Selected results in hadronic final state in DIS at HERA

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1 Stathes Paganis Columbia Univ., Nevis Labs on behalf of H1 and ZEUS collaborations Recontres de Moriond - March Outline Forward jet and π production in DIS First observation of K s K s resonances in DIS

2 Multi-parton dynamics at low x Multi-parton emissions are described only by approximations Everything beyond O(a s a s ) is put into Evolution Equations DGLAP, BFKL, CCFM evolution schemes. DGLAP: ordered in k t DGLAP+resolved photon: CCFM BFKL: not 2 ladders ordered in k t ordered in k t k t k t k t 2

3 Parton dynamics at small x: forward jets and forward π Central region x Bj small An extended parton ladder at low x leads to high k T partonic emission in the forward region A forward parton can be tagged by a jet OR by a single forward particle (like a π ) Forward region forwardπ x π = E π E proton = large DGLAP (strictly increasing gluon virtuality from proton to γ* ) works very well in the central rapidity region How about the forward region (small x)? Can we see any evidence for BFKL? (in BFKL the parton propagator virtualities perform a random walk ) 3

4 Forward Jet production: E T flow Transverse energy flow around the selected forward jet as a function of η and φ DGLAP + resolved photon describes the Et flow better than CDM which simulates higher order QCD radiation without strong ordering in k t of emitted partons (similar to BFKL) φ Jet η Jet 4

5 Forward jet production x Bj small forward jet x jet = E E jet proton = large DGLAP (dashed) too small DGLAP + resolved photon describes well the data CCFM (CASCADE) too large Color Dipole Model (CDM) simulates higher order QCD radiation without strong ordering in k t of emitted partons (similar to BFKL): describes well the data 5

6 Fwd jet production: p T dependence x Bj small forward jet x jet = E E jet proton = large CCFM (CASCADE) gets larger with increasing p T Color Dipole Model (CDM) describes better the data DGLAP + resolved photon describes well the data DGLAP (dashed) too small 6

7 Forward π production x Bj small forwardπ x π = E π E proton = large DGLAP (dashed) too small DGLAP + resolved photon describes well the data CCFM too small at small x 7

8 Forward π : E T -flow around π in γ*p CMS π close to proton η*: p-rapidity in the γ*p CMS frame Energy flow is highly collimated around the direction of the π Large amounts of transverse energy are also produced away from the π Transverse Energy flow around the π reflects how the transverse momentum of the jet is compensated along the ladder DGLAP+resolved photon describes better the E t flow when π is close to the proton π towards photon 8

9 K s K s final state in DIS K s K s couples to meson states with J CP =(even) ++ Scalar meson sector is not fully understood: there are too many candidates for the two I= available positions in the nonet Lattice QCD predicts the existence of hadrons made up by gluons (glueballs): the lightest glueball has J CP = ++ with a mass 173±1MeV ep is gluon rich 9

10 K 2 + K 2 Tensor J CP =2 ++ Nonet - a 2 (132) f 2 (8) f 2 (1) a 2 (132) + a 2 (132) f 2 (8) f 2 (1) f 2 (127) ~ uu+dd f 2 (1525) ~ ss - K 2 K 2 a 2 (132) ~ uu dd K + K Scalar J CP = ++ Nonet - a (????) f (8) f (1) a (????) + a (????) f (8) f (1) f (137) ~ uu+dd f (15) ~?? f (171) ~ ss - K K J= glueball can mix with the I= scalar mesons! 1

11 x vs Q 2 and K s mass DIS events with at least 2 K s were selected Very clean Ks sample 11

12 First observation of J CP =(even) ++ in DIS: two states are observed: a state consistent with f 2 (1525) and X(1726) (is this the f (171)?) F( M ) dn 3 i = = dm i= 1 2 π B C M 2mKs ( 2m ) e A M N ( M M K s Γ ), i i 2 + Γ 2 i + / 4 Problematic region Threshold Enhancement due to f (98)/a (98) Several states have been observed in the 2GeV region (see PDG2) f (98)/a (98) gives K s pair with very small opening angle in the lab. We would like to remove collinear K s pairs and then fit the spectrum. 12

13 Observation of K s K s resonances in DIS Applied cut: cosk s K s <.92 to remove threshold enhancement Attempt to fit with 4 Breit-Wigner 13

14 current K s K s in the Breit Frame r r 2 xp + q = Current region in DIS is equivalent to an e + e - hemisphere target θ 12 -Q/2 Θ γ -Q Z P P Q (1- x) 2x n c n t P z (KsKs)< (7%) P z (KsKs)> (93%) Increasing x p 78% of the KsKs pairs have x p >1 P q = Q 2, x MAX p = P MAX K K s P q s = 1 x x 14

15 Summary New high statistics measurement of forward jets and pions performed Data discriminate between different models Cross sections much larger than standard DGLAP but DGLAP including the partonic substructure of the virtual photon describes the data First observation of J PC =even ++ resonances in K s K s final state in inclusive DIS a 2 (132)/f 2 (127) and f 2 (1525) observed X(1726) is observed, this is probably the f (171) (glueball candidate) 15