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Inclusive Photoproduction of  0 , K * 0 ,  Mesons at HERA

Inclusive Photoproduction of  0 , K * 0 ,  Mesons at HERA. • Introduction • Cross section measurements : r (770) 0 , K* 0 (892), f (1020) meson s • Comparison with models • Comparison with RHIC result s • Summary. Grażyna Nowak IFJ PAN Kraków. representing

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Inclusive Photoproduction of  0 , K * 0 ,  Mesons at HERA

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  1. Inclusive Photoproduction of 0, K*0,  Mesons at HERA • Introduction • Cross section measurements: r(770)0, K*0(892), f(1020) mesons • Comparison with models • Comparison with RHIC results •Summary Grażyna Nowak IFJ PAN Kraków representing the H1 Collaboration (H1 Collab., Phys. Lett. B 673 (2009) 119-126) G.NowakInxlusivePhotoproduction of ρ0, K*0,φ Mesonsat HERAEPS HEP 2009

  2. The HERA Collider p e± 27.6 GeV 820, 920 GeV p ZEUS HERA H1 e HERA I unpolarised e± beams 1992-2000 HERA II polarised e± beams 2002-2007 0.5 fb-1 per experiment (H1 and ZEUS) G.NowakInxlusivePhotoproduction of ρ0, K*0,φ Mesonsat HERAEPS HEP 2009

  3. ep kinematics at HERA q2 xBj W (k’) (k) (P) epc.m.energy:s =(P+k)2 *p c.m. energy: W = (P+q)2 exchanged momentum squared (photon virtuality) Q2= - q2= -(k-k’)2 Q2≈ 0 GeV2―photoproduction Q2> 1 GeV2―electroproduction (DIS) G.NowakInxlusivePhotoproduction of ρ0, K*0,φ Mesonsat HERAEPS HEP 2009

  4. Motivation √s ~ 90 GeV e+ e- ≈ √sNN ~ 200 GeV Wgp ~ 210 GeV e’ e p p (Au) p (Au) simple complex g* • e+e- collisions at LEP: distortion ofρ0line shape and shift towards lower masses was observed • RHIC:• H1: inclusive ρ(770)0, K*(892)0 and (1020) a unique opportunity to make comparison of RHIC results with simpler interaction system at HERA r0, K*0(892), f(1020)measurements at HERA help to study hadronisation G.NowakInxlusivePhotoproduction of ρ0, K*0,φ Mesonsat HERAEPS HEP 2009

  5. Selection e p e’ ET Main selection criteria for photoproduction events: • H1 data 2000 withL= 36.5 pb-1 • scattered electron e’ measured in ET (electron tagger) (Q2 < 0.01 GeV2) • trigger requires at least 3 tracks in the Central Tracker with pT > 0.4 GeV • 174 < W < 256 GeV  <W> = 210 GeV Meson identification; ρ0p+p-K*0 Kπf  K+K- G.NowakInxlusive Photoproduction of ρ0, K*0,φ Mesonsat HERAEPS HEP 2009

  6. r0, K*0andfsignals Fit function: F(m) = S(m) + R(m) + B(m) Signal Reflection Comb. background Clear signalsofr0, K*0andfmesons are observed G.NowakInxlusivePhotoproduction of ρ0, K*0,φ Mesonsat HERAEPS HEP 2009

  7. Bose-Einstein Correlations (BEC) BEC effect r0 p+ p+ ρ0signal p- p+ unlike-signpp—like-signpp e p p- p+ distortion ofρ0mass spectrum due to BEC (similar effects observed at RHIC and LEP) The Monte Carlo model with BEC is in agreement with the data in the region ofthe0 resonance, whereas the model without BEC fails to describe the di-pion mass spectrum. G.NowakInxlusivePhotoproduction of ρ0, K*0,φ Mesonsat HERAEPS HEP 2009

  8. r0, K*0andf: inclusive cross sections Kinematic region: Q2 < 0.01 GeV2, 174 < W < 256 GeV reconstructed neutral mesons: pT > 0.5 GeV, rapidity |ylab| < 1: σgpvis(gp→ ρ0X) = 25600 ±1800 (stat.)± 2700(syst.)nb σgpvis(gp → K*0X) = 6260 ± 350 (stat.) ± 860 (syst.) nb σgpvis(gp→ fX) = 2400 ± 180 (stat.) ± 340 (syst.) nb ) (K*0 = G.NowakInxlusivePhotoproduction of ρ0, K*0,φ Mesonsat HERAEPS HEP 2009

  9. r0, K*0 andf: differential cross sections PHOJET10: DPM PYTHIA6.2: LO QCD ME with PS and Lund string model for hadronisation • invariant differential cross section can be described by power law distribution • within rapidity range, the meson production rates are constant as a function of rapidity, within errors • PYTHIA and PHOJET models do not describe the shape of the measured pT spectrum G.NowakInxlusivePhotoproduction of ρ0, K*0,φ Mesonsat HERAEPS HEP 2009

  10. r0, K*0andf: a power law distribution is extrapolated cross section in all pT range Invariant differential x-section of the produced hadrons can be parametrised as: pQCD thermodynamic model nominal resonance mass transverse kinetic energy T0 - free parameter A – normalisation factor independent of pT G.NowakInxlusivePhotoproduction of ρ0, K*0,φ Mesonsat HERAEPS HEP 2009

  11. r0, K*0andf: cross section fit parameters ET0/n = • r0, K*0andfare produced with about the same value of the average <ETkin> supports a thermodynamic picture of hadronic interactions • <pT> inp is in agreement with RHIC pp and is lower than in RHIC Au-Au collisions G.NowakInxlusivePhotoproduction of ρ0, K*0,φ Mesonsat HERAEPS HEP 2009

  12. The cross sectionratio R(/K*0): comparison with RHIC The ratiosR(f/K*0) of the total cross sections for andK*0production ingp and pp interactions are very close and below the result for Au-Au interactions measured at about the same collision energy at RHIC G.NowakInxlusivePhotoproduction of ρ0, K*0,φ Mesonsat HERAEPS HEP 2009

  13. Hadron photoproduction at H1 All inclusive photoproduction cross sections measured at H1 are described by power law distribution with the same n = 6.7 calculated from charged hadrons G.NowakInxlusivePhotoproduction of ρ0, K*0,φ Mesonsat HERAEPS HEP 2009

  14. Summary • first measurement of the inclusive photoproduction of 0(770), K*0(892) and (1020) mesons in photoproduction at HERA, • the description of the shape of the ρ0resonance is improved by taking Bose-Einstein correlations into account, • pT-spectra are described by power law distribution, • r0, K*0andfare produced with about the same value of the average transverse kinetic energy  supports a thermodynamic picture of hadronic interactions • the comparison with RHIC results at similarp and nucleon-nucleon collision energy: • the cross-section ratioR(f/K*0) measured in gp is in agreement with pp results • Some tendency forfmeson production to be more abundant in Au-Au collisions is observed • universality inpT-spectra of hadrons at H1 is observed G.NowakInxlusivePhotoproduction of ρ0, K*0,φ Mesonsat HERAEPS HEP 2009

  15. Back up G.NowakInxlusivePhotoproduction of ρ0, K*0,φ Mesonsat HERAEPS HEP 2009

  16. r0, K* and f: visible kinematical range All mesons are analyzed in following: - |y|< 1 in 7 pT bins: 1 bin 2 bin 3 bin 4 bin 5 bin 6 bin 7 bin 0.5-0.75 0.75-1. 1.-1.5 1.5-2. 2.-3. 3.-4. 4.-7. GeV Extra cuts for mesons: K*0: 1 bin: Kaon dE/dx ident. && cos* < 0; 2-3 bin: Kaon dE/dx ident. f: 1-3 bin: Kaon dE/dx identification bin pT: 0.-0.25 GeV is excluded due to non description DATA and MC bin pT: 0.25-0.5 GeV is excluded due to big Background for K*0 and small  meson reconstructed efficiency - pT > 0.5 GeV in 4 y bins: 1 bin 2 bin 3 bin 4 bin -1.:-0.5 -0.5-0. 0.-0.5 0.5-1. Extra cuts for mesons: K*0: 1-4 bin: Kaon dE/dx ident. && cos* < 0 f: 1-4 bin: Kaon dE/dx identification y – rapidity of mesons pT – transverse momentum of mesons K*0 K+ * p- polarization G.NowakInxlusivePhotoproduction of ρ0, K*0,φ Mesonsat HERAEPS HEP 2009

  17. Fit Procedure ρ0p+p- K*0 Kπf  K+K- Fit function: F(m) = S(m) + R(m) + B(m) Signal S(m) = convolution of BW(m) and res(m, m’) rel. Breit-Wigner BW(m)= Amm0Γ(m)/[(m2-m02)2 +m02Γ2(m)] Γ(m) =Γ0(q/q0)2l+1m0/m resolution function res(m, m’) = 1/[2p] • Γres/[(m-m’)2 +(Γres/2)2] reflection R(m): for ρ0: K*0 Kπ and ω p+p-(π0) for K*0 : ρ0p+p-, ω p+p-(π0), f  K+K- and self-reflection K*0 Kπ for f: — combinatorial background B(m): for ρ0 and K*0: B(m)= {M(π±π±)orM(K±π±))} •{Pol(2-3) or (a1+a2•x)•exp(-a3•x-a4•x2)} for f: B(m)= b1•(m2 – 4mK2)b2• exp(-b3•m) G.NowakInxlusivePhotoproduction of ρ0, K*0,φ Mesonsat HERAEPS HEP 2009

  18. r0, K* and f: cross section calculation Invariant differential cross section: Differential cross section: N – number of mesons from fit ∆pT2 and ∆ylab – bin widths L= 36.5 pb-1 Fg = 0.0127 – photon flux BR = 1. for r0, 0.67 for K*0 and 0.49 for f e=erec • Aetag • A3 • etrig - efficiency reconstruction efficiency for the meson erec varies from 45% to 90% (using Monte Carlo) positron tagger acceptance Aetag = 48.5% trigger acceptance A3 varies from 50% to 95% (using Monte Carlo) trigger efficiency etrig ~ 90% (using Monitor Triggers) G.NowakInxlusivePhotoproduction of ρ0, K*0,φ Mesonsat HERAEPS HEP 2009

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