Transcript 反陽子ビームを用いたΦ中間子原子核探索実験

Investigation of the nuclear medium
property using f meson as a probe
Hiroaki Ohnishi
Advanced meson science Laboratory
RIKEN
Introduction
 Origin of hadron mass
→ Spontaneous breaking of chiral symmetry！
 Under the extreme condition such as high temperature
and/or density, restoration of its broken chiral symmetry
has been expected
SPS, RHIC, LHC
KEK-PS
J-PARC
T. Hatsuda, H. Shiomi and H. Kuwabara
Prog. Theor. Phys. 95(1996)1009
W.Weise NPA553, 59 (1993).
Prediction from theory tells us,
Mass of vector meson in medium
will be decreasing
when density increasing
Introduction
 Experiments have been done to study property
of the vector meson in medium, so far
High energy heavy ion collisons
→creating high temperature/density
medium and vector meson dynamically
CERES
Width boarding
of ρmeson?
Vector meson production in p-A or γ-A
→ vector mesons are creating dynamically
Mass shift of
Φ/ω mesons in
normal nuclear mater
SPS, RHIC, LHC
KEK-PS
KEK-PS E325 PRL98(2007)042501
NA60
W.Weise NPA553, 59 (1993).
CBELSA-TAPS PRL94(2005)192303
f-Nucleus interaction？
 What we learn from KEK-PS E325 results （PRL98(2007)042501）
Reduction of the f meson mass observed ! (about 3%),
when we selected slowly moving f mesons
ここで、山縣さんに理論計算を紹介してもらいます
f meson
in nucleusmeasurement
can be modeled
More advanced
will as
be performed
f as
meson
in the energy pocket created by
at J-PARC
E16 is
experiment.
nuclear potential i.e. Mass reduced due to
binding energy of the system
Formation of the f-mesic nucleus?? Is it possible to create
3% mass reduction on f meson,
expected depth of the potential must be about 30 MeV
f mesic nucleus with
such a small potential depth?
f meson bound state exist？
 There are many hints inΛhypernucleus production
 Potential depth of Λ-Nucleus ～３０ＭｅＶ
 Mass ofΛ＝１１１６ ＭｅＶ/c2
Those conditions are very similar with the case for f meson
 In the case of Λ hypernucleus production via (p,K) reaction,
momentum transfer for the reaction is about 400 MeV/c.
This is far away from recoilless condition.
Analogy from L hyper nucleus production,
f meson bound state will be produced
even if we selecting elementary process
which has large momentum transfer
How to produce f with low momentum
efficiently?
 f production via p(p-,n)f reaction
 Missing mass spectroscopy can be
done with forward going neutron.
 Cross section ~ 20 ub
 Momentum transfer ~ 400 MeV/c
 f production via p(p,f)f reaction
 Missing mass spectroscopy can be
done with forward going f meson.
 Cross section ~ 4 ub
 Momentum transfer ~ 200 MeV/c
How to produce f with low momentum
efficiently?
 f production via p(p-,n)f reaction
 Background = Huge!!!
Quesi-free hyperon production etc.
 f production via p(p,f)f reaction
 Background = Huge!
But, once one can identify third
strangeness in the event, then
event sample will be
almost background free
f meson production with anti-proton will be primary candidate of the
elementary process for the f mesoic-nucleus production.
How to identify f meson bound state
 Let’s focusing on decay mode
 Mass of the f meson will be decreasing about 30 MeV.
 i.e. 1019 MeV – 30 MeV = 989 MeV ~ 2 x MKaon
Main decay mode for Φmeson, Φ→K+K-, will be suppress.
 However, Φ meson is in nucleus.
There are many nucleon surrounding them.
1019 MeV – 30 MeV + 938 MeV(proton)
＝ 1927 MeV > MKaon+MΛ
i.e. Φp→K+Λ will be a dominant decay mode,
if f meson is in nucleus. (This mode is not suppressed
by OZI role )
s
s
i.e. K+L in final state will be
a good signal to ensure
f meson in medium
Φ
s
u
p u
d
u
K+
s
uΛ
d
Concept for the experiment
Anti-proton
Nuclear
target
Reaction
f meson
bound
state
Decay
K+
L
Outgoing
f meson
Experimental setup
 Good tracking chamber and PID detector around target
 Cylindrical Drift Chamber ＋ Kaon ID detector
 f meson emitted to forward direction must be detect
efficiently.
Experimental setup(2)
 Conventional
 LEPS like setup
 But large dipole magnet
behind solenoid magnet
to maintain large forward
angle acceptance
 Challenging setup
 Everything inside large solenoid
magnet(~3m long, 1m diameter )
Event rate estimation (2)
 Comparison parameters in hypernuclear formation at KEK-SKS
and new experiment for f meson bound state
～ 240 Events are expected for one month of data taking period
Summary
 Based on the results reported by KEK-PS E325 (mass shift of
f meson) together with a similarity between L hyper nucleus
production via (p,K) reaction strongly suggested that the
production of f mesic nucleus can be possible.
 The most promising elementary process for
the f mesic nucleus production will be pp→ff channel.
(Background free experiment can be achieved, in principle)
 Naïve event rate estimation tells us that 240 events
candidate for f mesic nucleus will be produce per month,
with beam intensity, 2x106/spill, for 1.3 GeV/c anti-proton.
おまけ。。。。。。。
Invariant mass spectra of f in nuclear
medium via lepton pairs
 Final state interaction の影響が少ないレプトン対測定
は、核物質の性質をさぐる有力なツールとなる。
 ＫＥＫ－ＰＳ Ｅ３２５実験の成功。（f->ee）
 J-PARC でさらに詳細の研究が行なわれる
J-PARC E1６ 実験
 ミュオン対測定 ： 可能である？がそもそも、出てくる
ミュオン運動量が低い。。。
 ee 測定とは相補的。それだけ？
そもそも、なぜ f->mm measurement????
 私がＣＥＲＮ－ＮＡ６０で 実験をしていたとき、
（高エネルギー重イオン衝突におけるミュオン対測定実験）
 ＣＥＲＮ－ＮＡ４５実験
（高エネルギー重イオン衝突における電子‐陽電子対測定実験）
が終わりレプトン対測定つながりでＮＡ６０に参戦してきた
Ｈ．Ｓｐｅｃｈｔ教授（当時ハイデルベルグ大）がＮＡ６０最初の
実験データ収集時に言っていた一言。。。
 ＣＥＲＥＳで１年かかってとったデータ量を４分でとっている。。。
 違いは、ＣＥＲＥＳには電子‐陽電子対トリガーが無い。
ＮＡ６０にはミューオン対トリガーがある。
 ミューオン対測定なので標的が厚い！！！
（インジウム標的、1g/cm2 を５枚～5g/cm2 を使用。）
 ただし、ＣＥＲＮではビーム運動量は 核子あたり158 GeV/c、
相手にしてるミュオン運動量は数十ＧｅＶ！だから勝負になった。
 Ｊ－ＰＡＲＣで、測定したい low momentum f から崩壊する
ミュオン対測定って可能？ まず狙ってる運動量は？
f->mm measurement の可能性
 素過程として p(p-,n)f を選択
 Beam momentum = 2 GeV/c とすると 生成断面積は 20 mb
 生成されるf meson の運動量分布 0.4< bg < 1.6
KEK-E325 のbg分布
 いま、検出器として標的を囲むようなＣＤＣ型のものを考える。
カバーする範囲をビーム軸に対し
 ミュオン対がアクセプタンスに
入る場合の f の運動量分布
0.5< q < p-0.5 とする。
しかし、ミュオンの運動量分布は
こんな低運動量ミュオントリガーは可能？
How to measure low momentum f
 One of the example
SND detector
ee collider 実験 ( sqrt(s) < 2GeV )
f->mm branching ratio を測定した（する）実験
この検出器ではミュオン
４００ＭｅＶ以上 ５３０ＭｅＶ以下を９０％以上の効率でＩＤ
How to measure low momentum f -(2)
 500 MeV/c まではmuon ID 出来そう。
では、500 MeV/c 以上 1200 MeV/c 以下のミュオンは？
Belle KLM detector
~3GeV/c までなら捕まえる検出器が作れる！
f meson physics at J-PARC
 K中間子原子核探索実験
Ｊ－ＰＡＲＣ Ｅ１５ (on going!)
anti-Ｋ N の相互作用の明確な答えを出す
 原子核中で生成された f->ee 測定
Ｊ－ＰＡＲＣ Ｅ１６（on going!）
 f 中間子原子核生成 探索実験
Ｊ－ＰＡＲＣ ＬｏＩ
 原子核中で生成された f->mm 測定
アイディアのみ（出来たらいいな）
 必要なものは？ どうやって？ 今後の課題？
Muon detector
f->mm 測定同時に出来ない？
~40cm
1.2m
MuonEMCal
absorber
~3m
CDC
CDC
標的周りを
z
z
 さて、 f 中間子原子核探索実験と
MuonEMCal
absorber
Muon detector
まとめ
 Ｊ－ＰＡＲＣをfを用いた物質質量の起源探索の
最終試験場にする！
 その第一弾がすでにＥ１５，Ｅ１６として準備中
 第二弾実施のためには、
 大強度反陽子ビームライン！
 標的周りを囲む検出器システム！
 大立体核前方スペクトロメーター
の建設が必要。
 なにはともあれ、(小沢さん的に言うと) 夢を共有していた
だけるＣｏｌｌａｂｏｒａｔｏｒ が必要（切実。。。）
現在 ７名。。。。
実験の具体化はこれから
f->mm を測ると何がすばらしいのか？
 標的原子核中での
How to produce f with low momentum
efficiently?
 f production via p(p-,n)f reaction
 Background = Huge!!!
Quesi-free hyperon production etc.
 Momentum of f generated
 f production via p(p,f)f reaction
 Cross section ~ 4 ub
 Momentum of f generated
Today’s topics
 Is there any way to embedded f meson in nuclear
matter?
 Analogy of pionic, kaonic nucleus
 Study of invariant mass spectra
of low momentum f meson in nuclear medium
 study of fe+e- : has been proposed as J-PARC E16
 study of fm+m- :
idea of the measurement will be presented in this talk!
Event rate estimation
 Event rate for f meson bound state formation are estimated
based on the hypernuclear formation rate obtained at KEK-SKS
 Event rate seen in hypernuclear formation via (p+,K+)
reaction at KEK-PS/K6 with SKS spectrometer
 1x109 p induced on 1g/cm2 Carbon target,
about 20 grand state
12
LC
produced
 Basic numbers used for the estimation







Beam intensity Ip = 2.0 x 106 / spill
Beam momentum used for the experiment = 1.3 GeV/c
Momentum transfer = 200 MeV/c
p-p →ΦΦ cross section = 4/4π(mb/sr)=0.32(mb/sr)
Target thickness 2g/cm2
Acceptance for forward spectrometer (120 msr)
K+Λ trigger efficiency
(ΩCDC x BR(Φp→K+Λ) xBR(Λ→pπ)) = 1.7 sr
 Relative capture rate （sticking probability）
 Rcapture = exp(-q2/qF2) , q: momentum transfer, qF: fermi momentum
Experimental setup(2)
 Conventional
 LEPS like setup
 But large dipole magnet
behind solenoid magnet
to maintain large forward
angle acceptance
Muon detector
EMCal
Aerogel+Hodoscope
CDC
z
Experimental setup(2)
 Conventional
 LEPS like setup
 But large dipole magnet
behind solenoid magnet
to maintain large forward
angle acceptance
If we designed acceptance coverage
for the forward spectrometer ~ 120 mSr