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TRANSCRIPT
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
Thomas Burton SQM 2013
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
Thomas Burton SQM 2013
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?
Thomas Burton SQM 2013
• Kinematics entirely defined by scattered electron5
DeeplyInelasticScattering
(an aside on DIS kinematics)
“resolution”
“inelasticity”
Thomas Burton SQM 2013
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
Thomas Burton SQM 2013
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
Thomas Burton SQM 2013
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
Thomas Burton SQM 2013
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
Thomas Burton SQM 2013
• 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
Thomas Burton SQM 2013
eRHIC eA kinematics
10
Extend reach far beyond
existing data
•Access saturated regime•Precise studies of nuclear structure
Thomas Burton SQM 2013
Key measurements
11
Thomas Burton SQM 2013
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 )
Beam Energies A $Ldt5 on 50 GeV 2 fb-1 5 on 75 GeV 4 fb-15 on 100 GeV 4 fb-1
stat. errors enlarged (# 5)sys. uncertainty bar to scale
F2 sensitive to quarksFL sensitive to gluonsSeparation requires variable energy
large uncertainties on
DGLAP predictions
Systematics-dominated
Thomas Burton SQM 2013
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 )
Beam Energies A $Ldt5 on 50 GeV 2 fb-1 5 on 75 GeV 4 fb-15 on 100 GeV 4 fb-1
stat. errors enlarged (# 5)sys. uncertainty bar to scale
F2 sensitive to quarksFL sensitive to gluonsSeparation requires variable energy
large uncertainties on
DGLAP predictions
Systematics-dominated
0.00.20.40.60.81.01.21.4
0.00.20.40.60.81.01.21.4
10-4 10-3 10-2 10-1 10.00.20.40.60.81.01.21.4
0.00.20.40.60.81.01.21.4
10-4 10-3 10-2 10-110-4 10-3 10-2 10-10.00.20.40.60.81.01.21.4
10-4 10-3 10-2 10-110-4 10-3 10-2 10-1
Baseline fitPseudodata fit
x
RvalencePb
x
RseaPb
x
RgluonPb
Ri(x,Q
2 =1.69GeV
2 )Pb
Thomas Burton SQM 2013
Diffraction
13
colour-neutral exchange
e.g. 2 gluons
Signature: absence of activity in
detector over wide rapidity
Measure additional variable:4-momentum transfer
t = p - p`
Ideal for studying gluons:σ ~ g(x, Q2)2
15% of HERA cross section
25-40% in eA!
Thomas Burton SQM 2013
Diffraction
• Ideal tool for both
‣ studying saturation
‣ imaging gluons
• “Coherent”: nucleus intact
• “Incoherent”: nucleus breaks up (no diffraction pattern)
14
Thomas Burton SQM 2013
Diffraction: saturation
• No saturation: eA/ep ratio ~ 1
• Saturation: enhances σdiff in eA vs. ep
‣ strong distinguishing power at eRHIC
15
1 100
0.5
1
1.5
2
2.5
3
Ratio
of d
iffrac
tive-
to-to
tal c
ross
-se
ction
for e
Au o
ver t
hat in
ep
non-saturation model (LTS)
saturation model
stat. errors & syst. uncertainties enlarged (! 10)
Q2 = 5 GeV2x = 3.3!10-3eAu stage-I
Mx2 (GeV2)
!Ldt = 10 fb-1/A
Thomas Burton SQM 2013
Exclusive vector mesons
• Measure t via exclusive final state
• Clear difference between saturated and unsaturated
16
0.2
0.4
0.6
0.8
1
1.2
Coherent events only!Ldt = 10 fb-1/Ax < 0.01Experimental Cuts:|!(edecay)| < 4p(edecay) > 1 GeV/c
Coherent events only!Ldt = 10 fb-1/Ax < 0.01
1 2 3 4 5 6 7 8 9 10
(1/A
4/3 ) "
(eAu
)/"(e
p)
Q2 (GeV2)
no saturationsaturation (bSat)
no saturationsaturation (bSat)
e ee + p(Au) # e’ + p’(Au’) + J/$
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
Thomas Burton SQM 2013
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)
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)
Thomas Burton SQM 2013
Diffraction: imaging
➡ gluon imaging
• Strict detector demands
17
• t is conjugate of impact parameter, b
dσ/dt F(b)FourierTransform
|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)
coherent - no saturationincoherent - no saturationcoherent - saturation (bSat)incoherent - saturation (bSat)
PRC 87 024913 (2013)
Thomas Burton SQM 2013
Diffraction: imaging
➡ gluon imaging
• Strict detector demands
17
• t is conjugate of impact parameter, b
dσ/dt F(b)FourierTransform
|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)
coherent - no saturationincoherent - no saturationcoherent - saturation (bSat)incoherent - saturation (bSat)
PRC 87 024913 (2013)
Thomas Burton SQM 2013
Diffraction: imaging
➡ gluon imaging
• Strict detector demands
17
• t is conjugate of impact parameter, b
dσ/dt F(b)FourierTransform
|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)
coherent - no saturationincoherent - no saturationcoherent - saturation (bSat)incoherent - saturation (bSat)
PRC 87 024913 (2013)
Thomas Burton SQM 2013
Detector and machine
18
Thomas Burton SQM 2013
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
Thomas Burton SQM 2013
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
Thomas Burton SQM 2013
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
Thomas Burton SQM 2013
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
Thomas Burton SQM 2013
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
Thomas Burton SQM 2013
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
Thomas Burton SQM 2013
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
Thomas Burton SQM 2013
Fourier transform
25
Measure more minima
Better measure of b-dependence
Thomas Burton SQM 2013
Fourier transform
25
Measure more minima
Better measure of b-dependence
Thomas Burton SQM 2013
Fourier transform
25
Measure more minima
Better measure of b-dependence
Thomas Burton SQM 2013
Fourier transform
25
Measure more minima
Better measure of b-dependence
Thomas Burton SQM 2013
Fourier transform
25
Measure more minima
Better measure of b-dependence
Thomas Burton SQM 2013
Fourier transform
25
Measure more minima
Better measure of b-dependence
Thomas Burton SQM 2013
Fourier transform
25
Measure more minima
Better measure of b-dependence
Thomas Burton SQM 2013
Fourier transform
25
Measure more minima
Better measure of b-dependence
Thomas Burton SQM 2013
( )
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
+ +
Thomas Burton SQM 2013
• 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
Thomas Burton SQM 2013
• Gives additional hadron information
‣ extract “transverse-momentum-dependent distributions”: TMDs
27
2) Identify hadrons: decompose flavour dependence
Alexei Prokudin
x = 0.1
SIDIS
Thomas Burton SQM 2013
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
Thomas Burton SQM 2013
Nucleon tomography
29
Generalised Parton Distributions → b-dependence
Thomas Burton SQM 2013
Spin dependence
Nucleon tomography
29
Generalised Parton Distributions → b-dependence
Thomas Burton SQM 2013
Spin dependence
Nucleon tomography
29
PET brain image
Generalised Parton Distributions → b-dependence