Download Fluctuations of kinematic quantities in p+p interactions at the CERN

Fluctuations of kinematic quantities in p+p interactions
at the CERN SPS
Bartosz Maksiak and Tobiasz Czopowicz
for the NA61 Collaboration
Faculty of Physics
Warsaw University of Technology
11 IX 2012
WPCF-2012
Bartosz Maksiak, Tobiasz Czopowicz (WUT)
Fluctuations of kinematic quantities in p+p
11 IX 2012
1 / 24
Outline
1
The NA61 experiment
2
Transverse momentum fluctuations
ΦpT measure
Correction method
Results
3
Two-particle correlations in ∆η, ∆φ
Introduction
Results
4
Summary
Bartosz Maksiak, Tobiasz Czopowicz (WUT)
Fluctuations of kinematic quantities in p+p
11 IX 2012
2 / 24
The NA61 experiment
The NA61 experiment
Fixed target experiment.
Located in the North Area
of the CERN SPS accelerator.
Large acceptance (≈ 50% at
pT < 2.5 GeV/c).
High momentum resolution:
σ(p)
≈ 10−4 [GeV/c]−1
p2
(at full 9 Tm magnetic field)
Good particle identification:
σ(TOF) ≈ 60 ÷ 120 ps,
σ(dE/dx)
≈ 0.04,
hdE/dxi
σ(minv ) ≈ 5 MeV.
Within the Ion Program we look
for the Critical Point and study
the properties of the Onset
of Deconfinement.
Bartosz Maksiak, Tobiasz Czopowicz (WUT)
Fluctuations of kinematic quantities in p+p
11 IX 2012
3 / 24
The NA61 experiment
Searching for the Critical Point
Effects of the Critical Point are expected
to be observable in SPS energy range.
Predictions: (Fodor, Katz, JHEP 0404, 050 (2004))
TCP = 162 ± 2 MeV,
µCP
B = 360 ± 40 MeV.
In the region close to critical point,
strong fluctuations should occur (hill
of fluctuations)
Bartosz Maksiak, Tobiasz Czopowicz (WUT)
Fluctuations of kinematic quantities in p+p
11 IX 2012
4 / 24
Transverse momentum fluctuations
Φp
T
measure
Φ - strongly intensive measure of fluctuations
Φ is a strongly intensive measure of fluctuations. In Wounded Nucleon Model it
does not depend on number of wounded nucleons and on fluctuations of
the number of wounded nucleons. In thermodynamical models Φ does not depend
on volume and volume fluctuations.
We want to measure event-by-event transverse momentum fluctuations
for inelastic p+p collisions (ΦpT )
ΦpT can be expressed using event quantities
ΦpT formula
Φ pT ≡
q
hX2 i
hNi
−
2hXi hNXi
hNi2
+
hXi2 hN2 i
hNi3
−
q
hX2 i
hNi
−
hXi2
hNi2
N
P
pTi
i=0
N def P
X2 =
pT 2
i
i=0
def
X =
Mrowczynski, Phys.Lett.B465, 8 (1999),
Liu, Tai, Gazdzicki Stock, Eur.Phys.J.C8 (1999) 649
Bartosz Maksiak, Tobiasz Czopowicz (WUT)
Fluctuations of kinematic quantities in p+p
11 IX 2012
5 / 24
Transverse momentum fluctuations
Correction method
Corrections (1)
0
Define acceptance in which analysis is performed; Example of Particle
Population Matrix at 20 and 158 GeV/c for all charged particles.
Acceptance for 20 GeV/c
1
Acceptance for 158 GeV/c
Prepare two histograms for each data type: sum of pT vs mean multiplicity
and sum of squared pT .
Bartosz Maksiak, Tobiasz Czopowicz (WUT)
Fluctuations of kinematic quantities in p+p
11 IX 2012
6 / 24
Transverse momentum fluctuations
Correction method
Corrections (2)
2
Correct above distributions for non-target interactions.
In case of p+p interactions in the NA61 experiment proton target is a 20 cm long
cylinder filled with liquid hydrogen (LH), therefore the contamination
from non-target interactions may appear (e.g. collision with cylinder walls).
In order to correct data for non-target interactions, NA61 acquires data of both
FULL (with the LH cylinder filled) and EMPTY target (with the LH empty
cylinder) collisions. Then, in the analysis procedure, non-target interactions are
subtracted. Below, example of z position of the fitted vertex for 158 GeV/c.
Bartosz Maksiak, Tobiasz Czopowicz (WUT)
Fluctuations of kinematic quantities in p+p
11 IX 2012
7 / 24
Transverse momentum fluctuations
Correction method
Corrections (3)
Full target
3
Extracted (FT − c · ET )
Empty target
Correct for detector effects (detector inefficiencies, trigger bias): calculate
reconstructed
inverse correction factor by dividing distributions MC
.
MCgenerated
VENUS reconstructed
Bartosz Maksiak, Tobiasz Czopowicz (WUT)
VENUS generated
Inverse correction factor
Fluctuations of kinematic quantities in p+p
Corrected (Extracted · Inv.corr.fact)
11 IX 2012
8 / 24
Transverse momentum fluctuations
Correction method
Corrections (4)
4
Obtain quantities needed to calculate ΦpT from the corrected distributions
(i.e. hNi, hN2 i, hXi, hX2 i, hNXi, hX2 i).
5
Calculate ΦpT .
Bartosz Maksiak, Tobiasz Czopowicz (WUT)
Fluctuations of kinematic quantities in p+p
11 IX 2012
9 / 24
Transverse momentum fluctuations
Results
Results (1)
Study of correction factors of instrumental and physics biases correction factors is
still ongoing. Uncorrected results (corrected only for non-target interactions) from
the ΦpT analysis were obtained for p+p collisions at beam momenta: 20, 31, 40,
80, 158 GeV/c.
Bartosz Maksiak, Tobiasz Czopowicz (WUT)
Fluctuations of kinematic quantities in p+p
11 IX 2012
10 / 24
Transverse momentum fluctuations
Results
Results (2)
Next steps:
Correct data for trigger bias and detector inefficiencies (see previous slides).
Calculate systematic uncertainty of ΦpT .
Bartosz Maksiak, Tobiasz Czopowicz (WUT)
Fluctuations of kinematic quantities in p+p
11 IX 2012
11 / 24
Two-particle correlations in ∆η, ∆φ
Introduction
Two-particle correlations - introduction (1)
Two-particle correlations
in ∆η, ∆φ.
Studied extensively at RHIC
and LHC.
Interesting structures have
been discovered.
This method allows
to disentangle different
sources of correlations:
jets,
flow,
resonance decays,
quantum statistics
effects,
conservation laws.
Bartosz Maksiak, Tobiasz Czopowicz (WUT)
M. Janik, PoS(WPCF2011) 026
Fluctuations of kinematic quantities in p+p
11 IX 2012
12 / 24
Two-particle correlations in ∆η, ∆φ
Introduction
Two-particle correlations - introduction (1)
Correlations are calculated by finding the difference in pseudo-rapidity and
azimuthal angle between two particles in the same event.
∆η = |η1 − η2 |
η transformed from LAB to CMS assuming pion mass
∆φ = |φ1 − φ2 |
The azimuthal angle is folded (to improve statistics):
if ∆φ > π then ∆φ = 2π − ∆φ.
Correlation function
C (∆η, ∆φ) =
S(∆η, ∆φ) =
d 2 N signal
d∆ηd∆φ ;
pairs
Nmixed
S(∆η,∆φ)
pairs M(∆η,∆φ) ;
Ndata
M(∆η, ∆φ) =
d 2 N mixed
d∆ηd∆φ
Correlation function ratio is calculated and normalized in restricted ∆η region:
0 < ∆η < 3.
Event and track cuts were chosen to select only inelastic interactions with particles
produced in strong and EM processes within the NA61/SHINE acceptance.
Bartosz Maksiak, Tobiasz Czopowicz (WUT)
Fluctuations of kinematic quantities in p+p
11 IX 2012
13 / 24
Two-particle correlations in ∆η, ∆φ
Results
C (∆η, ∆φ) - p+p at 158 GeV/c (NA61 data, all charged)
Significant maximum at (∆η, ∆φ) = (0, π),
better visible in narrow multiplicity bins.
Resonance decays and momentum
conservation.
Coulomb and quantum effects contribute to
a weak enhancement at (0, 0).
Bartosz Maksiak, Tobiasz Czopowicz (WUT)
Fluctuations of kinematic quantities in p+p
11 IX 2012
14 / 24
Two-particle correlations in ∆η, ∆φ
Results
C (∆η, ∆φ) - p+p at 158 GeV/c (VENUS, all charged)
VENUS data shows similar structures as
NA61 data; resonance decays and
momentum conservation near (0, π) - better
visible in narrow multiplicity bins.
But hill around (0, 0) is not present.
Because VENUS does not generate
Coulomb and quantum effects.
Remark: Here VENUS events, in contrary to Φp
T
analysis, were not processed
through Geant and reconstrucion but the same acceptance as in NA61 was applied.
Bartosz Maksiak, Tobiasz Czopowicz (WUT)
Fluctuations of kinematic quantities in p+p
11 IX 2012
15 / 24
Two-particle correlations in ∆η, ∆φ
Results
C (∆η, ∆φ) - p+p at 158 GeV/c (NA61 data vs. VENUS, all charged)
Real data and VENUS distributions are similar except of (0, 0) region: VENUS
does not implement Coulomb and quantum effects.
Bartosz Maksiak, Tobiasz Czopowicz (WUT)
Fluctuations of kinematic quantities in p+p
11 IX 2012
16 / 24
Two-particle correlations in ∆η, ∆φ
Results
C (∆η, ∆φ) - p+p at 158 GeV/c (NA61 data, positively charged)
Low resonance (possible ∆++ ) and
momentum conservation hill at (0, π) for
averaged distribution. Better visible for
narrow multiplicity bins.
Hill in (∆η, ∆φ) = (0, 0): quantum
statistics effects.
Bartosz Maksiak, Tobiasz Czopowicz (WUT)
Fluctuations of kinematic quantities in p+p
11 IX 2012
17 / 24
Two-particle correlations in ∆η, ∆φ
Results
C (∆η, ∆φ) - p+p at 158 GeV/c (VENUS, positively charged)
Resonance decays and momentum
conservation hill also present in VENUS.
This hill is at (0, π) - much better visible in
multiplicity bins, but
No hill at (0, 0). Quantum statistics effects
not implemented in VENUS.
Bartosz Maksiak, Tobiasz Czopowicz (WUT)
Fluctuations of kinematic quantities in p+p
11 IX 2012
18 / 24
Two-particle correlations in ∆η, ∆φ
Results
C (∆η, ∆φ) - p+p at 158 GeV/c (NA61 data vs. VENUS, positively
charged)
(0, π) resonance and momentum conservation hill is lower than in all charged.
No quantum statistics hill in VENUS at (0, 0): VENUS does not implement
quantum statistics effects.
Bartosz Maksiak, Tobiasz Czopowicz (WUT)
Fluctuations of kinematic quantities in p+p
11 IX 2012
19 / 24
Two-particle correlations in ∆η, ∆φ
Results
C (∆η, ∆φ) - p+p at 158 GeV/c (NA61 data, negatively charged)
No resonance which decay into two
negatively charged particles.
Very low momentum conservation hill visible
at (0, π) on averaged distribution and on
multiplicity bins distributions. Quite difficult
to observe, because it is masked by:
Quantum statistics hill at (0, 0).
For mult. bins hill at (3, π). Probabaly
global momentum conservation.
Bartosz Maksiak, Tobiasz Czopowicz (WUT)
Fluctuations of kinematic quantities in p+p
11 IX 2012
20 / 24
Two-particle correlations in ∆η, ∆φ
Results
C (∆η, ∆φ) - p+p at 158 GeV/c (VENUS, negatively charged)
Momentum conservation hill (0, π) visible
on averaged distribution and on multiplicity
bins.
No quantum statistics hill (not implemented
in VENUS).
Bartosz Maksiak, Tobiasz Czopowicz (WUT)
Fluctuations of kinematic quantities in p+p
11 IX 2012
21 / 24
Two-particle correlations in ∆η, ∆φ
Results
C (∆η, ∆φ) - p+p at 158 GeV/c (NA61 data vs. VENUS, negatively
charged)
Quantum statistics hill (0, 0) visible only in data (effects not implemented in
VENUS).
Momentum conservation hill (0, π) visible for data and for VENUS.
Bartosz Maksiak, Tobiasz Czopowicz (WUT)
Fluctuations of kinematic quantities in p+p
11 IX 2012
22 / 24
Summary
Summary
Event-by-event transverse momentum fluctuations (ΦpT ):
New method of correcting results on fluctuations for experimental and
physics biases was introduced.
Uncorrected ΦpT results for p+p collisions at beam momenta: 20, 31, 40, 80,
158 GeV/c were presented. Soon corrected results will be shown.
Two-particle correlations in azimuthal angle and pseudo-rapidity:
Two-particle correlations in ∆η and ∆φ were obtained for p+p interactions
at 158 GeV/c both for NA61 data and for the VENUS model.
The analysis showed several structures. They depend on the multiplicity
selection and may be related to quantum effects, resonance decays and
conservation laws.
Dividing into narrow multiplicity bins allows to better see correlation
structures (consistent with LHC observations for p+p at 7 TeV - see
introduction to ∆η∆φ correlations).
Bartosz Maksiak, Tobiasz Czopowicz (WUT)
Fluctuations of kinematic quantities in p+p
11 IX 2012
23 / 24
Summary
Thank you
Bartosz Maksiak, Tobiasz Czopowicz (WUT)
Fluctuations of kinematic quantities in p+p
11 IX 2012
24 / 24