The ALICE experiment has measured production of hadronic resonances such a

Riabov, V G

English

KnE Publishing Platform

 KnE Energy & PhysicsICPPA 2017The 3rd International Conference on Particle Physics and AstrophysicsVolume 2018Conference PaperMeasurement of hadronic resonances withALICE at the LHCV G Riabov1,2 for the ALICE collaboration1PNPI of NRC “Kurchatov Institute”, Orova rostcha-1, Gatchina, 188300, Russia2National Research Nuclear University MEPhI (Moscow Engineering Physics Institute),Kashirskoe highway 31, Moscow, 115409, RussiaAbstractThe ALICE experiment has measured production of hadronic resonances such as𝜌(770)0, K∗(892)0, 𝜙(1020), Λ(1520) and Ξ(1530)0 in pp, p-Pb and Pb-Pb collisions atvarious energies. Due to their short lifetimes, the hadronic resonances are sensitive tothe re-scattering and regeneration processes occurring in the time interval betweenthe chemical and the kinetic freeze-outs in heavy-ion collisions. Measurementof resonance yields and their ratios to the long-lived particles are used to studyproperties and lifetime of the late hadronic phase. In these proceedings, we presentthe most recent ALICE results on resonance production including the latest resultsfrom the LHC Run 2.1. IntroductionOver the years, a wide variety of resonances has been measured and studied withALICE detector at the LHC. Resonances are excited hadronic states with lifetimes com-parable to that of the fireball produced in heavy-ion collisions. Many of resonancesdecay inside themedium before the interacting system breaks up. Among other things,resonances are sensitive to re-scattering and regeneration occurring between thechemical and the kinetic freeze-outs. Hence, resonances can be used to study proper-ties of the late hadronic phase.2. Particle ratios and properties of the hadronic phaseProcesses happening in the hadronic phase depend on lifetime of the hadronic phase,resonance lifetime and scattering cross sections, which depend on daughter particletypes and momenta. Table below gives a list of resonances measured at mid-rapidityHow to cite this article: V G Riabov, (2018), “Measurement of hadronic resonances with ALICE at the LHC” in The 3rd International Conference onParticle Physics and Astrophysics, KnE Energy & Physics, pages 429–434. DOI 10.18502/ken.v3i1.1778 Page 429Corresponding Author:V G Riabovriabovvg@pnpi.nrcki.ruReceived: 25 December 2017Accepted: 2 February 2018Published: 9 April 2018Publishing services provided byKnowledge EV G Riabov. This article isdistributed under the terms ofthe Creative CommonsAttribution License, whichpermits unrestricted use andredistribution provided that theoriginal author and source arecredited.Selection and Peer-reviewunder the responsibility of theICPPA Conference Committee. KnE Energy & Physics ICPPA 2017T 1𝜌(770)0 K∗(892)0 Λ(1520) Ξ(1530)0 𝜙(1020)c𝜏 (fm/c) 1.3 4.2 12.7 21.7 46.2Decaychannel𝜋𝜋 K𝜋 pK 𝜋Ξ KKwith ALICE detector in pp, p-Pb and Pb-Pb collisions at various energies. The res-onances are reconstructed in the hadronic decay channels and have very differentlifetimes.Figure 1 shows a ratio of integrated yields, 𝜌(770)0/𝜋, measured as a function ofmultiplicity in pp and Pb-Pb collisions at ps𝑁𝑁 = 2.76 TeV. The 𝜌(770)0 is a very short-lived resonance, its daughter particles are expected to interact with the surroundinghadrons thus affecting the measured yields. One can see that production of 𝜌(770)0meson is suppressed going from pp to peripheral and then to central Pb-Pb collisions.The value of the ratio measured in central collisions is inconsistent with prediction ofgrand-canonical thermal model with a chemical freeze-out temperature of 156 MeV[1, 2]. However, EPOS3 event generator [3], which includes the UrQMD [4, 5] to simulatethe late hadronic cascade describes the observed multiplicity dependence of the ratiowell. At this, EPOS3 predict a flat ratio when UrQMD is disabled in the simulation.The measurement is consistent with loss of 𝜌(770)0 signal due to re-scattering of thedaughter pions in the hadronic phase.Two panels of Figure 2 show K∗(892)0/K and 𝜙(1020)/K ratios measured as a functionof multiplicity in pp, p-Pb and Pb-Pb collisions at different energies [6-8]. The K∗(892)0has three times longer lifetime than 𝜌(770)0 and yet it is only ∼ 4.2 fm/c. Hence onecan expect similar effects for K∗(892)0 as for 𝜌(770)0. On the other hand 𝜙(1020) mesonlives ten times longer than K∗(892)0 and one can expect that it behaves as a quasi-stable particle. Indeed one can see that 𝜙(1020)/K ratio does not change much and itis consistent between pp, p-Pb and different centrality Pb-Pb collisions. At the sametime K∗(892)0/K ratio, similar to 𝜌(770)0/𝜋 ratio, exhibits a suppression from pp tocentral Pb-Pb collisions. Ratio K∗(892)0/K in central Pb-Pb collisions is not consistentwith thermal model prediction [9]. Measured K∗(892)0/K ratio is compared to EPOS3calculation [3] in the figure. One can see that EPOS3 reasonably well reproduces themeasured multiplicity dependence. Again this behavior of the ratios is in agreementwith expectations from re-scattering of decay products of very short-lived K∗(892)0in the hadronic phase. At this 𝜙(1020) meson behaves as a stable particle becauseof much longer lifetime. It is interesting to note that multiplicity dependent measure-ments in pp and p-Pb show smooth transition between pp and peripheral Pb-Pb points,DOI 10.18502/ken.v3i1.1778 Page 430 KnE Energy & Physics ICPPA 2017Figure 1: Ratio of integrated yields, 𝜌(770)0/𝜋, in pp and 0–20%, 20–40%, 40–60%, 60–80% central Pb-Pb collisions at √s𝑁𝑁 = 2.76 TeV as a function of multiplicity. Statistical uncertainties are shown as bars.The total and uncorrelated systematic uncertainties are shown with open and shaded boxes, respectively.The measurements are compared to EPOS3 calculations [3] and grand canonical thermal model prediction[1, 2].probably indicating presence of the hadronic medium even in small systems at highmultiplicity. Right panel of Figure 2 also compares measurements performed at√s𝑁𝑁= 2.76 TeV and 5.02 TeV. Within uncertainties, there is no energy dependence of theratios.Figure 2: Ratios of integrated yields, K∗(892)0/K and 𝜙(1020)/K, in pp, p-Pb and Pb-Pb collisions atdifferent energies as a function of multiplicity [6-8]. Statistical uncertainties are shown as bars. The totaland uncorrelated systematic uncertainties are shown with open and shaded boxes, respectively. Themeasurements are compared to EPOS3 calculations [3] and grand canonical thermal model prediction [9].DOI 10.18502/ken.v3i1.1778 Page 431 KnE Energy & Physics ICPPA 2017Figure 3: Ratio of integrated yields, Λ(1520)/Λ, in pp, d-Au, p-Pb, Au-Au and Pb-Pb collisions at differentenergies as a function of multiplicity. Statistical uncertainties are shown as bars. The total and uncorrelatedsystematic uncertainties are shown with open and shaded boxes, respectively. The measurements inPb-Pb collisions are compared to EPOS3 calculations [3] and grand canonical thermal model predictions[10-12].Figure 3 shows results for Λ(1520)/Λ ratio measured in pp, p-Pb and Pb-Pb collisionsat different energies. Λ(1520) lives ten times longer than 𝜌(770)0, ∼ 13 fm/c. The ratiostays constant in pp and different multiplicity p-Pb collisions. However, it becomesmore and more suppressed going from peripheral to central Pb-Pb interactions. As forother short-lived resonances, ratio in central collisions is not reproduced by thermalmodel predictions [10-12]. The multiplicity dependence of suppression is qualitativelyreproduced by EPOS3 calculations [3] although absolute scaling is not perfect. The LHCpoints are also consistent with previous measurements by STAR at√s𝑁𝑁 = 200 GeV.Figure 4 shows the multiplicity dependence of Ξ(1530)0/Ξ ratio in pp, p-Pb and Pb-Pb collisions at different energies. The Ξ(1530)0 lives two times longer than Λ(1520) forwhich we observed the suppression. However, it lives two times shorter than 𝜙(1020)for which we observed nomultiplicity dependent effects. The ratio wasmeasured withhigh precision in pp and p-Pb collisions and at these multiplicities the ratio stays con-stant. There is a hint of suppression observed in Pb-Pb collisions although within largesystematic uncertainties. Thermal models [1,2,10-12] overestimate the ratio in Pb-Pb,DOI 10.18502/ken.v3i1.1778 Page 432 KnE Energy & Physics ICPPA 2017while Pythia8 [13] and DPMJET [14] underestimate it in pp and p-Pb, respectively. TheEPOS3 [3], which was very successful for other resonances does not predict significantmultiplicity dependence of the ratio in Pb-Pb collisions. Experimental uncertainties ofthe measurements in Pb-Pb should be reduced in order to be conclusive.Figure 4: atio of integrated yields, Ξ(1530)0/Ξ, in pp, p-Pb and Pb-Pb collisions at different energiesas a function of multiplicity. Statistical uncertainties are shown as bars. The total and uncorrelatedsystematic uncertainties are shown with open and shaded boxes, respectively. The measurements inPb-Pb collisions are compared to EPOS3 calculations [3] and grand canonical thermal model predictions[1,2,10-12]. Measurements in pp and p-Pb are compared to predictions of Pythia 8 [13] and DPMJET [14]event generators.3. ConclusionFrom the 𝜌(770)0/𝜋, K∗(892)0/K, Λ(1520)/Λ, Ξ(1530)0/Ξ and 𝜙(1020)/K ratios shownin these proceedings one can see that as the resonance lifetimes becomes largerthe suppression of the yields becomes less prominent or absent as for the case of𝜙(1020). Ratios are reasonable well reproduced by EPOS3 event generator [3] thatmodels hadronic cascade with UrQMD [4, 5]. Obtained results support the existenceof the hadronic phase, which lasts long enough to cause a significant reduction of thereconstructed yields of short-lived resonances. The measured ratios coupled to modelpredictions can be used to estimate the hadronic phase lifetime. Current lower limit forthe hadronic phase lifetime is 2 fm/c [15, 16].DOI 10.18502/ken.v3i1.1778 Page 433 KnE Energy & Physics ICPPA 2017AcknowledgementThis work was supported by the Competitiveness Growth Program at the NationalResearch Nuclear University “MEPhI” (Moscow Engineering Physics Institute).References[1] Stachel J et al. 2014 J. Phys.: Conf. Ser. 509 012019[2] Andronic A et al. 2009 Phys. Lett. B 673 142-145, Erratum: 2009 Phys. Lett. B 678516[3] Knospe A G et al. 2016 Phys. Rev. C 93 014911[4] Bass S A et al., 1998 Prog. Part. Nucl. Phys. 41 255-369[5] Bleicher M et al., 1999 J. Phys. G 25 1859-1896[6] Abelev B et al., 2015 Phys. Rev. C 91 024609[7] Adam J et al., 2016 Eur. Phys. J. C 76 245[8] Adam J et al., 2017 Phys. Rev. C 95 064606[9] Stachel J et al., 2014 J. Phys.: Conf. Ser. 509, 012019[10] Andronic A et al., 2006 Nucl. Phys. A 772, 167[11] Wheaton S et al., 2005 J. Phys. G 31, S1069[12] Petran M et al., 2014 Comput. Phys. Commun. 185, 2056[13] Sjo¨strand T et al., 2008 Comput. Phys. Commun. 178, 852–867[14] Roesler S et al., 2000 arXiv:hep-ph/0012252[15] Torrieri G et al. 2002 J. Phys. G 28, 1911-1919[16] Markert C et al., 2002 arXiv:hep-ph/0206260v2DOI 10.18502/ken.v3i1.1778 Page 434

Measurement of Hadronic Resonances with ALICE at the LHC

The ALICE experiment has measured production of hadronic resonances such as ρ(770)0 , K *(892)0 , ϕ (1020), Λ (1520) and Ξ(1530)0 in pp, p-Pb and Pb-Pb collisions at various energies. Due to their short lifetimes, the hadronic resonances are sensitive to the re-scattering and regeneration processes occurring in the time interval between the chemical and the kinetic freeze-outs in heavy-ion collisions. Measurement of resonance yields and their ratios to the long-lived particles are used to study properties and lifetime of the late hadronic phase. In these proceedings, we present the most recent ALICE results on resonance production including the latest results from the LHC Run 2

Measurement of Hadronic Resonances with ALICE at the LHC

Abstract

Similar works

Full text

Available Versions

KnE Publishing Platform

CERN Document Server

Crossref