Particle Physics Aspects of Antihydrogen Studies with ALPHA at CERN

Fujiwara, M.; Andresen, Gorm Bruun; Bertsche, W.; Bowe, P. D.; Bray, C. C.; Butler, E.; Cesar, C. L.; Chapman, S.; Charlton, M.; Fajans, J.; Funakoshi, R.; Gill, D. R.; Hangst, J. S.; Hardy, W. N.; Hayano, R.; Hayden, M. E.; Humphries, A. J.; Hydomako, R.; Jenkins, Michael J.; Jørgensen, L. V.; Kurchaninov, L. L.; Lai, W. P.; Lambo, R.; Madsen, N.; Nolan, P.; Olchanski, K.; Olin, Å.; Povilus, A.; Pusa, P.; Robicheaux, F.; Sarid, E.; Nasr, S. Seif El; Silveira, D. M.; Storey, J. W.; Thompson, R. I.; Werf, D. P. van der; Wasilenko, L.; Wurtele, J. S.; Kanai, Yasuyuki; Yamazaki, Y.

doi:10.1063/1.2977840

Cited by 11 publications

(4 citation statements)

References 24 publications

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“…Antihydrogen, when released from the magnetic trap, annihilates on the Penning trap electrodes. The antiproton annihilation events are registered using a silicon vertex detector [ 36,37 ]. For most of the data presented here, an axial, static, electric bias field of 500 Vm -1 was applied during the confinement and shutdown stages to deflect bare antiprotons which may have been trapped via the magnetic mirror effect [ 17 ].…”

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confidence: 99%

Confinement of antihydrogen for 1,000 seconds

et al. 2011

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Reported trapping times of magnetically confined (matter) atoms range from <1 s in the first, room temperature, traps [ 18 ] to 10 to 30 minutes in cryogenic devices [ 19,20,21,22 ]. However, antimatter atoms can annihilate on background gases. Also, the loading of our trap (i.e., anti-atom production via merging of cold plasmas) is different from that of ordinary atom traps, and the loading dynamics could adversely affect the trapping and orbit dynamics. Mechanisms exist for temporary magnetic trapping of particles (e.g., in quasi-stable trapping orbits [ 23 ], or in excited internal states [ 24 ]); such particles could be short-lived with a trapping time of a few 100 ms. Thus, it is not a priori obvious what trapping time should be expected for antihydrogen. 5In this article, we report the first systematic investigations of the characteristics of trapped antihydrogen. These studies were made possible by significant advances in our trapping techniques subsequent to Ref. [ 17 ]. These developments, including incorporation of evaporative antiproton cooling[ 25 ] into our trapping operation, and optimisation of autoresonant mixing [ 26 ], resulted in up to a factor of five increase in the number of trapped atoms per attempt. A total sample of 309 trapped antihydrogen annihilation events was studied, a large increase from the previously published 38 events.Here we report trapping of antihydrogen for 1000 s, extending earlier results [ 17 ] by nearly four orders of magnitude. Further, we have exploited the temporal and spatial resolution of our detector system to perform a detailed analysis of the antihydrogen release process, from which we infer information on the trapped antihydrogen kinetic energy distribution.The ALPHA antihydrogen trap [ 27,28 ] is comprised of the superposition of a Penning trap for antihydrogen production and a magnetic field configuration that has a three-dimensional minimum in magnitude (Fig. 1). For ground-state antihydrogen, our trap well-depth is 0.54 K (in temperature units).The large discrepancy in the energy scales between the magnetic trap depth (~50 eV), and the characteristic energy scale of the trapped plasmas (a few eV) presents a formidable challenge to trapping neutral anti-atoms. antiprotons at ~100K, with radius 0.4 mm and density 7x10 7 cm -3 is prepared for mixing with positrons.Independently, the positron plasma, accumulated in a Surko-type buffer gas accumulator [ 33 ,34 ], is transferred to the mixing region, and is also radially compressed. The magnetic trap is then energized, 6 and the positron plasma is cooled further via evaporation, resulting in a plasma with a radius of 0.8 mm and containing 1x10 6 positrons at a density of 5x10 7 cm -3 and a temperature of ~40 K. The silicon vertex detector, surrounding the mixing trap in three layers (Fig. 1 a) ]. Knowledge of annihilation positions also provides sensitivity to the antihydrogen energy distribution, as we will show.In Table 1 and Fig. 2, we present the results for a series of measurements, wherein the confinemen...

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confidence: 99%

Confinement of antihydrogen for 1,000 seconds

et al. 2011

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“…The 2008 experimental program in ALPHA will focus on careful manipulations and mixing techniques designed to minimize the temperature of the produced antihydrogen atoms. In these endeavours, we expect to benefit both from the novel diagnostic techniques reported elsewhere in these proceedings [7] and from the ALPHA imaging silicon detector [12], expected to be installed in 2008.…”

Section: Discussionmentioning

confidence: 99%

“…We have no direct measurement of the field decay in the superconducting magnet. The mirror coils have a slightly faster e-folding time of 8.3 ms. For the measurements described in the following section, the apparatus was equipped with scintillation detectors read out by avalanche photodiodes (APD) [12]. The detec-tors were placed inside the outer solenoid and adjacent to the mixing trap ( Figure 1).…”

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First Attempts at Antihydrogen Trapping in ALPHA

Andresen¹,

Bertsche²,

Bowe³

et al. 2008

AIP Conference Proceedings

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The ALPHA apparatus is designed to produce and trap antihydrogen atoms. The device comprises a multifunction Penning trap and a superconducting, neutral atom trap having a minimum-B configuration. The atom trap features an octupole magnet for transverse confinement and solenoidal mirror coils for longitudinal confinement. The magnetic trap employs a fast shutdown system to maximize the probability of detecting the annihilation of released antihydrogen. In this article we describe the first attempts to observe antihydrogen trapping.

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“…§ Because of the interaction between the mirror and octupole fields, the magnetic field minimum is actually slightly radially displaced from the trap center, not at the trap center itself. [3,7,8]. The detector is sensitive only to the charged particles produced by antiproton annihilations; it cannot detect the gamma rays from positron annihilations.…”

Section: Introductionmentioning

confidence: 99%

Discriminating between antihydrogen and mirror-trapped antiprotons in a minimum-B trap

et al. 2012

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Recently, antihydrogen atoms were trapped at CERN in a magnetic minimum (minimum-B) trap formed by superconducting octupole and mirror magnet coils. The trapped antiatoms were detected by rapidly turning off these magnets, thereby eliminating the magnetic minimum and releasing any antiatoms contained in the trap. Once released, these antiatoms quickly hit the trap wall, whereupon the positrons and antiprotons in the antiatoms annihilate. The antiproton annihilations produce easily detected signals; we used these signals to prove that we trapped antihydrogen. However, our technique could be confounded by mirror-trapped antiprotons, which would produce seemingly identical annihilation signals upon hitting the trap wall. In this paper, we discuss possible sources of mirror-trapped antiprotons and show that antihydrogen and antiprotons can be readily distinguished, often with the aid of applied electric fields, by analyzing the annihilation locations and times. We further discuss the general properties of antiproton and antihydrogen trajectories in this magnetic geometry, and reconstruct the antihydrogen energy distribution from the measured annihilation time history.

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Particle Physics Aspects of Antihydrogen Studies with ALPHA at CERN

Cited by 11 publications

References 24 publications

Confinement of antihydrogen for 1,000 seconds

Confinement of antihydrogen for 1,000 seconds

First Attempts at Antihydrogen Trapping in ALPHA

Discriminating between antihydrogen and mirror-trapped antiprotons in a minimum-B trap

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