Michelle Nicol
The b->s gamma transition proceeds through flavour changing neutral currents, and thus is particularly sensitive to the effects of new physics. An overview of the method to measure the photon polarisation at the LHCb experiment via an angular analysis of B->K*e+e- at low q^2 is presented. The status of the B->K*mu+mu- analysis with 309 pb-1 of pp collisions at sqrt(s)=7 TeV at LHCb is also given.
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LHCb is the dedicated B physics experiment at the LHC and is due to start data taking later this year. Its goal is to search for new physics in very rare processes and make precision measurements of CP violation in B decays. The CKM angle gamma plays an important role in flavour physics in the Standard Model. LHCb will exploit the large variety of B hadrons produced by the 14 TeV pp collisions, performing gamma measurements to the precision of a few degrees. Here, we will present a summary of the expected gamma sensitivities LHCb will reach during its first years of data taking, with contribut…
$b \to c l \barν$ decays at LHCb
该研究在LHCb实验开展两项半轻子$b$强子衰变测量，检验轻子味普适性并分析$D^{*+}$纵向极化，发现$R(D)$、$R(D^*)$世界平均值仍与标准模型有3倍以上标准差偏差，极化结果则与模型相符。
The status and prospects of time-integrated measurements of the CKM angle gamma at LHCb, the LHC's dedicated flavor physics experiment, are reviewed. Yields obtained from early data taking are presented and extrapolations are made to estimate what can be expected to be obtained from the 2011 data. The conclusions drawn from these extrapolations are that LHCb will produce the world's best measurement of gamma by the end of 2011 and that the long-term outlook is excellent.
We review the first measurements of the CKM angle gamma from LHCb. These measurements have been performed with b-hadron decays dominated by b -> u and b -> c tree-level amplitudes, from which gamma can be determined without theoretical uncertainties. Precision is achieved by averaging results from B- -> Dh- (h= K,pi) decays with D -> h+h-, D -> K+pi-, and D -> K+pi-pi+pi-, and D -> K_S^0h+h-. Prospects for these and future measurements of gamma using neutral b-hadron decays are briefly discussed.
One of the most promising ways to determine the angle gamma of the CKM unitarity triangle is through measurement of the tree level processes B to DK. The LHCb collaboration has studied the potential of these decays employing the Atwood-Dunietz-Soni (ADS) and Dalitz methods, making use of a large sample of simulated data. For each method the expected sensitivities to the angle gamma are presented in this report.
An overview of plans for the measurement of gamma at the LHCb experiment will be shown. The gamma angle is the least accurately known parameter of the CKM unitary triangle. The LHCb experiment at the CERN LHC aims to perform precision heavy flavour and CP violation measurements, including improving the knowledge of gamma. Focus will be put on methods using B meson decays at the tree level, within the Standard Model framework. The early data recorded by the experiment, from pp collisions at sqrt{s} = 7 TeV, allowed observations of the first signals of the B decay modes that will be used to perf…
The LHCb collaboration has studied various promising ways to determine the Unitarity Triangle angle $γ$. Three complementary methods will be considered. The potential of the $B \to DK^{(*)}$ decays has been studied by employing the combined Gronau-London-Wyler (GLW) and the Atwood-Dunietz-Soni (ADS) methods, making use of a large sample of simulated data. $γ$ can also be extracted with a time-dependent analysis of $B_s \to D_s K$ decays, provided that the $B_s$ mixing phase is measured independently. In addition, the combined measurement of the $B^0 \to π^+ π^-$ and $B^0_s \to K^+K^-$ time-dep…
Of the three angles that make up the CKM matrix, the least well known is gamma. A precision measurement of this quantity is highly desirable as it forms one of the arbitrary parameters in the Standard Model. Moreover, this is the one angle of the CKM triangle that can be determined in channels that occur via tree-level decays. While loop-level processes could have sensitivity to physics beyond the standard model, tree level processes are expected to be unaltered. Hence a measurement of gamma in tree level processes leads to a standard model benchmark measurement against which other loop-driven…
We present studies from the LHCb experiment of decays of the type H_b to H_c X, where H_b represents a beauty hadron (B+, B0 or Lambda_b) and H_c a charmed hadron (D0, D(*)+, Ds or Lambda_c). Such decays are important for the determination of the CKM angle gamma, a key goal of the LHCb physics programme. We exploit the data accumulated in 2010, and in the early months of the 2011 run. We report on the observation of new decay modes, and first measurements on the road to a precise determination of gamma.
The startup of the LHC opens many new frontiers in precision flavour physics, in particular expanding the field of precision time-dependent CP violation measurements to the $B^0_s$ system. This contribution reviews the status of time-dependent measurements of the CKM angle $γ$ at the LHC's dedicated flavour physics experiment, LHCb. Particular attention is given to the measurement of $γ$ from the decay mode \DsK, a theoretically clean and precise method which is unique to LHCb. The performance of the LHCb detector for this and related modes is reviewed in light of early data taking and found t…
The B^0_s -> J/psi K_S decay has recently been observed by the CDF collaboration and will be of interest for the LHCb experiment. It is the U-spin partner of the golden B^0_d -> J/psi K_S channel and offers a determination of the angle gamma of the unitarity triangle. Moreover, it allows us to control the hadronic penguin effects in the extraction of the B^0_d-\bar B^0_d mixing phase phi_d through a measurement of CP violation in B^0_d^0 -> J/psi K_S. We discuss the picture emerging for these measurements from an LHCb feasibility study. While LHCb will be able to extract gamma from the CP viol…
The LHCb experiment, bolstered up by the 10^12 b-hadrons to be produced yearly in its interaction region, is an excellent place to study rare B decays. Flavor-changing neutral currents are forbidden at tree level in the Standard Model. They proceed through loop diagrams and hence are indirectly sensitive to New Physics through the effect of new particles on observable quantities. In this paper, we present preparation studies of the three most promising B rare decay analyzes. These aim at the observation of the photon polarization in B_s to phi gamma, the measurement of the angular distribution…
The B_s^0 -> J/psi K_S decay has recently been observed by the CDF collaboration and will be of interest for the LHCb experiment. This channel will offer a new tool to extract the angle gamma of the unitarity triangle and to control doubly Cabibbo-suppressed penguin corrections to the determination of sin(2beta) from the well-known B_d^0 -> J/psi K_S mode with the help of the U-spin symmetry of strong interactions. While any competitive determination of gamma is interesting, the latter aspect is particularly relevant as LHCb will enter a territory of precision which makes the control of doubly…
Rare flavour changing neutral current (FCNC) decays of top, beauty and charm quarks can provide a powerful probe for as yet unobserved particles. Recent results on FCNC $b \to s$, $c \to u$ and $t$ transitions from the LHC experiments are reviewed. Particular attention is paid to the angular distribution of the $B^{0} \to K^{*0} μ^{+} μ^{-}$ decay, where a measurement performed by LHCb shows a local discrepancy of 3.7 standard deviations with respect to the SM prediction. Using the decay $B^{+} \to K^{+}π^{-}π^{+}γ$, LHCb have also been able to demonstrate the polarisation of photons produced …
The time-dependent $CP$ asymmetry in $B^0 \to K_{\rm res} γ\to π^+ π^- K^0_{\scriptscriptstyle S} γ$ is sensitive to the photon polarisation in the quark level process $b \to s γ$. While this polarisation is predominantly left-handed in the standard model, it could be modified by the existence of new physics contributions that may possess different $CP$ properties. In this paper, we derive the $CP$ violation formulae for $B^0 \to K_{\rm res} γ\to π^+ π^- K^0_{\scriptscriptstyle S} γ$ including the most dominant intermediate states. We propose a new observable that could be measured in a time-d…
New Crystal Barrel data are reported for pbar-p -> omega-eta and pbar-p -> omega-pizero-pizero with omega decaying to piplus-piminus-pizero. The omega-eta data confirm angular distributions obtained earlier from data where omega -> pizero-gamma. The new omega-eta data provide accurate measurements of vector and tensor polarisations of the omega and lead to considerable improvements in masses and widths of s-channel resonances. A new J^PC = 3^+- I = 0 resonance is observed with mass M = 2025+-20 MeV and width Gamma = 145+-30 MeV. Polarisation is close to zero everywhere and tensor polarisations…
We analyse the performance of a gas time projection chamber (TPC) as a high-performance gamma-ray telescope and polarimeter in the e$^+$e$^-$ pair creation regime. We use data collected at a gamma-ray beam of known polarisation. The TPC provides two orthogonal projections $(x,z)$ and $(y,z)$ of the tracks induced by each conversion in the gas volume. We use a simple vertex finder in which vertices and pseudo-tracks exiting from them are identified. We study the various contributions to the single-photon angular resolution using Monte Carlo simulations and compare them with the experimental dat…
Current γ-ray telescopes based on photon conversions to electron-positron pairs, such as Fermi, use tungsten converters. They suffer of limited angular resolution at low energies, and their sensitivity drops below 1 GeV. The low multiple scattering in a gaseous detector gives access to higher angular resolution in the MeV-GeV range, and to the linear polarisation of the photons through the azimuthal angle of the electron-positron pair. HARPO is an R&D program to characterise the operation of a TPC (Time Projection Chamber) as a high angular-resolution and sensitivity telescope and polarimeter …
We perform model-independent statistical analyses of three scenarios accommodating New Physics (NP) in Delta F=2 flavour-changing neutral current amplitudes. In a scenario in which NP in B_d-B_d-bar and B_s-B_s-bar is uncorrelated, we find the parameter point representing the Standard-Model disfavoured by 2.4 standard deviations. However, recent LHCb data on B_s neutral-meson mixing forbid a good accommodation of the D0 data on the semileptonic CP asymmetry A_SL. We introduce a fourth scenario with NP in both M_12^d,s and Gamma_12^d,s, which can accommodate all data. We discuss the viability o…
The Large Hadron Collider will be a unique place to find new physics in the next decade. A huge production of b and c quarks will allow a rich programme of Heavy Flavour Physics to be carried out either by the multipurpose experiments ATLAS and CMS or by LHCb, the experiment designed for such physics. An overview of the LHC machine and experiments' performances will be given with the first 2010 data. The start-up is very bright and some first LHC heavy flavour results will be presented. The b physics program at LHC will be illustrated with three examples: the searches for rare decays such as B…
An angular analysis of the $B^0 \to K^{*0} e^+ e^-$ decay is performed using a data sample corresponding to an integrated luminosity of $9~{\rm fb}^{-1}$ of $pp$ collisions collected with the LHCb experiment. The analysis is conducted in the very low dielectron mass squared ($q^2$) interval between $0.0008$ and $0.257~{\rm GeV}^2$, where the rate is dominated by the $B^0\to K^{\ast 0}γ$ transition with a virtual photon. The fraction of longitudinal polarisation of the $K^{\ast 0}$ meson, $F_{\rm L}$, is measured to be $F_{\rm L} = (4.4 \pm 2.6 \pm 1.4)\%$, where the first uncertainty is statis…
Constraints on the photon polarisation in $b \to s γ$ transitions using $B_s^0 \rightarrow ϕe^+e^-$ decays
本文利用 LHCb 数据对 $B_s^0 \rightarrow \phi e^+e^-$ 衰变进行角分析，测量 $\phi$ 介子极化分数及多个 CP 不对称可观测量，从而约束 $b \to s \gamma$ 跃迁中的光子极化，结果与标准模型一致。
Using the latest LHCb measurements of time-dependent CP violation in the B^0_s -> K^+K^- decay, a U-spin relation between the decay amplitudes of B^0_s -> K^+K^- and B^0 -> π^+π^- decay processes allows constraints to be placed on the angle gamma of the unitarity triangle and on the B^0_s mixing phase -2β_s. Results from an extended approach, which uses additional inputs on B^0 -> π^0π^0 and B^+ -> π^+π^0 decays from other experiments and exploits isospin symmetry, are also presented. The dependence of the results on the maximum allowed amount of U-spin breaking is studied. At 68% probability,…
Using data collected with the LHCb detector in proton-proton collisions at a centre-of-mass energy of 7 TeV, the hadronic decay Bs -> J/psi f0(980) is observed. This CP eigenstate mode could be used to measure mixing-induced CP violation in the B_s system. Using a fit to the pi+ pi- mass spectrum with interfering resonances gives R_{f0/phi} = [Gamma(Bs -> J/psi f0, f0 -> pi+ pi-)]/[Gamma(Bs -> J/psi phi, phi -> K+K-)] = 0.252^{+0.046+0.027}_{-0.032-0.033}, where the uncertainties are statistical and systematic, respectively.
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