AFP Introduction

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ALFA and AFP Detectors

• t=-pT2 and x= DE/E0

• In diffraction, coherent interaction of proton is soft pT ~ 1 GeV• Elastic scattering: x= 0, diffraction: x<0.2

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MAD-X + MC generator-level

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Very low luminosity

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• ATLAS and CMS agree within systematic uncertainties (hadron | |h <4.7 vs. | |h <4.9: 5%Diff. model for unfolding: 10%)

1) CMS sytematically above ATLAS2) Pythia8 predicts SD~DD

• Proton tagging could shed light on 1) and 2)• More generally, the possibility to tag diffractive protons with AFP will improve the

quality of the interpretation• Underlying event• MPI• All the other soft QCD measurements performed using only the central detector

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Low/Medium luminosity

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“Standalone” MC simulations

High lumi program

• QUARTIC Gauge Couplings – testing BSM models

• Reaching limits predicted by string theory and grand unification models (10-

14-10-13 for gggg)• Exc. Jets – verification of QCD production

models, unintegrated gluon PDFs• Program will be discussed in ATLAS when

data on beam background available• gggg requires moderate timing, the

other final states ≤ 10 ps

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Exclusive Jets

γ

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First Integrated AFP Prototype

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The AFP Testbeam Team

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Tracking-Timing Correlations(Preliminary Analysis)

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Time resolution between LQbars(Preliminary Analysis)

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Oscilloscope Measurement

HV=1900 V

Conclusions• AFP will give ATLAS the possibility to complete and

enhance the forward physics program initiated by ALFA• ALFA and AFP have complementary characteristics for

high b* running• AFP has unique characteristics for low b* running and

will allow to exploit an interesting QCD program at low-m, and an exciting program at high-m, if the beam background conditions will allow the latter

• The detector, including its beam interface, will be built using very advanced and solid technology

• A prototype of the full detector (tracking+timing) has been recently tested on beam successfully proving the integration of the two parts in a common TDAQ scheme

• The group has proven motivation and skill in the last years and the collaboration with ALFA is now well grounded

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Backup

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ATLAS and its Forward Detectors

• Example of ATLAS measurement• Rapidity gap cross sections• ALFA elastic ds/dt and stot at sqrt(s) = 7 TeV

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AFP

LUCID

p-p @14 TeV (DPMJET)

Running Scenario at low-m

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Program approved by ATLAS (pending resources)No or loose (~50 ps) timing needed from AFP

Importance of ToF

• Significance >100 for 0.1<m<1 also with no ToF

• Factor 10 pile-up reduction in AFP for m~50 for ToF with Dt~10 ps

• Conclusion: High performance ToF needed mainly for the high-lumi program (and not for the approved program in RUN2)

• AFP trigger is instead needed for RUN2: but in this case also a system based on scintillators or Silicon/Diamond will be sufficient to fully exploit the approved program

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0.3

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AFP Full Simulation

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Full Simulation results

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AFP Detector System Performance

• Results from full simulation of AFP detectors and the whole forward region

• Mild degradation of performance due to pile-up• Detector capable of running in pile-up conditions• x acceptance in the range 1.5%-15%

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Classification of diffractive events

• Diffractive and elastic events: ~ 40% of LHC pp collisions• Traditional measurements use rapidity gap method to

separate contributions of inelastic non diffractive production• ATLAS has |h|<4.9 coverage which doesn’t work for “too”

small (order of 10 GeV) Mx=sqrt(sx) of diffractive system because Dh=-log(x)• The Indirect measurement of x via energy seen in calorimeter

is not very precise due to invisible energy and it works only in a limited region of x

• No measurement of t• Proton tagging is the only way for a more detailed probing

of diffraction

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Diffractive processes at ATLAS

• Forward rapidity gaps defined as larger DhF region on detector edge (h=±4.9) devoid of pT>200 MeV particles

• Measured ds/ DhF ~ 1 mb for DhF > 3• Default PHOJET and PYTHIA do not describe

the rise of the cross section observed at DhF > 5• Rise interpreted from a triple Pomeron

contribution with a Pomeron intercept aP(0) > 1

• Slope very sensitive to the precise value of aP(0)

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Eur. Phys. J. C72 (2012) 1926

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The AFP detectors

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• Purpose:Tag and measure diffractive protons at 210 m (two arms) providing x, t

• Precision MASS SPECTROMETER. In case of exclusive production (Double Tag)

M= sqrt(x1x2s) • Detectors (in 2+2 Horizontal RP)• Radiation hard “edgeless” 3D Silicon detectors

with ~mrad angular resolution for proton tracks reconstruction (204m,212m)

• High performing timing detectors (212m)(~ 10ps resolution, for proton pile-up background rejection at high mu)

0.3

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Horizontal RPHorizontal RP

AFP Detector System

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Tracking+Timing in one RP

1 1XM s

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