Документ взят из кэша поисковой машины. Адрес оригинального документа : http://nuclphys.sinp.msu.ru/conf/lpp14/250809/Vysotsky.pdf Дата изменения: Thu Mar 25 10:51:49 2010 Дата индексирования: Tue Oct 2 00:41:35 2012 Кодировка:

Bounds on new light particles from very small momentum transfer np elastic scattering data
Yuri Kamyshkov, Jeffrey Tithof, University of Tennessee, TN 37996-1200, USA Mikhail Vysotsky ITEP, Moscow, 117218, Russia Phys.Rev.D78:114029,2008 14'th Lomonosov Conference, MSU, August 25 , 2009
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NA-6 experiment, CERN SPS, Results published in 1984
En = 100 - 400 GeV, gaseous hydrogen target

very small |t|

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102

d /dt[(mb/(GeV/c)2]

Coulomb Interference

pp Experiments I

Pure Hadronic Diffraction

NA6 np Scattering Experiment I Pure Hadronic Diffraction Schwinger Scattering
Contribution

10 10-6

10-5

10-4

10-3

10-2

10-1

1

|t| [(GeV/c)2]

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d = Aexp[bt] - 2 dt

kn mn

2

, t

(1)

where A = (79.78 ± 0.26)mb/GeV2 and b = (11.63 ± 0.08) GeV-2 were determined from the fit to the data; kn = -1.91 is the neutron magnetic moment in nuclear magnetons; factor "2" in the Schwinger term accounts for noncoherent sum of the scattering of neutron magnetic moment on proton and electron electric charges

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NP
di |Ai |2 (g , µ)|new = , 2) dt 16 s(s - 4m
(2)

where s = (pn + pp )2 is the invariant energy square and m is the nucleon mass.

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4 gS |AS |2 = (4m2 - t)2 , (t - µ2 )2 4 gP t2 |AP |2 = (t - µ2 ) 2

(3)

,

(4)

4 4gV 12 2 2 4 2 [s - 4m s + 4m + st + t ] , |AV | = 2 )2 (t - µ 2

(5)

4 4gA 1 2 4m4 t2 8m4 t [s2 + 4m2 s + 4m4 + st + t + + 2], |AA |2 = 2 )2 4 (t - µ 2 µ µ

(6)

ii 2 where coupling constants gi gp gn . A s ; AP t
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Lack of fundamental theory for SI np scattering amplitude does not prevent us from excluding light new par ticles as far as there are NO SI par ticles lighter than pion, m = 140M eV

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d /dt[(mb/(GeV/c)2]

102

10-6

10-5

10-4

10-3

10-2

10-1

1

|t| [(GeV/c)2]

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104 103 102 Coupling, g2 10 1 10-1 10 10
-2

Pseudoscalar

X

]
Scalar

]
Vector Axial Vector
10 10-2 Mass, µ [GeV]
-3

-3

10-4 -4 10

90% C.L. bounds

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2 2 Our bounds on the parameters gV and gA are rather strong; 2 say for µ = 10 MeV, gV ,A < 5 · 10-3 at 90% C.L., which corresponds to

g

V ,A N

< 0.071 ,

(7)

four times smaller than the QED coupling constant 4 0.3. For scalar exchange, taking µ = 10 MeV, we 2 get a much weaker bound, gS < 1.4.

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It is quite natural to suppose that couplings of a new light par ticle with nucleons originate from its couplings with quarks. In this case AV and AA are modified. For vector exchange the induced magnetic moment interaction term should be added to the scattering amplitude. Since its numerator contains momentum transfer divided by mN which in considered kinematics gives a factor much smaller than 1, we can safely neglect it. The case of axial exchange is more delicate:

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~ A A = g n 5 n g Ї
2 A





g

µ

2 k k (m4 - 2µ2 m2 + k 2 µ2 ) gA g - 2 =2 2 2 - m2 ) 2 k -µ µ (k n 5 np 5 p Ї Ї (8)

kµ k -2 k -m

k k -2 k -m

(g
2

µ 2

k-

-

k k µ2 µ2

µ

)



2

p 5 p = Ї

for massless pion the axial current is conserved, while term k k /k 2 - m2 /k 2 in the amplitude leads to regular diff. N crossection at t - 0.
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literature 1
m1 m2 [1 + G exp(-r/)] , V (r ) = -G N r G = g
2 V ,S n

(9)

4 GN mp m

= 1.35 · 1037 g

2 V ,S

, lg = lg g

2 V ,S

+ 37.13
(10)

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literature 2
low energy (KeV) n -
208

Pb scattering
(11)

d 0 = [1 + E cos ] , d 4 | | = g
2 V ,S

16m

2 gn A . 4 0 /4 4 µ

2 n

(12)

< 4 · 10-6 for 10MeV boson

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40 35 30 25
G)

Scalar Vector

This Work Bordag et al. Nesvizhevsky & Protasov

Pokotilovski

log(

20 15 10 5 0

Nesvizhevsky et al.

Mohideen et al.

Mostepanenko et al.

Decca et al. Lamoreaux Stanford Seattle

-14

-12

-10

-8

-6

-4

log( /1m)
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literature 3
Couplings of new light bosons with quarks are bounded by pion and kaon decays:
B r( 0 ) < 2.7 · 10- B r( 0 ) < 6 · 10-
7

4 10

B r(K + + + ) < 2 · 10-

Bounds on axial and scalar couplings are considerably stronger while the bound on vector coupling is comparable with those from np scattering

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literature 4
NP contribution to nuclear matter EOS; neutron stars Krivoruchenko, Simkovic, Faessler, 2009 the fact that the bounds are similar to ours is not surprising: V g 2 /µ2 , so precision data on np - scattering compete with information from observations of neutron stars.

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Conclusions
Electric neutrality of neutron allows to look for large distance NP effects in small angle neutron scattering data High energy scattering gives access to small values of vector and axial coupling constants Our bound on gV is comparable with bounds from neutral pion and kaon decays

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