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Bedanga Mohanty,VECC, Kolkata (Pawan Kumar Netrakanti and Zhangbu Xu

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1 Identified hadron spectra at large transverse momentum in p+p and d+Au collisions at 200 GeV
Bedanga Mohanty,VECC, Kolkata (Pawan Kumar Netrakanti and Zhangbu Xu for the STAR Collaboration) Bedanga Mohanty BNL Seminar, November 22nd 2005

2 BNL Seminar, November 22nd 2005
Outline STAR preliminary Motivation Method of analysis Results from p+p collisions Results from d+Au collisions Summary     STAR preliminary Bedanga Mohanty BNL Seminar, November 22nd 2005

3 BNL Seminar, November 22nd 2005
Motivation High pT PID in TPC Test predictions (certain aspects) of pQCD Understanding Nuclear effects in d+Au collisions Bedanga Mohanty BNL Seminar, November 22nd 2005

4 Low pT – Time Of Flight (TOF)
Method of analysis Low pT – Time Of Flight (TOF) High pT – Time Projection Chamber (TPC) Detectors : K. H. Ackerman et al., Nucl. Instrum. Methods Phys. Res., Sect. A 499 (2003) 624 TOF low pT results : STAR Collaboration, J. Adams et al., Phys. Lett. B 616 (2005) 8 Trigger & centrality : STAR Collaboration, J. Adams et al., Phys. Rev. Lett. 91 (2003) Phys. Rev. Lett. 92 (2004) rdE/dx method : M. Shao, et al., arXiv:nucl-ex/ Bedanga Mohanty BNL Seminar, November 22nd 2005

5 Method of analysis : Detector - TOF
Hadron identification: STAR Collaboration, nucl-ex/ PMD A new technology ---- Multigap Resistive Plate Chamber (MRPC) adopted from CERN-Alice. Intrinsic timing resolution: 85 ps in STAR Coverage : -1.0 < h < 0.0 and p/30 in f low pT particle identification ( < 2.5 GeV/c) in this study Bedanga Mohanty BNL Seminar, November 22nd 2005

6 Method of analysis : Detector - TPC
Time projection Chamber Log10(p) Log10(dE/dx) 45 padrows, radius 2 meters, |h|<1.8, full f and s(dE/dx) ~ 8% High pT : Extend particle identification in TPC by exploiting the relativistic rise in ionization energy loss. Low pT Momentum: GeV/c dE/dx of p (K,p) separation: 2s Bedanga Mohanty BNL Seminar, November 22nd 2005

7 BNL Seminar, November 22nd 2005
Method of analysis We obtain the ns(p) distribution for each pT bin Then simultaneously fit them to 6 Gaussians Constraints put by studying various parameters of dE/dx Proton yields : h ~ π + K + p (a) c1 p + c2 K=X (b) c1 p + c2 K=X where K is constrained by K0s c1, c2 are K, p contributions, and X is the total yield in the counting region Bedanga Mohanty BNL Seminar, November 22nd 2005

8 Theory of particle production in p+p collisions
How quarks are distributed in hadrons we collide How quarks and gluons fragment into hadrons What is the probability that 2 quarks will interact Quark Distribution Functions determined from deep-inelastic lepton-hadron collisions Hadron # 1 collide Quarks – fragment into hadrons Hadron # 2 Quark-Quark Cross-Section Determined from hadron-hadron collisions. Quark Fragmentation Functions determined from e+e- annihilations Bedanga Mohanty BNL Seminar, November 22nd 2005

9 Why study particle production in p+p collisions at high pT
Provides a testing ground for next to leading order pQCD P. Aurenche et al., EPJ C13, 347 (2000) PHENIX : PRL 91 (2003) What about p, protons and anti-protons ? Proton spectra : FF from e++e- works or not in p+p collisions ? pQCD works best for scales pT >> mass Bedanga Mohanty BNL Seminar, November 22nd 2005

10 Why study particle production in p+p collisions at high pT
Hadronization (by quark fragmentation ?) If : p/p = q p / q p (p/p)AA ~ (p/p)pp p/p << 1 Nuclear effects (presence or absence ?) Crucial data for models : Jet quenching and Recombination Bedanga Mohanty BNL Seminar, November 22nd 2005

11 Transverse Momentum Spectra
STAR preliminary Power law function ~ pQCD inspired Levy ~ exponential + power law Power law : ( A/(1 + pT/p0)n) Levy : (B/(1+(mT-m0)/nT)n) Power law behaviour for p+p collisions at high pT Bedanga Mohanty BNL Seminar, November 22nd 2005

12 p+p collisions and pQCD (Kretzer)
STAR preliminary NLO pQCD calculations with Kretzer FF inconsistent with data at midrapidity STAR preliminary S. Kretzer, Phys. Rev. D 62 (2000) Bedanga Mohanty BNL Seminar, November 22nd 2005

13 p+p collisions and pQCD (KKP)
NLO pQCD calculations with KKP FF are consistent with pion data at high pT (> 2 GeV/c) They are inconsistent with the proton+anti-proton data STAR preliminary STAR preliminary B. A. Kniehl, G. Kraner and B. Potter, Nucl. Phys. B 597 (2001) 337 NLO pQCD calculations by W. Vogelsang Bedanga Mohanty BNL Seminar, November 22nd 2005

14 p+p collisions and pQCD (higher rapidity)
Inclusive forward p0 production in p+p collisions at 200 GeV consistent with NLO pQCD calculations At small h, data consistent with KKP, as h increases data approaches cal. with Kretzer set of FF G. Rakness, nucl-ex/ and D.A. Morozov, , hep-ex/ Bedanga Mohanty BNL Seminar, November 22nd 2005

15 p+p collisions and pQCD (AKK)
NLO pQCD calculations with AKK FF are consistent with pion data at high pT (> 2 GeV/c) NLO pQCD calculations only with AKK FF (Nucl.Phys.B725: ,2005) consistent with the p+pbar data STAR preliminary AKK differ from KKP, in the way the light flavor FF are obtained OPAL Collaboration : Eur. Phys. J. C 17 (2000) 207 Bedanga Mohanty BNL Seminar, November 22nd 2005

16 p+p collisions : Gluon or quark fragmentation
NLO pQCD calculations with AKK FF shows significant contribution to pion production from gluon fragmentation at high pT STAR preliminary NLO pQCD calculations only with AKK FF shows gluon fragmentation dominant contributor to p+pbar yield at high pT Bedanga Mohanty BNL Seminar, November 22nd 2005

17 Scaling in e++e- collisions
e+ and e- does not have a parton distribution function There is no (sNN )nor (pT)n factor multiplied to cross section What happens in hadron-hadron collisions ? TPC Collaboration, H. Aihara, et al., Phys. Rev. Lett. 61 (1988) 1263 ARGUS Collaboration, H. Albrecht, et al., Z. Phys. C 44 (1989) 547 ALEPH Collaboration, D. Buskulic, et al., Z. Phys. C 66 (1995) 355 Bedanga Mohanty BNL Seminar, November 22nd 2005

18 Scaling in p+p collisions
    STAR preliminary Spectra fitted to pTn (1-xT)m n ~ 4 for basic scattering process n ~ 8 quark-meson scattering by exchange a quark Pions,protons and anti-protons show the xT (= 2pT/s) scaling for pT > 2 GeV/c at various CM energies Bedanga Mohanty BNL Seminar, November 22nd 2005

19 p+p collisions and phenomenological model
STAR preliminary Phenomenological EPOS Model are consistent with pion data, even at low pT. Phenomenological EPOS Model are consistent with p + pbar data, even at low pT. Interesting to observe that two different models (pQCD and EPOS) do a reasonable job in pp collisions K. Werner, F. Liu and T. Pierog, hep-ph/ Bedanga Mohanty BNL Seminar, November 22nd 2005

20 BNL Seminar, November 22nd 2005
Conclusions so far…. For the first time it is observed that the proton + anti-proton spectra is consistent with NLO pQCD calculations using the AKK fragmentation functions. The AKK fragmentation functions are obtained from the light-flavor separated measurements on light charged hadrons in e+e- collisions by OPAL Collaboration     The pion, proton, and anti-proton production at high pT is consistent with pQCD calculations This is independently verified by the observed xT scaling in pions, protons, and anti protons. Bedanga Mohanty BNL Seminar, November 22nd 2005

21 d+Au collisions helps p+p  Au+Au collisions
p + p collisions Au + Au collisions Parton Distribution Function Hard-scattering cross-section Fragmentation Function Parton Distribution Function Intrinsic kT , Cronin Effect Shadowing, EMC Effect Hard-scattering cross-section Partonic Energy Loss Fragmentation Function Bedanga Mohanty BNL Seminar, November 22nd 2005

22 What we know so far in d+Au collisions
Phys. Rev. Lett. 91 (2003) Phys. Rev. Lett. 91, No. 7, August 15, 2003 Bedanga Mohanty BNL Seminar, November 22nd 2005

23 What more to study d+Au collisions at high pT
Cp ~ CK < Cp Does pQCD still work ? Do we understand RdAu (Cronin effect …recombination,shadowing, energy loss in cold nuclear matter ?) CGC models : Classical gluon production leads to Cronin effect. Nucleus pushes gluons To higher pT. At high energy and rapidity, the Cronin peak decreases. J. W. Cronin, et al., Phys. Rev. D 11 (1975) 3105 D. Kharzeev, Y. Kovchegov and K. Tuchin, PLB 599 (2004) 23 Bedanga Mohanty BNL Seminar, November 22nd 2005

24 What more to study d+Au collisions at high pT
Cronin effect through recombination models Role of shadowing cannot be neglected Identified hadron data available (charged pions, protons and anti-protons) at high pT further our understanding R.C. Hwa and C. B. Yang, Phys. Rev. C 70 (2004) R. Vogt, Phys. Rev. C 70 (2004) Bedanga Mohanty BNL Seminar, November 22nd 2005

25 Transverse Momentum Spectra
STAR preliminary Power law : ( A/(1 + pT/p0)n) Levy : (B/(1+(mT-m0)/nT)n) Power law function ~ pQCD inspired Levy ~ exponential + power law Power law type behavior for d+Au collisions at high pT Bedanga Mohanty BNL Seminar, November 22nd 2005

26 d+Au collisions and models
NLO pQCD calculations with KKP and AKK FF and phenomenological EPOS Model are consistent with pion data at high pT (> 4 GeV/c) pQCD calculations with Kretzer FF under predicts pion data NLO pQCD calculations with only AKK fragmentation function consistent with the p+pbar data Parton distribution functions : L. Frankfurt, et al., Phys. Rev. D 71 (2005) D. De Florian and R. Sassot, PRD 69 (2004) Bedanga Mohanty BNL Seminar, November 22nd 2005

27 Scaling of particle production
STAR preliminary mT scaling observed for 1 < mT < 2 GeV/c2 Another way of saying absence of flow effects At high pT : no scaling Mass effect Or baryon-meson effect Bedanga Mohanty BNL Seminar, November 22nd 2005

28 Nuclear Modification Factor : d+Au collisions
STAR preliminary Phys. Rev. Lett. 91 (2003) RdAu for p > 1, Cronin effect Absence of high pT suppression in particle production RdAu (p + pbar) > RdAu (p) 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) Bedanga Mohanty BNL Seminar, November 22nd 2005

29 RdAu : Centrality dependence
RdAu increases with centrality Bedanga Mohanty BNL Seminar, November 22nd 2005

30 BNL Seminar, November 22nd 2005
Conclusion so far Pion spectra for high pT is well explained using KKP & AKK type of fragmentation function in d+Au collisions. NLO pQCD calculations with only AKK fragmentation functions explain the proton+anti-proton spectra Significant Cronin effect in pion production in d+Au collisions. The nuclear modification factor for baryons is higher than mesons in intermediate region of pT Bedanga Mohanty BNL Seminar, November 22nd 2005

31 Particle Ratios – in p+p and p+A collisions
Same-charge particle ratios for high pT hadrons p/p+ Vs. pT reflects FF ratio Dpu /Dp+ u A rapid drop of p/p+ with pT followed by a high pT flattening – scattered point-like diquarks as a source of high pT protons (Phys.Lett.B149:509,1984) A rapid drop of p/p+ with pT is reflective of Q2 dependence of diquark form factor pbar/p- : pbar must be produced by scattering of sea-quarks or gluons or rank ordering Decrease in pbar/p-  decreasing importance of these processes Opposite-charge particle ratios for high pT hadrons p-/p+ Vs. pT or x may reflect the d/u structure function ratio in protons pbar/p Vs. pT : p has valence quarks common with nucleons, so it may reflect the on fraction of protons of gluonic origin (assuming that gluons fragment equally into p and pbar). Bedanga Mohanty BNL Seminar, November 22nd 2005

32 Particle Ratios – p+p collisions
Phys. Rev D 19 (1979) 764 p-/p+ decreases with pT in p+p collisions from ~1.0 to 0.5 p-/p+ independent of pT in p+n collisions Bedanga Mohanty BNL Seminar, November 22nd 2005

33 Particle Ratios – p+A collisions
p-/p+ decreases with pT from ~0.9 to ~ 0.6 pbar/p decreases with pT from ~ 0.1 to 0.03 p/p+ and pbar/p- decreases for pT > 4 GeV/c from ~ 0.6 to Phys. Rev D 45 (1992) 3030 Bedanga Mohanty BNL Seminar, November 22nd 2005

34 Particle Ratios – p+p collisions
STAR preliminary p-/p+ ~ 1 and pbar/p ~ 0.8 JETSET predicts a more prominent pT dependence Phys.Rev.C 58 (1998) 2321 p/p+ and pbar/p- increases with pT ~ 2 GeV/c and then decreases to ~ 0.2 p/p+ agrees with lower energy results. pbar/p- shows a distinct energy dependence         Bedanga Mohanty BNL Seminar, November 22nd 2005

35 Particle Ratios – d+Au collisions
    STAR preliminary p-/p+ ~ 1- independent of pT pbar/p decreases with pT p/p+ and pbar/p- increases with pT up to 2 GeV/c and then decreases. Bedanga Mohanty BNL Seminar, November 22nd 2005

36 BNL Seminar, November 22nd 2005
Summary Obtained the pT spectra for charged pions, protons and anti-protons up to 10 GeV/c. Method used in high pT : relativistic rise in ionization energy loss in TPC pT 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 pT The anti-proton/proton ratio is around 0.8 for p+p collisions. It seems to decrease with pT for d+Au collisions     Bedanga Mohanty BNL Seminar, November 22nd 2005

37 BNL Seminar, November 22nd 2005
Summary (Contd…) Pion spectra for high pT 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. mT scaling of pions and protons in p+p and d+Au collisions for mT < 2 GeV/c2     Thanks Bedanga Mohanty BNL Seminar, November 22nd 2005

38 BNL Seminar, November 22nd 2005
Conclusion so far Bedanga Mohanty BNL Seminar, November 22nd 2005

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