Browsing by Author "Roberts, Jabus B."
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Item A 200 MeV proton spin polarimeter(1983) Rice, James Allen; Roberts, Jabus B.; Corcoran, Marjorie D.; Huang, Huey W.The design, construction, and calibration of a 2 MeV proton spin polarimeter are described. This polarimeter monitors the beam at the transfer point between the linear accelerator and the Alternating Gradient Synchrotron at Brookhaven National Laboratory. The polarimeter determines the beam polarization to an accuracy of 1% in less than ten minutes real time, for the anticipated beam current and pulse repetition rate of the polarized beam, with a carbon filament target that intercepts 1% of the beam particles. Scattered beam particles are collected at 12 and 16 degrees to determine left-right and up-down asymmetries and detect beam angle deviations.Item A phenomenological study of proton-proton elastic shattering near 700 MeV(1982) Turpin, Stephen E.; Duck, Ian M.; Roberts, Jabus B.; Miettinen, Hannu E.Proton-proton elastic scattering experiments are now of sufficient number and quality below 8 MeV to tightly constrain almost all isovector phase shifts which are significantly sensitive to elastic scattering parameters. A study of the sensitivity of various experimental observables to small changes in the phase parameter indicates which experiments might be most profitable in further constraining the phase shifts. There exists drastic disagreement between the measurements of Aj at 7 MeV in a recent experiment and current phase shift solutions, and since reasonable variations of the phase parameters do not produce significant improvement in the fit, the suspicion of some normalization error in the experiment is raised.Item A precise measurement of the polarization of a 200 GeV muon beam in a polarized deep inelastic scattering experiment at CERN(1997) Eichblatt, Stephen Lynn; Roberts, Jabus B.The Spin Muon Collaboration (SMC) measures the spin dependent structure function $g\sb1$ of the proton and nentron by measuring the scattering asymmetry of polarized 200 GeV muons off polarized protons and deuterons. The structure functions enable tests of theoretical sum rules, and a measurement of the spin contribution of the quarks to the nucleon. The uncertainty of the muon beam polarization was a major source of error in preliminary measurements of proton structure functions. A muon polarimeter measuring the shape of the Michel spectrum of positrons from muon decay was built. In this polarimeter muons enter and are allowed to decay $(\mu\sp+ \to e\sp+\nu\sb{e}\bar\nu\sb{\mu})$ in a 35 meter length. The shape of the momentum spectrum of electrons is sensitive to the muon polarization. The decay positrons are momentum-analyzed and the measured spectrum is fit to the Michel formula to determine the polarization. A data sample with a $\mu\sp-$ beam was used to estimate the effects of background events in the spectrum. Careful analysis of the polarimeter data determined the polarization to within 3%. The muon polarization was found to be stable in time and to vary with muon momentum. This variation will be included in the structure function analysis. A second polarimeter measuring the scattering asymmetry of polarized muons off polarized electrons obtained consistent results. The two independent polarization measurements were combined to give a polarization of $-$0.778 $\pm$ 0.019 at 186.9 GeV. With the improved structure function measurements, the Bjorken sum rule was tested and confirmed. Assuming that the gluons are unpolarized, the contribution of the quarks to the nucleon spin was estimated to be 20%, and the strange quark sea negatively polarized.Item Calibration of a leadglass lead-scintillator photon detector at Fermilab experiment E-704 (Lead-scintillator)(1988) Nguyen, Chau T.; Roberts, Jabus B.We calibrated a leadglass Pb-scintillator photon detector with a positron beam of 30 GeV. The detector consisted of a segmented leadglass counter in front and a Pb-scintillator sandwich counter in the back. The response of the sandwich counter exhibited an exponential dependence on the position of the incident particle. The calibration constants of the leadglass segments were obtained by an iterative method. The results of our analysis showed an energy resolution of $\sigma ({\rm E})\over {\rm E}$ = 24%/$\surd$E. A monitoring system using LED and $\sp{241}$Am sources regularly checked the stability of all modules. A typical photomultiplier's gain factor deviated no more than 6% from the mean value at any time during a period of three months.Item Construction of a new detector, and calibration strategies, for start timing in the STAR experiment at RHIC(2007) Zhou, Jianhang; Roberts, Jabus B.The Time of Flight (TOF) system of the Solenoidal Tracker at RHIC (STAR) at the Relativistic Heavy Ion Collider (RHIC) consists of two different subsystems: the start detector and the stop detector. Described in this thesis is the design, construc tion, and operation of a new start detector for STAR. This new start detector, called the Upgraded Pseudo Vertex Position Detector (upVPD) provides many improvements to the old start detector, called the Pseudo Vertex Position Detector (pVPD). The upVPD is expected to have better efficiency per event and better start timing and primary vertex location resolution compared to the pVPD, which will improve the performance of the STAR TOF and STAR Trigger systems. Timing offsets and the slewing effect smear the raw data read-out by the detectors and require offline calibration. The general approach and a few possible algorithms for such calibrations are also described. The analysis results from both the pVPD and the upVPD detectors are presented. Additional cosmic ray tests of the upVPD detectors were also performed, and the calibration results from these data are also discussed.Item Design and construction of a large area multi-wire proportional chamber(1992) Eichblatt, Stephen L.; Roberts, Jabus B.The concepts involved in the design and operation of a multi-wire proportional chamber are reviewed. The design and construction of two chambers for the SMC (Spin Muon Collaboration) muon polarimeter are described in some detail so that one can use this thesis as an aid in the construction of a similar detector.Item Light (anti-)nuclei production in the STAR experiment at RHIC(2009) Zhou, Jianhang; Roberts, Jabus B.Presented in this thesis is the study of light (anti-)nuclei production in ultra-relativistic heavy ion collisions. In these collisions hot dense matter is created, in which the quarks and gluons are deconfined. As this hot dense matter expands and cools down, quarks recombine together to form new hadrons. At the final stage called thermal freeze-out, nucleons can combine into light nuclei. Therefore the study of light nuclei production provides a probe for understanding the physical properties of the expanding system at the thermal freeze-out, such as the temperature and the eccentricity. In this thesis, the transverse momentum ( p T ) spectra, and the elliptic flow ( v 2 ) of the anti-deuteron, and the coalescence parameters B 2 for d, d and B 3 for 3 He, from STAR Run-V Cu+Cu 200 GeV collisions are studied and compared with STAR Run-VI Au+Au 200 GeV results. Based on the Au+Au collision results, a blast-wave (BW) model is used to fit the transverse momentum spectra and elliptic flow of hadrons. These fit parameters are used in the BW model to predict the deuteron and helium production. The comparison between the BW predicted and the experimentally measured results leads to a consistent understanding of the freeze-out features. Also presented in the thesis is the search for the anti-alpha particle ( 4 He), which has never been discovered before. The search for heavier anti-nuclei is interesting as they are predicted by the theory but hard to find in real world. The anti-deuteron was discovered many years ago and 3 He was found recently. The anti-alpha particles, if confirmed, will be the heaviest anti particles ever found. In this thesis two anti-alpha candidates are shown. Both are found in STAR Run-VII Au+Au collisions. With the accumulated events and the new particle identification method in the future runs, there is hope to find and confirm more candidates.Item Measurement of spin parameters A and Ann in np and pp elastic scattering at 6 G3V/c(1981) Calkin, Mark M.; Mietinen, Hannu E.; Duck, Ian M.; Roberts, Jabus B.The spin parameters A and Ann have been measured for np and pp elastic scattering at 6 GeV/c using a 12 GeV/c polarized deuteron beam and a polarized proton target at the Argonne ZGS. The recoil proton was measured by a conventional magnetic spectrometer, while the scattered neiitron/proton was detected in a brass-scintillator neutron converter/detector. Clean elastic signals were seen in both reactions. Our results on pp elastic scattering show that A and Ann are small and positive, in agreement with previous measurements. In np elastic scattering, we find that Ann -1% over the t-range .25<-t<.6 (GeV/c)2.Item Measurement of the analyzing power in inclusive, high-x(F) charged pion production with a 200 GeV/c polarized proton beam(1991) White, Joseph LaSalle; Roberts, Jabus B.The analyzing power, A$\sb{\rm N},$ in inclusive $\pi\sp{+}$ and $\pi{-}$ production by a 200 GeV/c polarized proton beam was found to have a striking $x\sb{F}$ dependence in which the magnitude of A$\sb{\rm N}$ increases from 0 to 0.42 for the $\pi\sp{+}$ data and decreases from 0 to $-0.38$ for the $\pi\sp{-}$ data for increasing $x\sb{F}$ over the kinematic range $0.2 \le x\sb{F} \le 0.9$ and 0.2$GeV/c \le p\sb{T} \le 2.0GeV/c.$ The higher values of $x\sb{F}$ and $p\sb{T}$ in these kinematic ranges insure that the measured particle came from an interaction of the beam and target through a direct channel and that quark scattering through gluon exchange is the dominant interaction. The charged pions were identified and tracked with a large forward multi-particle spectrometer based upon a Helium gas threshold Cherenkov counter. A simple parton recombination model correctly predicts the signs of the spin parameters measured in this experiment. It also correctly predicts the magnitudes of the $\pi\sp{+}$ and $\pi\sp\circ$ analyzing power at high $x\sb{F}$ but the $\pi\sp{-}$ analyzing power is twice the predicted value. The $\pi\sp{+},$ $\pi\sp{-},$ and $\pi\sp\circ$ analyzing powers were also measured with a polarized anti-proton beam. These data and their interpretation with the simple model suggest that the transverse spin of the proton can be correlated with its quarks in certain kinematic regions, however, the details are still not well understood.Item Measurement of the analyzing power in inclusive, high-x(F) neutral pion production at 185 GeV/c(1989) White, Joseph LaSalle; Roberts, Jabus B.The analyzing power, A, in inclusive $\pi\sp0$ production by a polarized proton beam at 185 GeV/c was found to be 0.10 $\pm$ 0.03 for $\langle$x$\sb{\rm F}\rangle$ = 0.52 and $\langle$p$\sb{\rm T}\rangle$ = 0.8 Gev/c. The $\pi\sp0$'s were detected using a combined lead-glass, lead-scintillator photon absorption calorimeter constructed at the Bonner Lab. Using a simple parton recombination model applied to spin parameter measurements, A$\sb{\rm N}$ = 0.19 $\pm$ 0.02 for this reaction. Since the measured A is consistent with this model, it suggests that the leading quark in a high energy scattering reaction retains the transversity of the incident proton. This can be generalized to suggest that a valence quark model can be used to describe the spin of the proton in certain kinematic regions. A polarized antiproton beam was also produced and A was observed to be nonzero but with low statistics due to short running time. These results show that spin effects continue to be present and have importance at the highest measured energies.Item QNS measurement of translational and notational water motion in polynox-water gels and hydrated artemia cysts(1983) Heidorn, Douglas; Rorschach, Harold E.; Hannon, James P.; Roberts, Jabus B.Quasielastic Neutron Scattering is a useful technique for obtaining information about the self-diffusion of water molecules in heterogeneous systems. Quasielastic neutron spectra have been obtained for hydrated brine shrimp (Artemia) cysts (1.2 g water/g solid) and water-polyox (1.67 g/g and 4 g/g) and deuterium-polyox (4 g/g) gels as a function of momentum transfer, Q. A triple axis spectrometer at the Oak Ridge research reactor, HFIR, was used to measure linewidths in the range .33-.1 THz at Q-values ranging from .5 to 1.9 A. A jump-diffusion model was used to describe the translational motion of the water molecules in both the brine shrimp and the polyox systems. The fitting routine employs Marquardt's algorithm which minimizes chi-squared in parameter space and determines parameters such as the Lorentzian linewidth as a function of Q . Results for the brine shrimp indicate that translational as well as rotational motion contributes to the linewidth. The measured linewidth is .329 THz at Q=.5 A, which is about twice the linewidth for pure water at the same O-value. Data for the 2% ployox in DgO mixture shows a large Lorentzian component. The magnitude of this component introduces large errors in the measurement of the motion of the water molecules in the water-polyox gels, due to the subtraction method used to determine the water spectra.Item Spin effects in inclusive Lambda production using 200 GeV polarized protons(1991) Nguyen, Chau; Roberts, Jabus B.We have used the Fermilab Polarized Proton Beam Facility to measure the Analyzing Power and the Depolarization parameters of the inclusive reaction p$\uparrow$ + p $\to$ $\Lambda$ + X. The $\Lambda$ Polarization was also observed as a consistency check against existing data. The kinematic range of the accepted $\Lambda$'s centers at $x\sb{F}$ = 0.5 and $p\sb{t}$ = 0.6 $GeV/c$, with $x\sb{F}$ reaching up to 0.8 and $p\sb{T}$ up to 1.1 $GeV/c$. The Polarization was found to be consistent with previous measurements. The Analyzing Power and Depolarization were found to be near zero at all kinematics bins and in agreement with the only set of existing data which were measured at much lower energies. Beam energy independency was confirmed. The results from our $\Lambda$ data do not contradict predictions made by the Thomas precession model which implies that the proton's spin is carried by the valence quarks.Item Study of high transverse energy processes in 400 GeV proton-nucleus collisions(1989) Marcin, Martin Richard; Roberts, Jabus B.A study has been made of 400 GeV proton-nucleus collisions using a large acceptance calorimeter. The targets used were LH$\sb2$, He, Be, C, Al, Cu, Sn and Pb. A geometrically unbiased trigger efficient at selecting hadronic jet events was utilized. The A-dependence of the production of jet-like events is like that seen in high transverse momentum single- and di-hadron production. The dependence upon A of high E$\sb{\rm T}$ production is found to weaken with increasing planarity and when the observed event p$\sb{\rm T}$ balance improves. The flow of energy in the events is found to have a number of features in common with soft high-energy proton-nucleus collisions.Item The calibration, response, and energy resolution of a segmented, sampling hadron calorimeter between 10 and 130 GEV/C(1983) Johns, Kenneth Arthur; Roberts, Jabus B.; Miettinen, Hannu E.; Jeys, Thomas H.A large acceptance sampling calorimeter with wavelength shifter readout for studying high p^ hadronic interactions has been assembled at Fermilab. The calorimeter consists of a 132 segment tower structure of S-8.5 radiation lengths of lead followed by 6-8 absorption lengths of iron. A procedure to balance the responses of all 528 calorimeter modules using muons steered by a computer controlled rotating dipole is described. Results on the resolution, linearity, and uniformity of the calorimeter obtained with electrons and hadrons in the momentum range 1-13 GeV/c are presented. For iron sampling thicknesses of 1.3cm, 1.9cm, and 2.8cm the hadron energy resolution is found to be .76, .82, .91/E respectively, while the electron energy resolution obtained is .27, .35, and .37/E.Item The lambda trigger for the E704 Forward Spectrometer(1991) Cranshaw, Jack Mark; Roberts, Jabus B.The E704 Forward Spectrometer was designed to detect the inclusive production of hyperons ($\Lambda\sp0, \Sigma\sp0$) by a 200 GeV/c polarized proton beam incident upon an unpolarized liquid hydrogen target. This measurement used a four level trigger to detect lambdas, both from direct production and from $\Sigma\sp0$ decay. This trigger used four hodoscopes and two levels of programmable logic. The correlations fed into the programmable logic (Memory Lookup Units and Programmable Logic Units) were calculated using a GEANT3 Monte Carlo program. The trigger was tested and then used during the 1990/91 fixed-target run at Fermilab. It was gradually refined during the run. We were eventually able to see lambdas, but the reconstruction rate was low due to tracking limitations, chamber inefficiencies, background processes, etc.Item The SMC muon-electron elastic scattering polarimeter(1995) Cranshaw, Jack Mark; Roberts, Jabus B.The Spin Muon Collaboration was formed to measure the spin dependent structure function $g\sb1$ of both the proton and the neutron. This was done by scattering polarized muons off of polarized protons or deuterons. The results provided a test of three sum rules: the Ellis-Jaffe sum rule for the proton, the Ellis-Jaffe sum rule for the neutron, and the Bjorken sum rule. Two polarimeters were used to measure the beam polarization. The polarimeter discussed in this thesis used elastic scattering from polarized electrons to measure the muon beam polarization. It gave a result in agreement with both the previous measurement using muon decay and a simulation of the beamline. These measurements helped reduce the systematic error on the measurement and improve the measurements of the sum rules. The results from the experiment showed that both Ellis-Jaffe sum rules were violated while the Bjorken sum rule was confirmed.