Probing the Pomeron quark structure using γ+jet and dijet events

Transcription

1 Probing the Pomeron quark structure using γ+jet and dijet events M. Saimpert, C. Royon, D. Werder, C. Marquet CEA Saclay - Irfu/SPP May 16th 2013 Probing the Pomeron quark structure using γ+jet and dijet events May 16th / 17

2 Introduction Resolved Pomeron model Protons interact via a double Pomeron exchange Diffractive mass produced from the interaction of two quarks/gluons from each of Pomerons Probing the Pomeron quark structure using γ+jet and dijet events May 16th / 17

3 Introduction Resolved Pomeron model Protons interact via a double Pomeron exchange Diffractive mass produced from the interaction of two quarks/gluons from each of Pomerons Pomeron structure Never been checked experimentally at 14 TeV Constraints exist on the sum of quark density and the gluon distribution from F2 D measurement (HERA) assuming the Pomeron is made of quarks and gluons u=d=s and q=qbar have been assumed so far Probing the Pomeron quark structure using γ+jet and dijet events May 16th / 17

4 Introduction Resolved Pomeron model Protons interact via a double Pomeron exchange Diffractive mass produced from the interaction of two quarks/gluons from each of Pomerons Pomeron structure Never been checked experimentally at 14 TeV Constraints exist on the sum of quark density and the gluon distribution from F2 D measurement (HERA) assuming the Pomeron is made of quarks and gluons u=d=s and q=qbar have been assumed so far With the LHC Possible check of Pomeron universality between hadronic and ep colliders New constraints on quark densities difference Probing the Pomeron quark structure using γ+jet and dijet events May 16th / 17

5 Introduction Resolved Pomeron model Protons interact via a double Pomeron exchange Diffractive mass produced from the interaction of two quarks/gluons from each of Pomerons Pomeron structure Never been checked experimentally at 14 TeV Constraints exist on the sum of quark density and the gluon distribution from F2 D measurement (HERA) assuming the Pomeron is made of quarks and gluons u=d=s and q=qbar have been assumed so far With the LHC Possible check of Pomeron universality between hadronic and ep colliders New constraints on quark densities difference Other models as Soft Color Interaction (SCI) model does not use Pomeron to describe DPE Probing the Pomeron quark structure using γ+jet and dijet events May 16th / 17

6 Why γ+jet and dijet events? γ+jet inclusive production Herwig process ID 1800 Main mechanism : q+g High σ dependance on quark PDFs σ 1 pb after cuts and selection dijet inclusive production Herwig process ID 1500 Main mechanism : g+g Low σ dependance on quark PDFs σ 1,000 pb after cuts and selection All leading order subprocesses implemented Purpose: evaluate σ γ+jet σ dijet for various PDFs patterns to determine if measurement is sensitive to Pomeron quark structure Probing the Pomeron quark structure using γ+jet and dijet events May 16th / 17

7 Herwig ID 1800 and 1500: list of Subprocesses Probing the Pomeron quark structure using γ+jet and dijet events May 16th / 17

8 Simulation parameters and Cuts FPMC generator has been used (N = 1,000,000 events for each interaction) < ξ < 0.15 (AFP 210 metres) < ξ < 0.15 (AFP metres) Jet reconstruction with antikt algorithm (FastJet package) R = 0.6 (ATLAS Standard) p T,jet(s) > 20 GeV Photon selection: p T,γ > 20 GeV Photons and jets are central in ATLAS (η < 2.5) Data normalized for L = 300pb 1 (3 weeks low luminosity dedicated run) u+d+s = constant, d=s and d/u {0.25,0.5,1,2,4} u+d+s = constant, d=u and d/s {0.25,0.5,1,2,4} Probing the Pomeron quark structure using γ+jet and dijet events May 16th / 17

9 d/u results : cross-section ratio dijet /σ d = s, u + d + s = const. γjet σ < ξ < d/u Cross-sections after jet and γ selection (p T > 20 GeV ) Cross-sections ratio varies by a factor 2.5 Probing the Pomeron quark structure using γ+jet and dijet events May 16th / 17

10 d/u results : p T,jet differential cross-section ratio, s = 14 TeV 3 10 T T γ+jet 1 d = s, u + d + s = const., d/u = 1 ; L = 300pb; < ξ < 0.15 events 300 /dp dijet /dσ /dp γjet dσ T T 3 10 d = s, u + d + s = const < ξ < 0.15 d/u = 0.25 d/u = 0.5 d/u = 1 d/u = 2 d/u = 4 Dijet p (GeV) 1 d = s, u + d + s = const., d/u = 1 ; L = 300pb; < ξ < 0.15 events p (GeV) T p (GeV) Cross-sections integrated on 2.5 GeV bins Cross-sections ratio varies by a factor 4 Jet Energy Scale (JES) systematics should compensate (but not resolution) Statistical uncertainty driven by γ+jet Probing the Pomeron quark structure using γ+jet and dijet events May 16th / 17

11 d/u results : p T,jet differential cross-section ratio, s = 14 TeV Statistical uncertainty (L = 300 pb 1, AFP 210m) γjet events/dijets events pt(gev) Probing the Pomeron quark structure using γ+jet and dijet events May 16th / 17

12 d/u results : p T,jet differential cross-section ratio, s = 14 TeV Statistical uncertainty (L = 300 pb 1, AFP m) γjet events/dijets events pt(gev) Probing the Pomeron quark structure using γ+jet and dijet events May 16th / 17

13 d/u results : M p p (= ξ 1 ξ 2 s) differential cross-section ratio, s = 14 TeV 3 10 /dm dijet /dm/dσ γjet dσ d = s, u + d + s = const < ξ < Ldt=300pb d/u = 0.25 d/u = 0.5 d/u = 1 d/u = 2 d/u = 4 γ+jet Dijet events d = s, u + d + s = const., d/u = 1 ; L = 300pb; < ξ < M(GeV) 1 d = s, u + d + s = const., d/u = 1 ; L = 300pb; < ξ < events M(GeV) M(GeV) Cross-sections integrated on 250 GeV bins Cross-sections ratio varies by a factor 1.5 Systematics should almost compensate (AFP measurement) Statistical uncertainty driven by γ+jet Probing the Pomeron quark structure using γ+jet and dijet events May 16th / 17

14 d/u results : M p p (= ξ 1 ξ 2 s) differential cross-section ratio, s = 14 TeV 3 10 /dm dijet /dm/dσ γjet dσ d = s, u + d + s = const < ξ < Ldt=300pb d/u = 0.25 d/u = 0.5 d/u = 1 d/u = 2 d/u = 4 γ+jet Dijet events d = s, u + d + s = const., d/u = 1 ; L = 300pb ; < ξ < M(GeV) 1 d = s, u + d + s = const., d/u = 1 ; L = 300pb ; < ξ < events M(GeV) M(GeV) Cross-sections integrated on 250 GeV bins Cross-sections ratio varies by a factor 2.5 Systematics should almost compensate (AFP measurement) Statistical uncertainty driven by γ+jet Probing the Pomeron quark structure using γ+jet and dijet events May 16th / 17

15 M p p (= ξ 1 ξ 2 s) observable : A way to discriminate Pomeron from SCI model? events γjet/dijets d = s, u + d + s = const < ξ < 0.02 d/u = 0.25 d/u = 0.5 d/u = 1 d/u = 2 d/u = 4 SCI model M(GeV) Need to be out from the SCI background : ξ < 0.02 (probably overestimated) SCI : flat distribution Preliminary plot Probing the Pomeron quark structure using γ+jet and dijet events May 16th / 17

16 Conclusion γ+jet/dijet events study is a good probe of Pomeron structure Requires dedicated low luminosity runs Measurement would be relevant as of L = 300 pb 1 ( 3 weeks of data) with AFP 210 m Statistical uncertainty driven by γ+jet Probing the Pomeron quark structure using γ+jet and dijet events May 16th / 17

17 Conclusion γ+jet/dijet events study is a good probe of Pomeron structure Requires dedicated low luminosity runs Measurement would be relevant as of L = 300 pb 1 ( 3 weeks of data) with AFP 210 m Statistical uncertainty driven by γ+jet Test of the Pomeron model Universality of the Pomeron between ep (HERA) and hadronic (LHC) colliders New constrains on quark PDFs are possible with the LHC Probing the Pomeron quark structure using γ+jet and dijet events May 16th / 17

18 Conclusion γ+jet/dijet events study is a good probe of Pomeron structure Requires dedicated low luminosity runs Measurement would be relevant as of L = 300 pb 1 ( 3 weeks of data) with AFP 210 m Statistical uncertainty driven by γ+jet Test of the Pomeron model Universality of the Pomeron between ep (HERA) and hadronic (LHC) colliders New constrains on quark PDFs are possible with the LHC Possible way to discriminate Pomeron model from Soft Color Interaction model (preliminary results) Probing the Pomeron quark structure using γ+jet and dijet events May 16th / 17

19 Conclusion γ+jet/dijet events study is a good probe of Pomeron structure Requires dedicated low luminosity runs Measurement would be relevant as of L = 300 pb 1 ( 3 weeks of data) with AFP 210 m Statistical uncertainty driven by γ+jet Test of the Pomeron model Universality of the Pomeron between ep (HERA) and hadronic (LHC) colliders New constrains on quark PDFs are possible with the LHC Possible way to discriminate Pomeron model from Soft Color Interaction model (preliminary results) Study of d/s in progress. A paper is being drafted. Probing the Pomeron quark structure using γ+jet and dijet events May 16th / 17

20 Back-up slides May 16th / 17 Back-up slides M. Saimpert, C. Royon, D. Werder, C. Marquet CEA Saclay - Irfu/SPP May 16th 2013

21 Back-up slides May 16th / 17 F D 2 variations F 2d F 2d d/u

22 d/u results : cross-section ratio dijet /σ d = s, u + d + s = const. γjet σ < ξ < d/u Cross-sections after jet and γ selection (p T > 20 GeV ) Cross-sections ratio varies by a factor 2.5 Back-up slides May 16th / 17

23 d/u results : p T,jet differential cross-section ratio Back-up slides May 16th / T T γ+jet 1 d = s, u + d + s = const., d/u = 1 ; L = 300pb ; < ξ < 0.15 events 500 /dp dijet /dσ /dp γjet dσ T T 3 10 d = s, u + d + s = const < ξ < 0.15 d/u = 0.25 d/u = 0.5 d/u = 1 d/u = 2 d/u = 4 Dijet events p (GeV) 1 d = s, u + d + s = const., d/u = 1 ; L = 300pb ; < ξ < p (GeV) T p (GeV) Cross-sections integrated on 2.5 GeV bins Cross-sections ratio varies by a factor 4 Jet Energy Scale (JES) systematics should compensate (but not resolution) Statistical uncertainty driven by γ+jet