central exclusive ultraperipheral results and prospects · LTA_W LTA_S EPS09 Goncalves et al....

central exclusive ultraperipheral results and prospectssecond heavy ion and fixed target workshop, Chia, Sardinia

Albert Frithjof Bursche1, on behalf of the LHCb collaboration.

6th September 2019

1Universita degli Studi di Cagliari and INFN Cagliari, Italy

1 the pastLHCb detector2015 preliminary ultraperipheral J/ψ

2 the presentHeRSCheL - forward scintillators2015 ultraperipheral J/ψ paper2018 ultraperipheral J/ψ paper

3 the futuregeneral

as Sergio Leone didn’t say...

Albert Bursche CEP and UPC 6th September 2019 2 / 24

the past LHCb detector

LHCb experiment

z

y

VELO TT T1-3 Muon-System

IP optimal µ p,K±, π± produced inside the VELO

ok K 0S , Λ0, γ, e±, π0

challenging stable neutral hadrons n, K 0L


the past

the past 2015 preliminary ultraperipheral J/ψ

event selection

J/ψ →µ+µ− events with no additional activityfrom the same vertexmuon selection

pTµ > 500 MeV2.0 < ηµ < 4.5

J/ψ selectionpTJ/ψ < 1 GeV

Using data taken in lead-lead collisions at√sNN = 5.02 TeV in 2015


b>R +R

Z

Z

A B

diagram from Phys.Rept. 458 (2008) 1-171

https://inspirehep.net/record/753911


introduction

(a)

t

AγW

A A

A A

γ ψJ/


diagrams from Cepila, Jan et al. Phys.Rev. C97 (2018) no.2, 024901



introduction

(b)

t

AγW

A A

A(*)

A

γ ψJ/


diagrams from Cepila, Jan et al. Phys.Rev. C97 (2018) no.2, 024901



mass fit

invariant mass fit discriminate γ γ →µ+µ− process from J/ψ production

non-resonant Exponential times straight lineJ/ψ Double sided Crystal Ball function

ψ(2S) Double sided Crystal Ball function with all parameters apart fromnormalisation and mean constrained to be identical to J/ψ



the mass fit

Dimuon mass [MeV]3000 3500 4000

Can

dida

tes

/ ( 1

3 M

eV )

1−10

1

10

210

310 LHCb Preliminary = 5 TeVNNsPb-Pb

dataψJ/(2S)ψ

non-resonantsum


LHCb-CONF-2018-003

https://cds.cern.ch/search?ln=en&cc=LHCb+Conference+Contributions&p=LHCb-CONF-2018-003


transverse momentum fit

transverse momentum fit to determine the number of coherent events

non-resonant STARlight template, normalisation is fixed by Gaussian constraintto the result of the mass fit

incoherent J/ψ production STARlight template, this also accounts for feeddownψ(2S) →J/ψ X

coherent J/ψ production STARlight template

The STARlight templates are from the generated events smeared with aresolution model

~pµ = G (px , 10MeV)~ex + G (py , 10MeV)~ey + G (pz , 10MeV)~ez (1)



the transverse momentum fit

10− 5− 0)2/GeV2

Tlog(p

0

10

20

30

40

50

Can

dida

tes

/ 0.1

5 datacoherentincoherent+feed-downnon-resonantsum

LHCb Preliminary = 5 TeVNNsPb-Pb


LHCb-CONF-2018-003



differential coherent cross section

LHCb preliminaryσ = 5.27± 0.21

stat± 0.49

sys± 0.68

lumimb

The analysis is repeated inbins of half unit rapidity yJ/ψ

Uncertainties for statistics,systematic and luminosity areof comparable magnitude

The LHCb acceptance isinteresting to discriminatebetween the models 0 1 2 3 4 5

y

00.5

11.5

22.5

33.5

44.5

5

/dy

[mb]

σd

Guzey et al.

LTA_W

LTA_S

EPS09

Goncalves et al.

IP-SAT+GLC

IIM+BG

Cepila et al.

GG-hs+BG

GS-hs+BG

ntysaari et al.aM

IS fluct. +GLC

no fluct. +GLC

=5 TeVNNsPb-Pb

LHCb Preliminary


LHCb-CONF-2018-003



systematic uncertainties

Source Relative uncertainty (%)Selection efficiency 3.2Reconstruction efficiency 2.1− 4.5Hardware trigger efficiency 3.0Software trigger efficiency 1.6− 5.3Momentum smearing model 3.3Mass fit model 3.9Feed-down background 5.8Branching fraction 0.6Luminosity 13.0


LHCb-CONF-2018-003


the present

the present HeRSCheL - forward scintillators

HeRSCHeL - forward scintillators



HeRSCheL concept

If the nucleon breaks up it will leave debris in5.0 < η < 7.5

Extend present LHCb to observe this debris

Much easier than proton taggers inside thebeam pipe (“Roman Pots”)

illu

stra

tion

Melody Ravonel Salzgeber: 29.09.2016


Melody Ravonel Salzgeber: 29.09.2016Melody Ravonel Salzgeber: 29.09.2016Melody Ravonel Salzgeber: 29.09.2016Melody Ravonel Salzgeber: 29.09.2016Melody Ravonel Salzgeber: 29.09.2016

-15 15 0 5-5 10-10

LHCb HeRSCheL

(gap)

(gap)

(gap)(gap)

(gap)

(gap)

(gap)

Single diffraction

Double diffraction

CEP elastic

CEP inelastic

CEP inelastic

Elastic scattering



-15 15 0 5-5 10-10

LHCb HeRSCheL

(gap)

(gap)

(gap)(gap)

(gap)

(gap)

(gap)

Single diffraction

Double diffraction

CEP elastic

CEP inelastic

CEP inelastic

Elastic scattering



-15 15 0 5-5 10-10

LHCb HeRSCheL

(gap)

(gap)

(gap)(gap)

(gap)

(gap)

(gap)

Single diffraction

Double diffraction

CEP elastic

CEP inelastic

CEP inelastic

Elastic scattering

pseudorapidity η



separation of coherent and incoherent

)2/GeV2

Tlog(p

10− 5− 0

Eve

nts

/ 0.6

020406080

100120140160180200220 data without Herschel

data with Herschel

LHCb Preliminary = 5 TeVNNsPb-Pb

The use of the HeRSCHeL detector does remove a lot of the incoherent backgroundsAlbert Bursche CEP and UPC 6th September 2019 16 / 24

LHCb-CONF-2018-003


the present 2015 ultraperipheral J/ψ paper

paper using 2015 datasetthe pathfinder

Improved on most systematics (not lumi)

Use of full simulation instead of smearing MS truth for templates

Use of Herschel for better control of the background

Luminosity uncertainty remains the limiting factor

Internal review is progressing well



paper using 2018 datasetthe precision measurement

Use the experience gained on 2015 to improve the resultusing an order of magnitude more data

Start improvements at the trigger

Will include J/ψ/ψ(2S) cross section ratios

Luminosity still to be determined

Internal review imminent



central exclusive production of J/ψ mesons and ψ(2S)mesons at 13 TeV

2000 3000 4000) [MeV]−µ+µMass(

1

10

210

310

410

Can

dida

tes

per

10 M

eV =13 TeV)sLHCb (

Total fitNonresonant background

0 0.5 1 1.5 2]2[GeV)−µ+µ(2

Tp

10

210

310

4102C

andi

date

s pe

r 0.

04 G

eV =13 TeV)sL (HE RSCE LHCb w/o H=13 TeV)sL (HE RSCE LHCb w/ H

Total fitInelastic background


JHEP 10 (2018) 167

http://lhcbproject.web.cern.ch/lhcbproject/Publications/LHCbProjectPublic/LHCb-PAPER-2018-011.html



2000 3000 4000) [MeV]−µ+µMass(

1

10

210

310

410

Can

dida

tes

per

10 M

eV =13 TeV)sLHCb (

Total fitNonresonant background

0 0.5 1 1.5 2]2[GeV)−µ+µ(2

Tp

10

210

310

4102C

andi

date

s pe

r 0.

04 G

eV =13 TeV)sL (HE RSCE LHCb w/o H=13 TeV)sL (HE RSCE LHCb w/ H

Total fitInelastic background


similar game

use 204± 8 pb−1 lumiat 13 TeV

fit exponential insteadof simulation

Herschel reduces thebackground

JHEP 10 (2018) 167




2 3 4 rapidityψJ/

0

1

2

3

4

5

6

7

8

9

[nb

]p

ψ p

J/→

pp

dyσd

JMRT LO

JMRT NLO

=13 TeV)sLHCb (

2 3 4 rapidity(2S)ψ

00.20.40.60.8

11.21.41.61.8

22.2

[nb

](2

S)p

ψ p

→ p

p

dyσd

JMRT LO

JMRT NLO

=13 TeV)sLHCb (


JHEP 10 (2018) 167




210 310W [GeV]

10

210

310

[nb

]p

ψ J

/→

p γσ = 13 TeV)sLHCb (= 7 TeV)sLHCb (

ALICEH1ZEUSFixed target exp.

Power law fit to H1 data

JMRT NLO prediction

210 310W [GeV]

1−10

1

10

210 [nb

](2

S)p

ψ →

p γσ = 13 TeV)sLHCb (= 7 TeV)sLHCb (

H1

power law scaled by 0.166ψJ/H1


JHEP 10 (2018) 167


the future

the future general

use hadronic final states

Trigger was improved for PbPb 2018 run

Trigger will be completely independent of the calorimeters in the upgrade

There are narrow states; wide states; and opportunities for spectroscopy

Cross sections are so high we run out of dimensions to measure differentially in

The slides ahead are heavily censored.

The slides ahead are mildly edited for compliancewith administrative measures


the future general

conclusion

There are great LHCb results in the pipeline

There are even more data there being analysed

There are even better data to come


central exclusive ultraperipheral results and prospects · LTA_W LTA_S EPS09 Goncalves et al....

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