hadroproduction with the v inclusive selex experiment at ... filewhy did we perform our measurements...
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4th MPI Young Scientist Workshop: Hot Topics in Particle and Astroparticle PhysicsRingberg Castle, Tegernsee, July 18-22, 2005
Inclusive V 0 Hadroproduction with the
SELEX Experiment at FERMILAB
Miguel Angel Olivo Gomez, MPI fur Physik, Munchen
O U T L I N E
• Introduction
• The SELEX (E781) Experiment
• The Measurement Technique
• The Preliminary Results
• Summary
I N T R O D U C T I O N
Miguel Angel Olivo Gomez, MPI fur Physik 4th MPI Young Scientist Workshop, Jul 18-22, 2005 Page 2
WHY DID WE PERFORM OUR MEASUREMENTS ? ? ?
• Basically, No Theory based on first principles for hadroproduction.
• No high statistics hadroproduction measurements for strange particles.
• These measurements had never been done in a single experiment.
• These measurements could either support or not the current models.
Miguel Angel Olivo Gomez, MPI fur Physik 4th MPI Young Scientist Workshop, Jul 18-22, 2005 Page 3
PARTICLE PRODUCTION FOR PEDESTRIANS
• The particle production is classified by:
⋆ Inclusive Production: Only one of the produced particles is identifiedin each collision. For example, p p → Λ X.
⋆ Exclusive Production: When all of the produced particles are identifiedin each collision. For example, p p → p Λ Σ+ n.
• The particle production is characterized by:
⋆ The transverse momentum: pT
⋆ The longitudinal momentum: pL
• For the longitudinal momentum we use the Feynman scaling variable:
xF =pcm
L
pcmmax
Miguel Angel Olivo Gomez, MPI fur Physik 4th MPI Young Scientist Workshop, Jul 18-22, 2005 Page 4
INCLUSIVE Λ, Λ AND Ks PRODUCTION MEASUREMENTS
• HERA-B used a proton beam at 920 GeV/c on C, Al, Ti and W targetsand measured: (Eur.Phys.J. C 29 (2003), 181)
dσ/dxF over −0.12 ≤ xF ≤ 0.
dσ/dp2T over 0 ≤ p2
T ≤ 1.2 (GeV/c)2.
• WA89 used Σ− and π− beams at 345 GeV/c on Cu and C targets andmeasured: (Eur.Phys.J. C 26 (2003), 357)
dσ/dxF over 0 ≤ xF ≤ 0.8 for Λ and Λ.
dσ/dxF over 0 ≤ xF ≤ 0.7 for Ks.
dσ/dp2T over 0 ≤ p2
T ≤ 4 (GeV/c)2 with Σ− beam.
dσ/dp2T over 0 ≤ p2
T ≤ 2.2 (GeV/c)2 with π− beam.
Miguel Angel Olivo Gomez, MPI fur Physik 4th MPI Young Scientist Workshop, Jul 18-22, 2005 Page 5
INCLUSIVE Λ AND Λ PRODUCTION MEASUREMENTS
• E769 used π±, K± and p beams at 250 GeV/c on Be, Al and Wtargets and measured Λ-Λ asymmetry as a function of xF and p2
T over:(Phys.Lett. B 559 (2003), 179)
−0.12 ≤ xF ≤ 0.12 and 0 ≤ p2T ≤ 3 (GeV/c)2 for + beams.
−0.16 ≤ xF ≤ 0.4 and 0 ≤ p2T ≤ 10 (GeV/c)2 for − beams.
• E791 used a π− beam at 500 GeV/c on 4 diamond and 1 platinumtargets and measured Λ-Λ asymmetry as a function of: (Phys.Lett. B496 (2000), 9)
xF over −0.12 ≤ xF ≤ 0.12.
p2T over 0 ≤ p2
T ≤ 4 (GeV/c)2.
Miguel Angel Olivo Gomez, MPI fur Physik 4th MPI Young Scientist Workshop, Jul 18-22, 2005 Page 6
SELEX (E781) MEASUREMENTS
• We used 4 beams: Σ− (at 611 GeV/c), π− (at 604 GeV/c), proton(at 525 GeV/c) and π+ (at 520 GeV/c) on 2 Cu and 3 diamond targetsand measured:
dσ/dxF over 0.1 ≤ xF ≤ 1.
dσ/dpT over 0 ≤ pT ≤ 3.25 (GeV/c).
dσ/dp2T over 0 ≤ p2
T ≤ 11 (GeV/c)2.
• And we measured Λ-Λ asymmetry as a function of xF and pT over:
0.1 ≤ xF ≤ 1.
0 ≤ pT ≤ 3.25 (GeV/c).
Miguel Angel Olivo Gomez, MPI fur Physik 4th MPI Young Scientist Workshop, Jul 18-22, 2005 Page 7
A HADROPRODUCTION MODEL IN EHEP
• A model based on quark counting rules and phase arguments:
Blankenbecler and Brodsky (Phys.Rev. D 10 (1974), 2973)
dσ
dxFdp2T
∝(
1 − xF)n
exp(
− bp2T
)
Miguel Angel Olivo Gomez, MPI fur Physik 4th MPI Young Scientist Workshop, Jul 18-22, 2005 Page 8
THE SELEX (E781) EXPERIMENT
Miguel Angel Olivo Gomez, MPI fur Physik 4th MPI Young Scientist Workshop, Jul 18-22, 2005 Page 9
THE SELEX SPECTROMETER
• A Fixed Target Experiment with forward production (xF > 0.1)
• Data taken 1996/97. RICH PID above ≈ 22 GeV/c
• 20 highly-efficient SSD’s with 6.5 µm resolution
Elevator
E
S N
AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA
AAAAAAAA
AAAA
Gas House
H yperon M agnet Photon 2
AA
TargetVertexregion
M1
Photon 1
DC PWC
BTRD
M2
PWC
AAAA
HO
D1 A
AeTRD R I C H
neutron calorimeter
Photon3M3
PC3 PC4
Vee A Vee B Vee C
.
PWC
0 m 20 m 40 m 50 m
HO
D2
10 m 30 m 6Miguel Angel Olivo Gomez, MPI fur Physik 4th MPI Young Scientist Workshop, Jul 18-22, 2005 Page 10
THE SELEX SPECTROMETER
AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA
AAAAAAAAA
AA
AAAA
AA
20 µm pitch VX Si detectors
25 µm pitch VX Si detectors
u y x
20 µm pitch Beam Si detectors
TargetsCu Diamond
InteractionScintillators
0 20-20 40 Z [cm]
-2
0
+2
X [cm]
Vertex RegionS4 Beam Scintillator
Interaction Veto (V5) Scintillator
30 50-10 10
x y 1 u v x y 2 u v
x y 3 u v x y 4 u v x v 5 u x
Miguel Angel Olivo Gomez, MPI fur Physik 4th MPI Young Scientist Workshop, Jul 18-22, 2005 Page 11
THE BEAM TRANSITION RADIATION DETECTOR (BTRD)
• 10 modules, each of them with a radiator and 3 PWC (Planes).
• The radiation emission probability is proportional to γ
• A π with the same energy than a Σ or proton, activates more planes.
• k = activated planes number.
0
2
4
6
8
10
12
14
16
18
0 5 10 15 20
BTRD signal
sum of signals (fit)
baryon signal (fit)
meson signal (fit)
region for baryonselection
region for mesonselection
TRD plane count k
sign
al p
roba
bilit
y [%
]Fig. 2. A typi al BTRD signal spe trum obtained for 600GeV/ negatively hargedse ondaries.Ea h BTRD PC gives a digital output when it dete ts an energy depositionabove a �xed threshold. The sum of all PCs dete ting a signal above thresh-old is the TRD plane ount k. A typi al probability spe trum of TRD plane ounts, a BTRD signal spe trum, is shown in �gure 2. It shows the baryonand meson responses at low and high TRD plane ounts, respe tively.The signal omponents are separated by �tting the fun tion:p�t(k) = 2Xi=1 �i nk!pki (1� pi)n�k| {z }baryon signal + 4Xi=3 �i nk!pki (1� pi)n�k| {z }meson signal (1)to the normalized BTRD signal spe trum. Here, pi and �i are �t-parameterswith the onstraints 1 = �1 + �2 + �3 + �4 and p1, p2 < p3, p4 and n is themaximum possible TRD plane ount. The �t-parameters pi have the meaningof a PC response probability, when a meson (light parti le) or baryon (heavyparti le) passes. Thus, we obtain from (1) the meson fra tion (�3 + �4) andthe baryon fra tion (�1 + �2) of the beam.The target is followed by the vertex spe trometer, whi h onsists of 22 sili onmi rostrip dete tors grouped into 6 stations (VSSD1, ... , VSSD5 and HSD3).All VSSDs have a resolution of 5:8�m, and ex ept for one plane, whi h hasa redu ed eÆ ien y of 68%, all others have an average eÆ ien y of 98.8%. Atthe end of the vertex spe trometer, station HSD3 is mounted to the RF age.Although the total ross-se tion measurements presented in this arti le are6
Miguel Angel Olivo Gomez, MPI fur Physik 4th MPI Young Scientist Workshop, Jul 18-22, 2005 Page 12
THE BEAM COMPOSITION
• The negative beam consists of: (Nucl.Phys. B 579 (2000), 277):
• The baryon fraction = 47.5 ± 1.6 %
• 97.52 ± 4.70 % of Σ−
• 2.48 ± 0.15 % of Ξ−
• The meson fraction = 52.5 ± 1.6 %
• 96.95 ± 4.71 % of π−
• 3.05 ± 1.91 % of K−
• The positive beam consists of: (Nucl.Phys. B 579 (2000), 277):
• The baryon fraction = 91.9 ± 1.4 %
• 97.06 ± 2.28 % of protons
• 2.94 ± 0.76 % of Σ+
• The meson fraction = 8.1 ± 1.4 %
• 70 % of π+
• 30 % of K+
Miguel Angel Olivo Gomez, MPI fur Physik 4th MPI Young Scientist Workshop, Jul 18-22, 2005 Page 13
NEGATIVE BEAM MOMENTUM DISTRIBUTIONS
0
2000
4000
6000
8000
10000
x 10 2
450 500 550 600 650 700 750
MeanRMSALLCHAN
611.1 35.94
0.1449E+08
p (GeV/c)
Ev
en
ts/5
Ge
V/c
Haz de Σ-
0
200
400
600
800
1000
1200
x 10 2
450 500 550 600 650 700 750
MeanRMSALLCHAN
603.6 35.92
0.1936E+07
p (GeV/c)
Ev
en
ts/5
Ge
V/c
Haz de π-
Miguel Angel Olivo Gomez, MPI fur Physik 4th MPI Young Scientist Workshop, Jul 18-22, 2005 Page 14
POSITIVE BEAM MOMENTUM DISTRIBUTIONS
0
200
400
600
800
1000
1200
1400
1600
1800
x 10 2
400 450 500 550 600 650
MeanRMSALLCHAN
524.8 31.18
0.2223E+07
p (GeV/c)
Even
ts/5
GeV
/c
Haz de p
0
2000
4000
6000
8000
10000
12000
14000
16000
18000
400 450 500 550 600 650
MeanRMSALLCHAN
520.4 30.54
0.2204E+06
p (GeV/c)
Even
ts/5
GeV
/cHaz de π+
Miguel Angel Olivo Gomez, MPI fur Physik 4th MPI Young Scientist Workshop, Jul 18-22, 2005 Page 15
MEASUREMENT TECHNIQUE
Miguel Angel Olivo Gomez, MPI fur Physik 4th MPI Young Scientist Workshop, Jul 18-22, 2005 Page 16
PARTICLE CANDIDATE IDENTIFICATIONSOAP~���Target region~
************************
� L -HHHHj�����p��������� ^p �s
�pb-Beam
5. RECON:� Re onstruye las part�� ulas.� Asigna masa a las traye torias re onstru��das. Las ombina iones aleatorias de lastraye torias produ en ba kground en la distribu i�on de la masa. La masa de lapart�� ula re onstru��da est�a dentro de un intervalo.� Se usa una tabla de re onstru iones para que SOAP onoz a que part�� ulare onstruir�a, que rutina usar�a, que de aimiento de las part�� ulas bus ar�a, querango de la masa invariante usar�a, y que ortes en L=� usar�a.Miguel Angel Olivo Gomez, MPI fur Physik 4th MPI Young Scientist Workshop, Jul 18-22, 2005 Page 17
CANDIDATE INVARIANT MASS DISTRIBUTION
0
1000
2000
3000
4000
5000
x 10 2
1.09 1.095 1.1 1.105 1.11 1.115 1.12 1.125 1.13 1.135 1.14
MeanRMSALLCHAN
1.116 0.9097E-02 0.2967E+07
0.2876E+05/ 95P1 0.1700E+07 1384.P2 1.116 0.2170E-05P3 0.1395E-02 0.1180E-05P4 0.1247E+05 12.27P5 0.7645E+05 751.2
Mass (GeV/c2)
Even
ts/0
.5 M
eV
/c2
Λ
→→→
0
1000
2000
3000
4000
5000
6000
7000
8000
9000
x 10 2
0.47 0.48 0.49 0.5 0.51 0.52 0.53
MeanRMSALLCHAN
0.4989 0.1420E-01 0.1639E+08
0.1788E+05/ 95P1 0.6504E+07 3915.P2 0.4976 0.1423E-05P3 0.3410E-02 0.2201E-05P4 0.1099E+06 41.81P5 -0.1792E+06 2068.
Mass (GeV/c2)
Even
ts/0
.5 M
eV
/c2
Ks
→→→
Miguel Angel Olivo Gomez, MPI fur Physik 4th MPI Young Scientist Workshop, Jul 18-22, 2005 Page 18
CANDIDATE XF DISTRIBUTION FOR EACH BEAM
10 2
10 3
10 4
10 5
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
MeanRMSALLCHAN
0.1905 0.1486
0.2281E+07
xF
Eve
nts/
bin
Σ- N → Λ X
Miguel Angel Olivo Gomez, MPI fur Physik 4th MPI Young Scientist Workshop, Jul 18-22, 2005 Page 19
SIDEBAND SUSTRACTION TECHNIQUE
(µ − 3σ, µ + 3σ) = A = Signal + Bckgr C = B − A = Bckgr
(µ − 6σ, µ + 6σ) = B = Signal + 2∗Bakgr Signal = A − C
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
1.09 1.095 1.1 1.105 1.11 1.115 1.12 1.125 1.13 1.135 1.14
Mass (GeV/c2)
x FΣ- N → Λ X
||||||||
||||||||
| |↔3σ
Miguel Angel Olivo Gomez, MPI fur Physik 4th MPI Young Scientist Workshop, Jul 18-22, 2005 Page 20
Λ DISTRIBUTION AS A FUNCTION OF XF
10
10 2
10 3
10 4
10 5
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
MeanRMSALLCHAN
0.2115 0.1499
0.1321E+07
xF
Eve
nts/
bin
Σ- N → Λ X
• With Background
• Without Background
Miguel Angel Olivo Gomez, MPI fur Physik 4th MPI Young Scientist Workshop, Jul 18-22, 2005 Page 21
THE ACCEPTANCE
What does it mean?
Experiment (hardware and software) efficiency for reconstructing a particleas a function of xF .
How do we obtain the acceptance?
• 106 Λ are generated with EDG based on model A (n = 0 and b = 2).
• Embedding: These Λ are embedded in a sample of 106 real events fromSELEX, and only some of them are reconstructed by SOAP. Forexample, 103.
• Acceptance = 103(xF )/106(xF )
Miguel Angel Olivo Gomez, MPI fur Physik 4th MPI Young Scientist Workshop, Jul 18-22, 2005 Page 22
THE ACCEPTANCE AS A FUNCTION OF XF AND PT
10-3
10-2
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
xF
Ac
ce
pta
nc
e/b
in
Acceptance for
Σ- N → Λ X
0
0.001
0.002
0.003
0.004
0.005
0.006
0.007
0.008
0 0.2 0.4 0.6 0.8 1
8.910 / 10P1 0.3749E-02 0.1030E-03
PT (GeV/c)
Accep
tan
ce/0
.1 G
eV
/cAcceptance for Λ
Miguel Angel Olivo Gomez, MPI fur Physik 4th MPI Young Scientist Workshop, Jul 18-22, 2005 Page 23
THE ACCEPTANCE EVENT CORRECTION
• But a smooth acceptance distribution is needed. This is NOT our case.
• Survival probability: Probability that a particle travels a distance x.
P (x) = exp
(
−x
γcτ
)
• Acceptance = Prob. that a particle decays where it can be identified.Let d be the distance throughout the length of the detector where ithappens, therefore,
Acceptance =
∫ d0 P (x)dx
∫ ∞0 P (x)dx
Acceptance(xF ) ≈ 1 − exp
−d
cτ
√
(
pbeamc xFMc2
)2+ 1
Miguel Angel Olivo Gomez, MPI fur Physik 4th MPI Young Scientist Workshop, Jul 18-22, 2005 Page 24
THE ACCEPTANCE EVENT CORRECTION
• Then, the following function is fitted to the acceptance (non-smooth)xF distribution of the produced Λ by the Σ− beam.
Acceptance(xF ) = p1 − exp
−p2
7.89
√
(
611.1 xF1.115683
)2+ 1
• We use this function with the fit-parameters to perform the acceptanceevent correction.
Miguel Angel Olivo Gomez, MPI fur Physik 4th MPI Young Scientist Workshop, Jul 18-22, 2005 Page 25
THE ACCEPTANCE EVENT CORRECTION
10-3
10-2
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
38.81 / 34P1 0.9988 0.1174E-03P2 7.416 0.3082
xF
Accep
tan
ce/b
in
Acceptance for
Σ- N → Λ X 10 4
10 5
10 6
10 7
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
MeanRMSALLCHAN
0.3466 0.1792
0.2154E+09
xF
Co
rre
cte
d e
ve
nts
/bin
Σ- N → Λ X
Miguel Angel Olivo Gomez, MPI fur Physik 4th MPI Young Scientist Workshop, Jul 18-22, 2005 Page 26
P R E L I M I N A R Y R E S U L T S
Miguel Angel Olivo Gomez, MPI fur Physik 4th MPI Young Scientist Workshop, Jul 18-22, 2005 Page 27
PRELIMINARY RESULTS ! ! !
• Only Statistical Errors •
10 4
10 5
10 6
10 7
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
MeanRMSALLCHAN
0.3466 0.1792
0.2154E+09
xF
Co
rre
cte
d e
ve
nts
/bin
Σ- N → Λ X
10 3
10 4
10 5
10 6
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
MeanRMSALLCHAN
0.1619 0.1307
0.7320E+07
xF
Co
rre
cte
d e
ve
nts
/bin
Σ- N → Λ−
X
Miguel Angel Olivo Gomez, MPI fur Physik 4th MPI Young Scientist Workshop, Jul 18-22, 2005 Page 28
PRELIMINARY RESULTS ! ! !
• Only Statistical Errors •
10 3
10 4
10 5
10 6
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
MeanRMSALLCHAN
0.2883 0.1755
0.1726E+08
xF
Co
rre
cte
d e
ve
nts
/bin
p N → Λ X
10 3
10 4
10 5
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
MeanRMSALLCHAN
0.1594 0.1154
0.2174E+07
xF
Co
rre
cte
d e
ve
nts
/bin
p N → Λ−
X
Miguel Angel Olivo Gomez, MPI fur Physik 4th MPI Young Scientist Workshop, Jul 18-22, 2005 Page 29
PRELIMINARY RESULTS ! ! !
Asimmetry =Npar−NantiparNpar+Nantipar
0
0.2
0.4
0.6
0.8
1
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1xF
As
imm
etr
y
• Σ- beam production
• π- beam production
• proton beam production
• π+ beam production
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
0 0.5 1 1.5 2 2.5 3pT (GeV/c)
As
imm
etr
y• Σ- beam production• π- beam production• proton beam production• π+ beam production
Miguel Angel Olivo Gomez, MPI fur Physik 4th MPI Young Scientist Workshop, Jul 18-22, 2005 Page 30
IN COMPARISON TO . . .
0
0.2
0.4
0.6
0.8
1
-0.2 0 0.2 0.4 0.6 0.8 1xF
As
imm
etr
y
π- beam production
• SELEX Collaboration
• E769 Collaboration
• E791 Collaboration
0
0.2
0.4
0.6
0.8
1
-0.2 0 0.2 0.4 0.6 0.8 1xF
Asim
metr
y
π+ beam production
• SELEX Collaboration
• E769 Collaboration
Miguel Angel Olivo Gomez, MPI fur Physik 4th MPI Young Scientist Workshop, Jul 18-22, 2005 Page 31
IN COMPARISON TO . . .
0
0.2
0.4
0.6
0.8
1
-0.2 0 0.2 0.4 0.6 0.8 1xF
Asim
metr
y
Proton beam production
• SELEX Collaboration
• E769 Collaboration
Miguel Angel Olivo Gomez, MPI fur Physik 4th MPI Young Scientist Workshop, Jul 18-22, 2005 Page 32
MODEL: DOES NOT WORK !!!
P1(
1 − xF)P2 exp
(
P1 + P2 · p2T
)
10 4
10 5
10 6
10 7
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
MeanRMSALLCHAN
0.3466 0.1792
0.2154E+09 107.3 / 18
P1 0.3273E+08 0.2897E+06P2 2.227 0.1157E-01
xF
Co
rre
cte
d e
ve
nts
/bin
Σ- N → Λ X
10
10 2
10 3
10 4
10 5
10 6
0 2 4 6 8 10
MeanRMSALLCHAN
0.6188 0.4496
0.1321E+07 3944. / 2
P1 15.17 0.1290E-02P2 -2.357 0.2207E-02
10
10 2
10 3
10 4
10 5
10 6
0 2 4 6 8 10
23.66 / 6P1 11.85 0.1772P2 -1.077 0.3434E-01
p2T (GeV/c)2
Ev
en
ts /
(G
eV
/c)2
Σ- N → Λ X
Miguel Angel Olivo Gomez, MPI fur Physik 4th MPI Young Scientist Workshop, Jul 18-22, 2005 Page 33
S U M M A R Y
Miguel Angel Olivo Gomez, MPI fur Physik 4th MPI Young Scientist Workshop, Jul 18-22, 2005 Page 34
SUMMARY
• Inclusive differential cross sections dσdxF
and dσdpT
for the production of
Λ, Λ and Ks in π−, π+, Σ− and proton-nucleon collisions weremeasured over the ranges 0.1 ≤ xF ≤ 1, 0 ≤ pT ≤ 3.25 GeV/cand 0 ≤ p2
T ≤ 11 (GeV/c)2.
• Besides, the Λ-Λ production asymmetries as a function of xF and pTwere measured for each beam over the ranges 0.1 ≤ xF ≤ 1 and0 ≤ pT ≤ 3.25 GeV/c and 0 ≤ p2
T ≤ 11 (GeV/c)2.
• The Blankenbecler and Brodsky model does NOT work for the inclusiveproduction of Λ, Λ and Ks as a function of xF and pT .
Miguel Angel Olivo Gomez, MPI fur Physik 4th MPI Young Scientist Workshop, Jul 18-22, 2005 Page 35