Low mass diffraction at ATLAS-LHCf

Low mass diffraction at ATLAS-LHCf Qi-Dong hou Nagoya University (JP) France-Japan SAKURA Workshop on small-x physics at the LHC 6..9

Outline Diffractive dissociation A MC study about contribution of diffractive and non-diffractive interactions to the LHCf spectra. Low-mass diffraction issue in the determination of inelastic cross section. ATLAS-LHCf common operation (MC study). Detector acceptance Efficiency and purity of diffraction identification by common data Detection of low-mass diffraction

Diffractive dissociation contribute 5%~% of total cross sections. P Pomeron quantum number of vacuum ξ P X Rapidity gap P M X X M X P Y M Y P P P P 4 X P P P P P (a) (b) (c) Single-diffraction Double-diffraction Central-diffraction Experimentally, the measurement of diffraction Tagging protons directly, Measuring the rapidity rap. ξ (fractional momentum loss of protons) strongly correlated with rapidity gap size ξ=(m(x)/ s ), Δη~-lnξ

Impact of diffraction collisions to Xmax Kinel= ΔE/E ~ exp(-δη) << (inelasticity) (ΔE: the energy loss of the leading secondary nucleon). diffraction collision is relate to the Xmax The higher rate of diffractive collision, the deeper Xmax S. Ostapchenko, et al., Phy. Rev. D 89, 749 (4) dσsd/dδη[mb] Δη σ σ + σ DD QGSJET-Ⅱ-4 Option σ σ + σ DD σ σ + σ DD Option + Option - QGSJET-Ⅱ-4 Option + 4

Issue of diffraction implemented in the model collisions: diffraction + non-diffraction = +DD+CD The excess of PYTHIA8 at E>TeV due to over contribution from diffraction 5

Forward photon spectrum comparison η>.94 dn γ /de inel /N p-p, s = TeV η>.94 p-p, s = TeV η>.94 Model comparison = diff. + non-diff. dn γ /de inel /N SIBYLL. p-p, s = TeV η>.94 dn γ /de inel /N PYTHIA8 p-p, s = TeV η>.94 SIBYLL. PYTHIA8 5 4 5 6 4 5 6 Models/ 4 5 6 5 5 4 5 6 4 5 6 @PYTHIA8 @EPOS LHC 6

Forward neutron spectrum comparison dn n /de inel /N p-p, s = TeV η>.94 η>.94 p-p, s = TeV η>.94 dn n /de SIBYLL. p-p, s = TeV η>.94 dn n /de SIBYLL. p-p, s = TeV η>.94 inel /N inel /N 5 4 5 6 4 5 6 Dominated by diff. or non-diff.? Models/ 5 4 5 6 5 4 5 6 4 5 6 7

σinel issue: low-mass diffraction cross section of TOTEM and ATLAS ALFA: optical theorem. ATLAS MBTS see 9~95% of all inelastic events. Invisible parts: low mass diffraction. Extrapolated at full range base on MC. Eur. Phys. J.C7 () 96 [mb] σ inel ATLAS (MBTS) ATLAS (ALFA) 9 TOTEM ALICE 8 LHCb Auger 7 pp (non-lhc) pp 6 5 4 arxiv:66.65 Pythia 8 EPOS LHC QGSJET-II ATLAS 7 8 9 8 75 7 65 LHC region 4 s ξ=(m(x)/ s ) ~ e -Δη ξ: fractional momentum loss of proton 8

dn events dn MBTS events n Data Diffractive mass distribution arxiv:66.65 Pythia8 SS Pythia8 DL, ε =.6 Pythia8 DL, ε =.85 Pythia8 DL, ε =. MBR Pomeron flux options in PYTHIA EPOS LHC QGSJET-II ATLAS - TeV, 6. µb Single-sided selection MC/data.5.5 4 6 8 n MBTS arxiv:5.894v )] (ξ X )[mb/log (ξ X dσ /dlog 6 4 )] (ξ )[mb/log (ξ /dlog dσ X X.4..8.6 7 6 log (ξ ) X SIBYLL. PYTHIA8-SS PYTHIA8-DL log (ξ ) X Regge trajectory: αp(t)=+ε+αt=.85+.5t as default Pomeron flux is an extremely important parameter for modeling diffraction 9

Investigation of PYTHIA8 diffraction dn γ /de inel /N p-p, s = TeV η>.94 η>.94 p-p, s = TeV η>.94 Pomeron flux options in PYTHIA dn γ /de inel /N PYTHIA8 DL p-p, s = TeV η>.94 dn γ /de inel /N PYTHIA8 p-p, s = TeV η>.94 Models/ 5 4 5 6 4 5 6 4 5 6 5 5 4 5 6 4 5 6 arxiv:5.894v Regge trajectory: αp(t)=.85+.5t as default PYTHIA8DL gives better agreement to ATLAS n(mbts) distribution [ATLAS-CONF- 5-8]. However,it give too much diffraction at E>TeV to LHCf spectra

LHCf has unique sensitivity to the lowmass diffraction, ATLAS rapidity rap information can classify the detected LHCf events to diffraction and non-diffraction. ATLAS-LHCf common experiment

Location of the LHCf experiment LHCf and ATLAS are observing the particles from the same collision, but different position. η=8.4 LHCf Arm η <.5 Collision η=-8.4 Gamma LHCf Arm

ATLAS-LHCf common operation LHCf ATLAS Final trigger DATA record LID hardware signals Final trigger DATA record Beam condition β*=9m μ=.~. Common data acquisition for the minimum bias measurement. LHCf detectors were incorporated into ATLAS readout system. LHCf triggers ATLAS with trigger rate ~4Hz. The event matching was done offline by using ATLAS LID. Event matching succeed, data analysis on going

Detector acceptance p p Δη p X M(x) ξ=(m(x)/ s ) ~ e -Δη Trigger efficiency (only with ) Trigger condition of LHCf Photon: Eγ > GeV : En > 5GeV ATLAS Pass MBTS hit selection Nhit> ) (N Efficiency MBTS.8.6.4...8.6.4 ATLAS Pythia SS Pythia SS DD QGSJet-II s = TeV Simulation SIBYLL. ATLAS-CONF-5-8 PYTHIA8 log (ξ) LHCf preliminary LHCf and ATLAS cover different diffractive mass range.. M(x)<GeV log (ξ ) X 4

LHCf event selection w/ ATLAS central trackers Δη Rapidity gap ATLAS Inner detector (tracking system) Condition: Charged particle (PT >MeV) number at η <.5 Diffractive like (ATLAS veto) Tracks = Tracks <= Tracks <= Tracks <=5 Efficiency.49.56.6.69 Purity.995.99.98.95 Efficiency.8.6 p-p, s = TeV : charged, η <.5, p >MeV T N Track = N Track <= N Track <= N Track <=5.4 identification: No charged particle (tracks=) at η <.5 was employed in this analysis. Non-Diff Central-Diff Single-Diff Double-Diff 5

Performance of w/ ATLAS veto for diffraction dn γ /de /N inel p-p, s = TeV η>.94 ATLAS veto η>.94 @veto @veto p-p, s = TeV η>.94 ATLAS veto @veto @veto : MC true ATLAS veto: tracks=@ η <.5 @veto overlap ATLAS veto dn γ /de /N inel SIBYLL. p-p, s = TeV η>.94 ATLAS veto @veto @veto dn γ /de /N inel 4 5 6 PYTHIA8 p-p, s = TeV η>.94 ATLAS veto @veto @veto 4 5 6 high diff. selection purity Miss selection efficiency = Diff.@ATLASveto Diff. Efficiency..5 η>.94 purity = Diff.@ATLASveto (Diff.+ NonDiff.)@ATLASveto Purity.. 4 5 6.5 SIBYLL. PYTHIA8. 4 5 6 High purity model independently. Efficiency ~5%, EPOS and QGSJET give almost consistent efficiency. 6

LHCf neutron spectrum w/ ATLAS veto p-p, s = TeV η>.94 @veto @veto η>.94 p-p, s = TeV η>.94 p-p, s = TeV 8.8<η<8.99 8.8<η<8.99 @veto @veto p-p, s = TeV 8.8<η<8.99 4 5 6 SIBYLL. p-p, s = TeV η>.94 4 5 6 PYTHIA8DL p-p, s = TeV η>.94 SIBYLL. p-p, s = TeV 8.8<η<8.99 4 5 6 PYTHIA8DL p-p, s = TeV 8.8<η<8.99 Model/EPOS 4 5 6 4 5 6 E SIBYLL. PYTHIA8DL 4 5 6 Model/EPOS 4 5 6 4 5 6 E 4 5 6 SIBYLL. PYTHIA8DL Efficiency. η>.94 Efficiency. 8.8<η<8.99.5.5 Purity.. 4 5 6 Purity...5 SIBYLL. PYTHIA8.5 SIBYLL. PYTHIA8 DL. 4 5 6. 4 5 6 7

LHCf spectrum w/ ATLAS veto p-p, s = TeV <P T <. <PT<. @veto @veto p-p, s = TeV <P T <. @veto @veto p-p, s = TeV.8<P T <..8<PT<. @veto @veto p-p, s = TeV.8<P T <. @veto @veto 4 5 6 4 5 6 SIBYLL. p-p, s = TeV PYTHIA8DL p-p, s = TeV <P T <. @veto @veto <P T <. @veto @veto SIBYLL. p-p, s = TeV.8<P T <. @veto @veto 4 5 6 PYTHIA8DL p-p, s = TeV.8<P T <. @veto @veto Model/EPOS 4 5 6 4 5 6 SIBYLL. PYTHIA8DL 4 5 6 p z Model/EPOS 4 5 6 4 5 6 4 5 6 p z SIBYLL. PYTHIA8DL Efficiency. <P T <. Efficiency..<P T <.4.5.5 Purity.. 4 5 6 P z Purity...5 SIBYLL. PYTHIA8.5 SIBYLL. PYTHIA8. 4 5 6 P z. 4 5 6 P z 8

Detection of low-mass diffraction The inefficiency parts of ATLAS-veto are high mass diff.. ATLAS-LHCf can access the low mass single diffraction region, with high efficiency, experimentally. σ QGSJET-Ⅱ-4 σ + σ DD CMS data Efficiency Detection efficiency of LHCf..8.6.4. SIBYLL. PYTHIA8 (ξ)[mb] dσ/dlog 4 p-p, s = TeV M(x)<5GeV M(x)<GeV (pp -> Xp) w/ ATLAS veto. log (ξ ) X log (ξ) 9

Summary The identification of diffraction can verify and improve the hadronic interaction models. The efficiency and purity of diffractive event identification by ATLAS-LHCf common operation were estimated. - The efficiency of diffraction identification is approximately 5%,with 99% purity. LHCf detectors have high sensitivity at log(ξ) < -6 Application of ATLAS veto to the LHCf data purifies low-mass diffraction event samples

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Photon spectrum comparison η>.94 8.8<η<8.99 p-p, s = TeV η>.94 Photon p-p, s = TeV η>.94 Photon p-p, s = TeV 8.8<η<8.99 Photon p-p, s = TeV 8.8<η<8.99 Photon SIBYLL. p-p, s = TeV η>.94 Photon PYTHIA8DL p-p, s = TeV η>.94 4 5 6 SIBYLL. p-p, s = TeV 8.8<η<8.99 Photon 4 5 6 PYTHIA8DL p-p, s = TeV 8.8<η<8.99 Photon 4 5 6 4 5 6 4 5 6 4 5 6 Models/ SIBYLL. PYTHIA8DL 4 5 6 Non-diff 4 5 6 Diff 4 5 6 Models/ 4 5 6 Non-diff 4 5 6 Diff 4 5 6

spectrum comparison η>.94 8.8<η<8.99 p-p, s = TeV η>.94 p-p, s = TeV η>.94 p-p, s = TeV 8.8<η<8.99 p-p, s = TeV 8.8<η<8.99 SIBYLL. p-p, s = TeV η>.94 PYTHIA8DL p-p, s = TeV η>.94 4 5 6 SIBYLL. p-p, s = TeV 8.8<η<8.99 4 5 6 PYTHIA8DL p-p, s = E TeV 8.8<η<8.99 Models/ 4 5 6 4 5 6 4 5 6 Non-diff SIBYLL. PYTHIA8DL 4 5 6 Diff 4 5 6 Models/ 4 5 6 4 5 6 4 5 6 Non-diff 4 5 6 Diff 4 5 6

spectrum comparison <PT<..8<PT<. p-p, s = TeV <P T <. p-p, s = TeV <P T <. p-p, s = TeV.<P T <.4 p-p, s = TeV.<P T <.4 SIBYLL. p-p, s = TeV <P T <. PYTHIA8DL p-p, s = TeV <P T <. 4 5 6 4 5 6 SIBYLL. p-p, s = TeV PYTHIA8DL p-p, s = TeV.<P T <.4.<P T <.4 Models/ 4 5 6 P z 4 5 6 4 5 6 Non-diff SIBYLL. PYTHIA8DL 4 5 6 Diff 4 5 6 P z P z P z Models/ 4 5 6 P z 4 5 6 4 5 6 Non-diff 4 5 6 Diff 4 5 6 P z P z P z 4

/N inel Low mass diffraction (photon) p-p, s = TeV η>.94 LM η>.94 /N inel p-p, s = TeV η>.94 LM M(x)<5GeV /N inel p-p, s = TeV 8.8< η<8.99 8.8<η<8.99 LM /N inel p-p, s = TeV 8.8< η<8.99 LM /N inel 4 5 6 4 5 6 SIBYLL. = TeV p-p, s PYTHIA8 p-p, s = TeV η>.94 LM /N inel η>.94 LM /N inel 4 5 6 SIBYLL. p-p, s = TeV 8.8<η<8.99 LM /N inel 4 5 6 PYTHIA8 p-p, s = TeV 8.8<η<8.99 LM 4 5 6 4 5 6 4 5 6 4 5 6 /N inel p-p, s = TeV η>.94 LM p-p, s = TeV η>.94 LM /N inel p-p, s = TeV 8.8< η<8.99 LM /N inel p-p, s = TeV 8.8< η<8.99 LM /N inel SIBYLL. p-p, s = TeV η>.94 LM PYTHIA8 η>.94 p-p, s = TeV LM /N inel 4 5 6 SIBYLL. p-p, s = TeV 8.8< η<8.99 LM /N inel 4 5 6 PYTHIA8 p-p, s = TeV 8.8< η<8.99 LM 4 5 6 4 5 6 4 5 6 4 5 6 5

/N inel Low mass diffraction (neutron) p-p, s = TeV η>.94 η>.94 p-p, s = TeV η>.94 M(x)<5GeV /N inel p-p, s = TeV 8.8<η<8.99 8.8<η<8.99 LM /N inel p-p, s = TeV 8.8<η<8.99 LM LM LM /N inel SIBYLL. p-p, s = TeV η>.94 PYTHIA8 η>.94 p-p, s = TeV /N inel 4 5 6 SIBYLL. p-p, s = TeV 8.8<η<8.99 LM /N inel 4 5 6 PYTHIA8 p-p, s = TeV 8.8<η<8.99 LM 4 5 6 LM 4 5 6 LM 4 5 6 4 5 6 /N inel p-p, s = TeV η>.94 LM /N inel p-p, s = TeV η>.94 LM /N inel p-p, s = TeV 8.8< η<8.99 LM /N inel p-p, s = TeV 8.8< η<8.99 LM /N inel SIBYLL. p-p, s = TeV η>.94 LM /N inel 4 5 6 PYTHIA8 p-p, s = TeV η>.94 LM /N inel 4 5 6 SIBYLL. p-p, s = TeV 8.8<η<8.99 LM /N inel 4 5 6 PYTHIA8 p-p, s = TeV 8.8<η<8.99 LM 4 5 6 4 5 6 4 5 6 4 5 6 6

/σ inel p-p, s = TeV <PT <. Low mass diffraction ( ) <PT<. LM /σ inel p-p, s = TeV <PT <. LM M(x)<5GeV /σ inel p-p, s = TeV.8<PT <..8<PT<. LM /σ inel p-p, s = TeV.8<PT <. LM /σ inel 4 5 6 SIBYLL. p-p, s = TeV <P <. T LM /σ inel 4 5 6 PYTHIA8 p-p, s = TeV <P <. T LM /σ inel 4 5 6 SIBYLL. p-p, s = TeV.8<P <. T LM /σ inel 4 5 6 PYTHIA8 p-p, s = TeV.8<P <. T LM 4 5 6 4 5 6 4 5 6 4 5 6 p-p, s = TeV <PT <. LM p-p, s = TeV <PT <. LM p-p, s = TeV.8<PT <. LM p-p, s = TeV.8<PT <. LM /σ inel /σ inel /σ inel /σ inel SIBYLL. p-p, s = TeV <P <. T LM PYTHIA8 p-p, s = TeV <P <. T LM /σ inel 4 5 6 SIBYLL. p-p, s = TeV.8<P <. T LM /σ inel 4 5 6 PYTHIA8 p-p, s = TeV.8<P <. T LM 4 5 6 4 5 6 4 5 6 4 5 6 7