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New results from PHENIX What’s happening at high p T ?. A preview of PRL covers to come. Barbara V. Jacak Stony Brook October 2, 2002. Outline & summary. The high p T suppression is real! Continues to higher p T In both p 0 and charged particles - PowerPoint PPT Presentation
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New results from PHENIXWhat’s happening at high pT?
A preview of PRL covers to come
Outline & summary
The high pT suppression is real!
Continues to higher pT
In both 0 and charged particles
High pT particles do come from jets!Must use caution to avoid confusion with v2
Hadronic composition at high pT
Is mysteriousChanges with centrality
Goals of RHIC
Collide Au + Au ions at high energy130 GeV/nucleon pair c.m. energy in 2000s = 200 GeV/nucleon pair in 2001
Create in the laboratory high temperature and density matteras existed ~1 sec after the Big Banginter-hadron distances comparable to that in neutron starsheavy ions to achieve maximum volume
Study the hot, dense systemthermal equilibrium?do the nuclei dissolve into a quark gluon plasma?characteristics of the phase transition?transport properties of plasma? equation of state?
QCD Phase Transition
transition affects evolution of early universelatent heat & surface tension matter inhomogeneity in evolving universe?
equation of state of nuclear matter compression in stellar explosions
we don’t understandhow process of quark confinement workshow symmetries are broken by nature massive particles from ~ massless quarks
did something new happen at RHIC?
Study collision dynamics (via final state)
Probe the early (hot) phase
Equilibrium?hadron spectra, yields
Collective behaviori.e. pressure and expansion?elliptic, radial flow
vacuum
QGP
Particles created early in predictable quantity interact differently in QGP vs. hadron matterfast quarks, J/fast quarks, J/, strange, strangequark content, quark content, thermal radiation
PHENIX at RHIC
2 Central spectrometers
2 Forward spectrometers
3 Global detectors
PHENIX philosophy: optimize for
signals / sample soft physics
fast partons as probe of the plasma
hadrons
q
q
hadronsleadingparticle
leading particle
schematic view of jet productionJets in heavy ion collisions: observed via fast leading particles or azimuthal correlations between the leading particles
But, before they create jets, the scattered quarks radiate energy in the colored medium
decreases their momentum fewer high pt particles“jet quenching” affect away side jet
Pion spectrum - at low pTs = 200 GeV per nucleon pair
Pion spectrum - 0 to high pT
Pion spectrum – charged at very high pT
Use RICH to taghigh pT pions
PHENIX 0 spectrum in p-p collisions
Measure reference spectrum in the SAME experiment
Remove extrapolation errors
Reach higher pT than UA1
Agrees with NLO calculation
Compare Au+Au to p+p
Use measured p+p to predict rate of plasma probe in Au+Au
Hard scattering probability scales with # of binary nucleon-nucleon collisions
Construct RAA = pp
centralbinarycentral
Yield
NYield /
RAA should be 1 if nothing happens to the probe
0 yield in AuAu vs. p-p collisions
70-80% PeripheralNcoll =12.3 ±4.0
30-40% Semi-centralNcoll =220±14
PHENIX Preliminary
pp
centralbinarycentral
Yield
NYield /
Suppression due to parton energy loss?
Data not consistent with predictions including no energy loss
GLV L/ =4 somewhat better agreement
Both predictions including energy loss consistent with data up to 5 or 6 GeV/c
but maybe not quite…
P.Levai, Nuclear Physics A698 (2002) 631.
X.N. Wang, Phys. Rev. C61, 064910 (2000).
Charged particle pT spectra from 200 GeV
pT <2 GeV/c, slope increase flow
pT >2 GeV/c, slope decrease suppression
h+ + h-
Centrality dependence of change
suppression stronger with centrality & increased pT
peripheralbinaryperipheral
centralbinarycentral
NYield
NYield
//
Suppression to 9 GeV/c!
Factor consistent for 3 independent measurements
Difference in charged hadron ratio and neutral pion ratio accounted for by particle composition
Comparing different channels
How do high pT yields scale?
vs. binary collisions:continuous decrease as
function of centralityfactor ~ 3.5 from
peripheral to central vs. participants:
first increase, then decrease as function of centrality
for Npart > 100 have 3 change (scaling or no?)
surface emission? re-interactions?accident?
18% scaling uncertainty from corrections
x of struck parton
• if pT(had) / pT(jet) ~ 1 then xT ~ x(parton) at y=0
• SPS and RHIC at different x!
RHIC:~1.6 x 10-2 at 200 GeVstill not very small…
xT =
Learn from xT
Hard scatterings most probably of gluons Shadowing not a large effect as x is not very small
Beyond leading twist not as clear… Natural to compare with gluon jets studied in e+e-, BUT
Our leading hadrons are very soft (<10 GeV/c)We mostly see just part of the fragmentation functionjet falls faster thanD(z), so we probe“kinematic limit”with large zhadron spectra maybe dominated by q jets
Parent x for 4 GeV/c hadron
From X.N. Wang
High pT hadrons do come from jets
Look at particle correlations for jet signature“trigger” on leading photon with pT > 2.5 GeV/calso look at charged-charged correlationsJets are observed in Au + Au
v2 (nominally collectively elliptic flow) at high pT is also sensitive to jets
Bias effect:Trigger requirement requires leading particle!Systematic study via trigger , hadron
use 2.5 GeV , perhaps NOT dominated by 0…?
Identifying Jets - Angular Correlations
Remove soft background by subtraction of mixed event distribution
Fit remainder:Jet correlation in ; shape taken from PYTHIAAdditional v2 component to correct flow effects
PHENIX Preliminaryraw differential yields
2-4 GeV
Verify PYTHIA using p+p collisions
(neutral E>2.5 GeV + 1-2 GeV/c charged partner)
||<.35 ||>.35
ake cuts in to enhance near or far-side correlationsBlue = PYTHIA
In Au+Au collisions
1-2 GeV partner
(neutral E>2.5 GeV + charged partner)
||<.35 ||>.35
1/N
trig d
N/d
1/N
trig d
N/d
Correlation after mixed event background subtraction
Clear jet signal in Au + AuDifferent away side effect than in p+p
Jet strengthSee non-zero jet strength as partner pT increases!
jets or flow correlations? fit pythia + 2v2vjcos(2)
partner = .3-.6 GeV .6-1.0 GeV/c 2-4 GeV/c
1/N
trig d
N/d
v2
vj
1-2 GeV/c
min bias 200 GeV Au+ Au
v2 at high pT
v2 via reaction plane at =3-4 and via 2-particle correlations similarNo jet contamination of
reaction planeDiverge at pT> 4 GeV/c?
Low pT as expected from hydrodynamics
v2 > 0.15 at pT>3 GeV/c interpretation? 15% jets per STARflow vs. hard processes
contribution unclear
Au+Au at sNN=200GeV
v2
r.p. ||=3~4min. bias
v2 of identified hadrons
Negativespi-&K-,pbar
Positivespi+&K+,p
PHENIX Preliminary PHENIX Preliminary
pT (GeV/c) pT (GeV/c)
v2
p cross ,K
not expected from hydro
modifiedand p not??
Look at charged particle spectra
0 – 5 % 5 -10 %10- 15 %15 – 20 %20 – 30 %30 – 40 %40 – 50 %50 – 60 %60 – 70 %70 – 80 %
80 – 93 %
Au+Au at s = 200 GeV PHENIX preliminary
PHENIX Preliminary
hydrodynamic analysis of spectra
PHENIX Preliminary
T = 1224 MeVt = 0.72 0.012/dof = 30.0/40.0
Simultaneous fit tomT-m0 < 1 Gev/C
Au+Au at s = 130 GeV
200 GeV similar but T, a bit
Extrapolate soft component using hydrodynamics
Hydrodynamic flow modifies pt threshold where hard physics starts to dominate
physics has soft (thermal) contributions until pt 3 GeV/c
Calculate spectra usinghydro parametersh+ + h - = , K, p
Compare sum to measured Charged particle pT spectrum
J. Burward-Hoy
Particle composition?
Dynamics affect p/pion ratios
hydro boosts baryons to higher pt Jet quenching should reduce yield
(by ~3-5)baryons less depleted as less likely to be jet leading particles
Vitev & Gyulassy nucl-th/0104066
pbar/ pi-
Ratio of protons to pions ~1 at high pT for central collisions
Flattens. Turnover not seen.
Now extend to higher energy, pT
Centrality dependence of p/pi
+
-
•Ratios reach ~1 for central collisions
•Peripheral collisions lower, but still above gluon jet ratios at high pT
•Maybe not so surprising 1)“peripheral” means 60-91.4% of total
2) p/pi = 0.3 at ISR
How do protons scale with Ncoll/Npart?
Scale with Ncoll (unlike )?!
High pT baryons scale with Ncoll!
Low pT near Npart scaling
But baryons with pT > 2 GeV/cbehave very differently!From jets? Unsuppressed??
J. Velkovska
Use pi/h to look at higher pT
What’s this?protons??
How about electrons?
PHENIX looks for J/ e+e- and
There is the electron.
A needle in a haystack:find electron without mistaking a pion at the level of one in 10,000
Ring Imaging Cherenkovcounter to tag the electrons“RICH”
uses optical “boom” whenvpart. > cmedium
We do find the electrons
Energy/Momentum
Electron enriched sample (using RICH)
All tracks
And J/
Centrality dependence of charm
conclusions
The high pT suppression is real!
Continues to higher pT
In both 0 and charged particlesCharmed quarks do not show energy loss
High pT particles do come from jets!Must use caution to avoid confusion with v2
Hadronic composition at high pT
Is mysteriousChanges with centralityWhat’s going on with protons & antiprotons??
Need theoretical help!!
3 GeV/c region of spectrum is complicatedMix of soft & hard processes
via single particle extrapolationv2 large & not a measurement artefact
Large proton contribution to spectrumflow seems a reasonable explanation
BUT – why is pi/h so low out to 8 GeV/c????
Suppression of pions, but not leading baryons?PHENIX has and correlations to help figure it out
Charmed quarks do not indicate large energy loss
Backup slides
Charged hadron correlations - small
•Fit charged correlations with v2 + Gaussian (fixed pT)
•Jet signal visible via Width of near-side Gaussian decreases with pT
No significant centrality dependence on near-side
Cor
rela
tion
wid
th
jT
pT Correlation width jT/pT
Note pbar/p behavior
Centrality dependence only for pT > 3 GeV/c
Peripheral collisions have quite a few protons at mid-y
Considerable baryon stopping still! Caution for high pT physics interpretation!!
High pT -/+ ratio
ratio ~1 at high pT in Minimum Bias data
Slightly decreasing in large Npart region?
Hydrodynamics-inspired fit
emperatureFreezeOutTT
ocitySurfaceVelR
r
dT
pI
T
mKfmA
dmm
dN
FO
s
ns
FO
T
FO
TT
TT
)(tanh;
)sinh()cosh()(
1
01
After Schnedermann, et al. Phys. Rev. C48, 2462 (1993)
<pt> increases with centrality
Expect such a trend from radial flowbut also from partonic multiple scatteringand gluon saturation
don’t know whether final or initial state effect
Can also get v2 from correlations
PHENIX (and PHOBOS) measure correlation function in azimuthal angle
from same event
from mixed events
C() =ratio
dN/d() [1 + 21cos() + 22cos(2)] 2 v2Impose pT threshold & see jet correlations
At high pT
jet correlations weak or missing!
Reaction plane results a mystery...
Hydrodynamicsno longer dominates
Correlation method on HIJING picks out back-to-back particles from jets
For datacorrelation & reaction plane methods agree
J. Rak
hard/soft competition as probe
22/ 1 2v ( ) cos 2T TdN dydp d p
Above pt ~ 1.5 GeV/c, hydrodynamic flow in the reaction plane has competition from hard processes, which are not correlated with that plane
so look for disappearance of elliptic flowdepends on amount of energy loss!
Nuclear effects in initial stage
Structure functions are modified in nuclei Shadowing in small-x region
due to high parton density from superposition of all the nucleons
F2A(x)
---------AF2
N(x)
Accessible at RHIC
Measure radial expansion
Teff = Tfo + m <radial>2
Tfo = 140 - 150 MeV radial = 0.5 - 0.6 (higher for central collisions)
was 0.4 at lower energyless flow in peripheral collisions!
baryon yields
PHENIX preliminary
antiproton dN/dy = 20!
Was 0.18 at SPS
strangeness production
PHENIX preliminary
s=17 GeV Pb+PbPhys.Lett.B 471, 6 (1999)
Both K+/ and K-/increase with NpartPeripheral collisions near pp valueK+/ and K-/do not diverge as at SPS,AGS
K/ ats=200 p+p
Z.Phys.C41,179(1988)(UA5)
For RHIC and CERNThanks to Xin-Nian Wang!
For pt = 4 GeV/c hadron from jet fragmentation, what is x distribution of parent parton?
Does not include ktbroadening
From Xin-Nian’s calculation
For CERN energy<z> ~ 0.87distribution is fairly symmetric
for RHICpeak z ~ 1long tail to higher x parent parton
i.e. tail to smaller zestimate with z range 0.7-1.0
remake x plot
more realistic fragmentation function
z range indicated by horizontal bar:answer is not very different
to excludeknown softphysicsregime
PT = 3 GeV/c(is a safer boundary for hard processes)
Thanks to X.N. Wang