• Motivation
• Selection of K+ and π± mesons
• Registration efficiency correction
• Relative cross section normalisation
• Influence of trigger conditions
• Comparison with KaoS (minimum bias conditions)
A. Sadovsky
Forschungszentrum Rossendorf, Dresden
HADES PID meeting
Řež 12-14th December 2005
An estimate of the K+ cross sectionin the reaction C+C @ 2 AGeV
Selection of K+ (MdcSegment Fit and Vertex cuts)
HMdcSeg1 χ2cut
HMdcSeg2 χ2cut
ZMdcSeg1 [mm] ZMdcSeg1 [mm]
RM
dc
Seg
1 [m
m]
RM
dc
Seg
1 [m
m]
Selection of K+ (matching with META and cuts on β2·dE/dx)
MDC-META
matching cut
Cou
nts
Selection of K+ (Runge Kutta χ2-cut and p vs. m2-plot)
No cuts
After all cuts, but χ2
RK
After all cuts and χ2
RK
All cuts, but RK remove ≈80% of MetaMatch track candidates
χ2RK cut remove ≈30% from left over
After all quality cuts only about 15% left to be used for K+ selection see below:
Selection of K+ (slices with different momentum)
Registration efficiency correction for K+ (simulation)
Pluto: 10*106
only K+ tracks (T=88 MeV, βr=0.3)
dpd
NdpfPluto
2
),(
hGeant with realistic settings for Nov02
DST with Hydra:
Nov02/gen3-like
Analysis, K+ cuts (micro DST‘s) like for real data
dpd
NdpfPGHAC
2
),(
),(
),(),(
pf
pfpc
PGHAC
PlutoREG
dpd
Ndpc
dpd
Nd
22
),(
Registration efficiency correction for K+ (TOF/TOFINO)
),(),(),()()(
2
pfpfpfdpd
Nd
TOFPGHAC
TofinoPGHACPGHAC
PGHAC
Ratio of K+ counts distribution after
Pluto / PGHAC (Pluto+Geant+Hydra+Analysis+Cuts)
p [MeV/c]
°
(Sector 0)
Tofino
Tofino dpd
Ndpf
2
),(
TOF
TOF dpd
Ndpf
2
),(
Selected K+
Momentum
range
[MeV/c]
TOFINObg/(sig+bg)S0 S3
TOFbg/(sig+bg)S0 S3
TOFINO
N(K+)/N(bg)
S0 S3
TOF
N(K+)/N(bg)
S0 S3
200<p·q<300
300<p·q<400
400<p·q<500
500<p·q<600
600<p·q<700
<10% <10%
25% 20%
26% 36%
-------//--------
-------//--------
<10% <10%
8% 13%
9% 12%
20% 28%
42% 45%
13/2 21/4
60/20 124/31
274/95 313/178
-------//-------
-------//-------
40/6? 25/3?
232/21 171/26
400/61 327/43
303/76 251/98
120/90 126/108
Nov02/gen3 DST 166 106 events
3686 tracks identified as K+ in S0+S3
Background contribution less than 30%
i.e. N(K+)/N(bg) = 2562/1124 = 2.3
Average significance = 42.2
N(K+) =124
N(bg) = 31
Co
un
ts
m [MeV/c2]
Selection of π± (same quality cuts as for K+)
π± PID selection:
• only for TOF region
• graphical cut
• 300<p<1000 [MeV/c]
• π- 40° < < 72°
• π+ 46° < < 82°
(SIM) admixture of other particles < 3%
TOF
π± (registration efficiency correction)Tracking efficiency (hit registration and algorithm)
Decays (for unstable particles)Registered (EXP) Corrected (EXP)
Cross section (how-to approach)
Target, beam intensity and trigger conditions
Lab
REG
cuttrackMDCtrigdeadbeamALabdpd
Nd
pNdN
M
dpd
d
22
,
11
Lab
REG
cuttrackMDCtrigdeadbeamALabdpd
Nd
pNdN
M
dpd
d
22
,
11
Lab
REG
Labdpd
NdpcConst
dpd
d
22
,
Correction
efficiency of hit registration, tracking performance
and quality selection (cuts)
Cross section (extrapolation to 4π)
0 0
2
0 0
2
sin,sin dpddpd
NdpcConstdpd
dpd
d REGtot
max
min
max
min
sin,sin2
)()(
)(
0 0
)(2
dpddpd
NdpcConst
N
Ndpd
dpd
dp
p
REG
part
tottot
While measuring only a part of total phase space one needs extrapolation:
Technique for Ntot /Npart correction is Pluto or URQMD generator
Cross section (relative normalisation)
)(
}{ }{
)(
)(
)()( sin
ij
pi jijj
part
tottot NcConst
N
N
[email protected] pion cross sections are from KaoS (F.Laue at al. Eur.Phys.J., 397-410, A9, 2000)
9.7534601251763
10][1.069.0 )(
7
Constb
6.10353961618061
10][1.064.0 )(
7
Constb
][100002.1 7)( bConst
][101463.1 7)( bConst
][10)115.0073.1( 7)( bConst
π+
π-
][9.15.176.10166622506
10 )(7
mbConstNotCorr
Ktot
No corrections are taken into account (background, trigger, energy scaling) !!!
Cross section correction (beam energy scaling)
C+C pion cross section
Scaling from KaoS
1.8AGeV 2.0AGeV
(C.Sturm at al. PRL,
86:39-42, 2001)
Factor 1.106 to be used π± and K+ cross sections
Multiplicity trigger (normalisation to minimum bias)
Nov02 – C+C@2AGeV experiment
85% events multiplicity trigg ≥ 4
15% events multiplicity trigg ≥ 2
partAM
α=1 for π (P.Senger NP, A685, 2001)
α=1.64 for K+ taken from
measurements [email protected],
[email protected] R.Barth at al.
(PRL, 78, 1997)
Applied for C+C@2AGeV
bpart
triggpart
b
trigg
A
A
M
M.min..min
Apart depends on
impact parameter b
b
<Apart > = f(<b>)
cut-off approx. w.
„solid sphere model“
Apart1Apart2
Apart
Multiplicity trigger (normalisation to minimum bias)
mean impact parameter
C+C@2AGeV simulation
107 UrQMD events
impact parameter distribution for minimum bias events and for events providing at least 2 (or 4) charged tracks in HADES acceptance (22°< < 86°)
<bmin.b> =3.888 [fm]
<bm2&π>=3.146 [fm]
<bm4&π>=2.569 [fm]
<bm2&K>=2.480 [fm]
<bm4&K>=2.155 [fm]
(15%)(85%)
<btriggπ>=2.66 [fm]
<btriggK>=2.20 [fm]
Enhancement compared with minimum bias
876.100.6
26.111
897.3
00.6
75.1364.1
..min bpart
triggpart
A
A
..min
..min08.2b
Kb
trigg
Ktrigg
M
M
M
MK+/pion ratio is influenced by the multiplicity trigger compared to minimum bias:
“solid sphere model” approximation <Apart > = f(<b>)
<Apart>min.b.=6.00 <Apart>triggπ=11.26 <Apart>triggK=13.75
Electron trigger (LVL2 / LVL1 trigger normalisation)
C+C@2AGeV experiment
Nov02/gen3 DST 166 106 events
LVL1 fraction=53.78%
LVL2 fraction=46.22%
using π+ yeld in
registration area
(300<p<1000) MeV/c
(46° < < 82°)
0.8931
1054538.5146875
104.76584112709
7
7
1
2
LVLevents
counts
LVLevents
counts
N
N
N
N
(w/o registration eff. correction)
0.8999
1054538.59.1129772104.76584
873822.0
7
7
1
2
LVLevents
counts
LVLevents
counts
N
N
N
N
(with registration eff. correction)
If normalising by LVL1 events (1.000) x 53.78% + (0.899) x 46.22% = 95.37%
Considering LVL1+LVL2 events together leads to lower π+ yeld estimate=>correction
Assuming the same behavior for K+ one corrects for 1.0/0.954=1.048 when taking into account LVL2 events (as LVL1 events).Finally normalisation of LVL2 to LVL1 trigger gives scaling factor
1.048
K+ total cross section (at minimum bias conditions)
][9.15.176.10166622506
10 )(7
mbConstNotCorr
Ktot
x 0.765 Background (-23.5% for K+ in TOF)
x 1.106 π± scaling (1.8 2.0)AGeV
x 1/2.08 Multiplicity trigger (LVL1)
? 1.048 Electron trigger (LVL2) admixture
][8.01.7][08.2
106.1765.0)9.15.17(
2@
mbmbAGeVCC
HADESKtot
The corresponding KaoS measurement for C+C@2AGeV (F.Laue PRL, 82,1999)
][5.00.52@
mbAGeVCC
KaoSKtot
HADES measurement is 42% larger
Errors of approximations are not included
BACKUPSLIDES
Motivation
K+ production in collisions of C+C @ 2AGeV is a rare process
• Strong requirements to tracking and detector performance
• Survey HADES potential towards rare hadronic channels
• Supplementary independent measurement to KaoS and FOPI
• Investigation of strangeness production and ratio
Results
K+ experiment correctedp t
[M
eV/c
]
p t [
MeV
/c]
Y0=Y/Ycm-1
Y
=88°
=44°
=18°
=88°
=44°
=18°
p t [
MeV
/c]
p t [
MeV
/c] K+ Pluto
Binning N1 Binning N2
Y
Y0=Y/Ycm-1
mt-m0 spectra (binning N1)
TB=60.7±1.2 [MeV]TB=60.6±1.6 [MeV]TB=62.4±3.1 [MeV]
TB=72.2±1.3 [MeV]TB=69.9±1.2 [MeV] TB=80.7±1.9 [MeV]
NB: Errors are stat. Full bins selection from p-acceptance. Fit function:
B
t
tt T
mC
dydm
Nd
mexp
1
0
2
2
mt-m0 spectra (binning N2)
TB=61.0±1.1 [MeV]TB=59.4±1.5 [MeV]TB=53.4±1.6 [MeV]
TB=82.4±1.5 [MeV]TB=71.0±1.3 [MeV] TB=82.0±2.5 [MeV]
NB: Errors are stat. Full bins selection from p-acceptance. Fit function:
B
t
tt T
mC
dydm
Nd
mexp
1
0
2
2
Preliminary results from mt-m0 spectra
1. Systematic errors are not taken into account
2. Absolute normalization for dN/dY0 is not provided yet
Binning N1 Binning N2
32
0
122
1exp
Kmk
kkkC
dY
dN
)cosh( cmKYYm
Tk
TB [
MeV
]dN
/dY
0
Y0
Y0
TB [
MeV
]dN
/dY
0
Y0
Y0
Comparison with other experiments (EkinCM-spectra)
KaoS data scanned from F.Laue et al. PRL 82(1999)1640
Normalization of HADES data not performed yet
HADES C+C@2AGeV vs. KaoS [email protected]
T
E
CM
cm
cmCM
CM
eECdp
dE
3
3
K
CMKIN
CM mEE
T=(70.4±3.2) MeV
Comparison with other experiments (mt-m0 spectra)
FOPI data and fits: dissertation of K. Wisniewski
HADES extends (mt-m0) - range compared to FOPI
Normalization of HADES data not performed yet
HADES C+C@2AGeV vs. FOPI Ru+Ru(Zr)@1.69AGeV
B
t
tt T
mC
dydm
Nd
mexp
1
0
2
2
Comparison with other experiments (mt-m0 spectra)
FOPI data and fits NPA 625(1997)755
HADES extends (mt-m0) - range compared to FOPI
Normalisation of HADES data not performed yet
HADES C+C@2AGeV vs. FOPI [email protected]
B
t
tt T
mC
dydm
Nd
mexp
1
0
2
2
-0.7<Y0<-0.5 x1 (Ni+Ni)
-0.9<Y0<-0.7 x10 (Ni+Ni)-1.3<Y0<-1.1 x1000 (Ni+Ni)
-1.3<Y0<-1.1 x100 (Ni+Ni)
-0.6<Y0<-0.4 x1 (C+C)
-0.8<Y0<-0.6 x10 (C+C)
C+C@2AGeVC+C@2AGeV
Results (Simulation Nov02/gen3)p t
[M
eV/c
] K+ Pluto
Y
Y0=Y/Ycm-1
p t [
MeV
/c]
Y0=Y/Ycm-1
p t [
MeV
/c]
=88°
=44°
=18°
=88°
=44°
=18°
Binning N1 Binning N2
Simulation C+C@2AGeV (Nov02/gen3)
71·106 events
3026 K+ tracks (incl. bg<15%)
The same cuts and correction as for experimental data
Results from simulation mt-m0 spectra
1. Systematic errors are not taken into account
2. Absolute normalisation for dN/dY0 is not provided yet
Binning N1 Binning N2
32
0
122
1exp
Kmk
kkkC
dY
dN
)cosh( cmKYYm
Tk
TB [
MeV
]dN
/dY
0
Y0
Y0
Y0
Y0
TB [
MeV
]dN
/dY
0
Summary and outlook
1. K+ identification with HADES
• possible for 250MeV<p<500MeV (TOFINO), 200MeV<p<700MeV (TOF)
2. 2562 K+ from 166*106 events
3. Y and mt spectra deduced
4. Slope parameters are in agreement with previous experiments
• KaoS measured K+ production from C+C system at beam kinetic energies:
1.8 AGeV for (28°,52°) and (56°,64°), N(K+)=17000
2.0 AGeV for (28°,44°), N(K+)=11000
• HADES extends the acceptance of C+C towards target rapidity at
2.0 AGeV for (30°,83°), N(K+)= 2562
(HADES specific measurement -0.9<Y0<-0.7)
To do list:
Absolute normalization to the beam particles
Investigation of systematical errors influence
