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Jet Structure From Di-hadron Correlations in d+Au Collisions

Jet Structure From Di-hadron Correlations in d+Au Collisions. Nathan Grau Iowa State University For the PHENIX Collaboration. Outline. The Cronin effect and theoretical models of d+Au collisions with hard-scattering events Di-hadron correlations in d+Au Results on k T z trig

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Jet Structure From Di-hadron Correlations in d+Au Collisions

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  1. Jet Structure From Di-hadron Correlations in d+Au Collisions Nathan Grau Iowa State University For the PHENIX Collaboration

  2. Outline • The Cronin effect and theoretical models of d+Au collisions with hard-scattering events • Di-hadron correlations in d+Au • Results on kTztrig • Results on dN/dxE N. Grau Jet Correlations at RHIC 03/10/05

  3. Cronin Effect • Cronin enhancement of the single particle spectrum has been measured at RHIC. • Common interpretation: multiple scattering of parton prior to hard scattering. • Increase pT of parton – kT • Increase in di-jet acoplanarity PRL91, 072303(2003) Enhancement in d+Au collisions N. Grau Jet Correlations at RHIC 03/10/05

  4. p  400 GeV p  800 GeV = 21 GeV E557 E683 E609 Broadening at Lower Energies Previous Fermilab fixed-target experiments have measured a sizable increase in the di-jet broadening in h+A collisions. RHIC data will extend the energy dependence of the effect. N. Grau Jet Correlations at RHIC 03/10/05

  5. Theoretical Models • In multiple scattering models the increase in kT is related to TA(b) • Compare d+Au to p+p and measure centrality dependence – compare directly to models • Compare also to Hwa and Yang: recombination in cold nuclear matter. Predict little increase in kT and increase in near-side yield. N. Grau Jet Correlations at RHIC 03/10/05

  6. dN/dxE Distributions Definition of xE. Pioneered at ISR to approximate the fragmentation variable z At high pT, i.e. when di-jets are nearly back-to-back. N. Grau Jet Correlations at RHIC 03/10/05

  7. Data overview • Trigger hadrons used: h+/-, p0, p+/- • All correlated with h+/- • p0 identified by gg decay channel • High-pTp+/- identified in RICH (cerenkov threshold of 4.9 GeV/c) • Data spans trigger pT range from 3-16 GeV/c • Corresponds roughly to a Q2 of 10-1500 (GeV/c)2 • Examined both p+p and d+Au data from Run-3 RHIC N. Grau Jet Correlations at RHIC 03/10/05

  8. Correlation Functions in p+p and d+Au Pion trigger 5-10 GeV/c N. Grau Jet Correlations at RHIC 03/10/05

  9. Jet Structures from Azimuthal Correlations • Peak at Df = 0  di-hadron fragmentation • Yield related to D(ztrig,zassoc) • z = pT/pTjet • Peak at Df = p Two parton fragmentation • Width related to kTztrig • Yield related to the product of fragmentation functions D(ztrig)D(zassoc) N. Grau Jet Correlations at RHIC 03/10/05

  10. Angular Widths • Widths from gaussian fits • Far side width > Near side width N. Grau Jet Correlations at RHIC 03/10/05

  11. Parton Transverse Momentum • kT quoted is per parton • kTy perpendicular to trigger particle. N. Grau Jet Correlations at RHIC 03/10/05

  12. kTyztrig • kTyztrig for different trigger pT ranges and different trigger particles • kTyztrig flat with pT,trig d+Au Min Bias N. Grau Jet Correlations at RHIC 03/10/05

  13. Comparison to p+p • Weighted averages of separate data • Weighted average of combined data N. Grau Jet Correlations at RHIC 03/10/05

  14. Model Comparison • Limit set on increase in kT • ztrig ~ [0.5-0.7] implies kT2 increase < [0.6 - 1.2] (GeV/c)2 in d+Au • Qiu and Vitev, PLB 570, 161 (2003) • Semi-hard multiple scattering model • Predicted kT2 increase of ~1 (GeV/c)2 • Hwa and Yang, PRL 93, 082302 (2004) • Recombination of soft and hard partons • Reproduce RdAu and predict little increase in kT2 • Although prediction of increase in near-side yield is not seen N. Grau Jet Correlations at RHIC 03/10/05

  15. <(kTyztrig)2> (GeV/c)2 <(kTyztrig)2> (GeV/c)2 TA(b) (mb-1) TA(b) (mb-1) Centrality Dependence p0 p+/- TA(b) dependence of kTyztrig for different trigger ranges Simultaneous fit with common slope, slope consistent with 0. N. Grau Jet Correlations at RHIC 03/10/05

  16. Summary of kT results • kTztrig is flat vs. pT,trig with a value of • No significant increase over p+p collisions is seen • No significant trend in centrality seen • Data sets an upper bound on nuclear effects on di-jet acoplanarity in d+Au collisions N. Grau Jet Correlations at RHIC 03/10/05

  17. dN/dxE Results • xE distributions for trigger p+/- for several different trigger ranges • Overlap of data consistent with fragmentation being independent of parton momentum. N. Grau Jet Correlations at RHIC 03/10/05

  18. Scaling of dN/dxE d+Au Min Bias p+p Scaling with pTtrig found at lower root-s at ISR Scaling holds for p+p and d+Au at RHIC. N. Grau Jet Correlations at RHIC 03/10/05

  19. Scaling Violation of dN/dxE • Fit to find the fractional change with pT • Scaling in both p+p and d+Au and no systematic difference between them. N. Grau Jet Correlations at RHIC 03/10/05

  20. Summary and Conclusions • PHENIX has measured jet structures in d+Au collisions with a number of different hadrons over a large pT range. • No significant increase in kT compared to p+p collisions is observed and no significant centrality dependence is seen. • dN/dxE distributions scale in both p+p and d+Au collisions and no systematic difference between the two systems is observed. • Data places a limit on the cold nuclear medium modification to di-jet structure. • Data also provides a baseline for measurements in Au+Au collisions. N. Grau Jet Correlations at RHIC 03/10/05

  21. Backup Slides

  22. p0 Identification • Instead of Jet reconstruction – use a high-pT trigger particle • Lvl-1 EmCal-RICH trigger • Large increase in photon statistics • Excellent p0 detection • S/B ~10-20 for p0 > 5 GeV N. Grau Jet Correlations at RHIC 03/10/05

  23. p+/- Identification • RICH fires on charged pions > 4.9 GeV/c • Use EmCal to reject other background • Total background < 5% above 5 GeV/c N. Grau Jet Correlations at RHIC 03/10/05

  24. Extracting Quantities Jet properties extracted from azimuthal correlation shape background jet di-jet N. Grau Jet Correlations at RHIC 03/10/05

  25. Detailed jT, kT formulae N. Grau Jet Correlations at RHIC 03/10/05

  26. jTy N. Grau Jet Correlations at RHIC 03/10/05

  27. Centrality Dependence of Yields pT-dependence of the associated hadron yields. N. Grau Jet Correlations at RHIC 03/10/05

  28. Yield Comparison to p+p Ratio of yields to p+p collisions. No systematic deviation. Contrast to the prediction of Hwa and Yang for an increase in the near-side yield for recombination by a factor of 2. N. Grau Jet Correlations at RHIC 03/10/05

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