Exclusive Vector Meson Production and Inclusive K 0 S K0 S Final State in DIS at HERA Photon003, Frascati 07-11/04 McGill University For the H1 and Zeus Collaboration Outline: Exclusive vector meson production Summary First observation of resonances in inclusive K S0 K S0 final state in DIS Summary
e p soft W γp Q Soft ( Regge + VDM ) At low t Exclusive Vector Meson Production γ * P d P ) t σ ( W ) W 0. e' VM (M VM ) At HERA: p' p γ * hard Cross section σ ( W ) W q δ q R VM = ρ, ω, φ, J/y, ψ(s), etc p' σ VM γ* p p' Hard ( pqcd ) [ xg x, Q )] σ 4( α ( t) 1 ) b( W t x 1/W dt W ' b( W) = b + 4 lnw 0 α e ' α ( t) = α (0) + α P P P b R t ( eff Gluon from fit to F scaling violation σ ( W ) W Scale Q, t, M VM Transv. size of the interaction region VM 0.8 Small size. No W dependence.
Exclusive Vector Meson Production Elastic VM in photoproduction (Q = 0) A first look: e γ * e' VM P M VM p p' Fit σ W δ : δ 0. for ρ 0, ω, φ δ 0.8 for J/ψ high M VM sets hard scale
Exclusive Vector Meson Production J/ψ Photoprod. in bins of W and comparison to LLA calculations Looking at high M VM (consistent with hard regime previous slide) Leading Log. Approx. (LLA) pqcd with different gluon parametrisations Models sensitive to input parametrisation of the gluon density Models with σ [ xg x, Q ] ) ( eff in reasonable agreement with data Indeed, M VM is a hard scale
Exclusive Vector Meson Production Steepness of ρ 0 and J/Ψ cross-section Can Q provide a hard scale? b (GeV - ) ρ 0 d σ e dt b R R p + R VM bbt t R is the transverse size of the interaction region J/ψ b 0,5 GeV - proton size Q (GeV ) R decreases with Q for ρ 0 R already small for J/ψ at small Q And the power-law W δ dependence?
W-dependence of elastic ρ 0 and J/ψ in bins of Q (PhP and DIS) Can Q provide a hard scale? Exclusive Vector Meson Production ρ 0 transition soft hard J/ψ already steep at Q = 0 σ tot (γp J/ψp)[nb] J/ψ Flat δ Data fitted with W δ pqcd models consistent with data Q also provides a hard scale. Q [GeV ] W [GeV]
Exclusive Vector Meson Production Photoproduction of proton-dissoc. VM at high t What about t? Typical elastic VM production has t <1GeV. Use proton dissociation to reach higher t γp ρy γ* VM p Y γp φy Use BFKL LLA approach to fit data (Forshaw and Poludniowski) γp J/ψY BFKL LLA approach is in agreement with data t sets a hard scale
Exclusive Vector Meson Production Summary Q, M VM and t set a hard scale. Perturbative QCD predictions agree with data
Inclusive K 0 S K 0 S final state in DIS QCD predicts the existence of hadrons made up by gluons (glueballs). From Lattice QCD calculations, the lightest glueball has J CP =0 ++ with a mass 1730±100 MeV. K S0 K S0 couples to meson states with J CP =(even) ++ 0 + Tensor J CP = ++ Nonet K (1430) K (1430) - a (130) f (8) f (1) 0 a (130) + a (130) f (8) f (1) f (170) ~ uu+dd f (155) ~ ss - K (1430) 0 K (1430) a 0 (130) ~ uu d d 0 K 0 (1430) - a 0 (????) - K 0 (1430) + K 0 (1430) f 0 (8) f 0 (1) 0 a 0 (????) 0 K 0 (1430) + a 0 (????) Scalar J CP =0 ++ Nonet 3 candidates for spots f 0 (8) f 0 (1) f 0 (1370) ~ uu+dd f 0 (1500) ~?? f 0 (1710) ~ ss f 0 (1710) is a glueball candidate
Inclusive K 0 S K 0 S final state in DIS A total luminosity of 11 pb -1 was used Only events with at least K 0 S were selected Clean K 0 S sample
Inclusive K 0 S K 0 S final state in DIS First observation of J CP =(even) ++ in DIS. Two states are observed a state consistent with f (155) X(176) (is this the f 0 (1710)?) A third state is observed in the (problematic) 1300 MeV mass region, consistent with the f(170)/a(130) interference Several states have been observed in the GeV region (see PDG0) F( M ) dn 3 i = = dm i= 1 π B C M mks ( m ) e A M N ( M M K s Γ ) 0, i i + Γ i + / 4
K S 0 K S 0 in the Breit-frame Inclusive K 0 S K 0 S final state in DIS Current region in DIS is equivalent to an e + e - hemisphere r r xp + q = 0 Increasing x p 78% of the KsKs pairs have x p >1 P z (KsKs)<0 (7%) P z (KsKs)>0 (93%) More gluons P q = Q, x MAX p = P MAX K K s P q s 1 x = x
Inclusive K 0 S K 0 S final state in DIS Summary First observation of resonances in K S 0 K S 0 final state in DIS was reported Two states are observed in the 1300 MeV, 1500 MeV mass region consistent with f (170)/a (130) and f (155) Another state X(176) is observed, probably the f 0 (1710) (a glueball candidate) States are produced in a gluon rich environment
Extra Slides
Vector Meson Production e W γp Q γ * P e' VM (M VM ) e γ * P e' VM p t p' Elastic p Proton Dissociative Y (M Y ) Hard regime (pqcd) γ * q q R p p' pqcd VM Q = γ * virtuality; Q < 100 GeV W γp = γ * p CMS energy; 0 < W γp < 90 GeV t = 4-mom. transf. squared; t < 0 GeV VM = ρ, ω, φ, J/ψ, ψ', Υ R = 1/[ z(1-z) Q + m q ] 1/ ; z = E q / E γ*
Vector Meson Production Soft regime ( Regge + VMD ) γ * em VM /g V VM Photon transversally polarized ; low Q or t dσ dt W W 0 [ α ( t) 1] P e b ' α P ( t) = α P (0) + α P t = 1.08 + 0. 5 0 t t b( W ) p p' ' = b 0 + α ln W P W0 ( Donnachie-Landshoff ) ( Shrinkage ) σ rising weakly with W: σ( W) W δ, ' δ 4( α P (0) 1 α P b) σ steep exponential t dependence (shrinkage): d b( W) σ dt e t At low t, t < 1.5 GeV δ = 0.
Vector Meson Production Hard regime ( pqcd ) Photon mainly longitudinally polarized Large Q, M VM or t qq system is small, probes the proton Two-gluon-exchange approach at LO Gluon ladder (LLA approach) σ L 1 6 s ( Qeff ) eff ) x Q α W 0.8, ( x 1 W ) [ ] [ ] 0. xg( x, Q Gluon from F scaling violations p γ* γ * q q R p' VM At which scale Q eff should xg be evaluated? For ex.: Q eff =¼ (Q + M VM + t ) (Ryskin Model) σ rising steeper than expected from Regge+VMD p p'
Dependence at large t not exponential: dσ d t t n indication that large t may provide a hard scale to apply perturbative QCD Forshaw and Poludniowski fitted the ZEUS data for p-dissociative photoproduction of ρ 0, φ and J/ψ mesons (hep-ph/0107068): VM > BFKL LLA approach: consistent with data Vector Meson Production Photoprod. of proton-dissoc. VM at high t γ p γ* t Y J/ψ dσ/dt (nb/gev ) two gluon two gluon γ*p J/ψY LLA BFKL γ*p φy LLA BFKL γ*p ρ 0 Y LLA BFKL p > two-gluon-exchange approach at LO: inadequate p' two gluon
Vector Meson Production J/ψ cross-section and QCD models (PhP and DIS) Fit with 1 ( Q + ) n M J / ψ QCD models FKS and MRT(CTEQ5M) are in good agreement with M. data Barbi
Vector Meson Production Diffractive Photoproduction of ψ(s) - pqcd > Cross-section suppressed with respect to that of J/y > Steeper W dependence ψ(s) wavefunction has a node p γ * q q pqcd VM p' > Overall R 0.166 consistent with pqcd prediction > Fit W δ δ 0.4 consistent with W dependence for ψ(s)
Vector Meson Production W-dependence of elastic ρ 0 and J/ψ in bins of Q (PhP and DIS) Fit σ W δ : ρ 0 transition soft hard J/ψ already steep at Q = 0 Q provides a hard scale
Extras.. KsKs final state
Scalar and Tensor Mesons Quark Model (u,d,s) Scalars J PC = 0 ++ q S=1 q S I=0 L=1 J PC = ++ Tensors I P = (-1)x(+1)x(-1) L = (-1) L+1 C = (-1) L+S J = 0 or Masses 1- GeV, scalar and tensor mesons much heavier than the pseudoscalars
QCD: richer than Quark Model, predicts gluon states with J PC = 0 ++, ++, I=0 Is this a qq state? g mix f 0 (1370) f 0 (1500) f 0 (1710) Observed States Ks: has S=L=0, P=-1, C=+1 KsKs: has P=+1, C=+1 J=even KsKs final state couples only to J PC =(even) ++ and it is CLEAN. This is the golden channel (given statistics) to look for scalar and tensor meson resonances
Production mechanisms in DIS Gluon poor processes Odderon Exchange VM Radiative decays In quark Jets Gluon rich processes In gluon jets
K 0 S K 0 S final state in DIS First observation of J CP =(even) ++ in DIS. Two states are observed: a state consistent with f (155) X(176) (is this the f 0 (1710)?) Fit 3 Breit-Wigner and a backg. function: F( M ) dn 3 i = = dm i= 1 π B C M mk s ( m ) e A M N ( M M K s Γ 0, i i ) + Γ i + / 4 Problematic region Threshold Enhancement due to f (980)/a (980) Several states have been observed in the GeV region (see PDG0) f 0 (980)/a 0 (980) 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.
Observation of J=even meson resonances in ep coskk < 0.9 cut
K 0 S K 0 S final state in DIS Attempt to include the 1980 MeV mass region Fit with 4 Breit-Wigner
How well a smooth background describes the data: SL 1 π χ e x n 1 / dx It is less than 1% likely that a smooth distribution describes the data.
If f(1710) is a glueball it should have small coupling to γγ e + e - γγ K s K s