V. Berardi

First measurement of the total proton-proton cross-section at the LHC energy of \chem{\sqrt{s} = 7\,TeV}

TOTEM has measured the differential cross-section for elastic proton-proton scattering at the LHC energy of analysing data from a short run with dedicated large-β* optics. A single exponential fit with a slope B=(20.1±0.2stat±0.3syst) GeV−2 describes the range of the four-momentum transfer squared |t| from 0.02 to 0.33 GeV2. After the extrapolation to |t|=0, a total elastic scattering cross-section of (24.8±0.2stat±1.2syst) mb was obtained. Applying the optical theorem and using the luminosity measurement from CMS, a total proton-proton cross-section of (98.3±0.2stat±2.8syst) mb was deduced which is in good agreement with the expectation from the overall fit of previously measured data over a large range of center-of-mass energies. From the total and elastic pp cross-section measurements, an inelastic pp cross-section of was inferred.

Measurement of proton-proton elastic scattering and total cross-section at \chem{\sqrt {s} = 7\,TeV}

At the LHC energy of , under various beam and background conditions, luminosities, and Roman Pot positions, TOTEM has measured the differential cross-section for proton-proton elastic scattering as a function of the four-momentum transfer squared t. The results of the different analyses are in excellent agreement demonstrating no sizeable dependence on the beam conditions. Due to the very close approach of the Roman Pot detectors to the beam center (?5?beam) in a dedicated run with ?*?=?90?m, |t|-values down to 5?10?3?GeV2 were reached. The exponential slope of the differential elastic cross-section in this newly explored |t|-region remained unchanged and thus an exponential fit with only one constant B?=?(19.9???0.3)?GeV?2 over the large |t|-range from 0.005 to 0.2?GeV2 describes the differential distribution well. The high precision of the measurement and the large fit range lead to an error on the slope parameter B which is remarkably small compared to previous experiments. It allows a precise extrapolation over the non-visible cross-section (only 9%) to t?=?0. With the luminosity from CMS, the elastic cross-section was determined to be (25.4???1.1)?mb, and using in addition the optical theorem, the total pp cross-section was derived to be (98.6???2.2)?mb. For model comparisons the t-distributions are tabulated including the large |t|-range of the previous measurement (TOTEM Collaboration (Antchev G. et al), EPL, 95 (2011) 41001).

Proton-proton elastic scattering at the LHC energy of \chem{\sqrt{s} = 7\,TeV}

Proton-proton elastic scattering has been measured by the TOTEM experiment at the CERN Large Hadron Collider at √ s = 7 TeV in dedicated runs with the Roman Pot detectors placed as close as seven times the transverse beam size (σbeam) from the outgoing beams. After careful study of the accelerator optics and the detector alignment, |t|, the square of four-momentum transferred in the elastic scattering process, has been determined with an uncertainty of δt = 0.1 GeV p |t|. In this letter, first results of the differential cross-section are presented covering a |t|-range from 0.36 to 2.5 GeV 2 . The differential cross-section in the range 0.36 < |t| < 0.47 GeV 2 is described by an exponential with a slope parameter B =( 23.6 ± 0.5 stat ± 0.4 syst )G eV −2 , followed by a significant diffractive minimum at |t| =( 0.53 ± 0.01 stat ± 0.01 syst )G eV 2 .F or|t|-values larger than ∼ 1. 5G eV 2 , the cross-section exhibits a power law behaviour with an exponent of −7.8 ± 0.3 stat ± 0.1 syst . When compared to predictions based on the different available models, the data show a strong discriminative power despite the small t-range covered. open access Copyright c EPLA, 2011

Phase-conjugate mirror via two-photon thermal light imaging

We report on a two-photon imaging experiment in which a thermal light source behaves like a phase-conjugate mirror, which produces a real image of an object. The result offers a novel scheme of imaging and thus suggests useful applications.

Realization and Characterization of a Two-Photon Four-Qubit Linear Cluster State

Cluster states, recently introduced as a fundamental resource for one-way quantum computation, represent genuine multiqubits entangled states. The one-way model is based on the initial preparation of entangled qubits in the cluster state, followed by single qubits measurements and feed-forwards. All the difficulties present in the standard computation model, for instance the implementation of two qubits gates, are transferred in the one-way model to the state preparation.

Evidence for non-exponential elastic proton-proton differential cross-section at low |t| and √ s = 8 TeV by TOTEM

Abstract The TOTEM experiment has made a precise measurement of the elastic proton–proton differential cross-section at the centre-of-mass energy s = 8 TeV based on a high-statistics data sample obtained with the β ⁎ = 90 m 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 σ . 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.

Measurement of the forward charged-particle pseudorapidity density in pp collisions at ?s = 7?TeV with the TOTEM experiment

The TOTEM experiment has measured the charged-particle pseudorapidity density dNch/d? in pp collisions at for 5.3<|?|<6.4 in events with at least one charged particle with transverse momentum above 40?MeV/c in this pseudorapidity range. This extends the analogous measurement performed by the other LHC experiments to the previously unexplored forward ? region. The measurement refers to more than 99% of non-diffractive processes and to single and double diffractive processes with diffractive masses above ~3.4?GeV/c2, corresponding to about 95% of the total inelastic cross-section. The dNch/d? has been found to decrease with |?|, from 3.84 ? 0.01(stat) ? 0.37(syst) at |?|=5.375 to 2.38?0.01(stat)?0.21(syst) at |?|=6.375. Several MC generators have been compared to data; none of them has been found to fully describe the measurement.

Measurement of proton-proton inelastic scattering cross-section at \chem{\sqrt {s} = 7\,{\mathrm {TeV}}}

The TOTEM experiment at the LHC has measured the inelastic proton-proton cross-section at in a ?*?=?90?m run with low inelastic pile-up. The measurement was based on events with at least one charged particle in the T2 telescope acceptance of 5.3?<?|?|?<?6.5 in pseudorapidity. Combined with data from the T1 telescope, covering 3.1?<?|?|?<?4.7, the cross-section for inelastic events with at least one |?|???6.5 final-state particle was determined to be (70.5???2.9)?mb. This cross-section includes all central diffractive events of which maximally 0.25?mb is estimated to escape the detection of the telescopes. Based on models for low mass diffraction, the total inelastic cross-section was deduced to be (73.7???3.4)?mb. An upper limit of 6.31?mb at 95% confidence level on the cross-section for events with diffractive masses below 3.4?GeV was obtained from the difference between the overall inelastic cross-section obtained by TOTEM using elastic scattering and the cross-section for inelastic events with at least one |?|???6.5 final-state particle.

Planar edgeless silicon detectors for the TOTEM experiment

Silicon detectors for the Roman Pots of the the large hadron collider TOTEM experiment aim for full sensitivity at the edge where a terminating structure is required for electrical stability. This work provides an innovative approach reducing the conventional width of the terminating structure to less than 100 /spl mu/m, still using standard planar fabrication technology. The objective of this new development is to decouple the electric behavior of the surface from the sensitive volume within a few tens of micrometers. The explanation of the basic principle of this new approach together with the experimental confirmation via electric measurements and beam test are presented in this paper, demonstrating that silicon detectors with this new terminating structure are fully operational and efficient to under 60 /spl mu/m from the die cut.

High fluence laser ablation of aluminum targets: Time-of-flight mass analysis of plasmas produced at wavelengths 532 and 355 nm

We report on Time-of-Flight Mass Spectrometry (TOFMS) analysis of plasmas produced in laser ablation of Al targets. We used both the second (532 nm) and third (355 nm) harmonic of a Nd: YAG laser system, carrying out the investigation in a regime of relatively high laser fluence (up to 70 J/cm2), where the production of ionized species in the plume is maximized. We present TOF mass spectra of ions in the laser-produced plasma, and a detailed analysis of the relative abundance of different charged species as a function of the laser fluence. The presence of single, doubly and triply ionized Al atoms has been observed and the fluence threshold for their production is reported. We also studied the total ion and electron yield at different laser fluences, its saturation above specific energy densities, and singly ionized cluster-ions produced in the laser plasma.