Central Exclusive Production (CEP) at LHCb Ronan McNulty (UCD - - PowerPoint PPT Presentation

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Central Exclusive Production (CEP) at LHCb Ronan McNulty (UCD - - PowerPoint PPT Presentation

Apr 11, 2023 420 likes •1.02k views

Central Exclusive Production (CEP) at LHCb Ronan McNulty (UCD Dublin) on behalf of the LHCb collaboration Meson 2018 12 June 2018, Krakow. 1 R. McNulty, CEP at LHCb Overview 1. Central Exclusive Physics (CEP) 2. LHCb and HeRSCheL Detector 3.

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Central Exclusive Production (CEP) at LHCb

Ronan McNulty (UCD Dublin)

  • n behalf of the LHCb collaboration

Meson 2018 12 June 2018, Krakow.

  • R. McNulty, CEP at LHCb

1

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Overview

  • 1. Central Exclusive Physics (CEP)
  • 2. LHCb and HeRSCheL Detector
  • 3. Analyses:
  • pp at 13 TeV
  • PbPb at √sNN = 5 TeV
  • pPb and Pb-p at 8 TeV
  • 4. Physics reach for CEP
  • R. McNulty, CEP at LHCb

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NEW

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Elastic scattering

p p

σelastic ≈ 35% σdiffractive ≈ 10% σinelastic ≈ 55%

  • R. McNulty, CEP at LHCb

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σelastic ≈ 35% σdiffractive ≈ 10% σinelastic ≈ 55%

Elastic scattering

p p It’s QCD – but not as we normally see it. It’s colour-free

0+

Pomeron (soft)

  • R. McNulty, CEP at LHCb

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σelastic ≈ 35% σdiffractive ≈ 10% σinelastic ≈ 55%

Elastic scattering

p p It’s QCD – but not as we normally see it. It’s colour-free

0+

Pomeron (soft)

  • R. McNulty, CEP at LHCb

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Theory Experiment Future J/ψ , ϒ χc J/ψ J/ψ

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σelastic ≈ 35% σdiffractive ≈ 10% σinelastic ≈ 55%

Diffraction

p p

0+

Pomeron (hard and soft)

No activity “rapidity gap”

  • R. McNulty, CEP at LHCb

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σelastic ≈ 35% σdiffractive ≈ 10% σinelastic ≈ 55%

Central Exclusive Production (CEP)

p p Photon / Pomeron

“rapidity gap” “rapidity gap”

Photon / Pomeron Elastic diffractive: clean environment to study vacuum, and to produce mesons.

  • R. McNulty, CEP at LHCb

7

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QED Photo-production Double pomeron exchange Laboratory to study

  • physics of the vacuum
  • soft/hard QCD
  • saturation
  • exotics (tetraquarks, glueballs, hybrids)
  • R. McNulty, CEP at LHCb

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Central Exclusive Production (CEP)

Experimentally: Reconstruct central system and identify rapidity gaps

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Elastic Scattering Single Diffraction Double Diffraction Central Exclusive Production (elastic) Central Exclusive Production (inelastic)

y=-10 y=-2 y=0 y=2 y=10 Rough LHCb coverage

  • R. McNulty, CEP at LHCb

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Veto (Run 1)

7,8 TeV

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Elastic Scattering Single Diffraction Double Diffraction Central Exclusive Production (elastic) Central Exclusive Production (inelastic)

y=-10 y=-2 y=0 y=2 y=10 Rough LHCb coverage

  • R. McNulty, CEP at LHCb

10

Veto (Run 2)

13 TeV

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Overview

  • 1. Central Exclusive Physics
  • 2. LHCb and HeRSCheL Detector
  • 3. Analyses:
  • pp at 13 TeV
  • pPb and Pb-p at 8 TeV
  • PbPb at √sNN = 5 TeV
  • 4. Physics reach for CEP
  • R. McNulty, CEP at LHCb

11

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The LHCb detector

Fully instrumented: 2 < η < 5 Veto region (Run 1): -3.5<η<-1.5 Veto region (Run 2): -10<η<-5, 5<η<10

  • R. McNulty, CEP at LHCb

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  • Int. J. Mod. Phys. A 30 (2015) 1530022

300 mrad

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  • R. McNulty, CEP at LHCb

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  • R. McNulty, CEP at LHCb

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  • R. McNulty, CEP at LHCb

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High Rapidity Shower Counters at LHCb (HeRSCheL)

JINST 13 (2018) P04017

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  • R. McNulty, CEP at LHCb

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Scintillators, light-guides and PMTs

  • R. McNulty, CEP at LHCb

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Backward stations

Installation finished in 2014

  • R. McNulty, CEP at LHCb

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  • 114 m -19.7 m -7.5 m
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Acceptance

  • R. McNulty, CEP at LHCb

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Showers induced by high-rapidity particles interacting with machine elements Ideally wish to veto on any activity: threshold depends on signal and noise. JINST 13 (2018) P04017

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Sample 1: Response to CEP events (QED µµ)

  • R. McNulty, CEP at LHCb

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arXiv:1806.04079

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Sample 1: Response to CEP events

  • R. McNulty, CEP at LHCb

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First bin is > 95% pure CEP QED di-muons.

arXiv:1806.04079

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Sample 2: Non-CEP events (J/ψ dissociation)

  • R. McNulty, CEP at LHCb

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arXiv:1806.04079

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HeRSCheL discriminant for physics signals

  • R. McNulty, CEP at LHCb

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CEP QED looks like empty-empty events Evidence for pile-up (much reduced in p-Pb/Pb-p running)

arXiv:1806.04079

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Overview

  • 1. Central Exclusive Physics
  • 2. LHCb and HeRSCheL Detector
  • 3. Analyses:
  • pp at 13 TeV
  • PbPb at √sNN = 5 TeV
  • pPb and Pb-p at 8 TeV
  • 4. Physics reach for CEP
  • R. McNulty, CEP at LHCb

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pp / p-Pb / Pb-p / PbPb data-taking

  • R. McNulty, CEP at LHCb

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γγ γP PP p-p Dominant p-Pb Enhanced Supressed Pb-Pb Strongly enhanced Enhanced Supressed

p/A p/A

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Data-taking year Energy Integrated Luminosity Paper 2011 7 TeV 945 pb-1 JPG 41 (2014) 115002 2012 8 TeV 1985 pb-1 Data-taking year Energy Integrated Luminosity Paper 2011 7 TeV 945 pb-1 JHEP 09 (2015) 084 2012 8 TeV 1985 pb-1

Vector meson production in pp collisions

Data-taking year Energy Integrated Luminosity Paper 2010 7 TeV 37 pb-1 JPG 40 (2013) 045001 2011 7 TeV 930 pb-1 JPG 41 (2014) 055002 2015 13 TeV 204 pb-1 arXiv:1806.04079

  • R. McNulty, CEP at LHCb

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J/ψ ψ(2S) ϒ J/ψ+J/ψ J/ψ+ψ(2S) NEW

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Note:

  • soft/hard transition
  • g(x,Q2)

(down to x=2E-6)

Photo-production

  • R. McNulty, CEP at LHCb

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σ ~ xλ

10.3204/DESY-PROC-2012-03/58 JHEP 11 (2013) 085

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Cross-section measurement J/ψ / ψ(2S)

dσ dy = pN AεLΔy

Purity: (found from data)

  • 1. non-resonant bkg (1% / 16%)
  • 2. Feeddown (5% / 0%)
  • 3. Inelastic J/ψ / ψ(2S) production (18% / 11%)

Number of events

  • bserved

Luminosity Efficiency: (found from data)

  • 1. Trigger
  • 2. Tracking & muon id.
  • 3. Single interaction beam-crossing

P(n) = µ ne−µ n!

Acceptance (MC)

  • R. McNulty, CEP at LHCb

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Sample: events with two muons and no

  • ther charged or neutral activity.
  • R. McNulty, CEP at LHCb

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arXiv:1806.04079

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Inelastic background

Signal Background

  • R. McNulty, CEP at LHCb

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dσ dt ~ exp(bsigt)

Regge theory:

dσ dt ~ exp(bbkgt) bsig ~ 6 GeV−2 bbkg ~1 GeV−2

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Inelastic background J/ψ

dσ dt ~ ebt

Regge theory:

  • R. McNulty, CEP at LHCb

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b-slope of signal is same with/without HeRSCheL b-slope of bkg changes (because you veto higher-pT events) New Technique:

NHRC = εNsig + β(pT)Nbkg Nanti-HRC = [1-ε]Nsig + [1-β(pT)] Nbkg

ε known from QED sample Pure bkg sample obtained Subtract bkg from total => Signal derived

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Sample purity

  • R. McNulty, CEP at LHCb

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(consistent with 7 TeV pp and HERA extrapolation)

arXiv:1806.04079

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Cross-section measured in LHCb acceptance

  • R. McNulty, CEP at LHCb

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Systematic uncertainties factor two smaller than previous analysis

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Differential cross-sections J/ψ and ψ(2S)

NLO agrees better than LO

  • R. McNulty, CEP at LHCb

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arXiv:1806.04079

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Photo-production cross-section

LHCb measure Gap Survival Photon Flux Photo-production (HERA / fixed target) HERA measured power-law: Use this for W- solution (in previously measured region). LHCb measures W+

  • R. McNulty, CEP at LHCb

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Photo-production cross-section

  • R. McNulty, CEP at LHCb

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J/ψ

arXiv:1806.04079

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Photo-production cross-section

  • R. McNulty, CEP at LHCb

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ψ(2S)

arXiv:1806.04079:

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Pb-Pb collisions

  • R. McNulty, CEP at LHCb

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LHCb-CONF-2018-003 (in preparation)

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Pb-Pb collisions

  • R. McNulty, CEP at LHCb

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Coherent Incoherent (sensitive to nPDF and saturation)

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Pb-Pb collisions

  • R. McNulty, CEP at LHCb

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HeRSCheL suppresses incoherent events Coherent Incoherent

LHCb-CONF-2018-003 (in preparation)

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Pb-Pb collisions

  • R. McNulty, CEP at LHCb

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LHCb-CONF-2018-003 (in preparation)

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Dipions in pA/Ap

  • R. McNulty, CEP at LHCb

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  • pp->p(ππ)p has contributions

from double-Pomeron-exchange (f0, f2 etc) & photoproduction (ρ).

  • Difficult to disentangle (e.g. f0

appearing as shoulder on ρ)

  • Difficult to separate exclusive

from dissociation

  • pA->p(ππ)A has enhanced

photoproduction

  • Remarkably clean resonance
  • x down to 10-6, W up to 1 TeV

p/A

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Overview

  • 1. Central Exclusive Physics
  • 2. LHCb and Herschel Detector
  • 3. Analyses:
  • pp at 13 TeV
  • PbPb at √sNN = 5 TeV
  • pPb and Pb-p at 8 TeV
  • 4. Physics reach for CEP
  • R. McNulty, CEP at LHCb

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Odderon

  • R. McNulty, Central Exclusive Production at LHCb

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g Bzdak, Motyka, Szymanowski, Cudell PRD 75 (2007) 094023 arXiv:0808.2216

Predictions in pessimistic-central-optimistic scenarios

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  • R. McNulty, CEP at LHCb

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Brodsky, Rathsman, Merino, PLB461 (1998) 114. Hagler, Pire, Szymanowski, Teryaev, EPJ26 (2002) 261. Bolz, Ewerz, Maniatis, Nachtmann, Sauter, Schoening, JHEP 1501 (2015) 151.

Odderon-Pomeron Interference

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  • 6 -5 -4 -3 -2 -1 0

log10(x) 9 8 7 6 5 log10(Q2) [GeV2] 4 3 2 1

  • 1

LHCb:

Collision between one well understood parton and

  • ne unknown or large

DGLAP-evolved parton.

  • R. McNulty, CEP at LHCb

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y: 6 4 2 0 2 4 6

Saturation

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  • 6 -5 -4 -3 -2 -1 0

log10(x) 9 8 7 6 5 log10(Q2) [GeV2] 4 3 2 1

  • 1

LHCb:

Collision between one well understood parton and

  • ne unknown or large

DGLAP-evolved parton.

J/ψ

  • R. McNulty, CEP at LHCb

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y: 6 4 2 0 2 4 6

Saturation

ρ

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Exotics: Glueballs, Hybrids, Tetraquarks etc.

  • R. McNulty, CEP at LHCb

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Double-pomeron-exchange processes Glue Laboratory Eur.Phys.J. C72 (2012) 1972 Inclusive X(3872) Clean environment for meson production. Spin and parity analysis possible.

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e.g. Select 4-muon exclusive events

  • R. McNulty, Central Exclusive Production at LHCb

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Dimuon spectrum having required

  • ther two muons have J/ψ mass

JPG 41 (2014) 115002 JPG 41 (2014) 115002

J/ψ J/ψ ψ(2S)

Selection requirement: Require precisely 4 tracks, at least three identified as muons

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Double J/ψ production

  • R. McNulty, Central Exclusive Production at LHCb

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LHCb estimates exclusive cross-section. 24+-9 pb Harland-Lang, Khoze, Ryskin: JPG 42 (2015) 5,055001 2-7 pb

Shape agrees well (theory normalised to data).

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Summary

  • Several CEP pp measurements at 7, 8 and (new) 13 TeV

using muons.

  • New Herschel detector extends detection of rapidity gap

and reduces experimental uncertainty.

  • Measurements underway in proton-lead and lead-lead

collisions

  • Excellent laboratory for producing mesons cleanly: large

physics reach.

  • R. McNulty, CEP at LHCb

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BACKUP

  • R. McNulty, CEP at LHCb

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VELO sub-detector

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Use of backwards tracks

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Use of backwards tracks

Clearly not exclusive

  • R. McNulty, CEP at LHCb

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  • R. McNulty, CEP at LHCb

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Ion Collider Ion fixed target

(indicative luminosities)

(~1nb-1) (~30nb-1) (~4ub-1) (~0.4ub-1)

Collisions

pp Collider

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Candidate for χc decay to J/ψ+γ

  • R. McNulty, CEP at LHCb

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Selected χc0,1,2 candidates

  • R. McNulty, CEP at LHCb

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LHCb-CONF-2011-022

χc0 χc1 χc2

Ldt = 37pb−1

∫