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Register a new userEvidence for non-exponential elastic proton-proton differential cross-section at low |t| and sqrt(s) = 8 TeV by TOTEM
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The TOTEM experiment has made a precise measurement of the elastic proton-proton differential cross-section at the centre-of-mass energy sqrt(s) = 8 TeV based on a high-statistics data sample obtained with the beta* = 90 optics. Both the statistical and systematic uncertainties remain below 1%, except for the t-independent contribution from the overall normalisation. This unprecedented precision allows to exclude a purely exponential differential cross-section in the range of four-momentum transfer squared 0.027 < |t| < 0.2 GeV^2 with a significance greater than 7 sigma. Two extended parametrisations, with quadratic and cubic polynomials in the exponent, are shown to be well compatible with the data. Using them for the differential cross-section extrapolation to t = 0, and further applying the optical theorem, yields total cross-section estimates of (101.5 +- 2.1) mb and (101.9 +- 2.1) mb, respectively, in agreement with previous TOTEM measurements.
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The TOTEM collaboration has measured the elastic proton-proton differential cross section ${rm d}sigma/{rm d}t$ at $sqrt{s}=13$ TeV LHC energy using dedicated $beta^{*}=90$ m beam optics. The Roman Pot detectors were inserted to 10$sigma$ distance from the LHC beam, which allowed the measurement of the range $[0.04$ GeV$^{2}$$; 4 $GeV$^{2}$$]$ in four-momentum transfer squared $|t|$. The efficient data acquisition allowed to collect about 10$^{9}$ elastic events to precisely measure the differential cross-section including the diffractive minimum (dip), the subsequent maximum (bump) and the large-$|t|$ tail. The average nuclear slope has been found to be $B=(20.40 pm 0.002^{rm stat} pm 0.01^{rm syst})~$GeV$^{-2}$ in the $|t|$-range $0.04~$GeV$^{2}$ to $0.2~$GeV$^{2}$. The dip position is $|t_{rm dip}|=(0.47 pm 0.004^{rm stat} pm 0.01^{rm syst})~$GeV$^{2}$. The differential cross section ratio at the bump vs. at the dip $R=1.77pm0.01^{rm stat}$ has been measured with high precision. The series of TOTEM elastic pp measurements show that the dip is a permanent feature of the pp differential cross-section at the TeV scale.
Pseudorapidity (eta) distributions of charged particles produced in proton-proton collisions at a centre-of-mass energy of 8 TeV are measured in the ranges abs(eta) < 2.2 and 5.3 < abs(eta) < 6.4 covered by the CMS and TOTEM detectors, respectively. The data correspond to an integrated luminosity of 45 inverse microbarns. Measurements are presented for three event categories. The most inclusive category is sensitive to 91-96% of the total inelastic proton-proton cross section. The other two categories are disjoint subsets of the inclusive sample that are either enhanced or depleted in single diffractive dissociation events. The data are compared to models used to describe high-energy hadronic interactions. None of the models considered provide a consistent description of the measured distributions.
The TOTEM collaboration has measured the proton-proton total cross section at $sqrt{s}=13$ TeV with a luminosity-independent method. Using dedicated $beta^{*}=90$ m beam optics, the Roman Pots were inserted very close to the beam. The inelastic scattering rate has been measured by the T1 and T2 telescopes during the same LHC fill. After applying the optical theorem the total proton-proton cross section is $sigma_{rm tot}=(110.6 pm 3.4$) mb, well in agreement with the extrapolation from lower energies. This method also allows one to derive the luminosity-independent elastic and inelastic cross sections: $sigma_{rm el} = (31.0 pm 1.7)$ mb and $sigma_{rm inel} = (79.5 pm 1.8)$ mb.
Production of $B_c^+$ mesons in proton-proton collisions at a center-of-mass energy of 8 TeV is studied with data corresponding to an integrated luminosity of $2.0~{rm fb}^{-1}$ recorded by the LHCb experiment. The ratio of production cross-sections times branching fractions between the $B_c^+to J/psi pi^+$ and $B^+to J/psi K^+$ decays is measured as a function of transverse momentum and rapidity in the regions $0 < p_{rm T} < 20~{rm GeV}/c$ and $2.0 < y < 4.5$. The ratio in this kinematic range is measured to be $(0.683pm0.018pm0.009)%$, where the first uncertainty is statistical and the second systematic.
A measurement of $Zrightarrowtau^+tau^-$ production cross-section is presented using data, corresponding to an integrated luminosity of 2 fb$^{-1}$, from $pp$ collisions at $sqrt{s}=8$ TeV collected by the LHCb experiment. The $tau^+tau^-$ candidates are reconstructed in final states with the first tau lepton decaying leptonically, and the second decaying either leptonically or to one or three charged hadrons. The production cross-section is measured for $Z$ bosons with invariant mass between 60 and 120 GeV/$c^2$, which decay to tau leptons with transverse momenta greater than 20 GeV/$c$ and pseudorapidities between 2.0 and 4.5. The cross-section is determined to be $sigma_{pprightarrow{}Zrightarrow{}tau^+tau^-} = 95.8 pm 2.1 pm 4.6 pm 0.2 pm 1.1 mathrm{pb}$, where the first uncertainty is statistical, the second is systematic, the third is due to the LHC beam energy uncertainty, and the fourth to the integrated luminosity uncertainty. This result is compatible with NNLO Standard model predictions. The ratio of the cross-sections for $Zrightarrowtau^+tau^-$ to $Zrightarrowmu^+mu^-$ ($Zrightarrow{}e^+e^-$), determined to be $1.01 pm 0.05$ ($1.02 pm 0.06$), is consistent with the lepton-universality hypothesis in $Z$ decays.
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