eRHIC - Brookhaven National LaboratoryeRHIC 15 1 10 0 0.5 1 1.5 2 2.5 3 Ratio of diffractive-to-total cross- section for eAu over that in ep non-saturation model (LTS) saturation model

$Page 1: eRHIC - Brookhaven National LaboratoryeRHIC 15 1 10 0 0.5 1 1.5 2 2.5 3 Ratio of diffractive-to-total cross- section for eAu over that in ep non-saturation model (LTS) saturation model$
eRHICA Precision Tool for Studying

Nuclear StructureThomas Burton

On behalf of the EIC Science Task Force

SQM18th July 2013

Thomas Burton SQM 2013

Introduction

• eRHIC and DIS overview

• Key eA measurements

• Detector concept

• Machine design

2

Boost


What is eRHIC?

• Adds ep and eA capability to RHIC

• Utilises much current investment

• Builds on successes of both RHIC and HERA

3

Relativistic Heavy Ion Collider+

Electron beam/linac

Electron-Ion Collider (EIC)situated at BNL


Why eA collisions?

• Electrons give three advantages

‣ Clean: no “spectator” background

‣ Clear: distinguish initial/final-state effects

‣ Precise: direct access to parton-level kinematics via deeply inelastic scattering

4

• RHIC is a successful hadronic machine

‣ so why bother with electrons?


• Kinematics entirely defined by scattered electron5

DeeplyInelasticScattering

(an aside on DIS kinematics)

“resolution”

“inelasticity”


Overview• eRHIC physics goals

‣ impossible to give more than a taste here

‣ eA

‣ Saturation

‣ Imaging

‣ Nuclear PDFs

‣ Hadronisation in strongly interacting medium

‣ ep (not covered here)

‣ nucleon imaging (impact parameter dependence)

‣ unintegrated PDFs (pT-dependence)

‣ spin sum rule (origin of spin-1/2 proton/neutron)

6

Nuclear initial state:vital to understanding

nuclear collisions


Gluons at small x• QCD interaction accounts for

99% of proton mass

‣ c.f. 1% Higgs mass of quarks

• Gluon PDFs from DIS show explosive growth at small x

‣ must be tamed at some point

• non-linear evolution e.g. BK alternative to DGLAP, BFKL, account for gluon recombination

7

0.2

0.4

0.6

0.8

1

10-4 10-3 10-2 10-1 1

experimental uncertainty model uncertainty parametrization uncertainty

HERAPDF1.7 (prel.) HERAPDF1.6 (prel.)

xxf(

x, Q2 )

Q2 = 10 GeV2

vxu

vxd

xS (! 0.05)

xG (! 0.05)

HERA


Gluons at small x• QCD interaction accounts for

99% of proton mass

‣ c.f. 1% Higgs mass of quarks

• Gluon PDFs from DIS show explosive growth at small x

‣ must be tamed at some point

• non-linear evolution e.g. BK alternative to DGLAP, BFKL, account for gluon recombination

7

“Saturation scale” at which

phenomena manifest

splitting recombination


An eA collider: why use nuclei?

8

Reaching predicted saturation scale in e-p needs very low x

→1-2 TeV machine

But...in a high-E collision gluon

density scales ~ nuclear radius

Boost

Need even lower x than HERA accessed


• Nuclear amplification of saturation scale

• “Effective x” is much smaller in nuclei

Nuclear amplification

9

-510 -410 -310 -210-110

1

10

-510 -410 -310 -210-110

1

10

x x

Q2 (GeV

2 )

Q2 (GeV

2 )

Q2s,quark Model-I

b=0Au, median bCa, median bp, median b

Q2s,quark, all b=0

Au, Model-II

Ca, Model-IICa, Model-I

Au, Model-I

xBJ ! 300

~ A1/3

Au

Au

pCa

Ca

→Access saturation with ~100 GeV eA machine


eRHIC eA kinematics

10

Extend reach far beyond

existing data

•Access saturated regime•Precise studies of nuclear structure


Key measurements

11


Structure functions

• precision nuclear PDFs

• indications of saturation/non-linearity

12

A!⁄" A!⁄"

rcBKEPS09 (CTEQ)

Q2 = 2.7 GeV2, x = 10-3Q2 = 2.7 GeV2, x = 10-3

rcBKEPS09 (CTEQ)

stat. errors enlarged (# 50)sys. uncertainty bar to scale

Cu AuSi

Beam Energies A $Ldt5 on 50 GeV 2 fb-1 5 on 75 GeV 4 fb-15 on 100 GeV 4 fb-1

1 2 3 4 5 6 70

0.2

0.4

0.6

0.8

1

1.2

1 2 3 4 5 6 70

0.2

0.4

0.6

0.8

1

1.2

R 2 =

F 2A /(A F

2p )

R L =

F LA /(A F

Lp )



F2 sensitive to quarksFL sensitive to gluonsSeparation requires variable energy

large uncertainties on

DGLAP predictions

Systematics-dominated


Structure functions

• precision nuclear PDFs

• indications of saturation/non-linearity

12

A!⁄" A!⁄"

rcBKEPS09 (CTEQ)

Q2 = 2.7 GeV2, x = 10-3Q2 = 2.7 GeV2, x = 10-3

rcBKEPS09 (CTEQ)


Cu AuSi


1 2 3 4 5 6 70

0.2

0.4

0.6

0.8

1

1.2

1 2 3 4 5 6 70

0.2

0.4

0.6

0.8

1

1.2

R 2 =

F 2A /(A F

2p )

R L =

F LA /(A F

Lp )



F2 sensitive to quarksFL sensitive to gluonsSeparation requires variable energy

large uncertainties on

DGLAP predictions

Systematics-dominated

0.00.20.40.60.81.01.21.4

0.00.20.40.60.81.01.21.4

10-4 10-3 10-2 10-1 10.00.20.40.60.81.01.21.4

0.00.20.40.60.81.01.21.4

10-4 10-3 10-2 10-110-4 10-3 10-2 10-10.00.20.40.60.81.01.21.4

10-4 10-3 10-2 10-110-4 10-3 10-2 10-1

Baseline fitPseudodata fit

x

RvalencePb

x

RseaPb

x

RgluonPb

Ri(x,Q

2 =1.69GeV

2 )Pb


Diffraction

13

colour-neutral exchange

e.g. 2 gluons

Signature: absence of activity in

detector over wide rapidity

Measure additional variable:4-momentum transfer

t = p - p`

Ideal for studying gluons:σ ~ g(x, Q2)2

15% of HERA cross section

25-40% in eA!


Diffraction

• Ideal tool for both

‣ studying saturation

‣ imaging gluons

• “Coherent”: nucleus intact

• “Incoherent”: nucleus breaks up (no diffraction pattern)

14


Diffraction: saturation

• No saturation: eA/ep ratio ~ 1

• Saturation: enhances σdiff in eA vs. ep

‣ strong distinguishing power at eRHIC

15

1 100

0.5

1

1.5

2

2.5

3

Ratio

of d

iffrac

tive-

to-to

tal c

ross

-se

ction

for e

Au o

ver t

hat in

ep

non-saturation model (LTS)

saturation model

stat. errors & syst. uncertainties enlarged (! 10)

Q2 = 5 GeV2x = 3.3!10-3eAu stage-I

Mx2 (GeV2)

!Ldt = 10 fb-1/A


Exclusive vector mesons

• Measure t via exclusive final state

• Clear difference between saturated and unsaturated

16

0.2

0.4

0.6

0.8

1

1.2

Coherent events only!Ldt = 10 fb-1/Ax < 0.01Experimental Cuts:|!(edecay)| < 4p(edecay) > 1 GeV/c

Coherent events only!Ldt = 10 fb-1/Ax < 0.01

1 2 3 4 5 6 7 8 9 10

(1/A

4/3 ) "

(eAu

)/"(e

p)

Q2 (GeV2)

no saturationsaturation (bSat)

no saturationsaturation (bSat)

e ee + p(Au) # e’ + p’(Au’) + J/$

1 2 3 4 5 6 7 8 9 10

(1/A

4/3 ) "

(eAu

)/"(e

p)

Q2 (GeV2)

2.2

2.0

1.8

1.6

1.4

1.2

1

0.8

0.6

0.4

0.2

0

e + p(Au) # e’ + p’(Au’) + %K K

Experimental Cuts:|!(Kdecay)| < 4p(Kdecay) > 1 GeV/c

code.google.com/p/sartre-mc/

e + A → e` + A` + VM

https://code.google.com/p/sartre-mc/

https://code.google.com/p/sartre-mc/


Diffraction: imaging

➡ gluon imaging

• Strict detector demands

17

|t | (GeV2) |t | (GeV2)0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18

)2 /d

t (nb

/GeV

e’ +

Au’

+ J/!)

!(e

+ A

u "d

)2 /d

t (nb

/GeV

e’ +

Au’

+ #)

!(e

+ A

u "d

J/$ #

"Ldt = 10 fb-1/A1 < Q2 < 10 GeV2x < 0.01|#(edecay)| < 4p(edecay) > 1 GeV/c%t/t = 5%

"Ldt = 10 fb-1/A1 < Q2 < 10 GeV2x < 0.01|#(Kdecay)| < 4p(Kdecay) > 1 GeV/c%t/t = 5%

104

103

102

10

1

10-1

10-2

105

104

103

102

10

1

10-1

10-2

coherent - no saturationincoherent - no saturationcoherent - saturation (bSat)incoherent - saturation (bSat)


• t is conjugate of impact parameter, b

dσ/dt F(b)FourierTransform

PRC 87 024913 (2013)



➡ gluon imaging


17



|t | (GeV2) |t | (GeV2)0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18

)2 /d

t (nb

/GeV

e’ +

Au’

+ J/!)

!(e

+ A

u "d

)2 /d

t (nb

/GeV

e’ +

Au’

+ #)

!(e

+ A

u "d

J/$ #



104

103

102

10

1

10-1

10-2

105

104

103

102

10

1

10-1

10-2



PRC 87 024913 (2013)



➡ gluon imaging


17



|t | (GeV2) |t | (GeV2)0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18

)2 /d

t (nb

/GeV

e’ +

Au’

+ J/!)

!(e

+ A

u "d

)2 /d

t (nb

/GeV

e’ +

Au’

+ #)

!(e

+ A

u "d

J/$ #



104

103

102

10

1

10-1

10-2

105

104

103

102

10

1

10-1

10-2



PRC 87 024913 (2013)



➡ gluon imaging


17



|t | (GeV2) |t | (GeV2)0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18

)2 /d

t (nb

/GeV

e’ +

Au’

+ J/!)

!(e

+ A

u "d

)2 /d

t (nb

/GeV

e’ +

Au’

+ #)

!(e

+ A

u "d

J/$ #



104

103

102

10

1

10-1

10-2

105

104

103

102

10

1

10-1

10-2



PRC 87 024913 (2013)


Detector and machine

18


Detector concept

19

• Largely hermetic

‣ needed e.g. to detect rapidity gap

To Roman pots, ZDCs

ZDC: breakup neutrons give

~100% efficiency to

detect incoherent eA


Detector concept

19

• Largely hermetic

‣ needed e.g. to detect rapidity gap

To Roman pots, ZDCs

ZDC: breakup neutrons give

~100% efficiency to

detect incoherent eAGeant simulations under way


eRHIC

• 4 goals of machine design:

1. Variable beams species

2. Variable beam energies

3. High luminosity ~1034

4. e- polarisation ~80%

• Maximise use of existing infrastructure and investment

20

5-20(30) GeV

p

e-

100-250 GeV

50-100 GeV Cu, Au, U...

Ep (GeV)

Ee (

GeV

)

3.1034

2.5.1034

2.1034

1.5.1034

1.1034

0.5.1034

0.25.1034

0.1.1034 Luminosity in cm-2s-1


eRHIC

21

Electron &Existing beams

• Re-use of existing infrastructure

• Two linacs

‣ multiple passes

• Stageable energy

‣ add RF cavities

• New high-intensity polarised e- source


Conclusions

• eRHIC: ep/A collider at BNL

• Rich programme of eA (and ep physics)

• Further reading

‣ arXiv:1212.1701

‣ arXiv:1108.1713

22

‣ wiki.bnl.gov/eic/index.php/Main_Page

http://arxiv.org/abs/1212.1701



https://wiki.bnl.gov/eic/index.php/Main_Page

https://wiki.bnl.gov/eic/index.php/Main_Page


Dihadron correlations

• “Semi-inclusive” DIS

• Multiple gluon re-scattering, emission in saturation framework washes out correlation

• Ratio = 1 in absence of collective nuclear effects

• Shaded: uncertainties in knowledge of saturation scale

• ep baseline needed, but cancels various uncertainties

23

2 2.5 3 3.5 4 4.50

0.020.040.060.08

0.10.120.140.160.18

eAueAu - sat

eAu - nosateCa

pTtrigger > 2 GeV/c

1 < pTassoc < pT

trigger

|!|<4

ep Q2 = 1 GeV2

!"!"

C(!"

)

C eAu

(!"

)

2 2.5 3 3.5 4 4.50

0.05

0.1

0.15

0.2EIC stage-II# Ldt = 10 fb-1/A

2 2.5 3 3.5 4 4.50

0.020.040.060.08

0.10.120.140.160.18

eAueAu - sat

eAu - nosateCa

pTtrigger > 2 GeV/c

1 < pTassoc < pT

trigger

|!|<4

ep Q2 = 1 GeV2

!"!"

C(!"

)

C eAu

(!"

)

2 2.5 3 3.5 4 4.50

0.05

0.1

0.15

0.2EIC stage-II# Ldt = 10 fb-1/A


DIS with polarised beams

24

Q2 = 10 GeV

DSSV+EICEIC

5!1005!25020!250

all uncertainties for !"2=9

-1

-0.5

0

0.5

1

0.3 0.35 0.4 0.45

currentdata

2

g(x,Q

2 ) dx

1

0.00

1

(x,Q2) dx1

0.001

Measure quark/gluon helicity


Fourier transform

25

Measure more minima

Better measure of b-dependence


Fourier transform

25

Measure more minima



Fourier transform

25

Measure more minima



Fourier transform

25

Measure more minima



Fourier transform

25

Measure more minima



Fourier transform

25

Measure more minima



Fourier transform

25

Measure more minima



Fourier transform

25

Measure more minima



( )

x

y

z

!S

!

Ph

S"

kk

q

z

SIDIS

26

Semi-Inclusive Deeply Inelastic

Scattering

Measure theelectron + asingle hadron

⇓characterised via

(z, pT)

DISx, Q2

semi-inclusive

z, pT

spinϕ

Multi-dimensional

+ +


• Gives additional hadron information

‣ extract “transverse-momentum-dependent distributions”: TMDs

27

1) Spin-dependence:see deformation of parton distribution

e.g. Sivers functionSp

in

Alexei Prokudin

x = 0.1

SIDIS


• Gives additional hadron information

‣ extract “transverse-momentum-dependent distributions”: TMDs

27

2) Identify hadrons: decompose flavour dependence

Alexei Prokudin

x = 0.1

SIDIS


J/psi production

28

0

1

2

3

4

5

6

7

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6

0.0016 < xV < 0.002515.8 GeV2 < Q2 + M2

J/! < 25.1 GeV2

x V F

(x V,b

T) (f

m"2 )

x V F

(x V,b

T) (f

m"2 )

bT (fm)

-t (GeV2)

BR(J/!

# e+ e-

) $ d%

/dt (

pb/G

eV2 )

1

10

102

103

104

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6

!Ldt = 10 fb-120 GeV on 250 GeV

&' + p # J/! + p

0

0.01

0.02

1.4 1.6

0.03

1.80

0.01

0.02

0.03

1.4 1.6 1.8

10-1

1

10

102

103

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6

0.16 < xV < 0.2515.8 GeV2 < Q2 + M2

J/! < 25.1 GeV2

!Ldt = 10 fb-15 GeV on 100 GeV

&' + p # J/! + p

BR(J/!

# e+ e-

) $ d%

/dt (

pb/G

eV2 )

-t (GeV2)

bT (fm)

0

0.5

1

1.5

2

2.5

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6

Fouriertransform

Tiny statistical errors in < 1 year running

Fine binning in (x, Q2, t)

t

b


Nucleon tomography

29

Generalised Parton Distributions → b-dependence


Spin dependence

Nucleon tomography

29



Spin dependence

Nucleon tomography

29

PET brain image


eRHIC - Brookhaven National LaboratoryeRHIC 15 1 10 0 0.5 1 1.5 2 2.5 3 Ratio of diffractive-to-total cross- section for eAu over that in ep non-saturation model (LTS) saturation model

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