charmonium production in ultra-peripheral heavy-ion

collisions at LHCbQuark Matter 2018, Venezia, Italia

Albert Frithjof Bursche1, on behalf of the LHCb collaboration.

14th May 2018

1Universita degli Studi di Cagliari and INFN Cagliari, Italy

experimental setup LHCb detector

LHCb experiment

z

y

VELO TT T1-3 Muon-System

IP

Albert Bursche UPC J/ψ 14th May 2018 2 / 14

experimental setup LHCb detector

LHCb experiment

z

y

VELO TT T1-3 Muon-System

IP

Kaon Identificationε ≈ 90%, mis-ID< 5%

Muon Identificationε ≈ 97%, mis-ID≈ 0.7% athigh pT

Acceptance 2 < η < 5

Albert Bursche UPC J/ψ 14th May 2018 2 / 14

experimental setup 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

Albert Bursche UPC J/ψ 14th May 2018 2 / 14

analysis introduction

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

Albert Bursche UPC J/ψ 14th May 2018 3 / 14

b>R +R

Z

Z

A B

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

analysis introduction

introduction

(a)

t

AγW

A A

A A

γ ψJ/

Albert Bursche UPC J/ψ 14th May 2018 4 / 14

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

analysis introduction

introduction

(b)

t

AγW

A A

A(*)

A

γ ψJ/

Albert Bursche UPC J/ψ 14th May 2018 4 / 14

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

analysis introduction

introduction

(a)

t

AγW

A A

A A

γ ψJ/

Albert Bursche UPC J/ψ 14th May 2018 4 / 14

Sensitive to gluons at lowBjorken-x , nuclear PDFs,saturation physics,colour glass condensate

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

analysis signal determination

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

Albert Bursche UPC J/ψ 14th May 2018 5 / 14

analysis signal determination

the mass fit

Dimuon mass [MeV]3000 3500 4000

Eve

nts

/ ( 1

3 M

eV )

1−10

1

10

210

310 LHCb Preliminary = 5 TeVNNsPb-Pb

data(1S)ψJ/

(2S)ψnon-resonantsum

Albert Bursche UPC J/ψ 14th May 2018 6 / 14

LHCb-CONF-2018-003

analysis signal determination

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)

Albert Bursche UPC J/ψ 14th May 2018 7 / 14

analysis signal determination

the transverse momentum fit

10− 5− 0)2/GeV2

Tlog(p

0

10

20

30

40

50

Eve

nts

/ 0.1

5 data

coherent

incoherent+feed-down

non-resonant

sum

LHCb Preliminary = 5 TeVNNsPb-Pb

Albert Bursche UPC J/ψ 14th May 2018 8 / 14

LHCb-CONF-2018-003

analysis result

differential coherent cross section

LHCb preliminaryσ = 5.27± 0.21± 0.49± 0.68mb

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

ψJ/y

00.5

11.5

22.5

33.5

44.5

5

[m

b]ψ

J//d

yσd

Guzey et al.

LTA_W

LTA_S

EPS09

Goncalves et al

IP-SAT

IIM

Cepila et al.

GG-hs

GS-hs

=5 TeVNNsPb-Pb

LHCb Preliminary

Albert Bursche UPC J/ψ 14th May 2018 9 / 14

LHCb-CONF-2018-003

analysis systematic uncertainties

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

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LHCb-CONF-2018-003

analysis HeRSCheL - forward scintillators

HeRSCHeL - forward scintillators

Albert Bursche UPC J/ψ 14th May 2018 11 / 14

analysis HeRSCheL - forward scintillators

HeRSCHeL - forward scintillators

Albert Bursche UPC J/ψ 14th May 2018 11 / 14

analysis 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: 29.09.2016

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

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

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

pseudorapidity η

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analysis HeRSCheL - forward scintillators

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 UPC J/ψ 14th May 2018 13 / 14

LHCb-CONF-2018-003

analysis HeRSCheL - forward scintillators

conclusion

LHCb has measured the cross section for coherent J/ψ production in lead-leadcollisions

We have potential to improve the precision of this measurement

We are looking forward to a larger data set in fall 2018

Thank You!

Albert Bursche UPC J/ψ 14th May 2018 14 / 14