PoS(ICRC2019)134 8 , 5 , 1 ¶ , 2 http://pos.sissa.it/ , K. C. Kim 4 , R. Orito 4 and K. Yoshimura 3 , R. E. Streitmatter 5 , M. Nozaki , M. Hasegawa 6 9 , , T. Yoshida 1 4 , E. S. Seo 9 , 1 , T. Hams 4§ , J. Nishimura 1 , A. Yamamoto 1 , M. Sasaki 5 , S. Haino 3 , N. Thakur , J. W. Mitchell 4 4 ‡ , H. Fuke 2 , N. Picot-Clemente 7 † , K. Abe 9 , K. Tanaka , Y. Makida , 4 5 1 ∗ High-precision measurements of the cosmic-ray antiproton spectrummological and sensitive antihelium search for have cos- been publishedExperiment with using a the Superconducting data Spectrometer)early from Universe flight BESS-Polar using in II elementary 2007/2008 particle (Balloon-borne for measurements.reported a used The the core most data sensitive study obtained antideuteron of by search solar BESS97, the minimum BESS98, BESS99, period and in BESS00, 1997.sensitivity which using include BESS-Polar the We II performed data a thatsolar search is minimum more for conditions. than antideuterons ten The with times searchdark-matter unprecedented the for candidates. statistics antideuteron of probes BESS97 possible in exotic near sources, such as Speaker. E-mail: [email protected] Present address: Kamioka Observatory, ICRR, ThePresent University address: of Tokyo, Institute Hida, of Gifu Physics, 506-1205, AcademiaPresent Japan. Sinica, address: Nankang, Tokushima Taipei University, 11529, Tokushima, Tokushima Taiwan. 770-8502, Japan. § † ‡ ∗ ¶ Copyright owned by the author(s) under the terms of the Creative Commons NASA-Goddard Space Flight Center (NASA-GSFC), Greenbelt,MDKobe 20771, University, USA Kobe, Hyogo 657-8501, Japan Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency High Energy Accelerator Research Organization (KEK),IPST, Tsukuba, University Ibaraki of 305-0801, Maryland, Japan College Park, MDThe 20742, University USA of Tokyo, Bunkyo, Tokyo 113-0033,University Japan of Denver, Denver, CO 80208, USA Okayama University, Okayama, Okayama 700-0082, Japan Center for Research and Exploration in Space Science and Technology (CRESST) c Attribution-NonCommercial-NoDerivatives 4.0 International License (CC BY-NC-ND 4.0). 36th International Cosmic Ray Conference -ICRC2019- July 24th - August 1st, 2019 Madison, WI, U.S.A. (ISAS/JAXA), Sagamihara, Kanagawa 252-5210, Japan J. Suzuki K. Sakai Search for Cosmic-Ray Antideuterons with BESS-Polar II M. H. Lee J. F. Ormes 1 2 3 4 5 6 7 8 9 PoS(ICRC2019)134 ¯ d ’s. As ¯ K. Sakai d ]. 1 ’s. An experiment with ¯ ’s) is crucially important d p 05day 04day 06day 03day 02day 03day 22day 02day 07day 01day 04day 21day candidate was observed yet. The best limit 01day 23day ¯ 08day 20day d 19day Launch 05day 24day 09day 1 18day 06day 07day 10day 25day 17day 08day 26day Landing (Polar-I) 11day 27day 29day 28day 16day 12day 15day 13day ’s) are in a different situation. Thanks to their heavier mass, the 14day ¯ d ] was developed as a high-resolution magnetic-rigidity spectrometer ’s are a severe background in identifying 3 Landing (Polar-II) p , 2 Flight trajectory of the 2007 BESS-Polar II over Antarctica from Williams Field (first orbit blue, The BESS instrument [ The precise measurement of the cosmic-ray antiproton spectrum ( ¯ Cosmic-ray antideuterons ( large exposure factor and goodsuch, few particle searches identification have been devices carried is outwas so necessary reported far by to and the no investigate BESS experiment obtained during last solar minimum period [ Figure 1: second orbit red) with 2004 BESS-Polar[Launch]S77-51,E166-40, I 06:27(McM) flight 12/23 (green). 2007 [Recovery]S83-51,W073-04, 09:02(UTC) 1/21 2008 event would be a direct evidence ofsmall. novel primary The origins. However, more the numerous expected flux is ¯ extremely 2. BESS Program for cosmic-ray antiparticles and precise measurementscomponents. of the absolute The fluxes of original variousthe cosmic-ray BESS period experiment of performed 1993 9 through flights 2002 over with northern continuous Canada improvement during in the instrument. The BESS- BESS-Polar II ANTIDEUTERON SEARCH 1. Introduction to the investigation of elementary particlecosmic-ray phenomena antiprotons in are the early well Universe. understoodcosmic-rays Most as and of secondary the the products observed interstellar of medium.peaks collisions near between The primary 2 energy GeV, spectrumantiproton and of production decreases and such to “secondary” sharply the antiprotons local below interstellar and (LIS) proton above spectrum. theprobability peak, of production due in cosmic-ray to interactions the iscause much of kinematics smaller, the especially very of at low low production energies, cross-section be- and strict kinematical requirements. So one single PoS(ICRC2019)134 m µ 140 K. Sakai ∼ resolution of 1 − 4% at 1 GV and a ] and BESS-Polar β . 15 , 14 ) resolution of 0 ], AMS-02 [ Ze / on average), and the cutoff rigidity was 13 2 , Pc at 95% confidence, the lowest limit to date. 12 ≡ ]. Incorporating considerable improvements , a uniform field of 0.8 T is produced by a 8 7 events with no inflight event selection as 13.6 2 − 9 10 10 2 × × ] and the absolute spectra for cosmic-ray protons and 9 7 . . 10 sr and for proton and helium measurements the acceptance 2 ] has produced three papers giving precise measurements of an- 8 measurements and the event trigger. For antiproton measurements, Cross sectional view of BESS-Polar II spectrometer dx / dE ). 1 ]. The first scientific flight of the BESS-Polar instrument was launched near 6 at high-energies. Figure 2: , E cosmic-ray events were recorded [ 5 ]. The antiproton spectrum measured by BESS-Polar II shows good consistency σ 8 , 4 11 10 × ], a sensitive antihelium search [ sr. The timing resolution of the TOF system is 120 ps, giving a 9 2 In the BESS-Polar instruments shown in Fig. The BESS-Polar II program [ Proton and helium spectra observed from PAMELA [ the acceptance of BESS-Polar is 0.23 m 3. BESS-Polar Instrument helium nuclei [ agree within one thin superconducting solenoid, and theTracking field is region is performed filled by with fittingin drift-chamber up the tracking bending to detectors. plane, 52 resulting hit inmaximum points a detectable with magnetic-rigidity rigidity ( a (MDR) of characteristic 240time-of-flight resolution (TOF) GV. of Upper and and lower scintillator hodoscopes provide is 0.18 m 2.5%. The instrument also incorporates a threshold-type Cherenkov counter using a silica aerogel with secondary antiproton calculationsthe and evaporation no of evidence primordial of black holes. primarypossible antihelium And antiprotons to antihelium originating measured work from helium has of set 6 a new limit in the ratio of McMurdo Station, on Decembermore 13th, than 9 2004 (UTC). Thein instrument flight and duration payload was systemslaunched over compared on to 8.5 December BESS-Polar 23, days I, 2007, and from theand Williams BESS-Polar circulated Field II around near instrument the the US South was McMurdo Polefloat Station for altitude in 24.5 was Antarctica 34 days km of to observation 38 with km the (residual magnet air energized. of The 5.8 g/cm tiprotons [ Polar project was proposedflights as over an Antarctica advanced (around BESS themeasurements [ program south pole) using to long provide duration high-statistics, balloon low-energy (LDB) cosmic-ray BESS-Polar II ANTIDEUTERON SEARCH below 0.5 GV. BESS-Polar II accumulated 4 terabytes of data (Fig. PoS(ICRC2019)134 ) 1 3 p ( ¯ ∼ ¯ d K. Sakai after the R analysis. To prevent vs p 1 − β . The superimposed 3 backgrounds by a factor of 12000 − ’s by using positive curvature events ¯ d µ and BESS-Polar II proton, deuteron (top) − e 3 selections shown in Fig. Figure 4: and helium (bottom) bands in lines show the selection criteriahelium. for protons and The insetthose selections graphs above 30 show GV. the results of dx / dE , improved tracking quality was required by eliminating noisy ¯ d are basically identical to what were applied in ¯ ¯ d 03 (ACC) that can reject . 1 = n ’s from such backgrounds up to 3.5 GeV. ) except for their deflection thanks to the cylindrical symmetry of the BESS-Polar p p ( d Proton and deuteron bands in (top: UTOF, middle: LTOF, bottom: JET) In the first stage of data analysis, we selected events with a single track fully contained inside R ). The selection criteria of background contamination into d ¯ p spectrometer. We can also estimate various efficiencies for behave like of the full acceptance, but itrigidity ensured measurement. the longest A track single-track fittingtrack event and and was thus one defined the or highest as two resolution hit aneliminated in counters rare event the in which interacting each events. has layer only of ToCarlo one estimate the simulations TOF the isolated hodoscopes. with efficiency of GEANT4 The single-track thepositive were selection and single-track performed. negative selection, curvature Monte events At are this applied point, under the the assumption same that selection non-interactive criteria for ( the fiducial volume defined by theThis central definition four of columns the out fiducial of volume eight reduced columns in the the effective JET geometrical chamber. acceptance down to 4. Data analysis Figure 3: vs from BESS-Polar II.show the The selection criteria superimposed for Z=1ticles. lines and The Z=2 inset par- graphs show theselections results above of 30 those GV. and distinguish ¯ IDC hit events, and selecting events that pass through center region of JET. BESS-Polar II ANTIDEUTERON SEARCH radiator with index PoS(ICRC2019)134 center K. Sakai p and ACC dx / ’s must have the information. We dE d β vs rigidity after the region from ¯ 1 − and σ β dx and ACC cut in BESS-Polar II / ’s as well as dx dE ¯ / d dE vs rigidity plot after excluding 3.5 ¯ 1 d − β shows scatter plot of 4 4 for upper and lower TOF and JET chamber. Figure vs rigidity plot after dx 1 / − β . Figure dE 3 ’s. The rejection power is 43000, more than three times of that in the p . 3 vs rigidity plot for each detector. We require that shows surviving single-charge events in candidates are then selected by using combination of dx contamination. While total number of background is calculated to be 0.3 events, we 5 / ¯ candidates. d p ¯ Surviving single-charge events in d dE inside the band shown in Fig. and samples as well as ¯ Figure d dx π / / analysis. Blue shaded band denotes signal region for shows µ ¯ p data Figure 5: 5. Antideuteron identification cut. Higher ACCe/ threshold was employed to prevent background contamination of relativistic 3 BESS-Polar II ANTIDEUTERON SEARCH first apply band selections according to dE selections shown in Fig. to prevent ¯ found no PoS(ICRC2019)134 114 30 115 (2011), (2016). K. Sakai Phys. , (Mar, 332 A518 108 Science Phys. Rev. Lett. Adv. Space Res. , , Phys. Rev. Lett. , , (2004) 31. (Aug, 2005) 081101. Phys. Rev. Lett. , Nucl. Instrum. Meth. 95 134 , (Jan, 2012) 051102. (2016), no. 2 65 (16pp). (2004) 1755. 108 822 33 Advances in Space Research (In Press) , Phys. Rev. Lett. , 5 Astrophys. J. Phys. Rev. Lett. , , Adv. Space Res. Nucl. Phys. (Proc. Suppl.) , , (2000) 71. A superconducting solenoidal spectrometer for a balloon- borne A443 (2008) 103. B670 The BESS program BESS and its future prospect for polar long duration flights Precision measurement of the helium flux in primary cosmic rays of rigidities 1.9 gv Precision measurement of the proton flux in primary cosmic rays from rigidity 1 gv The pamela mission: Heralding a new era in precision cosmic ray physics Pamela measurements of cosmic-ray proton and helium spectra BESS-polar experiment Phys. Lett. Progress of the BESS superconducting spectrometer , Search for cosmic-ray antideuterons Search for antihelium with the bess-polar spectrometer Measurements of cosmic-ray proton and helium spectra from the bess-polar Measurement of the cosmic-ray antiproton spectrum at solar minimum with a Measurement of cosmic-ray low-energy antiproton spectrum with the first BESS-Polar The results from bess-polar experiment candidate was found, we calculated the resultant 95% C.L. upper limit on the Nucl. Instrum. Meth. ¯ , d (2014), no. 4 323–370. Collaboration, Y. Ajima et al., 544 (Nov, 2015) 211101 (9pp). to 3 tv with the alpha magnetic spectrometer on the international space station (Apr, 2015) 171103. to 1.8 tv with the alpha magnetic spectrometer on the international space station 2012) 131301. long-duration balloon flights over antarctica no. 6025 69–72. Rep. long-duration balloon flight over antarctica Antarctic flight (2004) 167. (2002) 1253. BESS experiment Since no The BESS-Polar program is a Japan-United States collaboration, supported in Japan by the [9] K. Abe et al., [8] K. Abe et al., [7] K. Abe et al., [6] T. Yoshida et al., [4] A. Yamamoto et al., [5] J. W. Mitchell et al., [2] [3] S. Haino et al., [1] H. Fuke et al., [15] M. Aguilar et al., [10] K. Abe et al., [11] K. Abe et al., [13] O. Adriani et al., [14] M. Aguilar et al., [12] O. Adriani et al., Grant-in-Aid ‘KAKENHI’ for Specially Promoted andU.S. Basic by Researches, NASA. MEXT-JSPS, Balloon and flight in operationsloon the Facility were and carried the out National by Science Foundation theto United NASA express States Columbia our Antarctic Scientific sincere Program. Bal- thanks We would for like their continuous professional support. References BESS-Polar II ANTIDEUTERON SEARCH 6. Conclusion deuteron flux. It will be reported in the conference. Acknowledgements