Strange Sea Contribution to the Nucleon Spin

Transcription

1 Strange Sea Contribution to the Nucleon Spin Fatiha Benmokhtar Carnegie ellon University USA with A. l Alaoui Alaoui (LPC renoble France H. Avakian (JlabUSA K. Hafidi (ANL USA F. Benmokhtar RICH workshop 1

2 Strange Sea Contribution to the Nucleon Spin Outline Strange quark contributions to the nucleon properties (in general. Strange quark contribution to the nucleon spin. World data on ΔS Semi Inclusive DIS: - Five flavor tagging - Isosclar ethod DeltaS with CLAS1? F. Benmokhtar RICH workshop

3 Nucleon constituents P uud u u d d s s g... valence «sea virtual pairs» - The sea contains all flavors but the u and d sea can t be distinguished from the valence the heavier quarks (cbt are too heavy to contribute much Strange quark is the natural candidate to study the sea. With how much do virtual pairs contribute to the structure of the nucleon? ass? omentum? Charge & agnetisation and Spin? F. Benmokhtar RICH workshop 3

4 Strange Quark Contribution to the Nucleon Properties (in brief ass: Hyp -> π-n -> 130 ev 0 to 30 % with big theoretical uncertainties Longitudinal omentum: -Study the spectral functions q( -From unpol DI νμ-nucleon scattering (NuTeV 1. For <0.1 Difficult to connect with (s( s( d ~ 4% 0 ordinary observable lectromagnetic Form Factors: Parity violation eperiments: 0 HAPPX PVA4. γ p γ n Z p ( 1 4 θ s sin W Underway F. Benmokhtar RICH workshop 4

5 What about the contribution to the Nucleon Spin? N s 5 γ μ γ s N??? F. Benmokhtar RICH workshop 5

6 Strangeness Contribution to the Nucleon Spin 1 S Σ Σ 4 3 d 1 3 BUT In 1989 C measured Σ 0.10 ± > ~0 % of the nucleon spin!!! Spin Crisis! ± F. Benmokhtar RICH workshop 6

7 Strangeness Contribution to the Nucleon Spin S q -> luon spin Δ -> Sea quark spin Δq -> Orbital Angular omentum L and L q 1 Lattice Calculations predict: Δs 0. F. Benmokhtar RICH workshop 7

8 World Data on ΔS Polarized deep-inelastic inclusive scattering (SC Δu Δd Δs Δs 0.1± ± ν-p elastic scattering (734 BNL Δs 0.15 ± 0.09 Polarized Semi-Inclusive DIS (HRS * 5 flavor tagging published * Isoscalar method-> preliminary Δs ~ So far the results vary widely and the uncertainties are big N s 5 γ μ γ s N??? F. Benmokhtar RICH workshop 8

9 Semi Inclusive DIS σ ( e p e hx Sidis Selection: ν - Q /( ν y ν / W - ν -Q Q 4 sin (θ/ d σ dωd ' α Q 4 ' L μν W μν Hadron Selection: z h / ν F p / W F. Benmokhtar RICH workshop 9

10 Spin Asymmetries ρ ρ σ q ( S S 1/ σ q ( 1 / ~ γ N ρ ρ 3 / ~ Sγ SN 3/ Select q - ( or q ( by changing the orientation of target nucleon spin or helicity of incident lepton beam Spin Independent Structure Function F 1 Spin Dependent Structure Function g 1 1 ( σ σ g ( e ( q ( q ( 1 σ 1/ σ3 / F1 ( e q ( q ( 1/ 3 / 1 f F. Benmokhtar RICH workshop 10 f q

11 easurement of Δq in Semi-Inclusive DIS ~ e q h ( dzdq ( z h q ( dzd ( z q q e q q q P h q ( z - P q h Purity is a conditional probability that a hadron of type h observed in the final state is originated from a struck quark of flavor q in case of unpolarized beam/target. Δq q ( ( ρ A ρ P Q 1 - D q h is a measure of the probability that a quark of flavor q will fragment into a hadron of type h fragmentation function F. Benmokhtar RICH workshop 11

12 ΔS from SIDIS ρ A P ρ Q 1 1- Five flavor decomposition (Δq -Isoscalar etraction of ΔS F. Benmokhtar RICH workshop 1

13 Five flavor decomposition (Δq with SIDIS ρ A 1 A A A A A 1 p π 1 p π 1 p 1 d K 1 d P h q ( e q q h ( dzdq ( z h q ( dzd ( z e q q q Δu / u Δd / d ρ Q Δu / u Δd / d Δs / s Phys.Rev.D71( Δu Δd -HRS: Purities calculated from C simulation of the entire scattering process Δu Q.5 ev RSV 000 LO std BB01 LO Δu 0.601± 0.039± Δu 0.00± ± Δd Δd 0.6 ± ± Δd ± 0.033± Δs 0.08± 0.033± Δs F. Benmokhtar RICH workshop 13

14 Isoscalar etraction of ΔS K us K us Need a longitudinally polarized deuterium target - strange quark in proton and neutron identical - fragmentation simplifies Assumptions: - isospin symmetry between proton and neutron - charge-conjugation invariance in fragmentation traction from data of: - inclusive A 1d (Q and kaon A 1dK (Q double spin asymmetries - kaon multiplicities F. Benmokhtar RICH workshop 14

15 F. Benmokhtar RICH workshop 15 Isoscalar etraction of ΔS: ( ( 5 ( ( ( ( 5 ( 5 ( S Q S P S Q Q P S Q ( ( ( ( ( ( ( ( d d u u Q s s S Δ Δ Δ Δ Δ Δ Δ Δ tract isoscalar combinations of Q( and S( easure inclusive asymmetry A 1d and kaon asymmetries A 1(K K - Inclusive purities from PDFs (CTQ6 RST RV Kaon purities can be computed from the kaon multiplicities and the pdfs: How?

16 Kaon ultiplicities - Using charge symmetry K K K K D ( z D ( z q q easure ultiplicities Fit parameters F. Benmokhtar RICH workshop 16

17 HRS Preliminary results (isoscalar H..Jackson proceedings in PJ 006 F. Benmokhtar RICH workshop 17

18 What can we do with CLAS1? F. Benmokhtar RICH workshop 18

19 11eV Wide detector and physics acceptance (current/target fragmentation High beam polarization 85% High target polarization 85% NH 3 ND 3 targets Track resolutions: δp (ev/c 0.003p 0.001p δθ (mr < 1 δφ (mr < 3 Lumi > cm -1 s -1 F. Benmokhtar RICH workshop 19

20 CLAS1 Kaon Distributions - SIDIS kinematics Q > 1 ev W > 4 ev y < > z > 0.7 X > ev F. Benmokhtar RICH workshop 0

21 CLAS1 kaon SIDIS Simulations K Kaon ultiplicities K- Inclusive Asymmetry Kaon Asymmetry F. Benmokhtar RICH workshop 1

22 CLAS1 points - Overlap with Hermes - What can one do with the data at >0.1? F. Benmokhtar RICH workshop

23 -Does it worth it to go ahead with a proposal? F. Benmokhtar RICH workshop 3

24 Support slides. F. Benmokhtar RICH workshop 4

25 Beam time??? clasdisde.p1.e emn0.75tmn.1.s57.78nb.dis9.dat Data analyzed with 00 runs pol 00 runs pol- & 450 runs unpol > for what? 57.78nb per.dat Number of events: per dat. We have 400.dat polarized file in this simulation. --> total events. Lumi > cm -1 s -1 F. Benmokhtar RICH workshop 5

26 Neutrino-p technique.ν-p elastic scattering (734 BNL.Cross section contains a form factor.. s 1 s 1 (Q > 0 Δs Δs 0.15 ± 0.09 F. Benmokhtar RICH workshop 6

27 Parity Violation and DeltaS Neutral weak probes have sensitivity to Ds Ds contributes to parity violation electron scattering however its sensitivity is suppressed due to the smallness of electron weak charge (at least at forward angles. The contribution of Ds is not suppressed in elastic neutrino-nucleon scattering. It can be determined by fitting the cross section with nucleon form factors inputs. small and negative! Strange aial form factor behaves as Ae at Q->0 F. Benmokhtar RICH workshop 7

28 CLAS1: Kinematical coverage eπx SIDIS kinematics Q >1eV W >4 ev (10 y<0.85 X >ev 0.3 Q ~ ev (CLAS ~5 ev (HRS ~15 ev (COPASS Large Q accessible with CLAS1 are important for separation of HT contributions need to change this. DIS kinematics Q >1 ev W >4 ev y< >z>0.7 X > ev F. Benmokhtar RICH workshop 8

29 Strangeness Contribution to the Nucleon Longitudinal omentum -Study the spectral functions q( ν -From unpolarized deep inelastic νμ-nucleon scattering periments (NuTeV muon from charm quark production: omentum fraction ν μ s c X μ μ ν μ 1 (s ( s ( d 4 %. For <0.1 Difficult to connect with 0 ordinary observable ~ F. Benmokhtar RICH workshop 9

30 Strangeness Contribution to the Nucleon ass ass of the Nucleon: N N H QCD N Quark mass term 0 0 Chiral limit: -> gluon and condensate. N Turn on the quark masses: H QCD m i i N q i q qq σ σ i 0 s heavy quark term σ and σ : scaler FF. f(q s σ m N uu dd N σ s 1 ms N ss N m ( m u m d F. Benmokhtar RICH workshop 30

31 -First constraint: Hyperon mass splitting due the SU(3 flavor symmetry breaking effect. 1 3 (1 m s m (1 yσˆ Λ Ξ y N ss N N uu dd N strange content of the nucleon m s m - canonical ratio: 6 - assume y 0 - Higher order chiral corrections -Second constraint: π N sigma term ˆ 35 ev σ Which is related to the isospin even N scattering amplitude. s invariant mass of the N system t four-momentum transfer Lowest order PQCD low energy theorem states: ( t 0 π trapolation Σ π N Fπ D ( s N t π m Σπ N ˆ( σ t m π σˆ 45 ev F. Benmokhtar RICH workshop 31 π

32 Strangeness Contribution to the Nucleon ass Hyp -> π-n -> σˆ 35 ev ˆ 45eV σ y % Sea quark contribute to a sizable amount to the nucleon mass! However: uncertainty quiet large due to many theoretical or eperimental factors.. Other lattice calculation lead to: σ ~ 53 ev and y perimental input suggests sigma ~90-8 ev. Analysis based on dispersion sum rules: sigma ~ 70-9 ev. tc.. Conclusion ass : 0 to 30 % with big uncertainties 130eV F. Benmokhtar RICH workshop 3

33 F. Benmokhtar RICH workshop 33 Strange lectromagnetic Form Factors Strange lectromagnetic Form Factors q q e J q μ μ γ γ μ N J N Define vector ( form factors: s u d n s d u p γ γ Distribution of nucleon s charge and magnetization. Need one more constraint s d u γ. Charge symmetry n s p s n u p d n d p u ; ; γ

34 F. Benmokhtar RICH workshop 34 Neutralweak Neutralweak Form Factors Form Factors Additional Constraint Additional Constraint s W d W u W p Z sin sin sin θ θ θ Flavor decomposition of proton neutral weak form factor: Z V NC N J N μ ( p Z n p W s sin 4 1 γ γ θ Quark weak charges in the unified electroweak theory in S sin θ W 0.31 ± Z γ Z

35 Parity Violation Asymmetry γ Z Interference: σ ~ NC Re( * NC Scatter polarized electrons off unpolarized target Tiny (~10-6 cross section asymmetry isolates weak interaction γ 10 Z 5 A PV σ σ R R σ σ L L ~ NC PV ~ Q ( Z A PV 4ππ F Q A A σ p A A F. Benmokhtar RICH workshop 35 lectric agnetic Aial