ALICE mesurements of heavy-flavour production in pp and p-Pb collisions at the LHC

0.24 MB·

by  Grazia Luparello

Nuclearand
ParticlePhysics
Proceedings
NuclearandParticlePhysicsProceedings00(2017)1–3
ALICE mesurements of heavy-flavour production in pp and p-Pb collisions at the
LHC
G.LuparellofortheALICECollaboration
UniversityofTriesteandINFNTrieste,ViaA.Valerio2,Trieste,Italy
7
1
0
2

n
Abstract
a
√
J The D meson yields as a function of charged-particle multiplicity in pp collisions at s = 7 TeV and in p-Pb
√
1 collisionsat s =5.02TeVarepresented. Themeasurementoftheyieldsofelectronsfromheavy-flavourhadron
NN √
1 decaysasafunctionofcharged-particlemultiplicityinp-Pbcollisionsat s = 5.02TeVareshownaswell. The
NN √
measurementofazimuthalcorrelationsofpromptDmesonsandchargedhadronsinppcollisionsat s=7TeVand
] √
x inp-Pbcollisionsat s =5.02TeVarealsopresented. Theresultsarecomparedwithexpectationsfrommodels.
NN
e
- Keywords: ALICE,heavy-flavour,correlations
l
c
u
n
1. Introduction sionsaresensitivetothedependenceofCNMeffectson
[
the collision geometry and on the density of final-state

1 The study of the production of hadrons containing particles. The measurement of azimuthal correlations
v
3 charm and beauty quarks in proton-proton (pp) colli- ofDmesonsandchargedparticlesinppcollisionspro-
6 sions at the LHC provides a way to test calculations videsawaytocharacterizecharmproductionandfrag-
0 basedonperturbativeQCDathighcollisionenergy. In mentationprocesses,whileinp-Pbcollisionstheycould
3 p-Pbcollisions,heavy-flavourhadronproductionissen- giveinsightsintopossiblecollectiveeffectsinsmallsys-
0 sitivetoColdNuclearMatter(CNM)effectssuchasthe tems.
.
1 modificationofthepartondistributionsfunctionsinthe TheexcellentperformanceoftheALICEdetector[4]
0 nucleusatsmallBjorken-x(seee.g.[1]),thepartonen- allowsforopenheavy-flavourmeasurementsinseveral
7
ergylossintheinitialstagesofthecollisionviainitial- decaychannelsandinawiderapidityrange. Thiscon-
1
: stateradiation[2]andthetransversemomentumbroad- tribution focuses on the measurements at mid-rapidity
v eningduetosoftscatteringsofthepartonsintheincom- where open heavy-flavour production is studied by
i
X ingnucleus[3]. means of fully reconstructed D mesons (in the decay
channelsD0 →K−π+,D+ →K−π+π+,D∗+ →D0π+ →
r Inadditiontotransversemomentumandrapiditydif-
a K−π+π−,D+ → φπ+ → K−K+π+ andtheirchargecon-
ferential distributions, measurements as a function of s
jugates)andinthesemi-electronicdecaychannels.
multiplicityandstudiesofangularcorrelationsprovide
further constraints on the description of heavy-flavour
productioninppandp-Pbcollisions. Themeasurement 2. Heavy-flavourproductionasafunctionofmulti-
of heavy-flavour production in pp collisions as a func- plicity
tion of the charged-particle multiplicity could provide
insightsintotheroleofmulti-partoninteractions(MPI) The study of heavy-flavour production as a func-
andtheinterplaybetweenhardandsoftmechanismsin tionofthecharged-particlemultiplicityispresentedvia
particle production. The multiplicity-differential mea- the self-normalised yields, i.e. the corrected per-event
surements of heavy-flavour production in p-Pb colli- yield in a given multiplicity interval normalised to the
G.LuparellofortheALICECollaboration/NuclearandParticlePhysicsProceedings00(2017)1–3 2
count for the decay kinematics. The increasing trend
〉T
p 25 ALICE ofDmesonsandelectronsfromdecayofheavyflavour
dyd Average D0, D+, D*+ meson hadrons is compatible within uncertainties. No depen-
/ 2<p <4 GeV/c, |y |<0.5
N 20 T lab denceontheelectrontransversemomentumisobserved
2d〈 pp, s = 7 TeV also for p >∼4 GeV/c where a strong contribution
) / T15 p Pb, sNN = 5.02 TeV from beautTy-hadron decays has to be considered. The
p
d measurement gives a hint that the production mecha-
y
/d 10 nisms of charm and beauty as a function of the multi-
N
2d plicity are similar in p-Pb collisions. The results from
(
5 +6%/ 3% (3.1%) in pp (p Pb) modelcalculationsusingEPOS3eventgenerator[7]for
normalisation unc. not shown
± 6% (6.3%) unc. in pp (p Pb) D mesons considering two approaches, i.e. with and
on (dNch/dη)/〈dNch/dη〉 not shown
nc. 0.4 B fraction hypothesis in pp and p Pb: × 1/2 (2) at low (high) multiplicity withouthydrodynamicalevolutionofthesimulatedini-
n u 0.2 tial conditions, are also shown. The calculations using
dow 0 ahydrodynamicevolutionareinbetteragreementwith
d −0.2
ee−0.4 thefaster-than-linearincreaseoftheD-mesonmeasure-
B f 0 1 2 3 4 5(dN 6/dη) /7 〈dN8/dη〉9 ment,suggestingthatcollectiveeffectscouldplayarole
ALI−PUB−105454 ch ch
in particle production in high-multiplicity p-Pb colli-
Figure 1: Self-normalised yields of D mesons as a function of the sions.
charged-particlemultiplicityestimatedatmid-rapidityinpp(red)and
p-Pb(green)collisions.
3. Azimuthalcorrelations
Theazimuthalcorrelationsarebuiltbycalculatingthe
multiplicity-integrated value. Multiplicity intervals at differencein∆ηand∆φbetweenareconstructedDme-
mid-rapidity are defined by measuring the number of
son (trigger particle) andthe primary charged particles
tracklets(tracksegmentsjoiningapairofparticlehitsin
(associated particles) [8]. Corrections for limited de-
thetwolayersoftheSiliconPixelDetectorandaligned
tector acceptance, spatial inhomogeneities, trigger and
with the reconstructed primary vertex) in the pseudo- associated particle selection efficiency, as well as sec-
rapidity interval |η| < 1. The number of tracklets is
ondary track contamination are applied. The contri-
converted to the charged-particle multiplicity at mid-
bution due to the azimuthal correlations of D mesons
rapidity (dN /dη) by means of a Monte Carlo simula-
ch frombeauty-hadrondecaysandchargedparticlesisob-
tion.D0,D+andD∗+self-normalisedyieldsarecompat-
tained with PYTHIA simulations and subtracted. Dif-
iblewitheachotherwithinuncertaintiesintheanalyzed ferent ranges of the D-meson (3 < pD < 16 GeV/c
multiplicity and pT intervals. The average D0, D+ and in pp, 5 < pD < 16 GeV/c in p-Pb)Tand associated
D∗+self-normalisedyieldsasafunctionofthecharged- particle p (staTrtingfrom passoc > 0.3GeV/c)arestud-
particlemultiplicityatmid-rapidityinppcollisionsand T T
ied. Theazimuthalcorrelationdistributionisfittedwith
inp-PbcollisionsareshowninFig.1. Asimilarfaster-
twoGaussianfunctions(oneforthenear-sidepeakcen-
than-linear increasing trend with charged-particle mul- tred at ∆φ = 0 and one for the away-side peak cen-
tiplicity is observed in the two colliding systems. In tred at ∆φ = π) on top of the baseline. The base-
Ref. [5] it is reported that the measurement in pp col- line is calculated from the region π/4 < |∆φ| < π/2,
lisions is qualitatively described by model calculations
and its variation upon redefinition of this interval is
takingintoaccounttheinfluenceoftheinteractionsbe-
treated as a systematic uncertainty. Figure 3 compares
tweencoloursourcesinthepercolationmodel[6], and
the baseline-subtracted D meson-charged particle az-
thecontributionofMPI,throughthePYTHIA8[10]as
imuthal correlation distributions extracted in pp colli-
wellastheEPOS3eventgenerators[7].
sionswithpredictionsbyPYTHIA6[9],PYTHIA8[10]
Figure 2 reports the self-normalised yields of elec- and POWHEG+PYTHIA6 [11, 12] simulations, as a
trons from semi-leptonic heavy-flavour hadron decays function of the D-meson p , for different associated
T
as a function of the charged-particle multiplicity esti- particle p ranges. The simulations reproduce the az-
T
matedatmid-rapidity,comparedwiththeDmesonmea- imuthal correlation distributions within uncertainties,
surement. The different kinematic ranges for the two though a hint for a more pronounced near-side peak
observables in each panel approximately account for in data than in models is visible in the 8 < pD < 16
T
the effect of the decay kinematics. in each panel ac- GeV/c range. The parameters extracted from the fit to
G.LuparellofortheALICECollaboration/NuclearandParticlePhysicsProceedings00(2017)1–3 3
pd〉T10 ALICE p−Pb, sNN = 5.02 TeV10 Electron: 0.5 < p < 2.0 GeV/c
2y/dNd 8 Ac,LbI C→E (Pe+re +li me i)n/2a,r y|ylab| < 0.6 8 D meson: 2.0 < pTT < 4.0 GeV/c
) / p〈T 6 aArvXeirva:1g6e0 D20.0, 7D2+,4 D0*+ meson, |ylab| < 0.5 6
d
yd 3.1% normalization unc. not shown
2/Nd 4 6.3% unc. on (dNch/dη) / 〈dNch/dη〉 not shown4
(
EPOS 3.116 (D meson)
2 with hydro 2
without hydro
〉T10 10
pdy DEl emcetrsoonn: :2 4.0.0 < < p pT < < 4 8.0.0 G GeeVV//cc EDl emcetrsoonn: :4 8.0.0 < < p pT < < 8 1.02 .G0 eGVe/Vc/c
d T T
/N 8 8
2d
) / 〈T 6 6
p
d
yd 4 4
/N
2d
( 2 2
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5
(dN /dη) / 〈dN /dη〉 (dN /dη) / 〈dN /dη〉
ALI−PREL−107478 ch ch ch ch
Figure2:Self-normalisedyieldsofDmesonsandofelectronsfromheavy-flavourhadrondecaysasafunctionofthecharged-particlemultiplicity
estimatedatmid-rapiditymeasuredinp-Pbcollisions.TheresultsofEPOS3modelcalculations[7]arealsoshown.
the correlation distributions allow for a more quantita- correlation distributions of D mesons and charged par-
tive comparison of the near-side peak properties. Fig- ticles, measured in pp and p-Pb collisions, as well as
ure 4 compares the near-side associated yields and the observables describing near-side peak properties, are
near-side peak widths extracted in pp and p-Pb colli- in agreement between each other within uncertainties.
sions. Compatible values of the near-side observables TheseobservablesarealsowelldescribedbyPYTHIA
areobtainedinppandp-Pbcollisions.Nomodifications andPOWHEG+PYTHIA6MonteCarlosimulations.
ofthenear-sidepeaksduetocoldnuclearmattereffects
are observed in p-Pb collisions with the current uncer-
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isobserved. Thefaster-than-linearincreasesuggestsan
interplay between MPIs and multiple binary nucleon-
nucleon collisions in p-Pb interactions. The azimuthal
G.LuparellofortheALICECollaboration/NuclearandParticlePhysicsProceedings00(2017)1–3 4
1)d 5 Average D0,D+,D*+ALICE 5 < pDT < 8 GeV/c, paTssoc > 0.3 GeV/c 8 < pDT < 16 GeV/c, paTssoc > 0.3 GeV/c
aseline (ra 34 3| y<cD pmppsDT|, << 5s0 .G=5 ,e7 |V∆ T/ηce|, V p< aT1ssoc > 0.3 GeV/c SimulaPPPtYYYioTTTnHHHs,III AAAp666p,,,, PPPseee rrr=uuu ggg7iii aaaT 022e00V1101 PPEYOPTOWHSHI A3E8.G1, 1+T7PuYneT H4ICA6
b baseline subtraction uncertainty
assocN dϕ∆ 21 −+1103%% scale uncertainty −+1103%% scale uncertainty −+1114%% scale uncertainty
d
1 ND 0
1)ad 1.5 3 < pDT < 5 GeV/c, 0.3 < paTssoc < 1 GeV/c 5 < pDT < 8 GeV/c, 0.3 < paTssoc < 1 GeV/c 8 < pDT < 16 GeV/c, 0.3 < paTssoc < 1 GeV/c
eline (r 1 −+1103%% scale uncertainty −+1103%% scale uncertainty −+1114%% scale uncertainty
as
b
assocN dϕ∆0.05
d
1 ND−0.5
1)d 2 3 < pDT < 5 GeV/c, paTssoc > 1 GeV/c 5 < pDT < 8 GeV/c, paTssoc > 1 GeV/c 8 < pDT < 16 GeV/c, paTssoc > 1 GeV/c
a
eline (r 1.5 −+1103%% scale uncertainty −+1103%% scale uncertainty −+1114%% scale uncertainty
bas 1
assocN dϕ∆0.5
d
1 ND 0
0 0.5 1 1.5 2 2.5 3 0 0.5 1 1.5 2 2.5 3 0 0.5 1 1.5 2 2.5 3
∆ϕ (rad) ∆ϕ (rad) ∆ϕ (rad)
ALI−PUB−106084
√
Figure3: Azimuthal-correlationdistributionsofpromptDmesonswithchargedparticlesmeasuredinppcollisionsat s=7TeVcomparedto
expectationsfromMonteCarlogeneratorsafterthesubtractionofthebaseline.
3 Near side ALICE pp, s = 7 TeV, |yD | < 0.5
cms
ed yield 2.25 paTssoc > 0.3 GeV/c, |∆η| < 1 e<n7e%rg p vy0a arP.ni9adbt6i o,r a n<p e sidyxNiptcDyNem c(=sPt ey <d5th .f0ir0ao.,2m 0P 4 eTdrifuefegVriae, n2t011) PsO =W 5H.0E2G T+ePVY,T wHitIhA 6E PppS 0s9im nuPlaDtiFon
ociat 1.5 0.3 < paTssoc < 1 GeV/c, |∆η| < 1 paTssoc > 1 GeV/c, |∆η| < 1
ss 1
A
0.5
0
0.6
0.5
d) 0.4
a
(rNS 0.3
σfit,
0.2
0.1
0
0 2 4 6 8 10 12 14 160 2 4 6 8 10 12 14 160 2 4 6 8 10 12 14 16
ALI−DER−106D2 m41eson p (GeV/c) D meson p (GeV/c) D meson p (GeV/c)
T T T
Figure4: Comparisonofthenear-sidepeakassociatedyield(toprow)andpeakwidth(bottomrow)inppandp-Pbcollisionswithexpectations
fromPOWHEG+PYTHIA6MonteCarlogenerator.