115315717
Analysis of the Feedback-Loop Stability in the RF System of the U-70 Synchrotron
We present a systematic approach for investigating the stability of the accelerating system used in the U-70 proton synchrotron (Institute for High-Energy Physics). This system employs tunable ferrite-loaded cavities and is encircled by six feedback loops (both dedicated and spurious) with a cross-talk through a heavy beam loading, high accelerating rate, and the overlapping of the loop passbands. Ensuring the safety margin against self-excitation of the RF system imposes constraints on the limiting intensity of the beam that is accelerated in the synchrotron
218611448
A STOCHASTIC SLOW EXTRACTION SCHEME FOR U70 SYNCHROTRON
Outcomes of a feasibility study for a low-budget stochastic slow extraction system in the U70 proton synchrotron of IHEP are reported. The existing 200 MHz (spill) RF system is to be employed as a longitudinal kicker. It will be driven by a sum of a non-random RF carrier plus an additive random amplitude-modulated signal — either quadrature or in-phase, or both. A few novel solutions to be implemented in the longitudinal diffusion technique that would force protons into the conventional 3-rd order transverse extraction resonance are foreseen so as to comply with the technical constraints inherent in U70. Getting a-few-seconds-long and high-quality spills is assessed as being viable with the system in question.
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.
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.
53956287
Upgrading the RF Cavity for U-70 Accelerator 0 -
This paper presents the results on the experimental invcstigation of the IJ-70 R.I: cavity with additional short circuit loops in thr RF magnetic field. These loops introduce a negative inductance impedanre into t,hc RF cavit,y circuit, and decreascx the cquivalcnt value of cavity inductance by about a factor of 10. This method allows at a low cost ‘,-fold increase the caparity of the accelerating gap for the 1!-70 cavity operating with the booster injection complex. ‘l’he lechnique of measuring the ferrite-dominated cavity pararncters is described.
182123800
Characteristics of Transversal Coherent Beam Instability on the Plateau of 386-Oe Magnetic Field at the SERPUKHOV Accelerator. (Talk, in Russian)
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].
42733826
Electric dipole moments in the limit of heavy superpartners.
Supersymmetric loop corrections induce potentially large CP-violating couplings of the Higgs bosons to nucleons and electrons that do not vanish in the limit of heavy superpartners. The Higgs-mediated CP-odd four-fermion operators are enhanced by tan((3)beta and induce electric dipole moments of heavy atoms which exceed the current experimental bounds for the electroweak scale Higgs masses and tan(beta greater, similar 10. If only the first two sfermion generations are heavy, the Higgs-mediated contributions typically dominate over the Barr-Zee type two-loop diagrams at tan(beta>30.
118714441
The NMSSM and string theory
Abstract We study the possibility of constructing the NMSSM from the heterotic string. String-derived NMSSMs are much more rare than MSSMs due to the extra requirement that there exist a light singlet which couples to the Higgs pairs. They share the common feature that the singlet self-interactions are typically suppressed, leading to either the “decoupling” or the Peccei–Quinn limit of the NMSSM. In the latter case, the spectrum contains a light pseudoscalar which may be relevant to the MSSM fine-tuning problem. We provide a Z 6 heterotic orbifold example of the NMSSM with approximate Peccei–Quinn symmetry, whose origin lies in the string selection rules combined with our choice of the vacuum configuration.
117878917
Spontaneous CP-Violation in Two Higgs Doublet Supersymmetric Models
Physics (ABSTRACT) An alternative approach to the problem of CP-violation is presented. It is based on the possibility of spontaneous CP-breakdown in models with two Higgs doublets. General features of the phenomenon such as stability of the vacuum and the existence of a light axion are discussed. We investigate the feasibility of spontaneously broken CP in the minimal supersymmetric models-the MSSM and NMSSM. The latter is shown to be experimentally viable. The phenomenological implications of the model such as CP-violating effects in the kaon systems and a nonzero neutron electric dipole moment are studied. Acknowledgements I am deeply indebted to Prof. Lay Nam Chang for sharing his intimate knowledge of physics, his keen insight into fundamental problems and, constant support. I greatly appreciate the help and attention of the Department's secretaries in various matters. I am very grateful to the members of my Ph.D. committee for their supervision and efforts to make this work possible.
14728513
A Note on fine-tuning in mirage mediation
Recent progress in string theory moduli stabilization has motivated a mixed modulus-anomaly mediated supersymmetry breaking scenario, also dubbed `mirage mediation'. This scenario has a number of phenomenologically attractive features, in particular with respect to the cosmological gravitino/moduli problem. In this note, we investigate the issues of fine-tuning associated with obtaining the correct electroweak symmetry breaking scale in the mirage mediation scenario. We find that, due to lighter gluinos, the fine-tuning is smaller than that in other mediation mechanisms.