Post on 17-Dec-2015
Midwest critical mass 2010
Measurement of two-particle correlations in pp collisions at sqrt(s) = 900 GeV as well as at sqrt(s) = 7 TeV with ALICE
The ALICE group
23. October 2010
Midwest critical mass 2010Toledo, Ohio
Sebastian Huber 2Midwest critical mass 2010
first paper on HBT by ALICE
two particle correlations in pp at sqrt(s) = 900 GeV
1 dimensional
Midwest critical mass 2010
motivation
Sebastian Huber – s.huber@gsi.de
• measuring space-time dimensions in pp collisions at sqrt(s) = 900 GeV with
ALICE
• investigating collective behaviour in pp collisions at LHC energies
• reference for heavy ion measurements starting in Nov 2010
• using Bose-Einstein enhancement of identical pion pairs to
get access to size of pion emitting source
• dependance of source size as function of event multiplicity dNCH/dη
an transverse momentum kT
Midwest critical mass 2010
HBT – Bose-Einstein correlations
Sebastian Huber – s.huber@gsi.de
„The only way to get access to space-time properties of the emitting source in elementary particle collisions is through the measurement of Bose-Einstein correlations (BEC) between identical pions“
• building the correlation function (CF)
• transformation in relative momenta q
• correlation function in the experiment
)()(
),(),(
21
21212 pPpP
ppPppC
22221 4)( mmppq Inv
)(
)()(2 qB
qAqC
A(q) is the measured distribution of the pair momentum difference q, whereas B(q) is a reference distribution build by using pairs of particles from different events (event-mixing) or by rotating on particle of the pair in the transverse ebene (rotation)
Reference distribution should be without Bose-Einstein correlations
Midwest critical mass 2010
Extracting the HBT radii
Sebastian Huber – s.huber@gsi.de
To get the HBT-radii out of the correlations one has to use a propper parametrization
If one asumes that the source function has a gaussian shape also the parametrization has a gaussian shape
A common parametrization is the following
))(exp(1)( 22 RqqC
R is the effective size of the emission region
λ is the coherence parameter measuring the strength of the Bose-Einstein correlation
Bose-Einstein correlation allows to distinguish between collision systems
HBT in pp at sqrt(S) = 7 TeV will be interconnection between small systems (pp) and heavy systems (AA) at lower energies
Midwest critical mass 2010
correlation of non-identical pions at sqrt(S) = 900 GeV
Sebastian Huber – s.huber@gsi.de
• π+π- correlations in comparisson with
PHOJET simulations
• description of the background of the CF
• rich spectrum of meson resonances
• coulomb effect in the first bins
• using the background of the CF later for the
parametrization of the CF of identical pions
• proper treatment of baseline very important
when studying the dependancy of the radii from
transverse momentum and multiplicity
• parametrization of the background
2)( InvInvInv cqbqaqD
Phys. Rev. D 82, 052001 (2010)
Midwest critical mass 2010
correlation of identical pions at sqrt(S) = 900 GeV
Sebastian Huber – s.huber@gsi.de
• π+π- correlations in one dimension
• 2009 data not enough statistics for 3D
• 3 bins in event multiplicity
• 5 bins in transverse momentum
• Bose-Einstein effect clearly visible
• fixing the baseline with simulations (see slide
before)
• developing of long range correlations with
increasing kT
• used parametrization
)())))(exp(1()()1(()( 22 InvInvInvInvInv qDqRqKqC
Midwest critical mass 2010
multiplicity dependance
Sebastian Huber – s.huber@gsi.de
• source radii increase with multiplicity
• same dependance like older measurements
• HBT radii seem to depend more on
multiplicity than on geometry (pp)
• grey shadowed band
Systematic error from:
• baseline assumption
• fitting
• background construction
• UNICOR vs ALIFEMTO
Midwest critical mass 2010
kT dependance - baseline
Sebastian Huber – s.huber@gsi.de
• source radii independant of kT a
• no sign of collective behaviour (presence of a bulk)
in pp
• very sensitive to basline assumption
• if fitted free (flat baseline) – dependance emerges
Midwest critical mass 2010
results
Sebastian Huber – s.huber@gsi.de
Parametrization with a gaussian
Parametrization with an exponential
dNCH/dη
dNCH/dη
λ
λ RInv/fm
RInv/fm
3.2
3.2
7.7
7.7
11.2
11.2
0.386 (0.022)
0.331 (0.023)
0.310 (0.026)
0.704 (0.048)
0.577 (0.054)
0.548 (0.051)
0.874 (stat 0.047) (sys 0.181)
1.082 (stat 0.068) (sys 0.206)
1.184 (stat 0.092) (sys 0.168)
0.808 (stat 0.061) (sys 0.208)
0.967 (stat 0.095) (sys 0.206)
1.069 (stat 0.104) (sys 0.203)
)()))(exp(1)()1(()( 22 InvInvInvInvInv qDqRqKqC
)()exp(1)(2 InvInvInvInv qDqRqC
Sebastian Huber 11Midwest critical mass 2010
ongoing work
two particle correlations in pp at sqrt(s) = 7 TeV1 dimensional
3 dimensional
Midwest critical mass 2010
motivation
Sebastian Huber – s.huber@gsi.de
• measuring space-time dimensions in pp collisions at sqrt(s) = 900 GeV and at
sqrt(s) = 7 TeV at ALICE
• investigating collective behaviour in pp collisions at LHC energies
• more statistics makes it possible to go into more than one dimension
• getting deeper into the physics of the system
• using Bose-Einstein enhancement of identical pion pairs to
get access to size of pion emitting source
• dependance of source size as function of event multiplicity dNCH/dη
and transverse momenta kT
• cartesian parametrization in out side and long (Bertsch-Pratt)
• expansion in spheriacal harmonics
• difference between 900 GeV and 7 TeV
• understanding the background – non BE correlations – EMCIC
• no gaussian shape of the CF
• collective behaviour of the pion emitting fireball
Midwest critical mass 2010
1 dim 7TeV – kT and dNCh/dη
Sebastian Huber – s.huber@gsi.de
•coulomb
•minijets
7 TeV π+π+
7 TeV π+π-
Midwest critical mass 2010
out
Sebastian Huber – s.huber@gsi.de
parametrization )))(exp(1())()()(exp(1()1(),,( 22222222 lsoBllssoolso qqqRqRqRqRKqqqC
holes due to combination of
single track acceptance pT and
Pair kT cut
Midwest critical mass 2010
side
Sebastian Huber – s.huber@gsi.de
Midwest critical mass 2010
long
Sebastian Huber – s.huber@gsi.de
edges due to acceptance of the
detector in η
Sebastian Huber 17Midwest critical mass 2010
ROut && RSide && RLong
• measurement of BE of identical pions at 900 GeV (newest results not shown) and 7 TeV with dependance on
multiplicity dNCh/dη and pair momentum kT
• 7 TeV data provide link between multiplicities in pp and AA
• 3D CF not gaussian
• non femtoscopic correlations in 7 TeV as well as in 900 GeV – minijets – simulated with PHOJET - baseline
Sebastian Huber 18Midwest critical mass 2010
ROut && RSide && RLong
• radii in 900 GeV and 7 TeV grow with multiplicity
• 900 GeV and 7 TeV behave equaly
• dependance of the radii with pair momentum – very sensitive to baseline
• using spherical harmonics to get a full sight of what is going on (Mikes idea!)
link to the AA data
Sebastian Huber 19Midwest critical mass 2010
Backup
Backup
Midwest critical mass 2010 Sebastian Huber – s.huber@gsi.de
holes and edges
• qlong and qside vanish
• pT is sum of pT1 and pT2
• kT is difference of pT1 and pT2
holes in qout
combination of single particle acceptance and two particle cut leads to holes
edges in qlong
η acceptance of the detector
Midwest critical mass 2010 Sebastian Huber – s.huber@gsi.de
event and track selectio
UNICOR 7 TeV pass2
900 GeV runs by mistake?
Sebastian Huber 22Midwest critical mass 2010
UNICOR 7TeV
HBT – UNICOR
7000 GeV p+p
Midwest critical mass 2010 Sebastian Huber – s.huber@gsi.de
one dimensional CF in LCMS
UNICOR 7 TeV pass2
• red – Pythia-Perugia LHC10d4
• red line – final parametrization• blue line – peak fit• green line – baseline fit
• no difference between fixed baseline fit and free fit
• baseline not as good fixed as in the 900GeV data
• only parts of the simulation LHC10d4 (Pythia-Perugia) taken
Midwest critical mass 2010 Sebastian Huber – s.huber@gsi.de
one dimensional CF in LCMS with kt-binning
UNICOR 7 TeV pass2
first and two last bins not usable – kT > 0.7 no HBT correlation!
new kT binning (see slide 10)
Midwest critical mass 2010 Sebastian Huber – s.huber@gsi.de
UNICOR 7 TeV pass2
one dimensional CF in LCMS with multiplicity-binning
• two highest multiplicity bins missing (by decission)
Midwest critical mass 2010 Sebastian Huber – s.huber@gsi.de
UNICOR 7 TeV pass2
one dimensional CF in LCMS with kt- and multiplicity-binning
binning in kt (7 bins)
dNCh/dη
Midwest critical mass 2010 Sebastian Huber – s.huber@gsi.de
UNICOR 7 TeV pass2
three dimensional CF in LCMS – out side long
• baseline fits do not match the Pythia-Perugia simulation
• please ignore the peak fit
• red – Pythia-Perugia LHC10d4
• red line – final parametrization• blue line – peak fit• green line – baseline fit
Midwest critical mass 2010 Sebastian Huber – s.huber@gsi.de
UNICOR 7 TeV pass2
three dimensional CF in LCMS with kt-binning – out side long
binning in kt (5 bins)
out
side
long
Midwest critical mass 2010 Sebastian Huber – s.huber@gsi.de
UNICOR 7 TeV pass2
three dimensional CF in LCMS with kt and multiplicity binning – out
binning in kt (5 bins)
dNCh/dη
Midwest critical mass 2010 Sebastian Huber – s.huber@gsi.de
UNICOR 7 TeV pass2
three dimensional CF in LCMS with kt and multiplicity binning – side
binning in kt (5 bins)
dNCh/dη
Midwest critical mass 2010 Sebastian Huber – s.huber@gsi.de
UNICOR 7 TeV pass2
three dimensional CF in LCMS with kt and multiplicity binning – long
binning in kt (5 bins)
dNCh/dη
Midwest critical mass 2010
• comparison mixing and rotation
• comparison π+π+ and π-π-
• CMS vs LCMS
• LHC10c vs LHC10b (7TeV)
• comparison of different magnetic field orientations (only in LHC10d)
• different background estimations (fixing the baseline out of simulations or π+π+)
• different fitting ranges
• comparison UNICOR and ALIFEMTO (ALIFEMTO results from Adam and own results)
Systematic error
Sebastian Huber – s.huber@gsi.de
Paper preparation
• variation of the event cuts
• variation of the track cuts
• variation of the pair cuts
• mixing (vertex binning and multiplicity binning)
Sebastian Huber 33Midwest critical mass 2010
dNCH and kT dependancy
Sebastian Huber 34Midwest critical mass 2010
ROut && RSide && RLong
Sebastian Huber 35Midwest critical mass 2010
ROut && RSide && RLong