Presentation on theme: "Future High Energy Electron – Hadron Scattering: The LHeC Project"— Presentation transcript:
1 Future High Energy Electron – Hadron Scattering: The LHeC Project Lepton-hadroncollider for the2020s, based onthe high lumi LHCCan we add ep and eAcollisions to the existing LHCpp, AA and pA programme?Paul NewmanBirmingham UniversityJammu, 8 September 2013
2 Conceptual Design Report (July 2012) [arXiv: ]630 pages, summarising 5 year workshop commissioned by CERN,ECFA and NuPECC~200 participants, 69 institutesAdditional material in subsequentupdates:“A Large Hadron Electron Collider at CERN” [arXiv: ]“On the Relation of the LHeC and the LHC” [arXiv: ]
3 DIS and HERA Q2: exchanged boson resolving power x: fractional momentumof struck quarkHERA Proton parton densities in x range well matched to LHC rapidity plateau … BUT…- Insufficient lumi for high xLack of Q2 lever-armfor low x gluonAssumptions on quarkflavour decompositionNo deuterons or heavy ions
4 Current PDFs & LHC Current uncertainties due to PDFs for particles on LHCrapidity plateau (NLO):- Most precise for quark initiated processes around EW scale- Gluon initiated processes lesswell knownAll uncertainties explode for largest masses
5 Beyond HERA: LHeC Context - LHeC is latest & most promising idea to take lepton-hadron physics to the TeV centre of mass scale- High luminosity:cm-2 s-1Runs simultaneouswith ATLAS / CMSin post-LS3 HL-LHC period
6 Baseline♯ Design (Electron “Linac”) Design constraint: power consumption < 100 MW Ee = 60 GeVTwo 10 GeV linacs,3 returns, 20 MV/mEnergy recovery insame structures[CERN plans energyrecovery prototype]ep Lumi 1033 – 1034 cm-2 s-1fb-1 per year100 fb-1 – 1 ab-1 totaleD and eA collisions have always been integral to programmee-nucleon Lumi estimates ~ 1031 (1032) cm-2 s-1 for eD (ePb)♯ Alternative designs based on electron ring and on higher energy, lowerluminosity, linac also exist
8 LHeC Detector Acceptance Requirements Access to Q2=1 GeV2 in ep mode for all x > 5 x 10-7 requires scatteredelectron acceptance to 179oSimilarly, need 1o acceptancein outgoing proton directionto contain hadrons at high x(essential for good kinematicreconstruction)
9 Detector OverviewepForward / backward asymmetry reflecting beam energiesPresent size 14m x 9m (c.f. CMS 21m x 15m, ATLAS 45m x 25m)ZDC, proton spectrometer integral to design from outset
10 Assumed Systematic Precision In the absence of a detailed simulation set-up, simulated `pseudo-data’ produced with reasonable assumptions on systematics (typically 2x better than H1 and ZEUS at HERA).
11 PDF Constraints at LHeC Full simulation of inclusive NC and CC DIS data, includingsystematics NLO DGLAP fit using HERA technology…GluonSea… impact at low x (kinematic range) and high x (luminosity)… precise light quark vector, axial couplings, weak mixing angle… full flavour decompositiond valence
12 Do we need to Care about High x? Ancient history (HERA, Tevatron)- Apparent excess in large ET jets at Tevatron turned out to be explained by too low high x gluon density in PDF sets- Confirmation of (non-resonant) new physics near LHC kinematic limit relies on breakdown of factorisation between ep and ppPRL 77 (1996) 438Searches near LHC kinematic boundary may ultimately belimited by knowledge of PDFs (especially gluon as x 1)
13 e.g. High Mass 2 Gluino Production - Signature is large invariant massExpected SM background (e.g. gg gg)poorly known for s-hat > 1 TeV.Both signal & backgrounduncertainties driven byerror on gluon density …Essentially unknown formasses much beyond 2 TeVSimilar conclusions forother non-resonant LHCsignals involving high xpartons (e.g. contactinteractions signal inDrell-Yan)
14 PDF Uncertainties for Higgs Physics Projected ExperimentalUncertaintiesTheory Cross SectionUncertainties(125 GeV HiggsJ Campbell, ICHEP’12)Similarly fermionic modes (bbbar, ccbar)… tests of Standard Model in Higgs sector may become limited by knowledge of PDFs in HL-LHC era[Dashed regions= scale & PDFcontributions
15 A Direct Higgs Study Dominant charged current process has similar cross section to linear e+e- colliderStudy of H bbbar in genericsimulated LHC detectormH = 120 GeV,LHeC with 10fb-1… + 90% lepton polarisation enhances signal by factor 1.9… + With 1034 luminosity, x10 more data ~5000 Ee = 60 GeV … Hbbbar coupling to ~ 1%.
16 Direct Sensitivity to New Physics The (pp) LHC has much better discovery potential than LHeC (unless Ee increases to >~500 GeV and 1034 lumi achieved)e.g. Expected quarkcompositeness limitsbelow m at LHeC… big improvement onHERA, but already beatenby LHCLHeC is competitive with LHC in cases where initialstate lepton is an advantage and offers cleaner final states~eq~0
17 Cross Sections and Rates for Heavy Flavours HERA 27.5 x 920CharmBeautyccsW cbW tttbar[1010 / 10 fb-1][108 / 10 fb-1][4.105 / 10 fb-1][105 / 10 fb-1][103 / 10 fb-1]c.f. luminosity of ~10 fb-1 per year …
18 Low-x Physics and Parton Saturation [HERAPDF1.6 NNLO]Somewhere & somehow, the low x growth of cross sectionsmust be tamed to satisfy unitarity … non-linear effects… new high density, small coupling parton regime of non-linear parton evolution dynamics (e.g. Colour Glass Condensate)? …… gluon dynamics confinement and hadronic mass generation
19 LHeC Strategy for making the target blacker LHeC delivers a 2-pronged approach: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]… Reachingsaturatedregion inboth ep & eAaccording tocurrent models
20 Establishing and Characterising Saturation With 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 EpLHeC can distinguish between different QCD-based models for the onset of non-linear dynamicsUnambiguous observation of saturation will be based on tensionbetween different observables e.g. F2 v FL in ep or F2 in ep v eA
21 Exclusive / Diffractive Channels and Saturation [Low-Nussinov] interpretation as 2 gluon exchange enhances sensitivity to low x gluonAdditional variable t gives access to impact parameter (b) dependent amplitudes Large t (small b) probes densestpacked part of proton?
22 e.g. J/y Photoproduction e.g. “b-Sat” Dipole model- “eikonalised”: with impact-parameterdependent saturation- “1 Pomeron”: non-saturatingSignificant non-lineareffects expected in LHeCkinematic range.Data shown areextrapolations ofHERA power law fitfor Ee = 150 GeV… Satn smoking gun?[2 fb-1]
23 LHeC as an Electron-ion Collider Four orders of magnitude increasein kinematic range over previousDIS experiments.Revolutionise ourview of the partonic structure ofnuclear matter.Study interactions of densely packed, but weakly coupled, partonsUltra-clean probe ofpassage of `struck’partons through cold nuclear mattereA
25 Current Status of Nuclear Parton Densities Complex nuclear effects,not yet fully understoodQuarks from DIS & DYGluon mainly from dAusingle p0 ratesAll partons poorlyconstrained for x < 10-2[ExistingDIS data]Ri = Nuclear PDF i / (A * proton PDF i)ValenceSeaGluon
26 Current Low x Understanding in LHC Ion Data Inclusive J/Y AA dataUncertainties in low-x nuclearPDFs preclude precisionstatements on medium producedin AA (e.g. extent of screeningof c-cbar potential)Minimum Bias pA datah dependence of pPb chargedparticle spectra best describedby shadowing-only models(saturation models too steep?)… progress with pPb, butuncertainties still large, detailedsituation far from clearPbp
27 Impact of eA F2 LHeC data Simulated LHeC ePb F2 measurement has huge impact on uncertaintiesMost striking effect for sea & gluonsHigh x gluon uncertainty still largeValenceSeaGlue[Examplepseudo-datafrom singleQ2 Value][Effectson EPS09nPDF fit]
28 Summary and Outlook LHC is new world for p-p physics (even more for heavy ion) physicsConceptual Design Report available.Timeline?... Optimalimpact by running inHigh Lumi LHC PhaseOngoing work …- Physics motivation- Detector / simulation- Superconducting RF,ERL, machine …More at:-- CDR [arXiv: ]- `Dig Deeper’,Newman & Stasto,Nature Physics 9 (2013) 448
29 … with thanks to Nestor Armesto, Max Klein, Anna Stasto and many experimentalist, theorist& accelerator scientist colleagues …LHeC study group …
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