The Large Hadron electron Collider - Stony Brook...
Transcript of The Large Hadron electron Collider - Stony Brook...
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The Large Hadron electron Collider
http://cern.ch/lhec
Can we add ep and eA collisions to the existing LHC pp, AA and pA programme?
… towards a full understandingof QCD at high temperatures, baryon and parton densities …
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Brian Cole, Columbia University using (mostly) slides from previous talks
by P. Newman and M. Klein
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Deep Inelastic Scattering [eh ! e’X]e+e-
hh
eh !
!
!
x = Q2
syQ2 = −(k− k ')2
ylab =1−Ee 'Ee
s= 4EeEp
Parton momentum fixed by electron kinematics
Incl. NC (γ,Z) and CC (W±) independent of hadronisation
Rigorous theory: Operator expansion (lightcone)
Parton momentum distributions to be measured in DIS
Collider- HERA: yh=ye : Redundant kinematics
HERA-LHeC-FCC-eh: finest microscopeswith resolution varying like 1/√Q2
X
electromagnetic radius
Finite p Radius
Quarks
QuarkGluonDynamics
?
Stanford
SLAC
FNAL
CERN
HERA
LHeC
FCC-he
100 years of lp scattering
!
5 orders of magnitude
deeper into matter
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DIS and HERAQ2: exchanged boson resolving power
x: fractional momentum of struck quark
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HERAPDF1.5 NNLO (prel.)
exp. uncert.
model uncert. parametrization uncert.
x
xf 2 = 10 GeV2Q
vxu
vxd
0.05)×xS (
0.05)×xg (
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H1 and ZEUS HERA I+II PDF Fit
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HERA Proton parton densities in x range well matched to LHC rapidity plateau … BUT…
- Insufficient lumi for high x
- Lack of Q2 lever-arm for low x gluon
- Assumptions on quarkflavour decomposition
- No deuterons or heavy ionsThursday, June 26, 14
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Conceptual Design Report (July 2012)
630 pages, summarising 5 year workshop commissioned by CERN, ECFA and NuPECC
~200 participants, 69 institutes
Additional material in subsequentupdates:
“A Large Hadron Electron Collider at CERN” [arXiv:1211.4831] “On the Relation of the LHeC and the LHC” [arXiv:1211.5102]
[arXiv:1206.2913]
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Latest & most promising idea to take lepton-hadron physics to the TeV centre-of-mass scale… at high luminosity
Designed to exploitintense hadron beams in high luminosity phase of LHC running from mid 2020s
LHeC Context
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High Q2
" HERA
LHeC
FCC-he175 GeV 60 GeV
Rutherford backscatteringof dozens of TeV e- energy
" ϑh=1o
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Low x
ß 179o
@ 180 GeV.. very low xrequires notthe maximumof Ee
-----------
For x < 10-3 no (average) energy deposition exceeding the electron beam energy
x
HERA
LHeC
FCC-he60 GeV
Very low xreaches directrange ofUHE neutrinophysics !
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Baseline♯ Design (Electron “Linac”)Design constraint: power consumption < 100 MW ! Ee = 60 GeV
• Two 10 GeV linacs, • 3 returns, 20 MV/m• Energy recovery insame structures[CERN plans energy recovery prototype]
• ep Lumi 1033 – 1034 cm-2 s-1
➡ 10 - 100 fb-1 per year ➡ 100 fb-1 – 1 ab-1 total • eD and eA collisions have always been integral to programme• e-nucleon Lumi estimates ~ 1031 (1032) cm-2 s-1 for eD (ePb)
Alternative designs based on electron ring and on higher energy, lower luminosity, linac also exist
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Detector Overview
e p
• Forward / backward asymmetry reflecting beam energies• Present size 14m x 9m (c.f. CMS 21m x 15m, ATLAS 45m x 25m)• ZDC, proton spectrometer integral to design from outset
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DIS: Parton Microscopy
Q2: exchanged boson resolving power x: fractional momentum of struck quark
Only previously studied in collidermode and in ep at HERA (1992-2007)
Proton parton density at Q2 = 10 GeV2 from HERA data alone[HERAPDF1.5 NNLO]
… Low x saturation?10
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LHeC Strategy for making the target blacker
Enhance target `blackness’ by: 1) Probing lower x at fixed Q2 in ep [evolution of a single source] 2) Increasing target matter in eA [overlapping many sources at fixed kinematics … density ~ A1/3 ~ 6 for Pb … worth 2 orders of magnitude in x]
LHeC delivers a 2-pronged approach:
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… Reachingsaturatedregion in both ep & eA according tocurrent models
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Establishing and Characterising SaturationWith 1 fb-1 (1 month at 1033 cm-2 s-1), F2 stat. < 0.1%, syst, 1-3%FL measurement to 8% with 1 year of varying Ee or Ep
• LHeC can distinguish between different QCD-based models for the onset of non-linear dynamics • Unambiguous observation of saturation will be based on tensionbetween different observables e.g. F2 v FL in ep or F2 in ep v eA
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Exclusive / Diffractive Channels and Saturation
1) [Low-Nussinov] interpretation as 2 gluon exchange enhances sensitivity to low x gluon
1) Additional variable t gives access to impact parameter (b) dependent amplitudes
! Large t (small b) probes densest packed part of proton?
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e.g. J/ψ Photoproductione.g. “b-Sat” Dipole model- “eikonalised”: with impact-parameter dependent saturation - “1 Pomeron”: non-saturating
• Significant non-linear effects expected in LHeC kinematic range.
• Data shown are extrapolations of HERA power law fit for Ee = 150 GeV… ! Satn smoking gun?
[2 fb-1]
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eA
Four orders of magnitude increase in kinematic range over previous
DIS experiments.
LHeC as an Electron-ion Collider
• Revolutionise our view of the partonic structure of nuclear matter.
• Study interactions of densely packed, but weakly coupled, partons
• Ultra-clean probe ofpassage of `struck’partons through cold nuclear matter 15
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LHeC-FCC_he: Electron Ion Collider
Precision QCD study of parton dynamics in nucleiInvestigation of high density matter and QGPGluon saturation at low x, in DIS region.
Extension of kinematic range in lAby 4-5 orders of magnitude willchange QCD view on nuclear structure and parton dynamics
May lead to genuine surprises…
- No saturation of xg (x,Q2) ?- Small fraction of diffraction ?- Broken isospin invariance ?- Flavour dependent shadowing ?
Expect saturation of rise at Q2
s ≈ xg αs ≈ c x-λA1/3
LHeC is part of NuPECCslong range plan since 2010LeN ~ 1032 cm-2 s-1
FCC-he
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Relation to the Heavy Ion Programme
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Current Status of Nuclear Parton Densities
[Existing DIS data]
Ri = Nuclear PDF i / (A * proton PDF i)
Valence Sea Gluon
• Complex nuclear effects,not yet fully understood
• Quarks from DIS & DY• Gluon mainly from dAusingle π0 rates
• All partons poorly constrained for x < 10-2
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Complementarity of pA and eA
• New effects likely to be revealed in tensions between eA and pA, AA, ep (breakdown of factorisation)
• Detailed precision understanding likely to come from eA- LHeC offers access to lower x than is realistically achievable
in pA at the LHC- Clean final states / theoretical control to (N)NLO in QCD
eA
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Current Low x Understanding in LHC Ion DataUncertainties in low-x nuclear PDFs preclude precision statements on medium produced in AA (e.g. extent of screeningof c-cbar potential)
Inclusive J/Ψ AA data
η dependence of pPb chargedparticle spectra best describedby shadowing-only models (saturation models too steep?)… progress with pPb, but uncertainties still large, detailedsituation far from clear
Minimum Bias pA data
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Jet production in pA at LHC
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[GeV]T
p
pPb
R +2.1 < y* < +2.8
ATLAS Preliminary
[GeV]T
p
pPb
R +0.8 < y* < +1.2
[GeV]T
p
pPb
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[GeV]T
p
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R -1.2 < y* < -0.8
= 5.02 TeVNNs+Pb p=0.4R, tkanti-
[GeV]T
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+Pb, 0-90%p
EPS09 calculation
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R +0.3 < y* < +0.8
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pPb
R -0.8 < y* < -0.3
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pPb
R -2.1 < y* < -1.2
∫ -1dt = 27.8 nbpPbL
∫ -1dt = 4.0 pbppL
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• Ratio of inclusive p+Pb jet yields to scaled p-p jet cross-sections
• Compared to NLO calculations by Armesto using EPS09 PDFs
• Good (but not perfect) agreement -- nPDF effects are small
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Jet production in p+A at LHC
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• But ratios of jet cross-sections between high- and low-multiplicity events show unexpected behavior at high pT, forward rapidities
[GeV]T
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CP
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ATLASPreliminary
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∫ -1dt = 27.8 nbL = 5.02 TeVNNs+Pb p
=0.4R, tkanti-
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CP
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Jet production in p+A at LHC
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• But ratios of jet cross-sections between high- and low-multiplicity events show unexpected behavior at high pT, forward rapidities• Scales with jet energy (x?) at forward rapidities.
[GeV]T
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CP
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ATLASPreliminary
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CP
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∫ -1dt = 27.8 nbL = 5.02 TeVNNs+Pb p
=0.4R, tkanti-
[GeV]T
pC
P R +2.8 < y* < +3.6
[GeV]T
p
CP
R +1.2 < y* < +2.1
[GeV]T
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0-10%/60-90%
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∫ -1dt = 27.8 nbL = 5.02 TeVNNs+Pb p
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ATLASPreliminary
+3.6 < y* < +4.4+2.8 < y* < +3.6+2.1 < y* < +2.8+1.2 < y* < +2.1+0.8 < y* < +1.2
+0.3 < y* < +0.8-0.3 < y* < +0.3-0.8 < y* < -0.3-1.2 < y* < -0.8-2.1 < y* < -1.2
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R
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Tp
∫ -1dt = 27.8 nbL = 5.02 TeVNNs+Pb p
0-10%
=0.4R, tkanti-
ATLASPreliminary
+3.6 < y* < +4.4+2.8 < y* < +3.6+2.1 < y* < +2.8+1.2 < y* < +2.1+0.8 < y* < +1.2
+0.3 < y* < +0.8-0.3 < y* < +0.3-0.8 < y* < -0.3-1.2 < y* < -0.8-2.1 < y* < -1.2
1.4
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R
40 100 1000 40 100 1000 cosh(<y*>) [GeV]×
Tp
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Jet production in p+A at LHC
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• Correlation between hard and soft production indicates breakdown of factorization• Likely due to correlation between parton x and proton configuration/size➡ need e+p measurements
[GeV]T
p
CP
R +3.6 < y* < +4.4
ATLASPreliminary
[GeV]T
p
CP
R +2.1 < y* < +2.8
[GeV]T
p
CP
R +0.8 < y* < +1.2
[GeV]T
p
CP
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[GeV]T
p
CP
R -1.2 < y* < -0.8
∫ -1dt = 27.8 nbL = 5.02 TeVNNs+Pb p
=0.4R, tkanti-
[GeV]T
pC
P R +2.8 < y* < +3.6
[GeV]T
p
CP
R +1.2 < y* < +2.1
[GeV]T
p
CP
R +0.3 < y* < +0.8
[GeV]T
p
CP
R -0.8 < y* < -0.3
[GeV]T
p
CP
R -2.1 < y* < -1.2
0-10%/60-90%
20-30%/60-90%
40-60%/60-90%
1.4
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CP
R
20 100 800 20 100 800 [GeV]
Tp
∫ -1dt = 27.8 nbL = 5.02 TeVNNs+Pb p
0-10%
=0.4R, tkanti-
ATLASPreliminary
+3.6 < y* < +4.4+2.8 < y* < +3.6+2.1 < y* < +2.8+1.2 < y* < +2.1+0.8 < y* < +1.2
+0.3 < y* < +0.8-0.3 < y* < +0.3-0.8 < y* < -0.3-1.2 < y* < -0.8-2.1 < y* < -1.2
1.4
1.0
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CP
R
40 100 1000 40 100 1000 cosh(<y*>) [GeV]×
Tp
∫ -1dt = 27.8 nbL = 5.02 TeVNNs+Pb p
0-10%
=0.4R, tkanti-
ATLASPreliminary
+3.6 < y* < +4.4+2.8 < y* < +3.6+2.1 < y* < +2.8+1.2 < y* < +2.1+0.8 < y* < +1.2
+0.3 < y* < +0.8-0.3 < y* < +0.3-0.8 < y* < -0.3-1.2 < y* < -0.8-2.1 < y* < -1.2
1.4
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R
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Tp
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p+Pb charged particle RpPb
• Puzzle from the Hard Probes 2013 conference:– CMS observes unexpected enhancement in high-pT charged
particle yield in p+Pb relative to p+p– Seen by ATLAS, not by ALICE
• Origin?– If the effect is real, likely due to poorly understood interplay
between nPDF modifications & FF. 25
[GeV/c]T
p1 10 210
pPb
R
0
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0.60.8
1
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|<1 CMηCMS Charged Particles |
y=00πEPS09 fDSS NLO
=6.9collN
CMS Preliminary = 5.02 TeVNNspPb
Helenius et.al, JHEP 1207 (2012) 073
[GeV]T
p10
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pPb
R
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2.2 PreliminaryATLAS
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p+Pb L=5.02 TeV
NNs
0-90%
-1<y*<1
Inclusive charged particle production in p+A at LHC
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Further Surprises from pA Data• “Ridge” observed in high multiplicity pPb collisions - due to saturation?
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Further Surprises from pA Data• “Ridge” observed in high multiplicity pPb collisions - due to saturation? • Or due to collective dynamics similar to that observed in Pb+Pb?
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Further Surprises from pA Data• “Ridge” observed in high multiplicity pPb collisions - due to saturation? • Or due to collective dynamics similar to that observed in Pb+Pb?
• Data suggest the latter
• My prediction: we will observe effects of strong coupling in e+p/A final states and can study with more control than in p+A
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• Simulated LHeC ePb F2 measurementhas huge impact on uncertainties
• Most striking effect for sea & gluons
• High x gluon uncertainty still large
Impact of eA F2 LHeC data
Valence
Sea
Glue [Example pseudo-datafrom single Q2 Value]
[Effects on EPS09nPDF fit] 29
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Exclusive Diffraction in eAExperimentally clear signatures and theoretically cleanly calculable saturation effects in coherent diffraction case (eA ! eVA)
Experimentalseparation ofincoherent diffraction based mainlyon ZDC… potential saturation smoking gun?30
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In-medium radiation and hadronisation effects
Ratio of π0 fragn functions Pb / p (Armesto et al.)
ν= struck parton energy in target rest frame
Small ν: Hadron formationmay be inside. Hadronic energy loss
Large ν: Hadronisation beyond medium. Partonic energy loss
How do virtual parton probes lose Virtuality and colour to hadronise?
31LHeC most sensitive to partonic loss. ! Baseline `cold matter’ input to use energy loss mechanisms to characterise QGP Thursday, June 26, 14
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Some other LHeC eA Studies …
Impact of eA charm &beauty data
Forward π0
production &fragmentation
Jet photoproduction
Inclusive ep diffractionv nuclearshadowing
Many more processes and observables still to be investigated
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Summary / Outlook
•Many reasons that new, high-luminosity e+p and e+A measurements are needed.
• LHeC is high-energy option complementary to EIC- 3-4 orders of magnitude in nPDF kinematic range
- New non-linear QCD dynamics of low x parton saturation? - Valuable input for heavy ion physics program at LHC
• Conceptual Design Report available.
• Ongoing work … - Further physics motivation - Detector / simulation, - Superconducting RF, ERL, machine
• Timeline?... Optimal impact by running in High Lumi LHC Phase
[More at http://cern.ch/lhec]
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Herwig Schopper (Chair IAC) at Chavannes in the Panel Discussion with the CERN Directorate
Clarification and Tradition
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Summary of the LHeC Physics ProgrammeCDR, arXiv:1211.4831 and 1211.5102 http://cern.ch/lhec
New since CDR: Higgs discovered, 1033 !1034, and the FCC horizon – much to do
Truth is stranger than fiction, but it is because fiction is obliged to stick to possibilitiesMark Twain, cited by Stan Brodsky at Chavannes
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… with thanks to Nestor Armesto, Max Klein, Anna Stasto and many experimentalist, theorist & accelerator scientist colleagues …
LHeC study group …
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