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Beauty Physics at LHCb. Andrey Golutvin Vladimir Shevchenko ITEP & CERN. 11th INTERNATIONAL MOSCOW SCHOOL OF PHYSICS Session « Particle Physics » February 8-16, 2008. Outline. ABC of LHC Flavor physics – informal introduction The CKM matrix and Unitarity Triangle LHCb detector

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## Beauty Physics at LHCb

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**Beauty Physics at LHCb**AndreyGolutvin Vladimir Shevchenko ITEP & CERN 11th INTERNATIONAL MOSCOW SCHOOL OF PHYSICS Session «Particle Physics» February 8-16, 2008**Outline**• ABC of LHC • Flavor physics – informal introduction • The CKM matrix and Unitarity Triangle • LHCb detector • Search for New Physics in CP violation • Physics of loops • Rare decays at LHCb • Conclusions 1 2**Jet d’ Eau**140 m Mont Blanc, 4808 m LHCb experiment: 700physicists 50 institutes 15countries CERN LHCb ATLAS CMS ALICE**ABC of LHC**• Tonnel length - 27 kilometers • Depth below ground - between 50 and 175 meters • p-p beams, 2808 bunches, 1.15×10 particles/bunch • v = 0.99999998 c • Energy • Nominal luminosity<L> ~ 1034 cм-2сек -1 11**Energy of a proton in the beam = 7 TeV = 10-6 J**It is about kinetic energy of a flying mosquito: Question: why not to use mosquitos in particle physics? Answer: because NAvogadro = 6.0221023 (mol)-1 Energy of a mosquito is distributed among ~ 1022 nucleons. On the other hand, total energy stored in each beam is 2808 bunches 1011 protons/bunch 7 TeV/proton = 360 MJ It is explosive energy of ~ 100 kg TNT or kinetic energy of “Admiral Kuznetsov” cruiser traveling at 8 knots.**Particle acceleration**• Charged particles influenced by applied electric and magnetic fields according to the Lorentz force: F = q (E + v B) = dp/dt E field → energy gain, B field → curvature • CERN has a wide variety of accelerators, some dating back to 1950s • LHC machine re-uses the tunnel excavated for previous accelerator (LEP)Others (PS/SPS) used to accelerate protons before injection into the LHC Neutrino beam,low energy beamsand p fixed-target beams all running in parallel with LHC**The LHC**Reality Originalidea From an article in the CERN Courier**Dipole magnets used to deflect the particlesRadius r [m] =**3.33 p [GeV] / B [T] • For the LHC, the machine has to fit in the existing 27 km tunnel, about 2/3 of which isused for active dipole field → r~ 2800 mSo to reach p = 7 TeV requires B = 8.3 T • Beams focused using quadrupole magnetsBy alternating Focusing and Defocusing quadrupoles, can focus in both x and y views The LHC has 1232 dipoles 392 quadrupoles**Flavor physics:**informal introduction**The Standard Model Zoo**SU(3)SU(2)U(1) [ g; W, Z; ] Masses come out of interactions in the Standard Model and these interactions conserve (or do not conserve…) particular symmetries. Mass hierarchies (from hep-ph/0603118). The heaviest fermion of a given type has unit mass.**Invariance properties with respect to transformations**have been always important in physics • momentum • angular momentum • energy • translations in • rotations in • time translations invariance conservation Gauge symmetry – invariance with respectto transformations in «internal» space In the SM this space has structure ofU(1) × SU(2) × SU(3)**U(1) × SU(2) × SU(3)**gluon photon Z, W And gravity is everywhere leptons quarks Quarks are unique probes of the whole «internal space», hence flavor physics has to deal with weak, electromagnetic and strong interactions altogether**Besides continuous symmetries of prime importance in high**energy physics are discrete transformations • С – charge conjugation • P – space inversion • Т – time reflection Experimental fact: strong and electromagnetic interactions in the SM are C, P, T, CP, CT, PT and CPTinvariant.**Maximal symmetry is not so interesting…**Beauty slightly broken symmetry**СРТ theorem:**Antiparticles and their interactions are indistinguishable from particles moving along the same world-lines but in opposite directions in 3+1 dimensional space-time. In particular, the mass of any particle is strictly equal to the mass of its antiparticle (experimentally checked in 1 part to 1018 in K-meson studies). The SM strictly conserves CPT. There are no however any theoretical reason why C, P and T should conserve separately. Often in physics if something can happen – it does.**Weak interactions violate P-parity**T.D.Lee, C.N.Yang, 1956 C.S.Wu, 1957**L.D.Landau, 1959:**hypothesis of combined CP-parity conservation J.Cronin, V.Fitch, 1964: CP-violation discovery in neutral K-mesons decays.****CP violation In the world of elementary particles: (CPLEAR 1999) neutral kaon decay time distribution anti-neutral kaon decay time distribution**Later CP-violation has been beautifully measured by**experimentsBaBar and BELLE at the B factories These are machines (in the US and Japan) running on the (4S) resonance: e+e-(4S) B0B0 or B+B- • The CP asymmetry A(t) = G(B0 J/yKS) -G(B0 J/yKS) G(B0 J/yKS) +G(B0 J/yKS) A(t) = -sin2b sinDmt in the Standard Model • BABAR+BELLE measuresin2b = 0.674 ± 0.026 • This can be compared withthe indirect measurementfrom other constraints on theUnitarity Triangle**M. Kobayashi, T.Maskawa, 1974:**theoretical mechanism for CP-violation in the SM Idea: nontrivial superposition of non-interacting particles forms flavor eigenstate that interacts weakly In other words: it is impossible to diagonalize simultaneously the mass term and charged currents interaction term:**It is easy to show that arbitrary complex unitaryN×N**matrix can be parameterized by N(N-1)/2 generalized Euler angles and (N-1)(N-2)/2 complex phases. ForN<3 the matrix can always be rotated to an equivalent one which is real. But not for N=3. In other words, there exist 3×3 unitary matrices which cannot be made real whatever phases quark fields are chosen to have.**Baryogenesis**• Big Bang (~ 14 billion years ago) → matter and antimatter equally produced; followed by annihilation → nbaryon/ng ~ 10-10Why didn’t all the matter annihilate (luckily for us)? • No evidence found for an “antimatter world” elsewhere in the Universe • One of the requirements to produce an asymmetric final state (our world) from a symmetric matter/antimatter initial state (the Big Bang)is that CP symmetry must violated [Sakharov, 1967] • CP is violated in the Standard Model, through the weak mixing of quarksFor CP violation to occur there must be at least 3 generations of quarksSo problem of baryogenesis may be connected to why three generations exist, even though all normal matter is made up from the first (u, d, e, e) • However, the CP violation in the SM is not sufficient for baryogenesisOther sources of CP violation expected → good field to search for new physics**CKM matrix can be parameterized by four parameters in many**different ways. The so called «Wolfenstein parametrization» is based on expansion in powers of**It is convenient to discuss the properties of CKM matrix**in parametrization-invariant terms. Such invariant are absolute values of the matrix elements and «angles» between them If any of these angles is different from zero, it means that there is a complex phase in CKM matrix which cannot be rotated away. This violates CP. «Jarlskog invariant»**Off-diagonal unitarity conditions can be represented as**triangles on complex plane. The Unitarity triangle: All 6 unitarity triangles have equal area but only two of them are not degenerate. B-mesons decays are very sensitive to СР ! **The Unitarity triangle**: Bdmixing phase : Bsmixing phase : weak decay phase Im 0 1 Re Im + Precise determination of parameters through B-decays study. 0 Re**UT as a standard approach to test the consistency of SM**Mean values of angles and sides of UT are consistent with SM predictions • Accuracy of sides is limited by theory: • Extraction of |Vub| • Lattice calculation of Accuracy of angles is limited by experiment: • = ±13° • b = ± 1° • = ± 25°**Standard method to search for New Physics**Define the apex of UT using at least 2 independent quantities out of 2 sides: and 3 angles: , and Extract quantities Rb and from the tree-mediated processes, that are expected to be unaffected by NP, and compare computed values for with direct measurements in the processes involving loop graphs. Interpret the difference as a signal of NP**W–**q1 b q b u, c, t q2 W− d, s mbγL+mqγR W − W − d (s) d (s) b u,c,t b u, c, t l+ q g Z, γ l− q Topologies in B decays Trees Penguins Boxes V*ib Viq q u,c,t b W− W+ u, c, t q b Viq V*ib**Standard method to search for New Physics**Define the apex of UT using at least 2 independent quantities out of 2 sides: and 3 angles: , and Extract quantities Rb and from the tree-mediated processes, that are expected to be unaffected by NP, and compare computed values for with direct measurements in the processes involving loop graphs. Interpret the difference as a signal of NP**The sensitivity of standard approach is limited due to:**- Geometry of UT (UT is almost rectangular) Comparison of precisely measured with is not meaningful due to error propagation: 3° window in corresponds to (245)° window in **Precision comparison of the angle and side Rt is very**meaningful !!! However in many NP scenarios, in particular with MFV, short-distance contributions are cancelled out in the ratio of Md/Ms. So the length of the Rt side may happen to be not sensitive to NP Precision measurement of will effectively constrain Rt and thus calibrate the lattice calculation of the parameter**Complementary Strategy**Compare observables and UT angles: , and measured in different topologies: In trees: Theoretical uncertainty in Vub extraction Set of observables for (at the moment not theoretically clean): Theoretical input: improved precision of lattice calculations for fB , BB and B,,K* formfactors Experimental input: precision measurement of BR(BK*, )**Search for NP comparing observables**measured in tree and loop topologies (peng+tree) in B,, (peng+box) in B Ks (peng+box) in Bs (tree+box) in B J/ Ks (tree) in many channels (tree+box) in Bs J/ New heavy particles, which may contribute to d- and s- penguins, could lead to some phase shifts in all three angles: (NP) = (peng+tree) - (tree) (NP) = (BKs) - (BJ/Ks) ≠ 0 (NP) = (Bs) - (BsJ/)**Search for NP comparing observables**measured in tree and loop topologies • Contribution of NP to processes mediated by loops • (present status) • to boxes: • vs |Vub / Vcb | is limited by theory (~10% precision in |Vub|) (d-box) • not measured with any accuracy (s-box) • to penguins: • ((NP)) ~ 30° (d-penguin) • ((NP)) ~8° (s-penguin) • ((NP)) not measured (s-penguin) • PS (NP) = (NP) • (NP) measured in B and B decays may differ depending • on penguin contribution to and final states**LHCb is aiming at search for**New Physics in CP-violation and Rare Decays**Large Hadron Collider - LHCb**• Bunch crossing frequency: ~ 40 MHz • Number of reactions in unit of time: • since pp inelastic ~ 80 mbarn • for nominal LHC luminosity • N ~ 8108 • For LHCb L ~ 2 × 1032 cm-2s-1 • (local defocusing of the beam) • → multi-body interactions are • subdominant Inelastic pp reactions**-**b b bb angular distribution PT of B-hadron 100μb 230μb Pythia η of B-hadron b b • vertices and momenta reconstruction • effective particle identification(π, К, μ, е, γ) • triggers**View of the LHCb cavern**Calorimeters Magnet Muon detector RICH-2 OT RICH-1 VELO It’s full! Installation of major structures is essentially complete**LHCb in its cavern**Offset interaction point (to make best use of existing cavern) Shielding wall(against radiation) Electronics + CPU farm Detectors can be moved away from beam-line for access**LHCb detector**~ 300 mrad p p 10 mrad Forward spectrometer (running in pp collider mode)Inner acceptance 10 mrad from conical beryllium beam pipe**LHCb detector** Vertex locator around the interaction region Silicon strip detector with ~ 30 mm impact-parameter resolution**Vertex detector**• Vertex detector has silicon microstrips with rf geometryapproaches to 8 mm from beam (inside complex secondary vacuum system) • Gives excellent proper time resolution of ~ 40 fs (important for Bs decays) Beam Vertex detector information is used in the trigger**LHCb detector** Tracking system and dipole magnet to measure angles and momenta Dp/p ~ 0.4 %, mass resolution ~ 14 MeV (for Bs DsK)**LHCb detector** Two RICH detectors for charged hadron identification**LHCb detector**e h Calorimeter system to identify electrons, hadrons and neutrals. Important for the first level of the trigger**LHCb detector**m Muon system to identify muons, also used in first level of trigger**S: LHC prospects**BsJ/ is the Bs counterpart of B0J/ KS • In SM S = - 2arg(Vts) = - 22 ~ - 0.04 • Sensitive to New Physics effects in the Bs-Bs system if NP in mixing S = S(SM) + S(NP) • 2 CP-even, 1 CP-odd amplitudes, angular analysis needed to separate, then fit to S, S, CP-odd fraction • LHCb yield in 2 fb-1 131k, B/S = 0.12 LHCb 0.021 0.021 ATLAS will reach s(s) ~ 0.08 (10/fb, ms=20/ps, 90k J/ evts)

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