particle production in p + p reactions at gev k. hagel cyclotron institute texas a & m...
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Particle Production in p + p Reactions at GeV
K. HagelCyclotron Institute
Texas A & M Universityfor the
BRAHMS Collaboration
200s
Outline• Description and characteristics of BRAHMS
• Particle spectra– Fits and fit parameters
• Rapidity densities
• Nuclear Stopping
• Limiting fragmentation
• High pt pQCD comparisons to data
• Strangeness
• Mid-rapidity Spectrometer– TPC, TOF, Cherenkov– 30o – 90o = 0 - 1.5
• Mid-rapidity Spectrometer– TPC, TOF, Cherenkov– 30o – 90o = 0 - 1.5
• Forward Spectromter– TPC, DC, TOF, Cherenkov, RICH
– 2.3o – 30o = 1.5 – 4
Particle Identification
1
L
TOFcpm
2
2222TIME-OF-FLIGHT
0<<1
(MRS)
1.5<<4
(FS)pmax
(2 cut)
TOFW (GeV/c)
TOFW2 (GeV/c)
TOF1 (GeV/c)
TOF2 (GeV/c)
K/ 2.0 2.5 3.0 4.5
K/p 3.5 4.0 5.5 7.5
RICH: Cherenkov light focusedon spherical mirror ring on image plane
Ring radius vs momentum gives PID / K separation 25 GeV/cProton ID up to 35 GeV/c
CHERENKOV
(2 settings)
Rotatable spectrometers give unique rapidity coverage :Broad RAnge Hadron Magnetic Spectrometers
The BRAHMS Acceptance
Tra
nsv
ers
e m
om
en
tum
[G
eV
/c]
Rapidity
Fitting particle spectra• One method to extrapolate to parts of the spectrum
not measured.• Different functions might (or might not) be appropriate
for different spectra.• It is still an extrapolation that adds to systematic
error.• Fit used in this work is Levy Function
n
TTT
nTmm
A
dydp
Nd
p
)(
12
1 2
Where22
02
TT pmm and )2(
)2)(1(
2
1
0
nmnTnT
nn
dy
dNA
• Performed global fit using T = T0 + ay, n = n0 + by
Stopping
• Obtained from net baryon dN/dy– Gives information on initial distribution of
baryonic matter at the first moment of the collision.
• Net-Baryon = Net(p)+Net()+Net(Casade)+Net(n), where each part involves feed-down corrections.
• We have measured net proton dN/dy
• Simply dN/dyp – dNdypbar shown previously
NLO pQCD comparisons to data at large rapidity
BRAHMS Phys. Rev. Lett. 98, 252001 (2007)
• Comparison of different fragmentation functions
– Modified KKP (Kniehl-Kramer-Potter) does better job than Kretzer (flavored FFs) on -, K+
• Difference driven by higher contributions from gluons fragmentating into pions– gg and gq processes dominate at mid rapidity (STAR PRL 91, 241803 (2003).
– Processes continue to dominate at larger rapidity.
– AKK (p+pbar)/2 (p~pbar) reproduces experimental p, but not pbar
Rapidity dependence of NLO pQCD comparison to data
• KKP describes data from mid-rapidity (PHENIX, 0) to large rapidity (BRAHMS, -; STAR 0)
Global fits to dataincluding BRAHMS large rapidity data
PRD 75, 114010 (2007)
• Charged separated fragmentation functions
• Fragmentation functions significantly constrained compared to previous “state of the art” when adding RHIC data into fits.
NLO pQCD comparisons of 62 GeV +, K+ data at large rapidity
• scale factor of μ=pT
• DSS also shown (dashed lines)• K- data suppressed order of
magnitude compared to K+ (valence quark effect).
• NLO pQCD using the recent DSS fragmentation functions give approximately same K-, K- yield (?) Related to fragmentation or PDFs?
- KKP+ KKP
Strangeness enhancement• p+p evolution with
pbar/p– cannonical K
suppression – larger for K-
• Larger values for Au+Au – strangeness effects turing on– More energy
available.
LHC p+p stopping prediction
• Merge limiting fragmentation plots
• Add LHC beam rapidity to them
• Fit with momGaus
y ~ 2• CMS will
measure to 2.2• Stopping with
energy (subtract from incoming energy)