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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
Murilo Rangel - IF/UFRJ 3
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
Murilo Rangel - IF/UFRJ 4
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
Murilo Rangel - IF/UFRJ 5
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
10–6 10–5 10–4 10–3 10–2 10–1 11
101
102
103
104
105
106
xA
Q2 [
GeV
2 ]
Freitag, 23. Mai 14
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
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
10–6 10–5 10–4 10–3 10–2 10–1 11
101
102
103
104
105
106
xA
Q2 [
GeV
2 ]
Freitag, 23. Mai 14
Murilo Rangel - IF/UFRJ 7
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
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= 5 TeVNNspPb LHCb(b)
Murilo Rangel - IF/UFRJ 7
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
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J/ψ Production
Pseudo proper time is used to evaluate prompt vs b hadron decay
JHEP02(2014)072
background from sideband
Forward Backward
Murilo Rangel - IF/UFRJ
[GeV/c]T
p0 5 10
b/(G
eV/c
)]µ [ T
/dp
σd
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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]
9
J/ψ Cross Sections JHEP02(2014)072
Murilo Rangel - IF/UFRJ
[GeV/c]T
p0 5 10
b/(G
eV/c
)]µ [ T
/dp
σd
1
10
210
310
410ψPrompt J/
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
J/ψ Cross Sections JHEP02(2014)072
Murilo Rangel - IF/UFRJ
!!!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
Murilo Rangel - IF/UFRJ
!!!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
Murilo Rangel - IF/UFRJ
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
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
< 14 GeV/cT
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
Murilo Rangel - IF/UFRJ
[GeV/c]T
p0 5 10
FBR
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6 ψLHCb, Prompt J/ from b ψLHCb, J/ = 5 TeVNNspPb
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
1
1.2
1.4
= 5 TeVNNspPb LHCb
EPS09 LOnDSg LO
from b ψLHCb, J/ < 14 GeV/c
Tp
(b)
|y|0 1 2 3 4 5
FBR
0.4
0.6
0.8
1
1.2
1.4
= 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
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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
Murilo Rangel - IF/UFRJ 14
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
Murilo Rangel - IF/UFRJ 14
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
➞ 3 interpolation functions: linear, exponential, power law (nominal)
LHCb-CONF-2014-003
JHEP07(2014)094
Murilo Rangel - IF/UFRJ 15
Y(1S) Production
y-4 -2 0 2 4
pPb
R
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1.4 = 5 TeVNNspPb
LHCb
E.loss+EPS09 NLO in Ref.[3]
(1S)ΥψPrompt J/
|y|0 1 2 3 4 5
FBR
0
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0.4
0.6
0.8
1
1.2 = 5 TeVNNspPb
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
Murilo Rangel - IF/UFRJ 16
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
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ndid
ates
/ (2
GeV
/
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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
Murilo Rangel - IF/UFRJ 17
Z Production
[nb]
−µ+
µ→Z
σ
0
10
20
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
Murilo Rangel - IF/UFRJ 18
LHCb - Fixed Target JINST 9 (2014) 12, P12005LHCb-CONF-2012-034
Murilo Rangel - IF/UFRJ 18
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
Murilo Rangel - IF/UFRJ 19
LHCb - Fixed Target - pNe
Clear observation of signals
LHCb-CONF-2012-034
Murilo Rangel - IF/UFRJ 20
LHCb - Fixed Target - PbNe
Murilo Rangel - IF/UFRJ 21
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
Murilo Rangel - IF/UFRJ 22
BACK UP
Murilo Rangel - IF/UFRJ 23
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
Murilo Rangel - IF/UFRJ
Number of tracks0 200 400 600
Arb
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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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J/ψ Production
Acceptance and efficiency from pp simulation re-weighted to track multiplicity
JHEP02(2014)072
Murilo Rangel - IF/UFRJ
⇒ 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]
+ largest systematic uncertainties
➢ mass model: 2.3-3.4%
➢ difference of pT and y distribution between simulation and data: 0.1-8.7%
➢ multiplicity reweighting: 0.1-4.3%
➢ tZ fit (only for J/ψ from b): 0.2-12%
[GeV/c]T
p0 5 10
b/(G
eV/c
)]µ
dy [
T/d
pσ2 d
-110
1
10
210
3101.5<y<2.02.0<y<2.52.5<y<3.03.0<y<3.53.5<y<4.0
= 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
210 1.5<y<2.02.0<y<2.52.5<y<3.03.0<y<3.53.5<y<4.0
= 5 TeVNNspPb(Fwd) LHCb
from bψJ/
(b)
25
J/ψ Cross Sections JHEP02(2014)072
Murilo Rangel - IF/UFRJ
⇒ 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]
+ largest systematic uncertainties
➢ mass model: 2.3-3.4%
➢ difference of pT and y distribution between simulation and data: 0.1-8.7%
➢ multiplicity reweighting: 0.1-4.3%
➢ tZ fit (only for J/ψ from b): 0.2-12%
25
J/ψ Cross Sections JHEP02(2014)072
Murilo Rangel - IF/UFRJ 26
Murilo Rangel - IF/UFRJ 27
Y(1S)
Murilo Rangel - IF/UFRJ 28
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
10–6 10–5 10–4 10–3 10–2 10–1 11
101
102
103
104
105
106
xA
Q2 [
GeV
2 ]
Freitag, 23. Mai 14
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LHCb VELO
VELO - surrounds the interaction point - allows backward tracks (-3.5<η<-1.5)
backward track
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