Dark sectors 2016 Workshop: community report

This report, based on the Dark Sectors workshop at SLAC in April 2016, summarizes the scientific importance of searches for dark sector dark matter and forces at masses beneath the weak-scale, the status of this broad international field, the important milestones motivating future exploration, and promising experimental opportunities to reach these milestones over the next 5-10 years

Development and test of a prototype for the PANDA Barrel DIRC detector at FAIR

Das PANDA (antiProton ANnihilations at DArmstadt) Experiment ist eines der vier Hauptexperimente an der geplanten Beschleunigeranlage FAIR (Facility for Antiproton and Ion Research), welches auf dem Gebiet der bestehenden GSI Helmholtzzentrum für Schwerionenforschung GmbH in Darmstadt entstehen wird. Das PANDA-Experiment wird Untersuchungen auf dem Sektor der Hadronenphysik auf sehr hohem Niveau durchführen, wobei hierfür ein gekühlter Antiprotonenstrahl bislang unerreichter Intensität im Impulsbereich von 1,5-15 GeV/c verwendet werden wird. Es werden zwei Synchrotrone, SIS100 und SIS300, zur Teilchenbeschleunigung zum Einsatz kommen, wobei die Teilchenpakete anschließend den Experimenten zur Verfügung gestellt werden. Die Antiprotonen werden durch Protonenstöße mit dünnen Ni-Targets erzeugt, anschließend akkumuliert, gekühlt und schließlich in den HESR (High Energy Storage Ring) geleitet, an dem sich der PANDA-Detektor befinden wird. Um den vollständigen Nachweis aller Wechselwirkungsprodukte zu gewährleisten, ist der PANDA Detektor in zwei Hauptkomponenten unterteilt: das Vorwärts-Spektrometer (FS) und das Target-Spektrometer (TS). Das TS mit Axialsymmetrie umgibt den Wechselwirkungspunkt und deckt Polarwinkel im Bereich über 22° ab. Das FS wird die Zerfallsprodukte der Teilchenkollisionen analysieren, die in einem engen Winkelkonus von pm5°vertikal und pm 10° horizontal emittiert werden. Zur Durchführung von Untersuchungen im open charm Sektor ist in der zentralen Region des TS (22 -140°), aufgrund des hohen pionischen Untergrundes, eine Pion-Kaon Separation auf dem Niveau von mindestens drei Standardabweichungen erforderlich. Das hierfür vorgesehene Subsystem muss die Teilchenidentifikation (PID) im Impulsbereich von 0,5-3,5 GeV/c gewährleisten und in dem 2 T Magnetfeld des Solenoids betrieben werden. Es muss in der Lage sein, die extrem hohe Wechselwirkungsrate von bis zu 50 MHz zu verarbeiten. Des Weiteren muss es kompakt genug sein um die Größe des sich nach außen anschließenden Elektromagnetischen Kalorimeters in einem akzeptablen Rahmen zu halten und den Einfluss auf die Performanz dieses Subdetektors zu minimieren. Der für PANDA wichtige Impulsbereich zwischen 0,5 und 3.5 GeV/c liegt im Einsatzbereich von Cherenkov-Zählern. RICH (Ring Imaging CHerenkov counter) Detektoren kommen in vielen Experimenten zur Identifikation von geladenen Teilchen zum Einsatz. Das Funktionsprinzip basiert auf der Abhängigkeit des Emissionswinkels der erzeugten Cherenkov-Strahlung und der Zahl der emittierten Photonen von der Geschwindigkeit des einfallenden Teilchens. Es gibt verschiedene Arten von RICH Detektoren, bei PANDA wird ein Detektor zum Einsatz kommen, der auf dem DIRC (Detection of Internally Reflected Cherenkov light) Prinzip basiert...The PANDA experiment at FAIR will perform world class physics studies using high-intensity cooled antiproton beams with momenta between 1.5 and 15 GeV/c. A rich physics program requires very good particle identification (PID). Charged hadron PID for the barrel section of the target spectrometer has to cover the angular range of 22-140° and separate pions from kaons for momenta up to 3.5 GeV/c with a separation power of at least 3 standard deviations. The system that will provide it has to be thin and operate in a strong magnetic field. A ring imaging Cherenkov detector using the DIRC principle meets those requirements. The design of the PANDA Barrel DIRC is based on the successful BABAR DIRC counter with several important changes to improve the performance and optimize the costs. The design options are being studied in detailed Monte Carlo simulation, and implemented in increasingly complex system prototypes and tested in particle beams. Before building the full system prototypes the radiator bars and lenses are measured on the test benches. The performance of the DIRC prototype was quantified in terms of the single photon Cherenkov angle resolution and the photon yield. Results for two full system prototypes will be presented. The prototype in 2011 aimed at investigating the full size expansion volume. It was found that the resolution for this configuration is at the level of in good agreement with ray tracing simulation results. A more complex prototype, tested in 2012, provided the first experience with a compact fused silica prism expansion volume, a wide radiator plate, and several advanced lens options for the focusing system. The performance of the baseline configuration of the prototype with a standard lens and an air gap met the requirements for the PANDA PID for most of the polar angle range but failed at polar angles around 90° due to photon loss at the air gap. Measurements with a prototype high-refractive index compound lens without an air gap at a polar angle of 128° beam angle showed a good resolution of σΘC = 11.8 ± 0.7 mrad and a high photon yield of Nph = 26.1 ± 0.4. Even at polar angles close to 90° the photon yield with this lens exceeded 15 detected photons per particle, meeting the PANDA Barrel DIRC PID requirements for the entire phase space and demonstrating that the compact focusing DIRC is a very promising option for PANDA

Decay of the Λ(1405) hyperon to Σ

Among the light baryons, the Jπ = 1/2− Λ(1405) hyperon is an important special case as it sits just below the N K̅ threshold and decays almost exclusively to Σπ. Some long-standing hypotheses for Λ(1405) are that it could be a N K̅ bound state or a Σπ continuum resonance. It may also be considered as a simple quark-model resonance, the P-wave companion of the Λ(1520). In recent years chiral unitary models have suggested that there are two isospin zero poles present in this mass region, and that the “line shape" of the Λ(1405) depends to what extent each of the two poles are stimulated in a given reaction. Below the N K̅ threshold, the Λ(1405) decays to the three Σπ charge combinations. The Σ0π0 mode is purely I = 0 and it is uncontaminated by complications arising from I = 1 scattering processes contributing to the reaction mechanism in the Σ+π− and Σ−π+ decays. It is also not affected from production and decay of the nearby Σ0(1385) hyperon. The GlueX experiment at Jefferson Lab has been used to study the Λ(1405) → Σ0π0 decay mode. We focus on the preliminary results of dσ/dMΣ0π0 and fits to the line shape of the Λ(1405) region in the −(t − tmin) range 0 - 1.5 GeV2 from analyzing the reaction γp → K+Λ* using the data collected during the first phase of the GlueX program

Physics with Positron Beams at Jefferson Lab 12 GeV

Positron beams, both polarized and unpolarized, are identified as essential ingredients for the experimental program at the next generation of lepton accelerators. In the context of the Hadronic Physics program at the Jefferson Laboratory (JLab), positron beams are complementary, even essential, tools for a precise understanding of the electromagnetic structure of the nucleon, in both the elastic and the deep-inelastic regimes. For instance, elastic scattering of (un)polarized electrons and positrons off the nucleon allows for a model independent determination of the electromagnetic form factors of the nucleon. Also, the deeply virtual Compton scattering of (un)polarized electrons and positrons allows us to separate unambiguously the different contributions to the cross section of the lepto-production of photons, enabling an accurate determination of the nucleon Generalized Parton Distributions (GPDs), and providing an access to its Gravitational Form Factors. Furthermore, positron beams offer the possibility of alternative tests of the Standard Model through the search of a dark photon or the precise measurement of electroweak couplings. This letter proposes to develop an experimental positron program at JLab to perform unique high impact measurements with respect to the two-photon exchange problem, the determination of the proton and the neutron GPDs, and the search for the $A^{\prime}$ dark photon

Strange Hadron Spectroscopy with Secondary KL Beam in Hall D

Final version of the KLF Proposal [C12-19-001] approved by JLab PAC48. The intermediate version of the proposal was posted in arXiv:1707.05284 [hep-ex]. 103 pages, 52 figures, 8 tables, 324 references. Several typos were fixedWe propose to create a secondary beam of neutral kaons in Hall D at Jefferson Lab to be used with the GlueX experimental setup for strange hadron spectroscopy. The superior CEBAF electron beam will enable a flux on the order of $1\times 10^4~K_L/sec$, which exceeds the flux of that previously attained at SLAC by three orders of magnitude. The use of a deuteron target will provide first measurements ever with neutral kaons on neutrons. The experiment will measure both differential cross sections and self-analyzed polarizations of the produced $\Lambda$, $\Sigma$, $\Xi$, and $\Omega$ hyperons using the GlueX detector at the Jefferson Lab Hall D. The measurements will span CM $\cos\theta$ from $-0.95$ to 0.95 in the range W = 1490 MeV to 2500 MeV. The new data will significantly constrain the partial wave analyses and reduce model-dependent uncertainties in the extraction of the properties and pole positions of the strange hyperon resonances, and establish the orbitally excited multiplets in the spectra of the $\Xi$ and $\Omega$ hyperons. Comparison with the corresponding multiplets in the spectra of the charm and bottom hyperons will provide insight into he accuracy of QCD-based calculations over a large range of masses. The proposed facility will have a defining impact in the strange meson sector through measurements of the final state $K\pi$ system up to 2 GeV invariant mass. This will allow the determination of pole positions and widths of all relevant $K^\ast(K\pi)$ $S$-,$P$-,$D$-,$F$-, and $G$-wave resonances, settle the question of the existence or nonexistence of scalar meson $\kappa/K_0^\ast(700)$ and improve the constrains on their pole parameters. Subsequently improving our knowledge of the low-lying scalar nonet in general