Upload
amie-thomas
View
224
Download
0
Tags:
Embed Size (px)
Citation preview
1
E895 - correlation analysis - Status ReportMike Lisa, The Ohio State University
• E895 Motivation and Measurement
• Status of HBT analysis
• Summary and plans
2
Lawrence Berkeley Lab D. Best, T. Case, K. Crowe, D. Olson, G. Rai, H.-G. Ritter, L. Schroeder, J. Symons, T. Wienold
Brookhaven National Lab S. Gushue, N. Stone
Carnegie Mellon University M. Kaplan, Z. Milosevich, J. Whitfield
Columbia University I. Chemakin, B. Cole, H. Hiejima, X. Yang, Y. Zhang
U.C. Davis P. Brady, B. Caskey, D. Cebra, J. Chance, J. Draper, M. Heffner, J. Romero, L. Wood
St. Mary’s College J. Kintner
Harbin Institute (China) L. Huo, Y. Liu, W. Zhang
Kent State Univeristy M. Justice, D. Keane, H. Liu, S. Panitkin, S. Wang, R. Witt
Lawrence Livermore Lab V. Cianciolo, R. Sotlz
Ohio State University A. Das, M. Lisa, R. Wells
University of Auckland (NZ) D. Krofcheck
Purdue University M. Gilkes, A. Hirsch, E. Hjort, N. Porile, R. Scharenberg, B. Srivastava
S.U.N.Y. Stony Brook N.N. Ajitanand, J. Alexander, P. Chung, R. Lacey, J. Lauret, E. LeBras, B. McGrath, C. Pinkenburg
3
Systematics/meta-analysis suggest approach to maximum AGS energy interesting...
P. Braun-Munzinger and J. Stachel,NPA606, 320 (1996)
4
Perhaps some signals only apparent near threshold
D. Rischke, NPA 610, c88 (1996)
E895 flow statusdiscussed by R. Lacey
5
Ideally, HBT gives a measure of source size
C k kP k k
P k P k
d x d x x x e
d x d x x x
Q
i k k x x
2 1 21 2
1 2
31
32 1 23
13
2 1 2
2
1
1
2 1 2 1
( , )( , )
( ) ( )
( ) ( )
( ) ( )
~( )
( ) ( )
r rr r
r r
r r
r r
r
r r r r
=⋅
= ± ⋅ ⋅ ⋅∫ ⋅⋅ ⋅ ⋅∫
= ±
⋅ − ⋅ −ρ ρρ ρ
ρ
PionSource ρ( )x
C (Qinv)
Qinv (GeV/c)
1
2
0.05 0.10
Width ~ 1/R
6
HBT systematics at AGS interesting in themselves,
& can look for suprises
“”“c”
Rischke & GyulassyNPA 608, 479 (1996)
May miss signal at “too high” Ebeam
7
HBT - another handle onmean field effects at AGS
Generated by H. Liu and S. Panitkin
8
AGS BevalacParticle reconstruction upgrades have taken huge effort,but have born fruit...
9
PID via dE/dxfor primaries
(negative particles cleaner)
2 AGeV
4 AGeV
8 AGeV
10
Strange neutrals reconstructed(& provide sensitive diagnostic of data quality)
plots from P. Chung, SUNY-SB
p + K0
11
Non-uniform trigger in dataset analysedWill be possible toselect top ~5% forall energies offline
Current analysis:2 GeV: b 0-8 fm4 GeV: b 0-8 fm8 GeV: b 0-3 fm
Otherwise seems OKe.g. log increase ofmultiplicity with Ebeam:Ebeam Ebeam
Mmax Mmax + 50M
max Mmax + 15
12
Singles coverage for pions
13
Large acceptance many -
But...phase space meansmost are at large Q
Background (denominator)generated with standardevent-mixing (15 previous)
4 GeV central
14
Pairwise cuts to remove track splitting effects“Raw” correlation functionshows encouraging structureat low Qinv
Simulations: requirement that> 50% of track is seenkills truly found pairs.
(Au+Be event)
15
Pairwise cuts, cont’Track-splitting virtually eliminated by pairwise cut:
require that sum of % track seen > 100% (applied to “real” and “mixed” pairs)
Next low-Q problem:track-merging.
16
Merging effect reduced by cut on projected seperation at exit of TPC.
Real pairs
Mixed pairs
17
Require particles to exit TPC 10 cm apart.
0 cm cut
5 cm cut
10 cm cut
15 cm cut
18
Overview of E895 HBT AnalysisOverview of E895 HBT Analysis
raw data
(pass1)
TRKS
HBT_SWHBT_EVENT_CUTHBT_TRK_CUTHBT_PAIR_CUT
• Embed MC pairs into raw data• perform pass1• correlate embedded, extracted particles
fit of singles distribution
generation of MC pairs(kuip macro files)
EMBED_PARTSTRKS
AM_PID AM_HBT
histogramsacceptance correctionscoulomb correctiondiagnostic ntuplescorrelation functions
19
Corrections - I
Ideally... C k kP k k
P k P kP k k
P k ktrue
mixed2 1 2
1 2
1 2
1 2
1 2
( , )( , )
( ) ( )( , )( , )
r rr r
r rr rr r=
⋅=
“Background” pair distribution contains all physicsand detector effects except for the BE symmetrization
Well-known deviation from this is due to final-state Coulomb repulsion...
Approximate correction - Gamow factor:
G Qe
m e
Qinvinv
( ) ;=−
=1
η ηη
h
(Better to do full Coulomb integration)
20
Corrections - IIDetector acceptance effects are more subtle, especially with a tracking detector
Original pion pair
k1
k2
MC Scattering
Pattern recognition
Digitization, thresholds
Pixel noise
Measuredparticle(s)
k1’, k2
’, (k3’...)
Track merging and splitting and momentum resolution and distortion.
Hit the low-Q pairs hardest, and affect the correlation signal significantly.
Effects depend on k1, k2 (six-dimensional!), as well as track and pair cuts!!!
Correcting for or minimizing these 2-particle effects requires detailed simulation.
21
Generating the Acceptance /Resolution Correction - I
C2(ideal)
C2(reconstructed)=
R(k1,k2)B(k1,k2)
R(k1,k2)B(k1,k2)
Kacceptance =
B(k1,k2) =d6N
d3k1d3k2
R(k1,k2) =d6N
d3k1d3k2
• C2(k1,k2)
for someset of cuts:
only phase space (k) cut applied(no track quality or 2-track cuts)
B(k1,k2) =d6N
d3k1d3k2
R(k1,k2) =d6N
d3k1d3k2
• C2(k1,k2)
apply same track and pair cuts as applied to data
(weighting by C2(k1,k2) implies foreknowledge of correlation function iterative approach)
22
Understanding close pairs
•Close pairs are embedded into real data events at pixel levelwith measured momentum distribution, to get correct noisetrack density environment•Full event reconstruction run•Gives momentum distortions, pair loss...
23
Resolution from the 4 GeV simulations...
10 MeV/c resolution(includes MCS)
finite resolution + phase spacegive Q distortion at low Q
(Qin > 40 MeV/c)
24
Pair loss from 4 GeV simulations
Pair loss constant above 50 MeV/c(statistical loss of single track)
Single pair in...
Lost pair Split track
25
Finally: “Correction to the Coulomb Correction”
In the measured ratios, we apply the Coulomb correction (currently the Gamowcorrection) according to the measured Q, not the true Q.
With the simulated pairs, we have the true and reconstructed momenta, socan account for this.
Then, the full acceptance/resolution correction function is:
R(k1,k2)B(k1,k2)
R(k1,k2)B(k1,k2)
G(k1,k2)
G(k1,k2)
26
Corrections for 10 cm exit seperation
27
Corrections for 2 cm exit separation
28
Acceptance/resolution well understood & accounted for
2 cm exit separation cut10 cm exit separation cut
Different cuts give very different raw correlation functions.But corrected correlation function is robust.
2 GeV results2 GeV results
29
Data points consistent - fits are sensitive
30
4 GeV results stable (and reasonable) as well
10 cm exit separation cut 2 cm exit separation cut
31
8 GeV results not stable or reasonable(under study)
10 cm exit separation cut 2 cm exit separation cut
32
SummarySummary• E895 can measure low-Q correlations well
• Difficulties of close pairs (splitters/mergers) largely addressed through pairwise cuts
• Detailed simulations generate corrections that track with cuts– These corrections are significant and important
• Different quality cuts very different measured correlation functions very different measured corrections NOT different corrected correlation functions
• Must figure out what is going on at high energy
• Multi-dimensional HBT and phase space cuts come next
(present analysis on < 5% of data)