Evidence for non-exponential elastic proton–proton differential cross-section at low |t| and s=8TeV 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 fourmomentum 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.This article is dedicated to the memory of Prof. E. Lippmaa and Prof. M. Lo Vetere who passed away recently

Elastic and inelastic diffraction at the LHC

“…As such, dip location reflects the "size" of proton, moving towards smaller |t| values as the total cross section increases with energy. The departure from the linear exponential behavior was confirmed by recent measurements by the TOTEM Collaboration at the CERN LHC, first at 8 TeV (with a significance greater then 7σ) [9] and subsequently at 13 TeV [10]. At the ISR the "break" was illustrated by plotting the local slope B(t) for several t-bins at fixed values of s.…”

“…To better demonstrate the goodness of our fit and to anticipate the comparison with the LHC data, we also present in Fig. 7 the ISR data in normalized form as used by TOTEM [9]:…”

Elastic amplitudes studied with the LHC measurements at 7 and 8 TeV

“…With an enormous gap in the center-of-mass energy with respect to previous data in pp and pp scattering, the Totem and Atlas experimental groups at LHC have recently measured dσ/dt in the forward t ranges at √ s = 7 and 8 TeV [1][2][3][4][5]. These measurements offer a unique opportunity to investigate the behavior of p-p collisions at the highest energies reached in laboratory.…”

“…The descriptions of the models differ for higher |t| about the position of this second real zero and about the existence of further imaginary or real zeros. Models describing large |t| ranges have different motivations and dynamical structures, and may be analytically very sophisticated, trying to represent the observed shapes of dip, bump, tail, in [1][2][3][4][5]. The ρ values for a b are taken from COM-PETE Collaboration [19].…”

Regge Phenomenology at LHC Energies

“…Although we are not considering in our fits the recent measurement of the σ tot from elastic scattering in pp collisions at √ s = 8 TeV from the ATLAS Collaboration 16 we decided at least to show the respectively datum by means of the discrepancy in comparison with the TOTEM results. For completeness the results of the fits to dσ el /d|t| obtained using the Born-level models are displayed together with predictions at √ s = 8 TeV and 13 TeV together with the recent experimental data 2 at √ s = 7 TeV and the preliminary data 6 , still under analysis but not considered in our fitting procedure, at √ s = 8 TeV. The values of the fitted parameters for all the five Born-level models are given in Table 1, where we also show the χ 2 /DoF (degree of freedom).…”