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Information from leading neutrons at HERA

Information from leading neutrons at HERA. V.A. K hoze, A.D. M artin, M.G. R yskin (also with A.B. Kaidalov). Alan Martin (Durham) 2 nd HERA-LHC Workshop CERN, 6-9 th June, 2006. Q 2. p exchange dominates for x L > 0.6, but absorptive effects

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Information from leading neutrons at HERA

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  1. Information from leading neutrons at HERA V.A. Khoze, A.D. Martin, M.G. Ryskin (also with A.B. Kaidalov) Alan Martin (Durham) 2nd HERA-LHC Workshop CERN, 6-9th June, 2006

  2. Q2 p exchange dominates for xL > 0.6, but absorptive effects Nikolaev,Speth,Zakarov; Alesio,Pirner W xL, pt Leading neutron data (Q2, xL, pt)  p structure fn, F2p(x,Q2) at small x  fpq,g sabs(qq-N)  check of S2 pion flux Bill Schmidke Mara Soares Michele Arneodo This study inspired by prelim. ZEUS data

  3. gap survival factor S2 ~ 0.48 for photoproduction AddveQM:

  4. Calculation of survival factor, S2(xL,pt2,Q2) g g g g g g (a) normal eikonal diagrams g g g g g g enhanced diag. need yi > 2-3: result ~ 15% (b) If enhanced diag were important, then n yield would be energy dep. Not seen in data. g space-time picture (a) (b)

  5. Photoproduction of leading n S2 ~ 0.48 Prelim. ZEUS data (DIS2006)

  6. Deep inelastic production AddveQM: gap survival factor expect S2=1 for high Q2 expect R = photoprod / DIS(high Q2) ~ 0.48 In practice, at finite Q2 abs. corr. remain; use two-ch eikonal with sqq-p ~ srp ~ spp ~ 31mb; compare with prelim. ZEUS data 

  7. R = photoprod / DIS sincl~ x -l (1 - xL) l(0) - l(Q2) precise data will yield information on both F2p and S2 …now the pt dep.

  8. Photoprod. pt2 dep. ~ exp(-bpt2) All p-exch. models fail !! F(t) no help. led to include r, a2-exch. 

  9. Including r and a2 exchange r, a2 Irving, Worden large flip enlarges s, more at larger pt leading to smaller slope, b Use r, a2 exch. degeneracy, additive QM Slope b now OK --- s too large --- adjust parameters to attempt to simultaneously describe s and b s ~ aS2 r2 now S2 ~ 0.4

  10. cross section pt2 slope now S2 ~ 0.4, instead of 0.48

  11. Slope b of pt2 distrib. Db = b(gprod) - b(DIS) p p,r,a2

  12. pion structure function F2p(xp,Q2) xp=0.001 better description with Q2 rescaled xp=0.01 xp=0.1 “global” parton analysis of p (data xp>0.2)

  13. Conclusions on leading neutrons at HERA Exploratory study of prelim. ZEUS data (Q2, xL, pt, W) very informative • exch (with abs.) describes s, but not pt2 slope b • need also r, a2 exchange turnover of slope as xL 1 (tmin 0) may be used to determine r,a2 versus p exchange contributions important for LHC Absorptive corrections important S2 ~ 0.4 Small contrib. from enhanced diagrams Simultaneous description all data (Q2, xL, pt dep.) difficult Precise data should determine F2p(x,Q2) and S2(xL,pt,Q2)

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