Experimental aspects on Low-x Physics at a Future EIC facility - … · 2012. 8. 16. · Bernd...

Bernd Surrow

Bernd SurrowPOETIC 2012 @ IU Bloomington WorkshopBloomington, IN, August 20-22, 2012

Experimental aspects onLow-x Physics

at a Future EIC facility- Concepts / Status / Projections -

1


Motivation2

Structure and dynamics of proton (mass / spin) (→ visible universe) originates from QCD-interactions!

Synergy of experimental progress and theory (Lattice QCD / Phenomenology incl. phenomenological fits / Modeling) critical!

(D. Leinweber: Action (~energy) density fluctuations of gluon-fields in QCD vacuum)

e�

X

e

p


Motivation3

The silent (low x) partners...: Gluons and QCD-Sea

x3

x1

x2

x2 < x1

x3 < x2

x

Fundamental questions:

What are the properties of gluons that bind strongly interacting particles?

What is the quark-gluon internal structure of nucleons?

What are the properties of quark-gluon matter at high density?

Q2

W

2 ' Q

2/x


Outline4

Concepts and Status

Future unpolarized low-x opportunities:

Unpolarized ep/eA physics

Summary and Outlook


5

Bernd Surrow

Low-x kinematicsAccess higher parton density system

Larger center-of-mass energy (√s): Smaller x at larger √s!

Forward direction: Smaller x at larger η!

eA vs. ep scattering: Probe higher parton density system in eA compared to ep!

e p e A

central(η ≈ 0)

collider

forward(η large)

(η ≈ 0)

fixed-target

Concepts and Status

e�

X

e

p

xQ2

W 2 � Q2/x

d�ep � F2 =�

q

xe2qfq(x)


6

Mom

entu

m

cont

ribu

tion

f(x) =

f+(x) + f�(x)

+

Spin contribution

�f(x) =

f+(x)� f�(x)

�

Probing the structure and dynamics of matter in ep vs. pp scattering

d�pp ⇥ f1 � f2 � �h �Dhf Factorization

Universality

Concepts and Status

p

x1

x2

Jet 1

Jet 2

p

e

p

px1

x2

W

�̄e

H1 and ZEUS

x = 0.00005, i=21x = 0.00008, i=20

x = 0.00013, i=19x = 0.00020, i=18

x = 0.00032, i=17x = 0.0005, i=16

x = 0.0008, i=15x = 0.0013, i=14

x = 0.0020, i=13x = 0.0032, i=12

x = 0.005, i=11x = 0.008, i=10

x = 0.013, i=9x = 0.02, i=8

x = 0.032, i=7x = 0.05, i=6

x = 0.08, i=5

x = 0.13, i=4

x = 0.18, i=3

x = 0.25, i=2

x = 0.40, i=1

x = 0.65, i=0

Q2/ GeV2

σr,

NC

(x,Q

2 ) x 2

i

+

HERA I NC e+pFixed TargetHERAPDF1.0

10-3

10-2

10-1

1

10

10 2

10 3

10 4

10 5

10 6

10 7

1 10 10 2 10 3 10 4 10 5

-310

-210

-110

1

10

-410 -310 -210 -110 1-310

-210

-110

1

10

HERAPDF1.0

exp. uncert.

model uncert.

parametrization uncert.

x

xf 2 = 1.9 GeV2Q

vxu

vxd

xS

xg

H1 and ZEUS

-310

-210

-110

1

10

-310

-210

-110

1

10

-410 -310 -210 -110 1-310

-210

-110

1

10

HERAPDF1.0

exp. uncert.

model uncert.

parametrization uncert.

x

xf 2 = 10 GeV2Q

vxu

vxd

xS

xg

H1 and ZEUS

-310

-210

-110

1

10


Concepts and StatusPicture of the proton from unpolarized ep scattering

7

Strong violation of scaling at low x and high Q2

In contrast to:

Low Q2 high x!

Huge gluon and QCD sea contribution!

d� =�

f1,f2

f1 � f2 � d�̂f1f2�fX � Dhf

�d2⇤

dydQ2

⇥=

2⇥�2Y+

yQ4

�F2 �

y2

Y+FL

⇥

Y+ = 1 + (1� y)2

��ptot = ��p

T + ��pL

FL =Q2

4⇥2�⇤��p

L � xgF2 =Q2

4⇥2�⇤��p

tot =�

f=qq̄

xe2qf

Universality

Factorization


8

Important: Complementary probes are required for unambiguous extraction of observables in high-energy density QCD region!

Probing the structure and dynamics of matter in eA / pA scattering

Concepts and Status

Qs2: Saturation scale ⇒ Characterize transition to

saturation region! Q2s ⇥ �s

1⇥R2

xG(x,Q2) �Q2 > Q2

s � �s = �s(Q2)

Q2 < Q2s � �s = �s(Q2

s)


Low-x basics (1)Dynamics: DGLAP / BFKL and CGC

9

A1/3x��Enhanced for eA compared to ep:

Qs(Y )Y = ln

�1x

⇥

Q2�2QCD

�s � 1 �s � 1

BFKL

DGLAP

CGC

CGC: Color-Glass-Condensate

BK/JIMWLK

Concepts and Status


10

Concepts and StatusLow-x basics (2)

Dipole modelConsider virtual photon-proton cross-section

Frame: Proton rest frame

Interaction time < Fluctuation time at low x

Dipole model: Interaction of quark/anti-quark pair with proton

Lowe

r x

Lower Q2DRAFT


11

APS DNP 2007 LRP Meeting - QCD and Hadron Physics Town MeetingRutgers University, Piscataway, NJ, January 13, 2007 Bernd Surrow

Concepts and StatusHERA: γ*p cross-section

Dipole-model approach: Successful description of

both inclusive and diffractive processes at low x

Change of Q2 dependence around 1GeV2!

D. Schildknecht, B.S., Phys. Lett. B499 (2001) 116. A.M. Stasto et al., PRL 86 (2001) 596.

DRAFT


12

APS DNP 2007 LRP Meeting - QCD and Hadron Physics Town MeetingRutgers University, Piscataway, NJ, January 13, 2007 Bernd Surrow

Concepts and StatusDiffraction

Ratio of diffractive to total cross-section

(200<W<245GeV): 15% at Q2=4GeV2

Dipole models: Successful description of inclusive and

various diffractive measurements (e.g. Ratio of

diffractive to inclusive cross-section, Diffractive Vector-

Meson production)

DRAFT

)c (GeV/T

p0 1 2 3 4 5

dA

uR

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2 = 3.2)! = 200 GeV (

NNs+X @ - h"d+Au

BRAHMS data

pQCD+shadow [Guzey et al.]

pQCD+shadow [Accardi]

CGC [Tuchin et al.]

CGC [Jalilian-Marian]


RHIC dA scattering at forward η

13

STAR

Forward identified hadron production at RHIC in dAu collisions: Sizable suppression of yields for charged hadrons and neutral pions observed

pQCD+shadowing calculations over-predict hadron yield suppression. Is this an indication for gluon saturation in Au nuclei?

More RHIC dAu are expected with enhanced detector capabilities (PHENIX/STAR)

Concepts and Status

DRAFT


Concepts and StatusFixed-target scattering experiments

14

Inclusive structure function ratio important to constrain nuclear modifications to gluon density

World data (Fixed target) are concentrated above x>0.01 in pQCD region

For x<0.01 only data in non-pQCD region


Future opportunitiesEIC facilities

15

ELIC

eRHIC (BNL)

Ee = 10 (20) GeVEA = 100 GeV (up to U)√seN = 63 (90) GeVLeAu (peak)/n ~ 2.9·1033 cm-2 s-1

ELIC (JLAB)

Ee = 9 GeVEA = 90 GeV (up to Au)√seN = 57 GeVLeAu (peak)/n ~ 1.6·1035 cm-2 s-1

Beam

dump

Polarized

e-gun0.6 GeV

eSTAR

ePHENIX

Cohe

rent

e-c

oole

r

New detector

0.6 GeV

30 GeV

30 GeV

27.55 GeV

22.65 GeV

17.75 GeV

12.85 GeV

3.05 GeV

7.95 GeV

Lina

c 2.4

5 Ge

V

Linac 2.45 GeV

25.1 GeV

20.2 GeV

15.3 GeV

10.4 GeV

30.0 GeV

5.50 GeV

27.55 GeV

0.60 GeV

DRAFT


Future OpportunitiesKinematics

Comparison HERA / EIC / Fixed-target experiments

16

ZEUS BPC 1995

ZEUS SVTX 1995

H1 SVTX 1995

HERA 1994

HERA 1993

NMC

BCDMS

E665

SLAC

CCFR

10-1

1

10

10 2

10 3

10 4

10-6

10-5

10-4

10-3

10-2

10-1

1x

Q2

VeG(

2 )

NMC

BCDMS

E665

SLAC

CCFR

10-1

1

10

10 2

10 3

10 4

10-6

10-5

10-4

10-3

10-2

10-1

1x

Q2

VeG(

2 )

NMC

BCDMS

E665

SLAC

CCFR

1=y

10-1

1

10

10 2

10 3

10 4

10-6

10-5

10-4

10-3

10-2

10-1

1x

Q2

VeG(

2 )

20 GeV + 100 GeV/n

10 GeV +100 GeV/n

9 GeV + 90 GeV/n

EIC e+Au

1=y

10-1

1

10

10 2

10 3

10 4

10-6

10-5

10-4

10-3

10-2

10-1

1x

Q2

VeG(

2 )

20 GeV + 100 GeV/n

10 GeV +100 GeV/n

9 GeV + 90 GeV/n

EIC e+Au

Q 2s proton

Q 2s Ca (central)

Q 2s Au (central)

Terra incognita:

small-x, Q≈Qs

high-x, large Q2


Future Opportunities17

Gluon distribution:

Space-Time distribution of gluon:

Interaction of fast probes with matter:

Impact of strong gluon fields on the role of color neutral excitations:

Key observables in electron-proton and electron-nucleus scattering

FL (Variable center-of-mass energy) and F2

Jet rates

Inelastic vector meson production (e.g. J/Psi)

FL (Variable center-of-mass energy) and F2

Deep virtual compton scattering (DVCS)

Exclusive final states (e.g. Vector meson production)

Hadronization, Fragmentation studies

Energy loss (Heavy quarks)

Diffractive structure functions

Diffractive vector meson production

DRAFT


Future Opportunities: Unpolarized eA physics 18

BNL EIC Task Force

DRAFT

FA2 ratio at EIC vs. A1/3

BNL EIC Task Force

Details



BNL EIC Task Force

DRAFT

Di-hadron correlation vs. x at EIC: Nuclear modification JeAu

BNL EIC Task Force

Details



BNL EIC Task Force

DRAFT

Di-hadron correlation at EICBNL EIC Task Force

Details



BNL EIC Task Force

DRAFT

BNL EIC Task Force

Diffractive VM production at EIC: J/Ψ and Φ (1)

Details



BNL EIC Task Force

DRAFT

Diffractive VM production at EIC: J/Ψ and Φ (2)

BNL EIC Task Force

Details


Summary and OutlookStatus and Concepts

HERA: Precision structure function measurements (F2) at low x

At low Q2 and low x: DGLAP (Leading twist) approach leads to valence-like gluon behavior

Diffraction: Important contribution to overall ep event yield

Dipole model: Allows to describe inclusive and diffractive measurements. Reach of saturation region at low x not conclusive

Lesson: Optimize any future EIC efforts for acceptance and luminosity

eA: No information in low-x region

dAu results at RHIC: Can saturation account for observed behavior? Complementary probes important (RHIC/LHC)!

Important constrain on gluon polarization at medium and higher x from semi-inclusive polarized DIS and RHIC-SPIN program (Hint for ΔG ≠ 0) - Complementary to EIC

23


Summary and OutlookFuture Opportunities

EIC: First polarized ep collider - Precision measurement of polarized gluon distribution at

low-x and quark flavor structure

EIC will allow to study the physics of strong color fields

Required: EIC at high luminosity and optimized detector

EIC will allow to bridge several QCD communities (Hadron structure and Relativistic

Heavy-Ion)

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Experimental aspects on Low-x Physics at a Future EIC facility - … · 2012. 8. 16. · Bernd...

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