低圧ガスにおけるダークマター探索実験 だあくまたん 中村輝石（京大理） 現在のNEWAGE 低圧ガスで感度アップ まとめ JPS2011秋季大会@弘前　2011/09/16 低圧ガスにおけるダークマター探索実験 だあくまたん 中村輝石（京大理） 谷森達、窪秀利、身内賢太朗 Parker Joseph、水本 哲矢、高田淳史 西村広展、岩城智、澤野達哉 松岡佳大、古村翔太郎、佐藤快 現在のNEWAGE 低圧ガスで感度アップ まとめ Hello. My name is Kiseki Nakamura, and I'm first year of doctor course in Kyoto University. In Kyoto university, we promote the direction-sensitive dark matter search experiment, name "NEWAGE". I will talk about this experiment. And using low pressure gas, the sensitivity of dark matter is expected to be improve. So today, I talk low pressure gas operation in detail.

NEWAGE 暗黒物質の到来方向異方性 ↓ 反跳原子核の飛跡を捉えて暗黒物質検出 暗黒物質 μ-TPC 電子 原子核 μ-PIC CF4ガス New general WIMP search with an Advanced Gaseous tracker Experiment 暗黒物質の到来方向異方性 　↓ 反跳原子核の飛跡を捉えて暗黒物質検出 暗黒物質 μ-TPC 1) 電子 M=80GeV σ=0.1pb 予想されるcosθ分布 CF4ガス 原子核 θ DM Nucleus 40 [count/3m3/year/bin] 20 μ-PIC 2) 2)μ-TPC ・・・ Micro Time Projection Chamber 1)μ-PIC ・・・ Micro Pixel Chamber -1 1 cosθ

現状＠神岡地下 40cm 方向に感度を持つ制限の更新 Phys.Lett.B686(2010)10 DAMA領域の 探索の為に 　現状＠神岡地下 40cm 方向に感度を持つ制限の更新 　　Phys.Lett.B686(2010)10 使用ガス：CF4　0.2atm DAMA領域の 探索の為に WIMP-陽子（SD）の制限曲線 σ[pb] 低閾値（100keV⇒50keV） 低圧ガス動作 低BG（1/10） ラドン除去システム 低放射能なモノ選び 飛跡の前後判定 TOTの測定（身内講演） 大型化(10倍) 60×60×50cm3　×2 104 102 1 10 102 103 mass [GeV/c2]

検出器＠京都 Drift plane m-PIC サイズ : 30x30cm ピッチ : 400mm GEM (8分割) 使用ガス：CF4　0.1atm 45cm 0.5cm 50cm Drift plane m-PIC サイズ : 30x30cm ピッチ : 400mm At NEWAGE experiment, we use u-PIC for MPGD readout. Also, we put GEM above u-PIC to obtain sufficient gain. u-PIC have been introduced at previous session, so I omit detail of u-PIC. In u-TPC, we use CF4 gas because fluorine have relatively large cross-section to neutralino. And, gas pressure is low like 0.1 to 0.2 atm. GEM (8分割) サイズ : 28x23cm 厚み : 50mm 穴径 : 70mm ピッチ : 140mm 30cm

Expected energy spectrum 閾値低下 Expected energy spectrum σ=1pb, M=100GeV, target:F エネルギー閾値 : 100keV -> 50keV -> 感度 : 約10倍 new threshold (plan) current threshold This graph is expected energy spectrum. If energy threshold decrease 100keV to 50keV, we became to detect red region in addition to blue region. So sensitivity for dark matter improve about 10 times. Then, how to make threshold lower? The answer is to using low pressure gas. If we reduce the pressure half, nuclear run 2 times longer. Then, we will obtain low energy tracks that couldn't detect because track was too short. In addition, being track longer, angular resolution is expected to improve. But low pressure gas have disadvantage that ionized electron density become half. So low pressure operation needs twice gas gain if we were to operate detector in the same condition to conventional pressure. 低圧ガス（152torr -> 76torr）で飛跡長 : 2倍 -> 低エネルギー（短い）飛跡に感度 -> 必要ゲイン : 2倍

ゲインカーブ m-TPCは0.1atmで動いた ゲインカーブ anode ( m-PIC 増幅 ) DGEM ( GEM 増幅 ) Drift Plane Drift -3.69kV m-TPCは0.1atmで動いた ゲインカーブ anode ( m-PIC 増幅 ) DGEM ( GEM 増幅 ) induction ( 透過率 ) GEMtop -500V GEM GEMbottom -280V Induction 5mm cathode GND m-PIC anode 515V gas gain gas gain gas gain GEM:-500/-280V anode:515V GEMbottom:-280V anode:515V DGEM:220V 2 times gain from 0.2atm We measured the gas gain to check u-TPC using 0.1atm gas works or not. The gas gain for each anode voltage behave monotonically increasing. But for delta-GEM and induction field, gain curves have maximal point. Using low pressure gas, gas gain behavior is not ordinary. At 0.1atm, necessary gain is twice of its at 0.2atm. In the graph, blue lines represent necessary gain level. Thus, we optimized u-PIC voltage and GEM voltage to these value. DGEM=GEMtop-GEMbottom EInduction=GEMbottom/5mm anode voltage[V] DGEM voltage[V] Einduction(Induction field)[V/mm] ゲインカーブはサチレート（電子の平均自由行程：数mm） 0.2atmから求まる必要ゲインには達した

角度分解能求め方 測定したcosθ分布をシミュレーションと比較 （シミュレーションは角度分解能ごとに生成） 252Cf neutron nuclear F-nucleus tracks 測定したcosθ分布をシミュレーションと比較 （シミュレーションは角度分解能ごとに生成） 252Cf Simulated distribution of cosθ (400-800keV) Distribution of cosθ(400-800keV) In order to detect the incoming direction of dark matter, our detector can detect forward scattering. We checked this ability by measuring angular resolution. We put neutron source Cf instead of dark matter, and measured scattered angle theta. On the other hand, we simulate same geometry assuming several angular resolution. This is the simulation data. If angular resolution is 0 degree, large asymmetric in cosine theta distribution is expected like black line. If angular resolution is 90 degree, the distribution become flat and we cannot distinguish to isotropic background. Comparing measured data to simulation, we obtained 49 degree angular resolution at 400-800keV energy region. χ2-values for each angle minimum Blue:measured Green:simulation(σ=49°)

角度分解能 エネルギーごとの角度分解能 新たに50-100keVの領域の角度分解能を求めた : 40[deg] angular resolution In order to detect the incoming direction of dark matter, our detector can detect forward scattering. We checked this ability by measuring angular resolution. We put neutron source Cf instead of dark matter, and measured scattered angle theta. On the other hand, we simulate same geometry assuming several angular resolution. This is the simulation data. If angular resolution is 0 degree, large asymmetric in cosine theta distribution is expected like black line. If angular resolution is 90 degree, the distribution become flat and we cannot distinguish to isotropic background. Comparing measured data to simulation, we obtained 49 degree angular resolution at 400-800keV energy region. Blue : This work (0.1atm) Red : Previous (0.2atm)

Expected energy spectrum 検出効率 測定したエネルギースペクトルとシミュレーションを比較 検出効率 : 0.6@50keV エネルギー閾値 : 100 -> 50keV angular resolution current threshold new threshold (plan) σ=1pb, M=100GeV, target:F Expected energy spectrum detection efficiency As stated, we checked forward scattering at 50-100keV region. And then, we measured the detection efficiency by comparing measured spectrum to simulation. We obtained 60% efficiency at 50keV. So, we might say that 50-100keV region is useful region.

まとめ 方向に感度を持つ暗黒物質探索実験NEWAGEにおいて 低圧試験(152torr⇒76torr) ガスゲイン 0.1atmのもと、十分なガスゲインで動作 角度分解能 40°+3.1-2.9@50-100keV 検出効率 0.6@50keV エネルギー閾値 : 100 -> 50keV 今後 GEMを厚くし、ゲインと検出効率の更なる増加を試みる 神岡の検出器に低圧ガスを適用 I'd like to summarize today's talk. NEWAGE is the direction sensitive dark matter search experiment using MPGD. Using low pressure gas, we checked following 3 points. First, u-PIC worked with sufficient gain Second, we measured angular resolution and make sure of forward scattering at 50-100keV energy region. Third, we checked detection efficiency and obtained 60% at 50keV. Thus we find out that 50-100keV region is useful. Finally I’d like to introduce you NEWAGE’s image character “daakumatan”. She will appear at the events related to NEWAGE. Thank you.

Thank you for your attention! まとめ 方向に感度を持つ暗黒物質探索実験NEWAGEにおいて 低圧試験(152torr⇒76torr) ガスゲイン 0.1atmのもと、十分なガスゲインで動作 角度分解能 40°+3.1-2.9@50-100keV 検出効率 0.6@50keV エネルギー閾値 : 100 -> 50keV 今後 GEMを厚くし、ゲインと検出効率の更なる増加を試みる 神岡の検出器に低圧ガスを適用 Thank you for your attention! NEWAGEイメージキャラクター "だあくまたん" I'd like to summarize today's talk. NEWAGE is the direction sensitive dark matter search experiment using MPGD. Using low pressure gas, we checked following 3 points. First, u-PIC worked with sufficient gain Second, we measured angular resolution and make sure of forward scattering at 50-100keV energy region. Third, we checked detection efficiency and obtained 60% at 50keV. Thus we find out that 50-100keV region is useful. Finally I’d like to introduce you NEWAGE’s image character “daakumatan”. She will appear at the events related to NEWAGE. Thank you.

まだだ、まだ終わらんよ