Heavy Quarks and Nucleon Spin Structure

Ernst Sichtermann (LBNL)

With thanks to: Feng Yuan, Xin Dong Wei Zhou Qinghua Xu Ming Liu and many others...

parton momentum fraction

Nucleon Structure

Heavy Quarks - Nucleon Structure

Major limitation for spin structure: proton beam at HERA not polarized, however, HERMES had a polarized internal target.

In probing the polarized proton,

Γ1 =

∫ 1

0

g1(x)dx =

∫ 1

0

(

1

2

∑

e2

q∆q(x)

)

dx =1

2

(

4

9∆1u +

1

9∆1d +

1

9∆1s

)

=1

12(!1u − !1d) +

1

36(!1u + !1d − 2!1s) +

1

9(!1u + !1d + !1s)

Known from weak neutron to proton decay

Known from weak neutron to proton decay,combined with weak ∑ to neutron decay

Unique to DIS

This becomes a prediction if , i.e. if strange quark spins do not contribute.

∆1s = 0

Spin - Weak Decay

Proton Spin Structure - circa 1985

Polarized DIS - European Muon Collaboration:

Quark spins carry only a small fraction of the proton spin,

Strange sea is negatively polarized.

SMC, E142, E143, E155, and Hermeshave since confirmed the EMC data.

∆Σ ! 0.2,∆s < 0

µ µ’

γN

X

have tested the Bjorken Sum to ~7% precision.

Some Open Questions

• Is the extrapolation over unmeasured small x justified?

• What does gluon polarization contribute to the proton spin?

• What are the quark and anti-quark polarizations by flavor?

• What orbital angular momenta do quarks and gluons carry?

• What is the role of transverse spins?

Asymptotically : Ji

Asymptotic Conjectures*,

* in leading order, if the intrinsic contributions do not overwhelm radiatively generated contributions, ... i.e. perhaps.

X. Ji

HERMES at DESY:27 GeV electron beam,fixed target,PID

COMPASS at CERN:160 GeV muon beam,fixed target,open spectrometer

STAR at RHIC:200-500 GeV Ecms,large acceptance

PHENIX at RHIC:high resolution,high rate

Active Spin Experiments

-0.1 0.1 0.3 0.5

0.171±0.074

0.254±0.101

0.165±0.048

0.204

0.150±0.061

-1 0 1

ΔΣ

Ave.

AAC06

GRSV01

LSS05

BB02

0.289±0.754

0.473±1.083

0.179±0.267

0.420

0.931±0.679

Δg

-0.1

0

0.1

0.2

0.3

0.001 0.01 0.1 1

AAC06GRSVBBLSS

-0.6-0.4-0.2

00.20.40.60.8

11.21.4

0.001 0.01 0.1 1x

xΔg(x)

Q2 = 1 GeV2

xΔΣ(x)

Polarized DIS - Scale Dependence

Polarized DIS - Heavy Quarks

Measurements of:

- open charm (clean, but rare), and

- high-pT hadron pairs (high and low Q2)

parto

n

parti

cle

etcpe

,,,π

γν ,,

gq,

dete

ctor

Polarized Proton Collisions at RHIC

PRL 97, 252001 (2006)

(∆)σ ∝ (∆)f ⊗ (∆)g ⊗ (∆)σ

!G

!G

!G

!q

!p + !p → jet(s) or "0(s) + X

Jager, Stratmann, Vogelsang - hep-ph/0404057

!q!G

!G!G

ALL !

Polarized Proton Collisions at RHIC

STAR - B. Abelev et al, hep-ex /0608030 PRL 97:252001 (2006)

Consistent with DIS and disfavors largevalues for !G

ALL =(σ++ + σ−−) ! (σ+− + σ−+)(σ++ + σ−−) + (σ+− + σ−+)

GRSV - Gluck et al, PR D63 094005 (2001).

(Scale uncertainty from polarization not included)

+

Statistics limited measurement; systematics ~0.015

Improved statistics 2005 (2006)

First Longitudinal Double-Spin Asymmetries from STAR

Similar PHENIX results on inclusive neutral pion production

!p + !p → cc, bb + X

!G

!G

L ! 3 " 8 · 102 pb!1, P = 0.4 " 0.7,#

s = 200 " 500 GeV

ALL =(σ++ + σ−−) ! (σ+− + σ−+)(σ++ + σ−−) + (σ+− + σ−+)

!p + !p ! γ + jet

!q

!G

!p + !p ! jet(s) + X

!G

!G

!G

!q

time

+

Clear need for data that are kinematically complete and process selective,

Clear need for data that are kinematically complete and process selective,

Future Polarized Proton Collisions at RHIC

Heavy Quark and Prompt Photon Production are complementary.

Heavy Quark Total Cross Section

Total cross section, e.g.P. Nason et al., NPB 303 (1988) 607

Quarkonium, e.g.G. Bodwin et al., PR D51 (1995) 1125; erratum ibid D55 (1997) 5883

Friday morning session at this workshop

... and its Spin Dependence

Contogouris et al., PLB 246 (1990) 523Karliner and Robinett, PLB 324 (1994) 209Lampe and Reya, Phys. Rept. 332 (2000) 1Bojak and Stratmann, PR D67 (2003) 034010

A ! !f " !g " a

a

Small total cross section asymmetry is a result from cancellation caused by mass.

GRSV best fit

GRSV minimumgluon polarization

GRSV maximumgluon polarization

ALL

Inclusive electrons from charm; ~100 pb-1, 70% pol.

Displaced Electrons from Charm in STAR

Beauty |asymmetries| are generally smaller at small pT

Heavy Quark Content of Jets

UA1, PLB 244 (1990) 566CDF, PRL 64 (1990) 348

Heavy Quark Content of Jets

UA1, PLB 244 (1990) 566CDF, PRL 64 (1990) 348

Heavy Quark Content of Jets

UA1, PLB 244 (1990) 566CDF, PRL 64 (1990) 348

Some Open Questions

• Is the extrapolation over unmeasured small x justified?

• What does gluon polarization contribute to the proton spin?

• What are the quark and anti-quark polarizations by flavor?

• What orbital angular momenta do quarks and gluons carry?

• What is the role of transverse spins?

Quark Structure at Hadron Colliders - Leptonic W-boson Decays

CDF Collaboration, Measurement of the lepton charge asymmetry in Wboson decays produced by ppbar collisions, PRL 81, 5754 (1998).

u + d ! W ! l + !

Acharge =!+

! !!

!+ + !!

- hard scale,- convolution with calculable V-A decay,- sensitive, at large |Lepton Rapidity|

Clean measurement:

More recent measurements (Phys.Rev.D71 - 2005):- transverse energy ET dependence

W+

νe

e

!

u d

AL(W+) =!!u(xa)d(xb) + !d(xa)u(xb)

u(xa)d(xb) + d(xa)u(xb)=

!

"

"

#

"

"

$

!!u(xa)u(xa)

, xa " 1

!d(xa)d(xa)

, xb " 1

AL(W!) =

!

"

"

#

"

"

$

!!d(xa)d(xa)

, xa " 1

!u(xa)u(xa)

, xb " 1

projections

Requires: - PHENIX and STAR upgrades - high integrated luminosity

Quark polarimetry with W-bosons:

Spin measurements:

Quark Polarimetry at RHIC - Leptonic W-boson Decays

!!Born("pp ! W+! e+#e) " #!u(xa)d(xb)(1+cos $)2+!d(xa)u(xb)(1#cos $)2

Quark Polarimetry at RHIC - Heavy Quark W-boson Decays?

Hadronic decays:

+ are 6x more abundant,

+ are kinematically complete,

- have challenging QCD backgrounds.

UA2, PLB 186 (1987) 452.

Quark Polarimetry at RHIC - Heavy Quark W-boson Decays?

Hadronic decays:

+ are 6x more abundant,

+ are kinematically complete,

- have challenging QCD backgrounds.

The requirement of charm

+ reduces QCD background > 10x,

+ reduces Z background 5x,

- reduces signal 2x.

mass [GeV]

mass [GeV]

RHIC

~10 pb-1

ALQCD = 0, ALW ~ 0.2, S/B can be optimized, W charge?W. Zhou (LBNL), E.S.

gives some sensitivity to !s,!s

W-boson Processes - Higher Orders...

Charm-associated W-boson production,

Hyperon spin transfer at RHIC (Q.H. Xu, E.S.), elastic neutrino scattering (BNL E734), semi-inclusive DIS at a future Electron Ion Collider

K. Sudoh, RHIC-II Science Workshop (2005)

L = 800 pb!1, P = 70%, !c = 10%

Some Open Questions

• Is the extrapolation over unmeasured small x justified?

• What does gluon polarization contribute to the proton spin?

• What are the quark and anti-quark polarizations by flavor?

• What orbital angular momenta do quarks and gluons carry?

• What is the role of transverse spins?

Feng Yuan

Feng Yuan

Feng Yuan

Some Open Questions

• Is the extrapolation over unmeasured small x justified?

• What does gluon polarization contribute to the proton spin?

• What are the quark and anti-quark polarizations by flavor?

• What orbital angular momenta do quarks and gluons carry?

• What is the role of transverse spins?

Other

Quarkonia

Considerable effort to understand the production mechanism

e.g. Cooper, Liu, Nayak

Any spin observables?

Quarkonia

Spin Transfer -

!c

A correlation between the spinsof initial and final particles.

!c

K. Sudoh, RHIC-II Science Workshop (2005)

Thanks!