K 0 S K± femtoscopy in Pb- Pb collisions at s NN = 2.76 TeV and pp collisions at s = 7 TeV from the LHC ALICE Experiment

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1 K 0 S K± femtoscopy in Pb- Pb collisions at s NN =.76 TeV and pp collisions at s = 7 TeV from the LHC ALICE Experiment Tom Humanic (Ohio State University) For the ALICE collaborajon XII Workshop on ParJcle CorrelaJons and Femtoscopy Nikhef, Amsterdam, The Netherlands June 14, 017

2 Outline Ø Mo?va?on for measuring K 0 S K± femtoscopy Ø Results from ALICE.76 TeV Pb- Pb collisions Ø Results from ALICE 7 TeV pp collisions Ø Summary

3 MoJvaJon for measuring K 0 S K± femtoscopy The ALICE collabora?on has published three femtoscopy papers using iden?cal kaon pairs to extract geometric informa?on about the collision interac?on region: q 7 TeV p+p à K 0 S K0 S Phys.LeW.B717 (01) q 7 TeV p+p à K ± K ± Phys.Rev.D87 (013) q.76 TeV Pb- Pb à K 0 S K0 S, K± K ± Phys.Rev.C9 (015) ARGED KAON FEMTOSCOPIC CORRELATIONS IN p (fm) R inv 8 6 ALICE Pb-Pb π ± π ± ± ± K 0 0 K S K S pp pp K s NN =.76 TeV 0-10% 10-30% 30-50% (fm) R inv ch ch ππ N ch 1-11 K K ππn ch ALICE pp s=7 TeV ππn ch > 0 0 KsK s N ch KsK s N ch > 11 ch ch K K N ch 1-11 ch ch K K N ch 1- ch ch K K N ch > m (GeV/c T ) (GeV/c ) m T 3

4 Why study K 0 S K± femtoscopy? Ø Pair- wise interacjons which are present for idenjcal kaon pairs: K ± K ± quantum sta?s?cs, Coulomb interac?on K 0 S K0 S quantum sta?s?cs, f 0 (980)/a 0 (980) strong interac?on From ParJcle Data Book for light quark- anjquark mesons f 0 (980) [j] I G (J PC )=0 + (0 ++ ) Mass m =990± 0 MeV Full width Γ =10to100MeV f 0 (980) DECAY MODES Fraction (Γ i /Γ) p (MeV/c) ππ dominant 476 K K seen 36 γγ seen 495 a 0 (980) [j] I G (J PC )=1 (0 ++ ) Mass m =980± 0 MeV Full width Γ =50to100MeV a 0 (980) DECAY MODES Fraction (Γ i /Γ) p (MeV/c) ηπ dominant 319 K K seen γγ seen 490 4

5 Why study K 0 S K± femtoscopy? Ø What pair- wise interacjons would be present (or absent) for K 0 S K± pairs? * since non- iden?cal pairs à no quantum sta?s?cs * since K 0 S is uncharged à no Coulomb interac?on * since f 0 (980) resonance is neutral à no f 0 (980) strong interac?on * since a 0 (980) resonance is isospin = 1 à a 0 (980) strong interac?on should be present for both K 0 S K+ and K 0 S K- pairs 5

6 Why study K 0 S K± femtoscopy? Ø What could be learned by looking at K 0 S K± femtoscopy? * Extract R using only the a 0 (980) strong interac?on - - act as a crosscheck of the published iden?cal kaon pair results - - K 0 S K± femtoscopy has never been published before * Since à (since S = 0 for a 0 ) are there differences in the extracted source parameters? * Study the proper?es of the a 0 (980) resonance - - check published a 0 (980) decay coupling parameters and mass - - the a 0 (980) is considered a candidate for a tetraquark state 6

7 PHYSICAL REVIEW D 79, (009) Global aspects of the scalar meson puzzle Amir H. Fariborz, 1, * Renata Jora,, and Joseph Schechter 3, 1 Department of Mathematics/Science, State University of New York Institute of Technology, Utica, New York , USA INFN Roma, Piazzale A Moro, Roma, I Italy 3 Department of Physics, Syracuse University, Syracuse, New York , USA (Received 16 February 009; published 16 April 009) A generalized linear sigma model for low-energy QCD is employed to study the quark structure of eight low-lying scalar isomultiplets as well as eight low-lying pseudoscalar isomultiplets. The model, building on earlier work, assumes the possible mixing of quark antiquark states with others made of two quarks and two antiquarks. No a priori assumption is made about the quark contents of the states, which emerge as predictions. An amusing and contrasting pattern for the quark structure is found; the lighter conventional pseudoscalars are, as expected, primarily of two-quark type whereas the lighter scalars have very large four-quark admixtures. The new feature of the present paper compared to earlier ones in this series involves the somewhat subtle and complicated effects of SU(3) flavor breaking. They do not alter the general pattern of two-quark vs four-quark mixing obtained in the SU(3)symmetric case but, of course, give a more detailed picture. TABLE II. m a and m a 0 are inputs. Typical predicted properties of scalar states: qq percentage (nd column), q q qq (3rd column) and masses (last column). The a 0 is thought to be a well- known candidate tetraquark but it is sjll listed in the ParJcle Data Book as a diquark state like the pion. State qq% q q qq% m (GeV) a a f f f f a 0 predicted to be 76% tetraquark What signatures of the a 0 quark content might we see in K 0 S K± femtoscopy? 7

8 ! λ λ K 0 K λ KK for ussd vs. ud a 0 expected from geometry PbPb Tetraquark a 0 - Diquark a 0 - K - us sd K 0 a 0 - us sd us sd! λ ~ 1 us sd us ss annihilation suppressed due to geometry sd! λ ~ 0 pp us sd us sd (ud) Non-resonant channel us λ! <1 sd us sd a 0 - ud us sd! λ ~ 1 8

9 à Measure K 0 S K± correlations in.76 TeV Pb-Pb and 7 TeV pp collisions in ALICE.76 TeV Pb-Pb Ø 0-10% centrality, η < 0.8 Ø Extract R and λ in three bins: 0 < < 4 GeV/c ( all ), < GeV/c, > GeV/c 7 TeV pp Ø All multiplicity, η < 1 Ø Extract R and λ in three bins: 0 < < 4 GeV/c ( all ), < 0.85 GeV/c, > 0.85 GeV/c C(k * ) is measured experimentally as ( ) = A ( k* ) B( k * ) C k * where A(k * ) is the measured distribution of pairs from the same event, and B(k * ) is the reference distribution of pairs from mixed events. 9

10 Version of R. Lednicky equajon used to extract (R, λ) for K 0 S K± R. Lednicky and V.L. Lyuboshits, Sov. J. Nucl. Phys. 35 (198) C(k * ) =1+ λα $ & %& f (k * ) R K 0 K + or K 0 K + 4Rf (k* ) π R F 1(Rk * ) If (k* ) R ' F (Rk * )) () Since à α = ½, assuming no asymmetry f (k * ) = γ a0 KK m a0 s iγ a0 KK k * iγ a0 πη k πη a 0 mass and coupling parameters (GeV) MarJn Antonelli Achasov1 Achasov m a0 γ a0 KK γ a0 πη Ø extracted mostly from model fits to KLOE φ- decay experiment: e.g. φ à Κ + Κ - à a 0 γ à π 0 ηγ Ø Mar?n uses a sum rule es?mate Martin et al, Nucl.Phys B11,514 (1977) Antonelli et al, hep-ex/ (00) Achasov et al, Phys.Rev.D68, (003) " " " " 10

11 C raw (k*)/(linear fit) fifed with the Lednicky equajon with Achasov parameters for ALICE.76 TeV Pb- Pb collisions arxiv: à submifed to PLB 1 Data stat. unc. Total unc. Lednicky fit All < GeV/c > GeV/c C(k * ) / (Linear fit to baseline) All < GeV/c > GeV/c k * (GeV/c) * The a 0 final state interacjon gives excellent fits to the data! * K 0 S K+ and K 0 S K- results agree within uncertainjes 11

12 Results for R and λ from.76 TeV Pb- Pb averaged over K 0 S K+ and K 0 S K- compared with published ALICE idenjcal- kaon pair results arxiv: à submifed to PLB Achasov parameters Achasov1 parameters R(fm) 4 K ± K ± K 0 K 0 S S K 0 K ± S Achasov parameters Achasov1 parameters Martin parameters λ K ± K ± K 0 K 0 S S K 0 K ± S Antonelli parameters Martin parameters Antonelli parameters * R and λ agree with idenjcal kaon results best for Achasov parameters * λ < 1 due to long- lived resonance decay (e.g. K*à Kπ) and non- Gaussian shape Agreement of λ with idenjcal kaons è FSI goes dominantly through a 0 channel è ContribuJon of non- resonant channel is insignificant 1

13 s = 7 TeV pp ALICE Preliminary K 0 K + S All Comparison of C(k*) from PYTHIA- Perugia011 with K 0 S K+ data for ALICE 7 TeV pp collisions data PYTHIA-Perugia011 C(k * ) < 0.85 GeV/c > 0.85 GeV/c Ø PYTHIA qualitajvely (but not quan?ta?vely) describes the trend of the baseline of the data Ø PYTHIA does not have the low- k* enhancement seen in the data thought to be due to the a 0 FSI à Use PYTHIA as a tesjng ground for the types of baseline funcjons that would be reasonable to use in fiong the data ALI-PREL k * (GeV/c) 13

14 C(k * ) Test of baseline fit funcjons with PYTHIA- Perugia s = 7 TeV pp ALICE Preliminary PYTHIA-Perugia011 K 0 K + S all k T k T < 0.85 GeV/c k T > 0.85 GeV/c quadratic fit gaussian fit exponential fit C ( quad k * ) = a( 1+ bk * + ck * ) C gauss k * C exp k * ( ) ( ) = a 1+ bexp( ck * ) ( ) ( ) = a 1+ bexp( ck * ) 0.04 ALI-PREL k * (GeV/c) All three funcjonal forms do a reasonable job of describing the PYTHIA C(k*) à use all three to determine systemajc errors, i.e. fit data with: C( k * ) = C ( Lednicky k * )C base (k * ), base = quad, gauss or exp 14

15 C raw (k*)/(baseline fit) fifed with the Lednicky equajon with Achasov parameters s = 7 TeV pp ALICE Preliminary K 0 K + S K 0 K + All < 0.85 GeV/c > 0.85 GeV/c Data stat. unc. Lednicky fit Total unc. S K 0 K + S 7 TeV pp C(k * )/quadratic K 0 K - S All K 0 K - S < 0.85 GeV/c K 0 K - S > 0.85 GeV/c The shape and magnitude of the K 0 S K± correlajon funcjons are qualitajvely different for smaller vs. larger kaon sources ALI-PREL k * (GeV/c) Data stat. unc. Lednicky fit 1 Total unc..76 TeV Pb- Pb Good test of Lednicky formalism and Achasov a 0 decay parameters used for the a 0 FSI since both sets of correlajon funcjons are described well! C(k * ) / (Linear fit to baseline) All All < GeV/c < GeV/c k * (GeV/c) > GeV/c > GeV/c

16 Comparison between R parameters extracted in 7 TeV pp à K 0 S K± and published ALICE results from idenjcal- kaon 7 TeV pp collisions 1.5 s = 7 TeV pp ALICE Preliminary R (fm) ALI-PREL K ± K ± K 0 K 0 S S K 0 K ± S k T (GeV/c) Used Achasov a 0 parameters For K 0 S K± Boxes give total uncertainjes * K 0 S K+ and K 0 S K- results in agreement with each other à averaged * R values from K 0 S K± agree with published results for idenjcal kaons within the error bars, as also observed in Pb- Pb * λ values are sjll under study 16

17 Summary of present results for K 0 S K± femtoscopy Results for ALICE.76 TeV Pb- Pb collisions à a 0 FSI gives a good representa?on of the signal region à K 0 S K+ and K 0 S K- results agree within uncertain?es à The R and λ parameters are in best agreement with iden?cal KK results using the Achasov a 0 parameter sets à The K 0 S K± FSI goes dominantly through the a 0 channel, sugges?ng that the a 0 is compa?ble with being a tetraquark state Results for ALICE 7 TeV pp collisions à a 0 FSI gives a good representa?on of the signal region à K 0 S K+ and K 0 S K- results agree within uncertain?es à The R parameters are in good agreement with iden?cal KK results for the Achasov a 0 parameter set à The λ parameter is s?ll under study 17

18 Backup slides

19 Analysis details for.76 TeV Pb- Pb Ø Data set used: 0-10% centrality, ~ M events Ø ParJcle pairs used: K 0 s K+ and K 0 s K- Ø General Cuts primary vertex: z < 10 cm, x,y < 1 mm TPC only tracking η < 0.8, K ch : 0.15 < p T < 1.5 GeV/c Ø K ch parjcle ID from TPC and TOF TPC: p < 0.5 GeV/c Nσ <, p > 0.5 GeV/c Nσ < 3 TOF: 0.5<p<0.8 Ns<, 0.8<p<1.0 Nσ<1.5, 1.0<p<1.5 Nσ<1 Ø K 0 s parjcle ID from decay to π+ + π- DCA between daughters < 0.3 cm DCA of v0 to primary vertex < 0.3 cm decay length < 30 cm M inv : GeV cut all K 0 s sharing same daughter ID daughter cuts: DCA > 0.4, p T > 0.15 GeV/c, η < 0.8 daughter ID: TPC: Nσ<3, TOF: p>0.8 Nσ<3 Ø K 0 s Kch pair cuts average separa?on cut between like- charged K ch and K 0 s daughter > 0 cm background pairs z < cm difference in primary vertex 19

20 Analysis details for 7 TeV pp à K 0 s K± Data set used All mul?plicity, ~374 M events ParJcle pairs used K 0 s K+ and K 0 s K- ranges used all, < 0.85 GeV/c, > 0.85 GeV/c General Cuts primary vertex: z < 10 cm, x,y < 1 mm TPC only tracking η < 1, K ± : 0.15 < p T < 1. GeV/c same as papers K ± parjcle ID from TPC and TOF p < 0.5 GeV/c TPC, p > 0.5 GeV/c TOF, Nσ < K 0 s parjcle ID from decay to π+ and π- DCA between daughters < 0.3 cm DCA of v0 to primary vertex < 0.3 cm decay length < 30 cm M inv : GeV cut all K 0 s sharing same daughter ID K 0 s K± pair cut average separa?on cut between like- charged K ± and K 0 s daughter > 13 cm 0

21 Consider the correlations of two identical bosons, e.g. pions or kaons, emitted from the interaction region strong final- state boson 1 interac?on InteracJon region Femtoscopy with quantum stajsjcs and strong final- state interacjons R. Lednicky and V.L. Lyuboshits, (Sov. J. Nucl. Phys. 35 (198))! k *! r * boson Symmetrize boson wavefunc?on boson detectors If! r * and! k * are the relative distance between the bosons and the momentum of each boson in the pair reference frame, then the non-symmetrized wavefunction describing the elastic interaction between the bosons is Ψ! k *! r * ( ) = e i! k *! r * + f plane wave! k * ( ) eik r * * r * s- wave FSI term S- wave scawering amplitude 1

22 Assume the boson source density in the pair reference frame is a Gaussian with radius parameter, R, ( ) ~ exp$ r* S r * " # 4R % ' & The two-boson correlation function is calculated by integrating over the symmetrized wavefunction weighted by the boson source density, C(k * ) = d 3! r * S r * ( ) Ψ! k * ( ) S! r * & =1+ λe 4k* R + λα( f (k* ) '( R quantum sta?s?cs term + 4Rf (k* ) π R F 1 (Rk* ) If (k* ) R Final- state interac?on term z z where F 1 ( z) = dx ex F 0 z z ( ) = 1 e z z ) F (Rk * ) + * + The parameter λ is an empirical parameter that measures the correlation strength, λ = 1 in the ideal case, and α = 0.5 for neutral kaon correlations.

23 Possible signature for forming a tetraquark a 0 state? e.g. two scenarios for K 0 K - à a 0 - : tetraquark and diquark 3 K - K 0 _ u s _ s d _ u s _ s d a 0 - Tetraquark forma?on is a 1 st - order process that proceeds through the direct transfer of exis?ng quarks to the a 0 from the collision of K 0 K - à an OZI superallowed collision à suggests lifle or no compejng non- resonant scafering K - K 0 _ u s _ s d _ u d a 0 - Diquark forma?on is a higher- order process requiring the annihila?on of the strange quarks in the K 0 K - collision and transfer of energy via gluons to a 0 à an OZI suppressed collision à suggests likely presence of compejng non- resonant scafering OZI rule: an inhibi?on associated with the crea?on or annihila?on of quark lines (Jaffe,PRD)

24 0 0.7<k <1 T ¼ ) C(q inv Sample CFs from 7 TeV pp data for K 0 S K+ vs. K ± K ± and K 0 S K0 S à All are using PYTHIA to determine the baseline 7 TeV pp à K ± K ±, from PRD87(013) Fit (line) of Coulomb*quantum stat. 1 N ch 11 1 N ch N ch 3 experiment simulation 7 TeV pp à K 0 S K0 S, from PLB717(01) Fit (line) of Lednicky*quantum sta?s?cs ALICE s = 7 TeV K 0 s K0 s k T < 0.85 GeV/c N ch 1-11 k T > 0.85 GeV/c N ch 1-11 ) C(q inv C(Q inv ) k T < 0.85 GeV/c N ch > 11 k T > 0.85 GeV/c N ch > 11 ) C(q inv < < < <0. 5.5< < Q (GeV/c) inv Fig. 5: Experimental K 0 s K0 s correlation functions divided by PYTHIA correlation functions for the four multiplicity ranges with femtoscopic fits using the Lednicky parametrization. 7 TeV pp à K 0 S K+ ) C(q inv q (GeV/c) q (GeV/c) q (GeV/c) inv inv ffiffi inv were found7 to TeV be p-p on the --> order K0sK+ of or greater than the size of the statistical uncertainties, as can be seen in Table 1. The method used to estimate the k < systematic 0.85 GeV/c uncertainty of using k > 0.85 PYTHIA GeV/c was to set the 1.5 all T PYTHIA K 0 s K0 s background T distribution equal to the experimental background distribution in the ratio of correlation functions, e.g. forcing the ratio plotted in Figure 3 to be exactly unity for all Q inv.theratioof correlation 1 functions then becomes the ratio of the experimental to PYTHIA real pair distributions, which is then fit with the Lednicky parametrization to extract the source parameters. Parameters extracted from data these correlation PYTHIA-Perugia011 functions were then averaged with those from Figure 5 and are given in Figures 6 and 7andTable ThismethodissimilartothatusedinestimatingsystematicuncertaintiesinotherK 0 sk 0 s measurements [6, 0. 8] k* (GeV/c) To see the effect of the a 0 / f 0 final-state interaction (FSI) term in the Lednicky parametrization, the correlation PYTHIA functionseems in Figure 5 were to fit describe with Eqs. (1)-(3) the for two cases: baseline 1) quantum statistics well + FSI terms, i.e. α = 0.5 ineq. (),and)quantumstatisticstermonly,i.e. α = 0inEq. (). Case) corresponds for K 0 tosthe K+ usual when Gaussian parametrization plofed for this R and way.. λ. Theresultsofthesefitsareshownin Table. Including the FSI term in the fit is seen to significantly reduce both R and λ, i.e.r by 30% and λ by 50%. The FSI is thus seen to enhance the correlation function for Q inv 0makingλ appear larger and making the enhancement region narrower resulting inanapparentlargerr. AreductioninR and λ when including the FSI term was also observed, but to a lesser extent, in the STAR Au Au K 0 K 0 C(k*) 4

25 Make a 5- parameter fit (R, λ, a, b, c) of C k * Fiong strategy for 7 TeV pp data ( ) = C Lednicky k * ( )C base (k * ), base = quad, gauss or exp to all, < 0.85 GeV/c and > 0.85 GeV/c in k* ranges GeV/c and GeV/c to K 0 s K+ and K 0 s K- data à # fits for each range and charge: 3 baselines x k* ranges Take the averages and variances of these to determine the final R and λ for each case and the combined systemajc error in the fit range and baseline Use Achasov parameter set since gives best fit in Pb- Pb 5