sign in sign up
<<
Home , Pentaquark

+ 0 Observation of a Θ - decay to pK S in K+ and interactions with nuclei

DIANA collaboration of ITEP, Moscow & Frascati: V.V. Barmin, V.S. Borisov, G.V. Davidenko, A.G. Dolgolenko, C. Guaraldo, I.F. Larin, V.A. Matveev, C.Petrascu,V.A.Shebanov, N.N. Shishov, L.I. Sokolov, G.K. Tumanov and re-analysis of data of Big Bubble Chamber Neutrino Collaboration by A. Asratyan, A. Dolgolenko, M. Kubantsev

M. Kubantsev, Pentaquark Workshop 2003, Nov 6-8, 1 ITEP/NWU Jlab Observation of Θ+ in the DIANA bubble chamber Separated beam of K+ with momentum of 750 MeV/c from ITEP 10 GeV accelerator irradiates DIANA chamber filled with liquid Xenon: density: 2.2 g/cm 3 Rad. length: 3.7 cm Volume: 700 liters Viewed with 4 cameras No magnetic field The DIANA chamber under preparation

M. Kubantsev, Pentaquark Workshop 2003, Nov 6-8, 2 ITEP/NWU Jlab Observation of Θ+ in the DIANA bubble chamber Charged : identified by ionization; Incoming K+ momentum measured by range. interacts here Interaction energy is determined K0 S by range of the before π- Proton interaction: stops here π+ K++N Θ+ P+ K0 ( +1 strangeness!) are identified by range. 0 K S are fitted to the vertex. About 25000 events with visible K0 0 + - 0 0 0 decays: K S π π and K S π π have been found. M. Kubantsev, Pentaquark Workshop 2003, Nov 6-8, 3 ITEP/NWU Jlab Observation of Θ+ in the DIANA bubble chamber

(1) K+ range distributions: (1) all incoming K+ : peak at 945 mm corresponds to decays of stopping ; (2) (2) K+ decays (mostly in rest); all kaon decays are uniquely identified (+branching ratios are verified);

(3) (3) charge exchange reaction events: K+Xe K0 X.

M. Kubantsev, Pentaquark Workshop 2003, Nov 6-8, 4 ITEP/NWU Jlab Observation of Θ+ in the DIANA bubble chamber

K+ with range more than 550 mm are selected: K+ momentum distribution has a peak at 470 MeV/c for events of reaction: K+Xe K0 pX

M. Kubantsev, Pentaquark Workshop 2003, Nov 6-8, 5 ITEP/NWU Jlab Observation of Θ+ in the DIANA bubble chamber

Estimation of K0 p effective reconstruction accuracy was made with observed decays Λ0 p π- observed value of mass (p π-) 1116 ±1 MeV/c2 and instrumental width : σ = 3.3± 1.0 MeV/c2 (in similar momentum range as in K0 p reaction !)

M. Kubantsev, Pentaquark Workshop 2003, Nov 6-8, 6 ITEP/NWU Jlab Observation of Θ+ in the DIANA bubble chamber

Effective mass of K0p system fitted by linear combination of Monte-Carlo simulated and random star background distributions. + π Qualitatively, there is a narrow enhancement at M ~ 1530-1540 MeV/c2 of 107 events over background of 84 (significance of 2.6 σ)

M. Kubantsev, Pentaquark Workshop 2003, Nov 6-8, 7 ITEP/NWU Jlab Observation of Θ+ in the DIANA bubble chamber

θK θP To remove events affected by re-scattering of reaction products topological cuts are applied: o o K+ θK <100 and θP <100 (p and K0 are selected mostly forward 0 in laboratory frame) ΦpK K and cos Φ < 0 Beam pK p (p and K0 are emitted back-to-back)

M. Kubantsev, Pentaquark Workshop 2003, Nov 6-8, 8 ITEP/NWU Jlab Observation of Θ+ in the DIANA bubble chamber

After above cuts the peak near 1540 MeV/c2 of total 73 events has estimated background of 44 events, resulting in statistical significance of 4.4 σ Gaussian fit of the peak yields: M = 1539 ± 2 MeV/c2 Γ <9MeV/ c2 (compatible with instrumental resolution) M. Kubantsev, Pentaquark Workshop 2003, Nov 6-8, 9 ITEP/NWU Jlab Observation of Θ+ in the DIANA bubble chamber

Above we presented direct approach to search for Θ+ analyzing effective mass of K0 p system. Another approach is to measure cross sections for formation of K0 p , K+n and K+ p final states as function of √ s : K K+ Θ+

N N Work on the K+ Xe cross section data continues.

M. Kubantsev, Pentaquark Workshop 2003, Nov 6-8, 10 ITEP/NWU Jlab Observation of Θ+ in the DIANA bubble chamber

PDG 2002 tables show very scarce cross section data in region of K+ momenta below 600 MeV/c.

M. Kubantsev, Pentaquark Workshop 2003, Nov 6-8, 11 ITEP/NWU Jlab Observation of Θ+ in the DIANA bubble chamber

J. Lannutti et al,Phys.Rev 109.2121(1958) B. Sechi-Zorn et al(ibid) + Θ ? Later K+A data from 1990’s also shows some hints at K+ momenta range of 400 –500 MeV/c: there is no good agreement with theory.

M. Kubantsev, Pentaquark Workshop 2003, Nov 6-8, 12 ITEP/NWU Jlab + 0 Observation Θ P+ K S in (Anti)Neutrino Interactions (strangeness is unidentified)

re-analysis of data of the Big Bubble Chamber Neutrino Collaboration are analysed by A. Asratyan, A. Dolgolenko and M. Kubantsev (ITEP, Moscow)

M. Kubantsev, Pentaquark Workshop 2003, Nov 6-8, 13 ITEP/NWU Jlab Observation of Θ+ in neutrino interactions

Two big bubble chambers: Fermilab 15’ and CERN BEBC, were close to each other in geometry, fiducial volume and operation conditions.Data were collected and processed using very similar techniques and algorithms.

Neutrino interactions were recorded in wide band neutrino beams of Fermilab 400 GeV accelerator (E180) and 800 GeV Tevatron (E632) with Neon-Hydrogen fill of 15’ BC and CERN 450 GeV accelerator with Hydrogen (WA21), Deuterium (WA25) and Neon (WA59) fills of BEBC.

M. Kubantsev, Pentaquark Workshop 2003, Nov 6-8, 14 ITEP/NWU Jlab Observation of Θ+ in neutrino interactions

These experimental data compiled by A. Asratyan (ITEP) comprise some 120000 (Anti)Neutrino charge current (CC) events*: - + νµ (νµ)+ A → µ (µ ) +X. Neutral current events: νµ(νµ)+A→ νµ(νµ) +X are not included (not measured systematically). Even after several decades the bubble chamber neutrino data are still unrivaled in quality and completeness of information. We analysed CC events with the system (X) containing 0 + - protons (identified) + K S →π π (fitted) +X’. ______

*Unfortunately E53 data are not included (61800 CC νµ Ne events)

M. Kubantsev, Pentaquark Workshop 2003, Nov 6-8, 15 ITEP/NWU Jlab Observation of Θ+ in neutrino interactions

E x p e r im e n t W A 21 W A 25 W A59 E 180 E 6 32 T o t a l Ch a m b e r B E B C B E B C B E B C 1 5 ' B. C. 1 5 ' B. C. Fill H ydr oge n D e ut e r iu m Ne o n -H 2 N e o n -H2 Ne o n -H 2 N e ut r inos: M e an , G e V 48. 8 51. 8 56. 8 52. 2 136. 8 59. 5 M e a n mo me n t u m of de t e c t e d K 0 S , G e V /c 5 .7 5 .7 4 .5 3 .4 7 .7 5 .8 All m e asu r e d C C e v e n t s 18746 2 6323 9753 882 5 621 6 1325 C C e v e n t s w it h K 0 S 1 050 1279 561 2 1 587 3498 C C even ts w ith K 0 S a n d id e n ti fi e d p r o to n s ( 9 00> P > 3 00 M e V /c) 78 128 1 93 8 157 564 A n tineut r inos: M e a n ,G e V 3 7 .5 3 7 .9 3 9 .5 3 3 .8 1 1 0 3 9 .5 M e a n mo me n t u m of de t e c t e d K , G e V /c 4 .2 4 .2 3 .5 3 .4 7 .6 4 .1 All m e asu r e d C C e v e n t s 13155 1 6314 15693 5927 1190 52279 C C e v e n t s w it h K 0 S 7 02 761 6 31 231 123 2448 C C even ts w ith K 0 S a n d id e n ti fi e d p r o to n s ( 9 00> P > 3 00 M e V /c) 43 57 185 5 4 2 8 3 67 M. Kubantsev, Pentaquark Workshop 2003, Nov 6-8, 16 ITEP/NWU Jlab Observation of Θ+ in neutrino interactions

Hydrogen data(WA21) Identified protons Accepted emitted in momentum range of 300

M. Kubantsev, Pentaquark Workshop 2003, Nov 6-8, 17 ITEP/NWU Jlab Observation of Θ+ in neutrino interactions

- + 0 νµ (νµ)+A→µ (µ )+P+K S+X’ Hydrogen Hydrogen Antineutrinos

Deuterium Deuterium Neutrinos Antineutrinos

Neon Neon Neutrinos Antineutrinos

M. Kubantsev, Pentaquark Workshop 2003, Nov 6-8, 18 ITEP/NWU Jlab Observation of Θ+ in neutrino interactions

0 K S p (identified) invariant mass distributions for

νµCC + νµCC events: random star background is shown by dots; open histogram is for Neon events with one identified proton only. Note: no events enter in the peak region twice.

M. Kubantsev, Pentaquark Workshop 2003, Nov 6-8, 19 ITEP/NWU Jlab Observation of Θ+ in neutrino interactions

K0 p (identified) invariant Neon plus Deuterium S mass for νµCC and νµCC events combined with the random star background: 27 events with ~8 events of the background;

Mass=1533 ± 5 MeV/c2 significance of 6.7 σ. The same distribution with bins Width <20MeV/c2 shifted by 5Mev is fitted to get mass and width of the peak. Width of the peak is compatible with instrumental resolution.

M. Kubantsev, Pentaquark Workshop 2003, Nov 6-8, 20 ITEP/NWU Jlab Observation of Θ+ in neutrino interactions

Peak events mean values of neutrino energy of Eν (57±10 GeV) and transverse 4-momentum Q2(12.5±3.3 GeV2) 0 are consistent with those for all events with K S. No strangeness determined ! – But there are no known Σ+ states in this region. We interpret the peak at 1533 MeV/c2 a signal of formation of the Θ+. Further observations: (1) Θ+ production cross section by neutrinos appears to increase with atomic number of the target nucleus; (2) Relative ν and ν yields of Θ+ are close; (3) Associated production of neutral strange particles is not different 0 0 from other events with K S (specially no excess of Λ ). M. Kubantsev, Pentaquark Workshop 2003, Nov 6-8, 21 ITEP/NWU Jlab Comparison of Θ+ and Σ +(1385) → Λ0 + π + in (anti)neutrino interactions Neutrino Antineutrino 2 25 2 25

Mass 1383 ± 2 /c MeV/c2 /c 20 20

Hydrogen eV Hydrogen eV 15 Width = 34 ± 3 Mev/c215 10M 10M / / s s 10 10 t t 5 5 ven ven E 0 E 0 1. 25 1. 3 1 . 3 5 1 . 4 1. 45 1. 25 1. 3 1 .35 1 . 4 1. 45 2 25 2

25 c / c M a ss ( Λ + π + ) , G e v/ c2 20 M ass 20 eV Deuterium ev/ Deuterium 15 15 10M / 10M

s 10 t s/ 10 t 5

5 ven ven E E 0 0 1. 25 1. 3 1 . 3 5 1 . 4 1. 45 25 1. 25 1. 3 1 . 3 5 1 . 4 1. 45 25

2 Neon Neutrinos 2 Ma s s c c / M ass( Λ + π +) , Ge v / c 2 20 Neon / 20

eV Neon eV 15

15 M / 10M s

t 10 s/ 10 t en

5 v 5 E ven E 0 0 1. 25 1. 3 1 . 3 5 1 . 4 1. 45 1. 25 1. 3 1 . 3 5 1 . 4 1. 45 M ass ( Λ + π + ) , G ev/ c2 Ma s s ( Λ + π +), G e v / c 2

M. Kubantsev, Pentaquark Workshop 2003, Nov 6-8, 22 ITEP/NWU Jlab Comparison of Θ+ and Σ +(1385) in (anti)neutrino interactions

+ Qualitatively we see most of Θ signal on Ne and small one on H2 and D with roughly the same luminosity. 2 + At the same conditions Σ (1385) signal is seen on H2 and D2 and it is not seen on neon. Observed ν and ν yields of Θ+ are about the same. Σ +(1385) is mostly produced in ν, not ν beam. Observed Θ+ are produced slow moving in lab system: may speculate that it is produced by re-scattering of secondary kaons(?) in nuclei. Σ+(1385) are produced at higher momenta and charge of interacting (+2/3 for ν and –1/3 for ν) is important. Re-interactions in nuclei apparently destroy Σ +(1385) peak.

M. Kubantsev, Pentaquark Workshop 2003, Nov 6-8, 23 ITEP/NWU Jlab Conclusions

+ 0 A signal of Θ pK S is observed on level of 4.4 σ in K + Xe and 6.7 σ in neutrino interactions with Neon and Deuterium. Mass values and widths are found: M = 1539±2 MeV/c2 and Γ(observed)<9MeV/c2(K+Xe) 2 2 M = 1533±5 MeV/c and Γ(observed)<20MeV/c (νNe+νD2) Low energy K+ cross sections with and nuclei are not well known, there are some hints of cross section enhancement at √ s ~ 1530-1540 MeV from old and not so old data. Work on the K+ Xe cross section data continues. The cross section of Θ+ production by neutrinos appears to increase with atomic number of the target nucleus.

M. Kubantsev, Pentaquark Workshop 2003, Nov 6-8, 24 ITEP/NWU Jlab