LPCC: LHeC miniworkshop CERN, April 18th 2013lhec.web.cern.ch/sites/lhec.web.cern.ch/files/armesto.lpcc__0.pdf · Small x and saturation: QCD radiation of partons when x decreases

��e

LHeC - Low x Kinematics

10-1

1

10

102

10-7

10-6

10-5

x

Q2/G

eV

2

x-610 -510 -410 -310 -210 -110 1

)2 (G

eV2

Q-110

1

10

210

310

410

510

610 )2(x,Q2,Anuclear DIS - F

Proposed facilities:

LHeC

Fixed-target data:

NMC

E772

E139

E665

EMC

(Pb, b=0 fm)2sQ

perturbative

non-perturbative

(70 GeV - 2.75 TeV)

e-Pb (LHeC)

Electron-ion physics with

the LHeCNéstor Armesto

Departamento de Física de Partículas and IGFAEUniversidade de Santiago de Compostela

[email protected]

for the LHeC Study group, http://cern.ch/lhec 1

LPCC: LHeC miniworkshopCERN, April 18th 2013

mailto:[email protected]

mailto:[email protected]

http://cern.ch/lhec

http://cern.ch/lhec

Contents:

Electron-ion physics with the LHeC. 2

I. Introduction.

2. eA at the LHeC and comparison to the LHC.

3. Physics case in eA:● Inclusive measurements and nuclear PDFs.● Diffraction.● Final states: dynamics of QCD radiation and hadronization.

4. Summary and outlook.

CDR, arXiv:1206.2913, J. Phys. G 39 (2012) 075001;arXiv:1211.4831; arXiv:1211.5102

http://arxiv.org/abs/arXiv:1206.2913






nPDFs:

3

Yellow Report on Hard Probes, 2004

● Lack of data ⇒ models give vastly different

results for the nuclear glue at small scales and x: problem for benchmarking in HIC.

● Available DGLAP analysis at NLO show large uncertainties at small scales and x.

-610 -510 -410 -310 -210 -110 10

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

x

)2(x,1.69 GeVvu

PbR

EPS09nDSHKN07

DSSZFGS10

)2=4 GeV2(Q

-610 -510 -410 -310 -210 -110 10

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

x

)2(x,1.69 GeVuPbR

-610 -510 -410 -310 -210 -110 10

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

x

)2(x,1.69 GeVgPbR

-610 -510 -410 -310 -210 -110 10

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

x

)2(x,100 GeVvu

PbR

EPS09nDSHKN07

DSSZFGS10

-610 -510 -410 -310 -210 -110 10

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

x

)2(x,100 GeVuPbR

-610 -510 -410 -310 -210 -110 10

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

x

)2(x,100 GeVgPbR

NLO analysis

Electron-ion physics with the LHeC: 1. Introduction.

R =fi/AAfi/p

≈ measuredexpected if no nuclear effects

nPDFs:

3

Yellow Report on Hard Probes, 2004

● Lack of data ⇒ models give vastly different

results for the nuclear glue at small scales and x: problem for benchmarking in HIC.

● Available DGLAP analysis at NLO show large uncertainties at small scales and x.

-610 -510 -410 -310 -210 -110 10

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

x

)2(x,1.69 GeVvu

PbR

EPS09nDSHKN07

DSSZFGS10

)2=4 GeV2(Q

-610 -510 -410 -310 -210 -110 10

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

x

)2(x,1.69 GeVuPbR

-610 -510 -410 -310 -210 -110 10

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

x

)2(x,1.69 GeVgPbR

-610 -510 -410 -310 -210 -110 10

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

x

)2(x,100 GeVvu

PbR

EPS09nDSHKN07

DSSZFGS10

-610 -510 -410 -310 -210 -110 10

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

x

)2(x,100 GeVuPbR

-610 -510 -410 -310 -210 -110 10

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

x

)2(x,100 GeVgPbR

NLO analysis

Inclusive J/ψ, 1202.1383Electron-ion physics with the LHeC: 1. Introduction.

R =fi/AAfi/p

≈ measuredexpected if no nuclear effects

4

Small x and saturation:

● QCD radiation of partons when x decreases leads to a large number of partons (gluons), provided each parton evolves independently (linearly, Δ[xg] ∝ xg).● This independent evolution breaks at high densities (small x or high mass number A): non-linear effects (gg→g, Δ[xg] ∝ xg - k(xg)2).


xGA(x,Q2s)

�R2AQ2

s

� 1 =⇥ Q2s ⇤ A1/3x⇥�0.3

4

Small x and saturation:

● QCD radiation of partons when x decreases leads to a large number of partons (gluons), provided each parton evolves independently (linearly, Δ[xg] ∝ xg).● This independent evolution breaks at high densities (small x or high mass number A): non-linear effects (gg→g, Δ[xg] ∝ xg - k(xg)2).


xGA(x,Q2s)

�R2AQ2

s

� 1 =⇥ Q2s ⇤ A1/3x⇥�0.3

DGLAP

BFKL

BK/JIMWLK

DILUTEREGION

DENSEREGION

saturat

ion scale

Q s(x)

ln Q

ln 1

/x

ln ,QCD

non-

pert

urba

tive

regi

on

DILUTEREGION

DENSEREGION

ln A

ln 1

/x

eAep

[fixed Q]

Status of small-x physics:● Three pQCD-based alternatives to describe small-x ep and eA data (differences at moderate Q2(>Λ2QCD) and small x):→ DGLAP evolution (fixed order perturbation theory).→ Resummation schemes: BFKL, CCFM, ABF, CCSS.→ Saturation (CGC, dipole models).● Non-linear effects (unitarity constraints) are density effects: where? ⇒ two-pronged approach at the LHeC: ↓ x / ↑ A.

5Electron-ion physics with the LHeC: 1. Introduction.

Relevance for the HI program:

6Electron-ion physics with the LHeC: 1. Introduction.


6

● Nuclear wave function at small x: nuclear structure functions.



6


● Particle production at the very beginning: which factorisation in eA?

● How does the system behave as ∼ isotropised so fast?: initial conditions for plasma formation to be studied in eA.



6


● Particle production at the very beginning: which factorisation in eA?

● How does the system behave as ∼ isotropised so fast?: initial conditions for plasma formation to be studied in eA.


● Probing the medium through energetic particles (jet quenching etc.): modification of QCD radiation and hadronization in the nuclear medium.

Contents:


I. Introduction.











Accelerator:

8

eD: LeN=ALeA>∼3×1031 cm-2s-1

Electron-ion physics with the LHeC: 2. eA at the LHeC and comparison to the LHC.

CDR numbers for luminosity, to be

considered now as lower bounds.

√s≃0.8 TeV/nucleon

Luminosity per nucleon

Kinematics:

9Electron-ion physics with the LHeC: 2. eA at the LHeC and comparison to the LHC.Black: HERA Green:100+20

Q2sat,GB

2081/3Q2sat,GB

● Small-x demands 1 degree acceptance.● Higher luminosity would benefit high-x and Q2 studies.

Kinematics:

9Electron-ion physics with the LHeC: 2. eA at the LHeC and comparison to the LHC.Black: HERA Green:100+20

Q2sat,GB

2081/3Q2sat,GB

● Small-x demands 1 degree acceptance.● Higher luminosity would benefit high-x and Q2 studies.

x-610 -510 -410 -310 -210 -110 1

)2 (G

eV2

Q

-110

1

10

210

310

410

510



LHeCFixed-target data:

NMC

E772

E139

E665

EMC

(Pb, b=0 fm)2sQ

perturbative

non-perturbative

(70 GeV - 2.75 TeV)

e-Pb (LHeC)

LHC vs. LHeC:

10x

-610 -510 -410 -310 -210 -110 1

)2 (G

eV2

Q

-210

-110

1

10

210

310

410

510 : QUltra-peripheral Q (|y| < 2.5)ΥLHC

(|y| < 2.5)ΨLHC J/

Nuclear DIS & DY data:NMC (DIS)SLAC-E139 (DIS)FNAL-E665 (DIS)EMC (DIS)FNAL-E772 (DY)

(Pb, b=0 fm)2sQ

perturbative

non-perturbative

PbPb@LHC

Ax-710 -610 -510 -410 -310 -210 -110 1

)2 (G

eV2

Q

1

10

210

310

410

510

610

710

810

(x)2sat,PbQ

PresentDIS+DY

p+Pb LHC (7 TeV+2.75 TeV)

Present nuclear DISand Drell-Yan in p+A

= 6laby

= 4laby

= 2laby

= 0laby

pPb@LHC


x-610 -510 -410 -310 -210 -110 1

)2 (G

eV2

Q

-110

1

10

210

310

410

510



LHeC

Fixed-target data:

NMC

E772

E139

E665

EMC

(Pb, b=0 fm)2sQ

perturbative

non-perturbative

(70 GeV - 2.75 TeV)

e-Pb (LHeC)

ePb@LHeC

LHC vs. LHeC:

10

● The LHeC will explore a region overlapping with the LHC:➜ in a cleaner experimental setup;➜ on firmer theoretical grounds.

x -610 -510 -410 -310 -210 -110 1

)2 (G

eV2

Q

-210

-110

1

10

210

310

410


(|y| < 2.5)ΨLHC J/


(Pb, b=0 fm)2sQ

perturbative

non-perturbative

PbPb@LHC

Ax-710 -610 -510 -410 -310 -210 -110 1

)2 (G

eV2

Q

1

10

210

310

410

510

610

710

810

(x)2sat,PbQ

PresentDIS+DY



= 6laby

= 4laby

= 2laby

= 0laby

pPb@LHC


x-610 -510 -410 -310 -210 -110 1

)2 (G

eV2

Q

-110

1

10

210

310

410

510



LHeC

Fixed-target data:

NMC

E772

E139

E665

EMC

(Pb, b=0 fm)2sQ

perturbative

non-perturbative

(70 GeV - 2.75 TeV)

e-Pb (LHeC)

ePb@LHeC

● PbPb:➜ EW bosons.➜ VMs in UPCs.➜ Ridge.➜ ...

● pPb:➜ Charged particles.➜ Ridge.➜ Flow.➜ Back-to-back correlations, central-forward and forward-forward?➜ EW bosons, DY?➜ VMs, HF?➜ UPCs?➜ Jets and interjet activity?➜ ...

LHC studies:

11






LHC studies:

11




ALICE, 1210.3615

ALICE, 1210.4520● PbPb:➜ EW bosons.➜ VMs in UPCs.➜ Ridge.➜ ...




LHC studies:

11




CMS, 1210.5482

ALICE, 1212.2001

ATLAS, 1212.5198





LHC studies:

11




ATLAS, 1303.2084





LHC studies:

11




ATLAS, 1303.2084



● The existence of collective effects in pPb is somewhat unexpected.● Are they really final state? Do they exist also in eA?

Contents:


I. Introduction.











eA inclusive: comparison

13

● Good precision can be obtained for F2(c,b) and FL at small x (Glauberized 3-5 flavor GBW model, NA ’02).

F2cPb F2bPb

-510 -410 -310 -210 -1100

0.2

0.4

0.6

0.8

1

1.2

x

)2(x,5 GeVLF

PbR

EPS09nDSHKN07

FGS10AKST

Data: LHeC-510 -410 -310 -210 -110

0

0.2

0.4

0.6

0.8

1

1.2

x

)2(x,5 GeV2F

PbR

EPS09nDSHKN07

DSSZFGS10AKST

Data: LHeC

Electron-ion physics with the LHeC: 3. Physics case in eA.

Note the

scale!!!

Not optimized!

Nuclear PDFs at small x:

14

● F2 data substantially reduce the uncertainties in DGLAP analysis; inclusion of charm, beauty (new!); and FL (new!) also give constraints.



14


0.20.40.60.81.01.21.4

0.20.40.60.81.01.21.4

0.00.20.40.60.81.01.21.4

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

Q2=100 GeV2

Q2=1.69 GeV2

EPS09NLOFit 1

EPS09NLOFit 1

Pb Pb Pb

(,

2 =100GeV

2 )Pb

(,

2 =1.69GeV

2 )Pb

F2 only

Valence

Sea

Glue



14


0.20.40.60.81.01.21.4

0.20.40.60.81.01.21.4

0.00.20.40.60.81.01.21.4

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

Q2=100 GeV2

Q2=1.69 GeV2

EPS09NLOFit 1

EPS09NLOFit 1

Pb Pb Pb

(,

2 =100GeV

2 )Pb

(,

2 =1.69GeV

2 )Pb

F2 only

Valence

Sea

GlueF2 + F2c,b + FL

F2 only


Diffraction in ep and shadowing:

15

e

● Diffraction is linked to nuclear shadowing through basic QFT (Gribov): eD to test and set the ‘benchmark’ for new effects.

1106.2019


Diffraction in ep and shadowing:

15

e

● Diffraction is linked to nuclear shadowing through basic QFT (Gribov): eD to test and set the ‘benchmark’ for new effects.

1106.2019


Elastic VM production in eA:

16

● For the coherent case, predictions available.

● Challenging experimental problem (neutron tagging in ZDC?).

coherent

incoherent

!*A " J/# A

W (GeV)

1/A

2 d

$/d

t (

µb

/GeV

2)

0

0.5

1

1.5

2

2.5

0 200 400 600 800 1000

Saturationeffects


Transverse scan: elastic VM

17

● t-differential measurements give a gluon tranverse mapping of the hadron/nucleus.


Transverse scan: elastic VM

17

● t-differential measurements give a gluon tranverse mapping of the hadron/nucleus.

● Large extent in t with good precision.● Sizable saturation effects expected.


Dihadron azimuthal decorrelation:

18

● Dihadron azimuthal decorrelation:currently discussed at RHIC assuggestive of saturation.● At the LHeC it could be studied far from the kinematical limits.

Albacete-Marquet ’10 pTlead>3 GeVpTass>2 GeVzlead=zass=0.3

y=0.7Q2=4 GeV2


xA<<xp

ΔΦ=Φ12

19

● Low energy: hadronization inside → formation time, (pre-)hadronic absorption,...

● LHeC: dynamics of QCD radiation and hadronization.● Most relevant for particle production off nuclei and for QGP analysis in HIC.

Radiation and hadronization:

● High energy: partonic evolution altered in the nuclear medium.


∼ratio of FFs A/pz=phadr/pparton

ν=Estruck partonhadron rest frame

19

● Low energy: hadronization inside → formation time, (pre-)hadronic absorption,...

● LHeC: dynamics of QCD radiation and hadronization.● Most relevant for particle production off nuclei and for QGP analysis in HIC.


● High energy: partonic evolution altered in the nuclear medium.

Electron-ion physics with the LHeC: 3. Physics case in eA.Fixed-target LHeC

∼ratio of FFs A/pz=phadr/pparton

ν=Estruck partonhadron rest frame

Jets:

20

● Jets: large ET even in eA.● Useful for studies of parton dynamics in nuclei (hard probes), and for photon structure.● Background subtraction, detailed reconstruction pending.


DGLAP

BFKL

BK/JIMWLK

DILUTEREGION

DENSEREGION

saturat

ion scale

Q s(x)

ln Q

ln 1

/x

ln ,QCD

non-

pert

urba

tive

regi

on

DILUTEREGION

DENSEREGION

ln A

ln 1

/x

eAep

[fixed Q]

Summary:

21

● At an LHeC@CERN:➜ High-precision tests of collinear factorization(s) and determination of PDFs.➜ Unprecedented access to small x in p and A.➜ Novel sensitivity to physics beyond standard pQCD.➜ Stringent tests of QCD radiation and hadronization.➜ Transverse scan of the hadron/nucleus at small x.➜ ... with implications on our understanding of QGP.

● The LHeC will answer the question of saturation/non-linear dynamics. For that, ep AND eA essential!!!

Electron-ion physics with the LHeC.

Outlook:

22

● With CERN and NuPECC mandate to further motivate the physics case and produce a TDR around 2015, several items have to be done/improved:

➜ Refine DGLAP fits with flavour decomposition (include neutrino data, relax assumptions) and optimized FL scenarios, and LHC data.➜ Monte Carlo generators!!!➜ Studies on diffraction: separation of coherent from incoherent, ndPDFs, dijets,...➜ Large x, EW bosons.➜ Nuclear GPDs: nuclear DVCS etc.➜ eD.➜ Jet reconstruction, angular decorrelation...➜ ...

➝ Cooperation with EIC in some of these items desirable.Electron-ion physics with the LHeC.

Outlook:

22




Thanks for your attention!

Backup:

23Electron-ion physics with the LHeC.

LHC vs. LHeC:

24

ePb@LHeC

x -610 -510 -410 -310 -210 -110 1

)2 (G

eV2

Q

-210

-110

1

10

210

310

410


(|y| < 2.5)ΨLHC J/


(Pb, b=0 fm)2sQ

perturbative

non-perturbative

PbPb@LHC

Ax-710 -610 -510 -410 -310 -210 -110 1

)2 (G

eV2

Q

1

10

210

310

410

510

610

710

810

(x)2sat,PbQ

PresentDIS+DY



= 6laby

= 4laby

= 2laby

= 0laby

pPb@LHC


LHC vs. LHeC:

24

● The LHeC will explore a region overlapping with the LHC:➜ in a cleaner experimental setup;➜ on firmer theoretical grounds.

ePb@LHeC

x -610 -510 -410 -310 -210 -110 1

)2 (G

eV2

Q

-210

-110

1

10

210

310

410


(|y| < 2.5)ΨLHC J/


(Pb, b=0 fm)2sQ

perturbative

non-perturbative

PbPb@LHC

Ax-710 -610 -510 -410 -310 -210 -110 1

)2 (G

eV2

Q

1

10

210

310

410

510

610

710

810

(x)2sat,PbQ

PresentDIS+DY



= 6laby

= 4laby

= 2laby

= 0laby

pPb@LHC


LHC studies:

25




LHC studies:

25



CMS, 1201.3093

CMS, 1205.6334

ATLAS, 1210.6486



CMS, 1102.5435


LHC studies:

25



ALICE, 1209.3715




LHC studies:

25



CMS, 1105.2438

ALICE, 1109.2501




LHC studies:

25




ALICE, 1210.3615

ALICE, 1210.4520● PbPb:➜ EW bosons.➜ VMs in UPCs.➜ Ridge.➜ ...


LHC studies:

25




CMS, 1210.5482

ALICE, 1212.2001

ATLAS, 1212.5198



LHC studies:

25




ATLAS, 1303.2084



LHC studies:

25




ATLAS, 1303.2084



● The existence of collective effects in pPb is somewhat unexpected.● Are they really final state? Do they exist also in eA?

LHeC scenarios:

26

● For FL: 10, 25, 50 + 2750 (7000); Q2≤sx; Lumi=5,10,100 pb-1 respectively; charm and beauty: same efficiencies in ep and eA.

10-310-310-3

I 50 3.5 Ca 5⋅10-3 ? 5⋅10-3 ? ? eCa

For F2


Note: FL in eA

27

● FL traces the nuclear effects on the glue (Cazarotto et al ’08).● Uncertainties in the extraction of F2 due to the unknown nuclear effects on FL of order 5 % (larger than expected stat.+syst.) ⇒

measure FL or use the reduced cross section (but then ratios at two energies...).

NA, Paukkunen, Salgado, Tywoniuk, ‘10

Electron-ion physics with the LHeC: 3 Physics case in eA.

Elastic VM production in ep:

28

● Elastic J/ψ production appears as a candidate to signal saturation effects at work!!!

p p!

!r

!bx x!

z

(1 " z)!r1 " z

"# E

Linear, sensitivity to (xg)2.

Non-linear, saturation.


Diffractive DIS on nuclear targets:

29

● Challenging experimental problem, requires Monte Carlo simulation with detailed understanding of the nuclear break-up.

● For the coherent case, predictions available.

0

0.05

0.1

0.15

10 -2

xIP=0.00001Q2=3 GeV2x IP

F 2D

10 -2

xIP=0.0001Q2=3 GeV2

10 -3 10 -1

xIP=0.001Q2=3 GeV2

10 -3 10 -1

xIP=0.01Q2=3 GeV2

00.020.040.060.08

0.1

10 -1 10 -1

xIP=0.0001Q2=30 GeV2

10 -2

xIP=0.001Q2=30 GeV2

10 -2

xIP=0.01Q2=30 GeV2

00.020.040.060.08

0.1

10 -1 10 -1 10 -2

xIP=0.001Q2=300 GeV2

10 -2

xIP=0.01Q2=300 GeV2

00.010.020.030.040.05

10-1

H1 fit BipsatbCGC

10-1

Pb

10-1

10-1

xIP=0.01Q2=3000 GeV2

βElectron-ion physics with the LHeC: 3 Physics case in eA.

5o<θπ<25o, xπ>0.01

Daleo et al. ’04Data: H1 ’04

formation timeeffects


30

● Large (NLO) yields at small-x (H1 cuts, 3 times higher if relaxed).● Nuclear effects in hadronization at small ν (LO plus QW, Arleo ’03).



30


0

1500

3000

4500

6000

0

200

400

600

d!

"/d

xB

(nb

)

2 # Q2 # 8 GeV

2MSTW-DSS (ep)

MSTW-DSS (ePb)

nDS-DSS (ePb)

nDS-nFF (ePb)

EPS09-DSS (ePb)

60+7000

60+2750

8 # Q2 # 20 GeV

2

xBj

20 # Q2 # 70 GeV

2

pT $ 3.5 GeV0

70

140

10-6

10-5

10-4

d!

"/d

pT

(pb

/GeV

)

2 # Q2 # 4.5 GeV

2

1

10

MSTW-DSS

MSTW-DSS (Pb)

nDSS-DSS (Pb)

nDS-nFF (Pb)

EPS-DSS (Pb)

60+7000

60+2750

4.5 # Q2 # 15 GeV

2

1

10

pT (GeV)

15 # Q2 #70 GeV

2

1

10

3 4 5 6 7 8 9 10 15



30



Outlook:

31




Outlook:

31




NuPECC LRP

Outlook:

31




Outlook:

31




Thanks for your attention!

Documents

LPCC: LHeC miniworkshop CERN, April 18th 2013lhec.web.cern.ch/sites/lhec.web.cern.ch/files/armesto.lpcc__0.pdf · Small x and saturation: QCD radiation of partons when x decreases