Measurement of differential cross sections for single diffractive dissociation in $$ \sqrt{s} $$ = 8 TeV pp collisions using the ATLAS ALFA spectrometer

Abstract

A dedicated sample of Large Hadron Collider proton-proton collision data at centre-of-mass energy √ s = 8 TeV is used to study inclusive single diffractive dissociation, pp → Xp. The intact final-state proton is reconstructed in the ATLAS ALFA forward spectrometer, while charged particles from the dissociated system X are measured in the central detector components. The fiducial range of the measurement is −4.0 < log 10 ξ < −1.6 and 0.016 < |t| < 0.43 GeV 2 , where ξ is the proton fractional energy loss and t is the squared four-momentum transfer. The total cross section integrated across the fiducial range is 1.59 ± 0.13 mb. Cross sections are also measured differentially as functions of ξ, t, and ∆η, a variable that characterises the rapidity gap separating the proton and the system X. The data are consistent with an exponential t dependence, dσ/dt ∝ e Bt with slope parameter B = 7.65 ± 0.34 GeV −2. Interpreted in the framework of triple Regge phenomenology, the ξ dependence leads to a pomeron intercept of α(0) = 1.07 ± 0.09.

Nucleon Structure and Soft QCD from ATLAS

“…P 8 event generator predictions for A2 and A3 [17] are = 7.82 GeV −2 , = 7.10 GeV −2 , respectively. The corresponding measurement is = 7.65 ± 0.26 (stat) ±0.22 (syst) GeV −2 [16].…”

“…The hadron-level cross-sections were studied versus , and Δ . This was the first measurement of the -spectrum in SD events at LHC [16]. The background events from non-SD collisions have correlated signals in ALFA and the Inner Detector (estimated from MC), and overlay background with coincidences of a signal in ALFA with an uncorrelated signal in the Inner Detector (data-driven estimate, contributes the largest uncertainty).…”

“…For this analysis, the ALFA Roman Pot stations in the outgoing LHC beams are used [16]. The data are recorded in special LHC runs with * = 90 m, √ = 8 TeV, L = 1.67 nb −1 and with a low number of interactions per bunch crossing < 0.08.…”

“…The event generators P 8 and H 7 describe the shape reasonably, but overestimate the production cross-section. Furthermore, the differential cross-section as function of | | was studied [16]. P 8 event generator predictions for A2 and A3 [17] are = 7.82 GeV −2 , = 7.10 GeV −2 , respectively.…”

Prospects for quarkonium studies at the high-luminosity LHC

“…However, order-of-magnitude differences occur at lower transverse momenta: the probability of ∆η > 4 in minimum bias pp events at √ s = 7 TeV was found to be about 0.1 using a cluster hadronisation model [336] and 0.02 for string fragmentation [337]. A recent measurement by ATLAS [338], comparing the largest gap in pp events at √ s = 8 TeV with pythia [339] and herwig++ [340] (Fig. 12, Left), shows that the data exhibit fewer large gaps than the models predict.…”