1 / 34

Insights from the International Workshop on High-Energy Scattering at Zero Degree, March 2013

This workshop, held at the Kobayashi-Maskawa Institute, Nagoya University, focused on forward physics and related subjects at the HERA collider. Key discussions included parton densities, diffraction phenomena, and the behavior of quark and gluon distributions during high-energy scattering. Notable topics included DGLAP evolution equations, scaling violations in deep inelastic scattering (DIS), and the role of the Pomeron in particle interactions. The workshop provided a platform for researchers to share insights and advancements in understanding the interplay of sea quarks, gluons, and partons in high-energy collisions.

bijan
Télécharger la présentation

Insights from the International Workshop on High-Energy Scattering at Zero Degree, March 2013

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. International workshop for High-Energy Scattering at Zero Degree 2-4 March 2013 at Kobayashi-Maskawa Institute, Nagoya University Yuji Yamazaki (Kobe University) 0 degree and DIS

  2. HERA 1992-2007 • The only collider,with the energy comparableto other and heavy ion colliders • 27.5 GeV920 GeV • Super microscope for the proton • 0.5on tape each

  3. Parton densities at low- • Rapid increase intowards low- rest of the proton Higher Q2 scattered quark Quark density decreasing at high-x with Q2

  4. e' e g* Higher Q2 evolution p p Scaling violation in DIS • behaviour described by pQCD • Sea quarks dynamically produced • DGLAP evolution equation fits data well • Gluon density obtainedthrough the DGLAP fit You cansee gluonsindirectly

  5. Extracting parton densities • Precise determination • ~ 5% for gluon, sea ~ 2% • In low- regime: • completely dominated bysea or gluon • gluon twice more than sea A lot of partons at low-, especially gluons

  6. Today’s menu • This talk covers the forward physics and related subjectsat the HERA collider • Introduction for 𝑒𝑝 scattering • Proton: many partons in low- regime • Forward scattering and low- physics • Diffraction • Leading baryons • Forward energy flow

  7. Low- forward • Protons almost unperturbed after small- partons taken out • Small- partons are pretty “backward” • Large rapidity interval between the small- parton and most forward particle remnant small large backward forward = 0 degree

  8. at low- is scattering • low- low-, photon regarded as hadron • centre-of-mass energy is higherfor lower- events • low- = larger rapidity interval • Fast rise in cross section: due to increase in partonphoton is not completely a hadron, rather a “hard” object

  9. Soft or hard? • Colourless particles appear more in forward (perhaps) • where is the transition, in which rapidity? small = hard very large = soft backward forward = 0 degree

  10. partons phase space = various phenomena particle exchange(one-pion exch. etc.) multi-partoninteraction • where colourless,where colourful? diffraction by “Pomeron” increasing forward E diffraction destroyed by multi-parton interaction Large RapidityGap (LRG) diffraction by 2-gluon

  11. Diffraction in high-energy DIS

  12. Diffraction in collisions: issues • Diffraction at HERA: • photon dissociates into small mass (X) • proton stays intact or proton dissociates into small mass (Y) • Standard view: • Pomeron emitted from proton,which is scattered off by a photonDIS of the Pomeron • Pomeron or 2-gluon ? • Is the diffraction peripheral ? diffraction by “Pomeron” Large RapidityGap (LRG) X Y diffraction by 2-gluon

  13. Diffractive DIS and diffractive PDFs • partonic structure of diffractive exchange (Pomeron) by • what to measure: • Structure function of diffractive process • Extracting diffractive PDFs (DPDFs)through scaling violation, using jets …(assuming factorisation theoremwould work for diffractive DIS) b: long. momentum fraction of the parton in the exchange xP : long. momentum fraction of the exchange in the proton : negative of momentum transfer squared

  14. Is Pomeron a “particle” ? • Check if the cross section can befactorised into: • the Pomeron flux and • the upper part • This holds pretty well: cross section shape in is independent of and • If 2-glu: depends on dependence steeper with Fit by slope parameterof the figure below

  15. Scaling violation analysis for in DPDF • Positive scaling violationin almost all values • Quarks dynamically produced through gluons • The exchanged object is gluon-richconsistent with naïve 2-gluon picture • some excess at low-(higher twist!):I will come to this point later

  16. Extracted diffractive parton densities • Gluons are not strongly constrained in diffractive DIS • Jet cross sections are used to constrain gluons • 63% is gluon at ZEUS dijet cross section and DPDF SJ Longitudinal fraction of momentum carreid by the dijet system, wrtPomeron

  17. Vector meson production in • Vector meson is higher twist (vector-meson dominance model) • Observing rapid rise of cross section in if a hard scale exists i.e. • if the VM is produced from a very virtual photon • or if the VM is heavy (, ) • Well explained by the 2-gluon picuture: • corresponds to vector meson

  18. Forward part: t-dependence of VMs • Measuring proton recoil • If steep, the process is peripheral • parameterised by • Observation: approaches to ~ 4 • the interaction becomes point-like • supporting the “hard” picuture of VM production

  19. Forward proton detectors at HERA • ZEUS LPS / H1 FPS: • rather complicated acceptancebut still covers: • at • some acceptance at the diffractivepeak • high acceptance for • H1 VFPS • very high acceptance for

  20. Is inclusive diffraction peripheral? • Not completely peripheral,not completely point-like • Pomeronis perhaps not completely a particle? … but the slope is independent of (unlike vector meson)

  21. Leading Baryon Production

  22. Issues on leading baryons • Is baryons produced by • fragmentation? • or particle exchange? • Is the “first vertex” peripheral? • is the leading baryonrescattered by additional partons? • What are the difference betweenproton and neutron production?

  23. Forward neutron detectors at HERA • Big space available there • proton beam is bent upward • the calorimeters are large and deep • Limited aperture due to Q magnets • Scintillator “tracker” • to detect precisely the positionof the first part of hadronic shower

  24. Leading neutron: fragmentation or pion? • Data show fragmentationnot sufficient, need OPE • One Pion Exchange:charge exch. • Fragmentation can take care ofonly component like OPE fragmentation extrapolation assuming exponential

  25. Leading proton? • very flat dependence • … which can be explained byan overlay of many trajectoriesin Regge-based framework … then, how does the productiondepend on the property of“the other side” of the ladder?

  26. Does the photon and proton talk each other? • Both proton and neutron production rates arefairly independent of and neutron proton supporting limiting fragmentation

  27. Is the leading baryon production “peripheral”? • Proton: (amazingly) flatat • Neutron: richer structure • sensitive to the pion flux neutron proton neutron

  28. Proton and neutron yield in DIS • Neutron yield is 20-30% fewer than naïve prediction of expected from isovector exchange • Protons are more than neutron • .. at least in very forward regionGeV2 • Not consistent with isovector exch. proton neutron neutron This is puzzling.

  29. Is neutron lost? • Neutron with PHP dijet • Resolved = “larger photon” is suppressed w.r.t. direct Ratio PHP/DIS Ratio resolved/direct • Photoproduction: “large photon” • more rescattering(more multi-parton scattering) • Phoproductionis suppressed

  30. Multi-parton phenomena

  31. Multi-parton interaction in photoproduction • Resolved photon: like a hadronmany partons can be exchanged • Excess observed in events with low- () jets • “Jet pedestal”: increasing energy flowoutside the jet core • particle flow direct → ←resolved Multi-parton interaction seems to exist in photoproduction resolved direct

  32. Radiation pattern in the middle of ladder • Many attempts to find“BFKL”-like dynamics in DIS • -disordering in radiation • Excess in forward energy flow • but no clear evidence of particularmodel: we always just learn thatfixed order calculation is not enough ordering in DGLAP ordering in BFKL

  33. Forward energy vs the length of the ladder • Y: rapidity interval measured from the scattered electron CCFM: angular ordering CDM (colour-dipole): some amount of disordering Forward energy is more than the prediction, but somewhat at the upper edge of the scale uncertainty

  34. Summary • Particle exchange model explains many features offorward production in DIS • diffraction (Pomeron-like) • leading baryon (OPE etc.) • Multi-parton phenomena becomes important as vertices get closer to the photon • low- rise of (1-glu) • quasi-elastic vector meson production (2-glu) • forward jets (multi-radiation, multi-parton interaction) • We did not have large-acceptance detector to see the interplay • at around

More Related