15685598
The Question of {CP} Noninvariance - as Seen Through the Eyes of Neutral Beauty
We present a detailed review of the expected phenomenology of CP violation in neutral B l&D] meson decays. When stating predictions as obtained from the standard model, we emphasize the basic concepts involved and give general expressions; the numbers that we quote are meant to illustrate the method and provide guidelines, not to be precise predictions. PROLOGUE Among the many statements that can and have been made on CP violation, three stand out since they are unassailable without being trivial: A breakdown of CP invariance has been directly observed in nature, namely in KL decays. CP violation, despite its shy appearance on the stage of physics, represents a truly fundamental phenomenon-as it has been duly recognized from the 9E beginning. We cannot claim to have developed a real understanding of this phenomenon. This -in view of the first two points-is highly unsatisfactory, if-not outright embarrassing; it actually refers to two different levels: *Work supported by the Department of Energy, contract DEAC03-76SF00515. SHeisenberg fellow. To be published in the Review Book of CP Violation C. Jarlskog, Editor, World Scientific, Singapore (a) Considerable progress has been made in ‘Theoretical Engineering;” we have developed a rather clear picture on the various generic ways of ‘. . imbedding CP violation into a given t+eory.‘l But we have been unable to decide which of these mechanisms is the source, or even the dominant source, of the observed CP violation. (b) Considering the fundamental importance of CP violation one yearns for a deeper understanding that goes beyond the question of which mechanism describes the data properly. We do not -have anything specific to say concerning point (b); however, we believe that it can hardly find a satisfactory answer if point (a) remains unanswered. Furthermore, we feel strongly that CP violation has to be found outside the decays of neutral kaons before light can be shed on the underlying source. Beauty hadrons carry excellent promise to exhibit large observable CP asymmetries in their decays. This holds, in particular, in the KobayashiMaskawa (KM) ansatz2] where it is the interplay of three quark families that makes the phases of the weak couplings and thus CP violation observable. Beauty decays are then the process of choice: b quarks belong to the third family, yet have to decay into members of the lower families; even the top quarks are drawn 1. into this affair via B”-r mixing. This argument can of course be made in a more precise way: the unitarity of the KM matrix V yields, among others, the following three relations which are evidently invariant under changes in the phase convention adopted for the quark fields V(ud)V*(td) + V(us)V*(ts) + V(ub)V*(tb) = 0 , (1) V(ub)V*(ud) + V(cb)V*(cd) + V(tb)V*(td) = 0 , (2) 2 V(cd)V*(td) + V(cs)V*(ts) + V(cb)V*(tb) = 0 . (3) -Up to small corrections of order sin2 8,, these equations can be rewritten in a simplified fashion: 2 V*(td) + XV*(ts) + V(ub) N 0 , V(ub) XV(cb) + V*(td) H 0 , -AV*(td) + V*(ts) + V(cb) N 0 , (4) (5) (6) where X-sin@, . These equations represent triangle relations in the complex plane and-as first pointed out by Bjorken, L.-L. Chau and Jarlskog25]-are quite accessible to geometric intuition: (i) Different parametrizations of the KM matrix correspond just to different rotations of these triangles. (ii) The two triangles defined by Eqs. (4) and (5) actually agree to this order in X since obviously V* (ts) N -V(cb). This triangle is shown in Fig. 1 with a shape that is “typical” as explained later. (iii) The triangle defined by Eq. (6) is quite a squashed one since IV(ts)I N IV(cb)l > XIV(td)l. 5928Al hV(cb) Fig. 1. Triangle depicting dominant relative phases in KM ansatz with three families. 3 Figure 1 contains the main observation: there are sizeable relative phases between V(ub), V(cb) and V(td). They can all be probed with high sensitivity in beauty decays (where V (td) drives Bd zd mixing). . In K and D decays, on the other hand, the situation is much less favorable: V (cs) contains a CP violating phase, but only at order X4; V(td) is quite crucial for EK and c’, yet its numerical impact is greatly reduced by the smallness of V(td)V* (ts); furthermore, the dynamical “accident” (as far as CP violation is concerned) of the AI = l/2 rule reduces CP asymmetries like c’ by an additional order of magnitude. For more detailed considerations it is still useful to employ an explicit form of the KM matrix d S b lix2 x AX3 (p irj (1 :A”}) : VKM = -A 1 ‘x2 2 irjA2X4 AX2(1 + +X2) AX3(1 p iv) -AX2 I t ’ 1 (7) where we have used the Wolfenstein expansion up to order X4(X6) for the real (imaginary) parts of the charged current couplings. 1. Meaningful bounds now exist on all these parameters; one typically finds A = 1.1 f0.2 from 78 , (8) 0.08 s p2 +v2 2 1.0 from B -+pFr(r) , Iv noncharm, (9) p < 0 from Bd Bd mixing . (10) To derive more specific numbers one has to proceed with considerable care and caution. For at present no precise scheme exists for describing weak decays that has been derived from first principles; instead one is limited to employing various phenomenological prescriptions whose reliability is not well established. Furthermore they introduce systematic correlations among the numerical values for the KM parameters as they are inferred from the data. Accordingly, one has to apply these schemes consistently. c
117871006
Pomeron universality from identical pion correlations at the LHC
Abstract Bose–Einstein correlations of identical pions produced in high-energy pp collisions at the LHC allow a probe of the Pomeron exchange mechanism. The size of the domain which emits the pions depends on the multiplicity of events, but not on the collider energy. This confirms the universal structure of Pomeron exchange. The data at relatively low multiplicities indicate that the size of the source created by one-Pomeron exchange is much less than the size of the proton.
119436494
QCD Interconnection Effects
Heavy objects like the W, Z and t are short-lived compared with typical hadronization times. When pairs of such particles are produced, the subsequent hadronic decay systems may therefore become interconnected. We study such potential effects at Linear Collider energies.
124029542
On the sensitivity of the inclusive distributions in parton jets to the coherence effects in QCD gluon cascades
The KNO multiplicity distributions and properties of two-particle correlations in QCD jets are considered in the framework of the perturbative approach accounting for effects of the coherence in the soft gluon bremsstrahlung.
119379184
Radiative corrections to the hadronic cross-section measurement at DA$\Phi$NE
Abstract. The hadronic invariant mass distribution for the process of electron–positron annihilation into a pair of charged pions accompanied by a photon radiated from the initial state has been studied for the region of DA$\Phi$NE energies. The Born cross–section and the electromagnetic radiative corrections to it are calculated for realistic conditions of the KLOE detector. The dependence on the physical parameters which define the event selection is obtained.
125850380
Multiple Hadron Production in Parton {QCD} Jets
119202861
Emergence of the electroweak scale through the Higgs portal
A bstractHaving discovered a candidate for the final piece of the Standard Model, the Higgs boson, the question remains why its vacuum expectation value and its mass are so much smaller than the Planck scale (or any other high scale of new physics). One elegant solution was provided by Coleman and Weinberg, where all mass scales are generated from dimensionless coupling constants via dimensional transmutation. However, the original Coleman-Weinberg scenario predicts a Higgs mass which is too light; it is parametrically suppressed compared to the mass of the vectors bosons, and hence is much lighter than the observed value. In this paper we argue that a mass scale, generated via the Coleman-Weinberg mechanism in a hidden sector and then transmitted to the Standard Model through a Higgs portal, can naturally explain the smallness of the electroweak scale compared to the UV cutoff scale, and at the same time be consistent with the observed value. We analyse the phenomenology of such a model in the context of present and future colliders and low energy measurements.
119258384
RG invariants, unification and the role of the messenger scale in General Gauge Mediation
In General Gauge Mediation (GGM) all MSSM soft sfermion masses at a high scale Mmess can be parameterised by three a priori independent scales ΛS; 1,2,3(Mmess). (Similarly the gaugino masses are given by ΛG; 1,2,3(Mmess).) For the first two generations this parameterisation in terms of a set of running ΛS; 1,2,3(μ) — conveniently obtained from appropriate RG invariants — continues to hold all the way down to the electroweak scale. This is not the case for the third generation because of the large Yukawa couplings. Together these two observations imply that the messenger scale is an additional parameter of GGM models.In models where all messengers are in complete GUT multiplets (without significant mass splittings), all ΛS,r are equal at Mmess. Starting from the observable mass spectrum at the electroweak scale we present a strategy to determine if this unification occurs and at which scale. This approach uses data accessible at colliders to gain insight into high scale unification physics beyond the unification of gauge couplings.
120263136
Higher twist effects in the Drell‐Yan process
We calculate the angular distribution of the lepton produced in the Drell‐Yan reaction taking into account pion bound state effects. We work in the kinematic region where one of the pion constituents goes far off shell, which allows us to treat the bound state problem pertubatively. We show that the angular distribution is very sensitive to the shape of the pion distribution amplitude. The model we discuss fits the data if we choose a two‐humped pion distribution amplitude suggested by QCD sum rules.
16492553
Magnetic mixing — electric minicharges from magnetic monopoles
Many extensions of the Standard Model require the existence of a ``hidden'' sector. We consider settings where the hidden sector in the infrared contains a U(1) gauge factor with magnetic monopoles, for instance 't Hooft-Polyakov monopoles of an underlying non-abelian gauge group. In the presence of CP violation these monopoles acquire an electric charge in the hidden sector due to the Witten effect. We show that quite generally they also acquire (small) electric charges under the visible electromagnetic gauge group. This is a result of ``magnetic mixing'' which, as we show, often arises as a natural partner of kinetic mixing. Both kinetic and magnetic mixing are naturally induced radiatively even if the low-energy U(1)s arise from a single non-abelian gauge group. We argue that the hidden sector monopoles can be light and their electric minicharges could thus be testable in current and near future low-energy experiments.
119007583
Interplay and Characterization of Dark Matter Searches at Colliders and in Direct Detection Experiments
In this White Paper we present and discuss a concrete proposal for the consistent interpretation of Dark Matter searches at colliders and in direct detection experiments. Based on a specific implementation of simplified models of vector and axial-vector mediator exchanges, this proposal demonstrates how the two search strategies can be compared on an equal footing.