Abstract
Measurements are presented of the single-diffractive dijet cross section and the diffractive cross section as a function of the proton fractional momentum loss xi and the four-momentum transfer squared t. Both processes {text{ p }{}{}} {text{ p }{}{}} rightarrow {text{ p }{}{}} {text{ X }} and {text{ p }{}{}} {text{ p }{}{}} rightarrow {text{ X }} {text{ p }{}{}} , i.e. with the proton scattering to either side of the interaction point, are measured, where {text{ X }} includes at least two jets; the results of the two processes are averaged. The analyses are based on data collected simultaneously with the CMS and TOTEM detectors at the LHC in proton–proton collisions at sqrt{s} = 8,text {Te}text {V} during a dedicated run with beta ^{*} = 90,text {m} at low instantaneous luminosity and correspond to an integrated luminosity of 37.5{,text {nb}^{-1}} . The single-diffractive dijet cross section sigma ^{{text{ p }{}{}} {text{ X }}}_{mathrm {jj}}, in the kinematic region xi < 0.1, 0.03< |t | < 1,text {Ge}text {V} ^2, with at least two jets with transverse momentum p_{mathrm {T}} > 40,text {Ge}text {V} , and pseudorapidity |eta | < 4.4, is 21.7 pm 0.9,text {(stat)} ,^{+3.0}_{-3.3},text {(syst)} pm 0.9,text {(lumi)} ,text {nb} . The ratio of the single-diffractive to inclusive dijet yields, normalised per unit of xi , is presented as a function of x, the longitudinal momentum fraction of the proton carried by the struck parton. The ratio in the kinematic region defined above, for x values in the range -2.9 le log _{10} x le -1.6, is R = (sigma ^{{text{ p }{}{}} {text{ X }}}_{mathrm {jj}}/Delta xi )/sigma _{mathrm {jj}} = 0.025 pm 0.001,text {(stat)} pm 0.003,text {(syst)} , where sigma ^{{text{ p }{}{}} {text{ X }}}_{mathrm {jj}} and sigma _{mathrm {jj}} are the single-diffractive and inclusive dijet cross sections, respectively. The results are compared with predictions from models of diffractive and nondiffractive interactions. Monte Carlo predictions based on the HERA diffractive parton distribution functions agree well with the data when corrected for the effect of soft rescattering between the spectator partons.
Highlights
In proton–proton collisions a significant fraction of the total cross section is attributed to diffractive processes
Diffractive events are characterised by at least one of the two incoming protons emerging from the interaction intact or excited into a low-mass state, with only a small energy loss. These processes can be explained by the exchange of a virtual object, the so-called Pomeron, with the vacuum quantum numbers [1]; no hadrons are produced in a large rapidity range adjacent to the scattered proton, yielding a so-called large rapidity gap (LRG)
Hard diffractive processes can be described in terms of the convolution of diffractive parton distribution functions and hard scattering cross sections, which can be calculated in perturbative quantum chromodynamics
Summary
In proton–proton (pp) collisions a significant fraction of the total cross section is attributed to diffractive processes. Diffractive events are characterised by at least one of the two incoming protons emerging from the interaction intact or excited into a low-mass state, with only a small energy loss. These processes can be explained by the exchange of a virtual object, the so-called Pomeron, with the vacuum quantum numbers [1]; no hadrons are produced in a large rapidity range adjacent to the scattered proton, yielding a so-called large rapidity gap (LRG). The ratio of the singlediffractive to inclusive dijet cross sections is measured as a function of x, the longitudinal momentum fraction of the proton carried by the struck parton for x values in the range. This is the first measurement of hard diffraction with a measured proton at the LHC
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
