Transcript 齊藤 直人，京大
ニュートリノ核子弾性散乱実験 齊藤 直人 （京都大学） NeuSpin Working Group • 東工大 – 柴田さん、宮地さん、武居くん、坂下くん • 阪大ＲＣＮＰ – 酒見さん • 京大 – 齊藤、今井さん • 理研 – 後藤さん • ＫＥＫ – 澤田さん • ＮＭＳＵ – S. Pate • その他にも興味を示してくれている方多数 Physics Goal • ストレンジネスの偏極Dsの直接測定 – ＤＩＳとバリオン８重項のβ崩壊定数から予測されるDs<0 は本当か？ • ニュートリノ核子の反応断面積の精密測定 • ニュートリノ原子核反応におけるコヒーレントパイオ ン生成断面積の測定 – K2K ＣＣの結果を更にimproveできるか？ – ＮＣ？ From g1(x,Q2) to DS • Integrate over x (0,1)！ 1 44 11 11 p Proton 1 11 1 1 1 4 Proton p n D U D D D S 0.119 n pe 1 1 2 9 DU 9 DD 9 DS 0.119 1 DU DD DS e 0.053 2 9 9 9 29 9 9 11 4 1 1n DUp DD DS 0.053 n 29 9 9 pe e Deuteron = Proton Neutron Deuteron 1 Octet Baryon b-Decay 1= Proton + +Neutron Utilize Constants！ p • n DU DD 1.2692 0.0112 DU DD 2DS 0.1952 0.0083 ( g A / gV ) np DU DD F D 1.2695 0.0029 – SU(2) OK！ 3 e e 3 ( g A / gV（Bjorken ) p (2DSR） U DD DS ) / 3 F DHe=Neutron /He=Neutron 3 0.718 0.015 ((D g AU/ ,gDV D ) , DS()DU DD 2DS ) / 3 F D / 3 0.25 0.05 S ne e ( 0 . 802 , 0 . 465 , 0 . 124 ) ( g A / gV ) Sn DD DS F D | 0.340 0.017 | DS 0.213 0.138 Constant in front of D/3 DS from SDIS and Global Analysis • Global Analyses suffer from a lack of DS data: SU(3) symmetric sea assumed • In SDIS, with Final State Hadron Detection, DS can be extracted ストレンジクォークは本当に偏極して るのか？ • Flavor Singlet ⇒Axial Anomaly – If Dg ~ 0.3 axial anomaly contribution alone ~ 0.15/2p ~ - 0.025 – So far DS = - 0.14 ± 0.05 (DIS + Baryon b) • Violation of Eliis-Jaffe Sum Rule ⇒DS≠０ • Independent DS measurement would be sufficient to obtain DS (together with Baryon b-decay) Why Should the Nucleon be Strange? • The vacuum is strange: chiral symmetry for π, K mesons → 0 |s s | 0 (0.8 0.1) 0 | qq | 0 • Cannot be expected to disappear when one inserts • • qqq ‘test charge’ into vacuum Expected to be generated in perturbative QCD: s sbar gluon quark Also, generated by non-perturbative effects: instantons, chiral soliton models How Strange is the Nucleon? • Momentum fraction at Q2=20 GeV2: Not very? Ps= 4% (CCFR) • Electric and magnetic form factors at Q2=0.48 (GeV)2 (HAPPEX) GsE + 0.39 GsM= 0.025 0.020 0.014 at Q2=0.23 (GeV)2 (A4) GsE + 0.225 GsM= 0.039 0.034 • Contribution to the nucleon magnetic moment -0.1 5.1% (SAMPLE) Pion-Nucleon σ Term • Related to strange scalar density y 2 p | ss | p p | uu | p p | dd | p • Two recent determinations: • Maybe y ~ ½ ? Important later for chiral soliton models of exotic baryons Trial Fit! • p0 LL A 22 c model 0 Utilized NLO p (0.73±0.39)x 10.8 calculation (thanks (-1.03±0.43)x 11.3 to Vogelsang and (5.74±3.10)x 2 10.8 Stratmann) (-9.64±2.99)x 2 10.5 – to find “relevant-x” for each pT bin 2 Dg Dg ALL b g g • Trial Fit to – A*x (GRSV ~ 1*x) – A*x*x Lepton Scatt. ndfprob.c22 ndfprob. 7 0.15 6.2 5 0.29 7 0.13 14.6 5 0.01 7 0.15 5.3 5 0.38 7 0.16 18.3 5 0.00 Dg 0.30 -0.42 0.35 -0.60 pT (GeV/c) Is this Dg Large or Small? • Expectation (Phenomenological) – Dg ~ 2 to save DS thru axial anomaly (if DS=0.58 ⇔Ds=0⇔EJ SR) – Dg ~ 0.3-0.4 to save “proton spin” • Model predictions – Dg ~ 2±1 (…) – Dg ~ -0.4 (Bag model) – No lattice prediction • Gauge Invariance – See Jaffe’s talk – (http://wwwctp.mit.edu/gluonspinbasics080203.pdf) • Scale Dependence of Dg – Product S Dg ~ constant – Dg(1 GeV)=0.3 ⇒Dg (MZ)=1.5 – “Fine tuning” by Lg ~ N f S DS DS Dg 2p 1 1 DS Dg LZ 2 2 Extend x Range • ALL(p0) from Run 6/7 (65 pb-1) will extend x range to larger x • STAR jet measurement also provides precision data • 500 GeV run will cover smaller xrange Direct photon in Run-2006/7 P1 k2 P2 k1 RHIC Spin and HERMES SIDIS • Complementary! – RHIC W • No fragmentation ambiguity • x-range limited • Useless for transversity studies • Otherwise WR! – HERMES SemiInclusive DIS • Wide x-range • Could be used for transversity studies Ds 測定がもたらす物理的インパクト • 核子のスピンフレーバー構造に対する理解が深 まる – Flavor SU(3) 仮定を超えて • 中性子のEDM J.Ellis and R.A.Flores PLB377(96)83 – n-EDM の予言は、 d n q-EDM and Dqに基づく (Dud Ddd Dsd ) mu Du md Dd ms Ds E E u E d • ダークマター探索 J.Ellis and M. Karliner Lecture at Erice School 95 hep-ph/9601280 – ダークマターと核子の相互作用 4 1 ( cp cp) Du (Dd Ds) (photino) or 9 9 17 5 Du (Dd Ds ) (pure U (1) gaugino) 36 36 E s 荷電カレントコヒーレントパイオン生成 • K2K results on CC coherent pion production – Phys. Rev. Lett. 95 252301 (2005) N 弾性散乱 • N 弾性散乱断面積 d GF2 Q 2 2 A BW CW dQ 2 2p E2 for ; for k W 4( E / M p ); Q 2 / 4M p2 – Where (Q2 dropped for brevity) k’ q P P’ 1 2 A G1 (1 ) F12 F22 (1 ) 4F1F2 4 s 2 1 0 . 631 G ( Q ) 2 1 B G1 F1 F2 G1 (Q ) 2 2 2 4 (1 Q / M A ) 2 2 M 1 p 2 2 2 s C G F F 1 1 2 2 G1 (0) Ds 16 Q BNL E734 (PRD 35 (87) 785) • Measurement of p and p elastic scattering •170 metric-ton segmented detector @ E~1.2 GeV ( m p m p) R 0.153 0.007 0.017 ( m n m p) •951 mp events •776 mp events R ( m p m p) 0.218 0.012 0.023 ( m p m n) ( m p m p) R 0.302 0.019 0.037 ( m n m p) 2.5+0.55 1019 pot Extraction of Strange FF • Fit cross section with dipole approximation BNL-Experiment 734 (L.A.Ahrens et.al PRD35(87)785; Reanalysis G.T. Garvey et. al PRC48(93)761) • Measured elastic scattering cross section p p and p p – Liquid scintillator + Drift 2 Cut-off Too High Q Tube 170 t Go to lower Q2 – 0.5E19 POT for neutrino and 2.5E19POT for antineutrino 79% from Carbon – Q2>0.40 GeV2 Extract Pure Proton N-Elastic Scattering Exp at J-PARC • On-axis at near detector hall for T2K Experiment • Utilize both two types of LiqScintillator with different H/C mixture for pure proton signal – e.g Bicron BC510A (H/C=1.212) and BC-533 (H/C=1.96) – Pure Carbon can be extracted for A Xsection – e.g. 5x5x5m3 ~ 125 t • 1E21 POT possible in one year (130 days) – 30 times BNL-E734 – Better with polarity change for v and Sensitivity for Ds • Assumptions – Similar Detection Efficiency to E734: • 7.6% for neutrino-N elastic • 5.4% for anti-neutrino-N elastic – However with lower Q2 cut-off : 0.1 GeV2 • Achievable with more uniform detector ? – 25 times more statistics but pure proton only 1/6 • Factor 2 reduction in statistical error – Systematic control improvements to ~5% • E734 7.6% dominated by Beam Flux and Nuclear Effects • Possible to remove Nuclear Effects which could be larger in lower Q2 region Comparison with E734 • If Ds is the only parameter to – E734: Ds 0.10 0.08 – J-PARC: Ds 0.10 0.03 • But… Ds and MA coupled = -Ds/gA(=1.256) be determined determination of Ds with – E734: Ds 0.10 0.27 Significantly improved Sytematics significantly Better – J-PARC: Ds 0.10 0.12 – N.B. other analysis of E734 Separation with provided better precision: MA might be Problematic G0 Physics Asymmetry • “no vector strange” asymmetry ⇒ ANVS – em form factors: Kelly PRC 70 (2004) 068202 • inside error bars: stat, outside: stat. & pt-pt syst. GEs and GMs extracted • Significant non-zero contributions Asymmetry measured… • Axial Form Factor contribution is suppressed by (1-4sZ2)=0.076 p n p n GF Q 2 G G G G 2 p n E E M M ALR (e p) (1 4 sin W )(1 RV ) (1 RV ) p 2 p 2 ( G ) ( G 4p 2 E M) p GF Q 2 G s E (1 RV( 0) ) G E p 2 p 2 ( G ) ( G ) 4p 2 E M GF Q 2 GMp (0) s (1 RV ) G (GEp ) 2 (GMp ) 2 M 4p 2 2 p ( 1 4 sin ) ' G GF Q 2 (0) W M ~p (1 RV ) GA p 2 p 2 (GE ) (GM ) 4p 2 ~p T 1 ( 3) T 0 (8) ( 0) s GA -1.65 A GA -0.44 A GA +0.45 A GA 陽子からの散乱と原子核からの散乱 • 原子核からが４～５倍 • Ｑ２分布の違い（モデル） Hi Intensity Proton Accelerators Completion of J-PARC • Power will evolve to ~1 MW in 5 years Summary • ストレンジクォークの核子中での役割は大き いと思われる • 偏極DSの測定は、素粒子・宇宙・原子核に渡 るインパクトがある • ニュートリノ散乱で得られる情報は大きい • 一緒に実験・解析について考えましょう！ – http://www.nucl.phys.titech.ac.jp/~neuspin/ http://www.nucl.phys.titech.ac.jp/~neuspin/ LSND (1993-98) Nearly 49,000 Coulombs of protons on target Baseline 30 m Neutrino Energy 20-55 MeV, 1280 phototubes 167 tons Liquid scintillator MiniBooNE (Started last year) MiniBooNE Signals (1021pot) Approximate number of electron neutrino-like events expected in MiniBooNE with two years of running before cuts Intrinsic e background: 1,000 events m mis-ID background: 500 events p0 mis-ID background: 500 events LSND-based me: 1,000 events Direct Measure of Ds(?) • Nucleon Neutral Weak Current J m N GA m 5 F1 m F2 m q N • g A 3 s 2 GA (q ) G ( q ) A 2 2 2 (1 q / M A ) Axial Form Factor: 2 • gA, F1,2pn known, F1,2s measured (PV e) s 2 G ( q • Strange Axial Form Factor: A 0) Ds (p p) yields Ds Elastic Scattering p p • Assuming no second-class current… Conclusion from E734 • No decisive determination of Ds due to … – Q2 extrapolation down to 0 – Possible contamination from nuclear effects • 79% from Carbon • 1.5 mm resolution should be improved • Pure Hydrogen desirable … at least BG subtraction preferred E734 Target and Detector • Calorimeter – Liquid Scintillator (80% of mass) – 79% protons are bound in Carbon 21% are free • Proportional Drift Tubes – 1.5 mm position resolution Beam Flux • Measured using CC Processes – Anti-nu contamination in nu beam 0.024+\-0.005 – Nu contamination in anti-nu beam 0.087+\0.013 m m • Time Structured Beam (every 224 nsec) for BG reduction 0.55e19 POT 5.5E5 nu events 2.5E19 POT 2.5E6 anti-nu events Event Topology Cuts& PID • Fully contained single track (= proton candidates) • Three PDT hits required – Q2 cut > 0.035 GeV2 • Likelihood Functions basing of energy deposit – P: Probability Density Fn A typical event PID Cuts • L (SCIN) and L (PDT)