The prompt production of charmonium I c and J / I states is studied in protonaproton collisions at a centre-of-mass energy of s = 7 TeV at the Large Hadron Collider. The I c and J / I mesons are ...identified through their decays I c a J / I gamma and J / I a mu + mu - using 36 pb - 1 of data collected by the LHCb detector in 2010. The ratio of the prompt production cross-sections for I c and J / I , I (I c a J / I gamma ) / I (J / I) , is determined as a function of the J / I transverse momentum in the range 2 < p T J / I < 15 GeV / c . The results are in excellent agreement with next-to-leading order non-relativistic expectations and show a significant discrepancy compared with the colour singlet model prediction at leading order, especially in the low p T J / I region.
A binned Dalitz plot analysis of B +/- a D K +/- decays, with D a K S 0 pi + pi - and D a K S 0 K + K - , is performed to measure the CP-violating observables x +/- and y +/- which are sensitive to ...the CKM angle gamma. The analysis exploits 1.0 fb - 1 of data collected by the LHCb experiment. The study makes no model-based assumption on the variation of the strong phase of the D decay amplitude over the Dalitz plot, but uses measurements of this quantity from CLEO-c as input. The values of the parameters are found to be x - = (0.0 +/- 4.3 +/- 1.5 +/- 0.6) X 10 - 2 , y - = (2.7 +/- 5.2 +/- 0.8 +/- 2.3) X 10 - 2 , x + = (- 10.3 +/- 4.5 +/- 1.8 +/- 1.4) X 10 - 2 and y + = (- 0.9 +/- 3.7 +/- 0.8 +/- 3.0) X 10 - 2 . The first, second, and third uncertainties are the statistical, the experimental systematic, and the error associated with the precision of the strong-phase parameters measured at CLEO-c, respectively. These results correspond to gamma = (44 - 38 + 43) degree , with a second solution at gamma a gamma + 180 degree , and r B = 0.07 +/- 0.04 , where r B is the ratio between the suppressed and favoured B decay amplitudes.
Measurement of the effective lifetime Aaij, R; Abellan Beteta, C; Adametz, A ...
Physics letters. B,
10/2012, Letnik:
716, Številka:
3-5
Journal Article
Recenzirano
A precise determination of the effective B s 0 ? K + K - lifetime can be used to constrain contributions from physics beyond the Standard Model in the B s 0 meson system. Conventional approaches ...select B meson decay products that are significantly displaced from the B meson production vertex. As a consequence, B mesons with low decay times are suppressed, introducing a bias to the decay time spectrum which must be corrected. This analysis uses a technique that explicitly avoids a lifetime bias by using a neural network based trigger and event selection. Using 1.0 fb - 1 of data recorded by the LHCb experiment, the effective B s 0 ? K + K - lifetime is measured as 1.455 +/- 0.046 (stat.) +/- 0.006 (syst.) ps .
The prompt production of the charmonium I c 1 and I c 2 mesons has been studied in proton-proton collisions at the Large Hadron Collider at a centre-of-mass energy of s = 7 TeV . The I c mesons are ...identified through their decays I c a J / I gamma with J / I a mu + mu a using 36 pb a 1 of data collected by the LHCb detector in 2010. The ratio of the prompt production cross-sections for the two I c spin states, I ( I c 2 ) / I ( I c 1 ) , has been determined as a function of the J / I transverse momentum, p T J / I , in the range from 2 to 15 GeV/c. The results are in agreement with the next-to-leading order non-relativistic QCD model at high p T J / I and lie consistently above the pure leading-order colour-singlet prediction.
We have studied the diffractive dissociation into dijets of 500 GeV/c pions scattering coherently from carbon and platinum targets. Extrapolating to asymptotically high energies (where t(min)-->0), ...we find that when the per-nucleus cross section for this process is parametrized as sigma = sigma0Aalpha, alpha has values near 1.6, the exact result depending on jet transverse momentum. These values are in agreement with those predicted by theoretical calculations of color-transparency.
Observation of CP violation in decays Aaij, R; Abellan Beteta, C; Adeva, B ...
Physics letters. B,
06/2012, Letnik:
712, Številka:
3
Journal Article
Recenzirano
An analysis of B-a D K-and B-a D I-decays is presented where the D meson is reconstructed in the two-body final states: K A- I a , K + K a and I + I a . Using 1.0 fba1 of s = 7 TeV pp collisions, ...measurements of several observables are made including the first observation of the suppressed mode B-a I-K a D K-. CP violation in B-a D K-decays is observed with 5.8I significance.
Using data from the FOCUS (E831) experiment, we have searched for T violation in charm meson decays using the four-body decay channels D0→K−K+π−π+, D+→KS0K+π−π+, and Ds+→KS0K+π−π+. The T violation ...asymmetry is obtained using triple-product correlations and assuming the validity of the CPT theorem. We find the asymmetry values to be ATviol(D0)=0.010±0.057(stat.)±0.037(syst.), ATviol(D+)=0.023±0.062(stat.)±0.022(syst.), and ATviol(Ds+)=−0.036±0.067(stat.)±0.023(syst.). Each measurement is consistent with no T violation. New measurements of the CP asymmetries for some of these decay modes are also presented.
The ratio of branching fractions of the radiative B decays B0 -> K*0 gamma and Bs0 phi gamma has been measured using an integrated luminosity of 1.0 fb-1 of pp collision data collected by the LHCb ...experiment at a centre-of-mass energy of sqrt(s)=7 TeV. The value obtained is BR(B0 -> K*0 gamma)/BR(Bs0 -> phi gamma) = 1.23 +/- 0.06(stat.) +/- 0.04(syst.) +/- 0.10(fs/fd), where the first uncertainty is statistical, the second is the experimental systematic uncertainty and the third is associated with the ratio of fragmentation fractions fs/fd. Using the world average value for BR(B0 -> K*0 gamma), the branching fraction BR(Bs0 -> phi gamma) is measured to be (3.5 +/- 0.4) x 10^{-5}. The direct CP asymmetry in B0 -> K*0 gamma decays has also been measured with the same data and found to be A(CP)(B0 -> K*0 gamma) = (0.8 +/- 1.7(stat.) +/- 0.9(syst.))%. Both measurements are the most precise to date and are in agreement with the previous experimental results and theoretical expectations.
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