Novel scenario for production of heavy flavored mesons in heavy ion collisions

0.48 MB·

by  B. Z. Kopeliovich

EPJWebofConferenceswillbesetbythepublisher
DOI:willbesetbythepublisher
(cid:13)c Ownedbytheauthors,publishedbyEDPSciences,2017
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Novel scenario for production of heavy flavored mesons
2
in heavy ion collisions
n
a
J
5 B.Z.Kopeliovich1a,J.Nemchik2,3,I.K.Potashnikova1,andIvanSchmidt1
2
1DepartamentodeFísica,UniversidadTécnicaFedericoSantaMaría;and

CentroCientífico-TecnológicodeValparaíso;Casilla110-V,Valparaíso,Chile
]
h 2CzechTechnicalUniversityinPrague,FNSPE,Brˇehová7,11519Prague,CzechRepublic
p 3InstituteofExperimentalPhysicsSAS,Watsonova47,04001Kosice,Slovakia
-
p
e
Abstract. The observed strong suppression of heavy flavored hadrons produced with
h
high p , is caused by final state interactions with the created dense medium. Vacuum
[ T
radiationofhigh-p heavyquarksceasesatashorttimescale,asisconfirmedbypQCD
T
1 calculationsandbyLEPmeasurementsofthefragmentationfunctionsofheavyquarks.
v
Productionofaheavyflavoredhadronsinadensemediumisconsiderablydelayeddue
1
topromptbreakupofthehadronsbythemedium. Thiscausesastrongsuppressionof
2
theheavyquarkyieldbecauseofthespecificshapeofthefragmentationfunction. The
1
parameter-freedescriptionisinagoodaccordwithavailabledata.
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.
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1 Introduction
7
1
: Inthepopularscenario,explainingjetquenching,observedinheavyioncollisions,byinducedenergy
v
lossinthehotmediumcreatedinthenuclearcollision, amuchweakersuppression, comparedwith
i
X lighthadrons,wasanticipated[1]forheavyflavors,causedbythedead-coneeffect.
r Later, however, measurements revealed similar magnitudes of suppression for heavy and light
a hadrons. Hereweproposeanalternativescenarioforproductionofheavyflavoredhadronsfromahot
medium. Thenovelmechanismwellexplainsdatainaparameter-freeway.
2 Hard parton collision
High-p parton-partonscatteringleadstoformationof4conesofgluonradiation:(i)thecolorfieldof
T
thecollidingpartonsisshakenoffinforward-backwarddirections;(ii)thescatteredpartonscarrying
no field up to transverse frequences k < p , are regenerating the lost components of their field,
T
radiatinggluonsandformingtwohigh-p jets. Thisprocessisillustratedinfigure1.
T
Thecoherencelength/timeofgluonradiationbyaquarkofmassm andenergyEhastheform,
q
2Ex(1−x)
l = , (1)
c k2+x2m2
q
ae-mail:[email protected]
EPJWebofConferences
Figure 1. High-p parton
T
scattering. The two forward-
Figure 2. Radiational energy
backwardjetsareformedbythe
shaken-off gluon fields. The loss of light, c and b quarks Figure3.Fractionalradiational
hloigsthfi-peTld,praardtoiantsinrgeggelunoernast.e the h(cid:113)apv2in+gmi2niti=al 1e5nGeregVy, Eversu=s eqnuearrgky, plroosdsucbeydawihthigdhi-ffpeTrebn-t
T q
initialenergies.
pathlength.
where xisthefractionallight-cone(LC)momentumoftheradiatedgluon. Apparently,firstofallare
radiatedandregeneratedgluonswithsmalllongitudinalandlargetransversemomenta.
The peculiar feature of these jets is closeness of their initial virtuality, imposed by p , and en-
(cid:113) T
ergy E = p2 +m2. Therefore, increasingthejetenergyoneunavoidablyintensifiesradiationand
T q
dissipationofenergy.
Itisinstructivetoevaluatetheamountofenergy,radiatedafterthehardcollisionbythescattered
partonoverpathlengthL[2],
(cid:90)p2T (cid:90)1
dn
∆E (L)= E dk2 dxx g Θ(L−l ), (2)
rad dxdk2 c
Λ2 0
wheretheradiationspectrumreads,
dn 2α (k2) k2[1+(1−x)2]
g = s . (3)
dxdk2 3πx [k2+x2m2]2
q
The results of calculations for absolute and fractional radiated energy loss are presented in fig-
ures 2 and 3 respectively. One can see that radiation of heavy quarks ceases shortly. Only a small
fractionoftheinitialquarkenergy,∆z = ∆E /E,isradiatedevenafteralongtimeinterval. Thisis
rad
quitedifferentfromthehadronizationpatternforlightquarks,whichkeepradiatinglongtimeandlose
mostoftheinitialenergy(seefigure2). Therefore, thefinal Bor Dmesonscarryalmostthewhole
momentumofthejet. Thisexpectationisconfirmedbythedirectmeasurementsofthefragmentation
functionsine+e− annihilation[3]. Theexampleoftheb→ Bfragmentationfunctiondepictedinfig-
ure4indeedshowsthatthedistributionstronglypeaksatz ∼ 0.85. Asimilarbehaviorwasobserved
alsoforthec→ Dfragmentationfunction[4]. Atthesametimethefragmentationfunctionsoflight
quarkstolightmesonsarewellknowntofallsteadilyandsteeplyfromsmallztowardsz=1[5]
3 Production length of heavy mesons
In what follows we mainly consider for concreteness B-meson production. If a B-meson (or a bq¯
dipole) is produced at the length l , the momentum of Bequals to the momentum of the b-quark at
p
ICNFP2016
Q
h
−
q
q }
X
Figure 6.
Redistribution of
Figure 4. The b → B fragmenta- the energy inside a Qq¯
tion function, from e+e− annihila- dipole by gluon radia-
tion. The curve is the DGLAP fit Figure5.Thel -distributionof tion by Q absorbed by
p
[3]. B-mesonsproducedwithdiffer- q¯.
entp inppcollisions.
T
thispoint. Thefractionofthemomentumcarriedbythelightqisverysmall,x≈m /m ,i.e. isabout
q b
5%. We neglect this correction in what follows. Since the radiational vacuum energy loss dE/dl is
known, we can directly relate the production length distribution W(l ) to the b → B fragmentation
p
functionD (z),
b/B (cid:12)
dW = ∂∆pb+/pb+(cid:12)(cid:12)(cid:12) D (z), (4)
dlp ∂l (cid:12)(cid:12)l=lp b/B
wheretheproductionlengthprobabilitydistributionandthefragmentationfunctionarenormalizedto
unity,(cid:82)∞dl dW/dl =1and(cid:82)1dzD (z)=1respectively;z≡ pB/pb =1−∆pb(l )/pb;and
0 p p 0 b/B + + + p +
(cid:90)lp
dpb(l)
∆pb(l )= dl + . (5)
+ p dl
0
(cid:113)
The rate of LC momentum loss is related to energy loss in accordance with pb = E + E2−m2.
+ b
Thus,knowledgeofD (z)anddE/dlgivesadirectrelationbetweenzandl . Asfarasweareable
b/B p
tocalculate∆z(L), wecanextracttheproductionlengthof B-mesonsdirectlyfromdatafor D (z).
b/B
The results for dW/dl are plotted vs l in figure 5. Remarkably, the mean value of l shrinks with
p p p
rising p ,likeithappensforproductionofhigh-p lighthadrons[6].
T T
Concluding, the fragmentation of a b-quark in vacuum looks like radiational energy loss up to
a point l = l , where it picks up a light q¯ forming a colorless bq¯ dipole, which performs a direct
p
transitiontoBwithoutlosstheb-quarkmomentum.
4 In-medium fragmentation
While in vacuum production of B at l = l is the end of the story, in a dense medium the B-meson
p
(or bq¯ dipole) can easily breakup interacting with the medium, and release the b-quark, which will
continuehadronizationandpick-upanotherlightantiquark,andsoon. Suchrecreationsandbreakups
ofB-mesonswillbemultiplyrepeated,untilthefinalproductionofthedetectedB-meson,whichwill
survive escaping from the medium. We should understand what happens with the b-quark, while it
propagateseitherasaconstituentofabq¯ dipole,orisreleasedandislosingenergytohadronization.
Afterthecoloroftheb-quarkisneutralizedbyq¯,thedipolepropagateswithoutradiationandloss
of energy. However, if the b-quark did not finish regeneration of its color field, it keeps radiating
EPJWebofConferences
insidethedipole. Theonlydifferencewiththeprecedingradiationprocessbyasinglequark,isthat
theradiationinsidethedipoleisreabsorbedbyaccompanyingq¯,asisillustratedinfigure6. Thus,the
bq¯ dipole does not radiate, its energy remains constant, however the b-quark energy is redistributed
insidethedipole,deceleratingtheb-quarkandacceleratingtheq¯.
Aswasemphasisedaboveanddemonstratedinfigures2,3,perturbativeradiationofaheavyquark
ceasesshortly, withinadistanceofabout1fm(foratypical p range). Onemightthink, lookingat
T
figure 2 that on longer distances the quark propagates like a free particle with a constant energy.
However, this would certainly contradict confinement. A popular model for the non-perturbative
mechanismofenergylossisthestringmodelwithdE /dl=−κ,wherethestringtensioninvacuum
str
isκ≈1GeV/fm.
While in vacuum a heavy flavored meson is produced on a very short length scale, l (cid:28) 1fm,
p
inahotmediumstrongabsorptionpushestheproductionpointtothedilutemediumsurface. There-
fore non-perturbative energy loss becomes important for such a long-lasting hadronization process,
which is continuing throughout the whole area occupied by the medium. However, in a deconfined
hotmediumnostringcanbeformed. Thereforethemagnitudeofthestringtension,andevenitsvery
existence,dependsonthemediumtemperature. Werelyonthemodel[7–9]basedonthelatticesim-
ulations, of temperaturedependence of the string tension, κ(T) = κ(1−T/T )1/3, where thecritical
c
temperatureisfixedatT =280MeV.
c
Thus,thefullrateofenergylosscomesfrombothperturbativeandnonperturbativemechanisms,
dE dE
= rad −κ(T). (6)
dl dl
Aftertheb-quarkhaspromptlyradiatedthewholespectrumofgluonsanddecreaseditsvirtuality
downtothesoftscale,thestringbecomestheonlysourceofenergyloss.Ifthebquarkpick-upalight
q¯ theyareconnectedbyastring,whichisalsodeceleratingtheb-quarkandacceleratingtheq¯ witha
rategivenbythestringtension. Suchanexchangeofenergybetweenbabdq¯ issimilartowhatwe
observedaboveforperturbativeradiation. Sowecanconcludethattheb-quarkisconstantlyloosing
energywitharate,whichdoesnotdependonwhetheritpropagatesalone,orasaconstituentofabq¯
dipole. Theprocesswillfinalizeonlyafterthelastrecreationofa B-meson,whichescapesfromthe
medium without further breakups. Apparently, the final B-meson will have a reduced energy com-
paredwitha B-mesonproducedatl = l invacuum,whereithasnopossibilityforfurtherbreakups.
p
In other words, with the same starting momentum pb the final momentum of the B coming out of
+
a medium, will be smaller than in vacuum. This causes suppression because of steeply falling p
T
distributionoftheperturbativelyproducedb-quarks,andduetothesteepfall-offoftheb-quarkfrag-
mentationfunctionatsmallz,asisshowninfigure4. Noticethatabovedescriptionoffragmentation
andtime-dependentenergylossholdsforcharmquarksaswell.
5 Where does the suppression come from?
ThecrosssectionofproductionofaB-mesonwithmomentum p in ppcollisionreads,
T
(cid:90)
dσ(pp→ BX) dσ(pp→ QX) 1
= d2pb D (z), (7)
d2p + d2pb z b/B
T +
(cid:113)
where pb = pb + (pb)2+m2istheinitialLCmomentumoftheb-quark;
+ T T b
(cid:113)
z≡ (pT + p2T +MB2) =1− ∆pb+(lp). (8)
pb pb
+ +
ICNFP2016
SimilarrelationholdsforAAcollisions,howeverlAA,theproductionlengthofthefinal,lastcreated
p
colorless Qq¯ dipole,islongerthanin ppcollisions,soLCmomentumloss∆pb islarger,andz is
+ AA
smaller.
Besides,the B-mesonproductioncrosssectionacquiresasuppressionfactorS(lAA),whichisthe
p
survival probability of the Qq¯ dipole, created at the point lAA, to escape the medium without being
p
broken-up,andtodevelopthehadronicwavefunction. ThusinAAcollisionEq.(7)ismodifiedas,
(cid:90)
dσ(AA→ BX) dσ(pp→ QX) 1
= d2pb D (z )S(lAA), (9)
d2p + d2pb z b/B AA p
T + AA
withz =1−∆pb(lAA)/pb.
AA + p +
ThelastfactorS(lAA)in(9)isanimportantplayer,makingthehadronizationprocessesin ppand
p
AAdifferent. Indeed,ifthisfactorwereunity,S =1,thentherewouldbenoreasontodelayproduc-
tion point to a longer distance lAA compared with hadronization in vacuum, equation (8). However,
p
absorptionterminatesthecolorlessbq¯ dipolesproduced"tooearly",soitpushestheproductionpoint
tothedilutedsurfaceofthehotmedium,makingtheproductionlengthlong,lAA (cid:29) l ,andz (cid:28) z,
p p AA
resultinginastrongsuppressionofthefragmentationfunctionD (z )accordingtofigure4.
b/B AA
Thus,thetwolastfactorsin(9)workinoppositedirections,causingsuppressionofproducedBor
Dmesons:
(i)ThefragmentationfunctionD (z),peakingatlargez(fig.4),tendstoreducemomentumloss
b/B
∆pb(lAA),selectingshorterlAA.
+ p p
(ii)However,ashorterlAA meansalongerpathlengthforfurtherpropagationofthecolorlessQq¯
p
dipoleinthemedium,increasingitschancetobrake-up.
6 Attenuation of a Qq¯ dipole in a hot medium
AQq¯ pairproducedperturbativelywithinitiallysmallseparation,quicklyexpands. Indeed,thelight
quarkinthe Qq¯-mesoncarriesatinyfractionofthemomentum, x ∼ m /m . Therefore,evenifthe
q Q
producedbq¯dipolehasasmalltransverseseparation,itssizeexpandswithahighspeed,enhancedby
1/x. TheformationtimeoftheB-mesonwavefunction(inthemediumrestframe)isveryshort,
(cid:113)
p2 +m2
tB = T B , (10)
f 2m ω
B
where ω = 300MeV is the oscillator frequency, which determines the splitting of the ground state
and the first radial excitation. For instance at p = 10GeV the B meson is formed on a distance
T
lB =0.8fm.
f
Thus,notasmall-sizer2 ∼1/p2 dipole,likeforlighthadronproduction[10],butanearlyformed
T
largeQq¯ dipoleispropagatingthroughthemedium. Itcanbeeasilybroken-up,soitsmeanfreepath
is quite short. Indeed, the B-meson is nearly as big as a pion, (cid:104)r2 (cid:105) = 0.378fm2 [11]. The mean
ch B
freepathofsuchamesoninahotmediumisveryshort,λ ∼(cid:104)qˆ(cid:104)r2(cid:105)(cid:105)−1,where(cid:104)r2(cid:105)=8(cid:104)r2 (cid:105)/3. The
B T T ch
so called transport coefficient qˆ is the rate of broadening of the quark transverse momentum in the
medium,thisiswhyitcontrolsthedipoleabsorptioncrosssection. Forinstance,atqˆ = 1GeV2/fm
(compare with [10]) the mean free path λ = 0.04fm, i.e. the b-quark propagates through the hot
B
medium, frequently picking up and losing light antiquark comovers. Meanwhile the b-quark keeps
losingenergywitharate,enhancedbymedium-inducedeffects. Eventuallythedetected B-mesonis
formedandcansurviveinthediluteperipheryofthemedium.
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6.1 ThesuppressionfactorS(lAA)
p
Thus,thefinallydetectedB-mesonisproducedatl=lAA.Inthelowenergylimittheformationlength
p
(10)isveryshortandonecanusetheeikonalGlauberapproximation,
 
S(lApA)=exp−(cid:104)r22B(cid:105)(cid:90)∞dlqˆ(l) , (11)
lApA
where(cid:104)r2(cid:105)≡(cid:104)r2(cid:105) =8(cid:104)r2 (cid:105) /3.
B T B ch B
Incontrast,inanotherextreme,thehigh-energylimit,thedipolesizeis"frozen"byLorentztime
dilation. Then,
 
S(lApA)=(cid:90) d2rdx |ΨB(r,x)|2exp−r22 (cid:90)∞dlqˆ(l) , (12)
lApA
whereΨ (r,x)istheLCwavefunctionoftheB-meson.
B
Thegeneraldescriptioninterpolatingbetweenthesetwolimits,isthepath-integraltechnique[12],
summingallpathsoftheQandq¯. Theresulthastheform,
(cid:12) (cid:12)
(cid:12)(cid:12)(cid:90)1 (cid:90) (cid:12)(cid:12)2
(cid:12) (cid:12)
S(l1,l2)∝(cid:12)(cid:12)(cid:12) dx d2r1d2r2Ψ†M(r2,x)GQq¯(l1,(cid:126)r1,x;l2,(cid:126)r2,x)Ψin(r1,x)(cid:12)(cid:12)(cid:12) , (13)
(cid:12) (cid:12)
(cid:12) (cid:12)
0
where in the case under consideration l = lAA, l → ∞. The initial distribution amplitude
1 p 2
Ψ (r ,x) is taken in the Gaussian form with mean separation (cid:104)r2(cid:105) = (cid:104)r2(cid:105). The Green function
in 1 1 B
G (l ,(cid:126)r ,x;l ,(cid:126)r ,x)describingpropagationofthedipolebetweenlongitudinalcoordinatesl , l with
Qq¯ 1 1 2 2 1 2
initialandfinalseparations(cid:126)r and(cid:126)r respectively,satisfiesthe2-dimensionalLCequation,
1 2
d (cid:34) ∆ (cid:35)
i G (l ,(cid:126)r ,x;l ,(cid:126)r ,x)= − r2 +V (l ,(cid:126)r ) G (l ,(cid:126)r ;l ,(cid:126)r ). (14)
dl Qq¯ 1 1 2 2 2p x(1−x) Qq¯ 2 2 Qq¯ 1 1 2 2
2 T
TheimaginarypartoftheLCpotentialisresponsibleforabsorption, ImV (l,(cid:126)r) = −qˆ(l)r2/4. The
Qq¯
realpartisthephenomenologicalCornell-typepotential,adjustedtoreproducethemassesanddecay
constantsforBandDmesons[11,13].
7 Results
While the employed phenomenology allows a parameter-free description of data, one parameters is
unavoidably present in such kind of analysis. This is the transport coefficient qˆ, which cannot be
reliably predicted, in particular its coordinate and time dependence. We employ here the popular
model[14],
qˆ l n ((cid:126)b,(cid:126)τ)
qˆ(l,(cid:126)b,(cid:126)τ)= 0 0 part Θ(l−l ), (15)
l n (0,0) 0
part
where(cid:126)b is the impact parameter of nuclear collision,(cid:126)τ is the impact parameter of the hard parton-
partoncollisionrelativetothecenterofoneofthenuclei,n ((cid:126)b,(cid:126)τ)isthenumberofparticipants,and
part
qˆ istherateofbroadeningofaquarkpropagatinginthemaximalmediumdensityproducedatimpact
0
ICNFP2016
parameterτ = 0incentralcollisions(b = 0)atthetimet = t afterthecollision. Thetimeinterval
0
after the hard collision is t = l/v where v is the speed of the Qq¯ dipole. We fixed the medium
Qq¯ Qq¯
equilibrationtimeatt =1fm.
0
In such a scheme qˆ is the only fitted parameter, which, however, has been already determined
0
from other hard processes in AA collisions. In particular, in the analysis [10] of data on quenching
√
oflighthigh-p hadronsitwasfoundqˆ = 1.6GeV2/fmat s = 200GeVandqˆ = 2GeV2/fmat
√ T 0 0
s=2760GeV.
Differentsourcesoftime-dependentmedium-inducedenergylosswereadded,includingradiative
andcollisionalmechanisms[15]. Medium-inducedenergylossismuchsmallerthanthevacuumone,
anddonotproduceadramaticeffect. Theyareparticularlysmallforheavyflavors.
TheresultsofcalculationsforB-mesonproductionarecomparedwithdataonindirectproduction
of J/ψ,originatingfrom Bdecays. Comparisonismadevs p andcentrality. Infigure7thedashed
T
curve is calculated with pure vacuum energy loss (radiative plus string) neglecting induced energy
loss for qˆ = 2.5GeV2/fm. The upper and bottom solid curves are calculated with qˆ = 2.5 and
0 √ 0
3GeV2/fmrespectively,at s=2.76TeVincomparisonwithdata[16].
1 1
Pb-Pb √—s = 2.76 TeV Pb-Pb √—s = 5.02 TeV
NN NN
B ⇒ J/Ψ, 0 - 100 %, CMS non-prompt J/Ψ, 0 - 80 %, ATLAS
0.75 0.75
A A
RA0.5 RA0.5
0.25 0.25
0 0
2
10 10 10
p (GeV) p (GeV)
T T
1 1
Pb-Pb √—s = 2.76 TeV Pb-Pb √—s = 5.02 TeV
NN NN
B ⇒ J/Ψ, 6.5 < p < 30 GeV, CMS
T
0.75 0.75
A A
RA0.5 RA0.5
0.25 0.25
non-prompt J/Ψ, 9 < p < 40 GeV, ATLAS
T
0 0
0 100 200 300 400 0 100 200 300 400
N N
part part
Figure7. ComparisonwithCMSdataforindi-
√
rectJ/ψproduction[17]at s=2.76TeV.The
√
dashedcurvesarecalculatedneglectinginduced Figure8. ThesameasinFig.7, butat s =
energyloss.Theupperandbottomsolidcurves 5.02TeV.Theupperandbottomcurvesarecal-
arecalculatedwithqˆ =2.5and3GeV2/fmre- culatedwithqˆ =2.6and3.2GeV2/fmrespec-
0 0
spectively. tively.Dataarefrom[17].
EPJWebofConferences
Figure 8 demonstrate comparison with recent data from ATLAS [17]. The upper and bottom
√
curves are calculated with qˆ = 2.6 and 3.2GeV2/fm respectively, at s = 5.02TeV. The lack of
0
riseofR athigh p indatalooksunusual,comparedwiththetypicalbehaviorofotherhadrons,so
AA T
wewouldrestrainofclaimingaseriousdisagreement.
Notice that the rise of qˆ with energy is natural, but its value, should not depend on the process
0
used to measure it. However, different analyses of different reactions rely on many simplifications
andmodel-dependentassumptions. Therefore,itwouldbenaivetoexpectexactcorrespondenceofqˆ
0
valuesextractedfromdataondifferenthardprocesses. Thevaluesfoundhereareprettyclosetothose
extractedin[10]fromdataonhigh-p productionoflighthadrons.
T
The approach developed here can also be applied to production of D-mesons. The results are
comparedwithdatainfigures9and10vs p andcentrality.
T
1.25 1
Pb-Pb √—sNN = 2.76 TeV Pb-Pb √—s = 5.02 TeV
NN
1 D mesons, 0 - 7.5 %, ALICE 0.8 D mesons, CMS
D mesons, 0 - 10 %, CMS
0.75 0.6
A A
A A
R R
0.5 0.4
0.25 0.2
0 - 10 %
0 0
2 2
10 10 1 10 10
p (GeV)
T
1
Pb-Pb √—s = 2.76 TeV
NN
D mesons, 8 < pT < 16 GeV, ALICE 0.8
0.75 D mesons, 8 < pT < 16 GeV, CMS
0.6
A A
RA0.5 RA
0.4
0.25
0.2
0 - 100 %
00 100 200 300 400 01 10 102
N
part p (GeV)
T
Figure 9. The same as in figure 7, but for
√
D-mesons at s = 2.76TeV. Calculations Figure 10. The same as in figure 9, but at
√
are done with the same values of qˆ = 2.5 s=5.02TeVforcentralities0-80%andmin-
0
and 3GeV2/fm. Data are from [18–20] and imum bias events. Data from CMS measure-
[21,22]. ments[23].
Notice that c-quarks radiate in vacuum much more energy than b-quarks, while the effects of
absorptionofcq¯andbq¯dipolesinthemediumaresimilar.Therefore,D-mesonsaresuppressedinAA
collisionsmorethanB-mesons.
ICNFP2016
8 Summary
Fragmentationofhigh-p heavyquarksexposenontrivialfeatures.
T
• Heavyandlightquarksproducedinhigh-p partoniccollisionsradiatedifferently.Heavyquarksre-
T
generatetheirstripped-offcolorfieldmuchfasterthanlightones,andradiateasignificantlysmaller
fractionoftheinitialenergy.
• This peculiar feature of heavy-quark jets leads to a specific shape of the fragmentation functions.
Differentlyfromlightflavors,theheavyquarkfragmentationfunctionsstronglypeakatlargefrac-
tionalmomentumz,i.e. theproducedheavy-lightmeson,BorD,carrythemainfractionofthejet
momentum. Thisisaclearevidenceofashortproductiontimeofheavy-lightmesons.
• Contrarytothepropagationofasmallq¯qdipole,whichsurvivesinthemediumduetocolortrans-
parency,aq¯Qdipolepromptlyexpandstoalargesize. Suchabigdipolehasnochancetosurvive
intactinahotmedium. Ontheotherhand,abreakupofsuchadipoledoesnotsuppressdirectlythe
productionrateofq¯Qcolorlessdipoles,butincreaseenergylossprecedingthefinalproductionofa
heavyflavoredmeson. Thisisdifferentfromthescenarioofhigh-p productionoflightq¯qmesons
T
[10].
• Data for production of high-p B and D mesons are explained in a parameter-free way. The ex-
T
tractedvaluesofthetransportcoefficientagreewiththeresultsofpreviousanalyseswithinunavoid-
ableuncertainties,relatedtoemployedsimplificationsandmodeldependentassumptions,madein
thecalculations.
• We havedisregarded sofar thesmall initial statesuppression ofheavy flavorsdue tohigher twist
heavydipoleattenuationandleadingtwistshadowing[24]. Inclusionoftheseeffectwillleadtoa
smalldecreaseofthevaluesofqˆ extractedfromtheanalysis.
0
Acknowledgements
ThisworkwassupportedinpartbyFondecyt(Chile)grants1130543,1130549,1140842,1140377,byProyecto
BasalFB0821(Chile),andbyCONICYTgrantPIAACT1406(Chile). J.N.workwaspartiallysupportedby
thegrant13-20841SoftheCzechScienceFoundation(GACˇR),bytheGrantMŠMTLG15001,bytheSlovak
ResearchandDevelopmentAgencyAPVV-0050-11andbytheSlovakFundingAgency,Grant2/0020/14.
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