Project Research and Development Scheme Case for Support for Superb Design Studies

Project Research and Development Scheme Case for Support for SuperB Design Studies

G. Bassi 1,4, G. Beck 2, A. Bevan 2∗, T. Gershon 5, P. F. Harrison 5, A. J. Martin 2, F. Wilson 3, A. Wolski,1,4

1 Cockcroft Institute, Daresbury, Warrington, WA4 4AD 2 Queen Mary, University of London, E1 4NS 3 Rutherford Appleton Laboratory, Chilton, Didcot, Oxon, OX11 0QX 4 University of Liverpool, Liverpool, L69 7ZE 5 University of Warwick, Coventry, CV4 7AL

1 Objectives

This is a proposal for a coherent R&D programme to contribute to the Technical Design Reports (TDR) for the SuperB experiment. The main physics goals of SuperB are to search for evidence of new physics through the study of rare B decays, search for Lepton Flavour Violation in τ lepton decays, precisely measure D0 −D0 mixing, search for CP violation in D meson decay and search for CPT violation in B and D decay. Most of the data recorded at SuperB will be taken at the Υ(4S) resonance, however data will be recorded at other centre-of-mass energies to test lepton universality, search for light dark matter and light neutral Higgs particles in Υ(NS) → `+`−, where N ≤ 3. The physics goals of the SuperB experiment are unique and not achievable in the CERN programme. There will be three TDRs for SuperB one for each of the following areas; Accelerator Design, Detector Design, and Physics Benchmarks. The TDR phase of SuperB will run for a two year period that will coincide with this requested funding: from April 2009 through until March 2011. The objectives of this proposal are such that the UK will take lead roles in vital areas of the design and optimisation of the SuperB programme whilst writing the TDRs. While there is no obligation to contribute beyond the TDR stage, the UK will be in an excellent position to make leading contributions to all areas of construction and physics analysis at SuperB should STFC decide to fund this experiment beyond March 2011. The objectives of this proposal are as follows:

1. Accelerator TDR: To achieve the luminosity goals, SuperB will need to operate in a regime where potentially limiting beam dynamics eﬀects are very much stronger than at any existing accelerator facility. We aim to perform detailed studies of certain key eﬀects, such as the beam-beam interaction and intra-beam scattering; the results of these studies will allow optimisations in the machine design.

∗Corresponding author: [email protected]

1 2. Detector TDR: The SuperB tracking system is vital to the experiment’s new physics search capability. The current proposal is for a Layer 0 of pixels, surrounded by a Silicon Strip Vertex Detector (SSVD) and a Drift Chamber. We aim to design and optimize the SSVD geometry and material composition using physics benchmark channels.

3. Physics TDR: In order to optimise the SSVD design in the context of the whole SuperB detector we will study several benchmark channels central to the new physics search capability of SuperB.

The project objectives and timescale are discussed in more detail in the ’Project Description’ and ’Timescale’ sections below. Sections 4 and 5 describe the physics aims of SuperB and how this ﬁts into STFC’s science programme and section 6 discusses competing experiments. The remaining sections of this proposal discuss the track record of the proposal authors, beneﬁts and knowledge exchange opportunities, training out outreach aspects and costs to STFC and cross-council funding opportunities.

2 Project Description

2.1 Introduction

The current B factories have been far more successful than was originally envisaged. Nevertheless recent developments have led to the possibility of a high luminosity successor to the current B factories that could collect 75 times the existing data over a running period of 5 years. This concept has been studied and documented in the SuperB Conceptual Design Report [1]. This next generation facility will produce more than 1011 B, D and τ mesons while running at the Υ(4S) center of mass energy as well as being able to operate at charm threshold and at other energies. The SuperB experiment is envisaged to operate at a luminosity of 1036 cm−2s−1 and integrate 75ab−1 of data at the Υ(4S) center of mass energy within the first 5 years of data taking. In the scenario that the LHC finds new physics SuperB may be able to probe its flavour structure. However if the LHC does not find evidence for new physics SuperB will be able to constrain non-minimal flavour violation new physics scenarios above an energy scale of 10 TeV. The SuperB accelerator and detector complex will be constructed at the campus of Roma Tor Vergata University which is situated near INFN Frascati in the suburbs of Rome, Italy. The university is currently in communication with INFN and the regional and national government to secure funding for the SuperB project. As part of this process INFN appointed an independent international review panel to assess the viability and physics goals of SuperB. This panel, chaired by Prof. John Dainton, has delivered its first report to INFN [2]. The conclusions of this report begin with:

‘We recommend strongly that work towards the realisation of a SuperB continues.’

The next step toward the realisation of the SuperB experiment requires the preparation of the TDRs which will be ﬁnalized in 2011. The deliverables of this proposal are contributions to the SuperB TDRs. The long term physics goals of SuperB are summarised in the ’Long Term Objectives’ section below.

2 SuperB will provide measurements of unparalleled sensitivity in a number of complementary channels that are sensitive to the effects of new physics. Most of these measurements are unique to SuperB and are not possible at the existing or planned CERN based experiments. There is considerable interest from the international community in SuperB, particularly from Europe and North America. INFN is already funding R&D on SuperB related activities and the rest of the international community is in the process of seeking funding for SuperB R&D. SuperB is scheduled to be discussed at the ECFA and CERN Strategy meetings on the 28th November at CERN. It is expected that steps toward the formation of a SuperB collaboration will occur toward the end of the R&D phase associated with the TDRs. Construction of the experiment is expected to begin once the TDRs have been finalised, and data taking is foreseen for 2015. From the very beginning of BABAR, the UK has played an important role in the detector and all of the main physics discoveries. We believe that now is the appropriate time for STFC to invest in R&D toward realizing the SuperB programme so that the UK will be able to build on its world leading reputation in flavour physics should the UK join the SuperB collaboration.

2.2 Project Description: Accelerator R&D

To achieve the luminosity goals, SuperB will need to operate in a regime where potentially limiting beam dynamics effects are very much stronger than at any existing accelerator facility. As part of this proposal, we aim to perform detailed studies of certain key effects, providing results that will allow optimisations in the machine design. Specifically, we will look at the beam-beam interaction, and intrabeam scattering (IBS). Both of these effects can lead to luminosity loss through increase of the beam emittances, and potentially to increased backgrounds by generation of beam halo. Appropriate parameter choices (for example, in the beam optics in the interaction region) can mitigate the impact of these effects. If found to be severe, then the design can be modified to include additional components (for example, damping wigglers to increase the synchrotron radiation damping rates) either at the outset, or as a potential upgrade. To achieve an appropriate balance of cost against technical risk, careful evaluation must be made to produce reliable results. The complexity of the phenomena underlying both the beam-beam interaction and IBS makes it especially challenging to assess these effects; and for the parameter regime of SuperB in particular, further development of physical models and computational tools will be needed to perform the assessments. High luminosity in a collider is achieved by a combination of high bunch charges, and small beam sizes at the interaction point. The bunch charge and beam size also determine the beam-beam tune shift, which characterises (in a linear approximation) the focusing force from the charge in one bunch on particles in the opposite bunch. Since the charge distribution in a bunch is (approximately) Gaussian, the focusing force is actually highly nonlinear, and depends also on the longitudinal position of a particle within the bunch. The beam-beam tune shift often indicates the severity of the nonlinear effects, but a proper understanding of the impact of the beam-beam interaction requires computationally demanding simulations. Adverse consequences of strong beam- beam effects include beam blow-up, luminosity loss, and generation of beam halo. The difficulties are illustrated by experience at KEKB. The 11 mrad crossing angle for collisions in KEKB was expected to reduce the luminosity; to compensate for the crossing angle, crab cavities were installed in 2007 [3]. Simulation studies indicated substantial improvement in luminosity: up to a factor two improvement in specific luminosity at high current. However, experience to date has been somewhat disappointing. While an improvement in specific luminosity is certainly seen

3 Figure 1: Crab waist collision. Left: with a crossing angle but without a crab waist, the focal plane for each bunch is tilted with respect to the direction of the opposite bunch. Right: using sextupole magnets to introduce a crab waist, the focal plane of each bunch can be brought parallel to the direction of motion of the opposite bunch; this maximises the particle density in the overlap between the bunches, increasing the luminosity.

at low current, at high current, where beam-beam effects play a significant role, the improvement is only marginal, for reasons that are not properly understood [4]. Use of novel schemes to improve luminosity, such as the crab waist [5] (see Figure 1) proposed for SuperB, further complicate the dynamics of the beam-beam interaction, although some schemes may limit the adverse effects. For example, beam blow-up can result from resonances driven by the beam-beam interaction; there is some evidence from simulations [6] that implementation of a crab waist can suppress these resonances. Observations in crab waist tests at DAΦNE [7] are consistent with these predictions; however, there remain significant uncertainties in extrapolating the results to the regime of SuperB. SuperB will need to operate with tune shifts much larger than those achieved in existing particle factories [8, 9]. Since the tune shift depends on the same quantities that determine the luminosity, operation in this novel and challenging regime is an inevitable consequence of the luminosity requirement. It is therefore essential, early in the design process, to characterise the beam- beam effects, and to develop a design that will have the capability to achieve the performance requirements, and the tuning flexibility to deal with imperfections and variations in the operational environment. We will address these issues as part of the studies within this proposal, collaborating with other groups to produce conclusions and design recommendations based on carefully developed and benchmarked simulations. Proper characterisation of the beam-beam effect in the novel parameter regime of SuperB is one of the most important and challenging issues facing the machine design, but a range of other beam dynamics effects also threaten to limit operational performance. For example, intrabeam scattering (IBS) has the potential to cause significant luminosity loss by degrading the beam emittances. IBS is the growth in emittance resulting from small-angle scattering of particles within a single bunch. This effect is normally associated with hadron machines, since the radiation damping in electron storage rings is normally rapid enough to overcome the emittance growth from IBS; however, the novel regime of low emittance and high bunch charge in SuperB leads to IBS growth rates that are comparable to the radiation damping rates, and makes IBS a potential limitation. A range of models, making various approximations, have been developed over the years to predict

4 the impact of IBS in the parameter regime of SuperB [10, 11, 12]. Initial assessments performed for the SuperB CDR [13] indicated that IBS could lead to vertical emittance growth of as much as 50% under some conditions; this would certainly have a significant impact on the luminosity. However, the IBS growth rates depend on a range of parameters and on the precise operational conditions, not all of which can be predicted in advance with any degree of certainty. For example, the vertical emittance growth from IBS depends on the relative contribution of vertical dispersion and betatron coupling to the vertical emittance; this in turn depends on the precise alignment of magnets in the storage rings. To understand properly the likely impact of IBS, a range of operational conditions will need to be considered. Previous studies have focused on luminosity degradation from IBS emittance growth; however, there is a concern that IBS can also generate beam halo, that could lead to increased backgrounds in the detector. Finally, there is the possibility of an interplay between IBS and beam-beam effects, since both effects depend on, and affect, the particle distributions within a bunch. To make an accurate assessment of all these issues will require further development of the physical models and computational tools. The Liverpool Accelerator Group (within the Cockcroft Institute) have the skills and access to facilities for high-performance computational modeling that will be required for understanding beam-beam and intra-beam scattering effects. The Group has led studies of low-emittance tuning for linear collider damping rings, and performed initial assessment of IBS effects for the SuperB CDR. The Group plans to collaborate with INFN-LNF on studies of beam-beam effects. As well as making a critical contribution to the SuperB design, undertaking these studies will support continued leadership of the Group in beam dynamics in ultra-low emittance storage rings for a variety of future applications. The Warwick group will target its effort on physics studies and the machine-detector interface, in order to provide coherence to the project. The project student, supervised by Gershon and Harrison, will work closely with Wolski and Bassi in studying the beam dynamics. This knowledge will then be deployed to develop realistic beam background simulations that will help to optimize the design of the SSVD described below.

2.3 Project Description: Silicon Strip Vertex Detector R&D

The baseline option for the SuperB silicon vertex detector consists of a Layer0 of pixels surrounded by a 5 double-sided layer SSVD. The asymmetric boost of SuperB will be half that of BABAR, so the SuperB vertex detector will have to have a separation power twice that of BABAR’s Silicon Vertex Tracker (SVT) in order to obtain a similar resolution to BABAR. The baseline design for the SSVD is based on the BABAR SVT. We also aim to increase the physical solid angle coverage beyond that achieved by BABAR. There is an ongoing R&D programme in Italy for Layer0 and beam-pipe related issues. This proposal is concerned with R&D required to produce an optimal design for the geometry and the layout of the silicon sensors in the SSVD (Layers 1 through 5). It is envisaged that the on- and oﬀ-hybrid electronics will be developed by another group, and work has already started toward that goal. We will work in cooperation with the groups developing readout of the SuperB silicon detector and Layer0. Figure 2 shows the r, φ view of the baseline option for the SuperB silicon detector. The innermost layer of pixels, Layer 0, is at a radius of 1.5cm and is surrounded by ﬁve layers of double sided silicon sensors with radii between 3 and 14cm. As with the BABAR SVT, the total length of the detector is 58cm, with an active area of 0.96m2. The BABAR SVT is described in more detail in

5 Ref. [14] and is shown in Figure 3.

Figure 2: Schematic of the SuperB silicon detector showing the r, φ view with Layer 0 inside a 5 layer SSVD.

The SSVD silicon sensors will be double sided, with orthogonal strip readout on each side so that one side gives an r, φ measurement and the other side provides z information for a hit. The strips will be read out by analogue ASICs in order to use charge-sharing between adjacent instrumented strips to determine the hit position. Where possible, we intend to retain similarities with the BABAR silicon sensor design as those sensors have performed well. The following is a list of requirements for the SuperB SSVD sensors:

• At most a 10 − 15µm single hit resolution for particles with a trajectory perpendicular to the sensor. There should be no more than a factor of three degradation for particles traversing the sensor with angles of up to 75◦ from normal.

• High single hit eﬃciency (> 95%).

• Single detector strip ineﬃciency less than 1%.

• Use poly-silicon bias resistors as these are radiation hard and can be readily incorporated in the silicon. BABAR used bias resistances of between 4 and 20 MΩ.

• Strips will be connected to the preampliﬁers through a coupling capacitor implanted on the sensors.

• The active region of the sensor should be as close to the edge of the sensor as possible, accounting for the need to have bias resistors and coupling capacitors implanted on the sensor, as well as the need to use a guard ring to gracefully reduce the electric ﬁeld close to the sensor edge.

6 Figure 3: The BABAR SVT showing the support frame and cabling; photo taken during the 2002 summer shutdown.

• The strip readout pitch will be studied in order to obtain the necessary physics performance. In particular it will be necessary to resolve vertices from two B meson decays in an event in order to perform searches for new physics using time-dependent CP asymmetry measurements. The nominal readout pitch in BABAR was between 25 and 50µm (layer dependent).

• Able to withstand a lifetime dose of 10Mrad, equivalent to 1012n/cm2/y for Layer 0. The signal to shot noise ratio at this level is expected to be 200:1 at 0◦ C, and 70:1 at 20◦ C.

• Suﬃcient cooling capacity. Based on the experience with ATLAS we would need to extract 3mW of power per channel (this is similar to the expected power output of electronics for BABAR). This estimate does not include any potential sensor heating, which would have to be studied.

• The hybrid and support material should be minimised while at the same time providing a rigid structure for the sensors.

• Suﬃcient overlap between adjacent sensors should be maintained in order to facilitate local alignment of individual components of the SSVD.

The radiation hardness requirements should be re-evaluated for Layer 1 as a function of φ as the values quoted here are based on the higher expectations for Layer 0. The level of Shot noise is acceptable for room temperature operation of the sensors, however we will need to study the eﬀects of radiation on eﬀective doping (depletion voltage required for sensor operation) and damage to sensor oxide charge and the related inter-strip isolation properties to verify that room temperature operation will be acceptable. All of the sensors will be mounted on a rigid structure that also supports the front end electronics (ASIC and voltage distribution etc.). In addition to bias voltage distribution and signal readout connections, it will be necessary to provide cooling to the hybrid. The material used for the

7 BABAR hybrids was Aluminum-Nitride (AlN) and the support material was a carbon-Kevlar based composite. Mechanical redesign, with the aim of reduced material and better rigidity, is one of the aims of this project and we are requesting mechanical support at RAL to work on this. The SSVD is constrained to surround the material, cooling and cabling infrastructure of Layer 0, and of the beryllium beam pipe. This places the minimum radius of Layer 1 at 3cm. The maximum radius of the outermost layer is 14cm as constrained by the desire to have the SuperB drift chamber and particle identiﬁcation system similar to the existing BABAR ones. A side view of the BABAR SVT is shown in Figure 4 which also shows the outer part of the beam-pipe cooling and dipole magnet structure of the accelerator lattice. The available space for cooling, readout and power-supply utility connection is the gap between the support frame of the SSVD and the beam- pipe/Interaction Point cooling and magnet infrastructure. The optimisation of utility connections will be challenging as Layer0 will require additional cabling not present in BABAR. A potential improvement to the design that would help alleviate this constraint is the use of redundant serial power connections between adjacent hybrids. The feasibility of this option will be studied.

Figure 4: Side view of the BABAR Silicon Vertex Tracker showing the 5 layers of silicon strip detectors showing the channel between the ﬁnal focusing dipole magnets and cooling pipes of the interaction region and the SVT mechanical support structure.

As the SuperB vertex detector will have a Layer0 we need to study the optimal number of layers, and their radii in SSVD. In addition to this, we intend to draw on the experience of LHC and LC detector R&D with regard to choice of support material for the different layers of the vertex detector and with regard to cooling the detector. The silicon wafers used by BABAR were 300µm thick double sided n−type silicon with n and p implants. These were manufactured by Micron in the UK, who at that time had a limited production capacity. Micron were able to produce the BABAR sensors with a 70-80% efficiency, and we don’t foresee any supply problems with respect to obtaining prototypes. There are several potential sensor suppliers so we do not anticipate any production bottlenecks for the potential SSVD production and assembly phase in the future. It is now possible to manufacture thinner wafers with suitable efficiency, so we intend to study the effect of wafer thickness between 200 and 300µm as well as strip pitch on the detector’s tracking performance. We assume that it is possible to use n−type silicon substrates for SuperB, however we will re-evaluating the suitability of both n− and p-type substrates after determining the lifetime radiation dose expected at Layer 1. A total of 150,000 channels are instrumented on existing BABAR SVT. We would anticipate a similar number of readout channels for the SSVD design, which translates into a 450W cooling

8 capacity requirement for the detector†. The end goal of the silicon detector is to provide localised hit points in an aligned 3D volume that can be combined with other parts of the tracking system to compute particle trajectories. These particle trajectories will come from the primary vertex as well as from secondary vertices. Many charged pions from D∗ decays will be reconstructed within the silicon detector alone, and these so-called slow pions will have a transverse momentum less than 100 MeV/c. We aim to achieve reconstruction eﬃciencies of at least 80 − 90% for such tracks. Other trajectories will originate 0 + − from secondary vertices such as KS → π π and may not have hits in all layers of the silicon. In addition to studying the physics impact of detector optimisation for tracks from primary vertices, we should also consider the physics impact of reconstructing slow pions and of reconstructing secondary vertices. To this end we intend to study golden new physics search channels such as B+ → τ +ν and τ + → µ+γ that have tracks from the primary vertex, decays with D∗ mesons in the 0 + − ﬁnal state in order to evaluate slow−π detection performance, and B → J/ψKS and B → π π decays which provide reference points validating detector performance. Once such measurements have been completed they will be used as benchmarks in the search for new physics using time- dependent CP asymmetry measurements of rare B meson decays such as B → (η0, φ, KK)K0. The following section discusses the benchmark channels in more detail. The following list summarises the required properties of the SuperB vertex detector (Layer 0 and the SSVD):

• Be able to resolve the vertices of individual B mesons in order to compute the proper time diﬀerence ∆t and perform time-dependent CP measurements with a boost factor βγ = 0.28. This boost is half of that used by BABAR.

• The lower boost at SuperB means that the angular coverage of 17◦ from horizontal in the forward direction and 30◦ in the backward direction corresponds to a better coverage than we had in BABAR.

• The SSVD will lie between the Layer 0 and drift chamber sub-systems, so between 3 and 14cm radii.

• Sensors will be no thicker than 300µm.

• At most there will be ﬁve layers of silicon strip detectors.

• Single track eﬃciency should be 80-90% for silicon detector only tracks.

• The mechanical support will be made from composite carbon materials. We will draw on developments made for the ATLAS and LC R&D programmes when considering the choice of material.

In addition to the people named on this proposal, we request funding for an additional 1.5FTE per year eﬀort for staﬀ at RAL and QMUL in order to complete the design of the silicon strip sensors, and the SSVD. Once the sensor design has been completed we will produce a batch of prototype sensors for detailed testing in the laboratory‡. It would be possible to test the developed sensors using commercial readout solution§. QMUL already has the appropriate test equipment in its clean

†This is compatible with the power output estimate for BABAR which was between 100 and 1000W. ‡The estimated cost of a batch of prototype sensors is £70K. §Several commercial readout solutions are available.

9 room required to characterize the electrical properties of these silicon sensors. In order to perform the detector optimization study we will use the existing SuperB GEANT4 and Fast Simulation programmes. If in the longer term SuperB progresses from an R&D project into an STFC funded experiment it would be possible to construct the SuperB SSVD at one of the institutes participating in this proposal, or alternatively at the TD Gateway centre that is currently in the process of being established.

It should be noted that we will obtain the original BABAR SVT design ﬁles from Pisa group, and there are two possible readout chips that should be suitable for our needs: one of these is the BTeV FSSR2 which has been used in the recent MAPS test beam at CERN, and the other is the CMS APV25 (and the sLHC updated design of this chip).

2.4 Project Description: Physics Studies

A signiﬁcant part of any detector design involves physics benchmark studies using fast simulation programs as well as a full GEANT simulation of the detector. The physics channels we are interested in studying are listed below and all of these are central to the SuperB new physics search capability:

• Reference points for new physics searches in ∆S measurements: we will use the reference 0 0 0 + − points of B → J/ΨKS and B → π π to evaluate detector performance for this set of analyses.

• Lepton Flavour Violation studies: We will evaluate detector sensitivity to τ + → µ+γ.

• As slow pions are an integral part of time-dependent CP asymmetry measurements for B0 decays, as well as an integral ingredient in charm mixing and CP violation studies (used in B and D flavour tagging), we will study detector resolution and efficiency effects for slow pions through B flavour tagging and charm mixing benchmark analyses.

• The new physics search capability of B+ → τ +ν will also be studies.

• Issues related to beam-background, luminosity and Interaction Point Phase Space measurement [21], and local alignment of the silicon detector are related to the Bhabha scattering process e+e− → µ+µ−. We will be using this channel as a benchmark for these reasons.

The RAL, QMUL, and Warwick groups will collaborate on performing these studies from the perspective of the SSVD as well as the whole SuperB detector. Collectively we have the necessary experience to perform these studies, as can be seen from our track record.

3 Timescale

The work in this proposal will run for two years, coincident with the preparation of TDRs for the SuperB project. We anticipate starting this work in April 2009, and completing UK contributions to the TDRs by March 2011. The project studentship will run over a three year period, where the third year will focus on consolidating results and writing up.

10 4 Long Term Objectives

The longer term physics goals of the SuperB experiment are unique and not achievable in the CERN programme. These are described in the following. The motivation for undertaking a new generation of experiments is to search for and measure effects of new physics on the decays of heavy quarks and leptons. Current limits in the flavour sector have imposed severe constraints on possible new physics and if new physics is observed at the LHC it is likely to have effects on heavy flavour decays. The detailed study and improved limits from heavy flavour physics will constrain models and be crucial to the understanding of any new physics found at the LHC. In order to constrain new physics, SuperB will carry out a broad programme of studies of the weak decays of b, c quarks and τ leptons. The experiment will measure CP asymmetries, rare branching fractions and interesting kinematic distributions to sufficient precision to observe or place constraining limits on the expected effects of new physics. Among the most important measurements that will be made are:

• Searches for lepton ﬂavour violation decays of the τ lepton to a sensitivity of O(10−9) for τ → µγ and O(10−10) for τ → µµµ.

• Searches for CP violation in kinematic distributions of multibody hadronic τ lepton decays.

• Measurements of the τ electric dipole moment and magnetic dipole moment.

• Measurement of the inclusive radiative B meson decay rate B(B → Xsγ) to a precision of about 3%.

• Measurement of CP violation in the above decay A(B → Xsγ) to a precision of about 0.5%. • Measurements of the polarization of the photon emitted in b → sγ decays using various diﬀerent techniques.

• Inclusive studies of the electroweak penguin process b → s`+`−; studies of decay rates, CP asymmetries and kinematic distributions such as forward-backward asymmetries.

• Studies of the processes B → K(∗)νν¯.

• Measurement of the branching fractions of purely leptonic B decays B(B+ → τ +ν) and B(B+ → µ+ν) to accuracy of about 5%.

• Precise overconstraining of the CKM Unitarity Triangle that will either observe new physics or constrain its eﬀects at the 1% level. This will be done through precision measurements of the angles and sides of the Unitarity Triangle, and through the aforementioned ∆S measurements in rare loop dominated processes which are sensitive to these angles.

• Precision tests of fundamental symmetries such as CPT and lepton universality.

• Searches for mixing-induced CP violation in D0 mixing to an accuracy of about 1%. The D0 mixing parameters x and y will be measured to ∼ 5 × 10−4.

11 5 STFC Science

The areas of STFC scientiﬁc research addressed by the SuperB physics programme are

• Why is there more matter than antimatter in the universe?

• What new physics scenarios are compatible with precision ﬂavour physics. The sensitivity of such measurements are (i) Minimal-Flavour-Violation models give multi TeV search capabilities (ii) non-Minimal-Flavour-Violation give search capabilities of 10-100TeV?

These areas of research are related to the new physics searches, CP violation measurements, CPT tests and Lepton Flavour Violation studies discussed in Section 4.

6 Competing Experiments

The main competitors to SuperB are the LHCb experiment at CERN and the proposed SuperKEKB upgrade programme at KEK. By 2014 LHCb is expected to have accumulated 10 fb−1 of data from pp collisions at a luminosity of ∼ 2 × 1032 cm−2s−1 [15]. Moreover, LHCb is planning an upgrade where they would run at 10 times the initial design luminosity and record a data sample of about 100 fb−1 [16, 17]. If one compares the physics case for LHCb with that for SuperB it is striking to see that the two experimental programmes are largely complementary. For example, the large boost of the B hadrons produced at LHCb allows time-dependent studies of the oscillations of Bs mesons while many of the measurements that constitute the primary physics motivation for SuperB cannot be performed in a high multiplicity hadronic environment. Rare decay modes with + + + + missing energy such as B → ` ν` and B → K νν¯, as well as lepton flavor violation searches in τ decays such as τ + → µ+γ are only accessible at an e+e− collider. Similarly the more copious di-lepton events (where both B mesons in an event decay semi-leptonically) only be used to test + − CPT in an e e collider. Measurements of the CKM matrix elements |Vub| and |Vcb| and inclusive analyses of processes such as b → sγ and b → s`+`− also benefit greatly from the clean and relatively simple e+e− collider environment. At LHCb the reconstruction efficiencies are reduced for channels containing several neutral particles and for studies where the B decay vertex must be determined 0 from a KS meson. SuperB is well placed to study possible new physics effects in hadronic b → s 0 penguin decays as it can measure precisely the CP asymmetries in many Bd decay modes including 0 0 0 0 0 0 0 0 φK , η K , KSKSKS and KSπ . It can also be used to measure the photon polarization via 0 0 0 mixing-induced CP violation in Bd → KSπ γ. It will be difficult for LHCb to study most of these 0 modes, however it can perform complementary measurements using decay modes such as Bs → φγ 0 and Bs → φφ for radiative and hadronic b → s transitions, respectively [18]. Where there is overlap, the strength of the SuperB programme in its ability to use multiple approaches to reach the objective becomes apparent. For example, LHCb should be able to improve the measurement of α from the current precision of 7◦ [19] to about 5◦ precision using B → ρπ [20], but will not be able to access the full information in the ππ and ρρ channels, which is necessary to reduce the uncertainty to the 1–2◦ level of SuperB. Similarly, LHCb can certainly measure sin(2β) 0 0 through mixing-induced CP violation in Bd → J/ψKS decay to high accuracy (about 0.01), but will have less sensitivity to make important complementary measurements (e.g., in J/ψ π0 and Dh0). While LHCb hopes to measure the angle γ with a precision of 2–3◦, extrapolations from current B factories show that SuperB is likely to be able to improve this precision to about 1◦.

12 LHCb can make a precise measurement of the zero of the forward-backward asymmetry in B0 → K∗0µ+µ−, but SuperB can also measure the inclusive channel b → s`+`−, which is theoretically a much cleaner and more powerful observable. The broader programme of SuperB provides a very comprehensive set of measurements in addition to its clean experimental environment and superior neutral detection capabilities. The SuperKEKB experiment is a proposed upgrade of the KEKB/Belle experimental programme. This aims to integrate 10ab−1 of data from e+e− collisions at the Υ(4S) center of mass energy with an initial luminosity of 2 × 1035 cm−2s−1 by 2015. The long term plan for the KEK facility is to integrate 50ab−1 of data at a luminosity of 8 × 1035 cm−2s−1 by 2020. The maximum luminosity of SuperKEKB is limited by the geological stability of the KEK site. It is very unlikely that they will be able to exceed 8 × 1035 cm−2s−1 as in order to do so, one would have to collide e+ and e− beams with very small emittance. By comparison SuperB will start to take data in 2015 and integrate 75ab−1 by 2020 with a luminosity of 1 × 1036 cm−2s−1. It is possible that the luminosity at SuperB will be able to reach a few times 1036 cm−2s−1 once a good understanding of the working accelerator has been obtained.

+ − In summary SuperB will have the worlds largest samples of Bd,Bu,D and τ decays from e e collisions at the Υ(4S) and will also be able to take data at other center of mass energies in order to facilitate a board spectrum of new physics searches and fundamental tests of the SM. The physics programme of SuperB and LHCb are complementary, and SuperB will record larger data sets than the proposed SuperKEKB experiment.

7 Track Record & Collaborative Projects

The team of scientists assembled for this proposal has an excellent track record in their respective specializations, which when combined will provide all of the necessary expertise to ensure that the objectives of this proposal will be achieved. The track record of members of the team is illustrated in the following:

• Bassi has expertise in modeling collective eﬀects in high intensity low-emittance machines and contributed in the development of a strong-strong beam-beam interaction code for hadron colliders. He has developed a Vlasov-Maxwell solver to study micro-bunching instability in Free Electron Lasers and implemented it on high-performance computer clusters.

• Beck is an expert on cooling in silicon vertex detectors and has considerable experience with design and testing for the OPAL and ATLAS silicon detectors.

• Bevan is a leading expert on CP violation and has made the worlds most precise measurements of α and β; verifying Kobayashi and Maskawa’s theory of three generation quark mixing. He also convenes the Charmless Quasi-Two-Body working group on BABAR, and has overseen 55 journal publications in this role. He is also on the SuperB outreach committee.

• Gershon is a respected B physics expert and was an editor of the Physics section of the SuperB Conceptual Design Report. He also helped organize the Valencia Physics Meeting in 2008 and several international conferences and workshops. He was the φ3/γ convener on Belle from January 2004 to May 2005 and runs the Heavy Flavor Averaging subgroup that computes world averages of the angles of the Unitarity Triangle.

13 • Harrison is on the SuperB Steering Committee, the CERN coordination group and the Governance Sub-committee.

• Martin worked on the original and upgraded OPAL silicon vertex detector and works on the ATLAS upgrade programme.

• Wilson is on a SLAC-based BABAR decommissioning committee. He is also the UK spokesperson of BABAR, convened the Charmless 3 body AWG on BABAR and has worked on searches for Lepton Flavour Violation.

• Wolski is an Linear Collider damping ring expert and a member of the SuperB mini Machine Advisory Committee (mini-MAC).

This team has performed world leading measurements of β and α as well as a number of ground breaking rare decay measurements and collectively has the experience to focus on searching for and elucidating new physics contributions through measurements in the flavour sector. They are planning to organise a SuperB Physics meeting in spring 2009 and are investigating the possibility of holding a SuperB general meeting in the autumn of 2009. The QMUL group has a long history of silicon detector development and have recently finished working on the ATLAS SCT. Members of QMUL’s ATLAS team have started to work on cooling and mechanical stability related issues for the ATLAS upgrade. This collective experience within the QMUL ATLAS team will be beneficial to the development of the SuperB SSVD. In addition to this, the Center for Materials Research and Nanoforce at QMUL provide expertise in novel materials that can be used for cooling and expertise in composite materials that can be used for structural support of the SSVD. The team at RAL provide expertise in electrical and mechanical engineering, and are local to the micro-electronics experts who designed one of the ASICS we intend to study for prototyping. This group of people will be augmented by 1.0FTE per year at QMUL and 0.5FTE per year at RAL to complete the detector development team. Should the experiment go ahead we would envisage working closely with the TD Gateway center to construct the SSVD.

RAL has extensive experience with the BABAR software infrastructure and QMUL has a large GridPP enabled computing farm. The QMUL farm currently has 1500 processors with 300Tb of storage space. Both of these sites have experience with running simulations using GRID interfaces and these sites could be used as the basis of the SuperB simulation production center and for generating simulated data for the studies proposed here. The accelerator part of this proposal will be achieved by the expertise listed above. The Cockcroft Institute provides the necessary support environment for Wolski and Bassi to achieve their goals. Their funding through this proposal at the level of 0.5FTE per year for Bassi will enable the Cockcroft team to achieve their goals. insert blub from harrison

8 Technology Transfer, Development, and Beneﬁciaries

There are several opportunities for knowledge exchange (KE) through the work outlined in this proposal. These include development of silicon sensors that can be used in medical imaging as well as dosimetry in hadron therapy, improvements in mechanical stability required for the detector

14 could be of general interest to industry. As such we aim to develop cordial interactions with prototype suppliers in order to place STFC in a strong position should there be an opportunity to exploit KE. The detector development required for this proposal to be successful requires application of existing techniques to the particular problem at hand. As such it is low risk, and the TDR SSVD design will be the ﬁnal design for SuperB. The proposed work has strong links with the interests of existing UK theoretical community, in particular Lattice QCD groups, IPPP and Cambridge. The experimental programme accessibly at SuperB provides a complementarity to the measurements to be produced by the LHCb experiment.

9 Training and Outreach

Opportunities exist to train several graduate students during the course of the research and development programme outlined in this proposal. The BABAR experiment has been enormously successful at training a generation of PPARC/STFC-funded graduate students in data analysis skills. The SuperB experiment will continue in this vein and provide opportunities to train a new generation of experimental and accelerator physicists. The many experimental results that will be obtained at SuperB will provide a more precise set of benchmarks for the next generation of theory students to compare calculations with. The physics motivation driving SuperB is an excellent basis to communicate cutting edge scientiﬁc research to the public. It also gives us an opportunity to communicate some core concepts of quantum mechanics such as the uncertainty principle, quantum interference, EPR correlations, and wave particle duality. Outreach activities including school visits to RAL and Masterclass events will beneﬁt from this proposal. Dissemination of the underlying physics goals and technological developments of SuperB will also be achieved through Bevan’s work on the SuperB outreach committee and via his outreach activities in the QMUL Physics Department.

10 Costs

Table 1 summarises the costs involved in this proposal. These are given for the whole of the project (i.e. for a 2 year period). We request funding for a total manpower eﬀort of 4FTEs over 2 years, and a project studentship which breaks down as follows:

• 0.5 FTE per year to fund the time of Bassi to perform the accelerator R&D outlined above,

• 1.0 FTE per year for a PDRA at QMUL to work on the SSVD design and optimisation programme,

• 0.5 FTE per year for staﬀ at RAL to work on the SSVD design and optimisation programme.

• A project studentship for Warwick in order to contribute to the accelerator R&D and physics studies.

15 In addition to this we request: travel funds of £9, 500 for travel between collaborating institutes and to SuperB related meetings and workshops, £2, 000 for consumables: computers and software, and £70, 000 for production of prototype silicon sensors.

Table 1: Cost of the project broken down into personnel resources, equipment and travel. The costs are summed over the two year period of the proposal.

Resource FTE (Total) Cost on bid People (Staff and Students) G. Bassi 1.0 £112,321 G. Beck 0.2 £0 A. Bevan 0.6 £0 T. Gershon 0.2 £0 P. Harrison 0.1 £0 A. J. Martin 0.2 £0 F. Wilson 0.4 £0 A. Wolski 0.4 £0 QMUL PDRA 2.0 £164,365 RAL Staff (Band 5) 1.0 £91,363 Project Student ... £50,040 Other Costs Equipment ... £70,000 Consumables ... £2,000 Travel ... £9,500 Totals Existing RG staff £203,684 New staff 4.0 £164,365 Project Student ... £50,040 Equipment/Consumables ... £72,000 Travel ... £9,500

The cost of existing staﬀ (including estates and overheads) to STFC not listed in Table 1 is £15,140 for Liverpool/Cockcroft, £43,878 for QMUL, £50,095 for RAL, and £13,120 for Warwick ¶. Table 2 gives a breakdown of cost per institute for this proposal (these are the costs on this proposal and the additional costs to STFC).

11 Cross-Council & Other Funding

This proposal will be part funded through the rolling grant contributions of the named participants, as well as through core funding of the Cockcroft Institute participants. The remaining costs would be borne by STFC through this proposal, as detailed in Table 1.

¶This calculation is based on 100% for STFC staﬀ, 60% of 60% for Academics and 80% for other posts, and numbers are quoted to the nearest pound.

16 Table 2: Cost of the project broken down by institute into staﬀ travel and equipment. Note that travel will be administered through RAL. Staﬀ costs quoted include indirect and estates costs and are rounded to the nearest pound.

Cost on Proposal (£) Other cost to STFC (£) Cockcroft Institute, University of Liverpool Academics 0 15,140 Rolling Grant Staff 112,321 0 Total Staff 112,321 15,140 Consumables 2,000 0 Total 114,321 15,140 Queen Mary, University of London Academics 0 26,758 Rolling Grant Staff 0 17,120 New Staff 164,365 0 Total Staff 164,365 0 Equipment 70,000 0 Total 234,365 43,878 Rutherford Appleton Laboratory Academics 0 50,095 RAL Support Staff 91,363 0 Total Staff 91,363 50,095 Travel 9,500 0 Total 100,863 50,095 University of Warwick Academics 0 13,120 Project Studentship 50,040 0 Total 50,040 13,120 Grand Total 499,589 122,233

The following is a list of grants held, or being applied for in parallel with this proposal that could beneﬁt the work outlined in this Case For Support. Dr Bevan is the holder of a Royal Society grant totalling £12,000 to work with Dr. G. Cavoto from INFN La Sapienza on physics analysis related to SuperB. This grant can only be used for travel between the two participating institutes. In addition to this, Dr. Bevan is seeking seed-corn funding through QMUL’s current CIF funding round at a level of approximately £60,000. Dr Martin is seeking £250,000 of CIF funds to expand the QMUL computing farm. The CIF applications described here are being considered, and the aim of it is to provide computing and test equipment to facilitate detector R&D at QMUL.

References

[1] SuperB Conceptual Design Report, arXiv:0709.0451, INFN/AE - 07/2, SLAC-R-856, LAL 07- 15. The Valencia Physics Workshop report is an addendum to the physics case outlined in the CDR. This report is D. Hitlin et al, arXiv:0810.1312.

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[13] SuperB CDR, p. 198 (2007).

[14] BABAR Collaboration, B. Aubert et al., Nucl. Instrum. Meth. A479, 1 (2002); Also see BABAR Notes 195 and 196.

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[19] See either the CKM Fitter, UTFit web pages for SU(2) based averages of α http://www.slac.stanford.edu/xorg/ckmﬁtter/ckm welcome.html and http://www.utﬁt.org/ respectively; Alternatively see B. Aubert et al., Phys. Rev. D72 052007 (2007).

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[21] W. Kozanecki, A. J. Bevan, B. F. Viaud, et al., SLAC-PUB-13383 (Submitted to Nucl. Instrum. Meth. A).