Heavy Ion Physics at LHCb - CERN · 2015. 4. 2. · of nucleon interactions [76,82,89]. ... Q2 cut...

Heavy Ion Physics at LHCb !

Murilo Rangel on behalf of the LHCb Collaboration

XIII Hadron Physics

Murilo Rangel - IF/UFRJ 2

Outline

◉ LHCb Experiment !

◉ Measurements pPb J/ψ production Y production Z boson production pNe / PbNe results !

◉ Summary


LHCb ExperimentLHCb is a single arm spectrometer fully instrumented in the forward region (2.0<η<5.0) Designed for heavy flavour physics ↔ Explored for general purpose physics (low x sensitive)

VELO ~20µm IP resolution for pT > 2 GeV

MUON Muon Identification ε~97% misID~2%

RICH ε(k→k)~95% for (π→k)~5%

TRACK 0.4%-0.6% momentum resolution

Trigger high efficiency for

low pT muon

IJMPA30(2015)1530022

http://www.worldscientific.com/doi/abs/10.1142/S0217751X15300227


Heavy Ion Physics at LHCb

proton-lead (pA) collisions - LHCb is fully instrumented in a unique kinematic region - factorise effects of Quark Gluon Plasma from Cold Nuclear Matter - sensitive to nuclear parton distribution function: low and high x

Great laboratory for phenomenological modelsNucl.Phys. A926 (2014) 24-33

LHCb accessible region for J/ψ, Υ and Z production: J/ψ: 1x10-5 < x < 1x10-4 , 7x10-3 < x < 7x10-2 Υ : 3x10-5 < x < 3x10-4 , 3x10-2 < x < 3x10-1 Z : 2x10-4 < x < 3x10-3 , 0.2 < x < 1

LHCb LHCb

JHEP 1309 (2013) 158

LHCb LHCb


LHCb pA Data

!E=4TeV

!EN=1.58TeV

pA (forward) at 5 TeV Integrated Luminosity = 1.1/nb Shift in rapidity Δy=ylab-y=0.47 ⇒ 1.5<y<4.0

y Lab

=6

Forward Backward

LHC

LHCb 2<|yLab|<5|yLab|<2.5

DIS + DY

RHIC

80 CHAPTER 9. THEORY OF Z PRODUCTION IN PA/AP COLLISIONS

There are several nPDFs at next-to-leading order (NLO) available. The latest ones are EPS09 [67],HKN07 [87], DSSZ [60] and nCTEQ [91, 92, 109]. These sets di↵er by the baseline free proton PDF(CTEQ6 set or MSTW08 and its predecessors). The data used in the PDF fits are from deep inelasticscattering (DIS) of lepton or proton and nuclei, in particular deuteron. Also neutrino-nuclei DIS aswell as deuteron-gold scattering at the Relativistic Heavy Ion Collider serve in some sets as input data.Table 9.1 summarizes the status of the di↵erent nPDF sets.The nuclear modification factor RA

a (x,Q2 ) shows – independently on the actual nPDF set – the same

Table 9.1: Summary of nuclear PDF properties and data included in the PDF fits (adapted from Refs [91]and [101])

Property nCTEQ DSSZ HKN07 EPS09

Neutral current DIS ` + A/` + d 3 3 3 3Drell-Yan DIS p + A/p + d 3 3 3 3RHIC ⇡0 d + Au/p + p 3 3⌫-A DIS 3Q2 cut in DIS 4 GeV2 1.69 GeV2 1 GeV2 4 GeV2

Basline free proton PDF CTEQ6M MSTW08 MRST98 CTEQ6.1Heavy quark treatmenta GM-VFNS GM-VFNS ZM-VFNS ZM-VFNSa ZM-VFNS: Zero Mass - Variable Flavour Number Scheme considers also c and b quarks as massless while the numberof light quark flavours increases with scale if µF > mb,c

GM-VFNS: General Mass - Variable Flavour Number Scheme considers the quarks as massive at low energy, but coincideswith the ZM-VFNS at high scale for µF � mb. So it can be considered as a merging of ZM-VFNS and a Fixed FlavourNumber Scheme (FFNS) where the later has the problem of treating only light quarks (u, d, s) and gluons as constituentsof the proton.

features as a function of x (cf. Fig. 9.1): At small-x values R is lower than 1 (Shadowing). This e↵ect canbe interpreted as quantum-mechanical interference between scattering amplitudes with di↵erent numberof nucleon interactions [76, 82,89].R is negative also for x values between about 0.4 and 0.8 which corresponds to the EMC-e↵ect. This e↵ecthas been first observed in DIS of muons on iron and deuteron nuclei by the European Muon Collaborationand is still yet not understood [25,119].At x values close to one R is above one as a result of the Fermi motion, so the quantum mechanicalmotion of nucleons inside their nucleus.Between the regimes of Shadowing and EMC-e↵ect there is interval in x (x ⇡ 0.1) where R is also positive.This e↵ect is called Anti-Shadowing. It is not associated to any particular dynamical e↵ect, but ratherto the sum rule of the PDF [42]. Figure 9.1 also reveals to other features about nPDFs: First they arevery poorly constrained especially at small-x values due to the existing data. Therefore measurementson QCD processes in the forward direction as they can be done at LHCb would serve as input for nPDFsfits at small-x values, similar to the impact of the corresponding measurements with pp data in LHCb.As LHCb is able to measure Z production up to a rapidity y of about 4.5 in the lab frame, there is asensitivity in x down to

Impact ParameterThe nPDFs describe the fractional momenta xA of the di↵erent parton types inside the protons and

the neutrons of nuclei. Due to the nuclear e↵ects the nPDFs can have significant deviations from thecorresponding bare parton distribution functions (PDF) of the proton, which can be seen in Fig. ??.So far the available experimental data to determine nPDFs come from nuclear Deep Inelastic Scattering(DIS). This sample contains in the perturbative region (energy scale of the scatter Q2 > 1 GeV2 ) onlydata for xA > 0.01.The most recent nPDF sets obtained from global fits at NLO to the available data are HKN07 [?],EPS09 [67], nDS [?] and CT

pspNsNN = 5 TeV

Z production

4 2 0 -2 -4 -6

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Murilo Rangel - IF/UFRJ

pPb

6

LHCb pA Data

!EN=1.58TeV

!E=4TeV

Ap (backward) at 5 TeV Integrated Luminosity = 0.5/nb Shift in rapidity Δy=ylab-y=0.47 ⇒ -5.0<y<-2.5

y Lab

=6

Forward Backward

LHC


DIS + DY

RHIC












pspNsNN = 5 TeV

Z production

4 2 0 -2 -4 -6

10–6 10–5 10–4 10–3 10–2 10–1 11

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Q2 [

GeV

2 ]

Freitag, 23. Mai 14


J/ψ ProductionData and General Strategy

- Trigger: - One track with hits in the muon stations with pT > 600 MeV

- Two Muons with 1.5<y<4.0 (-5.0<y<-2.5) for pA (Ap) and pT(J/ψ )<14GeV - Dedicate study for J/ψ from b decays (simultaneous fit to mass and pseudo-proper time)

!Backgrounds - combinatorial - exponential distribution !Signal - mass model - crystal-ball function

JHEP02(2014)072

]2 [MeV/cµµm3000 3050 3100 3150 3200

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p0 5 10

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0.040.06

0.080.1

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0.140.16


= 5 TeVNNspPb LHCb(b)

http://dx.doi.org/10.1007/JHEP02(2014)072


J/ψ ProductionData and General Strategy

- Trigger: - One track with hits in the muon stations with pT > 600 MeV

- Two Muons with 1.5<y<4.0 (-5.0<y<-2.5) for pA (Ap) and pT(J/ψ )<14GeV - Dedicate study for J/ψ from b decays (simultaneous fit to mass and pseudo-proper time)

!Backgrounds - combinatorial - exponential distribution !Signal - mass model - crystal-ball function

JHEP02(2014)072

]2 [MeV/cµµm3000 3050 3100 3150 3200

)2C

andi

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3.5−4.0 < y < −(b) Backward



J/ψ Production

Pseudo proper time is used to evaluate prompt vs b hadron decay

JHEP02(2014)072

background from sideband

Forward Backward



[GeV/c]T

p0 5 10

b/(G

eV/c

)]µ [ T

/dp

σd

1

10

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310

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from bψJ/ = 5 TeVNNspPb(Fwd)

LHCb1.5 < y < 4.0

(a)

[GeV/c]T

p0 5 10

b/(G

eV/c

)]µ [ T

/dp

σd

1

10

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310

410ψPrompt J/

from bψJ/ = 5 TeVNNspPb(Bwd)

LHCb2.5−5.0 < y < −

(b)

⇒ prompt J/ψ cross section about 10 times higher than J/ψ from b hadron decays

➢ similar to the values observed in pp collisions at 2.76, 7 and 8 TeV [JHEP 02 (2013) 041], [EPJC (2011) 71 1645], [JHEP 06 (2013) 064]

9

J/ψ Cross Sections JHEP02(2014)072



[GeV/c]T

p0 5 10

b/(G

eV/c

)]µ [ T

/dp

σd

1

10

210

310

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from bψJ/ = 5 TeVNNspPb(Fwd)

LHCb1.5 < y < 4.0

(a)

[GeV/c]T

p0 5 10

b/(G

eV/c

)]µ [ T

/dp

σd

1

10

210

310

410ψPrompt J/

from bψJ/ = 5 TeVNNspPb(Bwd)

LHCb2.5−5.0 < y < −

(b)

⇒ prompt J/ψ cross section about 10 times higher than J/ψ from b hadron decays

➢ similar to the values observed in pp collisions at 2.76, 7 and 8 TeV [JHEP 02 (2013) 041], [EPJC (2011) 71 1645], [JHEP 06 (2013) 064]

+ largest systematic uncertainties

➢ mass model: 2.3-3.4%

➢ difference of pT and y distribution between simulation and data: 0.1-8.7%

➢ multiplicity re-weighting: 0.1-4.3%

➢ tZ fit (only for J/ψ from b): 0.2-12%

9




!!!Nuclear modification factor in overlap region 2.5 < |y | < 4.0

➭ RpA=1 if pA collision is superposition of A pp collisions

➭ RpA<1 in case of suppression due to medium forward backward production ratio

pp cross section at 5 TeV is needed (LHCb-CONF-2013-013)

➞ not measured directly - interpolation 2.76, 7 and 8 TeV rescaled to common rapidity range

➞ 3 interpolation functions: linear, exponential, power law (nominal)

!!!Forward-Backward production ratio in overlap region 2.5 < |y | < 4.0

→ sensitive to cold nuclear matter effects

→ many uncertainties cancel and no reference cross section needed

10

Cold Nuclear Effects

LHC-CONF-2013-013


!!!Nuclear modification factor in overlap region 2.5 < |y | < 4.0

➭ RpA=1 if pA collision is superposition of A pp collisions

➭ RpA<1 in case of suppression due to medium forward backward production ratio

pp cross section at 5 TeV is needed (LHCb-CONF-2013-013)

➞ not measured directly - interpolation 2.76, 7 and 8 TeV rescaled to common rapidity range


!!!Forward-Backward production ratio in overlap region 2.5 < |y | < 4.0

→ sensitive to cold nuclear matter effects

→ many uncertainties cancel and no reference cross section needed

10

Cold Nuclear Effects


y-4 -2 0 2 4

pPb

R

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

< 14 GeV/cT

p

EPS09 LOnDSg LO

from b ψLHCb, J/ = 5 TeVNNspPb

LHCb(b)

y-4 -2 0 2 4

pPb

R

0

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p

EPS09 LOEPS09 NLOnDSg LOE. lossE. loss + EPS09 NLO

ψLHCb, Prompt J/ = 5 TeVNNspPb

LHCb(a)

11

J/ψ Production

prompt J/Ψ

+ significant sign of cold nuclear matter effects

+ measurements agree with most of the predictions

J/Ψ from b hadron decays + modest suppression with respect to pp

+ first indication of suppression of bottom hadron production in Pb

+ agreement with predictions in forward regionEPS09: JHEP 0904 (2009) 65, nDSG:Phys. Rev.D69(2004) 074028Energy loss: JHEP 03(2013) 122NLO: Phys. Rev. D17 (1978) 2324, LO: Nucl. Phys. B127 (1980) 425, Phys. Lett. B102, (1981) 364

JHEP02(2014)072



[GeV/c]T

p0 5 10

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LHCb

2.5 < |y| < 4.0

ψPrompt J/EPS09 NLOE. lossE. loss + EPS09 NLO

|y|0 1 2 3 4 5

FBR

0.4

0.6

0.8

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1.4

= 5 TeVNNspPb LHCb

EPS09 LOnDSg LO

from b ψLHCb, J/ < 14 GeV/c

Tp

(b)

|y|0 1 2 3 4 5

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0.4

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= 5 TeVNNspPb LHCb

EPS09 LOEPS09 NLOnDSg LOE. lossE. loss + EPS09 NLO

ψLHCb, Prompt J/

< 14 GeV/cT

p(a)

12

J/ψ Production

prompt J/Ψ

+ significant forward-backward asymmetry

+ better agreement with EPS09+Energy loss

J/Ψ from b hadron decays + smaller asymmetry with respect to pp

+ agreement with predictions in forward region

EPS09: JHEP 0904 (2009) 65, nDSG:Phys. Rev.D69(2004) 074028Energy loss: JHEP 03(2013) 122NLO: Phys. Rev. D17 (1978) 2324, LO: Nucl. Phys. B127 (1980) 425, Phys. Lett. B102, (1981) 364

JHEP02(2014)072

predictions only for prompt J/ψ



Y Production

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Data and General Strategy - Trigger:

- One track with hits in the muon stations with pT > 600 MeV - Two Muons with 1.5<y<4.0 (-5.0<y<-2.5) for pA (Ap) and pT(Y)<15GeV - Low statistics

!Backgrounds - combinatorial - exponential !Signal - mass model - 3 crystal-balls function

Forward

Backward

JHEP07(2014)094



Y Production

+ statistical uncertainty dominates (concentrate on Y(1S)) + dominant systematic uncertainties: → pT and y dependence of signal: 4%(forward) 7%(backward) → trigger efficiency : 2%(forward) 5%(backward)

Forward

Backward

JHEP07(2014)094



Y Production

+ statistical uncertainty dominates (concentrate on Y(1S)) + dominant systematic uncertainties: → pT and y dependence of signal: 4%(forward) 7%(backward) → trigger efficiency : 2%(forward) 5%(backward)

Forward

Backward

pp cross section at 5 TeV ➞ not measured directly - interpolation 2.76, 7 and 8 TeV rescaled to common rapidity range


LHCb-CONF-2014-003

JHEP07(2014)094



Y(1S) Production

y-4 -2 0 2 4

pPb

R

0

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LHCb

E.loss+EPS09 NLO in Ref.[3]

(1S)ΥψPrompt J/

|y|0 1 2 3 4 5

FBR

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LHCb

E.loss+EPS09 NLO in Ref.[3]

(1S)ΥψPrompt J/

+ RpPb measured in the common rapidity region 2.5<y<4.0 + complementary to J/ψ - different xA region + similar to J/ψ from b hadron decays → visible cold nuclear effect, in agreement with EPS09(NLO) - Ref.[3]

Nuclear modification factor

Forward-Backward ratio

JHEP07(2014)094

● Y(1S) △ J/ψ from b ☐ prompt J/ψ

● Y(1S) △ J/ψ from b ☐ prompt J/ψ

http://dx.doi.org/10.1142/S0218301313300075



Z ProductionData and General Strategy

- Trigger: - One track with hits in the muon stations with p>8GeV and pT > 4.8 MeV

- Two Muons with 2.0<ylab<4.5 and pT(𝝁)<20GeV - Low statistics

!Backgrounds - mis-identification+heavy-quark ⟹ purity>99.5% !Signal - shape from simulation / efficiency from pp analysis ⟹ efficiency>72%

]2c [GeV/−µ+µm60 80 100 120

)2 cCa

ndid

ates

/ (2

GeV

/

0

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= 5 TeVNNsPb pLHCb

= 5 TeVNNsPb pLHCb

backward

]2c [GeV/−µ+µm60 80 100 120

)2 cCa

ndid

ates

/ (2

GeV

/

0

1

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3

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= 5 TeVNNsPb pLHCb

= 5 TeVNNsPb pLHCb

forward

Pb data)p(−µ+µ→Z

(MC PYTHIA8)−µ+µ→Z

Pb data)p(−µ+µ→Z

(MC PYTHIA8)−µ+µ→Z

Forward Backward

JHEP09(2014)030



Z Production

[nb]

−µ+

µ→Z

σ

0

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30

40

forwardbackward

syst. stat.⊕syst.

FEWZ NNLO + MSTW08FEWZ NNLO + MSTW08 + EPS09 (NLO)

= 5 TeVNNsPb pLHCb+ efficiencies derived in data

+ measurement limited by statistics + theoretical predictions in agreement with measurement + higher statistics measurements will provide important informationon nuclear PDFs

FEWZ: Y.LiandF.Petriello,Phys.Rev.D86(2012)094034,arXiv:1208.5967.MSTW08: A. Martin, W. Stirling, R. Thorne, and G. Watt, Phys. J C63 (2009), no 2 189 EPS09: K. Eskola, H. Paukkunen, and C. Salgado,JHEP 04 (2009) 065, arXiv:0902.4154.

JHEP09(2014)030



LHCb - Fixed Target JINST 9 (2014) 12, P12005LHCb-CONF-2012-034


LHCb - Fixed Target

Injection of Ne gas into interaction region increases beam-gas interaction rate by 2 orders of magnitude

→ accurate measurement of beam profile - precise luminosity determination

→ also allows to study pNe interactions at 87 GeV

!++ shift of c.m. system by 4.5 units in rapidity in proton direction

→ LHCb is a central detector for fixed target collisions

JINST 9 (2014) 12, P12005LHCb-CONF-2012-034


LHCb - Fixed Target - pNe

Clear observation of signals

LHCb-CONF-2012-034


LHCb - Fixed Target - PbNe


Summary

◉ LHCb has a unique coverage to study Heavy Ion Physics !◉ J/ψ and Y Production o Visible cold nuclear effects for prompt J/ψ and Y o Evidence of cold nuclear effect for bottom production !◉ First observation of Z boson Production in proton-nucleus !◉ Measurements are limited by data size

!◉ Other studies and samples of pNe and PbNe ongoing


BACK UP


Data

- low pile-up (~ 1 primary vertex per beam crossing) - data-taking efficiency > 90%. - results based on 2 beam configurations and 2 magnet configurations.

Ap : L = 1.1 nb−1 pA : L = 0.5 nb−1


Number of tracks0 200 400 600

Arb

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) [GeV/c]ψ(J/T

p0 5 10

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) [GeV/c]ψp(J/0 50 100 150 200 250

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00.020.040.060.08

0.10.120.140.160.18

0.20.22 pPb(Fwd)

pPb(Bwd)pp MC

= 5 TeVNNspPb LHCb(c)

)ψ(J/lab

y2 3 4 5

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0.08


= 5 TeVNNspPb LHCb(d)

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J/ψ Production

Acceptance and efficiency from pp simulation re-weighted to track multiplicity

JHEP02(2014)072



⇒ prompt J/ψ cross section about 10 times higher than J/ψ from bottom, similar to the values observed in pp collisions at 2.76, 7 and 8 TeV

[JHEP 02 (2013) 041], [EPJC (2011) 71 1645], [JHEP 06 (2013) 064]




➢ multiplicity reweighting: 0.1-4.3%


[GeV/c]T

p0 5 10

b/(G

eV/c

)]µ

dy [

T/d

pσ2 d

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1

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= 5 TeVNNspPb(Fwd) LHCb

ψPrompt J/

(a)

[GeV/c]T

p0 5 10

b/(G

eV/c

)]µ

dy [

T/d

pσ2 d

-110

1

10

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= 5 TeVNNspPb(Fwd) LHCb

from bψJ/

(b)

25




⇒ prompt J/ψ cross section about 10 times higher than J/ψ from bottom, similar to the values observed in pp collisions at 2.76, 7 and 8 TeV

[JHEP 02 (2013) 041], [EPJC (2011) 71 1645], [JHEP 06 (2013) 064]




➢ multiplicity reweighting: 0.1-4.3%


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Y(1S)


y Lab

=6

Forward Backward

LHC


DIS + DY

RHIC












pspNsNN = 5 TeV

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10–6 10–5 10–4 10–3 10–2 10–1 11

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GeV

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Freitag, 23. Mai 14


LHCb VELO

VELO - surrounds the interaction point - allows backward tracks (-3.5<η<-1.5)

backward track

Heavy Ion Physics at LHCb - CERN · 2015. 4. 2. · of nucleon interactions [76,82,89]. ... Q2 cut...

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Transcript of Heavy Ion Physics at LHCb - CERN · 2015. 4. 2. · of nucleon interactions [76,82,89]. ... Q2 cut...