HERA Proton Ring Research Articles

Kinematic distributions and nuclear effects of J/ψ production in 920 GeV fixed-target proton-nucleus collisions

Measurements of the kinematic distributions of J/ψ mesons produced in p–C, p–Ti and p–W collisions at $\sqrt{s}=41.6~\mathrm{GeV}$ in the Feynman-x region −0.34<x F <0.14 and for transverse momentum up to p T =5.4 GeV/c are presented. The x F and p T dependencies of the nuclear suppression parameter, α, are also given. The results are based on 2.4×105 J/ψ mesons reconstructed in both the e + e − and μ + μ − decay channels. The data have been collected by the HERA-B experiment at the HERA proton ring of the DESY laboratory. The measurement explores the negative region of x F for the first time. The average value of α in the measured x F region is 0.981±0.015. The data suggest that the strong nuclear suppression of J/ψ production previously observed at high x F turns into an enhancement at negative x F .

Angular distributions of leptons from J/ψ’s produced in 920 GeV fixed-target proton-nucleus collisions

A study of the angular distributions of leptons from decays of J/ψ’s produced in p-C and p-W collisions at $\sqrt{s}=41.6\mbox{~GeV}$ has been performed in the J/ψ Feynman-x region −0.34<x F <0.14 and for J/ψ transverse momenta up to 5.4 GeV/c. The data were collected by the HERA-B experiment at the HERA proton ring of the DESY laboratory. The results, based on a clean selection of 2.3×105 J/ψ’s reconstructed in both the e + e − and μ + μ − decay channels, indicate that J/ψ’s are produced polarized. The magnitude of the effect is maximal at low p T . For p T >1 GeV/c a significant dependence on the reference frame is found: the polar anisotropy is more pronounced in the Collins-Soper frame and almost vanishes in the helicity frame, where, instead, a significant azimuthal anisotropy arises.

Optimal axes of Siberian snakes for polarized proton acceleration

Accelerating polarized proton beams and storing them for many turns can lead to a loss of polarization when accelerating through energies where a spin rotation frequency is in resonance with orbit oscillation frequencies. First-order resonance effects can be avoided by installing Siberian Snakes in the ring, devices which rotate the spin by 180 degrees around the snake axis while not changing the beam's orbit significantly. For large rings, several Siberian Snakes are required. Here a criterion will be derived that allows to find an optimal choice of the snake axes. Rings with super-period four are analyzed in detail, and the HERA proton ring is used as an example for approximate four-fold symmetry. The proposed arrangement of Siberian Snakes matches their effects so that all spin-orbit coupling integrals vanish at all energies and therefore there is no first-order spin-orbit coupling at all for this choice, which I call snakes matching. It will be shown that in general at least eight Siberian Snakes are needed and that there are exactly four possibilities to arrange their axes. When the betatron phase advance between snakes is chosen suitably, four Siberian Snakes can be sufficient. To show that favorable choice of snakes have been found, polarized protons are tracked for part of HERA-p's acceleration cycle which shows that polarization is preserved best for the here proposed arrangement of Siberian Snakes.

Track finding at 10-MHz hadronic event rate

Hera-B is a fixed target experiment using a halo target inside the HERA proton ring to generate B mesons in 920 GeV proton-nucleus interactions. The first-level trigger (FLT) of the experiment has to reduce the primary 10-MHz input rate by a factor 200 in less than 10 /spl mu/s to make it acceptable to the second level trigger (SLT). The trigger strategy is based on the tracking of charged particles and on the reconstruction of their kinematic parameters. The combination of track pairs can also be used for the final decision. A parallel and pipelined set of approximately 60 dedicated boards was designed and built to perform this job. In this paper, the working principle of the system and some results obtained by analyzing the data collected during the run in the year 2000 are described.

Formula omitted] based γp and γA colliders

Main parameters and physics search potential of γp and γA colliders, which will be available due to constructing the TESLA linear electron–positron collider tangentially to the HERA proton ring, are discussed.

Observation of coasting beam at the HERA proton-ring

We present data collected with the HERA-B wire target which prove the existence of coasting beam at the HERA proton storage ring. The presented measurements show a strong evidence that the proton machine operation contribute to the coasting beam production, which seems to be not dominated by target impacts.

Commissioning of the HERA-B internal target: using the HERA proton ring as a B-factory

HERA-B is a fixed target experiment using the 920 GeV HERA proton storage ring to produce B-mesons. The internal target consists out of eight thin ribbons, which are positioned around the beam, and operates in the beam halo. An interaction rate of 40 MHz is required to achieve the primary goal – a significant CP measurement in the gold-plated B decay mode B 0→J/ ψK S 0 within one year of data taking. The performance of the internal target has been studied in detail for several years. During the last two years the main effort was spent for a successful transition from a test setup to a continuous operational device and into the improvement of the efficiency. This paper reviews the requirements, the impacts and the performance of the HERA-B target.

Status of the HERA-B experiment

The current status of the preparation of the HERA-B experiment is reported. With this experiment CP violation in b-quark systems will be studied using an internal target in the HERA proton ring. The detector is scheduled to be complete for data taking in 1998.

Spin-transparent interaction regions for HERA

Special spin rotators are proposed for compensating the spin perturbation in vertical and horizontal bends around the interaction regions in the 820 GeV HERA proton ring. Installing a radial snake on each side of the interaction region would allow to have a spin-transparent interaction region.

HERA-B, an experiment to study CP violation at the HERA proton ring using an internal target

This paper discusses a dedicated fixed target experiment at the HERA proton ring with the goal to observe CP violation in the B → J ψK s 0 decay channel, using a detector with a highly selective trigger for lepton pairs from the J ψ decay. The precision of the asymmetry, sin 2β, is expected to reach 0.13 within one year of running.

HERA-B triggering

The HERA-B collaboration intends to obtain a first measurement of CP-violation in B decay by studying B-mesons produced in proton-nucleus collisions in a wire target positioned in the halo of the 820 GeV HERA proton ring. A high interaction rate coupled with the low rate of B-meson production place particularly stringent demands on the trigger. The goals and design of the HERA-B trigger system are discussed.

A fixed target B-physics experiment at the HERA proton ring

This contribution discusses some of the detector issues of HERA-B, a dedicated fixed target experiment at the HERA proton ring. The goal of the experiment is to observe CP violation in the B 0 → J / ψK s 0 decay channel using a detector with a highly selective trigger for lepton pairs from the J/ψ decay.

An experiment to study CP violation using an internal target at the HERA proton ring

The main goal of HERA-B is the detection of CP-violation in the B-system using a dedicated Jψ trigger. The HERA-B detector is a forward spectrometer designed to run with high efficiency at a 10 MHz rate of multiple interactions. The requirements for detector components like the silicon vertex detector, the high granularity tracker, and the detectors for particle identification, as well as those for the first level trigger are in many aspects similar to the demands on LHC experiments.

Test of internal halo targets in the HERA proton ring

Internal wire targets in the halo of stored proton beams provide a line source of proton-nucleus interactions for highest-rate fixed target experiments. We have studied such internal halo targets at the 820 GeV proton ring of the HERA ep collider. The tests showed that most of the protons in the beam halo — which would otherwise hit the collimators — can be brought to interaction in a relatively thin target wire at distances of 7 to 8 beam widths from the center of the beam. At less than 10% of the HERA total design current, and less than 20% of the current per bunch, interaction rates up to 8 MHz were observed, corresponding to more than 2 interactions per bunch crossing. The halo targets were used in parallel to the HERA luminosity operation; no significant disturbances of the HERA ep experiments, of the machine stability or beam quality were observed. We present data on the steady-state and transient behaviour of interaction rates and discuss the interpretation in terms of a simple beam dynamics model. Issues of short-, medium- and long-term rate fluctuations and of rate stabilization by feedback are addressed.

HERA-B, an experiment to study CP violation at the HERA proton ring using an internal target

This paper discusses a dedicated fixed target experiment at the HERA proton ring with the goal to observe CP violation in the B 0 → J/ψK s 0 decay channel, using a detector with a highly selective trigger for lepton pairs from the J/ψ decay. The precision of the asymmetry, sin 2β, is expected to reach 0.13 within one year of running.

Preservation of beam loss induced quenches, beam lifetime and beam loss measurements with the HERAp beam-loss-monitor system

The beam-loss-monitors (BLMs) in the HERA-proton-ring (HERAp) must fulfill the following requirements: They have to measure losses sensitive and fast enough to prevent the superconducting magnets from beam loss induced quenching; the dynamic range of the monitors must exceed several decades in order to measure losses during beam lifetimes of hundreds of hours as well as the much stronger losses that may quench superconducting magnets; they have to be insensitive to the synchrotron radiation of the adjacent electron-ring (HERAe); and their radiation hardness must allow a monitor-lifetime of a few years of HERA operation. These requirements are well satisfied by the HERAp-BLM-System.

An experiment to study CP violation in the B system using an internal target at the HERA proton ring

Using the HERA proton beam striking an internal wire target, sufficient numbers of B mesons are produced to allow a search for CP violation in B decays

The 50 MeV H− linear accelerator for HERA:LINAC3 collaboration

The components of the first 50 MeV accelerator in the chain of injectors to the 820 GeV HERA proton ring are described including the high energy transport line. An H− beam originates in the cesium loaded magnetron source, is preaccelerated by a radio frequency quadrupole to 750 keV, raised to 50 MeV energy in three rf resonators, and is analyzed in the transport line. The H− ions are converted to protons by stripping, when the beam is injected over several turns into the synchrotron DESY3.

Dynamic in situ bakeout for the HERA proton ring vacuum system

Due to the restricted space for the heaters and insulation in the normal conducting magnets of the HERA proton ring, the bakeout process must be done very carefully in order to prevent damage of the magnets. A special high temperature thermal insulating material allows bakeout of the stainless steel vacuum chambers by a heating jacket as thin as 3.5 mm. When built into a normal conducting accelerator magnet, a bakeout temperature of 300°C is achieved without overheating the surrounding magnet. After more than 24 h the maximum temperature of 68°C reached at the sensitive coil of the magnet is well below the 80°C critical temperature of the epoxy. With the described bakeout system no heat sink is necessary to protect the magnet's components from the high temperatures. Control and regulation of the temperature of the vacuum chambers are done by means of thermocouple probes, attached to the outer surface of the chambers near the coaxial heating elements.

The warm sections of the HERA proton ring vacuum system

The 1 km long ‘warm’ parts of the HERA proton ring vacuum system are currently being constructed. The layout and characteristics of the 10 −10 mbar system are described. Pump speed measurements for the UHV pumping stations are shown.