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UPC
V.L.Korotkikh, L.I. Sarycheva
Moscow State University, Scobeltsyn Institute of Nuclear Physics

RDMS, Minsk, September, 2008


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Motivation

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

Advantages:
· Large photon=photon energy in center mass system s (gg) < 300 GeV at LHC · Large electromagnetic crosssection of particle production EM ~ Z4 EM(PbPb) 200Kbarn EM(CaCa) 3Kbarn · Small background from the strong AA interactions

fusion

photodisintegration

grazing strong interaction


Peripheral Heavy Ion Collisions (b > RA1 + RA2 )
Program:
· Resonance production in g* g* -fusion
a)Quark content, g*g* ~ Q4, Q - quark charge, Gluebal is forbidden to first order b)Expectation of Higgs meson production at small background

Advantages:

· Large photon=photon energy · Exotic meson production g* + g* Hybrids (q, anti q, gluon) in center mass system g* + Pomeron Hybrids , Glueball s (gg) < 300 GeV at LHC Pomeron + Pomeron Hybrids , Glueba · Large electromagnetic cross- · Lepton pair production section of particle production g* + g* e e- (control QED, unitarity) g* + g* - (LHC luminosity) EM ~ Z4 g* + g* EM(PbPb) 200Kbarn · Vector meson production EM(CaCa) 3Kbarn g* + g* - , g* + g* 0 + X · Small background from the strong AA interactions

l


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


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`



Tot (CaCa ) 3.2 barn STR


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Phys.Rep., ..., 2007

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

The pure g*g* 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 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.


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Higgs


Higgs production by g* g* fusion g*g*
A p 208Pb 16O 8
208 16 16

H

0

bb , MH0=120GeV, (Hgg)=9 10-6, (Hbb)=1.7 10-4 GeV,
pT(b-jet)>20 GeV L,cm-2 s
-1

A.Kryukov, L.Sarycheva. 6 RDMS CMS,2001,p.560

L, pb

-1

82

1.0 10 4.2 10 1.4 10

34 26 31

3.15 10 0.013 441.5 0.013

5

, pb 1.0 1016.6 0.026 27.1

4

ev/year 31.5 0.22 11.5 0.35

Our calculations:

Pb

82

4.2 10

26 31 31

O8

1.4 10

441.5
441.5

0.05
~5 10
-4

21.6
~0.22

O8*(3-) 1.4 10


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Upsilon on CMS


UPC

·

Ultra Relativistic Heavy ions produce very high electromagnetic fields due to coherent action of all proton charges
These high energy photon beams can be used for non QGP studies :+ , +p, +A reactions

·

One can do precise QCD studies with less background and much simpler initial state than p+p p+A ,A+A collisions
12 Equivalent photon flux with b=2R(20f)


Motivations
+A reactions can lead to heavy vector mesons(j/psi,Upsilon) photo production. The cross section for heavy vector meson photo production is found to be depends quadratically on gluon density GA(x,A2)

13


Motivations
· Gluon distribution functions are very poorly establish for low x values (x<10-3 ). Small x values can be probed in +A collisions at LHC. for Upsilon photo production y=0 : x()~10-2 &y=2 :x()~10-4

·

14


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Backup slides


Pb+Pb(1s), (2s), (3s)
Simulation for Upsilon Production
· We use 50000 (1s)+ + events produced by Starlight Generator.
-

STARLIGHT[J.Nystrand,S.Klein,NPA752(2005)470

· ·

Starlight CMSSW. reconstruction with CMSSW_1_8_0_pre7

·

(2s) , (3s) also reconstructed according to their cross sections and BR
16


Results for (1s), (2s), (3s) mixed

Upsilon Pt & rapidity distributions
With pre selection of muon |Eta|<217


Generated & reconstructed InvMass
With globalMuon

18


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Nuclear g - radiation at LHC energies


Nuclear g - radiation at LHC energies
Motivation

g - radiation as a possible trigger for UPCs ·Nuclear beam monitoring at LHC
·


Decay of Nuclear Levels and g- radiation

GQR

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

P, Eg

0

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

Region of g - 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 g -rays Fe* Fe + g
Balashov,Korotkikh,Moscalenko. 21 ICRC, Adelaida, v2,1990,p.416


Kinematics of the Secondary g-radiation
Eg = gAE0g (1+cos qg )

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

Eg

g

Ca*

qg 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 rad < Energy of g'­radiation will 21 GeV <

TOTEM at 150 m qg' < 150 rad be corresponded to the region Eg' < 26 GeV

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


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Nuclear g`-radiation and +e- production e

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

E' 2AE0 21 GeV '

Properties of g'-radiation: · · · · Neutral radiation High energy Eg` at LHC Narrow collimation of g'-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
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, E0g')
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, E0g') Ca + g

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

int

= 5 barn


Comparison of g'-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-) g+Ca

p0 2 g

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

Angular distribution of secondary photons for three processes.


New Signature of UPCs
How to select the ultra-peripheral collisions without grazing strong interactions?
·
·

A+A



A* + A + M, A*



A+g`

Our suggestion is
to register the nuclear secondary g' 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 g`photon in the Roman Pot station 1 with Eg` ~20 GeV and qg` ~ 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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Beam Monitoring


Possibility of Nuclear Beam Monitoring at LHC by g-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

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


Geometry of the Roman pots in TOTEM LHC


Roman pot station 1 and g`radiation angles


Photon Registration Rate and Accuracy of Luminosity Monitoring
TOTEM LHC
Ca + Ca Ca + Ca*(3-) + e+e g' + Ca int = 5 barn L = (24)1030 cm-2 sec-1 qg' = 20150 rad jg' 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


Eg' = 25 GeV 4 radiation length eGeom 0.35

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


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Conclusion


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Backup slides

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

g

-radiation )

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

g

-rays detectors and for veto particle detectors?

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

g

-rays measurement?

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

g

-radiation from AA experiments with


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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 g' radiation of HI after interaction

· ·

·
·

But



(AA A*A) 0.1 mbarn

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


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Comparison of g'-rays Distributions for Various Processes
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`

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-) g+Ca

p0 2 g

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

Angular distribution of secondary photons for three processes.


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