54036066
Attainment of a High-Quality Electron Beam for Fermilab's 4.3 MeV Cooler
The recent demonstration of electron cooling of antiprotons in the Recycler ring required a stable 4.3 MeV electron beam with a DC current of hundreds of mA and an angular spread in the cooling section of a fraction of a mrad. This paper describes the achieved parameters of the Fermilab cooler’s electron beam and details of operation.
123613871
Observations of the transverse and longitudinal nature of the Fermilab linac beam
The installation of nonintercepting beam position monitors (BPMs) in the 200 MeV linac at Fermilab has facilitated several new observations on the character of the linac beam. In particular, two interesting phenomena have been discovered: a high-frequency change in the beam position and a slow variation in the phase-lock loops during a 30 mu s beam pulse. Progress in initiating the Delta -t measurement is being made. The Delta -t procedure adjusts the RF phase and amplitude in each of the accelerating modules of a linac. The procedure uses beam-induced signals from linac BPMs to determine changes in the times of flight of beam bunches when the tuned module is turned off and when it is turned on.<<ETX>>
723137
Status of the Fermilab electron cooling project
The first stage of the Fermilab Electron Cooling R&D program is now complete: technology necessary to generate hundreds of milliamps of electron beam current at MeV energies has been demonstrated. Conceptual design studies show that with an electron beam current of 200 mA and with a cooling section of 20 m electron cooling in the Fermilab Recycler ring can provide antiproton stacking rates suitable for the Tevatron upgrades beyond Run II luminosity goals. A prototype of such an electron cooling system is now being built at Fermilab as part of the continuing R&D program. This paper describes the electron cooling system design as well as the status of the Fermilab electron cooling R&D program.
121242219
Attainment of an MeV-range, DC electron beam for the Fermilab cooler
To prepare a beam generation device for Fermilab's future Recycler Electron Cooling system, an experimental set-up with a simplified beam line has been commissioned at Fermilab. Stable operation was achieved at an electron energy of 3.5 MeV and a DC beam current of up to 0.5 A. The main reason for interruptions of the operation was found to be microsecond long bursts of the cathode current. While the frequency of the interruptions is determined primarily by a flow of secondary ions, the resulting reduction in the duty factor depends on the beam optics, the protection systems, and the tube electric field strength.
118674965
Operation and improvements of the Fermilab 400 MeV Linac
The 400 MeV Fermilab Linac Upgrade commissioning began August 28, 1993. High energy physics collider operation (run 1b) began in November 1993 and ended March 1, 1996. The Linac, operating at 98% reliability, provided 400 MeV H{sup -} beam to the Booster and 66 MeV H{sup -} beam to the Neutron Therapy Facility. During this time, the beam intensity, which initially was administratively set to 35 MA, rose to a peak of 50 mA while losses decreased significantly. This paper discusses the Linac operation and reliability since the Upgrade.
113925183
Factors Affecting H- Beam Performance in the Fermilab Linac
5495552
The infrared behavior of one-loop gluon amplitudes at next-to-next-to-leading order
For the case of n-jet production at next-to-next-to-leading order in the QCD coupling, in the infrared divergent corners of phase space where particles are collinear or soft, one must evaluate (n + 1)-parton final-state one-loop amplitudes through O(ǫ2), where ǫ is the dimensional regularization parameter. For the case of gluons, we present to all orders in ǫ the required universal functions which describe the behavior of one-loop amplitudes in the soft and collinear regions of phase space. An explicit example is discussed for three-parton production in multi-Regge kinematics that has applications to the next-to-leading logarithmic corrections to the BFKL equation. ∗On leave of absence from I.N.F.N., Sezione di Torino, Italy. The quest to obtain ever increasing precision in perturbative QCD requires calculations to higher orders in the QCD coupling, αs. Over the years, significant effort has been expended on computing the next-to-leading order (NLO) contributions to multi-jet rates within perturbative QCD. An important next step in the endeavor to obtain higher precision would be the computation of next-to-next-to-leading-order (NNLO) contributions to multi-jet rates. As an example, although the NLO contributions to ee → 3 jets have been computed for some time now [1, 2], the NNLO contributions have yet to be obtained. A calculation of these NNLO contributions would be needed to further reduce the theoretical uncertainty in the determination of αs from event shape variables [3]. Considerable effort has also been expended in the computation of leading and next-to-leading logarithmic contributions to the BFKL equations for parton evolution at small x [4, 5]. These two problems are, of course, connected since the logarithms that are resummed in the BFKL equations also appear at fixed orders of perturbation theory. Indeed, the one-loop Lipatov vertex may be extracted [6, 7] from one-loop five-gluon helicity amplitudes [8]. In order to compute a cross section at NNLO, three series of amplitudes are required in the squared matrix elements: a) tree-level, one-loop, and two-loop amplitudes for the production of n particles; b) tree-level and one-loop amplitudes for the production of n + 1 particles; c) tree-level amplitudes for the production of n + 2 particles. For the case of NNLO ee → 3 jets the five-parton final-state tree [9] amplitudes, as well as four-parton final-state one-loop amplitudes exist in both helicity [10] and squared matrixelement forms [11], but as we discuss below, in order to be used in NNLO computations additional terms enter because of infrared issues. For the required two-loop three-parton final-state amplitudes no computations exist, as yet. Indeed, no two-loop amplitude computations exist for cases containing more than a single kinematic variable, except in the special cases of maximal supersymmetry [12]. Besides these amplitudes it is also important to have a detailed understanding of the infrared singularities that arise from virtual loops and from unresolved real emission when the momenta of particles become either soft or collinear. (For hadronic initial states infrared divergences are also associated with initial-state parton distribution functions.) These infrared divergences show themselves as poles in the dimensional regularization parameter ǫ = (4 − D)/2. By the Kinoshita-Lee-Nauenberg theorem [13] the infrared singularities must cancel for sufficiently inclusive physical quantities. However, it is only when the various contributions are combined that the infrared singularities cancel. At NLO the structure of the infrared singularities has been extensively studied. The singularities occur in a universal way, i.e. independent of the particular particle production amplitude considered. Accordingly, soft singularities have been accounted for by universal soft functions [14, 15], and collinear singularities by universal splitting functions [16]. A detailed discussion of the infrared singularities at NLO for ee → jets may be found, for example, in ref. [17].
118429632
Higgs Boson Cross Section from CTEQ-TEA Global Analysis
We study the uncertainties of the Higgs boson production cross section through the gluon fusion subprocess at the LHC (with $\sqrt s=7, 8$ and $14$ TeV) arising from the uncertainties of the parton distribution functions (PDFs) and of the value of the strong coupling constant $\alpha_s(M_Z)$. These uncertainties are computed by two complementary approaches, based on the Hessian and the Lagrange Multiplier methods within the CTEQ-TEA global analysis framework. We find that their predictions for the Higgs boson cross section are in good agreement. Furthermore, the result of the Lagrange Multiplier method supports the prescriptions we have previously provided for using the Hessian method to calculate the combined PDF and $\alpha_s$ uncertainties, and to estimate the uncertainties at the $68\%$ confidence level by scaling them from the $90\%$ confidence level.
17264957
An Effective Higgsless Theory: Satisfying Electroweak Constraints and a Heavy Top Quark
The main challenge faced by Higgsless models of electroweak symmetry breaking is to reconcile the experimental constraints imposed by the precision electroweak data and the top quark phenomenology with the unitarity constraints imposed by longitudinal gauge boson scattering amplitudes. In this paper we expand on previous work, giving details of how delocalized fermions can be used to adjust the S parameter to zero, while keeping the T and U parameters naturally suppressed. We also show that it is possible to obtain the top quark mass, without affecting the delay of unitarity violation of the W{sup +}W{sup -}{yields}W{sup +}W{sup -} scattering amplitude, by separating the mass scales of the fermion sector (1/R{sub f}) from that of the gauge sector (1/R{sub g}). The fermion sector scale 1/R{sub f} is only weakly constrained by unitarity of the tt{yields}W{sup +}W{sup -} scattering amplitude; thus the ratio R{sub g}/R{sub f} can be quite large, and the top mass can be achieved easily. Anomalous right-handed couplings involving the third generation quarks also avoid constraints from experimental data if 1/R{sub f} is sufficiently large.
118327970
Universal O(N) scaling and the chiral critical line in (2+1)-flavor QCD with small chemical potentials
We show that for small values of the chemical potential the curvature of the phase transition line can be deduced from an analysis of scaling properties of the chiral condensate and its susceptibilities. We make use of a recent analysis of the magnetic equation of state in (2+1)-flavor QCD where a connection between the QCD parameters and the universal scaling fields could be established. The remaining dependence of the reduced temperature on the chemical potential can be fixed by an analysis of a mixed susceptibility, obtained from a derivative with respect to quark mass and chemical potential. We extract this dependence which describes the curvature of the phase transition line, at two values of the cut-off, $aT=1/4$ and $1/8$. We find that cut-off effects are small for the curvature parameter and determine the transition line in the chiral limit to leading order in the light quark chemical potential. We obtain $T_c(\mu_B)/T_c(0) = 1 - 0.00656(66) (\mu_B/T)^2 +{\cal O}(\mu_B^4)$.
118579706
The strange degrees of freedom in QCD at high temperature
We discuss recent results on fluctuations of conserved charges, and their approach to the hadron resonance gas at temperatures below the chiral crossover (Tc) as well as to a gas of free quarks at very high temperatures. We will focus on the strange degrees of freedom and verify that they are consistent with those of an uncorrelated gas of hadrons for temperatures of T . 160 MeV and that they can be described by a quasi particle model at best for T & 2Tc. To extract this information we use all cumulants of net baryon number and net strangeness fluctuations and their correlations up to the fourth order. In particular we propose observables that serve as indicator for the validity of the hadronic degrees of freedom and show that the partial pressures from different strangeness sectors agree separately with HRG model predicions.