D-meson and charmed-baryon measurement in pp and p-pb collisions with ALICE at the LHC

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1 D-meson an charme-baryon measurement in pp an p-pb collisions with at the LHC on behalf of the Collaboration INFN an University of Salerno A Large Ion Collier Experiment () at CERN was esigne to stuy the strongly interacting meium create in heavy-ion collisions at the LHC, the Quark-Gluon Plasma (QGP). Heavy quarks (charm an beauty), prouce in the early stages of the collision, are among the most powerful probes to investigate QGP properties. On this regar, results from pp an p-pb collisions constitute the neee reference in orer to isentangle initial-state from QGP relate effects. Charme mesons (D, D, D an D s ) were reconstructe via their haronic ecays at mirapiity in pp collisions at s = 5., 7, 8 an 3 ev an in p-pb collisions at s NN = 5. ev. he first measurement of the charme baryon, Λ c, at mi-rapiity was performe in pp collisions at s = 7 ev an in p-pb collisions at s NN = 5. ev through the full reconstruction of two of its haronic ecay channels an the partial reconstruction of one of its semileptonic ecay channels. Moreover, the first measurement at the LHC of the Ξ c e Ξ ν e prouction cross section was performe in pp collisions at s = 7 ev. In this contribution recent results on charme meson an baryon prouction, measure with the etector in pp an p-pb collisions, will be presente. XVII International Conference on Haron Spectroscopy an Structure 5-9 September, 7 University of Salamanca, Salamanca, Spain Speaker. c Copyright owne by the author(s) uner the terms of the Creative Commons Attribution-NonCommercial-NoDerivatives 4. International License (CC BY-NC-ND 4.).

2 . Introuction Charm an beauty quarks are powerful probes to stuy the properties of the Quark-Gluon Plasma (QGP), the hot an ense state of strongly-interacting matter prouce in high-energy heavy-ion collisions. Prouce in har parton scattering processes occurring in the early stages of the collision, they traverse the hot meium, interact with its constituents an experience the whole evolution of the meium. he presence of a meium with a high ensity of econfine quarks can affect the heavy-quark haronisation mechanism. Charm an beauty quarks coul haronise via recombination (coalescence) with other quarks from the meium. Measuring the Λ c / D ratio in Pb-Pb collisions coul evience a moification of charm fragmentation with respect to the vacuum case an woul allow to constrain thermal an coalescence moels, which offer ifferent preictions. he interpretation of particle prouction measurements in Pb-Pb collisions requires etaile stuies also in pp an p-pb collisions: pp collisions provie the essential reference for measurements in Pb-Pb collisions an a sensitive test of perturbative Quantum ChromoDynamics (pqcd) preictions at the LHC energies. he measurement of heavy flavour haron prouction in p-pb collisions is crucial to access Col Nuclear Matter (CNM) effects in the initial an final states, such as moification of the Parton Distribution Functions in nuclei (npdf) [], gluon saturation at low Bjorken-x [], k broaening. Some insight into the role of Multi-Parton Interactions (MPI) an the interplay between har an soft mechanism for particle prouction can be obtaine by stuying heavy-flavour prouction as a function of the multiplicity of charge particles prouce in pp an p-pb collisions [3] [4].. Charm measurements with he etector, escribe in etail in [5] [6], consists of a central barrel at mi-rapiity ( η <.9), a muon spectrometer at forwar rapiity (-4. < η < -.5) an a set of etectors (at forwar an backwar rapiity) for global collision characterization an triggering purposes. In this paper, open heavy flavour measurements via haronic an semileptonic ecay reconstruction in the central barrel will be iscusse.. Charme-meson measurements own to p = in pp an p-pb collisions D mesons an their charge conjugates are reconstructe in via their haronic ecays at central rapiity ( y <.5): D K π, cτ = 3 µm, branching ratio (BR) = (3.93 ±.4)%; D K π π, cτ = 3 µm, BR = (9.46 ±.4)%; D D ( K π )π, strong ecay, BR = (67.7 ±.5)%; D s φ ( K K )π, cτ = 5 µm, BR = (.7 ±.8)%. he analyses are base on the reconstruction of the ecay vertices isplace by a few hunre µm from the interaction vertex, exploiting the high track-position resolution close to the interaction vertex provie by the Inner racking System (IS). he large combinatorial backgroun is reuce by selections applie on the ecay topology an by the ientification of charge kaons an pions via their specific energy loss in the ime Projection Chamber (PC) an their time-of-flight measure with the ime Of Flight (OF) etector. Raw D-meson yiels are obtaine from an invariant mass analysis of

3 pairs/triplets of tracks with proper charge sign combination. Prouction cross section measurements of prompt D mesons were performe in pp collisions at s = 7 ev an.76 ev [7, 8, 9, ] an foun to be well escribe by pqcd calculations. he p -ifferential cross sections for D at s = 5 ev an D s at s = 7 ev are shown in Fig., together with FONLL [] [] an GM-VFNS [3] pqcd calculations. he theoretical preictions ten to reprouce the measure cross sections within the large theoretical uncertainties. c) y) (µb GeV σ/(p Preliminary, pp, s =5 ev FONLL ALI PREL 3338 Prompt D, y <.5 ata FONLL ±.3% lumi, ±.% BR uncertainty not shown c) y) (µb GeV σ/(p ALI PUB 543 pp, s=7 ev Prompt D, y <.5 s ± 3.5% lumi, ± 3.5% BR uncertainty not shown Figure : ransverse momentum-ifferential cross sections of prompt D mesons in pp collisions at s = 5 ev (left panel) an prompt D s mesons in pp collisions at s = 7 ev (right panel, from []) compare with FONLL [] [] an GM-VFNS [3] theoretical calculations. In orer to exten the D measurement own to p =, where the ecay-vertex selection becomes very inefficient, a ifferent analysis technique, base on particle ientification (PID) an backgroun subtraction was evelope [4]. he cross section measurement obtaine for prompt D in pp collisions is shown in Fig.. Next, CNM effects on charm meson prouction are stuie. he nuclear moification factor R ppb is built as the ratio of the D-meson cross section in p-pb collisions relative to the one in pp collisions scale by the atomic mass number of the lea nucleus. Figure 3 shows the average of the non-strange D-meson R ppb in the interval < p < 36 GeV/c. he measure R ppb [6] is compare with theoretical calculations: moels incluing CNM effects [7, 8, 9, ], shown in Fig. 3 (left), escribe quite well the experimental results within uncertainties. he comparison is also one with the transport moel calculations Duke an POWLANG [], shown in Fig. 3 (right), which assume that a Quark-Gluon Plasma is forme also in p-pb collisions. he current precision of the measurement oes not allow to iscriminate between the two scenarios even though the ata seem to isfavour a suppression larger than 5-% at high p.. Charme-baryon measurements in pp an p-pb collisions he measurement of Λ c prouction [] was performe by reconstructing three ecay moes: Λ c pkπ with BR = (6.35 ±.33) %; Λ c pk S with BR = (.58 ±.8)% an K S π π with

4 c) y) (µb GeV σ/(p pp, s=7 ev Prompt D, y <.5 FONLL fact LO k ALI PUB 644 ± 3.5% lumi, ±.3% BR uncertainty not shown Figure : ransverse momentum-ifferential cross section of D mesons own to p =, for y <.5 in pp collisions at s = 7 ev [4]. FONLL [] [], GM-VFNS [3] an k -factorization [5] theoretical preictions are also shown. R ppb ALI PREL 354 Preliminary Prompt D mesons,.96<y <.4 cms Average D, D, D* D CGC (Fujii Watanabe) FONLL with EPPS6 npdf p Pb, =5. ev s NN Vitev et al.: power corr. k broa CNM Eloss Kang et al.: incoherent multiple scattering R ppb ALI PREL 397 Preliminary Duke Prompt D mesons,.96<y <.4 cms POWLANG (HL) Average D, D, D* D POWLANG (lqcd) p Pb, =5. ev s NN Figure 3: Left: Nuclear moification factor R ppb of prompt D mesons in p-pb collisions at s NN = 5. ev: average R ppb of D, D an D mesons in the interval < p < 36 GeV/c [6], shown together with the D R ppb in < p < GeV/c []. he ata are compare with theoretical calculations incluing only CNM effects (CGC [7], NLO pqcd [8] with EPS9 npdfs []), a LO pqcd calculation with CNM effects [9] an a calculation base on incoherent multiple scatterings []. Right: Same ata as on the left. he results are compare to the expectations from the Duke an POWLANG [] transport moels. BR = (69. ±.5) %; Λ c eνλ with BR = (3.6 ±.4)% Λ pπ with BR = (63.9 ±.5)%. he haronic ecays were fully reconstructe while the semileptonic ecay was partially reconstructe because the neutrino is not etectable with. he cross section of prompt Λ c baryons in pp collisions at s = 7 ev an in p-pb collisions at snn = 5. ev was extracte in the three ifferent ecay channels an using ifferent analysis techniques. o achieve higher precision, these results were average together, taking into account the correlation between the statistical an systematic uncertainties. In Fig. 4 on the left, the first measurement of Λ c -baryon prouction at LHC energies in pp collisions in the central rapiity region is shown an compare with GM-VFNS pqcd calculations [3] an with results from 3

5 POWHEG event generator [4]. he GM-VFNS preiction, existing only for p > 3 GeV/c, unerestimates the measure cross section by a factor higher than.5, while escribe well, within uncertainties, the D-meson cross sections at central rapiities [] an the Λ c cross section at forwar rapiity measure by LHCb [5]. POWHEG unerestimates the measure cross section by a factor between 4 an 8, while it also escribes the cross sections of D mesons in pp collisions. In Fig. 4 on the right, the Λ c cross section in p-pb collisions average from the measurements in two ecay channels is shown an compare with POWHEG calculations, which unerestimate the measure cross section by a factor similar to what is observe in pp collisions. Lansberg an Shao Preictions [6], base on a pp ata-riven moeling of the scattering at partonic level, unerestimate the measurements by a factor two. (µb/gev/c) σ/y p POWHEG ALI PUB 445 ± 3.5% lumi. uncertainty not shown pp, s = 7 ev Λ c combination of pk π, pk an e ν e Λ analyses S y <.5 POWHEG PYHIA6 5 (µb/gev/c) σ/y p POWHEG Shao et al. 4 3 ALI PUB 449 p Pb, s NN = 5. ev Λ c combination of pk π an pk analyses S.96 < y <.4 ± 3.7% lumi. uncertainty not shown POWHEG PYHIA6 Shao et al. with EPS9NLO npdf an multiplie by A 5 5 Figure 4: Prompt Λ c p -ifferential prouction cross section in pp collisions at s = 7 ev in the transverse momentum interval < p < 8 GeV/c (left) an in p-pb collisions at s NN = 5. ev in the transverse momentum interval < p < GeV/c (right) []. Comparisons with GM-VFNS calculation [3], POWHEG event generator [4] an with Lansberg an Shao preiction [6]. he results obtaine were use to extract the Λ c / D ratio, where for the D cross section recent measurements were taken into account [] [4]. Results in pp an p-pb collisions are shown in Fig. 5 an foun compatible with each other within uncertainties. Preictions for the pp ata sample from PYHIA8 with two tunes (the Monash 3 tune [7] an the Moe tune [8]), DIPSY [9] an HERWIG7 are superimpose. he PYHIA8 tune with enhance colour reconnection is closer to the ata an qualitatively better escribes the p tren. he p- Pb measurements are compare with calculations from Lansberg an Shao [6], which are, among the available preictions, the closest to the ata. he prouction of the charm-strange baryon Ξ c was measure for the first time at the LHC, through its semileptonic ecay into Ξ c e Ξ ν e in pp collisions at s = 7 ev [3]. Its p -ifferential cross section, multiplie by the branching ratio (currently unknown), in the p interval < p < 8 GeV/c at mi-rapiity, is shown in the left panel of Fig. 6. he ratio of the 4

6 / D Λ c.4 pp, s = 7 ev...8 y <.5 PYHIA8 (Monash) PYHIA8 (CR Moe) DIPSY (ropes) HERWIG7 p Pb, s NN = 5. ev.96 < y <.4 Shao et al. with EPS9NLO npdf ALI PUB 44 Figure 5: he Λ c / D ratio in pp an p-pb collisions []. he measurements from pp collisions are compare with ifferent event generators [8] [9]. p -ifferential cross section of Ξ c multiplie by the branching ratio to that of D [] is shown in Fig. 6 on the right, compare with preictions from PYHIA 8 event generator with ifferent tunes. heoretical calculations for the BR varies between.8% an 4.%, efining the uncertainties bans shown in the figure. All the preictions unerestimate significantly the measure ratio. As for the Λ c case, the Moe tune [8], with a specific tuning on colour reconnection mechanisms, gives a better escription of the Ξ c / D ratio. c) (µb GeV y σ/p ν e ) Ξ e BR(Ξ c ALI PUB 4339 ecays Not correcte for Ξ b ± 3.5% norm. uncertainty not shown pp, s = 7 ev y <.5 Ξ e c Ξ ν e ν e /D e Ξ Ξ c 3 4 ALI PUB 4335 (a) pp, s = 7 ev y <.5 PYHIA8 Monash [64] PYHIA8 (CR, Moe) [8] Figure 6: he inclusive Ξ c -baryon p -ifferential prouction cross section multiplie by the branching ratio in Ξ c e Ξ ν e (left) as a function of p in pp collisions at s = 7 ev. Right: Ξ c / D ratio as a function of p in pp collisions at s = 7 ev [3], compare with preictions from PYHIA 8 with ifferent tunes [7] [8]. 3. Conclusions Measurements of open charm prouction were carrie out successfully with the experiment at the LHC. he p -ifferential prouction cross sections for prompt D mesons in pp an p-pb collisions are reprouce within uncertainties by theoretical preictions base on pqcd calculations. he R ppb 5

7 of prompt D mesons in p-pb collisions is consistent with unity within uncertainties, however the current precision of the measurement oes not allow to iscriminate between CNM effects an effects relate to the possible QGP formation. he charm baryon Λ c prouction cross section was measure in pp collisions at s = 7 ev an p-pb collisions at s NN = 5. ev. heoretical calculations unerestimate the measure cross section. he Λ c / D yiel ratios measure in pp an p-pb collisions are compatible within uncertainties. Event generators with ifferent haronisation schemes unerestimate pp results. he first LHC measurement of the p -ifferential cross section of the charm-strange baryon Ξ c, multiplie by the branching ratio Ξ c e Ξ ν e was performe in pp collisions at s = 7 ev. Several event generators with various moels an tunes for the haronisation mechanism unerestimate unerestimate significantly the Ξ c / D ratio. he Λ c an Ξ c measurements presente can provie important constraints to the moels of charm quark haronisation. References [] K. J. Eskola, H. Paukkunen an C. A. Salgao, JHEP 94, 65 (9) [] I. Vitev, Phys. Rev. C 75, 6496 (7) [3]. Sjostran an M. van Zijl, Phys. Rev. D 36, 9 (987). [4] S. Porteboeuf an R. Granier e Cassagnac, Nucl. Phys. Proc. Suppl. 4, 8 () [5] B. Abelev et al. [ Collaboration], Int. J. Mo. Phys. A 9, 4344 (4) [6] K. Aamot et al. [ Collaboration], JINS 3, S8 (8). [7] B. Abelev et al. [ Collaboration], JHEP, 8 () [8] B. Abelev et al. [ Collaboration], Phys. Lett. B 78, 79 () [9] B. Abelev et al. [ Collaboration], JHEP 7, 9 () [] S. Acharya et al. [ Collaboration], Eur. Phys. J. C 77, no. 8, 55 (7) [] M. Cacciari, M. Greco an P. Nason, JHEP 985, 7 (998) [] M. Cacciari, S. Frixione, N. Houeau, M. L. Mangano, P. Nason an G. Riolfi, JHEP, 37 () [3] B. A. Kniehl, G. Kramer, I. Schienbein an H. Spiesberger, Phys. Rev. D 84, 946 () [4] J. Aam et al. [ Collaboration], Phys. Rev. C 94, no. 5, 5498 (6) [5] B. A. Kniehl, G. Kramer, I. Schienbein an H. Spiesberger, Eur. Phys. J. C 7, 8 () [6] B. B. Abelev et al. [ Collaboration], Phys. Rev. Lett. 3, no. 3, 33 (4) [7] H. Fujii an K. Watanabe, Nucl. Phys. A 95, (3) [8] S. Frixione, M. L. Mangano, P. Nason an G. Riolfi, Phys. Lett. B 38, 37 (993) [9] R. Sharma, I. Vitev an B. W. Zhang, Phys. Rev. C 8, 549 (9) [] Z. B. Kang, I. Vitev, E. Wang, H. Xing an C. Zhang, Phys. Lett. B 74, 3 (5) [] A. Berauo, A. De Pace, M. Monteno, M. Nari an F. Prino, JHEP 63, 3 (6) [] S. Acharya et al. [ Collaboration], arxiv:7.958 [nucl-ex]. 6

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