This report describes the recent analysis of identified charged particle
production at high rapidity performed on data collected from p+p collisions at
RHIC (sqrt{s}=200 GeV). The extracted invariant cross-sections compare well to
NLO pQCD calculations. However, a puzzling high yield of protons at high
rapidity and p_T has been found.Comment: 5 pages, four figures. The labels of the x-axis in figure 1 have been
  correcte

null null

R. Debbe

English

arXiv

This report describes the recent analysis of identified charged particle production at high rapidity performed on data collected from p+p collisions at RHIC ({radical}s = 200 GeV). The extracted invariant cross-sections compare well to NLO pQCD calculations. However, a puzzling high yield of protons at high rapidity and p{sub T} has been found

DEBBE,R.

UNT (University of North Texas) Digital Library

N ATI o p 4 ” ~  LAB o RATO RY ,) BNL-79565-2007-CP Charged Particle Production at High Rapidity in p+p Collisions at RHIC R. Debbe for the BRAHMS Collaboration Presented at the 9th Conference on the Intersections of Particle and Nuclear Physics Rio Grande, Puerto Rico May 30 - June 3,2006 Physics Department Heavy Ion Research Group Brookhaven National Laboratory P.O. Box 5000 Upton, NY 1 1 973-5000 www. brtl.gov Notice: This manuscript has been authored by employees of Brookhaven Science Associates, LLC under Contract No. DE-AC02- 98CH10886 with the U.S. Department of Energy. The publisher by accepting the manuscript for publication acknowledges that the United States Government retains a non-exclusive, paid-up, irrevocable, world-wide license to publish or reproduce the published form of this manuscript, or allow others to do so, for United States Government purposes. This preprint is intended for publication in a journal or proceedings. Since changes may be made before publication, it may not be cited or reproduced without the author’s permission. DISCLAIMER This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof, nor any of their employees, nor any of their contractors, subcontractors, or their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or any third party’s use or the results of such use of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise, does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof or its contractors or subcontractors. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof t Charged Particle Production at High Rapidity in p+p Collisions at RHIC R. Debbe for the BRAHMS Collaboration Brookhaven National Laboratory Abstract. This report describes the recent analysis of identified charged particle production at high rapidity performed on data collected from p+p collisions at RHIC (4 = 2OOGeV). The extracted invariant cross-sections compare well to NLO pQCD calculations. However, a puzzling high yield of protons at high rapidity and p~ has been found. Keywords: RHIC, pp cross-sections, NLO pQCD, baryon transport PACS: 13.85.Ni, 13.87.Fh, 25.75.Dw, 13.85.Hd, 25.75.-q INTRODUCTION The p+p system is used in many cases as a paradigm of the simple hadronic interac- tion. In particular, nuclear effects in p(d)+A and A+A collisions are extracted through their suitably normalized comparison to p+p collisions. In reality the p+p system is still waiting for a truly from-first-principle QCD based description that will include the pro- duction of particles and the distribution of the beam baryon number after the collision. As part of the RHIC heavy-ion and spin programs, p+p collisions at fi = 200 GeV have been produced during several runs providing a great opportunity to revisit the work done at SppS [ 1,2] and especially to fill the gaps left in the study of particle production at high rapidity. This report describes the production of charged particles in p+p collisions mea- sured by the BRAHMS Collaboration and their comparison to Next-to-Leading-Order perturbative Quantum Chromodynamics (NLO pQCD) calculations. It also presents a puzzling high yield of protons at high rapidity and transverse momentum. THE BRAHMS SETUP AND ANALYSIS DETAILS. The results reported here were obtained with the BRAHMS Forward Spectrometer (FS) that consists of five tracking stations measuring the momentum of charged particles deflected in the field of three warm magnets. The particle identification for this work was performed entirely with the BRAHMS Ring Imaging Cherenkov (RICH) detector. The efficiency of this detector was estimated from the data and reaches a constant value of 97%. The data used in this analysis were collected with two main triggers, a minimum bias trigger built from the signal produced in several stations of Cherenkov radiators placed near the beam pipe on both sides of the nominal interaction point called CC detectors, and a spectrometer trigger used to select events with tracks in the FS spectrometer. The CC detectors have an angular coverage the extends from 17 = 3.26 to 17 = 5.25. More details of the BRAHMS experimental setup can be found in [3]. The y=3.3 - - **-e 7 1. * . . .r..  . * . .  . . I . .  . . :-. . . . :\ 10.~ -1 :\ n: PRELIMINARY y=2.95 *+e **+ lo 10.~ - 10 A positive K 0 negative - - 10.~ - \%+ +-A- lo-' i \& -0-0- -?- 10.~ - 7 7 I * . _ _ _ .  C . . . . . . . . . . . . . . n  : . . . . . . . . n . . . J  2 3 4 5 1 2 3 4  5 p [GeV/c] p [GeV/c] FIGURE 1. Invariant cross-section for production of pions, kaons and protons. See text for details. CC detectors have been included into a thorough simulation of the BRAHMS setup, and it is estimated that they cover 70 f 1% of the 41mb total inelastic p+p cross-section at fi = 200 GeV. The spectrometer trigger was built with signals from three scintillator hodoscopes mounted on the spectrometer. Simulated events generated with PYTHIA [4] were processed with a GEANT simulation of the BRAHMS setup, the efficiency of the spectrometer trigger to detect truly minimum biased events was extracted from that simulation and was found to be equal to 82.6 f0 .8% and fairly independent of p ~ .  Figure 1 shows the invariant cross-section for pions (top), kaons (middle), and protons (bottom) at two rapidities y=2.95 on the left and y=3.3 on the right. In each panel the positive particles are shown with filled triangles and the negative ones with open circles. The spectra were extracted from narrow rapidity bins (Ay = 0.1) centered in regions of the spectrometer acceptance with the highest reach in p~ and may include up to five magnetic field settings. The spectra have been corrected for the spectrometer acceptance, tracking reconstruction inefficiencies that range from 80-90%, decays in flight, absorptions in the spectrometer and trigger bias. COMPARISONS WITH NLO PQCD CALCULATIONS The differential cross-sections at y=2.95 have been compared to NLO pQCD calcula- tions [5] that use a modified version of the "Kniehl-Kramer-Potter" (KKP) set of frag- mentation functions [6] referred here as mKKP as well as the "Kretzer" set [7]. Both cal- culations have been done with equal values of renormalization and factorization scales p = p ~ .  The functions from the KKP set fragment into sums: z+ + z-, K+ + K -  and FIGURE 2. Comparison between the measured cross sections for the production of negative pion, positive kaons and p + p at y=2.95 and the NLO calculations at the same rapidity. Calculations including the mKKP set of fragmentation functions are shown with a full line (red online), the ones using the K set are shown with dashed line (blue in online). The p + p  sum is shown with filled triangles in the right panel and is well described by the calculations including the AKK set (shown with a dashed curve (red online). The same panel displays the anti-proton cross-section with open circles and the NLO calculation for p + p using the KKP set of functions (full curve). The ratios (Data-NLO)/NLO for each of the comparisons mentioned above is shown in the three bottom panels. Filled triangles (red online) are used for the mKKP set and filled circles for the K set for pions and kaons. The comparison of the AKK and the measured p + jj cross-section is shown with filled circles (red online) and the one for the KKP set and anti-protons is shown with filled triangles. p + p .  Modifications were necessary to obtain fragmentation into separate charges for n and K: The fragmentation function for u and d quarks into n+ were obtained as the product DE' = (1 + z)D$ with DEo = @Et+R-  and the functions fragmenting i and d quarks into n+ are obtained in similar fashion but the factor changes to (1 - z). Similar operations are performed for fragmentation functions producing negative pions. In the case of kaons the operations involve the u, 6,  s, S quarks. The agreement between the measured cross-sections for negative pions and positive kaons at y=2.95 shown in the left and middle panels of Fig. 2 is remarkable. The calculation that incorporates the mKKP set is the one that describes best the produced particle distributions. Similar agreements have also been seen at mid-rapidity for no measured by PHENIX [8], and at high rapidity, for the STAR no measurement [9]. Figure 3 displays all three measurements showing how the distributions get stepper at higher rapidities while the NLO calculations using the KKP set reproduce the data within four units of rapidity starting at surprisingly low values of p ~ .  RATIOS Figure 4 shows the ratio of anti-particle to particle at both rapidities, as well as the ratio of protons to pion. The results obtained at y=2.95 are shown on the left column and the 0 PHENIXyd BRAHMSy=2.95 * STARy=3.8 78 n- PRELIMINARY 7co I O - g F '  ; ' ' ' ;  ' ' ' # \  ' ; " ' 10 I ' " 12 ' ' ' ' 14 I ' P, [GeV/cl FIGURE 3. Invariant cross-sections as function of p~ measured in p+p collisions at RHIC 4 = 200 GeV by PHENM at y=O (open circles), BRAHMS at y=2.95 (filled circles, blue online) and STAR at y=4 (stars, red online). The curve is the NLO calculation with the KKP set of fragmentation functions. The errors are statistical. ones at y=3.3 on the right one. The ratio x-/x+ shown on the top panels tends toward 1/2 in agreement with a simple valence quark counting in the proton beam. This hints to a possible dominance of valence quark fragmentation in the pion productions at these high rapidities. The ratio of p / p  shown in the two middle panels is small and drops fast as the p~ increases, indicating again the importance of beam protons. How did these protons acquire their moderately high p~ is an unknown. The successful reproduction of STAR proton cross-section at mid-rapidity in p+p collisions [ 101 with NLO calculations that make use of a newly released set of fragmentation functions dubbed the AKK set [ l l ] ,  has been advanced as an indication of the important contribution of the gluon fragmentation into protons or anti-protons. The same comparison, done with the p + p sum at y=2.95, can be seen in the right-most panel of Fig. 2. The calculation lies almost on top of the data points but it is in a clear contradiction with the measured p / p  ratios shown in the middle panels of Fig. 4. Gluons should fragment into p p  pairs and will produce p / p  with values close to 1 similar to the ones measured at mid-rapidity. The fact that the value of the p / p  ratio at high rapidity is so small invalidates the use of the AKK set at high rapidity. Figure 2 also shows the NLO calculation with the KKP set for the sum p + p in good agreement with the measured anti-protons cross-section. This could be a hint that factorized QCD and the parametrization of the fragmentation functions can describe the physics of produced particles but another approach is needed in order to include the protons and reach a truly complete description of high energy p+p collisions. The two bottom panels of Fig. 4 show the ratios p/x+ (filled triangles, red online) and p/x- (open circles) as function of p~ and at rapidity y=2.95 (left) and y=3.3 (right). The difference between the ratios of negative particles (produced) and positives is remarkable and shows that a factorized pQCD based description fails for protons. The ratio p/x- is closer to a rough parametrization extracted from e+e- annihilations. I I .- 'f PRELIMINARY 0 0 0 0 FIGURE 4. The n-/n+ ratios at both rapidities are shown on the top panels, the p / p  ratio is shown in the middle panel, the bottom panels show the p / n +  and p/n- ratios. Data from e+e- annihilations is shown with a dashed line [12]. The smooth curves are obtained from the NLO calculations of Fig. 2. SUMMARY We have presented the recently measured cross-sections for pions, kaons and protons at high rapidity in p+p collisions at RHIC. The NLO pQCD calculations incorporating the KKP fragmentation functions describe the pion and kaon cross-sections. Protons at high rapidity and p~ appear in unusually high numbers that do not fit into a factorized pQCD description based on parton-parton interactions. We thank Werner Vogelsang for providing us with the NLO pQCD calculations shown in this report. This work was supported by the Office of Nuclear Physics of the U.S. Department of Energy, the Danish Natural Science Research Council, the Research Council of Norway, the Polish State Committee for Scientific Research (KBN) and the Romanian Ministry of Research. REFERENCES 1. J. Alitti et aZ., Phys. Lett. B257 232, (1991). 2. E. Pare etaL, Phys. Lett. B242 531-535 (1990). 3. M. Adamczyk et aL, BRAHMS Collaboration, Nuclear Instruments and Methods, A499 437 (2003). 4. T. Sjostrand, et aL, Comp. Phys. Commun. 135,238, (2001). Version 6.303 was used. 5. B. Jager, A. Schafer, M. Stratmann and W. Vogelsang, Phys. Rev. D 67,054005 (2003). 6. B.A. Kniehl et aL, Nucl. Phys. B597,337 (2001). 7. S. Kretzer etal, Eur. Phys. J. C22,269 (2001). 8. S. S. Adler, etal., Phys. Rev. Lett. 91,241803 (2003). 9. J. Adams et aL, Phys. Rev. Lett. 92 171801 (2004). 10. J. Adams et al., Phys. Lett. bf B637, 161 (2006). 11. S. Albino, B.A. Kniehl and G. Kramer, Nucl. Phys. B725, 181, (2005). 12. P. Abreu et aL, Eur. Phys. J. C17,207, (2000); R. Barate et aL, Phys. Rept 294, 1-165, (1998). 

CHARGED PARTICLE PRODUCTION AT HIGH RAPIDITY IN p+p COLLISIONS AT RHIC.

Crossref

Charged Particle Production at High Rapidity in p+p Collisions at RHIC

ar
X
iv
:n
uc
l-e
x/
06
08
04
0v
3 
 2
8 
A
ug
 2
00
6
Charged Particle Production at High Rapidity in
p+p Collisions at RHIC
R. Debbe for the BRAHMS Collaboration
Brookhaven National Laboratory
Abstract. This report describes the recent analysis of identified charged particle production at high
rapidity performed on data collected from p+p collisions atRHIC (
√
s = 200GeV). The extracted
invariant cross-sections compare well to NLO pQCD calculations. However, a puzzling high yield
of protons at high rapidity andpT has been found.
INTRODUCTION
The p+p system is used in many cases as a paradigm of the simplehadronic interac-
tion. In particular, nuclear effects in p(d)+A and A+A collisions are extracted through
their suitably normalized comparison to p+p collisions. Inreality the p+p system is still
waiting for a truly from-first-principle QCD based description that will include the pro-
duction of particles and the distribution of the beam baryonnumber after the collision.
As part of the RHIC heavy-ion and spin programs, p+p collision at
√
s = 200 GeV have
been produced during several runs providing a great opportunity to revisit the work done
at SppS [1, 2] and especially to fill the gaps left in the study of particle production at high
rapidity. This report describes the production of charged particles in p+p collisions mea-
sured by the BRAHMS Collaboration and their comparison to Next-to-Leading-Order
perturbative Quantum Chromodynamics (NLO pQCD) calculations. It also presents a
puzzling high yield of protons at high rapidity and transverse momentum.
THE BRAHMS SETUP AND ANALYSIS DETAILS.
The results reported here were obtained with the BRAHMS Forward Spectrometer (FS)
that consists of five tracking stations measuring the momentum of charged particles
deflected in the field of three warm magnets. The particle ident fication for this work
was performed entirely with the BRAHMS Ring Imaging Cherenkov (RICH) detector.
The efficiency of this detector was estimated from the data and reaches a constant
value of 97%. The data used in this analysis were collected with t o main triggers,
a minimum bias trigger built from the signal produced in several stations of Cherenkov
radiators placed near the beam pipe on both sides of the nominal interaction point called
CC detectors, and a spectrometer trigger used to select evens with tracks in the FS
spectrometer. The CC detectors have an angular coverage theextends fromη = 3.26 to
η = 5.25. More details of the BRAHMS experimental setup can be found in [3]. The
 [GeV/c]
T
p
1 2 3 4 5
positive
negative
y=3.3
 [GeV/c]
T
p
1 2 3 4 5
-710
-510
-310
-110
10
 P 
]3 c
-2
 [m
b(
G
eV
/c
)
dy
T
dp
σ
2
d
 
T
 pπ2
1
-710
-510
-310
-110
10
K
-7
-510
-310
-110
10
y=2.95
π
PRELIMINARY
FIGURE 1. Invariant cross-section for production of pions, kaons andprotons. See text for details.
CC detectors have been included into a thorough simulation of the BRAHMS setup, and
it is estimated that they cover 70±1% of the 41mb total inelastic p+p cross-section at√
s = 200 GeV. The spectrometer trigger was built with signals from three scintillator
hodoscopes mounted on the spectrometer. Simulated events gerated with PYTHIA
[4] were processed with a GEANT simulation of the BRAHMS setup, the efficiency of
the spectrometer trigger to detect truly minimum biased events was extracted from that
simulation and was found to be equal to 82.6±0.8% and fairly independent ofpT .
Figure 1 shows the invariant cross-section for pions (top),kaons (middle), and protons
(bottom) at two rapidities y=2.95 on the left and y=3.3 on theright. In each panel
the positive particles are shown with filled triangles and the negative ones with open
circles. The spectra were extracted from narrow rapidity bins (∆y = 0.1) centered in
regions of the spectrometer acceptance with the highest reach in pT and may include
up to five magnetic field settings. The spectra have been corrected for the spectrometer
acceptance, tracking reconstruction inefficiencies that range from 80-90%, decays in
flight, absorptions in the spectrometer and trigger bias.
COMPARISONS WITH NLO PQCD CALCULATIONS
The differential cross-sections at y=2.95 have been compared to NLO pQCD calcula-
tions [5] that use a modified version of the "Kniehl-Kramer-Potter" (KKP) set of frag-
mentation functions [6] referred here as mKKP as well as the "Kr tzer" set [7]. Both cal-
culations have been done with equal values of renormalization and factorization scales
µ = pT . The functions from the KKP set fragment into sums:π++π−, K++K− and
1 2 3 4 5
N
LO
D
at
a-
N
LO
-2
-1.5
-1
-0.5
0
0.5
1
1.5
2
 [GeV/c]
T
p
1 2 3 4 5
N
LO
D
at
a-
N
LO
-2
-1.5
-1
-0.5
0
0.5
1
1.5
2
1 2 3 4 5
N
LO
D
at
a-
N
LO
-2
-1.5
-1
-0.5
0
0.5
1
1.5
2 K
mKKP
]3 c
-2
 [m
b(
G
eV
/c
)
η
d
T
dp
σ2
d
 
T
 pπ2
1
-710
-610
-510
-410
-310
-210
-110
1
10
y=2.95
pp+
p
 AKK
T
=pµ
 KKP
T
=pµ
]3 c
-2
 [m
b(
G
eV
/c
)
η
d
T
dp
σ2
d
 
T
 pπ2
1
-710
-610
-510
-410
-310
-210
-110
1
10
y=2.95
+K
 mKKP
T
=pµ
 K
T
=pµ
]3 c
-2
 [m
b(
G
eV
/c
)
η
d
T
dp
σ2
d
 
T
 pπ2
1
-710
-610
-510
-410
-310
-210
-110
1
10
y=2.95
-π
PRELIMINARY
 mKKP
T
=pµ
 K
T
=pµ
FIGURE 2. Comparison between the measured cross sections for the producti n of negative pion,
positive kaons andp+ p̄ at y=2.95 and the NLO calculations at the same rapidity. Calcul tions including
the mKKP set of fragmentation functions are shown with a fullline (red online), the ones using the K set
are shown with dashed line (blue in online). Thep+ p̄ sum is shown with filled triangles in the right panel
and is well described by the calculations including the AKK set (shown with a dashed curve (red online).
The same panel displays the anti-proton cross-section withopen circles and the NLO calculation forp+ p̄
using the KKP set of functions (full curve). The ratios (Data-NLO)/NLO for each of the comparisons
mentioned above is shown in the three bottom panels. Filled triangles (red online) are used for the mKKP
set and filled circles for the K set for pions and kaons. The comparison of the AKK and the measured
p+ p̄ cross-section is shown with filled circles (red online) and the one for the KKP set and anti-protons
is shown with filled triangles.
p+ p̄. Modifications were necessary to obtain fragmentation intoseparate charges for
π andK: The fragmentation function foru and d̄ quarks intoπ+ were obtained as the
productDπ
+
u = (1+ z)D
π0
u with D
π0
u =
1
2D
π++π−
u and the functions fragmenting ¯u andd
quarks intoπ+ are obtained in similar fashion but the factor changes to(1− z). Similar
operations are performed for fragmentation functions producing negative pions. In the
case of kaons the operations involve theu, ū,s, s̄ quarks.
The agreement between the measured cross-sections for negative pions and positive
kaons at y=2.95 shown in the left and middle panels of Fig. 2 isremarkable. The
calculation that incorporates the mKKP set is the one that describes best the produced
particle distributions. Similar agreements have also beenseen at mid-rapidity forπ0
measured by PHENIX [8], and at high rapidity, for the STARπ0 measurement [9].
Figure 3 displays all three measurements showing how the distributions get stepper
at higher rapidities while the NLO calculations using the KKP set reproduce the data
within four units of rapidity starting at surprisingly low values ofpT .
 [GeV/c]
T
p
2 4 6 8 10 12 14
]3 c
-2
 [m
b(
G
eV
/c
)
dy
T
dp
σ2
d
 
T
 pπ2
1
-910
-810
-710
-610
-510
-410
-310
-210
-110
1
PHENIX y=0
0π
BRAHMS y=2.95
  PRELIMINARY-π
STAR y=3.8
0π
 KKP
T
=pµ
FIGURE 3. Invariant cross-sections as function ofpT measured in p+p collisions at RHIC
√
s = 200
GeV by PHENIX at y=0 (open circles), BRAHMS at y=2.95 (filled circles, blue online) and STAR at y=4
(stars, red online). The curve is the NLO calculation with the KKP set of fragmentation functions. The
errors are statistical.
RATIOS
Figure 4 shows the ratio of anti-particle to particle at bothrapidities, as well as the ratio
of protons to pion. The results obtained at y=2.95 are shown on the left column and the
ones at y=3.3 on the right one. The ratioπ−/π+ shown on the top panels tends toward
1/2 in agreement with a simple valence quark counting in the proton beam. This hints
to a possible dominance of valence quark fragmentation in the pion productions at these
high rapidities. The ratio of ¯p/p shown in the two middle panels is small and drops fast
as thepT increases, indicating again the importance of beam protons. How did these
protons acquire their moderately highpT is an unknown. The successful reproduction of
STAR proton cross-section at mid-rapidity in p+p collisions [10] with NLO calculations
that make use of a newly released set of fragmentation functio s dubbed the AKK set
[11], has been advanced as an indication of the important contribution of the gluon
fragmentation into protons or anti-protons. The same comparison, done with thep+ p̄
sum at y=2.95, can be seen in the right-most panel of Fig. 2. The calculation lies almost
on top of the data points but it is in a clear contradiction with the measured ¯p/p ratios
shown in the middle panels of Fig. 4. Gluons should fragment into pp̄ pairs and will
produce ¯p/p with values close to 1 similar to the ones measured at mid-rapidity. The
fact that the value of the ¯p/p ratio at high rapidity is so small invalidates the use of
the AKK set at high rapidity. Figure 2 also shows the NLO calculation with the KKP
set for the sump+ p̄ in good agreement with the measured anti-protons cross-section.
This could be a hint that factorized QCD and the parametrization of the fragmentation
functions can describe the physics of produced particles but another approach is needed
in order to include the protons and reach a truly complete description of high energy p+p
collisions.
The two bottom panels of Fig. 4 show the ratiosp/π+ (filled triangles, red online) and
 [GeV/c]
T
p
0.5 1 1.5 2 2.5 3 3.5 4 4.5
 y=3.3 
 [GeV/c]
T
p
0.5 1 1.5 2 2.5 3 3.5 4 4.5
 πp
0
0.2
0.4
0.6
0.8
1
1.2
PRELIMINARY
 pp
0
0.05
0.1
0.15
0.2
 + π- π
0
0.5
1
1.5
2
y=2.95
FIGURE 4. The π−/π+ ratios at both rapidities are shown on the top panels, the ¯p/p ratio is shown
in the middle panel, the bottom panels show thep/π+ and p̄/π− ratios. Data frome+e− annihilations is
shown with a dashed line [12]. The smooth curves are obtainedfrom the NLO calculations of Fig. 2.
p̄/π− (open circles) as function ofpT and at rapidity y=2.95 (left) and y=3.3 (right). The
difference between the ratios of negative particles (produce ) and positives is remarkable
and shows that a factorized pQCD based description fails forprotons. The ratio ¯p/π− is
closer to a rough parametrization extracted frome+e− annihilations.
SUMMARY
We have presented the recently measured cross-sections forpions, kaons and protons at
high rapidity in p+p collisions at RHIC. The NLO pQCD calculations incorporating the
KKP fragmentation functions describe the pion and kaon cross-sections. Protons at high
rapidity andpT appear in unusually high numbers that do not fit into a factorized pQCD
description based on parton-parton interactions.
We thank Werner Vogelsang for providing us with the NLO pQCD calculations shown
in this report. This work was supported by the Office of Nuclear Physics of the U.S.
Department of Energy, the Danish Natural Science Research Council, the Research
Council of Norway, the Polish State Committee for ScientificResearch (KBN) and the
Romanian Ministry of Research.
REFERENCES
1. J. Alitti et al., Phys. Lett.B257 232, (1991).
2. E. Pareet al., Phys. Lett.B242 531-535 (1990).
3. M. Adamczyket al., BRAHMS Collaboration, Nuclear Instruments and Methods,A499 437 (2003).
4. T. Sjöstrand,et al., Comp. Phys. Commun.135, 238, (2001). Version 6.303 was used.
5. B. Jager, A. Schafer, M. Stratmann and W. Vogelsang, Phys.Rev. D67, 054005 (2003).
6. B.A. Kniehlet al., Nucl. Phys.B597, 337 (2001).
7. S. Kretzeret al, Eur. Phys. J.C22, 269 (2001).
8. S. S. Adler,et al., Phys. Rev. Lett.91, 241803 (2003).
9. J. Adamset al., Phys. Rev. Lett.92 171801 (2004).
10. J. Adamset al., Phys. Lett. bf B637, 161 (2006).
11. S. Albino, B.A. Kniehl and G. Kramer, Nucl. Phys.B725, 181, (2005).
12. P. Abreuet al., Eur. Phys. J.C17, 207, (2000); R. Baratet al., Phys. Rept294, 1-165, (1998).


https://digital.library.unt.edu/ark:/67531/metadc898291/m2/1/high_res_d/921925.pdf

Charged Particle Production at High Rapidity in p+p Collisions at RHIC

Abstract

Similar works

Full text

Available Versions

UNT (University of North Texas) Digital Library

Crossref

Crossref

Crossref

Crossref

Crossref

Crossref