFGD Ͱ͸ɼ৴߸͸ϯϞχλʔͰ͸ϏʔϜ‫౓ڧ‬΍ํ޲ͷ৘ใΛεϐϧ

100 nsec ͷ࣌ఆ਺Λ΋ͭϓϦΞϯϓͰ੒‫͞ܗ‬Ε͝ͱʹଌఆ͢Δ͜ͱ͕Ͱ͖ϦΞϧλΠϜͷϑΟʔͨ‫ޙ‬ɼ50 MHz(20 nsec ຖ) Ͱ 10 msec ʹΘͨͬͯυόοΫ͕ՄೳͰ͋Δ͕ɼϏʔϜμϯϓͷഎ‫ʹޙ‬αϯϓϦϯά͞ΕΔɻΤϨΫτϩχΫε͸ 1 νϟ͋ΔͨΊߴΤωϧΪʔ (> 5 GeV) ͷϛϡʔΦϯ

ϯωϧ 12 Ϗοτͷ෼ղೳΛ͕࣋ͭɼ৴߸Λ 2 ෼ʹ͔͠‫͘ͳ͕౓ײ‬ɼχϡʔτϦϊϑϥοΫεͷओׂ͠‫ݮ‬ਰൺ཰Λ 1 : 8 ʹௐ੔͢Δ͜ͱͰɼ࣮ޮ 15ཁͳ෦෼ͷ৘ใ͸௚઀ʹ͸ಘΒΕͳ͍ɻͦ͜Ͱɼ

Ϗοτͷ෼ղೳΛ༗͍ͯ͠Δɻ·ͨɼࣄ৅ຖʹύχϡʔτϦϊϏʔϜͷ҆ఆੑΛχϡʔτϦϊࣗϧε೾‫ܗ‬ΛϑΟοτ͢Δ͜ͱͰɼ3 nsec ͷ࣌ؒ෼ମͰ֬ೝ͢Δ͜ͱ͕ෆՄܽͰ͋Δɻલஔ‫ݕ‬ग़‫ث‬ͷղೳΛୡ੒͢ΔɻTPC ͷσʔλऩूγεςϜ͸

஍఺Ͱ͸χϡʔτϦϊϏʔϜ͸େ͖͘޿͕͓ͬͯ

25 MHz(40 nsec ຖ) ͰՔಇ͠ɼ20 msec ʹΘͨͬΓɼϏʔϜϓϩϑΝΠϧ‫ͦͼٴ‬ͷํ޲Λଌఆ͢Δ

ͯ৴߸ΛαϯϓϦϯάͰ͖ΔɻͨΊ͸ 10×10 m2 ఔ౓ͷྖҬΛΧόʔ͢Δඞཁ͕͋ΔɻχϡʔτϦϊͷ‫ݕ‬ग़ʹ͸େྔͷඪత͕ඞཁ

4.7

ͱͳΔ͕ɼ޿͍ྖҬΛશͯΧόʔ͢Δ‫ݕ‬ग़‫ث‬ΛஔΦϯΞΫγε‫ݕ‬ग़‫ث‬ɿINGRID͘ͷ͸‫࣮ݱ‬తͰͳ͍ɻͦ͜Ͱɼ̍୆໿ 10 τϯͷ

INGRID ‫ݕ‬ग़‫[ ث‬82–84] ͷओͳ໨త͸ɺχϡʔτϦϊϏʔϜ͕ਖ਼͘͠ҙਤͨ͠ํ޲ʹੜ੒͞Εͯଌఆ‫ث‬Λෳ਺άϦουঢ়ʹ഑ஔ͢Δ͜ͱͰɼϏʔϜϓϩϑΝΠϧΛଌఆ͢ΔσβΠϯͱͨ͠ɻ

͍Δ͜ͱΛ֬ೝ͠ɼ·ͨͦͷํ޲ͱ‫౓ڧ‬ͷ҆ఆੑଌఆ‫̍ث‬୆ʢINGRID Ϟδϡʔϧͱ‫Ϳݺ‬ʣ͸ɼΛϞχλʔ͢Δ͜ͱʹ͋ΔɻT2K Ͱ͸ΦϑΞΫγ

ਤ 16 ʹࣔ͢Α͏ʹ 11 ຕͷτϥοΩϯάϓϨʔτε๏ͷͨΊʹϏʔϜͷํ޲ͱ SK ʹ޲͔͏χϡʔ

ͱ 120 × 120 × 6.5 cm3 ͷమ൘ 9 ຕΛަ‫ʹޓ‬ฒ΂τϦϊΤωϧΪʔʹ͸‫͍ڧ‬૬͕ؔ͋Γɼ໨ඪͱ͢

ͨߏ଄Λ͍ͯ͠ΔɻτϥοΩϯάϓϨʔτ͸௕͞㸶㸫 ϧҰ୆͸ߏ଄ମ΋‫ؚ‬Ί໿ 9 τϯɼ14 ୆Λ߹ΘͤΔͱඪత࣭ྔ͕໿ 100 τϯͱͳΔɻ౰ॳͷ 14 ୆ͷϞδϡʔϧʹՃ͑ͯɼϏʔϜͷۭؒඇରশੑΛଌΔͨΊʹ 2 ୆ͷϞδϡʔϧ͕ेࣈ͔Β֎ΕͨҐஔʹɼ·ͨϏʔϜͷத৺্࣠ʹɼཅࢠ΍ π ʹର͢Δ
‫ݕ‬ग़ޮ཰Λ্͛ͯχϡʔτϦϊ൓ԠΛ‫͢ڀݚ‬Δ͜
ͱΛ໨తͱͯ͠ɼమ൘ͷͳ͍γϯνϨʔλ͚ͩͷϞδϡʔϧʢϓϩτϯϞδϡʔϧʣ [85] ͕ 1 ୆ઃஔ͞Εͨɻ
ਤ 16: INGRID Ϟδϡʔϧͷ໛ࣜਤ

4.8ΦϑΞΫγε‫ݕ‬ग़‫ث‬ɿND280

ND280 [86] Ͱ͸ɼεʔύʔΧϛΦΧϯσͰ‫؍‬ଌ͞ΕΔࣄ৅Λਫ਼౓Α͘༧૝͢ΔͨΊʹɼϛϡʔχϡʔτϦϊͷϑϥοΫε͓ΑͼΤωϧΪʔ෼෍΍ϏʔϜதͷిࢠχϡʔτϦϊͷϑϥοΫεΛଌఆ͢Δඞཁ͕͋Δɻ·ͨɼχϡʔτϦϊΤω

~10m
Designed
beam center

1.5m

ϧΪʔଌఆͷࡍʹόοΫάϥ΢ϯυͱͳΔɼՙి

YΧϨϯτඇ஄ੑࢄཚ΍ɼిࢠχϡʔτϦϊଌఆͷόοΫάϥ΢ϯυͱͳΔඇ஄ੑࢄཚʢओʹதੑΧX

Ϩϯτ π 0 ੜ੒൓Ԡʣ΋ଌఆ͢Δඞཁ͕͋Δɻ

Z

͜ΕΒͷཁ‫ٻ‬Λຬͨͨ͢ΊɼND280 ͸ɼ~10m• େ‫ܕ‬தۭి࣓ੴ

ਤ 17: ϏʔϜ্ྲྀଆ͔Β‫ ͨݟ‬INGRID Ϟδϡʔϧͷ഑ஔɻϓϩτϯϞδϡʔϧ͸ϏʔϜͷத৺্࣠ɼԖ௚ͷϞδϡʔϧͱͱਫฏͷϞδϡʔϧؒʹઃஔ͞Εͨɻ

• ࡉ෼ׂ͞Εͨߴղ૾౓χϡʔτϦϊ൓Ԡ఺‫ݕ‬ग़‫( ث‬FGD:Fine-Grained-Detector)• ߴਫ਼౓ɾେΞΫηϓλϯεͷτϥοΩϯάΛ
1.2 mɼ෯ 5 cmɼް͞ 1 cm ͷϓϥενοΫγϯν

ߦ͏ 3 ୆ͷ TPC

ϨʔλΛ 24 ‫ͭͣݸ‬ॎԣ 2 ૚ʹฒ΂ͨߏ଄ͱͳͬ• தੑΧϨϯτ π 0 ੜ੒൓ԠଌఆͷͨΊͷ‫ݕ‬ग़͍ͯΔɻ࠷‫ޙ‬ͷ 2 ຕͷτϥοΩϯάϓϨʔτؒʹ

͖ (P0D:Pi-zero Detector)͸మ൘͕ೖ͍ͬͯͳ͍ɻϞδϡʔϧͷଆ໘΍্Լͷ໘͸ɼӉ஦ઢ΍Ϟδϡʔϧ֎Ͱͷ൓Ԡ͔ΒདྷΔ• େཱମ֯Λ෴͏ి࣓ΧϩϦϝʔλ (ECAL)ཻࢠΛࣝผ͢ΔͨΊʹγϯνϨʔλ̍૚ͷ VETO

• େཱମ֯Λ෴͏ϛϡʔΦϯඈఔ‫ݕ‬ग़‫ث‬ϓϨʔτͰ෴ΘΕ͍ͯΔɻਤ 17 ͷΑ͏ʹɼਫฏɾ(SMRD: Side-Muon-Range-Detector)Ԗ௚ͦΕͧἘϞδϡʔϧͣͭΛฒ΂Δ͜ͱͰϏʔϜͷத৺͔Β ±5 m ΛΧόʔ͠ɼమͰ‫͖ͨى‬χϡʔτϦϊ൓Ԡࣄ৅ΛγϯνϨʔλͰ‫ݕ‬ग़͠ɼͦͷ਺ΛϞδϡʔϧ͝ͱʹ਺͑Δ͜ͱͰɺχϡʔτϦϊϏʔϜͷۭؒ෼෍Λ࠶ߏ੒͢ΔɻϞδϡʔΛ૊Έ߹Θͤͨଌఆ‫͍ͯͬͳͱث‬ΔɻND280 ͰͷϨϓτϯ (ϛϡʔΦϯͱిࢠ) ࣝผʹ͸ ECALͷϨεϙϯεͱ TPC Ͱͷ dE/dx ଌఆ͕࢖ΘΕΔɻ·ͨɼεʔύʔΧϛΦΧϯσͷχϡʔτϦϊ㸶㸫 

͞ 6.5 mɼ෯ 2.5 mɼߴ͞ 2.6 mʣ͕ஔ͔Ε͓ͯΓɼόεέοτ಺ଆʹ P0Dɼ3 ୆ͷ TPCɼ2 ୆ͷ

FGDɼDS-ECALʢ࠷Լྲྀͷి࣓ΧϩϦϝʔλʣ͕ઃஔ͞Ε͍ͯΔɻ

4.8.2

FGD

FGD(Fine Grained Detector) [87] ͸ࡉ෼ׂ͞ਤ 18: ND280 Ͱ‫؍‬ଌ͞ΕͨχϡʔτϦϊ൓Ԡࣄ৅ͷଆ໘ਤΕͨߏ଄ͷγϯνϨʔλτϥοΧʔͰɼχϡʔτϦϊ൓Ԡͷඪతཻ͔ͭࢠ‫ݕ‬ग़‫ͯ͠ͱث‬ಇ͖ɼχϡʔτϦϊ൓Ԡ఺ͷ‫ݕ‬ग़ͱ FGD ಺Ͱࢭ·Δ௿Τωϧ൓Ԡඪత͕ਫͰ͋Δ͜ͱ͔ΒɼFGD ͱ P0D ͸ଌΪʔཻࢠͷଌఆΛओ໨తͱ͢ΔɻFGD ͸൓Ԡ఺ఆ‫ʹ಺ث‬ਫඪతͷ෦෼Λ࣋ͭɻʹඈ੻Λ࢒͢ՙిཻࢠʹରͯ͠ෆ‫ྖײ‬Ҭ͕ͳ͍

ਤ 18 ʹ ND280 Ͱ‫؍‬ଌ͞ΕͨχϡʔτϦϊࣄΑ͏ʹɼେ෦෼͕γϯνϨʔλͷΈͰߏ੒͞Ε৅ͷҰྫΛࣔ͢ɻࠨ͔Βೖࣹͨ͠χϡʔτϦϊ͕

͍ͯΔɻ͜ͷઃ‫ࢥܭ‬૝͸ K2K ࣮‫ݧ‬ͷલஔ‫ݕ‬ग़‫ث‬P0D Ͱ൓ԠΛ‫͜͠ى‬ɼੜ੒͞Εཻͨࢠͷඈ੻͕ͱͯ͠։ൃ͞Εɼͦͷ‫ ޙ‬Fermilab ʹҠઃ͞Ε࣓ͯ৔Ͱ‫͛ۂ‬ΒΕͳ͕Β 3 ୆ͷ TPCɼ2 ୆ͷ FGDɼSciBooNE ࣮‫Ͱݧ‬΋࢖ΘΕͨ SciBar ଌఆ‫[ ث‬88]͓Αͼ࠷Լྲྀͷ ECAL(DSECAL) Λ௨͍ͬͯΔ

ͷσβΠϯΛ‫ܧ‬ঝ͓ͯ͠ΓɼSciBar(1.3×2.5 cm2 )ͷ͕෼͔Δɻ

ΑΓ΋͞Βʹࡉ෼ׂ͞ΕͨγϯνϨʔλΛ࠾༻͢લஔχϡʔτϦϊଌఆ‫ث‬͸‫ޙ‬ஔଌఆ‫͋Ͱث‬ΔεʔύʔΧϛΦΧϯσͱ·ͬͨ͘ҟͳΔλΠϓͷ

Δ͜ͱͰɼΑΓߴղ૾౓Λୡ੒Ͱ͖ΔΑ͏σβΠϯ͞Εͨɻ‫ݕ‬ग़‫͍ͯͬͳʹث‬Δ͕ɼ͜Ε͸ J-PARC ͷෑ஍಺

0.96 × 0.96 × 184.3 cm3 ͷ๮ঢ়γϯνϨʔλΛͰ͸χϡʔτϦϊϏʔϜͷ‫ͯ͗͢ڧ͕౓ڧ‬ɼҰମ

192 ຊฒ΂ͯҰ૚Λ‫ܗ‬੒͠ɼͦͷ૚ΛγϯνϨʔ‫ܕ‬ͷେ‫ܕ‬ਫνΣϨϯίϑଌఆ‫Ͱث‬͸̍౓ͷϏʔϜλ๮ͷॎํ޲ͱԣํ޲Λަ‫ʹޓ‬ม͑ͨੵ૚ߏ଄Ͱ

εϐϧͰଟ਺ͷΠϕϯτ͕ൃੜ͠ɼνΣϨϯίϑ

‫ݕ‬ग़‫ث‬Λߏ੒͢ΔɻFGD ͸ 2 ୆͋Γɼ্ྲྀଆΛޫ͕ॏͳͬͯ͏·͘‫ػ‬ೳ͠ͳ͍ͨΊͰ͋Δɻ

FGD1ɼԼྲྀଆΛ FGD2 ͱ‫ݺ‬ΜͰ͍ΔɻFGD1 ͸ҎԼʹɼ‫ݸ‬ʑͷଌఆ‫ث‬Λ؆୯ʹ঺հ͢Δɻ‫ ܭ‬30 ૚ɼ߹‫ ܭ‬5,760 ຊͷγϯνϨʔλͰߏ੒͞Ε͍ͯΔɻFGD2 ͸ 14 ૚ͷγϯνϨʔλ૚ͷؒ

4.8.1

ʹް͞ 2.5 cm ͷਫඪత૚ 6 ૚͕૊Έࠐ·Εͨߏ࣓ੴ଄ (γϯνϨʔλ 2 ૚͝ͱʹਫ 1 ૚) Ͱɼχϡʔτ

ND280 Ͱ࢖༻͍ͯ͠Δి࣓ੴ͸ɼ͔ͭͯ CERNͰ W/Z Λൃ‫ ͨ͠ݟ‬UA1 ࣮‫ݧ‬ͷͨΊʹ‫ݐ‬ઃ͞ΕϦϊͱਫͷ൓Ԡஅ໘ੵΛଌఆͰ͖ΔΑ͏σβΠϯ͞Ε͍ͯΔɻ

ͨ΋ͷͰɼCERN ͔Β‫د‬ଃ͞ΕͨɻUA1 ࣮‫ݧ‬ͷ‫ ͘͡ͳ͓ޙ‬CERN ͷ NOMARD ࣮‫͞༻࢖Ͱݧ‬Ε͍ͯΔͷͰɼT2K ࣮‫౓̏Ͱݧ‬໨ͷར༻ͱ͍͏͜ͱ

4.8.3

TPC

ʹͳΔɻి࣓ੴ͸ίΠϧͱϤʔΫ͔ΒͳΓɼϤʔFGD Ͱ‫ͨͬ͜ى‬χϡʔτϦϊ൓ԠͰੜ੒͞ΕͨΫ෦ͷ૯ॏྔ͸ 850 τϯɼ֎‫ܗ‬͸௕͞ 7.6 mɼ෯

ՙిཻࢠͷӡಈྔΛଌఆ͢Δ‫ݕ‬ग़‫ ͕ث‬TPCʢTime

5.6 mɼߴ͞ 6.1 m Ͱ಺ଆ 88 m3 ͷྖҬʹ 0.2 T

Projection ChamberʣͰ͋Δ [89]ɻTPC Λ௨աͷ࣓৔Λਫฏํ޲ʹҹՃ͢Δɻ࣓ੴͷ಺ଆʹ͸ό

͢Δՙిཻࢠ͸ɼਫฏํ޲ 0.2 T ͷ࣓৔ͰԖ௚ํ

εέοτͱ‫ݺ‬͹ΕΔ‫ݕ‬ग़‫ث‬Λઃஔ͢Δߏ଄ମʢ௕

޲ʹ‫͛ۂ‬ΒΕΔɻͦͷ‫཰ۂ‬Λଌఆ͢Δ͜ͱͰӡಈ㸶㸫 ྔ͕ଌఆͰ͖Δɻ·ͨՙిཻࢠͷ୯Ґ௕͞౰ͨΓͷ π 0 ੜ੒அ໘ੵ͕ଌఆՄೳͰ͋Δɻ

ͷΤωϧΪʔଛࣦʢdE/dxʣΛଌఆ͢Δ͜ͱͰɼɼཅࢠΛࣝผ͢Δ͜ͱిࢠɼμ ཻࢠʢ͓Αͼ π ± ʣ

4.8.5

ECAL

͕ՄೳͰ͋ΔɻిࢠχϡʔτϦϊग़‫ݱ‬ͷόοΫά
ϥ΢ϯυͱͳΔɼ࠷ॳ͔ΒϏʔϜதʹࠞೖ͍ͯ͠

ECAL (Electromagnetic Calorimeter) [91] ͸ΔిࢠχϡʔτϦϊΛଌఆ͢ΔͨΊʹɼTPC ͰϚάωοτ಺ଆͷ࠷֎૚ʹҐஔ͠ɼ಺෦ͷ‫ݕ‬ग़‫ث‬ͷిࢠࣝผ͸ ECAL ͰͷγϟϫʔࣝผͱฒΜͰͰ‫ͨͬ͜ى‬χϡʔτϦϊ൓ԠͰੜ੒͞ΕΔిࢠͱ‫ۃ‬ΊͯॏཁͰ͋Δɻγ ઢ (ओʹ π 0 ‫ )ݯى‬ͷి࣓γϟϫʔΛั͑ɼΤωϧ

T2K ࣮‫Ͱݧ‬͸֎‫͕ܗ‬෯ 2.5 mɼߴ͞ 2.5 mɼԞΪʔΛଌఆ͢Δ૷ஔͰ͋ΔɻECAL ͸࠷Լྲྀʹઃ

ߦ 0.9 m ͷେ‫ ܕ‬TPC Λ 3 ୆੍࡞ͨ͠ɻΨε͸֦ஔ͞Εͨ DS-ECAL(DownStream ECAL)ɼP0D

ࢄͷগͳ͍ Ar(95%)+iso-C4 H10 (2%)+CF4 (3%)ͷԣΛ෴͏ P0D-ECALɼTPC ͱ FGD ͷԣଆΛΛ࠾༻͠ɼϞδϡʔϧ֎૚ʹ CO2 Λຬͨ͢͜ͱ

෴͏ Barrel-ECAL ͔ΒͳΔɻஅ໘ 4 × 1 cm2 ͷͰෆ७෺ࠞೖΛ཈͍͑ͯΔɻిࢠͷ૿෯෦ʹ͸ඍγϯνϨʔλͱԖͷαϯυΠονߏ଄ͰɼαϯϓࡉՃ޻ٕज़Λ༻͍ͨϚΠΫϩύλʔϯΨε‫ݕ‬ग़‫ث‬Ϧϯά‫ܕ‬ͷΧϩϦϝʔλΛ‫ܗ‬੒͍ͯ͠ΔɻԖ૚ͷ

ʢMicro Pattern Gas Detector, MPGDʣͷ 1 छްΈ͸ DS-ECAL ͱ Barrel-ECAL Ͱ 1.75 mmɼ

Ͱ͋ΔϚΠΫϩϝΨε (micromegas ˹ MICROP0D-ECAL ͸ 5 mm Ͱ͋ΔɻDS-ECAL ͸શ 34

MEsh GAS counter) Λ࠾༻ͨ͠ɻ36 × 34 cm2

૚Ͱ 11X0 (์ࣹ௕)ɼBarrel-ECAL ͸શ 32 ૚ͰͷϞδϡʔϧͻͱͭʹ 6.9 × 9.7 mm2 ͷύου͕

10.5X0 ɼP0D-ECAL ͸ 6 ૚Ͱ 4.5X0 ͷްΈΛ΋

1,728 νϟϯωϧ͋Γɼ1 TPC Ϟδϡʔϧʹ͸ย

ͭɻP0D-ECAL ͷްΈ͕ബ͍ͷ͸ɼP0D ͦͷ΋୺ 12 ຕ (2 × 6)ɼ྆୺Ͱ 24 ຕͷϚΠΫϩϝΨε

ͷ͕ి࣓γϟϫʔʹରͯ͠ްΈΛ͓࣋ͬͯΓɼ࿙͕࢖༻͞Ε͍ͯΔɻMPGD ٕज़Λ͜Ε͚ͩͷେΕͯ͘Δి࣓γϟϫʔΛั͑Ε͹Α͍͔ΒͰ͋Δɻ໘ੵͷ‫ݕ‬ग़‫ͨ͠༻࢖ʹث‬ͷ΋ɼT2K ࣮‫ॳ͕ݧ‬ΊͯͰ͋ͬͨɻϏʔϜํ޲ʹ޲͔͏τϥοΫʹର͠ɼ

4.8.6

SMRD

ਨ௚ํ޲ʹ 0.6 mmɼਫฏํ޲ (υϦϑτํ޲) ʹ

ND280 ͷి࣓ੴͷϤʔΫ͸ɼ48 mm ްͷమ൘

1.42 mm ͷҐஔ෼ղೳΛୡ੒͍ͯ͠Δɻӡಈྔ͕ 17 mm ͷִؒΛ͚͋ͯฒͿߏ଄ͱͳ͍ͬͯΔɻ

෼ղೳ͸ 1GeV/c ͷཻࢠʹର͠໿ 7%Ͱ͋Δɻ͜ͷి࣓ੴΛ࠷ॳʹ࢖༻ͨ͠ CERN ͰͷίϥΠμʔ࣮‫ ݧ‬UA1 Ͱ͸ɼ͜ͷܺؒʹγϯνϨʔ λ

4.8.4

P0D

Λૠೖͯ͠λϫʔ‫ܕ‬ͷϋυϩϯΧϩϦϝʔλͱ

P0D (Pi 0[Zero] Detector) [90] ͸ɼ࣓ੴ಺ͷ࠷ͯ͠࢖༻͍ͯͨ͠ɻSMRD (Side Muon Range্ྲྀʹઃஔ͞Εͨ π 0 ੜ੒൓ԠଌఆʹಛԽͨ͠‫ݕ‬

Detector) [92] ͸͜ͷ 17 mm ͷִؒʹγϯνϨʔग़‫͋Ͱث‬ΔɻP0D ͸ 0.6 mm ްͷԖͱ 1.7 cm ްλϞδϡʔϧΛૠೖ͢Δ͜ͱͰɼ಺෦‫ݕ‬ग़‫Ͱث‬ͷͷγϯνϨʔλͷαϯυΠονߏ଄Λ࠾༻ͨ͠γχϡʔτϦϊ൓ԠͰੜ੒͞Εଆ໘ʹൈ͚ͨϛϡʔϯνϨʔλτϥοΧʔͰ͋Δɻ֤γϯνϨʔλ͸ΦϯͷඈఔΛଌΓɼӡಈྔΛଌఆ͢Δɻಛʹେ֯

෯ 3.25 cmɼߴ͞ 1.7 cmɼ௕͞ 210 cm(΋͘͠͸౓Ͱੜ੒͞Εଆ໘ʹඈͿϛϡʔΦϯ͸ TPC Λे

223 cm) ͷࡾ֯பγϯνϨʔλ๮Ͱɼ126 ຊ (΋෼ʹ௨աͤͣӡಈྔଌఆ͕Ͱ͖ͳ͍ͨΊɼSMRD

͘͠͸ 134 ຊ) Ͱ 1 ૚Λߏ੒͢Δɻ߹‫ ܭ‬40 ૚ͷԖʹΑΔӡಈྔଌఆ͸ॏཁͰ͋Δɻ·ͨɼͦͷେ͖

ഩ+γϯνϨʔλͰߏ੒͞Εɼ֎‫ܗ‬͸ 2.1 × 2.2 ×͞Λੜ͔ͯ͠ɼϏʔϜεϐϧͷ߹ؒʹֱਖ਼༻ͷӉ

2.4 m3 ɼ૯ॏྔ͸ 16 τϯͰ͋Δɻ·ͨɼ֤૚ͷ஦ઢσʔλΛऔಘ͢ΔͨΊͷτϦΨʔΛ‫ͯ͠څڙ‬ܺؒʹ͸ਫඪత૚͕૊Έࠐ·Ε͓ͯΓɼਫඪతͰ

͍Δɻ

㸶㸫 

χϡʔτϦϊৼಈղੳʹ͸ɼ̎ମ൓ԠͰ͋Δՙ
ిΧϨϯτ४஄ੑ൓Ԡʢν + n → − + p ·ͨ͸ ν̄ + p → + + nɼCharged Current Quasi-

Elastic:CCQEʣΛ৴߸ͱͯ͠બͿɻT2K Ͱ͸χϡʔτϦϊͷඈΜͰ͘Δํ޲͕Θ͔͍ͬͯΔͨΊɼՙిΧϨϯτ४஄ੑ൓ԠΛԾఆ͢Δͱऴঢ়ଶͷϨϓτϯͷํ޲ͱӡಈྔͷଌఆ͔Β‫ݩ‬ͷχϡʔτϦϊͷΤωϧΪʔ͕࠶ߏ੒ՄೳͰ͋ΔɻϛϡʔχϡʔτϦϊࣄ৅ͷબ୒Ͱ͸ɼ͞Βʹ• Ϧϯά͕ 1 ͚ͭͩͰɼཻࢠࣝผͰ μ-like ͱ൑ఆ͞ΕΔ• ϛϡʔΦϯͱԾఆͯ͠࠶ߏ੒͞Εͨӡಈྔ͕
>200 MeV/c
ਤ 19: εʔύʔΧϛΦΧϯσͰ‫؍‬ଌ͞ΕͨɼT2K
ࣄ৅ͷ࣌ؒ෼෍

4.9• ෇ਵ͢Δ่յిࢠͷ਺͕ 0 ͔ 1ͱ͍͏৚݅Λ՝͢ɻిࢠχϡʔτϦϊࣄ৅ͷબ୒Ͱ͸ɼ੒Ռ• Ϧϯά͕ 1 ͚ͭͩͰɼཻࢠࣝผͰ e-like ͱ൑

T2K ࣮‫͜Ͱݧ‬Ε·ͰʹಘΒΕͨ੒Ռʹ͍ͭͯɼఆ͞ΕΔ͘͝؆୯ʹड़΂ΔɻεʔύʔΧϛΦΧϯσͰͷࣄ৅બ୒• ిࢠͱԾఆͯ͠࠶ߏ੒͞ΕͨΤωϧΪʔ͕

T2K ͷσʔ>100 MeVλऩूதͷεʔύʔΧϛΦΧϯσͷՔಇ཰͸ɼ99%• ෇ਵ͢Δ่յిࢠͷ਺͕ 0

Ҏ্Ͱ͋ΔɻT2K ϏʔϜʹΑΔεʔύʔΧϛΦΧϯσͰͷࣄ৅ͷબ୒͸ɼ༧૝౸ୡ࣌ࠁͷ ±500μs• ࠶ߏ੒͞ΕͨχϡʔτϦϊͷΤωϧΪʔ͕Ҏ಺ͷσʔλ͔Βɼిࢠͱͯ͠‫ͨ͠ࢉ׵‬Τωϧ

1250 MeV ҎԼΪʔ͕ 30 MeV Ҏ্Ͱɼ֎ਫ૧ʹΞΫςϏςΟ͕
ͳ͍ʢFully ContainedɼFCʣࣄ৅ΛબͿ͜ͱ͔• தੑΧϨϯτ π 0 ੜ੒Ͱ π 0 → γγ ͷ γ ΛͻͱΒ࢝·Δɻਤ 19 ʹɼબ୒͞Εͨ FC ࣄ৅ͷ࣌ؒͭ‫ࢠిͱ͏ࣦݟ‬χϡʔτϦϊࣄ৅ͱ۠ผ͕ͭ

෼෍ 13 Λࣔ͢ɻJ-PARC ϝΠϯϦϯάͷ 8 όϯ͔ͳ͍ͨΊɼπ 0 Λ࠶ߏ੒͢ΔΞϧΰϦζϜ

νߏ଄ʹରԠ͢Δ࣌ؒ෼෍͕໌֬ʹΈ͓͑ͯΓɼͰ π 0 Λআ‫ڈ‬J-PARC Ճ଎‫͔ث‬ΒͷχϡʔτϦϊϏʔϜʹΑΔ

ͱ͍͏৚݅Λ՝͢ɻࣄ৅͕ଊ͑ΒΕ͍ͯΔ͜ͱ͕Θ͔Δɻ͔͜͜Β͞Βʹɼ൓Ԡ఺͕಺ਫ૧ͷน͔Β 2 m Ҏ্཭Ε͍ͯ
ΔʢFiducial Volume, FVʣ͜ͱΛཁ‫͢ٻ‬Δɻ͜
ͷ࣌఺Ͱɼେ‫ؾ‬χϡʔτϦϊʹΑΔόοΫάϥ΢
ϯυ͸ 10−2 ࣄ৅ͷΦʔμʔͰ͋Δɻ
13

ද 9 ʹϛϡʔχϡʔτϦϊʢ൓ϛϡʔχϡʔτϦϊʣͷࣄ৅બ୒Λɼද 10 ʹిࢠχϡʔτϦϊʢ൓ిࢠχϡʔτϦϊʣͷબ͹Εͨࣄ৅ͱϞϯςΧϧϩγϛϡϨʔγϣϯʹΑΔ༧૝Λ·ͱΊͨɻ৴߸ʹର͠ߴ͍ޮ཰Λ΋ͪɼόοΫάϥ΢ϯυ͸

ਫதͷޫͷ఻ൖ࣌ࠁ΍ɼ‫ݕ‬ग़‫಺ث‬ͷχϡʔτϦϊͷඈߦ࣌ؒΛิਖ਼ͨ͠΋ͷɻ௿͘཈͑ΒΕ͍ͯΔ͜ͱ͕Θ͔Δɻ·ͨɼਤ 20
ʹɼ2016 ೥Ն·ͰʹεʔύʔΧϛΦΧϯσͰ‫؍‬㸶㸫 ද 9: νμ ‫ࣄܕ‬৅બ୒ͷ·ͱΊόοΫάϥ΢ϯυ
νμ + ν μνe + ν eNC
non-CCQE
CC

ν Ϟʔυ

ࣄ৅਺
બ୒ޮ཰

ν̄ Ϟʔυ

ࣄ৅਺
બ୒ޮ཰

52.7
20.4%
27.8
24.6%

0.5
0.8%
0.1
0.6%

৴߸

8.8
2.7%
3.4
2.5%

νμ
CCQE
71.5
71.2%
13.2
65.8%

νμ
CCQE
4.6
71.7%
23.8
77.5%

༧૝߹‫ܭ‬

σʔλ

138.1

135

68.3

66

ද 10: νe ‫ࣄܕ‬৅બ୒ͷ·ͱΊ

ν Ϟʔυ

ࣄ৅਺
બ୒ޮ཰

ν̄ Ϟʔυࣄ৅਺બ୒ޮ཰νμ + ν μ
CC
0.1
0.0%
0.0
0.0%

όοΫάϥ΢ϯυ
νe + ν eνμ → νeNCCC(νμ → νe )

3.7
19.8%
1.6
17.5%

1.4
0.4%
0.6
0.4%

0.2
46.2%
1.0
45.7%

BG ߹‫ܭ‬
5.3
0.7%
3.2
1.1%

৴߸
νμ → νe(ν μ → ν e )

23.3
65.6%
3.0
70.8%

σʔλ

32
4

ଌ͞ΕͨχϡʔτϦϊࣄ৅ͷ࠶ߏ੒͞Εͨχϡʔσϧͷύϥϝʔλʹର͢Δ੍‫ݶ‬Λ͔͚Δ͜ͱ͕ͰτϦϊΤωϧΪʔ෼෍Λࣔ͢ɻ্ஈ͕χϡʔτϦ

͖ΔɻχϡʔτϦϊϞʔυͰͷɼલஔ‫ݕ‬ग़‫Ͱث‬ଌϊϏʔϜɼԼஈ͕൓χϡʔτϦϊϏʔϜͷσʔλΒΕͨϛϡʔΦϯͷӡಈྔ෼෍Λਤ 21 ʹࣔ͢ɻͰ͋ΓɼͦΕͧΕࠨଆ͕ μ-likeɼӈଆ͕ e-like ࣄղੳͰ͸ɼӡಈྔͱࢄཚ֯ͷ̎࣍‫ݩ‬ͷ৘ใΛ༻͍৅Λࣔ͢ɻͯϑΟοτΛߦ͏ɻ·ͨɼ൓χϡʔτϦϊϞʔυͷσʔλʹରͯ͠΋ɼಉ༷ͷղੳΛߦ͍ͬͯΔɻલஔ‫ݕ‬ग़‫ʹث‬ΑΔ‫ܥ‬౷‫ࠩޡ‬ͷ࡟‫ݮ‬લஔ‫ݕ‬ग़‫ث‬εʔύʔΧϛΦΧϯσͰ‫؍‬ଌ͞ΕΔిࢠχϡʔͰɼϛϡʔχϡʔτϦϊ൓ԠΛ࢖ͬͯχϡʔτϦτϦϊग़‫ࣄݱ‬৅਺ͷ༧૝஋ʹର͢Δ‫ܥ‬౷‫ࠩޡ‬ΛϊϏʔϜͷϑϥοΫεɼΤωϧΪʔεϖΫτϧɼද 11 ʹ·ͱΊΔɻલஔ‫ݕ‬ग़‫ث‬ͷଌఆʹΑΓχϡʔχϡʔτϦϊ൓ԠϞσϧͷύϥϝʔλʹ੍‫ݶ‬ΛτϦϊͷϑϥοΫεͱஅ໘ੵʹ੍‫ݶ‬Λ͔͚Δ͜ͱ

͔͚Δ͜ͱͰɼχϡʔτϦϊৼಈղੳͷ‫ܥ‬౷‫ࠩޡ‬Ͱɼ‫ܥ‬౷‫ࠩޡ‬Λ཈͑ΒΕ͍ͯΔ͜ͱ͕Θ͔ΔɻΛ࡟‫͢ݮ‬Δ͜ͱ͕Ͱ͖Δɻ࣮‫ݧ‬ͷॳ‫ʹظ‬͸શͯͷࣄ৅Λͻͱ͘͘Γʹͯ͠ղੳ͍͕ͯͨ͠ɼ‫ࡏݱ‬͸ిࢠχϡʔτϦϊग़‫ݱ‬ͷൃ‫ݟ‬σʔλ͕૿͑Δͱͱ΋ʹ‫ݕ‬ग़‫ث‬ͷཧղ͕ਐΈɼΑඪͰ͋ͬͨిࢠχϡʔτϦϊग़‫ݱ‬ͷൃ‫͋Ͱݟ‬Δ

Γৄࡉͳղੳ͕ՄೳͱͳͬͨɻϛϡʔχϡʔτϦ͕ɼ౦೔ຊେ਒ࡂ௚‫ޙ‬ͷ 2011 ೥ 6 ݄ʹ͸ɼ஍਒ϊͷ൓Ԡࣄ৅ʹର͠ɼϛϡʔΦϯʹՃ͑ͯ π + ͕ͷӨ‫͕ݧ࣮Ͱڹ‬ఀࢭ͢Δ௚લ·ͰͷσʔλΛ͢΂͍ͭ͘‫؍‬ଌ͞Ε͔ͨͰΧςΰϦʔ෼͚͢Δ͜ͱ

ͯղੳ͠ɼ6 ࣄ৅ͷީิΛΈ͚ͭɼ2.5 σ ͷ༗ҙ౓ͰɼͦΕͧΕͷαϯϓϧͰҟͳΔ൓ԠϞʔυΛΤͷஹީΛใࠂͨ͠ [93]ɻ͞Βʹͦͷ‫ޙ‬σʔλΛ૿ϯϋϯε͠ɼχϡʔτϦϊ൓ԠͷछྨʹԠͯ͡Ϟ΍ͯ͠ɼ2012 ೥ʹ͸ 11 ࣄ৅ [94]ɼ2013 ೥ʹ͸ 28㸶㸫 ࣮‫ݧ‬։͔࢝Βͷ໨

40

T2K Run 1-7c preliminary

35
30

No oscillation
Data
Best-fit

25
20

10

Number of events

Number of events

45

9
7
6
5
4

15

3
2

5

1

0
0

0
0

2

3

4

5

6

No oscillation
Data
Best-fit

8

10

1

T2K Run 1-7c preliminary

7

8

0.2

T2K Run 1-7c preliminary
12

No oscillation
Data
Best-fit

10
8

0.6

0.8

1

1.2

2.5

Number of events

Number of events

14

0.4

Reconstructed Neutrino Energy (GeV)

Reconstructed Neutrino Energy (GeV)

T2K Run 1-7c preliminary2

No oscillation
Data
Best-fit

1.5

6

1

4

0.5
2
0
0

1

2

3

4

5

6

7

0
0

8

0.2

0.4

0.6

0.8

1

1.2

Reconstructed Neutrino Energy (GeV)

Reconstructed Neutrino Energy (GeV)ਤ 20: T2K ࣮‫؍Ͱݧ‬ଌ͞ΕͨεʔύʔΧϛΦΧϯσͰͷχϡʔτϦϊࣄ৅ͷ࠶ߏ੒͞ΕͨχϡʔτϦϊΤωϧΪʔ෼෍ɻ্ஈ͕χϡʔτϦϊϏʔϜɼԼஈ͕൓χϡʔτϦϊϏʔϜͷσʔλɻͦΕͧΕࠨଆ͕
μ-likeɼӈଆ͕ e-like ࣄ৅ɻχϡʔτϦϊৼಈ͕Ծʹͳ͔ͬͨ৔߹ͱɼ΋ͬͱ΋σʔλͱϑΟοτ͢Δৼ
ಈύϥϝʔλΛԾఆͨ͠৔߹ͷ༧૝஋Λ࣮ઢͰࣔ͢ɻ
ࣄ৅ͷީิΛ֬ೝ͠ɼ༗ҙ౓Λ 7 σ Ҏ্ͱͯ͠ൃ

ৼಈͷ‫ۃ‬େ஋ʹχϡʔτϦϊϑϥοΫεͷϐʔΫ‫ݟ‬Λ࣮֬ʹͨ͠ [95]ɻਤ 22 ʹɼిࢠχϡʔτϦΛ߹ΘͤͨϏʔϜΛ࣮‫͓ͯ͠ݱ‬Γɼਫ਼౓ͷߴ͍ଌϊग़‫ࣄิީݱ‬৅ͷΠϕϯτσΟεϓϨΠΛࣔ͢ɻఆ͕Մೳͱͳͬͨɻ2013 ೥ͷ݁ՌͰେ‫ؾ‬χϡʔ͜ͷؒɼ2012 ೥ʹ͸΍͸Γ θ13 ʹ‫౓ײ‬ͷ͋Δ‫ݪ‬τϦϊͷଌఆΛਫ਼౓Ͱ্ճΓ [99]ɼҎ߱ੈք࠷ߴ

ࢠ࿍͔Βͷ൓ిࢠχϡʔτϦϊফࣦΛଌఆ͢Δ࣮ਫ਼౓ͷଌఆΛߦ͍ͬͯΔɻ‫͔ݧ‬Β΋݁Ռ͕࣍ʑʹใࠂ͞Ε [96–98]ɼθ13 ͕θ2014 ೥͔Βి࣓ϗʔϩͰͳ͘ɼҎલͷ࣮‫͔ݧ‬Βͷ্‫ݶ‬஋ͷ͙͢Լɼ໿

൓χϡʔτϦϊৼಈͷଌఆ8◦ Ͱ͋Δ͜ͱ͕Θ͔ͬͨɻϯͷిྲྀͷ޲͖Λ‫ͯ͠ʹٯ‬ɼ൓χϡʔτϦϊϏʔϜͰͷσʔλऩूΛߦ͍ͬͯΔɻ൓χϡʔτϦϊ

1998 ೥ͷͰ͸ɼ‫ͱ֩ࢠݪ‬ͷஅ໘ੵ͕໿ 1/3 Ͱ͋ΔͨΊ 14 ɼൃ‫ݟ‬Ҏ߱ɼࠞ߹֯ θ23 ͸εʔύʔΧϛΦΧϯσͰχϡʔτϦϊͱಉ͡ࣄ৅਺ΛಘΔͷʹσʔλ͕༨ͷେ‫ؾ‬χϡʔτϦϊʹΑΔଌఆ͕΋ͬͱ΋ਫ਼౓ͷ‫ʹܭ‬ඞཁͱͳΔɻ·ͨɼχϡʔτϦϊϏʔϜͰͷྑ͍݁ՌΛ༩͖͑ͯͨɻθ23 ͸ৼಈͷৼ෯͔Βܾ൓χϡʔτϦϊ੒෼͸அ໘ੵͷҧ͍͔ΒӨ‫͕ڹ‬ແ

·ΔͷͰɼͲͷ͘Β͍ͷ਺ͷϛϡʔχϡʔτϦϊ

ࢹͰ͖Δ͕ɼ൓χϡʔτϦϊϏʔϜͰͷχϡʔτϛϡʔχϡʔτϦϊফࣦͷਫ਼ີଌఆ͕‫͍ͯͬݮ‬Δ͔ΛଌΔඞཁ͕͋ΔɻT2K ࣮‫Ͱݧ‬͸ɼΦϑΞΫγε๏Λ༻͍Δ͜ͱͰχϡʔτϦϊ

14‫ݕ‬ग़‫ث‬͸෺࣭͔͠‫ؚ‬ΜͰ͍ͳ͍ͷͰɼ࣮‫૷ݧ‬ஔ͸ CP ରশੑΛഁ͍ͬͯΔɻ㸶㸫 

Events/(100 MeV/c)

Events/(100 MeV/c)

Data

2500

ν CCQEν CC 2p-2h

2000

ν CC Res 1π

1500

0
0

300

1000

1500

2000

2500

3000

Events/(100 MeV/c)

ν CC Otherν NC modes100

ν modes500

ν CC Res 1π
ν CC Coh 1π

150

ν NC modes

PRELIMINARYν CC 2p-2h200

ν CC Other

500

ν CCQE

350

250

ν CC Coh 1π

1000

Data
400

ν modes

50
0
0

3500
4000 4500
5000
Muon momentum (MeV/c)

500

1000

1500

2000

2500

PRELIMINARY

3000

3500
4000 4500
5000
Muon momentum (MeV/c)

Data
250

ν CCQEν CC 2p-2h200

ν CC Res 1π150ν CC Coh 1π
ν CC Other100

ν NC modes
50

00ν modes
500

1000

1500

2000

2500

3000

PRELIMINARY

5000
3500
4000 4500
Muon momentum (MeV/c)

ਤ 21: લஔ‫ݕ‬ग़‫Ͱث‬ͷΧςΰϦʔ෼͚͞Εͨࣄ৅ʹର͢ΔϛϡʔΦϯͷӡಈྔ෼෍ɻʢࠨ্ʣπ + ͕ͳ͍ʢԼʣͦΕҎ֎ɻώετάϥϜ͸σʔλʹϑΟοτͨ͠ࣄ৅ɼʢӈ্ʣπ + ͕ͻͱ͚ͭͩ‫؍‬ଌ͞Εͨࣄ৅ɼMC γϛϡϨʔγϣϯͷ༧૝Λ൓ԠϞʔυͰ෼͚ͨ΋ͷɻͦΕͧΕͷαϯϓϧͰɼҟͳΔϞʔυͷ൓Ԡ͕બ͹Ε͍ͯΔ͜ͱ͕Θ͔Δɻද 11: εʔύʔΧϛΦΧϯσͰͷిࢠχϡʔτϦϊग़‫ࣄݱ‬৅਺ͷ༧૝஋ʹର͢Δ‫ܥ‬౷‫ࠩޡ‬‫ܥ‬౷‫ࠩޡ‬ͷ‫ݪ‬ҼSK ‫ݕ‬ग़‫ث‬SK Ͱͷ֩಺ऴঢ়ଶ൓Ԡ/2 ࣍൓Ԡલஔ‫ݕ‬ग़‫ث‬ͷଌఆͰ੍‫ݶ‬Λ͔͚ͨϑϥοΫεͱஅ໘ੵதੑΧϨϯτ 1γ ੜ੒νe ͱ ν e ͷஅ໘ੵதੑΧϨϯτͷͦͷଞͷ൓Ԡ߹‫ܭ‬લஔ‫ݕ‬ग़‫ث‬ͷଌఆ͕ͳ͔ͬͨ৔߹

㸶㸫 

ν 1 Ϧϯά e
2.3%
2.6%
2.9%
1.5%
2.6%
0.2%
5.5%
(12.1%)

ν̄ 1 Ϧϯά e
3.1%
2.4%
3.2%
3.0%
1.5%
0.3%
6.3%
(13.5%)

ν/ν̄
1.6%
3.5%
2.3%
1.5%
3.1%
0.2%
5.9%

−3

5.5 ×102

Δ m32 or Δ m232 (eV2)5
4.5

MINOS ν best fit
Super-K ν best fit
T2K Run1-7 ν best fit
T2K Run1-7 ν best fit

MINOS ν 90% CL
Super-K ν 90% CL
T2K ν 90% CL
T2K Run1-7 ν 68% CL
T2K Run1-7 ν 90% CL

4
3.5
3
2.5
2
1.5
1
0.2

0.3

0.4

0.5
2

0.6

0.7

0.8

2

sin θ23 or sin θ23

ਤ 22: T2K ࣮‫Ͱݧ‬ɼϛϡʔχϡʔτϦϊ͕χϡʔτϦϊৼಈʹΑͬͯมԽͨ͠ిࢠχϡʔτϦϊʹ
ΑΔ൓Ԡࣄ৅ͷީิɻ࢛֯ͻͱͭͻͱ͕ͭޫిࢠ
૿ഒ؅Λද͠ɼେ͖͞͸‫ݕ‬ग़͞ΕͨޫͷྔΛɼ৭͸ͦΕͧΕͷޫిࢠ૿ഒ؅ʹ৴߸͕‫ݕ‬ग़͞Εͨ࣌ؒΛද͢ɻਤ 23: χϡʔτϦϊʹର͢Δ Δm232 ͓Αͼ θ23 ͱ൓χϡʔτϦϊʹର͢Δ Δm̄232 ͓Αͼ θ̄23 Λಠཱʹଌఆͨ͠৔߹ͷ 90%৴པ౓ͷ‫ڐ‬༰ྖҬɻଞͷ࣮‫ݧ‬ͷ݁Ռ΋ॏͶͯ͋Δɻ
४తͳ 3 ੈ୅ͷࠞ߹ߦྻͷ࿮૊ΈΛԾఆ͢Ε͹ɼχϡʔτϦϊϞʔυͷిࢠχϡʔτϦϊग़‫ݱ‬Λ‫ࢠݪ‬࿍൓χϡʔτϦϊফࣦ࣮‫ݧ‬ͷ݁Ռͱ૊Έ߹ΘϦϊ੒෼͸அ໘ੵ͕‫ʹٯ‬ಇ͖Ө‫͕ڹ‬େ͖͘ͳΔͨ

ͤΔ͜ͱͰɼδCP ʹؔ͢Δ੍‫ݶ‬ΛಘΔ͜ͱ͕Ͱ͖

Ίɼ஫ҙ͕ඞཁͰ͋ΔɻεʔύʔΧϛΦΧϯσͰΔɻ͜͏ͯ͠ɼੈքͰॳΊͯͷϨϓτϯηΫλʔ͸χϡʔτϦϊͱ൓χϡʔτϦϊͷ۠ผ͕‫ج‬ຊతͰͷ CP ରশੑͷഁΕʹؔ͢Δ੍‫ݶ‬Λ 2013 ೥ʹʹͰ͖ͳ͍͕ɼલஔ‫ݕ‬ग़‫Ͱث‬͸࣓৔͕͋ΔͨΊʹಘͨ [101]ɻ౷‫े͕ྔܭ‬෼Ͱ͸ͳ͍͕ɼ΋ͬͱ΋༻ҙʹ۠ผՄೳͰ͋ΔɻσʔλͱҰக͢Δͷ͸ɼCP ରশੑͷഁΕ͕࠷େ൓ϛϡʔχϡʔτϦϊফࣦͷଌఆ͔ΒɼχϡʔτϦϊͰͷৼಈύϥϝʔλ Δm232 ͓Αͼ θ23 ͱɼ൓χϡʔτϦϊͰͷύϥϝʔλ Δm̄232 ͓Αͼ θ̄23‫ʹݶ‬ഁΕ͍ͯΔɼδCP = −90◦ ෇ۙͷύϥϝʔλͰ͋ͬͨɻ͞Βʹ 2016 ೥Նʹ͸ɼT2K ࣮‫ݧ‬ͷχϡʔτϦΛಠཱͳύϥϝʔλͱ͢ΔղੳΛߦͬͨɻ΋͜͠ϊͱ൓χϡʔτϦϊͷσʔλ͢΂ͯΛ‫ࢠݪ‬࿍൓ΕΒ͕ҧ͍ͬͯͨ৔߹ʹ͸ CPT ରশੑ͕ഁΕͯχϡʔτϦϊ࣮‫ݧ‬ͷ݁Ռͱ߹ΘͤΔ͜ͱͰɼਤ 24

͍Δ͜ͱʹͳΔ͕ɼਤ 23 ʹࣔ͢௨ΓɼχϡʔτϦϊͷ৔߹ͱໃ६ͳ͍ύϥϝʔλͱ͍͏݁ՌͰ͋ͬ
ͨ [100]ɻ

ʹࣔ͢Α͏ʹɼδCP ʹର͠ 90%৴པ౓Ͱ [−179◦ <δCP < −22◦ ] ͱ͍͏੍‫ݶ‬ΛಘͨɻδCP = 0◦ ·ͨ͸ ±180◦ ͷ࣌ɼCP ରশੑ͕อଘ͞ΕΔͷͰɼ͜ͷ݁Ռ͸ 90%৴པ౓Ͱ CP ରশੑ͕อଘ͞ΕΔέʔCP ରশੑͷഁΕͷ୳ࡧ ిࢠχϡʔτϦϊग़‫ݱ‬εΛ‫غ‬٫͍ͯ͠Δ͜ͱʹͳΔɻNOνA ࣮‫Ͱݧ‬΋ɼΛൃ‫Ͱͱͨ͜͠ݟ‬ɼCP ରশੑͷഁΕʹؔ͢Δଌ

χϡʔτϦϊϞʔυ͚ͩͷσʔλͰ͋Γɼ·ͨ΍ఆ͕ՄೳͱͳͬͨɻT2K ͰͷిࢠχϡʔτϦϊ͸Γ౷‫ܭ‬͸গͳ͍ͳ͕Βɼಉ͡Α͏ͳ܏޲Λࣔ͢ग़‫ݱ‬ͷ֬཰͸ɼθ13 ͱ δCP ɼ͓Αͼ࣭ྔॱংʹґଘ݁Ռ͕ಘΒΕ͍ͯΔɻ·ͩσʔλ͕গͳ͘ɼ౷‫ܭ‬

͢Δ͕ɼ‫ࢠݪ‬࿍൓χϡʔτϦϊফࣦ࣮‫Ͱݧ‬͸΄΅త;Β͖͕ͭେ͖͍ঢ়‫͋Ͱگ‬ΔͨΊɼࠓ‫͞ޙ‬Βʹ७ਮʹ θ13 ͚ͩΛଌΔ͜ͱ͕Ͱ͖Δɻͦ͜Ͱɼඪ

σʔλΛ૿΍ͯ͠ΑΓ‫౓ײ‬ͷߴ͍ଌఆΛߦ͏ඞཁ㸶㸫 ) H2 to exclude sinICP=0

-2lnL

25
T2K Run1-7c preliminary
20

Normal Hierarchy
Inverted Hierarchy

15
10

15
w/ eff. stat. improvements (no sys. errors)
w/ eff. stat. & sys. improvements

10

w/ eff. stat. improvements & 2016 sys. errors
3X C.L.

99% C.L.

5
90% C.L.

0
0

5

5

10

15

20

21

Protons-on-Target (x10 )
0

-3

-2

-1

0

1

2

3

CP (radians)ਤ 25: T2K ͷσʔλऩूΛଓ͚ͨ৔߹ʹ CP ඇରশੑΛൃ‫͖Ͱݟ‬Δ‫౓ײ‬ͷ༧૝

) H2 to exclude sinICP=0ਤ 24: CP ରশੑΛഁΔҐ૬ͷύϥϝʔλЎ CPʹର͢Δɼnegative log likelihood ͷ஋ɻ௨ৗ࣭ྔ
ॱংͱ‫ॱྔ࣭ٯ‬ংͷ৔߹Λ෼͚ͯࣔ͢ɻϋονͷ͍ͭͨॎઢ͸௨ৗ࣭ྔॱং·ͨ͸‫ॱྔ࣭ٯ‬ংʹର͢Δ৴པ౓ 90%ͷ‫ڐ‬༰۠ؒΛද͢ɻT2K ࣮‫ݧ‬ͷ
2016 ೥Ն·ͰʹಘΒΕͨχϡʔτϦϊͱ൓χϡʔτϦϊͷσʔλΛɼ‫ࢠݪ‬࿍൓χϡʔτϦϊ࣮‫ݧ‬ͷ݁Ռͱ߹ΘͤͯಘΒΕͨ΋ͷɻΕ͓ͯΓɼ‫Ͱޙ‬ड़΂ΔΑ͏ʹࠓ‫ޙ‬ͷਐలʹ‫ظ‬଴͕
͔͔Δɻ
ͦͷଞ

True sin2V23=0.43
True sin2V23=0.50
True sin2V23=0.60

15

10

3X C.L.
99% C.L.

5
90% C.L.

100

0

100

200

True ICP(s)Εʹؔ͢Δଌఆͷୈ̍าΛ౿Έग़͢͜ͱ͕Ͱ͖ͨ
Ͱͷॳ‫ظ‬ͷσʔλ͔Β͢Ͱʹ‫ڵ‬ຯਂ͍݁Ռ͕ಘΒ

20x1021 POT w/ eff. stat. & sys. improvements
7.8x1021 POT w/ 2016 sys. errs.

0200͕͋Δ͕ɼϨϓτϯηΫλʔͰͷ CP ରশੑͷഁ͜ͱࣗମ͕େ͖ͳਐలͰ͋Δɻͳ͓͔ͭɼ͜Ε·20

ਤ 26: ਅͷ δCP ͷ஋ʹରͯ͠ CP ඇରশੑΛൃ‫͖Ͱݟ‬Δ‫౓ײ‬ɻ఺ઢ͸‫ࡏݱ‬ͷ T2K ࣮‫ݧ‬ͷ໨ඪɼ
7.8 × 1021 POT ͷ৔߹ɻ࣮ઢ͸ 20 × 1021 POT ͷσʔλΛͨΊͨͱ͖ʹɼ͍͔ͭ͘ͷ θ23 ͷ஋ΛԾఆͨ͠৔߹ɻ࣭ྔॱং͸‫ط‬஌ͱͯ͠ղੳ͍ͯ͠Δɻ

͜͜Ͱ঺հͨ͠χϡʔτϦϊৼಈͷଌఆҎ֎ʹ΋ɼલஔ‫ݕ‬ग़‫ث‬ͷσʔλʹΑΔχϡʔτϦΓฦ͠प‫ظ‬Λ‫ࡏݱ‬ͷ̎.48 ඵ͔Β 1 ඵۙ͘·Ͱ୹ϊ-‫֩ࢠݪ‬൓Ԡஅ໘ੵͷଌఆ΍εςϥΠϧχϡʔ

͘͢Δ͜ͱͰɼ>1 MW ͷϏʔϜύϫʔΛ໨ࢦτϦϊͳͲͷ৽෺ཧͷ୳ࡧͳͲɼ੒Ռ͕ଓʑͱ্

ͤΔ‫ݟ‬௨͕͋͠Δɻͦ͜ͰɼT2K ࣮‫Ͱݧ‬͸͜ͷ͕͍ͬͯΔɻͦΕΒʹ͍ͭͯ͸ɼT2K ࣮‫ݧ‬ͷҰൠϏʔϜ‫౓ڧ‬ͷ޲্Λੜ͔͠ɼ࣮‫ؒظݧ‬ΛԆ௕͠

޲͚ Web ϖʔδ [102] ͳͲΛ͝ཡ͍͖͍ͨͩͨɻ

ͯ 2 × 1022 POT ͷσʔλΛͨΊΔ͜ͱͰɼCPରশੑͷഁΕͷൃ‫ݟ‬Λ໨ࢦ͢͜ͱΛఏҊ͍ͯ͠

4.10

Δ [103]ɻ͜ͷԆ௕‫ܭ‬ըΛ T2K ϑΣʔζ̎ɼ͋Δࠓ‫ޙ‬ͷల๬

͍͸ T2K-II ͱ‫ݺ‬ΜͰ͍Δɻ

ϨϓτϯηΫλʔͰͷ CP ରশੑͷഁΕͷଌఆ

ਤ 25 ͸ɼԾʹਅͷ஋͕ δCP = −90◦ ͩͬͨ৔͸ɼΑ͏΍࢝͘·ͬͨ͹͔ΓͰ͋Δɻࠓ‫౓ײޙ‬Λ߹ʹɼsin δCP = 0 Λ‫غ‬٫Ͱ͖Δɼ͢ͳΘͪ CP

্͛Δʹ͸ɼԿΑΓ΋·ͣσʔλྔΛ૿΍͢͜ඇରশੑΛൃ‫͖Ͱݟ‬Δ‫౓ײ‬Λ POT ͷؔ਺ͱͯ͠

ͱ͕ॏཁͰ͋ΔɻJ-PARC Ճ଎‫ث‬͸ࠓ‫਺ޙ‬೥Ͱ‫܁‬ࣔͨ͠΋ͷͰ͋Δɻి࣓ϗʔϯͷిྲྀΛ૿΍ͨ͠㸶㸫 ΓɼղੳͷվળΛߦͬͨΓ͢Δ͜ͱͰɼ࣮ޮతͳ
ޮ཰Λ‫ࡏݱ‬ͷ 1.5 ഒʹ૿΍ͤΔͱԾఆ͍ͯ͠Δɻ
·ͨɼෳ਺͋Δઢ͸ɼ‫ܥ‬౷‫͍ͳ͕ࠩޡ‬৔߹ɼ‫ࡏݱ‬
ͷ··ͷ৔߹ɼվળ͕͋ͬͨ৔߹ɼΛ͍ࣔͯ͠Δɻ
ਤ 26 ͸ɼਅͷ δCP ͷ஋Λ͍Ζ͍ΖԾఆͨ͠৔߹
ʹɼCP ඇରশੑΛൃ‫͖Ͱݟ‬Δ‫Ͳ͕౓ײ‬ͷ͘Β͍͋Δ͔Λ͍ࣔͯ͠Δɻ2 × 1022 POT ͷσʔλΛ䜹䜴䞁䝖䜾䝷䝣䠄 ㍈䠅ूΊΕ͹ɼCP ରশੑͷഁΕ͕΋͠ൺֱతେ͖͚
Ε͹ɼ3 σ ͔ͦΕҎ্ͷ༗ҙ౓Ͱൃ‫͕ݟ‬Մೳͳ͜ਤ 27: ϋΠύʔΧϛΦΧϯσͷ֓೦ਤ

T2K-II ͷ໨ඪΛୡ੒͢ΔͨΊʹ‫ܥ‬౷‫ࠩޡ‬Λ͞Βʹ‫ݮ‬গͤ͞ΔͨΊͷΦϓγϣϯͱͯ͠ɼલஔ‫ݕ‬ग़‫ث‬ΛΞοϓάϨʔυ͢ΔՄೳੑ͕ٞ࿦͞Ε͍ͯ
R
Δɻվྑ‫ܕ‬ͷ MPPCΛ༻͍ͨ‫ݕ‬ग़‫ث‬΍ɼ৽ͨͳ

TPC Λ੍࡞ͯ͠ɼେ֯౓ʹग़ཻͨࢠͷ‫ݕ‬ग़ޮ཰Λվળ͢Δ͜ͱ͕‫ج‬ຊతͳߟ͑ํͰɼ‫ࡏݱ‬γϛϡϨʔγϣϯ౳Ͱ‫ݕ‬౼͕ਐΜͰ͍Δɻ·ͨɼ‫ࡏݱ‬ͷલஔ‫ݕ‬ग़‫ʹث‬Ճ͑ͯɼඪత͔Β 1–2 km ͷͱ͜Ζ

Relative single photoelectron hit efficiency

ͱ͕Θ͔Δɻ

ʹਫνΣϨϯίϑ‫ݕ‬ग़‫ث‬Λ‫ݐ‬ઃ͢Δதؒ‫ݕ‬ग़‫ث‬ͷΞΠσΞ΋ఏҊ͞Ε͓ͯΓ [104, 105]ɼࠓ‫͞ޙ‬Βʹٞ࿦͕ਐΉ΋ͷͱࢥΘΕΔɻ

5ϋΠύʔΧϛΦΧϯσ

2

1

0 -90 -80 -70 -60 -50 -40 -30 -20 -10 0 10 20 30 40 50 60 70 80 90
Position angle [degree]ਤ 28: εʔύʔΧϛΦΧϯσͷޫిࢠ૿ഒ؅ͱɼ
৽ͨʹ։ൃͨ͠৽‫ܕ‬ͷޫిࢠ૿ഒ؅ͷޫࢠ‫ݕ‬ग़ޮ཰ͷൺֱɻԣ࣠͸ޫి໘ʹޫࢠ͕ೖࣹ͢ΔҐஔΛ֯౓Ͱදͨ͠΋ͷɻεʔύʔΧϛΦΧϯσ͸࣮‫ݧ‬։͔࢝Β 20 ೥͕ମੵ͸ 19 ສτϯͰεʔύʔΧϛΦΧϯσͷ໿ 10‫ͪܦ‬ɼଟ͘ͷσʔλΛूΊ‫ڻ‬ҟతͳ੒ՌΛग़ͯ͠ഒʹͳΔɻνΣϨϯίϑޫΛͱΒ͑Δޫηϯαʔ͖ͨɻ͔͠͠ɼχϡʔτϦϊͷੑ࣭ʹӅ͞Ε͍ͯͷ਺͸ 40,000 ຊͱͳΔɻεʔύʔΧϛΦΧϯσ

ΔͰ͋Ζ͏ΑΓ‫ج‬ຊతͳ෺ཧ΍ɼ֩ࢠ่յͷൃ‫ݟ‬Ͱ࢖ΘΕ͍ͯΔ΋ͷΑΓ΋ɼ͞Βʹվྑͨ͠΋ͷʹΑΓେ౷Ұཧ࿦ʹഭΓɼΑΓਫ਼ີͳ‫ڀݚ‬Λߦ͏Λ࢖༻͢Δ༧ఆͰ͋ΔɻεʔύʔΧϛΦΧϯσͷ

ͨΊʹ͸ɼ͞Βʹଟ͘ͷσʔλ͕ඞཁͱͳΔɻͦ

ޫిࢠ૿ഒ؅ͱɼ৽ͨʹ։ൃͨ͠৽‫ܕ‬ͷޫిࢠ૿͜ͰɼεʔύʔΧϛΦΧϯσΑΓ΋͞ΒʹҰܻେഒ؅ͷޫࢠ‫ݕ‬ग़ޮ཰ͷൺֱΛਤ 28 ʹࣔ͢ɻ‫ߦݱ‬͖ͳ‫ݕ‬ग़‫ث‬Λ‫ݐ‬ઃ͠ɼχϡʔτϦϊͷ CP ඇରশͷޫిࢠ૿ഒ؅ʹൺ΂ɼ໿ 2 ഒͷޮ཰͕ಘΒΕͯੑ΍ཅࢠ่յͷ୳ࡧɼχϡʔτϦϊఱจֶͷ‫ڀݚ‬͍ΔɻϋΠύʔΧϛΦΧϯσ͕࣮‫͞ݱ‬ΕΕ͹ɼJ-PARCΛҰܻߴ͍‫͘΂͏ߦͰ౓ײ‬ఏҊ͞Ε͍ͯΔͷ͕ɼ͔Βͷ 1.3 MW ͷχϡʔτϦϊϏʔϜΛ࢖͏͜ͱϋΠύʔΧϛΦΧϯσ‫ܭ‬ը [106, 107] Ͱ͋Δɻ
ਤ 27 ʹϋΠύʔΧϛΦΧϯσͷ֓೦ਤΛࣔ͢ɻͰɼχϡʔτϦϊɾ൓χϡʔτϦϊͦΕͧΕ 1,000ϋΠύʔΧϛΦΧϯσ‫ݕ‬ग़‫ث‬͸ɼ௚‫ ܘ‬74 mɼਂ͞ࣄ৅ΦʔμʔͷిࢠχϡʔτϦϊग़‫ݱݱ‬৅Λ‫؍‬ଌ

60 m ͷԁ౵‫ܗ‬ͷλϯΫ̎‫͔ݸ‬Βߏ੒͞ΕΔɻλ͢Δ͜ͱ͕Ͱ͖ɼϨϓτϯηΫλʔͰ CP ରশੑϯΫͷମੵ͸ 1 ‫ͨ͋ج‬Γ 26 ສτϯͰ͋Γɼ༗ޮͷഁΕ͕΋͋͠Ε͹΄΅࣮֬ʹଊ͑ΒΕɼͦͷΑΓਫ਼ີͳ‫͕ڀݚ‬ՄೳʹͳΔͱࢥΘΕΔ [108]ɻ·㸶㸫 ͨɼେ‫ؾ‬χϡʔτϦϊ΍ଠཅχϡʔτϦϊͷ‫؍‬ଌ΋Ұܻଟ͘ͷࣄ৅ΛूΊΔ͜ͱͰΑΓਫ਼ີͳ‫ڀݚ‬͕ՄೳʹͳΓɼ௒৽੕χϡʔτϦϊͳͲͷχϡʔτϦϊఱจֶ΋ൃల͢Δͱ‫ظ‬଴͞ΕΔɻཅࢠ่յ
ͷण໋΋ൃ‫ ͕౓ײݟ‬1035 ೥ʹಧ͘‫ࠐݟ‬ΈͰ͋Γɼ਺े೥୳͠ଓ͚ͨ৴߸ͷൃ‫͍͕ݟ‬Α͍Α‫ظ‬଴Ͱ͖
ΔɻϋΠύʔΧϛΦΧϯσΛ‫ݐ‬ઃ͢ΔͨΊͷٕज़͸ɼେۭಎͷ۷࡟΍ߏ଄ମͷઃ‫ܭ‬ɼߴੑೳޫ‫ݕ‬ग़‫ث‬ɼ७ਫγεςϜΛ‫ؚ‬ΊεʔύʔΧϛΦΧϯσͷ
‫͍ͯͮ͞جʹݧܦ‬Βʹվྑ͞Εͨ΋ͷཱ͕֬ͯ͠
͓Γɼࠃࡍతͳ‫ڀݚ‬άϧʔϓͰ࣮‫ڀݚ͚ͨ޲ʹݱ‬͕ਪਐ͞Ε͍ͯΔɻࠓ‫ޙ‬΋ɼχϡʔτϦϊ‫ݕ‬ग़‫ث‬͸࠷ઌ୺ٕज़Ͱਐ
ԽΛଓ͚ɼૉཻࢠ΍Ӊ஦ʹؔ͢Δ‫͖΂͘ڻ‬ಾΛ໌Β͔ʹ͠ଓ͚ΔͩΖ͏ɻ

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