Improved simulation of beam backgrounds and collimation at SuperKEKB

Natochii, A.; Vahsen, S.; Nakayama, Hiroyuki; Ishibashi, Takuya; Terui, Shinji

doi:10.1103/physrevaccelbeams.24.081001

Cited by 17 publications

(25 citation statements)

References 20 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…However, several single beam background components appear incorrectly normalized. This discrepancy was also observed in other (nonneutron) early background studies at SuperKEKB [1], and has since been improved via an improved simulation of beam collimators [24].…”

Section: Discussionsupporting

confidence: 55%

“…Studies in later phases of BEAST II have indicated that this discrepancy between predicted and observed rates in the HER is most likely due to improper collimator simulations in the HER. A more thorough analysis of this effect will be studied and presented in future results [24]. For the scope of this result, we note the effect, but do not correct for it.…”

Section: Experimental Runs For Tpcsmentioning

confidence: 96%

See 1 more Smart Citation

First 3D vector tracking of helium recoils for fast neutron measurements at SuperKEKB

Hedges,

Vahsen,

Jaegle

et al. 2021

Preprint

Self Cite

View full text Add to dashboard Cite

We present results from the first deployment of novel, high definition, compact gas Time Projection Chambers (TPCs) with pixel chip readout as part of the BEAST II beam background measurement project at SuperKEKB. The TPCs provide detailed 3D imaging of ionization from neutron-induced nuclear recoils in a helium and carbon dioxide target gas mixture at standard temperature and pressure. We present the TPC performance and the neutron backgrounds observed during the initial stage of collider commissioning. We find excellent electron background rejection, leading to background-free nuclear recoil measurements above 50 keV ee , despite the extreme high-background environment. We measure an angular resolution better than 20 • for recoil tracks longer than 1.7 mm, corresponding to an average ionization energy of approximately 100 keV ee . We also obtain the full 3D vector direction of helium recoils by utilizing charge profile measurements along the recoil axis, with a correct head/tail assignment efficiency of approximately 80%. With this performance, we present comparisons between measured and simulated event rates, recoil energy spectra, and directional distributions originating from beam-gas and Touschek beam losses at SuperKEKB. We utilize head/tail recognition to distinguish neutron components travelling with positive radial velocity in the Belle II coordinate system from those travelling in the opposite direction. Finally, we present a novel method of discriminating beam-gas interactions from Touschek beam losses that can eliminate the need for dedicated accelerator runs for background measurements. This method is still statisticslimited. However, future studies should be able to verify this method, which in turn could lead to neutron background analysis runs symbiotic with normal Belle II operation. The capabilities demonstrated here also suggest that high definition recoil imaging in gas TPCs is applicable to low energy, low-background experiments, such as directional dark matter searches.

show abstract

Section: Discussionsupporting

confidence: 55%

Section: Experimental Runs For Tpcsmentioning

confidence: 96%

First 3D vector tracking of helium recoils for fast neutron measurements at SuperKEKB

Hedges,

Vahsen,

Jaegle

et al. 2021

Preprint

Self Cite

View full text Add to dashboard Cite

show abstract

“…Many improvements have been made recently to the implementation of tracking and recording SuperKEKB losses in SAD [32], as well as the implementation of accelerator and detector components for SuperKEKB and Belle II in Geant4 [18,19].…”

Section: Simulationmentioning

confidence: 99%

“…Machine parameters used in determining losses are summarized in Table 1. Collimator tip scattering and a more accurate beam pipe shape were also implemented in SAD [32], giving better confidence in the modeling of losses from circulating beams around the ring. For luminosity background samples, we found that the overwhelming majority of simulated radiative Bhabha background events come from the BBBREM event generator [37] (events leading to neutron recoils in the TPCs from the BHWIDE generator [38] TPC location were negligible and are thus not included in this analysis).…”

Section: Description Of Simulated Samples Generated For Analysismentioning

confidence: 99%

Application of recoil-imaging time projection chambers to directional neutron background measurements in the SuperKEKB accelerator tunnel

Schueler,

Vahsen,

Lewis

et al. 2021

Preprint

Self Cite

View full text Add to dashboard Cite

Gaseous time projection chambers (TPCs) with high readout segmentation are capable of reconstructing detailed 3D ionization distributions of nuclear recoils resulting from elastic neutron scattering. Using a system of six compact TPCs with pixel ASIC readout, filled with a 70:30 mixture of He:CO 2 gas, we analyze the first directional measurements of beam-induced neutron backgrounds in the tunnel regions surrounding the Belle II detector at the SuperKEKB e + e − collider. With the use of 3D recoil tracking, we show that these TPCs are capable of maintaining nearly 100% nuclear recoil purity to reconstructed ionization energies (E reco ) as low as 5 keV ee . Using a large sample of Monte-Carlo (MC)-simulated 4 He, 12 C, and 16 O recoil tracks, we find consistency between predicted and measured recoil energy spectra in five of the six TPCs, providing useful validation of the neutron production mechanisms modeled in simulation. Restricting this sample to 4 He recoil tracks with E reco > 40 keV ee , we further demonstrate axial angular resolutions within 8 • and we introduce a procedure that under suitable conditions, correctly assigns the vector direction to 91% of these simulated 4 He recoils. Applying this procedure to assign vector directions to measured 4 He recoil tracks, we observe consistency between the angular distributions of observed and simulated recoils in five of the six TPCs, providing first experimental evidence of localized neutron "hotspots" on either side of the Belle II detector. Observed rates of nuclear recoils in these TPCs suggest that simulation overestimates the neutron flux from these hotspots. Despite this, simulation predicts these hotspots to produce the majority of neutron backgrounds in the accelerator tunnel at SuperKEKB's design luminosity of 6 × 10 35 cm −2 s −1 , making them important regions to continue to monitor.

show abstract

“…Single-beam background rates depend very strongly on the collimation system settings. In our previous work on beam backgrounds, the simulation of the Su-perKEKB collimation system was substantially improved, and is now deemed reliable [1].…”

mentioning

confidence: 99%

Beam background expectations for Belle II at SuperKEKB

Natochii¹,

Browder²,

Cao³

et al. 2022

Preprint

Self Cite

View full text Add to dashboard Cite

The Belle II experiment at the SuperKEKB electron-positron collider aims to collect an unprecedented data set of 50 ab −1 to study CP -violation in the Bmeson system and to search for Physics beyond the Standard Model (BSM). SuperKEKB is already the world's highest-luminosity collider. In order to collect the planned data set within approximately one decade, the target is to reach a peak luminosity of 6.3 × 10 35 cm −2 s −1 by further increasing the beam currents and reducing the beam-size at the interaction point by squeezing the betatron function down to β * y = 0.3 mm. Beam backgrounds are a key challenge in this context. We estimate the expected background evolution in the next ten years and discuss potential challenges and background mitigation strategies. We find that backgrounds will remain high but acceptable until a luminosity of at least 2.8 × 10 35 cm −2 s −1 is reached at β * y = 0.6 mm. Beyond this luminosity, predictions are highly uncertain, owing to a planned redesign of the interaction region. Improved background estimates with reduced uncertainties for the final, maximum-luminosity operation will require completion of this redesign.

show abstract

Improved simulation of beam backgrounds and collimation at SuperKEKB

Cited by 17 publications

References 20 publications

First 3D vector tracking of helium recoils for fast neutron measurements at SuperKEKB

First 3D vector tracking of helium recoils for fast neutron measurements at SuperKEKB

Application of recoil-imaging time projection chambers to directional neutron background measurements in the SuperKEKB accelerator tunnel

Beam background expectations for Belle II at SuperKEKB

Contact Info

Product

Resources

About