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Fukutaro Kajihara
(CNS, Univ. of Tokyo)
Measurement of Single ElectronMeasurement of Single Electronfrom Semileptonic Decay from Semileptonic Decay of of Charm/Bottom QuarksCharm/Bottom Quarks
in RHIC-PHENIXin RHIC-PHENIX
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IntroductionIntroduction
RHIC で行われた二つの代表的な測定 楕円型フロー ジェット・クェンチング
Next Step は?これまでの成果は Soft probe (, K, p 等 ) による結果反応初期状態を直接的に probe する観測量が必要
「閉じ込めの破れ」の検証
Soft probe から Hard probe へ Heavy quark の測定
高密度状態完全流体性
熱的電磁輻射、 Heavy quarks (charm/bottom)
J/, Y, Heavy quark v2
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hA
hB
g
cg
c_(a)
(b) (c)
Heavy Quark ProductionHeavy Quark ProductionProduction
gg->QQ “gluon fusion”Sensitive to the initial gluon density
Mass is large s(mC2) ~ 0.3
can use pQCD
Cold nuclear matter effect(a) Cronin effect(b) (Anti-) shadowing(c) Absorption
Hot/dense matter effect(c) Energy lossNeed systematic study for entanglement.
p-p, d-Au
Au-Au
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c c
0D
間接測定 :Semileptonic decay からのレプトンを測定
0DK
+
K
How do We Measure Heavy Quarks?How do We Measure Heavy Quarks?
直接測定 :DK, DK
Meson D±,D0
Mass 1869(1865) GeV
BR D0 --> K (3.85 ± 0.10) %
BR --> e +X D±: 17.2, D0: 6.7 %
比較的大きな branching ratio
Single Electron/Prompt muon
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History of Single Electron MeasurementHistory of Single Electron MeasurementSingle electron は 1970 年代の初期に CERN-ISR において測定された . 当時は charm quark がまだ発見されていなかった .
F. W. Busser et al, PLB53, 212F. W. Busser et al, NPB113, 189
後に charm quark の semileptonic decay から生成された電子であると判明
I. Hunchlife and C. H. Llewellyn Smith, PLB61,472M. Bourquin and J.-M. Gaillard, NPB114,334
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Heavy Quark Measurement at RHICHeavy Quark Measurement at RHIC
PHENIXSingle electron measurements in p+p, d+Au, Au+Au sNN = 130,200,62.4 GeV
STARDirect D mesons hadronic decay channels in p+p/d+Au
D0KD±KD*±D0
Single electron measurements in p+p, d+Au
Phys. Rev. Lett. 88, 192303 (2002)
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実験とデータ解析
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A composite detector to measure leptons, photons and hadrons.
Beam
Beam
The PHENIX detectorThe PHENIX detector
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Event trigger is defined by beam-beam counters.
The PHENIX detectorThe PHENIX detector
Beam-beam counters
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Central arms
Tracking chambers
RICH counters Central arm
The PHENIX detectorThe PHENIX detector
EM calorimeters
TOF counters
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Cross-section of PHENIXCross-section of PHENIXPHENIX central arm:
|| < 0.35
= 2 x /2
p > 0.2 GeV/c
vertex: |zvtx| < 20 cm
Charged particle tracking analysis using DC and PC → p
Electron identificationRing Imaging Cherenkov detector (RICH)
Electro- Magnetic Calorimeter (EMC) → energy E
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Electron IDElectron ID
Electrons are identified by RICH and EMCal E/p matching, position matching, shower shape cut.
Energy-Momentum [GeV]
All charged tracks
Accidentalbackground
Net signal
Real
Apply RICH cut
RICH ring shape(signal accumulated)
Au-Au data
z [cm]
r [c
m]
Cerenkov photons from e+ or e- are detected by array of PMTs
mirror
Most hadrons do not emit Cerenkov light
Electrons emit Cerenkov photonsin RICH.
Central Magnet
RICH
PMT arrayPMT array
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Background for Inclusive ElectronMain source
Random combinations of EMC cluster and RICH ring
pT independent
Minor source
-electrons knocked by the hadron in RICH active volume
h<10-6
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E/p in Au+Au collisionsE/p in Au+Au collisions
Purity of e± sample excellent aftersubtraction of “random association” background
E/p cut
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Singnal and Background
Photon Conversion
Main photon source: → In material: → e+e- (Major contribution of photonic electron)
Dalitz decay of light neutral mesons→ e+e- (Large contribution of photonic)
The other Dalitz decays are small contributions Direct Photon (is estimated as very small contribution)
Heavy flavor electrons (the most of all non-photonic) Weak Kaon decays
Ke3: K± → e± e (< 3% of non-photonic in pT > 1.0 GeV/c) Vector Meson Decays
J → e+e-(< 2-3% of non-photonic in all pT.)
Photonic Electron
Non-photonic Electron
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Most sources of backgroundhave been measured in PHENIX
Decay kinematics and photon conversions can be reconstructed by detector simulation
Then, subtract “cocktail” of all background electrons from the inclusive spectrum
Advantage is small statistical error.
Background Subtraction: Cocktail Method
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Background Subtraction: Converter Method
We know precise radiation length (X0) of each detector material
The photonic electron yield can be measured by increase of
additional material (photon converter was installed)
Advantage is small systematic error in low pT region
Background in non-photonic issubtracted by cocktail method
Photon Converter (Brass: 1.7% X0)
Ne Electron yield
Material amounts:
0
0.4% 1.7%
Dalitz : 0.8% X0 equivalent radiation length
0
With converter
W/O converter
0.8%
Non-photonic
Photonic
converterCLp
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7
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Consistency Check of Two Methods
Both methods were checked each other
Left top figure shows Converter/Cocktail ratio of photonic electrons
Left bottom figure shows non-photon/photonic ratio
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Results and DiscussionResults and Discussion
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Result of p+p at s = 200 GeV
Heavy flavor electroncompared to FONLL
Data/FONLL = 1.71 +/- 0.019 (stat) +/- 0.18 (sys)
Tevatron の実験結果
PRL, 97, 252002 (2006)
Upper limit of FONLL
~factor 2
D0
CD
F,
PR
L 91
, 24
1804
(2
003)
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Drell-Yan processDrell-Yan process
FONLL calculation: Cacciari, Nason, Vogt, PRL95 (2005) 122001Drell-Yan from: Gavin et al., hep-ph/9502372Comparison: Armesto, Cacciari, Dainese, Salgado, Wiedemann, hep-ph/0511257
FONLL: electron spectrum may be ~50% c + ~50% b for 3 < pT < 8 GeV
Drell-Yan component investigated as well: < 10% up to 10 GeV
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Result of d+Au at Result of d+Au at ssNNNN=200 GeV=200 GeV
No strong modification compared to p+p
PHENIX PRELIMINARY
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Result of Au+Au at Result of Au+Au at ssNNNN = 200 GeV = 200 GeV
Heavy flavor electroncompared to binary scaledp+p data (FONLL*1.71)
Clear high pT suppression in central collisions
S/B > 1 for pT > 2 GeV/c
(according to inside figure)
Submitted to PRL (nucl-ex/0611018)
MB
p+p
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Energy Loss of Heavy QuarkEnergy Loss of Heavy Quark
In vacuum, < mQ/EQ では Gluon の制動放射が抑制される
“dead cone” effect
Heavy quark の energy loss は小さい (Dokshitzer-Kharzeev, 2001):放射された gluon のエネルギー分布 d/d は放出角依存性があり、抑制される
Q
Dokshitzer, Khoze, Troyan, JPG 17 (1991) 1602.Dokshitzer and Kharzeev, PLB 519 (2001) 199.
1
1d
d
d
d2
2
2
Q
Q
LIGHTHEAVY E
mII
22QQ
2 ])/([
1
Em
Gluonsstrahlung probability
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Nuclear Modification Factor: Nuclear Modification Factor: RRAAAA
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dpNdN
dPNdpR
ppcoll
AATAA
p+p reference:
Data (converter) for pT<1.6 [GeV/c]
1.71*FONLL for pT>1.6 [GeV/c]
Suppression level is the almost same as 0 and in high pT region
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RRAA AA vs. Nvs. Npartpart
横運動量で積分し、 Npart の関数として計算した
Binary scaling works well for pT>0.3 GeV/c integration
Clear suppression is seen for pT>3.0 GeV/c integration
Total error from p+p
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Dielectron Continuum Measurements Dielectron Continuum Measurements in √sin √sNNNN = 200GeV Au+Au = 200GeV Au+Au
schematic dilepton mass distribution
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Radiative Energy LossRadiative Energy Loss
Radiative Energy Loss with reasonable gluon densities do not explain the observed suppressionDjordjevic, Phys. Lett. B632 81 (2006)Armesto, Phys. Lett. B637 362 (2006)
DGLV Radiative Energy Loss Model
dNg/dy = 1000
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Collisional Energy LossCollisional Energy LossCollisional energy loss may be significant for heavy quarksWicks, nucl-th/0512076van Hess, Phys. Rev. C73 034913 (2006)
DGLV Radiative + Elastic Scattering
dNg/dy = 1000
van Hee & Rapp Elastic Scattering
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Other modelsOther models
Charm alone seems to describe better the suppression at high-pT
Dead cone is more significant for bottom quark Larger collisional (relative) Energy loss
DGLV Radiative + Elastic Scattering For Only Charm
Larger Dead Cone and Larger
Collisional E-loss For Bottom Quark
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Heavy Flavor RHeavy Flavor RAAAA at LHC at LHC>100 cc pairs and >5 bb pairs per central Pb-Pb collision
Baseline: PYTHIA to reproduce c and b pT distributions from NLO pQCD
MNR: Mangano, Nason, Ridolfi, NPB 373 (1992) 295.Armesto, Dainese, Salgado, Wiedemann, PRD 71 (2005) 054027. Eskola, Kajantie, Ruuskanen, Tuominen,
NPB 570 (2000) 379.
/fmGeV 10025ˆ7ˆ 2 RHICLHC qq
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SummarySummarysNN=200 GeV における Au+Au 衝突実験において、
mid rapidity 0.3 < pT < 9.0 GeV/c
Heavy quark からの寄与と考えられる電子を測定した Integrated yield (pT > 0.3 GeV/c) が Binary scaling している RAA が high pT 領域において強い抑制効果を示した 理論計算との比較
典型的な Radiative Energy Loss の Model が成り立たない 更なる発展には、 D/B の識別測定が必要不可欠
ه OutlookD meson measurement in p+p by electron ( K measurement )
High statistic Cu+Cu analysisSingle measurement in forward rapidityD/B direct measurement by Silicon Vertex Tracker
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Backup slides
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