decay, with a statistical significance exceeding six standard deviations, and the best measurement so far of its branching fraction. Furthermore, we obtained evidence for the B 0 ? m 1 m 2 decay with a statistical significance of three standard deviations. Both measurements are statistically compatible with standard model predictions and allow stringent constraints to be placed on theories beyond the standard model. The LHC experiments will resume taking data in 2015, recording proton-proton collisions at a centre-of-mass energy of 13 teraelectronvolts, which will approximately double the production rates of B 0 s and B 0 mesons and lead to further improvements in the precision of these crucial tests of the standard model.Experimental particle physicists have been testing the predictions of the standard model of particle physics (SM) with increasing precision since the 1970s. Theoretical developments have kept pace by improving the accuracy of the SM predictions as the experimental results gained in precision. In the course of the past few decades, the SM has passed critical tests derived from experiment, but it does not address some profound questions about the nature of the Universe. For example, the existence of dark matter, which has been confirmed by cosmological data 3 , is not accommodated by the SM. It also fails to explain the origin of the asymmetry between matter and antimatter, which after the Big Bang led to the survival of the tiny amount of matter currently present in the Universe Fig. 1c, is forbidden at the elementary level because the Z 0 cannot couple directly to quarks of different flavours, that is, there are no direct 'flavour changing neutral currents'. However, it is possible to respect this rule and still have this decay occur through 'higher order' transitions such as those shown in Fig. 1d and e. These are highly suppressed because each additional interaction vertex reduces their probability of occurring significantly. They are also helicity and CKM suppressed. Consequently, the branching fraction for the B 0 s ?m z m { decay is expected to be very small compared to the dominant b antiquark to c antiquark transitions. The corresponding decay of the B 0 meson, where a d quark replaces the s quark, is even more CKM suppressed because it requires a jump across two quark generations rather than just one.The branching fractions, B, of these two decays, accounting for higher-order electromagnetic and strong interaction effects, and using lattice quantum chromodynamics to compute the B 8,9 , such as in the diagrams shown in Fig. 1f and g, that can considerably modify the SM branching fractions. In particular, theories with additional Higgs bosons 10,11 predict possible enhancements to the branching fractions. A significant deviation of either of the two branching fraction measurements from the SM predictions would give insight on how the SM should be extended. Alternatively, a measurement compatible with the SM could provide strong constraints on BSM theories. . Both CMS and LHCb later ...

A search for narrow resonances and quantum black holes is performed in inclusive and b-tagged dijet mass spectra measured with the CMS detector at the LHC. The data set corresponds to 5 fb −1 of integrated luminosity collected in pp collisions at √ s = 7 TeV. No narrow resonances or quantum black holes are observed. Modelindependent upper limits at the 95% confidence level are obtained on the product of the cross section, branching fraction into dijets, and acceptance for three scenarios: decay into quark-quark, quark-gluon, and gluon-gluon pairs. Specific lower limits are set on the mass of string resonances (4.31 TeV), excited quarks (3.32 TeV), axigluons and colorons (3.36 TeV), scalar color-octet resonances (2.07 TeV), E 6 diquarks (3.75 TeV), and on the masses of W (1.92 TeV) and Z (1.47 TeV) bosons. The limits on the minimum mass of quantum black holes range from 4 to 5.3 TeV. In addition, b-quark tagging is applied to the two leading jets and upper limits are set on the production of narrow dijet resonances in a model-independent fashion as a function of the branching fraction to b-jet pairs.

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We present a measurement of the W + W − production cross section using 184 pb −1 of pp collisions at a center-of-mass energy of 1.96 TeV collected with the Collider Detector at Fermilab. Using the dilepton decay channel W + W − →ℓ + νℓ −ν , where the charged leptons can be either electrons or muons, we find 17 candidate events compared to an expected background of 5.0 +2.2 −0.8 events. The resulting W + W − production cross section measurement of σ(pp → W + W − ) = 14.6 +5.8 −5.1 (stat) +1.8 −3.0 (syst) ± 0.9(lum) pb agrees well with the Standard Model expectation.PACS numbers: 13.38.Be, 14.70.Fm 3The measurement of the W pair production crosssection in pp collisions at √ s = 1.96 TeV provides an important test of the Standard Model. Anomalous W W γ and W W Z triple gauge boson couplings [1], as well as the decays of new particles such as Higgs bosons [2], could result in a rate of W pair production that is larger than the Standard Model cross-section of 12.4±0.8 pb [3]. The first evidence for W pair production was found in pp collisions by the CDF collaboration at √ s = 1.8 TeV [4]. The properties of W pair production have been extensively studied by the LEP collaborations in e + e − collisions up to √ s = 209 GeV [5], and have been shown to be in good agreement with the Standard Model. The DØ experiment has recently reported a measurement of the W pair production cross section at Run II of the Tevatron [6].In this Letter we describe a measurement of the W + W − production cross section in the dilepton decay channel W + W − → ℓ + νℓ −ν (ℓ = e, µ), and compare the event kinematics with Standard Model predictions. The signature for W + W − → ℓ + νℓ −ν events is two high-P T leptons and missing transverse energy, E / T , from the undetected neutrinos [7]. Jets from the hadronization of additional partons in the event due to initial-state radiation may be present. This analysis is based on 184 ± 11 pb −1 of data collected by the upgraded Collider Detector at Fermilab (CDF) during the Tevatron Run II period.The CDF II detector [8] has undergone a major upgrade since the Run I data-taking period. The components relevant to this analysis are briefly described here. The Central Outer Tracker (COT) is a large-radius cylindrical drift chamber with 96 measurement layers organized into alternating axial and ±2 • stereo superlayers [9], and is used to reconstruct the trajectories (tracks) of charged particles and measure their momenta. The COT coverage extends to |η| = 1. A silicon microstrip detector [10,11] provides precise tracking information near the beamline in the region |η| < 2. The entire tracking volume sits inside a 1.4 T magnetic field. Segmented calorimeters, covering the pseudorapidity region |η| < 3.6, surround the tracking system. The central (|η| < 1) and forward (1 < |η| < 3.5) electromagnetic calorimeters are lead-scintillator sampling devices, instrumented with proportional and scintillating strip detectors that measure the position and transverse profile of electromagnetic showers. The hadron calorimete...

The 3 m + x 5 m long x 1.5 T superconducting solenoid for the Fermilab Collider Detector has been installed at Ferm.lab and was tested in early 1985 with a dedicated refrigeration system. The refrigerator and 5.6-Mg magnet cold mass were cooled to 5 K in 210 hours. After testing at low currents, the magnet was charged to the design current of 5 kA in 5-MJ steps. During a 390 A/min charge a spontaneous quench occurred at 4.5 kA due to insufficient liquid helium flow.Three other quenches ·occurred during "slow" discharges which were nevertheless fast enough to cause high eddy current heating in the outer support cylinder. Quench behavior is well understood and the magnet is now quite reliable.