Transcript Slide 1
Particle Production in p + p
s
K. Hagel Cyclotron Institute Texas A & M University for the BRAHMS Collaboration
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
Global Detectors Front Forward Spectrometer Back Forward Spectrometer
• Mid-rapidity Spectrometer – TPC, TOF, Cherenkov – 30 o – 90 o = 0 - 1.5
– 2.3
o • Mid-rapidity Spectrometer – TPC, TOF, Cherenkov – 30 o – 90 o = 1.5 = 0 - 1.5
Particle Identification
TIME-OF-FLIGHT
p max (2 cut) K/ m 2 p 2 c 2 TOF 2 L 2 1 0< <1 (MRS) TOFW (GeV/c) TOFW2 (GeV/c) 2.0
2.5
1.5< <4 TOF1 (GeV/c) 3.0
(FS) TOF2 (GeV/c) 4.5
K/p 3.5
4.0
5.5
7.5
CHERENKOV
RICH: Cherenkov light focused on spherical mirror ring on image plane (2 settings) Ring radius vs momentum / K separation 25 GeV/c Proton ID up to 35 GeV/c gives PID
The BRAHMS Acceptance
Rapidity Rotatable spectrometers give unique rapidity coverage :
B
road RA nge H adron M agnetic S pectrometers
Experimental Coverage
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 1 2
p T
Where
m d
2
N dydp T
2
T
A m
0 2 1 (
m T
nT m
)
p
2
T
and
n A
1 2
dN dy nT
(
n nT
1 )(
n m
0 (
n
2 ) 2 ) • Performed global fit using T = T 0 + ay, n = n 0 + by
200 GeV Pion Spectra T 0 = 0.058 GeV, n 0 = 4.45
T 0 = 0.056 GeV, n 0 = 4.38
200 GeV Kaon Spectra
T 0 = 0.127 GeV, n 0 = 6.44
T 0 = 0.125 GeV, n 0 = 6.23
200 GeV Proton Spectra
T 0 = 0.149 GeV, n 0 = 8.36
T 0 = 0.184 GeV, n 0 = 14.58
62 GeV p+p spectra
dN/dy
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(
L
)+
Net(Casade)+Net(n), where each part involves feed-down corrections.
• We have measured net proton dN/dy • Simply dN/dy p – dNdy pbar shown previously
net proton dN/dy
• • y ~ 1.26 (momgaus) y ~ 1.20 (Hijing/B; remember dN/dy!)
Limiting Fragmentation
Net proton dN/dy Limiting Fragmentation Nucl Phys. A661 (1999) 362.
Rapidity dependence of Mean pt
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 data including 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
-
+ KKP KKP
• • scale factor of μ=p T 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?
K/
K/
comparison to Au + Au
• Larger K/ for Au+Au – Radial flow – Absence of cannonical K suppression
K/
vs rapidity
• Increasing K + /K with suppression increasing rapidity
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.
What Can we say about LHC Physics • Net proton dN/dy – Use lower energy limiting fragmentation data
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)
Summary
• Particle production – dN/dy – Net proton dN/dy -> Stopping • Limiting Fragmentation – dN/dy – Net proton dN/dy • High pt pQCD calculations • Strangeness enhancement • Prediction for LHC