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  • charmonium production in ultra-peripheral heavy-ion

    collisions at LHCb Quark Matter 2018, Venezia, Italia

    Albert Frithjof Bursche1, on behalf of the LHCb collaboration.

    14th May 2018

    1Università 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 Identification ε ≈ 90%, mis-ID< 5%

    Muon Identification ε ≈ 97%, mis-ID≈ 0.7% at high 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 , Λ 0, 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 activity from the same vertex muon selection

    pTµ > 500 MeV 2.0 < ηµ < 4.5

    J/ψ selection pTJ/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

    https://inspirehep.net/record/753911

  • 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

    https://inspirehep.net/record/1634637

  • 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

    https://inspirehep.net/record/1634637

  • 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 low Bjorken-x , nuclear PDFs, saturation physics, colour glass condensate

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

    https://inspirehep.net/record/1634637

  • analysis signal determination

    mass fit

    invariant mass fit discriminate γ γ →µ+µ− process from J/ψ production non-resonant Exponential times straight line

    J/ψ Double sided Crystal Ball function ψ(2S) Double sided Crystal Ball function with all parameters apart from

    normalisation 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

    E ve

    nt s

    / ( 1

    3 M

    eV )

    1−10

    1

    10

    210

    310 LHCb Preliminary = 5 TeVNNsPb-Pb

    data (1S)ψJ/

    (2S)ψ non-resonant sum

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

    LHCb-CONF-2018-003

    https://cds.cern.ch/search?ln=en&cc=LHCb+Conference+Contributions&p=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 constraint to the result of the mass fit

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

    coherent J/ψ production STARlight template

    The STARlight templates are from the generated events smeared with a resolution 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

    T log(p

    0

    10

    20

    30

    40

    50

    E ve

    nt s

    / 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

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

  • analysis result

    differential coherent cross section

    LHCb preliminary σ = 5.27± 0.21± 0.49± 0.68mb

    The analysis is repeated in bins of half unit rapidity yJ/ψ

    Uncertainties for statistics, systematic and luminosity are of comparable magnitude

    The LHCb acceptance is interesting to discriminate between the models 0 1 2 3 4 5

    ψJ/ y

    0 0.5

    1 1.5

    2 2.5

    3 3.5

    4 4.5

    5

    [ m

    b] ψ

    J/ /d

    y σd

    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

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

  • analysis systematic uncertainties

    systematic uncertainties

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

    Albert Bursche UPC J/ψ 14th May 2018 10 / 14

    LHCb-CONF-2018-003

    https://cds.cern.ch/search?ln=en&cc=LHCb+Conference+Contributions&p=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 in 5.0 < η < 7.5

    Extend present LHCb to observe this debris

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

    il lu

    st ra

    ti on

    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

    Albert Bursche UPC J/ψ 14th May 2018 12 / 14

  • analysis HeRSCheL - forward scintillators

    separation of coherent and incoherent

    )2/GeV2 T

    log(p 10− 5− 0

    E ve

    nt s

    / 0 .6

    0 20 40 60 80

    100 120 140 160 180 200 220 data without Herschel

    data with Herschel

    LHCb Preliminary = 5 TeVNNsPb-Pb

    The use of the HeRSCHeL detector does remove a lot of the incoherent backgrounds Albert Bursche UPC J/ψ 14th May 2018 13 / 14

    LHCb-CONF-2018-003

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

  • analysis HeRSCheL - forward scintillators

    conclusion

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

    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

    experimental setup LHCb detector

    analysis introduction signal determination result systematic uncertainties HeRSCheL - forward scintillators