Pion Background Research Articles

The prototype of the front-end electronics for STCF muon detector

The muon detector (MUD), serving as the outermost detector of the high-precision spectrometer in STCF, is used to provide muon identification in the presence of a significant pion background. The accuracy of muon identification relies heavily on excellent momentum resolution, which can be determined by their flight trajectory positions. Physical simulations of the measurement precision for reconstructed muons indicate that a spatial resolution of 2 cm is required. In the barrel MUD, a double-ended readout is required to determine the hit position, with a time resolution requirement of approximately 500 ps. To meet the readout requirements of the MUD, a comprehensive scheme for the front-end readout electronics of the STCF MUD is proposed, and a prototype of MUD readout electronics is developed. To validate the final 8-channel application-specific integrated circuit (ASIC) design, an 8-channel time-to-digital converter (TDC) is implemented using a field programmable gate array (FPGA). The results of the electronics tests demonstrate that the average root mean square (RMS) precision ranges from 14 to 16 ps for each channel within a 1∼20 ns time interval. In the joint test with the detector, the system achieves a single-channel RMS precision of 297 ps, with a detection efficiency exceeding 95.5%. All indicators meet project requirements. This validates that the prototype is capable of preliminary evaluation and parameter optimization of the STCF MUD.

New perspective in searching for axionlike particles from flavor physics

We propose new perspective in searching for axion-like particles (ALPs) from quark and lepton flavor physics: measurements of the time-dependent CP asymmetry in $B^0 \to K_S^0 \pi^0 \gamma$ and the branching ratio of $B_s \to e^\pm \mu^\mp$ decay possess, along with the anomalous magnetic moment of muon. In the mass range of sub-GeV, accessible by the flavorful ALPs search, the experimental sensitivity for these flavor observables reaches the maximum at around the pion mass scale (called the {\it sweetest} spots), where a couple of loopholes (unexplored regions) for the ALP parameter space have heretofore been present, because of an unavoidable contamination with pion background events. The proposed complementary probes can precisely determine the ALP coupling to photon at these {\it sweetest} spots/loopholes, and will significantly help cover whole parameter spaces in the ALP search including the present loopholes in the future.

Physics object performance of the FCC-hh calorimeter system

The feasibility of a future proton-proton collider (FCC-hh) has been outined in Conceptual Design Reports published early 2019. FCC-hh would deliver collisions at a center of mass energy up to 100 TeV and unprecedented instantaneous luminosity (L=3 × 1034), resulting in extremely challenging radiation conditions up to a maximum of 5× 1018 neq/cm2 and a dose up to 5 GGy in the forward calorimeters (up to |η|=6) and up to 1000 simultaneous proton-proton interactions per bunch-crossing. By delivering an integrated luminosity of few tens of ab−1, the FCC-hh would provide an unrivalled discovery potential for new physics. Requiring high sensitivity for resonant searches at masses up to tens of TeV imposes strong constraints on the design of the calorimeters. Resonant searches in final states containing jets, taus and electrons require both excellent energy resolution at multi-TeV energies as well as outstanding ability to resolve highly collimated decay products resulting from extreme boosts. In addition, the FCC-hh provides the unique opportunity to precisely measure the Higgs self-coupling in the di-photon and b-jets channel. Excellent photon and jet energy resolution at low energies as well as excellent angular resolution for pion background rejection are required in this challenging environment. In this talk we will briefly review the electromagnetic and hadronic calorimeter current design and requirements (granularity, energy resolution, acceptance, …) and discuss the expected performance of the physics objects based on calorimeter reconstruction. We will then examine the impact of the object performance on the final sensitivity of the relevant benchmark physics analyses.

Physics requirements for the FCC-hh calorimeter system

The future proton-proton collider (FCC-hh) will deliver collisions at a center of mass energies up to √s = 100 TeV at an unprecedented instantaneous luminosity of L = 3 1035cm−2s−1, resulting in extremely challenging radiation conditions up to a maximum of 5 1018cm2MeV neutron equivalent fluence and dose up to 5 GGy in the forward calorimeters (up to |η| = 6) and up to 1000 simultaneous proton-proton interactions per bunch-crossing. By delivering an integrated luminosity of few tens of ab−1, the FCC-hh will provide an unrivalled discovery potential for new physics. Requiring high sensitivity for resonant searches at masses up to tens of TeV imposes strong constraints on the design of the calorimeters. Resonant searches in final states containing jets, taus and electrons require both excellent energy resolution at multi-TeV energies as well as outstanding ability to resolve highly collimated decay products resulting from extreme boosts. In addition, the FCC-hh provides the unique opportunity to precisely measure the Higgs self-coupling in the di-photon and b-jets channel. Excellent photon and jet energy resolution at low energies as well as excellent angular resolution for pion background rejection are required in this challenging environment.

Selection of electron (anti-)neutrinos at the T2K near detector ND280

The intrinsic electron neutrino contamination of the T2K neutrino beam provides the single largest background in the measurement of electron neutrino appearance in T2K. These electron neutrinos can be measured directly in the T2K near detector ND280. Measurements of the intrinsic electron (anti-)neutrino backgrounds from the anti-neutrino running are shown, including details on the event selections and rejection of the large background of muons, photons, protons and pions. The νe and beam compositions are then extracted and the rescaling parameters of the expected rate of νe and events are f(νe) = 1.250 ± 0.135(stats.) ± 0.122(syst.) and respectively.

Longitudinally segmented shashlik calorimeters with SiPM readout

The goal of the INFN SCENTT R&D project is to develop the calorimeter technologies for the instrumentation of decay tunnels in conventional neutrino beams. This instrumentation is required to achieve a substantial improvement in the uncertainty on neutrino fluxes for the next generation cross section experiments. In particular, we are designing a positron tagger based on purely calorimetric techniques that is able to measure the rate and the spectrum of the positrons produced in the K+→e+π0νe decay. The νe flux is inferred from the positron rate in the decay tunnel. Considering the large dimensions of the tagger, the most cost effective technology is based on small modules of Fe/Scintillator shashlik calorimeters, with adequate segmentation and energy resolution to efficiently tag the positrons over the charged pion background. This contribution presents preliminary results obtained with two shashlik calorimeter prototypes readout with an array of Silicon PhotoMultipliers and tested at the CERN PS-T9 beamline.

Mu2e: a Muon to Electron Conversion Experiment at Fermilab

We present the status of Mu2e, a proposed experiment to measure the rate of muon to electron conversion in the field of a nucleus. The Mu2e experiment will be hosted by Fermilab at a new muon campus, using a new beamline to deliver protons to the muon generation target. Mu2e will use a series of three solenoids to collect, transport, stop, and analyze the muons produced when the 8 GeV pulsed proton beam from the booster hits the tungsten production target. The 200 nsec wide proton pulse is designed to have a ratio of out-of-time to in-time protons better than 10−10, insuring a measurement time window of approximately 1 microsecond essentially free from beam pion background. A precision, low-mass straw tube tracker will measure electron momenta with a precision of 1/1000, allowing clean separation of the conversion signal from Decay In Orbit electrons, the principle experimental background. Extensive coverage of multi-layer scintillation counters will detect 99.99% of the cosmic muons which could generate fake signals. A crystal calorimeter will provide particle ID to further reduce backgrounds. Detailed simulations show a 3-year run with 7.56×1017 stopped muons will allow a Single Event Sensitivity of 2×10−17, allowing an estimated 90% confidence level sensitivity to Rμe of 6×10−17, a four-orders of magnitude improvement over existing limits. The Mu2e schedule is technically limited, with commissioning beginning in 2019. Mu2e may also run at Project X with 10× higher luminosity using either an aluminum or titanium target after minimal upgrades.

A scaler-based data acquisition system for measuring parity-violating asymmetry in deep inelastic scattering

An experiment that measured the parity-violating asymmetries in deep inelastic scattering was completed at the Thomas Jefferson National Accelerator Facility in experimental Hall A. From these asymmetries, a combination of the quark weak axial charge could be extracted with a factor of five improvement in precision over world data. To achieve this, asymmetries at the 10−4 level needed to be measured at event rates up to 600 kHz and the high pion background typical to deep inelastic scattering experiments needed to be rejected efficiently. A specialized data acquisition (DAQ) system with intrinsic particle identification (PID) was successfully developed and used: the pion contamination in the electron samples was controlled at the order of 2×10−4 or below with an electron efficiency of higher than 91% during most of the production period of the experiment, the systematic uncertainty in the measured asymmetry due to DAQ deadtime was below 0.5%, and the statistical quality of the asymmetry measurement agreed with the Gaussian distribution to over five orders of magnitudes. The DAQ system is presented here with an emphasis on its design scheme, the achieved PID performance, deadtime effect and the capability of measuring small asymmetries.

Peculiarities of applying the ω n k criterion for the electron identification problem based on the transition radiation detector in the compressed baryonic matter experiment

The problem of electron identification under conditions of a dominating pion background with the help of a multilayered transition radiation detector (TRD) in the Compressed Baryonic Matter (CBM) experiment is considered. With this aim, various mathematical methods, including methods based on the nonparametric goodness-of-fit ω criterion, have been elaborated and investigated. The characteristic properties of distributions of energy losses by electrons and pions in the TRD radiators are considered, and specific features of applying traditional statistical methods, methods based on the ω criterion, and artificial neural networks to the analyzed problem are discussed. The results of a comparative analysis of the power of these methods are presented, and recommendations for their usage are given.

10.1007/s11497-008-2009-3

The problem of electron/pion identification in the CBM experiment based on the measurements of energy losses and transition radiation in the TRD detector is discussed. Earlier we analyzed a possibility to solve such a problem using an artificial neural network (ANN) [1]. Here we consider an approach based on a nonparametric ω goodness-of-fit criterion, and comparison with the ANN method is also performed. We show that both methods provide a comparable level of pion suppression and electron identification, the ω test is more simple for practical applications, the ANN method provides the needed level of pions suppression only if “clever” variables are used. We demonstrate that application of the ω -criterion to the J/Ψ reconstruction provides a high level of pion background suppression and significantly improves a signal-to-background ratio.

10.1007/s11497-008-1008-8

The current status of construction and testing of Transition Radiation Detectors (TRD) for ALICE at LHE, JINR, is presented. The main purpose of this detector is electron identification at intensive pion background. The whole ALICE TRD system is comprised of 540 wire chambers of total sensitive area ∼750 m2. Each chamber consists of drift and amplifying gaps and a radiator. One hundred such TRD chambers will be constructed at LHE, JINR.

Electron/pion identification in the CBM TRD applying a ω n k goodness-of-fit criterion

The problem of electron/pion identification in the CBM experiment based on the measurements of energy losses and transition radiation in the TRD detector is discussed. Earlier we analyzed a possibility to solve such a problem using an artificial neural network (ANN) [1]. Here we consider an approach based on a nonparametric ωnk goodness-of-fit criterion, and comparison with the ANN method is also performed. We show that both methods provide a comparable level of pion suppression and electron identification, the ωnk test is more simple for practical applications, the ANN method provides the needed level of pions suppression only if “clever” variables are used. We demonstrate that application of the ωnk-criterion to the J/Ψ reconstruction provides a high level of pion background suppression and significantly improves a signal-to-background ratio.

Construction and testing of the ALICE TRD chambers at LHE, JINR

The current status of construction and testing of Transition Radiation Detectors (TRD) for ALICE at LHE, JINR, is presented. The main purpose of this detector is electron identification at intensive pion background. The whole ALICE TRD system is comprised of 540 wire chambers of total sensitive area ∼750 m2. Each chamber consists of drift and amplifying gaps and a radiator. One hundred such TRD chambers will be constructed at LHE, JINR.

Measurement of and on Nuclear Targets in the Nucleon Resonance Region

We report on progress of the analysis of experiments E02-109 and E04-001, which were carried out at the Thomas Jefferson National Accelerator Facility (Jlab). The analysis is in progress. Various efficiencies (tracking, Čerenkov, Calorimeter) were determined. Background events from electron-positron pairs, and from the aluminum walls of the cryogenic target cells were measured. Pion rejection was implemented in the hardware trigger, and the remaining pion background was cut by using information from the Čerenkov and Calorimeter detectors. Density corrections have been determined for local boiling effect in the cryogenic targets. Preliminary cross sections were calculated for all beam energies, angles and targets. All tables of the cross sections are available via web-page: http://hallcweb.jlab.org/elogs/Jan05+Experiments/ (items:65, 68–88).

Identification of K +-mesons from subthreshold pA collisions with ANKE at COSY-Jülich

The spectrometer ANKE has been put into operation at the accelerator COSY of the Forschungszentrum Jülich in spring 1998. An initial scientific goal is to study K +-production in pA collisions at subthreshold energies far below the free NN-threshold at T p=1.58 GeV. This requires the identification of K +-mesons in a background of pions and protons, about 10 6 times more intense. In this paper the sophisticated detection system and the software procedures for kaon identification are described. With the help of TOF, energy-loss and range measurements as well as the track information from wire chambers, it is possible to measure d 2σ/ dΩ dp for deep subthreshold K + production at beam energies down to T p=1.0 GeV.

First results from subthreshold K +-production measurements with ANKE

The new spectrometer ANKE has been put into operation at the accelerator COSY of the Forschungszentrum Jülich. An initial scientific goal is to study K +-production in pA collisions at subthreshold energies below the free NN-threshold of T = 1.58 GeV. First measurements of double differential cross sections in p 12C collisions at emission angles around 0° have been performed at T = 1.0, 1.2 and 2.0 GeV. The challenge is to identify the kaons in a huge background of pions and protons, since the signal to background ratio decreases to about 10 −6 at T = 1.0 GeV. For background suppression detectors and a trigger system based on energy-loss and time-of-flight measurements have been developed. In the analysis the decay of kaons ( τ = 12.4 ns) stopped in the detection system into μ + and π + is exploited as well as the track information from the wire chambers.

ϱ-meson production and decay in proton-nucleus collision

We analyze the production of ϱ-mesons in p + A reactions including both the production by proton-nucleon as well as pion-nucleon collisions within a coupled channel transport approach. The final state interactions of the ϱ-meson with nucleons are evaluated from a resonance model which allows to extract elastic and inelastic cross sections. We include the latter final state interactions, the ϱ-meson decay into two pions as well as the final pion-nucleon interactions within the transport approach. We find the invariant mass distribution of pion pairs to be sensitive to the ϱ-meson properties in the nuclear medium. However, due to the strong final state interactions of pions only light targets like 12C might be suited to extract a ϱ-signal from the uncorrelated two pion background which carries information about the in-medium properties of the ϱ-meson.

K +-meson production inpBe interactions atT p=2.9 GeV

The production ofK+ andπ+ mesons and protons inpBe collisions atTp=2.9 GeV has been studied at the ITEP proton synchrotron. Ejectiles with a momentum ofp=545 MeV/c were observed under an emission angle ϑ=17°. The detectors which have been developed for the identification of kaons out of a six orders of magnitude more intense background of pions and protons are described. A cross-section ratio d2σK+/dΩdp: d2σp/dΩdp: d2σp/dΩdp of (1±0.34):(85±1):(31±1) has been measured. Normalization with existing pion data yields an invariant differential cross sectionE·d3σK+/d3p=(3.1±1.2) mbGeV−2c3sr−1 and a total cross section of σtot(pBe)=(3.7±1.5) mb. These cross sections are compared with existing data and theoretical predictions. TheA dependence ofK+ production in the few-GeV range is analyzed.

The superconducting kaon spectrometer — SKS

A superconducting kaon spectrometer has been installed in the north experimental hall of the KEK 12-GeV proton synchrotron. The spectrometer was designed to serve for nuclear physics experiments with meson beams in the 1 GeV/ c region, particular emphasis being laid on study of Λ-hypernuclei via ( π +, K +) reactions. In order to obtain Λ-hypernuclear data with better statistics and energy resolution, it was designed to have a good momentum resolution of 0.1% FWHM and a large acceptance of 100 msr. It consists of a large superconducting dipole magnet, tracking chambers, and trigger counters that can efficiently select kaons from large background of pions and protons. The overall energy resolution for scattering is realized together with a beam-line spectrometer in the K6 beam line, the momentum resolution of which was also designed to be better than 0.1% FWHM. A good energy resolution of better than 2 MeV FWHM has been confirmed in π −- 12C elastic scattering and in the ( π +,K +) reaction on 12C.

Damage observed in silicon diodes after low energy pion irradiation

We present results of irradiation tests performed in the pion beam of the Paul Scherrer Institute. Our results confirm the prediction, that the Δ-resonance is reflected as an enhancement of the damage caused by low energy pions. At the peak of the Δ-resonance we measure a damage constant 1.5 times higher than generally adopted for neutrons and high energy protons. This result means that the lifetime of silicon detectors close to the vertex at LHC experiments will be limited by the pion background. We predict type inversion of high resistivity detectors to occur after two months of full luminosity and the depletion voltage to reach 200 V within the first four years, even if the detectors are operated at 0°C.