Extrac'ng Photon PDF and Proton PDFs at an EIC. Xiaoxuan Chu 褚晓璇 USTC, 9/11/2018

Transcription

1 Extrac'ng Photon PDF and Proton PDFs at an EIC Xiaoxuan Chu 褚晓璇 USC, 9//8

2 Outline. Possible realizations of an EIC. Photon structure studied at erhic Motivation and Introduction (Un)polarized photon structure Calculation of the underlying events effect 3. Extracting proton PDFs from EIC by a global analysis 4. Summary and outlook USC seminar Extracting Photon PDF and Proton PDFs at an EIC November 9, 8 / 3

3 Questions an EIC aims to answer he core questions described in the EIC white paper How are the sea quarks and gluons, and their spins, distributed in space and momentum inside the nucleon? - Polarization How do color-charged quarks and gluons distributed with a nuclear medium? - A range of center of mass energies & High Luminosity What happens to the gluon density in nuclei? Where does the saturation of gluon densities set in? - Ion beams hese questions call for facilities with capabilities that far exceed any current or past colliding beams accelerator facility: Electron Ion Collider (EIC) USC seminar Extracting Photon PDF and Proton PDFs at an EIC November 9, 8 3 / 3

4 Deep Inelastic Scattering Q = sxy s: center-of-mass energy squared Q : Resolution power x: he fraction of the nucleon s momentum carried by the struck quark y: Inelasticity Electron beams provide point-like probe - resolution Dit, model independent determination of partonic kinematics of physics processes High pision & access to partonic kinematics through scattered lepton Probe has complex structure No simple access to partonic kinematics USC seminar Extracting Photon PDF and Proton PDFs at an EIC November 9, 8 4 / 3

5 Physics cases of EIC in US BNL JLAB erhic: Center-of-mass energy (Ecm) of (9-4) GeV A luminosity of up to 34 cm s High polarization of electron and ion beams with frequent changes to the spin dition with polarizations well above 7% Collisions of electrons with a large range of light to heavy ions (protons to Gold ions) USC seminar Extracting Photon PDF and Proton PDFs at an EIC November 9, 8 5 / 3

6 Photon structure studied at EIC: Motivation Behavior of the exchanged photon: dit photon state, resolved photon state he internal structure of photons is a manifestation of quantum fluctuations: photon splits into parton content Photoproduction: low Q Parton Distribution Functions(PDFs) of Photon: q(x,q ), g(x,q ) Resolved state Dit state e γ q q q q e γ q q P P USC seminar Extracting Photon PDF and Proton PDFs at an EIC November 9, 8 6 / 3

7 Motivation: Existing experiment results [arxiv:9544, arxiv:978, Eur. Phys. J. C, (999), DESY 97-64] Lack of statistic, especially in the small x γ region which is important for the constrain of photon PDFs. Results from jet and charged particle measurements show that the best fit are GRV and SAS he nature of e + e collisions is two photon physics, the photon structure is very important for ILC γγ option. Polarized photon PDFs are never measured before. USC seminar Extracting Photon PDF and Proton PDFs at an EIC November 9, 8 7 / 3

8 Low Q tagger Outgoing electrons are onstructed in the tagger Acceptance for electrons is down to 5 GeV USC seminar Extracting Photon PDF and Proton PDFs at an EIC November 9, 8 8 / 3

9 Di-jet measurment Resolved process Dit process e γ q q q q e γ q q P P How to separate: Resolved: x γ < ; dit: x γ =. xγ = E (p ey e η + p e η ), y = Eγ. E e Parton densities can be extracted by measuring di-jet cross section: d σ dx γ dq = γ flux f γ(x γ, Q, µ) f p(x p, µ) σ ij, γ flux is calculable in QED, f p is the PDF of the proton, σ ij is the cross section of the hard process, which is calculable in pqcd USC seminar Extracting Photon PDF and Proton PDFs at an EIC November 9, 8 9 / 3

10 Reproduce HERA data Reproduce the inclusive cross section, photon PDF set is SAS, proton PDF is CEQ5m, 5 GeV < Q <GeV, L = fb. γp σ [µb] 8 6 Q =. GeV PYHIA HERA Data [µb] γp σ 4 Q =.5 GeV PYHIA HERA Data subprocess fraction.8 PYHIA resolved VMD dit. subprocess fraction.8 PYHIA. resolved VMD dit -5-4 [HERA Data: Phys. Rev. D 96 4(7)] -3 x Bj USC seminar Extracting Photon PDF and Proton PDFs at an EIC November 9, 8 / x Bj

11 Reproduce HERA data Reproduce the di-jet cross section, photon PDF set is SAS, proton PDF is CEQ5m, 5 GeV < Q <GeV. [nb] ) ) jets d σ dlog((e γ dx PYHIA H Data 6 x γ =.75 ( ) 5 x γ =.75 ( ) 4 x γ =.5 ( ) 3 x γ =.5 ( ) x γ =.3 ( ) Kinematics cuts from HERA: 7.5GeV 8 GeV,. < y <.83, η jets <, < η jet + η jet < 4, E jet E jet E jet, Ejet > 7.5GeV, + E jet > GeV, E jet /(Ejet +E jet ) <.5 Our simulation can match the existing data x γ =..3 ( ) x γ =.. (E 3 jets ) [GeV ] USC seminar Extracting Photon PDF and Proton PDFs at an EIC November 9, 8 / 3

12 Unpolarized photon structure at EIC GeV 5 GeV,. < y <.95, two highest p jets, p jet η jets < 4.5, stable particle p > 5 MeV. > 5GeV, p jet > p jet > 4.5 GeV, gen γ x.8 counts xγ. Resolved Dit x γ Di-jet method provides a good way to onstruct x γ, we can separate resolved/dit process(x γ < ). USC seminar Extracting Photon PDF and Proton PDFs at an EIC November 9, 8 / 3

13 Unpolarized photon structure at EIC GeV 5 GeV,. < y <.95, two highest p jets, p jet η jets < 4.5, stable particle p > 5 MeV. > 5GeV, p jet > p jet > 4.5 GeV, [nb] σ d ) ) di-jet dlog((p γ dx Ldt = fb x γ =.7- ( ) 6 x γ =-.7 ( ) 5 x γ =.5- ( ) 4 x γ =-.5 ( ) 3 x γ =.3- ( ) x γ =.-.3 ( ) x γ =.-. ( ) x γ =.-. di-jet (p ) [GeV ] he simulation shows the capability to measure the cross section for di-jet production at L = fb, with high accuracy in a wide kinematic range at EIC and extract the unpolarized photon PDFs from a global fit. USC seminar Extracting Photon PDF and Proton PDFs at an EIC November 9, 8 3 / 3

14 EIC advantages compared to HERA EIC [nb] σ d ) ) jets dlog((e γ dx HERA stat. uncertainty stat. uncertainty GeV < E jets H data.5 < GeV PYHIA HERA, µ PYHIA HERA, µ PYHIA HERA, µ - EIC, Ldt = fb = = = xγ x γ g HERA x γ range EIC x γ range - x γ High luminosity to define the uncertainty band Feasiblity to probe small x γ region USC seminar Extracting Photon PDF and Proton PDFs at an EIC November 9, 8 4 / 3

15 Method of flavor tagging he photon is in the hadronic state, can we expect to know the information of the parton content inside the photon? d σ dx γ dq = γ flux f γ(x γ, Q, µ) f p(x p, µ) σ ij From measuring the di-jet cross section, we can extract the total PDFs of the photon. We search the possibility of q/g discrimination. (will be discussed later) We do flavor tagging to achieve the goal of separating the contribution from different flavor partons. USC seminar Extracting Photon PDF and Proton PDFs at an EIC November 9, 8 5 / 3

16 Method of flavor tagging We will separate q/g jet first and select the jet from the parton which has the same flavor as the beamparton, which is marked with "jet from the photon side". USC seminar Extracting Photon PDF and Proton PDFs at an EIC November 9, 8 6 / 3

17 How to choose the jet from the photon side hadrons,η Lab > electrons,η Lab< counts 3.8 Jet from the photon side.6 qg qg qq qq.4 gq gq. gg gg Jet from the proton side qg qg qq qq gq gq gg gg counts.4. 3 qg qg qq qq gq gq gg gg jet η 4 4 η η γ p Conclusion: Influenced by the moving dition of the incoming electrons, the jets from the photon which is radiated from the electron, the pseudo-rapidity of jet from the photon is smaller than that of proton side jet What we can do in the experiment: take the jet with smaller η as the photon side jet USC seminar Extracting Photon PDF and Proton PDFs at an EIC November 9, 8 7 / 3

18 Flavor tagging he correlation between the beamparton flavor and the type of the leading hadron inside photon side jet. P P u quark u quark no cut p fraction> d quark p fraction> d quark s quark 5 p 5 K π π K p 5 5 p + K π 5 + π K p p5 K 5 π π K p s quark USC seminar Extracting Photon PDF and Proton PDFs at an EIC November 9, 8 8 / 3

19 Flavor tagging he correlation between the beamparton flavor and the type of the leading hadron inside photon side jet. P P π + π p fraction>.3 p fraction> p fraction> K s 5 u d d u s g s5 u d d u s g USC seminar Extracting Photon PDF and Proton PDFs at an EIC November 9, 8 9 / 3 K

20 USC seminar Extracting Photon PDF and Proton PDFs at an EIC November 9, 8 / 3

21 γ γ γ γ Input for polarized ep collision pol. photon PDFs pol. proton PDF min: f γ = ; max: f γ = f γ DSSV A γ = f γ /f γ u A max.pol.γ min.pol.γ d A x γ A s A g x γ USC seminar Extracting Photon PDF and Proton PDFs at an EIC November 9, 8 / 3

22 Polarized photon structure d σ dx γdq = γ flux f γ (x γ, Q, µ) f p (x p, µ) σ ij [nb] ) ) di-jet d σ dlog((p γ dx (p - Ldt = fb di-jet ) 7 x γ =.7- ( ) 6 x γ =-.7 ( ) 5 x γ =.5- ( ) 4 x γ =-.5 ( ) 3 x γ =.3- ( ) x γ =.-.3 ( ) x γ =.-. ( ) x γ =.-. 3 ] [GeV σ = (σ++ σ + ) he simulation shows the capability to measure the polarized cross section for di-jet production, with high accuracy in a wide kinematic range at EIC. First measurement of polarized photon PDFs with high pision. Flavor tagging can also be applied in polarized case. USC seminar Extracting Photon PDF and Proton PDFs at an EIC November 9, 8 / 3

23 A LL = σ/σ A LL L = fb, x < γ max.pol.γ min.pol.γ A LL xγ > di jet p [GeV] di jet p [GeV] A LL.5.4 γ x < A LL.5.4 γ x > di jet η di jet η he difference between max.pol. photon and min.pol. photon can be measured in experiment, the pol.photon PDFs can be constrained at EIC. USC seminar Extracting Photon PDF and Proton PDFs at an EIC November 9, 8 3 / 3

24 Underlying events: region method Underlying events: everything except the particles fragmented from the hard scatted partons. rigger Jet Dition φ ransverse oward Away ransverse φ π Away ransverse rigger Jet oward ransverse Away hree regions: ( Φ = Φ part Φ Jet ) Measurments: oward: Φ < 6 ransverse: 6 < Φ < Away: Φ > Charged multiplicity density, sum pt density Versus Φ Charged multiplicity density, sum pt density Versus p Jet η USC seminar Extracting Photon PDF and Proton PDFs at an EIC November 9, 8 4 / 3

25 Results from region method in 3.6 degree bin ch N..8. rigger jet p >5 GeV rigger jet p >8 GeV oward ransverse Away φ [rad] in 3.6 degree bin sum p rigger jet p >5 GeV rigger jet p >8 GeV oward ransverse Away φ [rad] in GeV/c bin ch N 4 oward Away ransverse rigger jet p [GeV] (GeV) in GeV/c bin Sum p rigger jet p [GeV] USC seminar Extracting Photon PDF and Proton PDFs at an EIC November 9, 8 5 / 3

26 Off-axis method Look at jets with high momentum, jet by jet wo off-axis cones are centered at the same η as the jet but ±π away in Φ from the jet ake the particles inside the cones as from underlying events. By using this method, the dependence on η is considered. USC seminar Extracting Photon PDF and Proton PDFs at an EIC November 9, 8 6 / 3

27 Comparison of the two methods d N /dφdη in GeV bin ch region method off axis method sum /dφdη in GeV bin p rigger jet p [GeV] d rigger jet p [GeV] Results from two different method are consistent, the dependence on η is minor he underlying event effect from EIC is comparable with the results from s = 5 GeV pp collisions at SAR USC seminar Extracting Photon PDF and Proton PDFs at an EIC November 9, 8 7 / 3

28 Proton PDFs extracted from inclusive CC ep scattering High x and high Q events he reduced cross section for inclusive Charged Current ep scattering are defined as σ r,cc = πx Bj [ M G W +Q ] d σ CC F MW dx Bj, in HERAFitter, the value of dq G F =.6 5 GeV and M W = GeV. CC structure function are defined as σ r,cc (xu + ( y) x D), U = xu + xc, D = x d + x s USC seminar Extracting Photon PDF and Proton PDFs at an EIC November 9, 8 8 / 3

29 Inclusive cross section σ/dxdq d - e p νx (CC), σ/dxdq d - e p νx (CC), - - heory/data EICsym Data Q δ δ uncorrelated total heory + shifts =.. HERAPDF. HERAPDF.-profiled x heory/data - EICsym Data Q δ uncorrelated = 3 δ total HERAPDF. -3 heory + shifts HERAPDF.-profiled x σ/dxdq d - e p νx (CC), - - σ/dxdq d - - e p νx (CC), heory/data -3-4 EICsym Data Q δ uncorrelated = heory/data - EICsym Data Q δ uncorrelated δ total δ total HERAPDF. HERAPDF. -5 heory + shifts HERAPDF.-profiled heory + shifts HERAPDF.-profiled x x = 4 USC seminar Extracting Photon PDF and Proton PDFs at an EIC November 9, 8 9 / 3

30 Extracting PDFs by a global fitting ) xu V (x,q.9 Q =.9 GeV HERAPDF..8 HERAPDF.-profiled.7 ) xd V (x,q Q =.9 GeV HERAPDF. HERAPDF.-profiled x x ) xg(x,q 3.5 Q =.9 GeV HERAPDF. 3 HERAPDF.-profiled.5 ) xσ(x,q.6.4. Q =.9 GeV HERAPDF. HERAPDF.-profiled x x USC seminar Extracting Photon PDF and Proton PDFs at an EIC November 9, 8 3 / 3

31 How well can EIC constrain PDFs? xu = xu + xc, x D = x d + x s U and D are better constrained compared with HERA USC seminar Extracting Photon PDF and Proton PDFs at an EIC November 9, 8 3 / 3

32 Summary and outlook he EIC will profoundly impact our understanding of QCD and its dynamics with high luminosity & high energy, nuclei & beam ploarization he structure of nucleons and nuclei Spin of the proton Will enable images of yet unexplored nonlinear regions hank you! USC seminar Extracting Photon PDF and Proton PDFs at an EIC November 9, 8 3 / 3

33 back up: he tracking system used in the model detector for erhic ime projection chamber (PC) η < Silicon trackers < η < 4 Electromagnetic Calorimeter (ECal) 4 < η < 4 Hadron Calorimeter (HCal): < η < 4 USC seminar Extracting Photon PDF and Proton PDFs at an EIC November 9, 8 3 / 3

34 Multivariable-distribution of q/g jet counts Quark jet Gluon jet p L /p jet fraction.5. Quark jet Gluon jet fraction quark jet gluon jet Mass [GeV] E jet GeV Gluon jets have a more uniform energy fragmentation, while quark jets are more likely to produce narrow jets with hard constituents that carry a significant fraction of the energy. USC seminar Extracting Photon PDF and Proton PDFs at an EIC November 9, 8 3 / 3

35 q/g jet discrimination fraction Quark jet Gluon jet fraction.8 quark jet gluon jet.6.4. fraction.35 quark jet gluon jet Girth Numbers of Particles inside jet R Some definitions: p L represents the highest p of the hadrons inside the jet; Girth = i cone p i p jet R i ; R is the distance between particle and jet axis Conclusion: Gluon jets are wider, with higher multiplicities, having a more uniform energy fragmentation, while quark jets are more likely to produce narrow jets with hard constituents that carry a significant fraction of the energy USC seminar Extracting Photon PDF and Proton PDFs at an EIC November 9, 8 3 / 3

36 MVA method oolkit for Mulivariate Data Analysis with ROO (MVA): for current study, we place cut where signal purity = signal efficiency USC seminar Extracting Photon PDF and Proton PDFs at an EIC November 9, 8 3 / 3

37 Di-jets at EIC from PYHIA Resolved Photon gluon fusion(pgf) QCD Compton(QCDC) * γ * γ q * γ q P g q q g he resolved, dit (PGF, QCDC) processes can produce di-jets. For each di-jet pair, we do geometry match in the simulation, then will know the jet is a quark/gluon jet. counts 4 trigger jet and its parton 3 associte jet and its parton two output partons di-jet match in each event, R < R USC seminar Extracting Photon PDF and Proton PDFs at an EIC November 9, 8 3 / 3

38 Jet algorithm Clustering Algorithms k : d i = p,i, d ij = min(p,i, p,j) R ij R = min(p,i, p,j) (yi yj) +(φ i φ j) R, if d min =min(d i, d ij ) is d ij ; else, remove j from the list as a jet. anti-k : d i =, d p ij = min(, ) R ij,i p,i p R.,j Given p,j is very small, also R ij R > : anti-k : d ij = p R ij R,i > p.,i It s more likely that j will be a candidate particle for jets by applying k algorithm that of anti-k. he back reaction sensitivity is highly suppressed by using anti-k algorithm in comparison with k algorithm. Cone-ype Algorithms SISCone: All circles defined by pairs of edge points are all stable cones. USC seminar Extracting Photon PDF and Proton PDFs at an EIC November 9, 8 3 / 3

39 Jet algorithm Profile(r).8 counts 4 3 counts 5 4. R =. anti-k k SISCone r R =., resolved process anti-k k SISCone Number of particles 3 R =., resolved process anti-k k SISCone Number of jets Some definitions: Profile(r) = p i r i <r p jet cone,r = η + φ ) inside the jet, with drawing a inner cone (r is the radius of this Result: While there are differences in the general behavior of different algorithms, they are relatively minor Conclusion: he choice of algorithm will have little impact, anti-k algorithm produces the most collimated jets with regular boundaries USC seminar Extracting Photon PDF and Proton PDFs at an EIC November 9, 8 3 / 3

40 Jet definition: jet radius R=,.7,.. ŝ is the input squared invariant mass of the two partons. di-jet mass is onstructed: M = p p (cosh( η) cos( Φ)). counts 3 anti-k, resolved R =. R =.7 R = di-jet mass [GeV] di-jet mass [GeV] R =, resolved s [GeV] di-jet mass [GeV] R =.7, resolved s [GeV] di-jet mass [GeV] R =., resolved s [GeV] USC seminar Extracting Photon PDF and Proton PDFs at an EIC November 9, 8 3 / 3

41 Motivation: Existing photon PDFs =. GeV =. GeV xu Q =. GeV P =. GeV DO GLO LAC G/GAL GLO GS GLO GS G 96LO GRV G/GRS GLO ACFGP/AFG GNLO WHI GLO SAS G(v/v)LO xd Q =. GeV P =. GeV DO GLO LAC G/GAL GLO GS GLO GS G 96LO GRV G/GRS GLO ACFGP/AFG GNLO WHI GLO SAS G(v/v)LO x 4 3 x xs Q =. GeV P =. GeV DO GLO LAC G/GAL GLO GS GLO GS G 96LO GRV G/GRS GLO ACFGP/AFG GNLO WHI GLO SAS G(v/v)LO xg Q P DO GLO LAC G/GAL GLO GS GLO GS G 96LO GRV G/GRS GLO ACFGP/AFG GNLO WHI GLO SAS G(v/v)LO x 4 3 x x is the momentum fraction of the parton from the photon, in the following section, it is marked with x γ USC seminar Extracting Photon PDF and Proton PDFs at an EIC November 9, 8 3 / 3