new results in forward physics at the star experiment at rhic l.c. bland brookhaven national...
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New Results In Forward Physicsat the STAR experiment at RHIC
L.C. BlandBrookhaven National LaboratoryQuantum Field Theory SymposiumSaclay, 25 April 2009
BRAHMS & PP2PP
STAR
PHENIX
AGS
LINACBOOSTER
Pol. H- Source
Spin Rotators(longitudinal polarization)
Siberian Snakes
200 MeV Polarimeter
RHIC pC PolarimetersAbsolute Polarimeter (H jet)
AGS pC PolarimeterStrong AGS Snake
Helical Partial Siberian Snake
PHOBOS
Spin Rotators(longitudinal polarization)
Siberian Snakes
25 April 2009 2
What are the goals?• How does the proton gets its spin from quarks and gluons?
• Where do conventional descriptions of particle production (e.g., perturbative QCD) apply?
• Are there new things to learn about partonic substructures at large x?
• Can we learn about low-x structure functions from hadronic interactions?
Edmond Iancu and Raju Venugopalan, Review for Quark Gluon Plasma 3, R.C. Hwa and X.-N. Wang (eds.), World Scientific, 2003 [hep-ph/0303204].
25 April 2009 3
<z>
<xq>
<xg>
• Large rapidity production ~4 probes asymmetric partonic collisions
• Mostly high-x valence quark + low-x gluon
• 0.3 < xq< 0.7
• 0.001< xg < 0.1
• <z> nearly constant and high 0.7 ~ 0.8
• Large-x quark polarization is known to be large from DIS
• Directly couple to gluons probe of low x gluons
NLO pQCDJaeger,Stratmann,Vogelsang,Kretzer
GeVspp 200,8.3,0
Why do forward production in a hadron collider?
pd
pAu
q
g
Q2 ~ pT2
s 2EN
ln(tan(2
))
xq xF / zEN
xqpxgp
xF 2E
s
z E
Eq
xg pT
se g
EN
(collinear approx.)
25 April 2009 4
STAR
Poletips provide unique windows for forward detectors
25 April 2009 5
1Brookhaven National Laboratory2University of California- Berkeley3Pennsylvania State University4IHEP, Protvino5Stony Brook University6Texas A&M University7Utrecht, the Netherlands
8Zagreb University
STAR Forward Calorimeter ProjectsF.Bieser2, L.Bland1, E. Braidot7, R.Brown1, H.Crawford2, A.Derevshchikov4, J.Drachenberg6, J.Engelage2, L.Eun3, M.Evans3, D.Fein3, C.Gagliardi6, A. Gordon1, S.Hepplemann3, E.Judd2, V.Kravtsov4, J. Langdon5, Yu.Matulenko4, A.Meschanin4, C.Miller5, N. Mineav4, D.Morozov4, M.Ng2, L.Nogach4, S.Nurushev4, A.Ogawa1, H. Okada1, J. Palmatier3, T.Peitzmann7, S. Perez5, C.Perkins2, M.Planinic8, N.Poljak8, G.Rakness1,3, A.Vasiliev4, N.Zachariou5
These people built the Forward Meson Spectrometer (FMS) and/or its components
25 April 2009 6
Early Results from STAR Forward Pion Detector (FPD)
View along beam from interaction point of left/right symmetric modular arrays
of lead-glass detectors
View along along axis of single lead-glass detector looking at
phototube
25 April 2009 7
Data: B.I. Abelev et al. (STAR), PRL 101 (2008) 222001Theory (red): M. Boglione, U. D’Alesio, F. Murgia, PRD 77 (2008) 051502Theory (blue): C. Kouvaris, J. Qiu, W. Vogelsang, F. Yuan, PRD 74 (2006) 114013
Spin Effects for Large-xF Neutral Pion Production
dσ↑(↓)=differential cross section when proton has spin up (down).
AN =d - d d + d
Run 6 Data
Even though the kinematics of the SIDIS measurement and the forward data have little overlap, it is possible to account for most of the features of the RHIC data by calculations based on phenomenological fits to the semi-inclusive DIS data
25 April 2009 8
Does pQCD describe particle production at RHIC?Compare cross sections measured for p+p +X at s=200 GeV
to next-to-leading order pQCD calculations
J. Adams et al. (STAR), PRL 97 (2006) 152302
Particle production cross sections for p+p collisions agree with NLO pQCD down to pT~2 GeV/c over a wide range, 0 < < 3.8, of pseudorapidity ( = -ln tan /2).
25 April 2009 9
Inclusive production from dAu
J. Adams et al. (STAR), PRL 97 (2006) 152302
Particle production cross sections for d+Au collisions are smaller than expectations from only shadowing at < =4.0, and the energy dependence is best described by CGC calculations (A. Dumitru et al. Nucl Phys A765 (2006) 464)
25 April 2009 10
Dependence of RdAu
• From isospin considerations, p + p h is expected to be suppressed relative to d + nucleon h at large [Guzey, Strikman and Vogelsang, Phys. Lett. B 603, 173 (2004)]
• Observe significant rapidity dependence similar to expectations from a “toy model” of RpA within the Color Glass Condensate framework.
y=0
As y grows
Kharzeev, Kovchegov, and Tuchin, Phys. Rev. D 68 , 094013 (2003)
See also J. Jalilian-Marian, Nucl. Phys. A739, 319 (2004)
J. Adams et al. (STAR), PRL 97 (2006) 152302
pp
dAu
pp
dAuinelasticdAubinary
inelasticpp
dAu
dpEd
dpEd
NR
1972
1
3
3
3
3
25 April 2009 11
STARSTAR • are suppressed at small <xF> and <pT,>
consistent with CGC picture
• are similar in d+Au and p+p at larger <xF> and <pT,>
as expected by HIJING
25<E<35GeV
Fixed as
E & pT grows
Forward + mid-rapidity correlations in d+Au
J. Adams et al. (STAR), PRL 97 (2006) 152302
25 April 2009 12
Run-8 Results from STAR Forward Meson Spectrometer
(FMS)
Full azimuth spanned with nearly contiguous electromagnetic calorimetry from -1<<4
approaching full acceptance detector
25 April 2009 13
Guzey, Strikman and Vogelsang Guzey, Strikman and Vogelsang Phys. Lett. B603 (2004) 173Phys. Lett. B603 (2004) 173
PYTHIA Simulation PYTHIA Simulation
• constrain x value of gluon probed by high-x quark by detection of second hadron serving as jet surrogate.
• span broad pseudorapidity range (-1<<+4) for second hadron span broad range of xgluon
• provide sensitivity to higher pT for forward reduce 23 (inelastic) parton process contributions thereby reducing uncorrelated background in correlation.
25 April 2009 14
d+Au d+Au +++X, pseudorapidity correlations with forward +X, pseudorapidity correlations with forward HIJIING 1.381 Simulations HIJIING 1.381 Simulations
• increased pT for forward over run-3 results is expected to reduce the background in correlation.
• detection of in interval -1<<+1 correlated with forward (3<<4) is expected to probe 0.01<xgluon<0.1 provides a universality test of nuclear gluon distribution determined from DIS.
• detection of in interval 1<<4 correlated with forward (3<<4) is expected to probe 0.001<xgluon<0.01 smallest x range until eRHIC.
• shadowing of gluon structure function is not expected to modify width of away-side peak in distribution caused by elastic parton scattering.
25 April 2009 15
STAR Forward Meson Spectrometer
Phys. Rev. Lett. 101:222001 (2008)
• 50 larger acceptance than the run-3 forward pion detector (FPD).
• azimuth for 2.5<<4.0
• Discriminate single from up to ~60 GeV
Runs 3-6
FPD
Run8
FMS
North half of FMS before closing
25 April 2009 16
“Jet-like” events in the FMSCone-based clustering of energy
near-side correlations
“Jet-shape” distribution of energy within jet-like objects in the FMS as a function of distance from the jet axis.
Caveat for Run 8: FMS data was acquired with a “high tower” trigger, which creates a bias towards “jets” that derive from a small number of high-z initial fragments
N. Poljak, SPIN08Plot from hep-ex/0901.2828
STAR Preliminary
Simulation and Data agree well for “jet-like” events
25 April 2009 17
STAR Detector• Large rapidity coverage for electromagnetic calorimetry (-
1<<+4) spanning full azimuth azimuthal correlations
• Run-8 was the first run for the Forward Meson Spectrometer (FMS)
25 April 2009 18
FMS-FPD comparison• Emulate FPD from run-8 FMS:
FMS photons: x>0cm
|TPC|<0.725 ; 3.8<FMS<4.1
pT(TPC)>0.5 GeV/c
30<EFMS<55 GeV
leading particle analysis
• Normalization requires further systematic studies
pile-up correction
vertex efficiency
run-3/run-8 trigger
• Reproduces Gaussian width and many other similarities
=0.949±0.121
=0.965±0.198
=1.073±0.335
=1.161±0.132
J. Adams et al. (STAR), PRL 97 (2006) 152302
Run-8 FMS preliminary results/E. Braidot QM09
25 April 2009 19
Azimuthal Correlations (3)
Unc
orre
cted
Coi
ncid
ence
P
roba
bilit
y (r
adia
n-1)
p+p+h±+X, s=200 GeV
requirements:
pT,>2.5 GeV/c
2.8<<3.8
h± requirements:
1.5<pT,h<pT,
h<0.9
• clear back-to-back peak observed, as expected for partonic 22 processes
• fixed and large trigger, with variable h map out Bjorken-x dependence
• of greatest interest for forward direct- trigger
E. Braidot, QM09
25 April 2009 20
Azimuthal Correlations (=0)
leading subleading
• Near-side and away-side correlations observed for forward- pair
• Clear increase of width of away-side peak as increases
Preliminary
25 April 2009 21
Azimuthal Correlations (3)
++X
+h±+X
Un
corr
ect
ed C
oin
cid
ence
Pro
bab
ilit
y (r
adia
n-1)
-lead
p+p d+Au
“GSV” Selection “GSV” Selection
2.5 GeV/c<pT(=3)
1.5 GeV/c<pT(||<0.9)<pT
(=3)
dAu – pp = 0.09±0.04
“GSV” selection leads to clear back-to-back peak with similar pp/dAu widths as expected by pQCD
E. Braidot, QM09
25 April 2009 22
Azimuthal Correlations (3)
++X
+h±+X
Un
corr
ect
ed C
oin
cid
ence
Pro
bab
ilit
y (r
adia
n-1)
-lead
p+p d+Au
“lower-pT” Selection “GSV” Selection
2.5 GeV/c<pT(=3)
1.5 GeV/c<pT(||<0.9)<pT
(=3)
dAu – pp = 0.09±0.04
“lower-pT” Selection
2.0 GeV/c<pT(=3)
1.0 GeV/c<pT(||<0.9)<pT
(=3)
dAu – pp = 0.19±0.03
Evidence of pT dependent azimuthal broadening of signal
E. Braidot, QM09
25 April 2009 23
Au-Side Multiplicity Dependence
FMS
bEMC
east BBCmultiplicity
d Au
Select events on east BBC phototube charge sum
• -5.0 < BBC < -3.4 (Au side)
• 18 counts on average from minimum ionizing particle
25 April 2009 24
Au-Side Multiplicity DependenceFMS+EMC events
Q FMS-bEMC
low
low Q
mid
mid Qhigh
high Q
p+p
d+Au
“lower-pT” Selection: 2.0 GeV/c<pT(=3), 1.0 GeV/c<pT
(||<0.9)<pT(<>=3)
• No forward multiplicity dependence of p+p (FMS-EMC) correlations
• Multiplicity dependence of d+Au (FMS-EMC) correlations is observed
Un
co
rrec
ted
Co
inc
ide
nc
e P
rob
ab
ility (ra
dia
n-1)
25 April 2009 25
Run 8 dataPythia+GEANT (background only) (simulation generation ongoing)
STAR Preliminary
Near-Side Correlations in FMSObservation of large-xF production
For this plot simulation is background only
Fit is gaussian + cubic polynomial μ=0.784±0.008 GeV σ=0.087±0.009 GeV Scale=1339±135 Events
Significant (10) 0 signal seen in the data.
Comparison to Run 8 dAu data and transverse SSA may be interesting.
p+p+X, s = 200 GeV
Etrip>30 GeV
pT,trip>2.5 GeV/c
pT( cluster)>1.5 GeV/c
pT()>1 GeV/c
A. Gordon, Moriond 2009
25 April 2009 26
Large-xF J/ ObservationC. Perkins (for STAR), Quark Matter 2009
2.5<clus<4.0
pT,clus>1 GeV/c
Epair > 60 GeV
p+pJ/+Xe+e¯ + X, s=200 GeV
4.5 significance
p+pJ/++Xe+e¯++X, s=200 GeV
2.9 significance
• high-xF J/ may have implications for intrinsic charm at large Bjorken-x in proton
• use to benchmark simulations for future transverse-spin Drell-Yan experiment
25 April 2009 27
Conclusions
• RHIC run 8 (dAu/pp) was a big success with 20x increase of forward acceptance at STAR enabling the study of pT depenence of azimuthal correlations.
• Run-8 FMS results reproduce run-3 FPD Gaussian widths and other features.
• Comparison of (FMS)+(EMC) for pp and dAu indicates azimuthal broadening in dAu.
• Data are qualitatively consistent with a pT dependent picture of gluon saturation of the gold nucleus.
25 April 2009 28
Outlook
• Extract for two forward for d+Au collisions
• Complete scan of pT range (from GSV to run-3)
• Scan for elastic parton scattering x dependence of nuclear gluon density
• Clustering: towards +jet or jet+jet
• Complete absolute normalizations and systematics studies