Overview ofStructure Function Measurements

at Jefferson Lab

International Workshop on Diffraction in High-Energy PhysicsSeptember 11, 2012

Wally Melnitchouk

Thomas Jefferson National Accelerator Facility

1

Brief tour of Jefferson Lab

Outlook

free neutron, duality, nuclear EMC effect

Unpolarized structure functions

Outline

Polarized structure functions

CTEQ-JLab (CJ) global PDF analysis

JLab Angular Momentum (JAM) global PDF analysis

remaining 6 GeV analysesplans for 12 GeV measurements

Yelena Prok (Wednesday, 16:30)

F2, FL,

longitudinal and transverse structure (DIS & SIDIS)

2

CEBAF(Continuous Electron Beam Accelerator Facility)

atJefferson Lab

3

Thomas Jefferson National Accelerator Facility(Jefferson Lab)

located in Newport News, Virginia

Jamestown:1st permanent

English settlement(1607)

4

Newport News, Virginia

5

Thomas Jefferson National Accelerator Facility(Jefferson Lab)

Hall AHall B Hall C

electron linacs

6 GeV polarized electron beamon (un)polarized targets

Hall D

6 GeV program ended in May, 2012

Upgrade to 12 GeV under way (restart ~ 2014-2015)

6

Experimental Halls

Hall A

Hall C

Hall B

Hall D

7

Experimental Halls

Hall A

Hall C

high luminosity

very high precisionmeasurements

precision structure functions,parity-violating e scattering,high Q form factors2

> 1038

cm2

s1

8

Experimental HallsHall B

large acceptance,lower luminosity 10

35cm

2s1

collect all data at once

N spectroscopy(multi-hadron final states),deep exclusive reactions(generalized parton distributions),structure function moments

*

CLAS(CEBAF Large Acceptance Spectrometer)

9

Experimental Halls

Hall D

new Hall just completed,as part of 12 GeV Upgrade

photon beam

exotic meson spectroscopy(qqg states)

acceptance4

_

10

JLab Kinematic Coverage

Q2

(GeV )2

11

Unpolarized Structure Functions

12

Proton structure functionF2

Christy, WMJPCS 299, 012004 (2011)

0

0.25

0

0.25

0

0.25

0

0.25

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

high precision measurements of resonance-DIS transition region (high x, low Q )2

13

Proton structure functionF2

Christy et al. (2011)

high precision tests of quark-hadron duality

x

square of sum sum of squares?coherent incoherent

14

0.60.8

11.21.41.6

0 3 6 90.60.8

11.21.41.6

0 3 6 9

0.60.8

11.21.41.6

0 3 6 9 0.60.8

11.21.41.6

0 3 6 9

0.60.8

11.21.41.6

0 3 6 9

1st

(a)

E00-116 (JLab)E94-110 (JLab)I. Niculescu (JLab)

4th

(d)

SLACSLAC (E8920)

2nd

(b)

F2p

(dat

a) d

x /

F2p

(ALE

KHIN

) dx

DIS

(e)

3rd

(c)

Q2 (GeV2)

global

(f)0.60.8

11.21.41.6

0 3 6 9

0.60.8

11.21.41.6

0 3 6 90.60.8

11.21.41.6

0 3 6 9

0.60.8

11.21.41.6

0 3 6 9 0.60.8

11.21.41.6

0 3 6 9

0.60.8

11.21.41.6

0 3 6 9

1st

(a)

E00-116 (JLab)E94-110 (JLab)I. Niculescu (JLab)

4th

(d)

SLACSLAC (E8920)

2nd

(b)

F2p

(dat

a) d

x /

F2p

(ALE

KHIN

) dx

DIS

(e)

3rd

(c)

Q2 (GeV2)

global

(f)0.60.8

11.21.41.6

0 3 6 9

Malace et al.PRC 80, 035207 (2009)

(W < 2 GeV)

Proton structure functionF2

Q2 > 1 GeV2higher twists 10-15% for

15

Proton structure functionFL

0

0.05

0.1

0.15

0.22 = 1.75 (GeV/c)2Q

E94110SLAC

0

0.05

0.1

0.15

0.22 = 2.5 (GeV/c)2Q

E99118NMC

0

0.05

0.1

0.15

0.22 = 6.5 (GeV/c)2Q

E140xHERA

x0 0.2 0.4 0.6 0.8 10

0.020.040.060.08

0.12 = 10.0 (GeV/c)2Q

)2(x

, QLF

(n=2

)L

M

0

10

20

30

40-310

total inelastic

-310

total

(n=4

)L

M

-1

0

1

2

3

4MSTW NLOCJ NLO

MSTW LO NLO NNLO

]2 [(GeV/c)2Q1 10

(n=6

)L

M

00.20.40.60.8

1ABKM NLO + HT

]2 [(GeV/c)2Q1 10 210

Monaghan et al. (2012)

moment analysis suggests larger gluon at high x(or significant higher twists in higher moments)

16

Neutron structure functionF2F2

Neutron structure more elusive because of absence offree neutron targets

new extraction method allows first determinationof in resonance regionFn2

test universality of quark-hadron duality!

Malace et al., PRL 104, 102001 (2010)

17

cats ears diagram (4-fermion higher twist ~ ) 1/Q2

i =jei ej

i

e2i

2

i

e2i

coherent incoherent

Duality from accidental cancellations of charges?

should not hold for neutron

proton

neutron

HT 1 2 4

9+

1

9

= 0 !

HT 0

4

9+ 2 1

9

= 0

Brodskyhep-ph/0006310

duality in proton a coincidence!

18

Neutron structure functionF2

theory: fit to W > 2 GeV dataAlekhin et al., PRD 81, 014032 (2010)

globally, violations < 10%

locally, violations of duality inresonance regions < 15-20%

duality not accidental !

Neutron structure more elusive because of absence offree neutron targets

new extraction method allows first determinationof in resonance regionFn2

Malace et al., PRL 104, 102001 (2010)

19

Neutron structure functionF2Model independent confirmation: the BoNuS experiment

tag slow, backward proton in SIDIS from deuteron,minimize off-shell extrapolation, rescattering

Spectator Tagging

!

pS = E S ,r p S( ) ; "S =

ES #r p S $ q

M D /2

!

pn = M D "E S ,"r p S( ) ; #n = 2"#S

!

W2 = pn + q( )

2= pn

pn + 2 (M D "Es )# "

r p n $

r q ( )"Q2

% M *2 +2M# (2"&S )"Q

2

!

x =Q2

2pnq

"Q2

2M# (2$%S )

!

W2

= M2

+ 2M" #Q2

*

target d

recoil p

Barely Off-shell Neutron Structure(Hall B)

pq > 100o

70 < ps < 100 MeV/cEbeam = 4 & 5 GeV

Baillie et al., PRL 108, 142001 (2012)

(Ciofi degli Atti, Kopeliovich, Simula, ...)

20

Neutron structure functionF2Model independent confirmation: the BoNuS experiment

tag slow, backward proton in SIDIS from deuteron,minimize off-shell extrapolation, rescattering

x0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8

p 2 /

F n 2F

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1W* > 1.8 GeVW* > 1.6 GeVW* > 1.4 GeVCJ

x0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8

p 2 /

F n 2F

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0.2 0.4 0.6 0.8

]2>

[GeV

2

CTEQ-JLab (CJ)Global PDF Analysis

CJ collaboration: A. Accardi, J. Owens, WM (theory) E. Christy, C. Keppel, P. Monaghan (expt.)

http://www.jlab.org/CJ/

22

http://www.jlab.org/GAUSTEQ/http://www.jlab.org/GAUSTEQ/

New global NLO analysis of expanded set of p and ddata (DIS, hadronic) including large-x, low-Q region2

Systematically study effects of Q & W cuts2

down to Q ~ m and W ~ 1.7 GeVc

Include subleading 1/Q corrections2

Dependence on choice of PDF parametrization

target mass, higher twist effects

Correct for nuclear smearing effects in the deuteron vital at large x, for all Q2

allow nonzero ratio at x = 1: d d + a xb u

23

cut0:cut1:

cut2:

cut3:

Q2 > 4 GeV2, W 2 > 12.25 GeV2

Q2 > 3 GeV2, W 2 > 8 GeV2

Q2 > 2 GeV2, W 2 > 4 GeV2

Q2 > m2c , W2 > 3 GeV2

x x

cut1cut2

cut3

cut0

NMCBCDMS

JLab

SLAC

p d

Q2

(GeV

2)

H1, ZEUS

factor 2 increasein DIS data fromcut0 cut3

CJ kinematic cuts

24

d quark behavior driven by nuclearcorrections at high x

Accardi et al.PRD 81, 034016 (2010)x

reference fit with cut0,no nuclear/HT corrections

PDFs remarkably stable with respect to cut reduction,as long as finite-Q corrections included2

25

Larger database with weaker cuts leads to significantly reduced errors, especially at large x

x x

Accardi et al.PRD 81, 034016 (2010)

up to 40-60% error reduction when cuts extended into resonance region

26

Accardi et al., PRD 84, 014008 (2011)

Vital for large-x analysis, which currently suffers fromlarge uncertainties (mostly due to nuclear corrections)

uncertainty in d feeds into larger uncertaintyin g at high x (important for LHC physics!)

CJ11 CJ11

27

Impact on collider physics

p

p

q

q

_W, Z

l

lx1

x2

28