Summary of Workshop on Spin of Nucleons from Low to High Energy Scales

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1 Summary of Workshop on Spin of Nucleons from Low to High Energy Scales Jen-Chieh Peng University of Illinois at Urbana-Champaign EINN2015, Paphos, Cyprus, Nov. 1-7,

2 Three Sessions of the Spin Workshop High Energy Spin Structure Peng, Armstrong, Eyser, Steffens, Contalbrigo, Baltzel, Kubarovsky Low Energy Spin Structure Chen, Collicott, Correa, Sparveris, Pascalutsa, Krebs, Pauk, Kallidonis New Directions and Discussion Reimer, Dashpande, Voutier 2

3 Main topics of this summary Flavor structure of the nucleon sea Flavor asymmetry of the light-quark sea (new data from Fermilab and RHIC. New results from lattice) Gluon polarization and OAM in the nucleon Results from COMPASS, RHIC, and JLab Nucleon polarizability and spin sum rules Data from MAMI and JLab. Comparison with theories 3

4 Flavor Structure of the Nucleon Sea 4

5 There was a time when a simple flavor structure of nucleon sea was assumed u( x) d ( x) s( x) s( x) SU(3) symmetric sea From Frank Close s textbook (1980) Questions Is u ( x) d ( x)? Is s ( x) u ( x)? Is s ( x) s( x)? Actually, the nucleon sea is more subtle 5

6 Is u d in the Proton? Expect d u since sea quarks are produced in g qq = 6

7 Is u d in the Proton? The Gottfried Sum Rule I constructed this sum rule in the hope of destroying the quark model Gottfried, S [( F ( x) F ( x)) / x] dx G 0 p n ( u ( ) ( )) p x d p x 1 ( if u p d p) 3 dx New Muon Collaboration (NMC) obtains S G = ± ( Significantly lower than 1/3! ) d u? Need an independent check! 7

8 Complimentality between DIS and Drell-Yan DIS Drell-Yan Ann.Rev.Nucl. Part. Sci. 49 (1999) 217 Both DIS and Drell-Yan process are tools to probe the quark and antiquark structure in hadrons (factorization, universality) 88

9 d / u flavor asymmetry from Drell-Yan d dx dx 4 9sx x DY a e q ( x ) q ( x ) q ( x ) q ( x ) 2 a a 1 a 2 a 1 a 2 mass spectrum 800 GeV proton beam on hydrogen and deuterium pd pp 1 Dr ell-yan: / 2 (1 d ( x2) / u( x2) ) 2 9

10 Some Theoretical Models for d / u Asymmetry Meson Cloud Models Chiral-Quark Soliton Model Instantons nucleon = chiral soliton expand in 1/Nc Quark degrees of freedom in a pion mean-field Meson cloud has significant contributions to sea-quark distributions The meson cloud has various implications on Asymmetry between s( x) and s( x)? Asymmetry between u ( x) and d( x)? Orbital angular momentum carried by the mesons? 10

11 What happens to d ( x) / u ( x) at large x? SeaQuest Experiment ( Unpolarized Drell-Yan using 120 GeV proton beam) Main goals: 1) Measure d / u flavor asymmet ry up to x ) Measure EMC effect of antiquarks up to x 0.45 Talk of Paul Reimer 11

12 Sign change of d ( x) u( x) at x ~ 0.25? (or d ( x) / u( x) 1 at x ~ 0.25?) Why is it interestin g? Meson cloud model (no models can explain it yet!) Chiral-quark soliton model Statistical model 12

13 Preliminary result from 5% of anticipated data Talk by Paul Reimer 13

14 First lattice calculation of u( x) d ( x) First time the x dependence, rather than the moment of quark distribution is calculated on lattice Using an algorithm proposed by X. Ji (PRL 110 (2013) ) [ d( x) u ( x)] dx consistent with the experiment x H.W. Lin et al,

15 Lattice Calculation of Polarized PDFs Talk by Fernanda Steffens q( x) q( x) d ( x) u( x) u( x) d( x) Steffens confirms the result d ( x) u( x) The calculation also predicts d ( x) u ( x) x 15

16 u ( x) and d ( x) from W production at RHIC-spin Oleg Eyser and Bernd Surrow x u ( x) x d ( x) u d consistent with some models and lattice 16

17 Gluon polarization and orbital angular momentum in the nucleon 17

18 Where does the spin of the proton come from? EMC experiment in 1988/1989 q q "Spin Crisis" q 18

19 World-wide effort to measure g 1p, g 1 d Spin-dependent DIS CERN: EMC, SMC, COMPASS SLAC: E80, E142, E143, E154, E155 DESY: HERMES JLab: Hall A, B, and C world data on g 1 p (hep-ex/ ) 19

20 NLO fit to world DIS g 1p, g 1 d data (arxiv: ) x g( x) Q 3 GeV 2 2 integrals: G 0.5 x u V ( x) x d V ( x) x S( x) 0.82 U D S

21 NLO fit to world DIS g 1p, g 1 d data (arxiv: ) Q 3 GeV 2 2 integrals: G U D S 0.08 ~1/3 of the proton's spin is carried by quark/antiquark's spin 21

22 Lattice result on ΔΣ q for hyperons and charmed baryons Talk by C. Kallidonis 22

23 NLO fit to world DIS g 1p, g 1 d data (arxiv: ) Q 3 GeV 2 2 integrals: G U D S 0.08 ~1/3 of the proton's spin is carried by quark/antiquark 's spin G is only loosely contrained by polarized DIS 23

24 Di-hadron production in polarized DIS PLB 718 (2013) 922 Photon-gluon fusion Di-hadron production data suggest positive Δg/g 24

25 Δg from RHIC-spin 0 A jet from PHENIX from STAR LL A LL Talk by Oleg Eyser PRD 90 (2014) PRL 115 (2015) Sensitive to Δg due to the q + g q + g underlying process 25

26 Δg from RHIC Talk by Oleg Eyser with published RHIC data until

27 Δg from EIC Talk by A. Deshpande 27

28 Extraction of orbital angular momentum via Generalized Parton Distribution (GPD) 28

29 M. Contalbrigo 29

30 Nathan Baltzell 30

31 Transversity GPD from Deeply Pseudoscalar Meson Production at JLab Talk by V. Kubarovsky Flavor separation is possible from π 0 and η production data 31

32 DVCS kinematic coverage 32

33 Nucleon polarizability and spin sum rules 33

34 34

35 35

36 Talk by Cristina Collicott 36

37 Cristina Collicott 37

38 Cristina Collicott 38

39 New measurement of generalized polarizabilities Loup Correa 2 2 E( Q ) and M( Q ) 39

40 Other ongoing and proposed measurements for generalized polarizabilities Nikos Sparveris 40

41 Moments of spin structure functions Jian-Ping Chen 41

42 Jian-Ping Chen The LT puzzle neutron New data on proton target are being analyzed 42

43 V. Pascalutsa 43

44 V. Pascalutsa 44

45 Hermann Krebs 45

46 Whitney Armstrong 46

47 Extraction of Whitney Armstrong d 2 for protn and neutron 47

48 Lepton universality test in lepton-pair production Vladimir Pauk p e e p versus p p 48

49 Lepton universality test in lepton-pair production Vladimir Pauk p e e p versus p p Relevant to the proton radius puzzle 49

50 Talk by E. Voutier

51 Eric Voutier 51

52 End of the Workshop Summary Thanks to all speakers and organizers! 52

Nucleon Spin Structure: Overview

Nucleon Spin Structure: Overview Jen-Chieh Peng University of Illinois at Urbana-Champaign Workshop on Spin Structure of Nucleons and Nuclei from Low to High Energy Scales EINN2015, Paphos, Cyprus, Nov.