Science & Technology Peer Review. Nucleon Spin Structure

Transcription

1 Sciece & Techology Peer Review Nucleo Spi Structure Kees de Jager S&T Review, july 15-17, 22,

2 Sciece & Techology Peer Review Nucleo Spi Structure Itroductio Q 2 -evolutio of GDH itegral Nucleo Spi Structure at large x Quark-Hadro (Spi) Duality R=σ L /σ T i Resoace Regio Real Compto Scatterig up to Large t-values Summary July 15-17, 22 Kees de Jager S&T Review, july 15-17, 22, 1

3 Spi Structure i Deep Ielastic Scatterig S z N = 1 2 = J q + J g = 1 2 Σ + L q + G + L g Study of ucleo spi structure started with EMC (~ 88): Σ = d+ u+ s=.12 ±.17 World-wide effort (SLAC, DESY, CERN) established that Σ ~.2.4 Focus shifted to other cotributios to <S z >: strage sea polarizatio semi-iclusive DSA gluo polarizatio ope charm, high p T hadro pairs orbital agular mometum Geeralized Parto Distributios S&T Review, july 15-17, 22, 2

4 Spi Structure i Deep Ielastic Scatterig * γ * γ σ partos partos - ~ q ~ + 1 / 2 (x) Nucleo σ q 3 / 2 (x) Nucleo Partoic Iterpretatio x = fractio of ucleo mometum carried by struck quark q +/- quark helicity parallel/atiparallel to photo helicity NO simple partoic picture of g 2 x = Q2 2Mν q(x) = q + (x) + q (x) F 1 (x) = 1 2 e 2 f q f (x) F 2 (x) = xf 1 (x) flavor q(x) = q + (x) q (x) A 1 (x) = g 1 (x) F 1 (x) g 1 (x) = 1 2 e 2 f q f (x) g 2 (x) = flavor S&T Review, july 15-17, 22, 3

5 Nucleo Spi Structure Fairly extesive data set o g 1 (x), but oly for x <.3 Low-x regio domiated by sea quarks, predictios difficult High-x regio (a sigle quark carries most of the ucleo mometum) domiated by valece quarks, predictios feasible Accurate data will allow selectio of models JLab uique combiatio of eergy ad lumiosity p g 1 g 1.8 SMC.7 EMC E143 HERMES.6 E SMC(2D).8 E142(3He) E143(2D).6 E154(3He) HERMES(3He) E155(2D).4 E99117(3He)(Prel.).2 x x S&T Review, july 15-17, 22, 4

6 Bjørke Sum Rule Γ 1 p (Q 2 ) Γ 1 (Q 2 ) = {g p 1 (x,q 2 ) g 1 (x,q 2 )}dx = 1 6 g C A NS g A =1.261 ±.25 eutro β-decay couplig costat C NS Q 2 -depedet QCD correctio Basic assumptios Isospi symmetry Curret Algebra or Operator Product Expasio withi QCD Preset status (at Q 2 = 5 (GeV/c) 2 ) Experimet.176 ±.3 ±.7 Theory.182 ±.5 Combied world data are cosistet with the Bjørke Sum Rule at 5 % level S&T Review, july 15-17, 22, 5

7 Gerasimov-Drell-Hear Sum Rule GDH Sum Rule ( σ 12 (ν ) σ 32 (ν)) dν 2 ν = 2π α EM κ 2 M 2 ν i The Gerasimov-Drell-Hear Sum Rule (at Q 2 = ) is a fudametal test of the relatio betwee the ucleo resoace excitatio ad its aomalous magetic momet Rests o basic physics priciples (Loretz ivariace, gauge ivariace, uitarity) ad o dispersio relatio applied to forward Compto amplitude Techical developmets have oly recetly allowed first measuremet of GDH itegral for the proto up to 8 MeV(Maiz) ad up to 3 GeV(Bo) Results agree with sum rule with assumptios for cotributios at higher eergies May facilities (GRAAL, SPrig-8, LEGS, HIGS, JLab) geared for extesive studies Will iclude data for the eutro from polarized deuterium S&T Review, july 15-17, 22, 6

8 Trasitio from Strog to Perturbative QCD Dispersio relatios o Compto Scatterig Amplitudes lead to extesio of GDH sum rule valid at all Q 2 (Ji ad Osbore) Q 2 -evolutio of Gerasimov-Drell-Hear Sum Rule provides quatitative measure of trasitio from resoace (strog QCD) to DIS (pqcd) regimes Trasitio from Bjørke sum rule dow to ~ 1 GeV 2 ca be predicted usig Operator Product Expasio of higher twist cotributios Trasitio from GDH sum rule up to ~.1 GeV 2 ca be predicted usig Chiral Perturbatio Theory For itermediate regio oe awaits Lattice QCD calculatios S&T Review, july 15-17, 22, 7

9 Why is I GDH (Q 2 ) iterestig? Oe of the few opportuities to "zoom out" from tiy legth scales (DIS) to large legth scales I GDH (Q 2 ) - 2π2 α 16π 2 α M 2 κ2 Γ Q 2 1 2π 2 αs 1 (;Q 2 ) Chiral pert. theory Higher twist correctios u d No-perturbative, cofiemet PQCD d u u GDH OPE, Bjorke, Ellis-Jaffe May of the uderlyig assumptios are the same as those beig tested i high-eergy spi-structure tests S&T Review, july 15-17, 22, 8

10 Polarized 3 He Target (Hall A) Polarized 3 He is best approximatio of polarized eutro P =87 % ad P p =2.7 % Requires correctios for uclear medium, ivestigated by may theorists Basic priciple: Optical pumpig of Rb, followed by polarizatio trasfer to 3 He through spi-exchage collisios Target polarizatio measured by EPR/NMR Polarizatio (%) e - beam 15 µ A Jue m 1 W Cell Pickup Coils NMR RF Drive Coils EPR Polarizatio, from July 3 to Sept.1, 21 Gore Diode Ove Laser Rb - 3 He mixture Helmholtz Coils e- beam glass cells 25 (4) cm log 1 atm 1 µm ed widows masig effect Target Tests July 3 Tilghma Prelimiary July 13 July 3 Shapiro Prelimiary Time (day) Va Oe Sept.2 S&T Review, july 15-17, 22, 9

11 Q 2 -Evolutio of the Gerasimov-Drell-Hear Itegral ( ) dν I GDH = σ 12 (ν,q 2 ) σ 32 (ν,q 2 ) ν = 2 σ TT ν i ν i dν 2 ν = 8π α MK ν i g 1 Q2 g dν ν 2 2 ν Logitudial ad trasverse target polarizatio allows separatio of g 1 ad g 2 Kiematic coverage sufficiet to itegrate to W 2 GeV Nuclear medium correctios from Ciofi degli Atti ad Scopetta Compared to calculatios by Drechsel et al. which eglect cotributios from DIS ad by Ji ad Berard based o Chiral Perturbatio Theory (bad shows ucertaity i cotributio from - resoace) GDH Itegral [µb] Hermes (DIS) GDH Sum Rule Resoace Resoace+DIS Hall A E Q 2 [GeV 2 ] S&T Review, july 15-17, 22, 1 1

12 Q 2 -Evolutio of the Gerasimov-Drell-Hear Itegral (cot.) 1 ( ) Γ 1 p / = g 1 p / (x Bj,Q 2 )dx Bj A // +αa 1 F 1 (x Bj,Q 2 )dx Bj Hall B E Γ p H(e,e )X Simula (Γ 1 = at Q 2 =.16±.4).5 Γ 1 JLab E941 3 He JLab E941 Neutro (Resoace) JLab E941 Neutro (Complete) SLAC E143 (Resoace) SLAC E143 (DIS) SLAC E142 HERMES Γ d per N.5 CLAS (W<2) CLAS + DIS SLAC pqcd (Larki) Burkert/Ioffe Soffer GDH Slope 2 H(e,e )X.5 Ji Meisser GDH Sum Rule Evolutio of SLAC DIS results Burkert & Ioffe Soffer Q 2 [(GeV/c) 2 ] Q 2 (GeV/c) 2 S&T Review, july 15-17, 22, 11

13 The eutro A 1 spi structure fuctio Naïve SU(6) predictios: A 1p = 5/9, A 1 = Broke SU(6): A 1 -> 1 as x -> 1 CQM: hyperfie perturbed with simple model for d/u LSS: NLO polarized parto desities Soffer: global NLO aalysis of (u)polarized DIS Duality: local QHD usig available G E, G M data 1 A E142( 3 He) E143( 2 H) E154( 3 He) E155( 2 H(g 1 /F 1 )) HERMES( 3 He) E99-117( 3 He) prelimiary Hall A E CQM (Isgur) E155 fit Soffer (Q 2 = 5) LSS (g 1 /F 1 ) Duality LSS (BSS) x S&T Review, july 15-17, 22, 12

14 Quark-Gluo Correlatios g 2 (x,q 2 ) = g 2 WW (x,q 2 ) + g 2 (x,q 2 ) g 2 WW (x,q 2 ) = g 1 (x,q 2 ) + g 1 (y,q 2 ) 1 x dy y I simple partoic picture g 2 (x)= Wadzura ad Wilczek have show that g 2 ca be writte i two parts: oe give by g 1 i twist-2 cotributios the other origiatig solely from quark-gluo correlatios (twist-3) Twist 2 Twist 3 1 d 2 (Q 2 ) = x 2 [ 2g 1 (x,q 2 ) + 3g 2 (x,q 2 )]dx d 2 = ( 2χ B + χ E )/3 S&T Review, july 15-17, 22, 13

15 The eutro g 2 structure fuctio.25 E97-13 g 2 (x,q ) 2 First measuremets of g 2 i Hall A order of magitude improvemet i accuracy over SLAC E155X Prelimiary data idicate sigificat excess over simple predictio First quatitative iformatio(?) of twist-3 effects Hall A E97-13 ) 2 (x,q g 2 ) 2 (x,q g Q = 3.7 M. Stratma, ZPC 6, 763 (1993) X. Sog, Phys. Rev. D 54, 1955 (1996) 2 g 2 (x,q ) from SLAC E155X data from fit to SLAC E155 A 1 data x Prelimiary g WW 2 Oly Statistical Errors are show for E97-13 data Prelimiary 2 ) E97-13 g 2 (x,q GS-A (NLO) Blumlei-Bottcher NLO Sceario 1 Blumlei-Bottcher NLO Sceario 2 WW g from fit to E155 A 1 Oly statistical errors are show data Q (GeV) S&T Review, july 15-17, 22, 14

16 Quark-Hadro Duality Quark-Hadro Duality implies that properly averaged hadroic observables ca be described by perturbative QCD i a certai kiematic regime QHD must hold i the scalig regio QHD must break dow at very low Q 2 Extesive data set from Hall C shows that QHD works well dow to Q 2 ~.5 GeV 2 Oce QHD has bee verified, it provides a relatio betwee the resoace regio ad the DIS regio p F Q 2 = 9 (GeV/c) 2 Q 2 = 7 (GeV/c) 2 Q 2 = 3.3 (GeV/c) 2 Q 2 = 3 (GeV/c) 2 Q 2 = 2.4 (GeV/c) 2 Q 2 = 1.7 (GeV/c) 2 Q 2 = 1.4 (GeV/c) 2 Q 2 =.85 (GeV/c) 2 Q 2 =.45 (GeV/c) 2 Q 2 =.2 (GeV/c) 2.6 < Q 2 <.9 (GeV/c) x S&T Review, july 15-17, 22, 15

17 R=σ L /σ T i Resoace Regio First measuremets of R (yieldig the logitudial structure fuctio F L ) i the resoace regio Surprisigly strog resoace structure evidet i F L Allows test of QHD i F L Momets of F L ca be directly compared to Lattice Gauge Theory calculatios Hall C E94-11 S&T Review, july 15-17, 22, 16

18 Spi Duality First prelimiary results of measuremets of g 1p i the resoace regio.4 F 2 = ν 2 W p g 1 Q 2 =1.2 Spi duality appears to set i at Q 2 > 1.5 GeV 2 Opes possibility to exted measuremets of spi structure fuctios to smaller values of W (larger values of x, show is the Nachtma variable ξ, which is x with a target mass correctio) Q 2 =1.4 Q 2 =1.7 Q 2 =2.1 Hall B E ζ.5 S&T Review, july 15-17, 22, 17

19 MAD Spectrometer i Hall A Large agular (3 msr) ad mometum (3%) acceptace Max. mometum 7 GeV/c Moderate resolutio S&T Review, july 15-17, 22, 18

20 Expected results with 12 GeV upgrade A CEBAF 11 GeV, W > 2 GeV CEBAF 11 GeV, W > 1.5 GeV CEBAF TJNAF 11 GeV, at 11GeV, W > A GeV SLAC E142 ( 3 He) SLAC E143 ( 2 H) SLAC E154 ( 3 He) HERMES ( 3 He) SMC ( 2 H) 2 < Q W 2 < 2 1 GeV (GeV/c ) 2 BBS (LSS) BBS Isgur LSS- MRST.1 x 2 g JLab 12 GeV projected errors SLAC E155x data ww g 2 Q 2 =3 GeV x d Bag Models Chiral Solito Lattice QCD SLAC Data JLab 11 GeV x Bjorke -.4 QCD Sum Rules S&T Review, july 15-17, 22, 19

21 Real Compto Scatterig Wide-Agle Compto Scatterig (WACS) provides iformatio o the partoic structure of the ucleo through the momets of the Geeralized Parto Distributios First, the domiat mechaism of Real Compto Scatterig at large values of s ad t (~1 GeV 2 ) has to be established: pqcd mometum shared by hard gluo exchage 3 active quarks valece cofiguratio domiates scalig: dσ/dt = f(θ CM )/s 6 Hadbag diagram hard scatterig from sigle quark mometum shared by soft overlap 1-body form factor soft gluo exchage eglected S&T Review, july 15-17, 22, 2

22 Real Compto Scatterig (cot.) 1 Proto Spectrometer/FPP 6% Cu Radiator 15 cm LH2 e - Beam Deflectio Maget Veto Leadglass Calorimeter i plae evets 3 Sweep maget essetial for electro/photo separatio electros 1 Hall A E φ θ 1 1 photos π o θ S&T Review, july 15-17, 22, 21

23 Real Compto Scatterig (cot.) O-lie aalysis of ~6 % of data Demostrates feasibility of WACS at high lumiosity (three orders higher tha at Corell) Proves domiace of softoverlap mechaism (hadbag) K LL Prelimiary CZ COZ hadbag AS, KS, COZ, CZ: -.2 KS variety of pqcd calculatios AS proto agle i CM system S&T Review, july 15-17, 22, 22

24 Summary Study of Nucleo Spi Structure provides fasciatig isight ito the partoic structure of the ucleo Recet results from Jefferso Lab have cotributed sigificatly to this field i a wide variety of aspects Sesitive measuremets of the Q 2 -evolutio of the GDH itegral First accurate measuremets of A 1 at large x ad of g 2 First L/T separatio i the resoace regio First high-lumiosity measuremet of Wide Agle Compto Scatterig These studies will cotiue ad be expaded strogly with the 12 GeV upgrade S&T Review, july 15-17, 22, 23

25 Proto S&T Review, july 15-17, 22, 24