Detection of low energy antiproton annihilations in a segmented silicon detector

Abstract

The goal of the AEḡIS experiment at the Antiproton Decelerator (AD) at CERN, is to measure directly the Earth's gravitational acceleration on antimatter by measuring the free fall of a pulsed, cold antihydrogen beam. The final position of the falling antihydrogen will be detected by a position sensitive detector. This detector will consist of an active silicon part, where the annihilations take place, followed by an emulsion part. Together, they allow to achieve 1% precision on the measurement ofḡ with about 600 reconstructed and time tagged annihilations. We present here the prospects for the development of the AEḡIS silicon position sentive detector and the results from the first beam tests on a monolithic silicon pixel sensor, along with a comparison to Monte Carlo simulations.-2 -2 antimatter by measuring the Earth's gravitational acceleration g for antihydrogen. Several attempts 3 have been made in the past to measure the gravitational constant for antimatter, both for charged 4 [2, 3] and neutral antiparticles [4, 5, 6]. However, none of these experiments brought to conclusive 5 results. Recently, a study from the ALPHA collaboration [7] sets limits to the ratio of gravitational 6 mass to the inertial mass of antimatter but is yet far from testing the equivalence principle. Another 7 experiment, GBAR, [8] has been proposed but not yet built. 8 Cold antihydrogen (100 mK) in Rydberg states will be produced through the charge exchange 9 reaction between Rydberg positronium and cold antiprotons stored in a Penning trap [9]. Applying 10 an appropriate electric field will accelerate the formed antihydrogen in a horizontal beam, with a 11 typical axial velocity distribution spanning a few 100 m/s [10]. 12Some of the trajectories will be selected through a moiré deflectometer [11], which will consist 13 of two vertical gratings producing a fringe pattern on a downstream annihilation plane (see fig. 2). 14 This plane will be the first layer of the position sensitive detector where the antihydrogen will 15 impinge with energies of the order of meV and annihilate. The vertical deflection of the pattern 16 is proportional to the gravitational constant to be measured. Over a flight path of ∼ 1 m, the 17 deflection is expected in the order of ∼ 20 µm for a 1 g vertical acceleration [1]. A vertical 18 resolution better than 10 µm is required to meet the goal of 1% precision on theḡ measurement 19 with 600 reconstructed and time tagged annihilations [12]. 20According to the current design, the position sensitive detector will be a hybrid detector con-21 sisting of an active silicon part, where the annihilation takes place, followed by an emulsion part 22 65 the fragmentation of excited hadronic systems into individual hadrons, whereas the FTFP model 66 [23] relies on a string model to describe the interactions between quarks. 67The CHIPS and FTFP models differ in the production rate and in the composition of the 68 annihilation products. CHIPS produces heavy nuclear fragments in only 20 % of the events while 69 FTFP...

Probing antimatter gravity – The AEGIS experiment at CERN

“…The detector will most likely consist of a combination of complementary technologies, including a nuclear photographic emulsion and a silicon strip or pixel detector. Both types of systems have been extensively tested in the AEGIS setup and found to deliver the required position resolution and detection efficiency for an antihydrogen gravity measurement [28,29]. …”

Antimatter annihilation detection with AEgIS

“…The development of the silicon position detector included several beam test periods with different detector technologies in order to study the annihilation of low energy antiprotons in silicon, to define the design specifications and to make estimations on the position resolution of the annihilation point. The results from the beam test campaigns elaborated here have been published [11,12,13] and what follows is a summary.…”

“…During the beam test campaigns, each of these detectors was placed at approximately the same position in a six-way cross attached at the end of the AEḡIS apparatus. A detailed description of the set-up is given in [11]. The first measurements were expected to be mainly used for the estimation of the energy deposited in the detector due to an annihilation.…”

“…The results also provided directions for improvements and tuning of these models. The measurements and the detailed results are presented and extensively elaborated in [11].…”

Hybrid Imaging and Timing Ps Laser Excitation Diagnostics for Pulsed Antihydrogen Production

“…Probing experimentally the gravitational acceleration of neutral antimatter atoms is the main goal of the AEḡIS collaboration based at CERN Antiproton Decelerator [1], aiming to use a Moiré deflectometer [2], combined with high-resolution position-sensitive and timing detectors [3,4], to detect the time-of-flight and the vertical free-fall displacement of a beam of antihydrogen atoms. PulsedH production, yet to be experimentally demonstrated, is the key advancement to pave the way to this approach, as it would open the possibility to measure the atoms' time-of-flight, unavailable from currently available trap-based methods [5,6].…”