Low Mass Diffraction Research Articles

Low-mass Diffraction Dissociation at the LHC. Role of the Background

A dual model with a nonlinear proton Regge trajectory in the missing mass (M2X) channel is constructed. A background based on a direct-channel exotic trajectory, developed and applied earlier for the inclusive electron-proton cross section description in the nucleon resonance region, is used. The parameters of the model are determined from the extrapolations to earlier experiments. Predictions for the low-mass (2 < M2X < 8 GeV2) diffraction dissociation cross sections at the LHC energies are given.

Study of contributions of diffractive processes to forward neutral particle production with the ATLAS-LHCf detector

LHCf is an experiment dedicated to verify the hadronic interaction models by measuring the forward neutral particle production at the LHC. Corresponding data are very important for understanding hadronic interactions occurring in air-shower development. According to the current LHCf results, no simulation model predicts the LHCf data perfectly. In order to provide more specific data, it is necessary to classify the LHCf observables into specific interaction types: diffraction or non-diffraction. Combining the information of ATLAS, LHCf is able to classify these specific interaction types experimentally. Especially, the ATLAS-LHCf joint experiment will have the unique sensitivity to low mass diffraction. LHCf and ATLAS have succeeded in the common data-taking in p-p collisions at √s = 13 TeV. We will report the first ATLAS-LHCf joint analysis result and discuss the impact of the corresponding joint analysis result to the determination of mass composition of ultra-high energy cosmic-rays.

Monte Carlo study of particle production in diffractive proton\u2013proton collisions at sqrt{s} = 13 TeV with the very forward detector combined with central information

Very forward (VF) detectors in hadron colliders, having unique sensitivity to diffractive processes, can be a powerful tool for studying diffractive dissociation by combining them with central detectors. Several Monte Carlo simulation samples in p–p collisions at sqrt{s} = 13 TeV were analyzed, and different nondiffractive and diffractive contributions were clarified through differential cross sections of forward neutral particles. Diffraction selection criteria in the VF-triggered-event samples were determined by using the central track information. The corresponding selection applicable in real experiments has approx 100% purity and 30–70% efficiency. Consequently, the central information enables classification of the forward productions into diffraction and nondiffraction categories; in particular, most of the surviving events from the selection belong to low-mass diffraction events at log _{10}(xi _{x}) < -5.5. Therefore, the combined method can uniquely access the low-mass diffraction regime experimentally.

Forward Physics with the CMS Experiment at LHC

Forward physics measurements with the Compact Muon Solenoid (CMS) experiment, one of the two large multi-purpose experiments at the Large Hadron Collider (LHC) at CERN, cover a wide range of physics subjects. The forward calorimeters of CMS, HF and CASTOR, are used to collect data up to a pseudo-rapidity of 6.6. These detectors provide sensitivity to a large part of the total inelastic cross section, including diffractive events that produce particles only at forward rapidity, with the exception of very low mass diffraction. The results obtained with a centre-of-mass energy of 13 TeV are presented. The measurements are compared to model predictions and provide valuable input for tuning of Monte Carlo models used to describe high-energy hadronic interactions.

The practical Pomeron for high energy proton collimation

We present a model which describes proton scattering data from ISR to Tevatron energies, and which can be applied to collimation n high energy accelerators, such as the LHC and FCC. Collimators remove beam halo particles, so that they do not impinge on vulnerable regions of the machine, such as the superconducting magnets and the experimental areas. In simulating the effect of the collimator jaws it is crucial to model the scattering of protons at small momentum transfer~$t$,as these protons can subsequently survive several turns of the ring before being lost. At high energies these soft processes are well described by Pomeron exchange models. We study the behaviour of elastic and single-diffractive dissociation cross sections over a wide range of energy, and show that the model can be used as a global description of the wide variety of high energy elastic and diffractive data presently available. In particular it models low mass diffraction dissociation, where a rich resonance structure is present, and thus predicts the differential and integrated cross sections in the kinematical range appropriate to the LHC.We incorporate the physics of this model into the beam tracking code MERLIN and use it to simulate the resulting loss maps of the beam halo lost in the collimators in the LHC.

Diffractive dissociation of gluons into heavy quark–antiquark pairs in proton–proton collisions

We discuss diffractive dissociation of gluons into heavy quark pairs. The particular mechanism is similar to the diffractive dissociation of virtual photons into quarks, which drives diffractive deep inelastic production of charm in the low-mass diffraction, or large β-region. There, it can be understood, with some reservations, in terms of a valence heavy quark content of the Pomeron. The amplitude for the gp→QQ¯p is derived in the impact parameter and momentum space. The cross section for single diffractive pp→QQ¯pX is calculated as a convolution of the elementary cross section and gluon distribution in the proton. Integrated cross section and the differential distributions in e.g. transverse momentum and rapidity of the charm and bottom quark and antiquark, as well as the quark–antiquark invariant mass are calculated for the nominal LHC energy for different unintegrated gluon distributions from the literature. The ratio of the bottom-to-charm cross sections are shown and discussed as a function of several kinematical variables.

Measurement of proton-proton inelastic scattering cross-section at

The TOTEM experiment at the LHC has measured the inelastic proton-proton cross-section at in a β* = 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 < |η| < 6.5 in pseudorapidity. Combined with data from the T1 telescope, covering 3.1 < |η| < 4.7, the cross-section for inelastic events with at least one |η| ⩽ 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 |η| ⩽ 6.5 final-state particle.

Dual-Regge approach to high-energy, low-mass diffraction dissociation

A dual-Regge model with a nonlinear proton Regge trajectory in the missing mass $({M}_{X}^{2})$ channel, describing the experimental data on low-mass single diffraction dissociation (SDD), is constructed. Predictions for the LHC energies are given.

A QCD motivated model for soft interactions at high energies

In this paper we develop an approach to soft scattering processes at high energies which is based on two elements: the Good–Walker mechanism for low mass diffraction and multi-pomeron interactions for high mass diffraction. The principal idea, which allows us to specify the theory for pomeron interactions, is that the so called soft processes occur at rather short distances (r 2 ∝1/〈p t 〉2 ∝ α′ℙ≈0.01 GeV−2), where perturbative QCD is valid. The value of the pomeron slope α′ℙ is obtained from a fit to the experimental data. Using this theoretical approach, we suggest a model that fits all soft data in the ISR-Tevatron energy range: total, elastic, single and double diffractive cross sections, as well as the t dependence of the differential elastic cross section, and the mass dependence of single diffraction. In this model we calculate the survival probability of diffractive Higgs production, and we obtain a value for this observable that is smaller than 1% at the LHC energy range.

QGSJET-II: towards reliable description of very high energy hadronic interactions

Since a number of years the QGSJET model has been successfully used by different groups in the field of high energy cosmic rays. Current work is devoted to the first general update of the model. The key improvement is connected to an account for non-linear interaction effects which are of crucial importance for reliable model extrapolation into ultra-high energy domain. The proposed formalism allows to obtain a consistent description of hadron-hadron cross sections and hadron structure functions and to treat non-linear effects explicitely in individual hadronic and nuclear collisions. Other ameliorations concern the treatment of low mass diffraction, employment of realistic nuclear density profiles, and re-calibration of model parameters using a wider set of accelerator data.

Photoproduction within the two-component Dual Parton Model: Amplitudes and cross sections

In the framework of the Dual Parton Model an approximation scheme to describe high energy photoproduction processes is presented. Based on the distinction between direct, resolved soft, and resolved hard interaction processes we construct effective impact parameter amplitudes. In order to treat low mass diffraction within the eikonal formalism in a consistent way a phenomenological ansatz is proposed. The free parameters of the model are determined by fits to high energy hadro- and photoproduction cross sections. We calculate the partial photoproduction cross sections and discuss predictions of the model at HERA energies. Using hadro- and photoproduction data together, the uncertainties of the model predictions are strongly reduced.

Partial Wave Amplitude for Low Mass N System Produced in Diffraction Dissociation

Partial wave amplitudes of the Drell-Hiida-Deck model and its unitarized version by the final state interaction are studied for the low mass Nn system produced in the diffraction dissociation process. The partial wave amplitude unitarized by the final state interaction can be divided into two components. The one has the minimum and the other the maximum at the resonance position. The resultant amplitudes violate the Gribov-Morrison rule and the conservation of the t-channel helicity. with small transferred four momen­ tum squared, t, at PL=5GeV/c to PL=40GeV/c have revealed the internal structures of a low mass diffraction dissociation (LMDD). These analyses seem to show that the A 1 enhancement cannot be a typical resonance with the Breit­ Wigner phase. If there are no axial vector mesons at all, our theoretical framework such as composite models or higher symmetries would encounter serious difficulties. It is, therefore, a highly important problem to clarify whether the A 1 enhancement in LMDD is really kinematical or not. For this purpose it is very useful to analyse an Nn system produced diffractively by a process nN--'>n(1\fn) for an example, because we can compare directly the structure of the Nn system with that in the nN phase shift analyses. Preliminary partial wave analyses on the diffractively produced Nn system have recently been started. oJ~n According to their analyses and other data on the Nn LMDDsJ. g) it is indicated that the Nn mass distribution at the smallest It I region has a peak at MN <1.35 Ge V which is much lower than that expected from the masses of the resonances. We have already encountered similar phenomena in the pion photoproduction processes at the resonance region10 J or in the p photo­ production process.ll) These phenomena are considered to be due to an interference effect between a resonance production term and some kind of background term. In this paper we study the partial wave analyses of the Drell-Hiida-Deck (DHD) modeP2J and of the unitarized version of the DHD model by the final state interaction. We do not use the Reggeized DHD amplitude, because we are interest­ ed in LMDD up to the third resonance region at most and its partial wave analysis. (The reason why we do not use the Reggeized DHD and the interpolation of the elementary pion-exchange amplitude to the Reggeized one will be discussed in

A two-component model for two-body nucleon diffraction dissociation and comparison with data from π-p at 3.9 GeV/ c and p-p at fermilab and ISR energies

The isospin | M 1 2 o| 2 amplitude measured by means of π ±p interactions at 3.9 GeV/ c is compared to the low mass diffraction dissociation distributions in the process p+p→p+X at incident momentum from 175 to 400 GeV/ c and p+p→(nπ +)+p at 1500 GeV/ c. The comparison is made within the framework of a two-component model which predicts that the properties of the |M 1 2 o | 2 amplitude at 3.9 GeV/ c should be describe the p-p process. This predictio n is shown to be in excellent agreement with the high energy data.

Diffraction, the bare Pomeron, and the multifireball expansion

A specific multifireball model incorporating a bare Pomeron with intercept 0.85 and a renormalized Pomeron with intercept 0.99 is used to study diffraction in inelastic processes. It is concluded that this effect can be much larger than the easily accessible low mass diffraction cross section. In particular, it is noted that experimentally, events with maximum rapidity gap greater than 2 form half the inelastic cross section at 200 GeV/ c, and that charge transfer zero predominates across the maximum gap.