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Nuclear - radiation on the flight at LHC energies
V.L.Korotkikh, L.I. Sarycheva
Moscow State University, Scobeltsyn Institute of Nuclear Physics

UPCs in Heavy Ion Collisions Wokshop, 8-9 March, 2002

·Ultra-peripheral nuclear collisions and the signatures ·Excitation of discrete nuclear levels in AA collisions · - radiation as a possible trigger for UPCs ·Nuclear beam monitoring at LHC ·Conclusions


Ultra-peripheral Heavy Ion Collisions (b > RA1 + RA2 )

fusion

Advantages:
· Large photon-photon energy in center mass system s () < 300 GeV at LHC · Large electromagnetic crosssection of particle production EM ~ Z4

photodisintegration

grazing strong interaction


Signatures of UPCs
G.Baur, K.Hencken, D.Trautmann, S.Sadovsky, Y.Kharlov. Phys.Rep.(in press), hep-ph/0112211

The pure ** processes with EM excitation of ions: ·a small multiplicity of charge particles ·a small total transverse momentum of particles ·a signal of neutron from GDR decay in ZDC The pure ** processes : ·a small multiplicity of charge particles ·a small total transverse momentum of particles ·the absence of any signal in ZDCs Additional signatures : ·a different total pT-distributions ·a different C-parity of system produced ·the net sum of charge particles is equal to zero

All these signatures don't exclude the disintegration of nucleus. Large part of nuclear fragments fly into beam tube of LHC.


p0 - rapidaty distribution for PbPb collisions at LHC

106 mbarn(incl), 36 mbarn(excl)

75 MeV 75 MeV

K.A.Chikin, V,L. Korotkikh, A.P.Krykov,L.I.Sarycheva, I.A.Pshenichnov, J.P.Bondorf, I.M.Mishustin. Eur.Phys.J.A8(2000)537




` Decay of Nuclear Levels and - radiation

GQR

Region of nucleon and cluster decays
E0 3 MeV '
5. 33 , 6.59 MeV 4. 3- , 6.29 MeV 2

P, E

0

Ca*(P,E0) Ca
A* 3500 at LHC

Region of - decay without nuclear disintegration

2. 21 , 3.90 MeV 1. 31 , 3.74 MeV

3. 51 , 4.49 MeV

E' 2AE0 21 GeV '

1

Discrete levels of Ca
Endt et al. NPA633 (1998)

1012-1014 eV cosmic -rays Fe* Fe +
Balashov,Korotkikh,Moscalenko. 21 ICRC, Adelaida, v2,1990,p.416


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Kinematics of the Secondary -radiation
E = AE0 (1+cos q )

Ca*(P,E0) Ca
Dependence between the energy E and the polar q of photon, emitted by the relativistic nucleus Ca*( P , E0 ) at LHC energy. Axis Z is along nuclear direction.

E



Ca*

q Ca
3. 51 , 4.49 MeV

The lines correspond to the discrete excited levels:
1. 31 , 3.74 MeV 2. 21 , 3.90 MeV 4. 3- , 6.29 MeV 5. 33 , 6.59 MeV 2

Roman pots of 20 mrad < Energy of '­radiation will 21 GeV <

TOTEM at 150 m q' < 150 mrad be corresponded to the region E' < 26 GeV




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Possible Signature of UPCs without Nuclear disintegration
A+A


How to select the ultra-peripheral collisions without grazing strong interactions?
·
·

A* + A + M, A*



A+`

Our suggestion is
to register the nuclear secondary ' radiation of HI after interaction and to use veto particle detectors in nuclear fragmentation region

·

·

A small total transverse momentum pt of produced system the absence of any signal of charge and neutral particles in nuclear fragmentation region (in the ZDC and the Roman pots) A signal of `photon in the Roman Pot station 1 with E` ~20 GeV and q` ~ 100 mikrorad To use time coincidence of Roman Pot signals in both arm detectors

particles



(AA A*A) @ 0.1 mbarn for Ca Ca collisions


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Nuclear `-radiation and e+e- production
e+e- production
E0 3 MeV '
A* 3500 at LHC
1

E' 2AE0 21 GeV '

Properties of '-radiation: · · · · Neutral radiation High energy E` at LHC Narrow collimation of '-radiation But the direct excitation of nucleus has a small cross-section ~ 0.1 mbarn

Huge cross-section: Pb Pb Pb Pb + e+e- (220 Kbarn) Ca Ca Ca Ca + e+e- (1.4 Kbarn)
Baron, Baur. Phys. Rev. D46 (1992) R3695 Baur et al. CMS Note 1998/009,hep-ph/9904361 Alscher et al. Phys. Rev. A55 (1997) 396


Two-step mechanism of nuclear excitation
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V.Korotkikh, K.Chikin Preprint INPH MSU 2001-1/641 nucl-th/0103018, EPJA (in press)

1. QED, Weizsacker-Williams (1934) 2. Ca + Ca Ca + Ca + e+eBaron,Baur(1992),Baur,Hencken(1999) 3. e + Ca e' + Ca*(P, E0')
Well definite form factors of discrete levels:

Gulkarov. Fis. Elem. Chast. at Nucl 1 9 (1 9 9 8 ) 3 4 5 4. Ca*(P, E0') Ca +

Ca + Ca Ca + Ca*(3-) + e+ e ' + Ca L = (24)1030 cm-2 sec-1 10 6 photon/sec

int

= 5 barn




Comparison of '-rays Distributions for Various Processes
-

`

5. barn, 1. Ca+Ca Ca+Ca*(3-)+e+e 0.1 mbarn, 2. Ca+Ca Ca + Ca*(3-) 0.2 mbarn, 3. Ca+Ca X1 + X2 + p0

Ca*(3-) +Ca

p0 2

Energy distribution of secondary photons. Numbers 1, 2, 3 correspond to three processes.

Angular distribution of secondary photons for three processes.




`



Tot (CaCa ) @ 3.2 barn STR




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Possibility of Nuclear Beam Monitoring at LHC by -radiation of Nuclei Recoil

Large problem at LHC is a monitoring · of nuclear beam · · luminosity

What is necessary to solve the problem: Choice of a process for AA interaction Large cross-section of the process Effective detectors for registration of the process · High accuracy of luminosity measurement


` Geometry of the Roman pots in TOTEM LHC




` Roman pot station 1 and `radiation angles






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Photon Registration Rate and Accuracy of Luminosity Monitoring
Ca + Ca Ca + Ca*(3-) + e+e ' + Ca int = 5 barn L = (24)1030 cm-2 sec-1 q' = 20150 mrad j' 0360
dN Lint Geom (3.5 7)106 photon / sec dt N 1 L N N dN /dt t 1 t dN /dt 2 L


TOTEM LHC

E' = 25 GeV 4 radiation length eGeom 0.35

dL = 1%, dN/dt = 106 photon/sec during Dt = 10 msec




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Next Steps of Study and Questions
· Cooperation with TOTEM group (simulation of nuclear beam transportation and the geometry of



-radiation )

· Is it possible to use the Roman pots after main TOTEM program for



-rays detectors and for veto particle detectors?

· Is it possible to use the upgrade ZDC for · What we know on the nuclear fix target?



-rays measurement?

· New calculations for Pb-Pb and Ar-Ar collisions at LHC



-radiation from AA experiments with


Nuclear - radiation on the flight at LHC energies and ZDC
A + A A*(JP) + A, A*(JP) A + , E =10-20 GeV


Nuclear - radiation on the flight at LHC energies and ZDC
A + A A*(JP) + A, A*(JP) A + , E =10-20 GeV ZDC

(3-, 6.59 MeV) (3-, 6.29 MeV) (5-, 4.49 MeV) (2+, 3.90 MeV)
(3-, 3.74 MeV)

Ca*(P,E0) Ca




`

Possible Signature of Peripheral AA collisions at LHC
How to select the peripheral collisions? Use the correlation of b and multiplicity n Use the correlation of b and transverse total energy Et Register the intact nuclei after interaction A+AA+A+M Use the small pt of produced particles

Our suggestion is
to register the nuclear secondary ' radiation of HI after interaction

· ·

·
·

But



(AA A*A) @ 0.1 mbarn


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Kinematics of the Secondary -radiation
Ca*(P,E0) Ca
Dependencebetweeen the nergy EEnand e polarla of of Dependence betw en the e energy a d th the po q r q *P 0 photon, emitted bby the elativistic nunucleus Ca*( P , E0 ) photon, emitted y the r relativistic cleus at LHC energgy.Axis Z isis lolong uclear direction. LHC ener y. Axis Z a a ng n nuclear direction. at The e lines correspond to the discrete eexcitedlevels: Th lines correspond to the discrete xcited levels:
1. 31 , 3.74 MeV

2. 21 , 3.90 MeV
3. 51 , 4.49 MeV

4. 3 -, 6.29 MeV 2
5. 33 , 6.59 MeV

Roman pots of TOTEM have Roman pots of TOTEM have 20 mrad < q' < 150 mrad 20 mrad < q' < 150 mrad Energy of '­radiation will be corresponded to the region Energy of '­radiation will be corresponded to the region 21 GeV < E' < 26 GeV
21 GeV < E' < 26 GeV


Nuclear - radiation on the flight at LHC energies and ZDC
A + A A*(JP) + A, A*(JP) A + , E =10-20 GeV ZDC

(3-, 6.59 MeV) (3-, 6.29 MeV) (5-, 4.49 MeV) (2+, 3.90 MeV)
(3-, 3.74 MeV)

Ca*(P,E0) Ca




Comparison of '-rays Distributions for Various Processes
-

`

5. barn, 1. Ca+Ca Ca+Ca*(3-)+e+e 0.1 mbarn, 2. Ca+Ca Ca + Ca*(3-) 0.2 mbarn, 3. Ca+Ca X1 + X2 + p0

Ca*(3-) +Ca

p0 2

Energy distribution of secondary photons. Numbers 1, 2, 3 correspond to three processes.

Angular distribution of secondary photons for three processes.