hadroproduction with the v inclusive selex experiment at ... filewhy did we perform our measurements...

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

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.


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


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.


T ≤ 4 (GeV/c)2 with Σ− beam.


T ≤ 2.2 (GeV/c)2 with π− beam.


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.


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).


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).


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

)


THE SELEX (E781) EXPERIMENT


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

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


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


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+


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-


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+


MEASUREMENT TECHNIQUE


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

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

→→→


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


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


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


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 )


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


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



• 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.



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


P R E L I M I N A R Y R E S U L T S


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



• 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



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


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


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




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




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


S U M M A R Y


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 .


hadroproduction with the v inclusive selex experiment at ... filewhy did we perform our measurements...

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