PRODUCTION OF (ANTI-)YPERNUCLEI WIT ALICE AT TE LC Stefano Piano on behalf of ALICE Collaboration INFN sez. Trieste ASTRA: Advances and open problems in low-energy nuclear and hadronic STRAngeness physics 27-1-217 Stefano Piano 1
MOTIVATION TO MEASURE (ANTI-)YPERNUCLEI IN Pb-Pb COLLISIONS WIT ALICE AT TE LC ALICE aims to study the formation of Quark-Gluon Plasma, its properties and evolution: (anti-)(hyper)nuclei yields are sensitive to the freeze-out temperature due to their large mass (e.g. in the Thermal Model yield scales roughly e (-M/Tchem) ) light (anti-)(hyper)nuclei, small binding energy and small separation energy, e.g. B ( ) =.1 ±.5 MeV [. Bando et al., Int. J. Mod. Phys. A 5 421 (199)] : light (anti-)(hyper)nuclei should dissociate in a medium with high T chem (~156 MeV) and be suppressed if light (anti-)(hyper)nuclei yields equal to thermal model prediction sign for adiabatic (isentropic) expansion in the hadronic phase A= (anti-)( e, t, ), a simple system of 9 valence quarks: / e and / t (and anti) -nucleon correlation (local baryon-strangeness correlation) t / e (and anti) local charge-baryon correlation YN & YY interaction (strangeness sector of hadronic EOS, cosmology, physics of neutron stars) Anti-nuclei in nature: matter antimatter asymmetry [J.Adam et al. (ALICE Collaboration), Nature Phys. 11, no.1, 811 (215) ] ASTRA: Advances and open problems in low-energy nuclear and hadronic STRAngeness physics 27-1-217 Stefano Piano 2
(ANTI-)(YPER)NUCLEI PRODUCTION IN URIC Statistical Thermal model Coalescence Thermodynamic approach to particle production in heavy-ion collisions Abundances fixed at chemical freeze-out (T chem ) (hyper)nuclei are very sensitive to T chem because of their large mass (M) If baryons at freeze-out are close enough in Phase Space an (anti-)(hyper)nucleus can be formed (yper)nuclei are formed by protons () and neutrons which have similar velocities after the freeze-out Exponential dependence of the yield e (-M/Tchem) A. Andronic et al., Phys. Lett. B 697, 2 (211) ASTRA: Advances and open problems in low-energy nuclear and hadronic STRAngeness physics 27-1-217 Stefano Piano G. Chen et al., Phys. Rev. C 88, 498 (21)
(ANTI-)(YPER)NUCLEI PRODUCTION AT LC Production yield estimate of (anti-)(hyper)nuclei in central heavy ion collisions at LC energy based on thermal model: A. Andronic et al., Phys. Lett. B 697, 2 (211) Yield/event at mid-rapidity and central collisions ~8 p ~4 ~ d ~.17 e ~.1 ~. Light nuclei (see Dönigus talk) ypertriton Search for: n, dibaryons LC A. Andronic et al., Phys. Lett. B 697, 2 (211) A. Andronic, private communication ASTRA: Advances and open problems in low-energy nuclear and hadronic STRAngeness physics 27-1-217 Stefano Piano 4
A LARGE ION COLLIDER EXPERIMENT ALICE particle identification capabilities are unique. Almost all known techniques are exploited: de/dx, time-offlight, transition radiation, Cherenkov radiation, calorimetry and decay topology (V, cascade) ITS: precise separation of primary particles and those from weak decays (hypernuclei) or knock-out from material K. Aamodt et al. (ALICE Collaboration), JINST (28) S82 B. B. Abelev et al. (ALICE Collaboration), Int. J. Mod. Phys. A 29 (214) 1444 ASTRA: Advances and open problems in low-energy nuclear and hadronic STRAngeness physics 27-1-217 Stefano Piano 5
A LARGE ION COLLIDER EXPERIMENT ALICE particle identification capabilities are unique. Almost all known techniques are exploited: de/dx, time-offlight, transition radiation, Cherenkov radiation, calorimetry and decay topology (V, cascade) ITS: precise separation of primary particles and those from weak decays (hypernuclei) or knock-out from material TPC: particle identification via de/dx (allows also separation of charges). K. Aamodt et al. (ALICE Collaboration), JINST (28) S82 B. B. Abelev et al. (ALICE Collaboration), Int. J. Mod. Phys. A 29 (214) 1444 ASTRA: Advances and open problems in low-energy nuclear and hadronic STRAngeness physics 27-1-217 Stefano Piano 6
A LARGE ION COLLIDER EXPERIMENT ALICE particle identification capabilities are unique. Almost all known techniques are exploited: de/dx, time-offlight, transition radiation, Cherenkov radiation, calorimetry and decay topology (V, cascade) ITS: precise separation of primary particles and those from weak decays (hypernuclei) or knock-out from material TPC: particle identification via de/dx (allows also separation of charges). TOF: particle identification via time-of-flight K. Aamodt et al. (ALICE Collaboration), JINST (28) S82 B. B. Abelev et al. (ALICE Collaboration), Int. J. Mod. Phys. A 29 (214) 1444 ASTRA: Advances and open problems in low-energy nuclear and hadronic STRAngeness physics 27-1-217 Stefano Piano 7
A LARGE ION COLLIDER EXPERIMENT ALICE particle identification capabilities are unique. Almost all known techniques are exploited: de/dx, time-offlight, transition radiation, Cherenkov radiation, calorimetry and decay topology (V, cascade) ITS: precise separation of primary particles and those from weak decays (hypernuclei) or knock-out from material TPC: particle identification via de/dx (allows also separation of charges). TOF: particle identification via time-of-flight TRD: electron identification via transition radiation ITSTPCTRD: excellent track reconstruction capabilities in a high track density environment K. Aamodt et al. (ALICE Collaboration), JINST (28) S82 B. B. Abelev et al. (ALICE Collaboration), Int. J. Mod. Phys. A 29 (214) 1444 ASTRA: Advances and open problems in low-energy nuclear and hadronic STRAngeness physics 27-1-217 Stefano Piano 8
A LARGE ION COLLIDER EXPERIMENT ALICE particle identification capabilities are unique. Almost all known techniques are exploited: de/dx, time-offlight, transition radiation, Cherenkov radiation, calorimetry and decay topology (V, cascade) K. Aamodt et al. (ALICE Collaboration), JINST (28) S82 B. B. Abelev et al. (ALICE Collaboration), Int. J. Mod. Phys. A 29 (214) 1444 ITS: precise separation of primary particles and those from weak decays (hypernuclei) or knock-out from material TPC: particle identification via de/dx (allows also separation of charges). TOF: particle identification via time-of-flight TRD: electron identification via transition radiation ITSTPCTRD: excellent track reconstruction capabilities in a high track density environment MPID: particle identification via Cherenkov radiation ASTRA: Advances and open problems in low-energy nuclear and hadronic STRAngeness physics 27-1-217 Stefano Piano 9
A LARGE ION COLLIDER EXPERIMENT ALICE particle identification capabilities are unique. Almost all known techniques are exploited: de/dx, time-offlight, transition radiation, Cherenkov radiation, calorimetry and decay topology (V, cascade) ITS: precise separation of primary particles and those from weak decays (hypernuclei) or knock-out from material TPC: particle identification via de/dx (allows also separation of charges). TOF: particle identification via time-of-flight TRD: electron identification via transition radiation ITSTPCTRD: excellent track reconstruction capabilities in a high track density environment ALICE is ideally suited for the identification of light (anti-)(hyper)nuclei MPID: particle identification via Cherenkov radiation ASTRA: Advances and open problems in low-energy nuclear and hadronic STRAngeness physics 27-1-217 Stefano Piano 1
COLLISION GEOMETRY Central collisions b Participants Spectators Peripheral collisions b Nuclei are extended objects Geometry not directly measurable Centrality (percentage of the total cross section of the nuclear collision) connected to observables via Glauber model Data classified into centrality percentiles for which the average impact parameter, number of participants, and number of binary collisions can be determined K. Aamodt et al. (ALICE Collaboration), Phys. Rev. Lett. 16, 21 (211) ASTRA: Advances and open problems in low-energy nuclear and hadronic STRAngeness physics 27-1-217 Stefano Piano 11
NUCLEI IDENTIFICATION Low momenta Nuclei identification via de/dx measurement in the TPC: de/dx resolution in central Pb-Pb collisions: ~7% Excellent separation of (anti-)nuclei from other particles over a wide momentum range About 1 anti-alpha candidates identified out of 2x1 6 events by combining TPC and TOF particle identification Phys. Rev. C 9 (215) 24917 igher momenta Excellent TOF performance: σ TOF 85 ps in Pb-Pb collisions allows identification of light nuclei over a wide momentum range Velocity measurement with the TOF detector is used to evaluate the m 2 distribution and to subtract background from the signal in each p T -bin by fitting the m 2 distribution ASTRA: Advances and open problems in low-energy nuclear and hadronic STRAngeness physics 27-1-217 Stefano Piano 12
(ANTI)YPERTRITON IDENTIFICATION Decay Channels e d p d n - - e d p d n BR =.25 (*) search via two-body decays into charged particles: Two body decay: lower combinatorial background Charged particles: ALICE acceptance and reconstruction efficiency for charged particles higher than for neutrals Signal Extraction: Identify e and Evaluate ( e,) invariant mass Apply topological cuts in order to: isolate secondary decay vertex and reduce combinatorial background APPLIED CUTS: Cos(Pointing Angle) >.99 DCA to PV >.4 cm DCA between tracks <.7 cm ( e,) p T > 2 GeV/c y 1 cτ > 1 cm (*) Kamada et al., PRC57(1998)4 ASTRA: Advances and open problems in low-energy nuclear and hadronic STRAngeness physics 27-1-217 Stefano Piano 1
TE EXPERIMENTAL CALLENGE The challenge: extract the signal from an overwhelming background At s NN = 2.76 TeV 5.2 TeV Centrality dn ch /dη ( η <.5) -5 % 161 ± 6 194 ± 54 e - K. Aamodt et al. (ALICE Collaboration) Phys. Rev. Lett. 16, 21 (211) ; J. Adam et al (ALICE Collaboration) Phys. Rev. Lett. 116, 2222 (216) 14 ASTRA: Advances and open problems in low-energy nuclear and hadronic STRAngeness physics 27-1-217 Stefano Piano
(ANTI-)YPERTRITON IDENTIFICATION Decay Channels Phys. Lett. B 754 (216) 6-72 e d p d n - - e d p d n search via two-body decays into charged particles: Two body decay: lower combinatorial background Charged particles: ALICE acceptance and reconstruction efficiency for charged particles higher than for neutrals Signal Extraction: Identify e and Evaluate ( e,) invariant mass Apply topological cuts in order to: isolate secondary decay vertex and reduce combinatorial background Background estimation: track rotated 2 times µ = 2.991 ±.1 ±. GeV/c 2 σ= (.1 ±.24)x1 - GeV/c 2 To be compared to literature value: µ= 2.9911 ±.5 GeV/c 2 [Juric, Nucl. Phys. B 52, 1 (197)] ASTRA: Advances and open problems in low-energy nuclear and hadronic STRAngeness physics 27-1-217 Stefano Piano 15
(ANTI-)YPERTRITON IDENTIFICATION Decay Channels Phys. Lett. B 754 (216) 6-72 e d p d n search via two-body decays into charged particles: Two body decay: lower combinatorial background Charged particles: ALICE acceptance and reconstruction efficiency for charged particles higher than for neutrals Signal Extraction: Identify e and Evaluate ( e,) invariant mass - - Apply topological cuts in order to: isolate secondary decay vertex and reduce combinatorial background e d p d n µ = 2.991 ±.1 ±. GeV/c 2 σ= (.1 ±.24)x1 - GeV/c 2 To be compared to literature value: µ= 2.9911 ±.5 GeV/c 2 [Juric, Nucl. Phys. B 52, 1 (197)] Background estimation: track rotated 2 times ASTRA: Advances and open problems in low-energy nuclear and hadronic STRAngeness physics 27-1-217 Stefano Piano 16
(ANTI-)YPERTRITON IDENTIFICATION ASTRA: Advances and open problems in low-energy nuclear and hadronic STRAngeness physics 27-1-217 Stefano Piano 17 Decay Channels - - n d p d e n d p d e New preliminary results at s NN = 5.2 TeV search via two-body decays into charged particles: Two body decay: lower combinatorial background Charged particles: ALICE acceptance and reconstruction efficiency for charged particles higher than for neutrals Signal Extraction: Identify e and Evaluate ( e,) invariant mass Apply topological cuts in order to: isolate secondary decay vertex and reduce combinatorial background Background estimation: track rotated 2 times
(ANTI-)YPERTRITON IDENTIFICATION search via three-body decays into charged particles: Three body decay: higher combinatorial background but igher B.R. ~ 41% (Kamada et al., PRC57(1998)4) Charged particles: ALICE acceptance and reconstruction efficiency for charged particles higher than for neutrals Signal Extraction: Identify d, p and and anti Evaluate (d,p,) invariant mass Apply topological cuts and background estimation ASTRA: Advances and open problems in low-energy nuclear and hadronic STRAngeness physics 27-1-217 Stefano Piano 18 Decay Channels - - n d p d e n d p d e New preliminary results: three body decay at s NN = 2.76 TeV
(ANTI-)YPERTRITON YIELDS Phys. Lett. B 754 (216) 6-72 Phys. Lett. B 754 (216) 6-72 dn/dy x B.R. ( e ) yield extracted in three p T bins for central (-1%) events for and separately Anti-hypermatter / ypermatter Ratio: R = STATISTICAL-TERMAL MODEL: R=.95 (Cleymans et al, PRC84(211) 54916) COALESCENCE MODEL:/p ~ / ~ 1 ASTRA: Advances and open problems in low-energy nuclear and hadronic STRAngeness physics 27-1-217 Stefano Piano 19
COMPARISON WIT TEORETICAL PREDICTIONS Phys. Lett. B 754 (216) 6-72 Three different theoretical predictions drawn as a function of BR( e - ) after being multiplied by BR: ybrid UrQMD: combines the hadronic transport approach with an initial hydrodynamical stage for the hot and dense medium (J. Steinheimer et al., Phys. Lett. B 714, 85 (212)) GSI-eidelberg: equilibrium statistical model with T chem =156 MeV (A. Andronic et al., Phys. Lett. B 697, 2 (211)) SARE: non-equilibrium thermal model with T chem =18. MeV (M. Petráň et al., Phys. Rev. C 88, 497 (21)) Great sensitivity to theoretical models parameters Non equilibrium statistical thermal model (Petran-Rafelsky SARE) provides better global fitting (χ 2 1) to lower mass hadrons but misses and light nuclei Experimental data closest to equilibrium thermal model with T chem = 156 MeV and to ybrid UrQMD ASTRA: Advances and open problems in low-energy nuclear and hadronic STRAngeness physics 27-1-217 Stefano Piano 2
YPERTRITON LIFETIME DETERMINATION Direct decay time measurement is difficult (~ps), but the excellent determination of primary and decay vertex allows measurement of lifetime via: where/ and / withthe hypertriton mass, the total momentum and the decay length 5.4.!. "#. $1. "&". 181 )* ( "#. $ "&". " Phys. Lett. B 754 (216) 6-72 ASTRA: Advances and open problems in low-energy nuclear and hadronic STRAngeness physics 27-1-217 Stefano Piano 21
YPERTRITON LIFETIME WORLD AVERAGE Phys. Lett. B 754 (216) 6-72 Re-evaluation of world average including ALICE result: - 215! " ALICE value compatible with the computed average ASTRA: Advances and open problems in low-energy nuclear and hadronic STRAngeness physics 27-1-217 Stefano Piano 22
YPERTRITON LIFETIME DETERMINATION Phys. Lett. B 754 (216) 6-72 New preliminary results at s NN = 5.2 TeV 5.4.!. "#. $1. "&". 181 )* ( "#. $ "&". " 7.1.//./ "#. $.5 "&". 27! "#. $17 "&". " ASTRA: Advances and open problems in low-energy nuclear and hadronic STRAngeness physics 27-1-217 Stefano Piano 2
YPERTRITON LIFETIME DETERMINATION Two methods for estimation: ct spectra fit (exponential fit to the differential yield in different ct bins) ct unbinned fit as crosscheck method New preliminary results at s NN = 5.2 TeV 7.1.//./ "#. $.5 "&". 27! "#. $17 "&". " ASTRA: Advances and open problems in low-energy nuclear and hadronic STRAngeness physics 27-1-217 Stefano Piano 24
YPERTRITON LIFETIME WORLD AVERAGE Previous heavy-ion experiment results show a trend well below the free lifetime ALICE preliminary result from Pb-Pb at 5.2 TeV is closer to the free lifetime ASTRA: Advances and open problems in low-energy nuclear and hadronic STRAngeness physics 27-1-217 Stefano Piano 25
YPERTRITON LIFETIME WORLD AVERAGE STAR Collaboration, arxiv:171.46v1 [nucl-ex] 142 * "#. $1 "&". " Previous heavy-ion experiment results show a trend well below the free lifetime ALICE preliminary result from Pb-Pb at 5.2 TeV is closer to the free lifetime STAR result from Au-Au collision is about 5% shorter than the free lifetime The puzzle of the lifetime is still open ASTRA: Advances and open problems in low-energy nuclear and hadronic STRAngeness physics 27-1-217 Stefano Piano 26
YPERTRITON LIFETIME WORLD AVERAGE Previous heavy-ion experiment results show a trend well below the free lifetime ALICE preliminary result from Pb-Pb at 5.2 TeV is closer to the free lifetime More precision, reducing the statistical uncertainties can be reached: Another Pb-Pb data sample will be collected in 218 at the LC: the expected statistics for is >~2x lifetime in the -body decay channel ASTRA: Advances and open problems in low-energy nuclear and hadronic STRAngeness physics 27-1-217 Stefano Piano 27
YPERTRITON LIFETIME UNCERTAINITIES 5.4.!. "#. $1. "&". 181 )* ( "#. $ "&". " Stat: % - 22% Syst: 18% Signal Extraction 9% Tracking Efficiency 1% Absorption 12% Phys. Lett. B 754 (216) 6-72 At the end of RUN: Statistical uncertainty will be negligible With the LS2 ALICE upgrades: Signal extraction and tracking efficiency uncertainties will be strongly reduced At the end of Pb-Pb during RUN2 (Nov. 218) the expected statistics for is >2x During the Long Shutdown 2 (219-22): New Inner Tracking System (ITS) improved pointing precision less material -> thinnest tracker at the LC Upgrade of Time Projection Chamber (TPC): new GEM technology for readout chambers continuous readout faster readout electronics igh Level Trigger (LT): new architecture on line tracking & data compression 5kz PbPb event rate At the end of RUN (22) (*) the expected Integrated Luminosity: ~1 nb -1 the expected statistics for is ~2x (*) Technical Design Report for the Upgrade of the ALICE Inner Tracking System B. Abelev et al. (The ALICE Collaboration) 214 J. Phys. G: Nucl. Part. Phys. 41 872 ASTRA: Advances and open problems in low-energy nuclear and hadronic STRAngeness physics 27-1-217 Stefano Piano 28
CONCLUSIONS Excellent ALICE performance allows for detection of light (anti-)nuclei and (anti-)hypernuclei Blast-Wave fits can be used to extrapolate the yields to the unmeasured p T region of light hypernuclei in Pb-Pb. ypertriton yield is in agreement with the current best thermal fit from equilibrium thermal model (T chem = 156 ± 2 MeV) The excellent determination of primary and decay vertices allows for the measurement of lifetime via exponential fit of the proper decay time distribution Re-evaluation of the hypertrion lifetime world average ALICE preliminary result from Pb-Pb at 5.2 TeV is close to the the free lifetime Future LC runs, RUN2 and RUN, and ALICE upgrades will allow for precise study of (anti)hypertriton production yield and lifetime ASTRA: Advances and open problems in low-energy nuclear and hadronic STRAngeness physics 27-1-217 Stefano Piano 29
(ANTI-)YPERTRITON YIELDS RATIOS Phys. Lett. B 754 (216) 6-72 Phys. Lett. B 754 (216) 6-72 ypermatter / Matter Ratio and Anti-hypermatter/ Anti-matter Ratio Anti-hypermatter / ypermatter Ratio: R = STATISTICAL-TERMAL MODEL: R=.95 (Cleymans et al, PRC84(211) 54916) ASTRA: Advances and open problems in low-energy nuclear and hadronic STRAngeness physics 27-1-217 Stefano Piano
YPERTRITON LIFETIME UNCERTAINITIES 5.4.!. "#. $1. "&". 181 )* ( "#. $ "&". " Stat: % - 22% Syst: 18% Signal Extraction 9% Tracking Efficiency 1% Absorption 12% Phys. Lett. B 754 (216) 6-72 (anti)hypertriton absorption is not negligible: (anti)hypertriton is barely bound: stronger absorption in matter than t or e distribution of the material well known from the distribution of reconstructed photon conversions more precise evaluation of absorption cross section of and e is needed ASTRA: Advances and open problems in low-energy nuclear and hadronic STRAngeness physics 27-1-217 Stefano Piano 1