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  • The ATLAS Forward Proton Project

    27FEB2017 1AFP@CTU

    EYETS2016-2017

    SD DPEjj CEPjj

    2016 2017 

    W,Z,γ

    W,Z,γ

    γγ→

    XRP Near

    –206m

    XRP Far

    –218m PatchPanel

    –212m

    Roman Pots and Stations installed

    Detector Assembly started (lasts 2-6 weeks)

    • AFP Physics • AFP Detectors • Plans for Run 2 and beyond

    Michael Rijssenbeek

    for the AFP Collaboration p

  • The ATLAS Forward Proton Project

    AFP 0+2 – First phase completed in March 2016:

    – single arm with two detectors (silicon trackers) and a Level-1 Trigger: single proton tag and measurement

    – Physics: • special runs: soft single diffraction, single diffractive jets, diffractive W, jet-gap-jet, exclusive

    jet production, … 2016: ~10hr (0.5 pb–1 at µ≲0.3)

    • high-lumi runs to gauge beam environment and backgrounds … 2016: max~35, ~15 hr (2 pb

    –1), NO issues observed, clean beam environment, …

    AFP 2+2 – second phase to be completed in March 2017:

    – two arms (2 detectors per arm), with time-of-flight detectors in the 2nd (far) stations – Physics:

    • special runs ~10 hrs @ µ≲3: soft central diffraction, central diffractive jets, jet-gap-jet, γ+jet • standard runs at 15σ: exclusive jet production, anomalous couplings, …

    27FEB2017 2AFP@CTU

    ALFA AFP ATLAS AFP ALFA

    Q7 Q6 Q5 Q4 D2 D1 Q3 Q2 Q1 Q1 Q2 Q3 D1 D2 Q4 Q5 Q6 Q7 Beam 1 Beam 2

  • Soft Processes

    • Rapidity gap based measurement in ATLAS: does not distinguish SD from DD

    – More information about the process is available with forward proton tagging

    & measurement …

    • High cross sections; only low lumi needed ! Good purity requires low pile-up

    Pile-up: at high luminosity many (µ) soft

    interactions accompany the high pT event

    special runs

    27FEB2017 3AFP@CTU

    Eur. Phys. J. C72 (2012) 1926

    Single Diffraction (SD) Double Diffraction (DD) Non-DiffractiveCentral Diffraction (CD)Elastic Scattering

    Color-less exchange

    (Pomeron)

     Rapidity Gap

    O(10 mb) Cross sections

  • Kinematic Variables

    27FEB2017 4AFP@CTU

    t p

    p

    β

    IP

    x

    ' ,( )p  

    IP

    t1 1 11'( , )p  1p

    2

    IP ,

    1 2

    ( ' )

    1 '

    i i i

    i B

    ii

    j

    i

    j pp

    t p p

    E E

    x

    M M s

     

     

     

     

    disappears

    down the

    beam pipe

    β1

    Double Diffractive Jet Production

  • Origin of Forward Protons • High-ξ protons in ND and DD due to hadronization • Significant differences between MC generators  tune • Important also for simulating cosmic air showers

    27FEB2017 5AFP@CTU

    Single Diffraction (SD) Double Diffraction (DD) Non-Diffractive

    p

    p

  • Single Diffractive Jet Production Motivation:

    – Measure cross section and gap survival probability

    – Possible presence of Reggeon contribution?

    – Study Pomeron structure and universality between

    ep and pp

    27FEB2017 6AFP@CTU

    Dijet production in 7 TeV pp collisions with

    large rapidity gaps at the ATLAS experiment

    Details in: “LHC Forward Physics” CERN-PH-LPCC-2015-001, J. Phys. G: Nucl. Part. Phys. 43 (2016) 110201

    p

    p

    β

    IP

    x

    Example: purity and statistical significance for AFP and β* = 0.55 m

  • Single Diffractive W/Z Production Motivation:

    – Measure cross section and gap survival probability

    – Study Pomeron structure and flavor composition

    – Search for charge-asymmetry

    27FEB2017 7AFP@CTU

    W asymmetry studies published in: Phys.Rev. D 84 (2011) 114006; more details in J. Phys. G: Nucl. Part. Phys. 43 (2016) 110201

    Example: W→lν; purity and stat. significance for AFP and β*=0.55 m

    p

    p

    IP

    x

    β

    W, Z

  • Summary of Single p-Tag Processes

    27FEB2017 8

    2

    IP

    ( ' )

    1 '

    t p p

    E E

    x

     

     

    t p

    p

    β

    IP

    x

    ' ,( )p   disappears

    down the

    beam pipe

    AFP@CTU

  • 2016 Data: Alignment • Geometric Acceptance: position based on

    Sep 2016 AFP Beam-Based Alignment:

    • Pots inserted to 20σ from beam center, + dead region: 0.3 mm (thin window)

    + 0.3 mm (to active sensor): ξmin≃3.5%

    – 2016: Further improvement

    expected with

    recent re-

    calibration of pots

    & detectors

    ⇦ 2017: for 15σ approach

    ξmin≃2.5%

    27FEB2017 9

    Station AFP position from x=0

    [mm]

    Beam position from x=0

    [mm]

    NEAR -5.652 -1.612

    FAR -2.576 -0.419

    2017 expected 2017 expected

    AFP@CTU

    2017 projection 2017 projection

  • 2016 Data: Trigger Rates • Detailed trigger simulation agrees well with rate data over wide µ-range:

    • from this: Mean Hit-in-AFP probability per MinBias interaction (pile-up event):

    • Pythia predictions lower by 2×; model tune + background ?

    27FEB2017 10

    Hit Probability per

    Pile-up interaction

    NEAR Pot FAR Pot

    Data (many runs) 1.46% 2.06%

    Pythia (un-tuned) 0.64% 0.88%

    Probability of Proton Left+Right Topology in AFP

    Empty AFP

    Prediction 2017

    AFP@CTU

  • Double Pomeron Exchange Jet Production

    Motivation:

    – Measure cross section and gap survival probability

    – Possible presence of Reggeon contribution?

    – Study the gluon content of the Pomeron

    27FEB2017 11AFP@CTU

    See: J. Phys. G: Nucl. Part. Phys. 43 (2016) 110201

    p

    p

    IP

    β jet

    jet

    Example: purity and statistical significance for AFP and β* = 0.55 m

    varying the gluon pdf

    parameter ν

     1 2jj d

    d M s

     

  • Benchmark: DPEjj Process – Fast & Full simulation of AFP + ATLAS, including pile-up

    • generator: PYTHIA 8.165 with POMFLUX = 1, 5(MBR) • 100 h (1 wk); 2808 bunches, μ=1

    – Event Selections: • pT(jet)> 20, 50, 100 GeV • double proton tag in AFP • matching with AFP vertex

    from timing (σt = 30 ps)

    • single vertex in ATLAS

    27FEB2017 12AFP@CTU

  • DPE γ+Jet Production

    Motivation:

    – Measure cross section and gap survival probability

    – sensitive to quark content in Pomeron (at HERA one assumed that 𝑢 = 𝑑 = 𝑠 = 𝑢 = 𝑑 = 𝑠)

    27FEB2017 13AFP@CTU

    See: Phys. Rev. D 88 (2013) 7, 074029

    p

    p

    IP

    β γ

    jet

  • DPE Jet-Gap-Jet Production

    Motivation:

    – Measure cross section and gap survival probability

    – test the BFKL model

    27FEB2017 14AFP@CTU

    See: Phys. Rev. D 87 (2013) 3, 034010

    p

    p

    IP jet

    y-gap

    jet

    IP

  • Central Exclusive Jet Production

    Motivation:

    – Measure cross section at the LHC,

    gap survival probability

    – constrain other exclusive production

    processes (e.g. Higgs)

    – also possible with single-tag !

    27FEB2017 15AFP@CTU See: ATL-PHYS-PUB-2015-003

    p

    p

    jet

    jet

    See: Eur. Phys. J. C 75 (2015) 320 and Acta Phys. Pol. B 47 (2016) 1745

    µ=23 µ=23

    small σ

    high(er)

    luminosity

    needed !

  • EM: Di-Muon Production γγ→µµ

    • Measurement without AFP:

    exclusive and

    dissociated events …

    • But: cross section with AFP is too small for double-tag measurement

    – Add selections based on kinematic correlations – Single tag: σ=40 fb for pT≥10 GeV

    and AFP at 2 mm from the beam

    • Use for alignment and optics calibration !

    27FEB2017 16

    1   

    

    Difference Δξ = ξAFP – ξµµ

    50 μmx  0 μmx 

    AFP@CTU

  • Anomalous Quartic Couplings • Low Cross sections: ~few fb

    – AFP has a Missing-Mass resolution (from the proton measurements) of 2-4 %

    • Match with invariant central object mass is efficient: (Z→ee, γγ) – powerful rejection of

    non-exclusive backgrounds

    • Much interest in this from theory side – e.g. “LHC Forward Physics” CERN-PH-LPCC-2015-001)

    27FEB2017 17

    p p

    pp

    W, Z, γ

    W, Z, γ

    “Probing anomalous

    quartic gauge couplings

    using proton tagging at

    the Large Hadron

    Collider”, M. Saimpert,

    E. Chapon, S. Fichet, G.

    von Gersdorff, O. Kepka,

    B. Lenzi, C. Royon;