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Laurent Schoeffel CEA/Saclay (DAPNIA/SPP)

HEP2005 Europhysics Conference in Lisboa, Portugal. Inclusive NC and CC Diffraction. Laurent Schoeffel CEA/Saclay (DAPNIA/SPP). On behalf of H1 and ZEUS collaborations. 1. Results from H1 and ZEUS experiments : Q²<120 GeV² 2. Interpretation in perturbative QCD

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Laurent Schoeffel CEA/Saclay (DAPNIA/SPP)

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  1. HEP2005 Europhysics Conference in Lisboa, Portugal Inclusive NC and CC Diffraction Laurent Schoeffel CEA/Saclay (DAPNIA/SPP) On behalf of H1 and ZEUS collaborations 1. Results from H1 and ZEUS experiments : Q²<120 GeV² 2. Interpretation in perturbative QCD 3. Large Q² Rapidity Gap Events (Q²>200 GeV²) : NC and CC

  2. Inclusive diffraction Diffractive event in the H1 detector : Kinematic variables : Y xIPfractional loss of the proton longitudinal momentum MX invariant mass of the diffractive final state  = xBj/xIPfraction of the + momentum carried by the interacting parton / Diff. Exchange Diffractive cross section : with rD ~ F2D F2D => diffractive parton densities of the Diffractive Exchange

  3. New measurement by ZEUS With the Forward Plug Calorimeter MY>2.3 GeV => EFPC>1 GeV recognised and rejected Mx selection method : d*pdiff /dlnMX² ~ constant for a diffractive event

  4. New measurement by ZEUS With the Forward Plug Calorimeter d*pdiff /dMX² ~ 1/MX² for a diffractive event… Mx=1120 GeV We observe : d*pdiff /dMX ~ Wa rising with W (a>0) From Regge theory : a=4(IP(t)-1) For soft IP (IP~1.08) => a ~ 0.2/0.3 (Mx<2 GeV) Note : d*pdiff /dMx²~4²/[Q²(Q²+Mx²)] xIPF2D

  5. Perturbative QCD and hard diffraction ddiff /dMX ~ Wa with a = 2.(2IP-2) MX < 2 GeV => soft pomeron MX > 2 GeV => transition from soft to hard process(Q²) => large Q² + large MX : perturbative regime Mx > 2 GeV Q² > 15 GeV²

  6. Scaling violations Large scaling violations even at large  => large Gluon Low xIP ~xIP F2D(3) Note : H1 measures in the range MY<1.6 GeV 97 data with 10 pb-1 for Q²>13.5 GeV²

  7. Combination of both data sets H1/ZEUS => Compatible After scaling the measurements in the same MY range Plot from the HERA/LHC workshop

  8. J. Bartels at al., Eur. Phys. J. C7, 443 (1999). Phenomenology of the 2-gluon exchange model LO realisation of the Singlet Exchange L or T =Q²/(Q²+Mx²) ~1/Q² at large  => HigherTwist behaviour

  9. Fraction of Diffraction vs the total cross-section Behaviour well explained in the dipolesaturation model Mx>8 GeV bins : => Diffraction is dominated by qq and qqg For example at very low , one gluon carries the momentum xBjp+ => We expect the same W dep. // F2

  10. Rapidity Gap Event at Large Q² NC/CC Example of event in the H1 detector X Rapidity Gap Missing transverse energy

  11. Results on CCDiff H1 : CCDiff/CCIncl = 2.50.80.6% NC ratio decreases with Q² : It was ~15/20% at medium Q² and it reaches ~2/3% for Q²>200 GeV² CC and NC fractions are compatible

  12. Conclusions New results from ZEUS with a Forward Plug Calorimeter to measure the forward activity : Ratio Diff/Incl ~ 15/20% at medium Q² Well described by the 2-gluon exchange in the perturbative domain A large gluon content of diffractive exchange is found by H1 by scaling violations (QCD fit) Rapidity Gap Events at large Q² : interesting as it gives access to CC events Fractions NCDiff/NCIncl and CCDiff/CCIncl are compatible and decreasing with Q² : CCDiff/CCIncl ~ 3% in the range of measurement (Q²>200 GeV²) : H1 and ZEUS give compatible results

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