Recent results on the antiproton-nucleus annihilation cross section at low energy

Transcription

1 Recent results on the antiroton-nucleus annihilation cross section at low energy Luca Venturelli for H. Aghai-Khozani 1, M. Corradini 2, R. Hayano 3, M. Hori 1, M.Leali 2, E. Lodi-Rizzini 2, V. Mascagna 2, Y. Murakami 3, M. Prest 4, E. Vallazza 5, L. Venturelli 2, H. Yamada 3 1 Max-Planck-Institut für Quantenotik, Hans-Kofermann-Strasse 1, D Garching, Germany 2 Diartimento di Ingegneria dell Informazione, Università di Brescia, I Brescia, Italy & INFN 3 Deartment of Physics, University of Tokyo, Tokyo , Jaan 4 Università degli Studi dell Insubria, I Como, Italy & INFN 5 Istituto Nazionale di Fisica Nucleare, Sezione di Trieste, I Trieste, Italy π A A-1 L. Venturelli - Antiroton-nucleus annih. cross-section - LEAP

2 Some toics of interest: Physics motivations Cosmology: matter-antimatter asymmetry in the Universe (One ossibility is that antimatter is distributed non-homogeneously in the Universe within the so-called islands of antimatter. In the border region between matter and antimatter, the role of annihilation is imortant.) Search of resonances Determine the interaction arameters Probe the external region of nucleus (both otential models and henomenological analyses state that the annihilations occur in a thin region laced just outside the nuclear volume: neutron/roton ratio or the extraction energy of the eriheral nucleons can be determined) L. Venturelli - Antiroton-nucleus annih. cross-section - LEAP

3 Existing data Antinucleon annihilation σ on nuclei 2011 L. Venturelli - Antiroton-nucleus annih. cross-section - LEAP

4 Existing data Antinucleon annihilation σ on nuclei 2011 Some agreement with exectations but some roblems L. Venturelli - Antiroton-nucleus annih. cross-section - LEAP

5 Some roblems 1 ) No resonancedetected. 2 ) inversion ( σ ann s on light nucleicross each other at 50 MeV/c) 3 ) ex. σ ann s are toohigh comaredtothe exectations At MeV/c σ ann forbarand nbarare similar(asexected) but are higher what exected from otical otential 4 ) nbar σ ann lookslikebar σ ann alsoat verylow energy At verylow energyitisexected: ( A) σ ( na) σ > due to the Coulomb attraction by nucleus ann ann L. Venturelli - Antiroton-nucleus annih. cross-section - LEAP

6 Some roblems 1 ) No resonancedetected. 2 ) inversion ( σ ann s on light nucleicross each other at 50 MeV/c) 3 ) ex. σ ann s are toohigh comaredtothe exectations At MeV/c σ ann forbarand nbarare similar(asexected) but are higher what exected from otical otential 4 ) nbar σ ann lookslikebar σ ann alsoat verylow energy At verylow energyitisexected: ( A) σ ( na) σ > due to the Coulomb attraction by nucleus ann ann L. Venturelli - Antiroton-nucleus annih. cross-section - LEAP

7 nbar σ ann lookslikebar σ ann at verylow energy roblem Only nbardata (from Astrua et al., NPA (2002)) Highlighted by Friedman NPA 2014 Nbarand bardata Bianconi et al., PLB (2011) Astrua et al., NPA (2002) Calculations based on otical otential (Friedman) which fits well antirotonic atoms More antiroton data are needed for direct data-to-data comarisons L. Venturelli- Antiroton-nucleus annih. cross-section- LEAP

8 New (2015) measurementofbar σ ann erformedbyasacusa L. Venturelli - Antiroton-nucleus annih. cross-section - LEAP

9 Measurementofbar carbon σ ann at 5.3 MeV 2015 ASACUSA CERN-AD Atomic Sectroscoy And Collisions Using Slow Antirotons ~ 40 members Sokeserson: R.S. Hayano, Tokyo University 1) Sectroscoy of He 2) Antihydrogen roduction and sectroscoy Talks: DIERMAIER, NAGATA, TAJIMA Posters: KOLBINGER, KURODA, RADICS, SIMON 3) annihilation cross-section Posters: MASCAGNA, MURAKAMI L. Venturelli - Antiroton-nucleus annih. cross-section - LEAP

10 AD delivers to the exeriments: antirotonser bunch ( ns length) - 1 bunch/ 100 s - Energy = 5.3 MeV(100 MeV/c) Antiroton Decelerator (AD) - CERN AD is the only source of low-energy antirotons For σ ann measurement: Mainroblem: -AntirotonbeamfromAD isulsed: a) several coincident annihilations saturate the acquisition; b) overlaing of target signal and annihilations on the walls Rise time =15ns Use of multile extraction mode: 1) Lower bar beam intensity 2) Shorter bunch length (40 ns) L. Venturelli - Antiroton-nucleus annih. cross-section - LEAP ns

11 Techniqueofthe σ ann measurement SIGNAL σ ann ( A) N N events beam Time to searate signal from BCK time 2 ring tocalibrate (Rutherford) the beam counter target 2 ring σ ann isindeendentfromdetector efficiency (samedetector tocountn events and N beam ) L. Venturelli - Antiroton-nucleus annih. cross-section - LEAP

12 σ ann set-u Posters: MASCAGNA, MURAKAMI BPM solid target BPM φ= 1200 L =1700 φ= 600 L =1300 BCM Scintillaror bars module Carbon targets: 700 nm, 1000 nm Cherenkov detector radius=5 cm L. Venturelli - Antiroton-nucleus annih. cross-section - LEAP

13 σ ann set-u 3 m L. Venturelli - Antiroton-nucleus annih. cross-section - LEAP

14 annihilation times Target only target annihilation on the target clearly aears TARGET END-WALL LATERAL WALLS L. Venturelli - Antiroton-nucleus annih. cross-section - LEAP 2016 ns 14

15 annihilation times Target only 20 ns target annihilation on the target clearly aears TARGET END-WALL The first 20-ns region is free from the annihilations on the walls LATERAL WALLS L. Venturelli - Antiroton-nucleus annih. cross-section - LEAP 2016 ns 15

16 annihilation times Inner modules Target + 2 ring target 2 ring Target only target L. Venturelli- Antiroton-nucleus annih. cross-section- LEAP ring 16

17 antiroton σ ann on carbonat 5.3 MeV Preliminary measurement σ ann ( C ) = ( 1.75 ± 0.35 )barn Present exeriment Exected final value with lowererror(10%) qualitatively agreement with the existing antineutron data. n Calculation(Friedman) L. Venturelli - Antiroton-nucleus annih. cross-section - LEAP

18 Present exeriment L. Venturelli - Antiroton-nucleus annih. cross-section - LEAP

19 At 5.3 MeV(AD) Possible extension of the measurement Monte Carlo simulations show that σ ann measurements even with medium-heavy targets are feasible at AD with the resent aaratus and technique Ni (400 nm) Signal (t<20 ns) well searated from BKG Also bar nuclear elastic σ could be measured(but more difficult) At 0.1 MeV(AD-ELENA) Method already demonstrated with ASACUSA-RFQD. Ultra-thin targets needed L. Venturelli - Antiroton-nucleus annih. cross-section - LEAP

20 Conclusions Antiroton-C σ ann measurement at 5.3 MeVhas been erformed by ASACUSA at the end of 2015 The result of a reliminary analysis shows a qualitatively agreement with the existing (antineutron) data. The final result is exected to be more recise and could be used as a benchmark to understand the σ ann (E, A) at low energies. The resent technique can be used even with heavier targets (if the 5.3 MeV antiroton beam will be available...) Measurements at lower energies (0.1 MeV) will be ossible with ELENA, as already demonstrated by ASACUSA. L. Venturelli - Antiroton-nucleus annih. cross-section - LEAP