182123800
Characteristics of Transversal Coherent Beam Instability on the Plateau of 386-Oe Magnetic Field at the SERPUKHOV Accelerator. (Talk, in Russian)
110736460
UPGRADING LONGITUDINAL BEAM BEHAVIOR IN IHEP BOOSTER
Operation of 1.5 GeV fast-cycling Booster proton synchrotron of IHEP has been long hampered by unwanted oscillations in bunch length. To identify the reason of such beam behavior, a dedicated beam-dynamics research program has been initiated. The scope of this activity has covered a variety of the might-be mechanisms behind — coherent instabilities, malfunction of voltage amplitude feedbacks, quality of the voltage program, etc. Ultimately, phase loop encircling the VCO has been upgraded, which resulted in a noticeably suppressed scale of both, dipole and quadrupole oscillations of beam. BEAM OBSERVATIONS Coherent oscillations in bunch length were incidentally observed during routine operation of the machine. These were monitored as a distortion of bunch shape prior to beam transfer. The process was accompanied by an occurrence of asymmetry in longitudinal density distribution. This picture had a rather uncertain cycle-to-cycle recurrence. Each time, the beam conduct was subject to improving noticeably with finer tuning the initial value of radio-frequency in the Booster. Still, a mismatch with phase-plane trajectories of the accepting ring, U70, persisted. It hampered subsequent accumulation and acceleration of a high intensity beam in U70. To this end, a dedicated R&D program was launched to study beam longitudinal oscillations through the entire cycle and elaborate technical cures against oscillations in bunch length, specifically.
122053065
Coasting Beam in HERA-p Ring
This document is a report on stud ies of production/tr ansport mechanisms resulting in and of cures against a coasting beam halo observed at the HERA proton ring of DESY. Noises in the 208 MHz RF system, drift beyond RF buckets due to energy loss through synchrotron radiation of the highenergy protons and effect of adding the 52 MHz RF voltage are claimed to account for the diverse observations over the halation effect available by now. The work was performed under Attachment #63 to the Agreement between DESY (Hamburg, Germany) and IHEP (Protvino, Russia), re: Coasting Beam in HERA-p Ring, June 2000.
126362745
A CAVITY FOR THE SECOND HARMONIC OF ACCELERATING-FIELD FREQUENCY IN THE IHEP SYNCHROTRON
109125768
A feedback circuit for the stochastic extraction of protons from the U-70 synchrotron: Development and beam tests
Results of research efforts in 2005 that were directed toward developing a system for stochastic (noise) slow extraction of the beam from the U-70 proton synchrotron of the Institute for High Energy Physics are presented. The goal of the study was to develop a full-function prototype of the stochastic slow extraction system and test it on the beam. This prototype, designed for trial operation during machine runs, is capable of producing lengthy flat-topped smooth spills and suppressing their ripple. Approaches to design of the feedback loop that affects the waiting beam stack (which is neither a linear nor time-invariant system) are discussed. A circuit model of the beam being extracted is proposed and analyzed. A dedicated electronic system for beam experiments is described. Results of the beam tests during the U-70 machine run of 2005, which confirm the serviceability of the noise extraction system prototype, are presented.
59025092
Decreasing transient beam loading in RF cavities of U-70 accelerator
The U-70 RF system was worked out to operate with the injector-linac at 100 MeV energy. A wide RF range was (2.6-6.1) MHz. For the U-70 injector Booster the wide RF range decreased and now it is (5.5-6.1) MHz. This fact and simplest method of changing the parameters in RF ferrite dominated cavities allow one to increase of the equivalent value of the cavity capacitance for the main frequency by about a factor of 2.7 and increase of the value of the cavity gap capacitance by about a factor of 5. The experimental investigation of the U-70 RF cavities due to the injection of bunches from the Booster into the U-70 orbit, near transition and on main flat-top is presented.
1934772
The CKM phase in heterotic orbifold models
Abstract We consider properties of the CKM phase in the heterotic orbifold models. We find that at the renormalizable level the CKM phase vanishes identically for the prime orbifolds, whereas it can be nonzero for some nonprime orbifolds. In particular, we study in detail the Z 6 -I orbifold which allows for a nontrivial CKM phase and analyze the modular properties of the corresponding Jarlskog invariant. The CKM phase is shown to vanish if the moduli fields are stabilized at Im T i =±1/2.
121021896
A Finite-Size Magnetic Monopole in Double-Potential Formalism
Using the double-potential formalism developed by Zwanziger, it is possible to construct nonsingular four-potentials corresponding to a given distribution of magnetic charge without violating the Bianchi identity. In this letter, we study a ball-like monopole with uniform distribution of magnetic charge. The corresponding four-potentials are found explicitly. We also construct the angular momentum operator of an electron in the field of such a monopole, which can be used to investigate the problem of electron-monopole scattering and to rectify Kazama–Yang–Goldhaber singularity.
14860374
SUSY phenomenology of KKLT flux compactifications
We study SUSY phenomenology of the KKLT (Kachru-Kallosh-Linde-Trivedi) scenario of string theory compactifications with fluxes. This setup leads to a specific pattern of soft masses and distinct phenomenological properties. In particular, it avoids the cosmological gravitino/moduli problems. Remarkably, the model allows for the correct abundance of SUSY dark matter consistently with all experimental constraints including the bound on the Higgs mass, b-->s gamma, etc. This occurs for both small and large tan beta, and requires the SUSY spectrum above 1 TeV.
16019794
A Stringy Solution to the FCNC Problem
The solution to the supersymmetric FCNC problem may not have a simple field theory interpretation. Here I advocate a possibility based on string selection rules. The requirement of non--trivial Yukawa structures restricts the form of the soft terms such that the FCNC problem often does not arise.
120557446
EDM constraints in SUSY models
We systematically analyze neutron, electron, and mercury EDM constraints in SUSY models. We nd that the addition of the mercury constraint practically rules out the EDM cancellation scenario and largely disfavors the decoupling scenario. On the other hand, models with approximate CP symmetry or o diagonal CP violation remain attractive. One of the most important tests of CP-violation comes from the measurements of the electric dipole moments (EDMs). Non-observation of the EDMs imposes severe constraints on models for physics beyond the Standard Model. The most stringent of these come from continued e orts to measure the EDMs of the neutron, electron, and mercury atom [1] dn < 6:3 10 26 e cm (90%CL); de < 4:3 10 27 e cm ; dHg < 2:1 10 28 e cm : (1) In particular, these constraints are a diÆcult hurdle for supersymmetric theories if they are to allow suÆcient baryogenesis. Indeed it is remarkable that the SM contribution to the EDM of the neutron is of order 10 30 e cm, whereas the \generic" supersymmetric value is 10 e cm. There are several proposals to reconcile the EDM constraints and supersymmetry. The EDM bounds may imply that the supersymmetric CP-phases are small [2] or the sfermions of the rst two generations are heavy [3]. Alternatively, they may imply that CP violation has a avor-o -diagonal character [4]. It has also been realized that in certain regions of the parameter space the constraints on the CP-phases are not severe due to the EDM cancellations (see Refs. in [5]). We examine in detail these four scenarios (for details see Refs.[5] and [6]). We impose the electron, neutron, and mercury EDM constraints simultaneously and study the viability of each mechanism to suppress the EDMs. For completeness, we analyze both the chiral and the parton quark neutron models. Neither of these models is suÆciently reliable by itself, however a combined analysis allows us to draw general conclusions. In addition, we have included the (usually neglected) Barr-Zee type contributions to the EDMs and the gluino-bottom-sbottom contribution to the Weinberg operator. The main new point of our analysis is the addition of the mercury EDM constraint. It has been realized that the mercury EDM is mostly sensitive to the quark chromomagnetic dipole moments and that the constraint dHg < 2:1 10 28 e cm can be translated into [7] jdd d C u 0:012d C s j=gs < 7 10 cm ; (2) where gs is the SU(3)c coupling constant and d C i are de ned in the standard way. This constraint will be crucial in our analysis. Let us now summarize the results of our numerical studies: (1). Small CP phases. This scenario implies that the supersymmetric CP phases are small: A 10 2 10 1 ; 10 3 10 2 ; gaug: 10 2 ; (3) where all the phases are taken at the GUT scale. This possibility can be motivated by approximate CP symmetry. This implies that the CKM phase is also small and the CP asymmetries in B decays are negligible. This is currently disfavored by experiment, however no conclusive statement can be made at this stage. If the experiments reveal that CP is substantially violated, it will be diÆcult to justify why the SUSY phases are small. (2). Heavy sfermions. This possibility is based on the decoupling property of SUSY contributions. We however nd that in order to suppress all the EDMs suÆciently, the sfermions must be very heavy: (m0)decoupl: ' 10 TeV (4) for = A = =2 and Mi(GUT) = 200 GeV. This creates a serious ne-tuning problem. Since 1=2m2Z = (m 2 H1 m2H2 tan 2 )=(tan 1) , a 1 % change inm2scalar would induce roughly a 5000 % change in m2Z . Since one of the primary motivations of supersymmetry is to solve the hierarchy problem, a reintroduction of such an extreme ne-tuning would be very unappealing. (3). EDM cancellations. In certain regions of the parameter space, cancellations among di erent contributions to the EDMs are possible. Such cancellations are accidental in the sense that they are not due to a symmetry and no model has been constructed that predicts such cancellations. Furthemore, the addition of the mercury constraint practically rules out large CP phases in the cancellation scenario. This is illustrated in Figs. 1 and 2 for the mSUGRA and D-brane model . We see that the cancellations allow only for 10 2 in the mSUGRA. The phase of the A-terms is not restricted, but the magnitude is ( 1=5 1=10 m0); as a result, the phase of the corresponding mass insertion is small since tan jAj and e ectively we are back to small phases. In the D-brane models the situation is even more transparent: clearly all the CP-phases must be small. The D-brane model of Ref.[8] is theoretically awed [6], however the same conclusion holds for more realistic D-brane models. One may argue that the EDMs of a neutron and mercury involve hadronic uncertainties and no conclusion can be drawn concerning the viability of the cancellations. However, we have performed a detailed comparative study of the neutron EDM using the chiral and the parton models, and found no signi cant di erence in the allowed regions of the CP{phases. The mercury EDM is certainly not free of uncertainties, however the main uncertainty lies in the overall normalization which does not a ect the cancellation bands. One may object that Eq.2 is not exact and there is a contribution of the electromagnetic operator which comes with a small coeÆcient. However, the quark CEDMs provide the dominant contribution to the mercury EDM in almost the entire parameter space. The electromagnetic contribution is non-negligible in small regions of the parameter space and thus cannot change the picture qualitatively. (3). O -diagonal CP violation. This possibility is quite attractive since it can be based on symmetry [4]. In addition, we have a good example of avor o -diagonal CP violation: the EDMs in the Standard Model are small because the CKM phase has a avor o -diagonal character (apart from the strong CP problem). A horizontal (or left-right) symmetry may require hermitian Yukawa and A-matrices, and avor-blind quantities ( ;Mi) to be real. This results in suppressed EDMs. The supersymmetry breaking dynamics in this case are CP-conserving which often happens in heterotic string models as a result of the e ective potential minimization. Flavor o -diagonal CP violation is also phenomenologically attractive since it allows for signi cant SUSY e ects in K and B physics [4].