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Pawan Kumar NetrakantiPANIC-2005, Santa Fe1 Pion, proton and anti-proton transverse momentum spectra in p+p and d+Au collisions at  s NN = 200 GeV Outline:

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Presentation on theme: "Pawan Kumar NetrakantiPANIC-2005, Santa Fe1 Pion, proton and anti-proton transverse momentum spectra in p+p and d+Au collisions at  s NN = 200 GeV Outline:"— Presentation transcript:

1 Pawan Kumar NetrakantiPANIC-2005, Santa Fe1 Pion, proton and anti-proton transverse momentum spectra in p+p and d+Au collisions at  s NN = 200 GeV Outline: Pawan Kumar Netrakanti,VECC, Kolkata ( for the STAR Collaboration ) Motivation Method of analysis Results * Nuclear Modification Factor * Particle Ratios * Model Comparison * Scaling of particle production Conclusions

2 Pawan Kumar NetrakantiPANIC-2005, Santa Fe2 Motivation  High p T spectra in p+p collisions - test predictions from pQCD  p T spectra in p+p and d+Au collisions provides a reference spectra for nucleus-nucleus collisions.  Solid ground for models based on jet quenching and quark recombination  Study of Nuclear Modification Factor in d+Au collisions  Particle ratios constrain particle production models

3 Pawan Kumar NetrakantiPANIC-2005, Santa Fe3 Method of analysis High p T : Extend particle identification in TPC by exploiting the relativistic rise in ionization energy loss. Log10(p) Log10(dE/dx) Momentum: GeV/c dE/dx of  K,p) separation: 2  Low p T : Particle identification by Time-Of-Flight ( p T < 2.5 GeV/c) Detectors used : Time projection Chamber (|  |<1.8, full  and 4.2 m long) Time-Of-Flight (–1.0 <  < 0 and  /30 in  )

4 Pawan Kumar NetrakantiPANIC-2005, Santa Fe4 Transverse Momentum Spectra Power law : ( A/(1 + p T /p 0 ) n ) Levy : (B/(1+(m T -m 0 )/nT) n ) Both functions give reasonable fits Power law function is pQCD inspired Levy ~ exponential + power law STAR preliminary

5 Pawan Kumar NetrakantiPANIC-2005, Santa Fe5 Nuclear Modification Factor  R dAu for  > 1, Cronin effect  Absence of high p T suppression in particle production  R dAu (p + pbar) > R dAu (  ) Similar dependence has been observed at lower energies. Phys. Rev D 19 (1979) 764 Qualitative agreement with recombination model for dAu collisions. Phys.Rev.Lett.93 (2004) STAR preliminary Phys. Rev. Lett. 91 (2003)

6 Pawan Kumar NetrakantiPANIC-2005, Santa Fe6 Particle Ratios – p+p collisions   - /  + ~ 1 and pbar/p ~ 0.8  JETSET predicts a more prominent p T dependence Phys.Rev.C 58 (1998) 2321  p/  + and pbar/  - increases with p T ~ 2 GeV/c and then decreases to ~ 0.2  p/  + agrees with lower energy results.  pbar/  - shows a distinct energy dependence STAR preliminary

7 Pawan Kumar NetrakantiPANIC-2005, Santa Fe7 Particle Ratios – d+Au collisions   - /  + ~ 1 independent of p T  pbar/p decreases with p T  p/  + and pbar/  - increases with p T up to 2 GeV/c and then decreases. STAR preliminary

8 Pawan Kumar NetrakantiPANIC-2005, Santa Fe8 Model comparison – p+p collisions  NLO pQCD KKP and AKK fragmentation function and phenomenological EPOS Model are consistent with pion data at high p T (> 2 GeV/c)  pQCD with Kretzer FF under predicts pion data  NLO pQCD only with AKK FFs ( Nucl.Phys.B725: ,2005 ) consistent with the p+pbar spectrum STAR preliminary

9 Pawan Kumar NetrakantiPANIC-2005, Santa Fe9 Model comparison – d+Au collisions  NLO pQCD with KKP and AKK FFs and EPOS are consistent with pion data at high p T (> 4 GeV/c)  pQCD with Kretzer FF under predicts pion data  NLO pQCD with only AKK FFs consistent with the p+pbar spectrum STAR preliminary Parton distribution functions : L. Frankfurt, et al., Phys. Rev. D 71 (2005) D. De Florian and R. Sassot, PRD 69 (2004)

10 Pawan Kumar NetrakantiPANIC-2005, Santa Fe10 Scaling of particle production ,p(pbar) show x T (= 2p T /  s) scaling for p T > 2 GeV/c at various CM energies m T scaling observed for 1 < m T < 2 GeV/c 2 STAR preliminary n ~ 4 for basic scattering process n ~ 8 quark meson scattering by exchanging a quark

11 Pawan Kumar NetrakantiPANIC-2005, Santa Fe11 Summary Obtained the p T spectra for charged pions, protons and anti- protons up to 10 GeV/c. Method used in high p T : relativistic rise in ionization energy loss in TPC p T spectra is fitted to both Power law and Levy distributions Significant Cronin effect in pion production in d+Au collisions. The nuclear modification factor for baryons is higher than mesons in intermediate region of p T The anti-proton/proton ratio is around 0.8 for p+p collisions. It seems to decrease with p T for d+Au collisions

12 Pawan Kumar NetrakantiPANIC-2005, Santa Fe12 Summary (Contd…) Pion spectra for high p T is well explained using KKP & AKK type of fragmentation function in p+p and d+Au collisions. NLO pQCD calculations with only AKK fragmentation functions explain the proton+anti-proton spectra A phenomenological model based on parton splitting (EPOS) also does a reasonable job Pions and protons exhibit xT scaling. m T scaling of pions and protons in p+p and d+Au collisions for m T < 2 GeV/c 2

13 Pawan Kumar NetrakantiPANIC-2005, Santa Fe13 Highlight NLO pQCD describes the p+pbar spectrum for the first time in p+p collisions Importance of the significant improvement of FF for baryons from the light-flavor separated measurements in e+e- collisions (OPAL) The observed x T scaling of ,p(pbar) at high pT also show dominance of hard processes related to PDF and FF Provide solid reference for effects of jet quenching and recombination in Nucleus-Nucleus collisions

14 Pawan Kumar NetrakantiPANIC-2005, Santa Fe14 Backup Slides (Comparison with PHENIX)

15 Pawan Kumar NetrakantiPANIC-2005, Santa Fe15 Backup Slides (e+e- scaling) Scaling in e+e- collisions


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