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Measurement of heavy flavour production in p-p and d-Au collisions at
RHIC by the detection of the inclusive
muonsJu Hwan Kang(Yonsei Univ.)
for the PHENIX collaboration
Lake Louise Winter Institute 2004Lake Louise, Alberta, Canada
15-21, February, 2004
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Motivation
Heavy flavour production in pp collisions at s1/2 = 200 GeV/cDifferential production cross section: How good is the description
by pQCD-driven parton model at this energy?Charge asymmetry (non-perturbative effect): How big is the
effect of higher twist (recombination)?
Heavy Flavor production in dAu and AuAu collisionsNuclear modification factor (Rcp): Does "binary scaling (by
number of nucleon-nucleon binary collisions)" work for these systems?
Evolution of charge asymmetry: How does the non-perturbative dynamics evolve from p+p to these systems?
Study of the forward/backward hadron production in dAu Probe different “x” ranges: (anti)shadowing/saturation(CGC).
periphcoll
periph
centcoll
cent
Tcp NN
NNyPR
/
/),(
central
peripheral
d2 Au197
3
d[A+BX] = ij f
i/Af
j/B d [ijcc+X] D
cH
+ ...
J.C.Collins,D.E.Soper and G.Sterman, Nucl. Phys. B263, 37(1986)
Factorization theorem for charmed hadron production
fi/A,fj/B
: distribution fuction for parton i,j
DcH
: fragmentation function for c
d [ijcc+X] : parton cross section
+ ... : higher twist (power suppressed by
QCD/m
c, or
QCD/p
t if p
t ≫m
c ) :
e.g. "recombination" PRL, 89 122002 (2002)
fi/Au
79 fi/p
+ 118 fi/n
197 fi/N
fi/d
fi/p
+ fi/n
2 fi/N
Application to nuclei:
An example: Does "binary scaling" work?
d+Au
Au+Au
Binary scaling not working for high pt particles in central AuAu collisions!PHENIX: PRL, 91, 072303 (2003)
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Muon Production
Origins of muonsPYTHIA p+p @
√s=200GeVlow PT:
light hadron decayshigh PT:
Heavy quark decays
Muon PT distribution
%63)(
%99.99)(
%10)(
%10)(
vKBR
vBR
XbBR
XcBR
Direct reconstruction of open charm is ideal, but difficult. Open Direct reconstruction of open charm is ideal, but difficult. Open charm and bottom can be measured via single muons.charm and bottom can be measured via single muons.
By removing muons from /K decays, heavy quark production can be measured.
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RHIC at Brookhaven National Laboratory
Dedicated (relativistic) heavy ion collider: P+P (can be polarized) at s = 200 GeV or s = 500 GeV A+A (d+Au, Au+Au, …) at s = 200 GeV
4 Exp's:PHENIX STAR
PHOBOS BRAHMS
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The PHENIX Experiment(12 Countries; 58 Institutions; 480 Participants as of January 2004)
Two central arms for measuring hadrons, photons and electrons
Two forward arms for measuring muons
Event characterization detectors in middle
The data for this talk is from the muon arms
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The PHENIX Muon Arms
Detect muons with ptot > 2 GeV/c -1.2 > > -2.2 (South Arm) or
1.2 < < 2.4 (North Arm)
Muon Tracker (MuTr)Measure momentum of muons
with cathode-readout strip chambers at 3 stations inside Muon Magnet
Muon Identifier (MuID)/µ separation with 5-layer
sandwich of chambers (Iarocci tubes) and steel
Trigger muons
MuID
MuTr Muon Magnet
Beam Pipe
IP
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1 : Hadrons, interacting and absorbed (4λ or 98%)2 : Charged/K's, "decaying" before absorber (≤1%)3 : Hadrons, penetrating and interacting ("stopped")4 : Hadrons, "punch-through"5 : Prompt muons, desired signal
TrackerIdentifier Absorber
Collision range
Collision1
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4
5
Muon HadronAbsorberSymbols
Detector
Major Sources of Inclusive Tracks
Items 2 and 4 are small fraction of the original hadrons, but are more than prompt muon signal 5.
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Case 2, Decaying hadrons
* We need to understand “Decaying hadrons” to determine background to “Prompt Muons”
* Daughter muons from the hadrons can be measured separately from other sources using the dependence of yields on the location of collision points.
The longer the distance from the collision point to the front absorber, the more daughter muons from hadrons.
Almost linear dependence:Flight distance is much smaller compared to the mean decay length.e-L/λ ~ (1-L/λ)=(1+Zcoll/λ)
Arb
itra
ry u
nit
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Measured decay muons with the
expectation
Green band represents systematic uncertainty.
Red and blue dotted linescorrespond to expectation.
Red and blue lines showstatistical uncertainty.μ -
μ +
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Tracks reaching the second last (4th) MuId layer exclusively are made up of stopping tracks & interacting hadrons.
Stoppingtracks
Interacting hadrons
Stopping (range-out) tracks: Lose all of its energy by ionization and stop before reaching the last MuId layer.
Interacting hadrons: Even when hadrons have large momenta to reach the last MuId layer, they can undergo hadron interaction in the last absorber layer to stop before reaching the last MuId layer.
Momentum distribution of the tracks with DEPTH 4
Use of interacting hadrons for data driven punch-through estimation?
Case 4, Punch-through hadrons
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Extraction of Interaction Length
There is relation between hadon flux at collision point (I0) and hadron flux at depth 4 (I4) obtained in the previous page. In simplified picture, assume hadrons experience damping by an exponential absorption, exp(-L as they propagate
through the absorber material.
Then, simplified picture works to the 1st order: some differences exist due to the details of hardon propagation (decay, shower, uncertainty on hadron interaction)
I0 : Flux at collision
I3 : Flux at 3rd ID layer
I4 : Flux at 4th ID layer
I5 : punch-through's
I0
I4
I5
I3
Estimate punch-through by extrapolating to depth 5
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d Au
Phenix Preliminary
Central
Depletion on the d-going side ( low x partons in Au) : Shadowing/suppression region (depletion of low x in Au compared to nucleon)
As a by-product, measured backgrounds (abundant hadrons, especially stopped hadrons in MuId) also lead to an interesting physics (study of shadowing/saturation).
Backgrounds is also Signals !
Rcp: nuclear modification factor
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Prompt muon production: In Progress
Remaining to the measurement of the prompt yields,N
inclusive – N
decay – N
punch through = N
prompt + N
background
In Control In Evaluation (about 10-20%)
Expected plot
No absolute value yet; final efforts in progress
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Summary
Systematic study of heavy flavor production at RHIC can be possible by measuring single muons resulting from semi-leptonic decays of heavy flavour.
From this study, perturbative and non-perturbative aspects of collisions (p+p, d+Au, Au+Au) can be explored.
As major sources of backgrounds, decays and punch-through's of the abundant hadrons were identified.
As a by-product, measured backgrounds (abundant hadrons; mostly )also lead to an interesting physics (study of shadowing/saturation by measuring Rcp in different x).
Final efforts to estimate non-trivial sources of backgrounds (10 ~ 20%) and determine prompt muon production is in progress.
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Backup Slides
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X pmean
Dominance of multiple scattering suggests
is distributed as
where is 0.13 (GeV/c).
DATA
How do we quantify purity of the selected tracks?We utilize multiple scattering!
)2
exp()(2
2
0 X
XCXf
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Observation of interests :1. Large charge asymmetry in interacting hadrons is seen in data and
simulation. This is mostly due to penetrating power of the K+ particlesaccording to the GEANT.
2. While data and simulations with different interaction models showqualitative agreement, quantitative description shows substancial difference.
Comparison with Models
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Probed “x” region of Au
Saturation?
shadowing
enhancement
EMC effect
Fermi Effect
Blue band: d directionShadowing/suppression regime
Yellow band: Au directionAnti-shadowing/Cronin regime
yes
Mx