physics 663 - university of chicagotheory.uchicago.edu/~smaria/sony_pcg/support/det5.pdf · 2002....
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Physics 663, lecture 8 1
Physics 663
Par t icle Physics Phenomenology
May 7, 2002
Physics 663, lecture 8 2
Det ect or s
• I nt er act ion of Char ged Par t icles and Radiat ion wit h Mat t er
– I onizat ion loss of char ged par t icles
– Coulomb scat t er ing– Radiat ion loss by elect r ons
– Absor pt ion of J�-r ays in Mat t er
• Det ect or s of Single Char ged Par t icles– Pr opor t ional count er s, Spar k and st r eamer chamber s, Dr if t chamber s,
Scint illat ion count er s, Cer enkov count er s, Solid-st at e count er s,
– Bubble chamber s
• Shower Det ect or s and Calor imet er s
– Elect r omagnet ic-shower det ect or s– Hadr on-shower det ect or s
• Ref er ences: Donald H. Per kins, I nt r oduct ion t o High Ener gy Physics, Four t h Edit ion• Par t icle Dat a Gr oup: pdg.lbl.gov
Physics 663, lecture 8 3
Shower Det ect or s and Calor imet er s
• Par t icle ener gies can be measur ed by absor bing t he ener gyof an incident par t icle and measur ing t he signals gener at ingin t he absor ber
• The absor bed ener gy appear s as ionizat ion, excit at ion,r adiat ion, or ot her signals pr opor t ional t o t he t ot al absor bedener gy
• Examples:– ionizat ion in liquid ar gon– Cer enkov r adiat ion in lead glass– scint illat ion light in scint illat ing plast ic
• Such devices ar e t he only met hod of det ect ion neut r alpar t icles, such as– gammas
– K0L
– neut r ons
Physics 663, lecture 8 4
Shower Det ect or s and Calor imet er s
• Typical t r acking det ect or s have r esolut ions t hat det er ior at ewit h incr easing ener gy since t he bending in a magnet ic f ieldis r educed
• Absor pt ion det ect or s, on t he cont r ar y, impr ove wit hincr eased ener gy, of t en impr oving as E-1/ 2
• Tot al absor pt ion det ect or s also pr ovide ver y f ast signals,which ar e of t en employed as f ast t r igger s f or exper iment s
Physics 663, lecture 8 5
Elect r omagnet ic Cascades
• Elect r omagnet ic cascades ar e t he basis f or elect r omagnet icshower det ect or s
• High-ener gy elect r ons and phot ons incident on an absor ber init iat eelect r omagnet ic cascades as pair pr oduct ion and br emsst r ahlunggener at e mor e elect r ons and phot ons wit h lower ener gy
• Longit udinal development is gover ned by t he high-ener gy par t oft he cascade, and scales as t he r adiat ion lengt h in t he mat er ial
• Elect r on ener gies event ually f all below t he cr it ical ener gy, andt hen dissipat e t heir ener gy by ionizat ion and excit at ion r at hert han by t he gener at ion of mor e shower par t icles.
• I n descr ibing shower behavior , it is t her ef or e convenient t oint r oduce t he scale var iables
t = x/ X0
y = E/ Ec
so dist ance is measur ed in unit s of r adiat ion lengt h and ener gy inunit s of cr it ical ener gy.
Physics 663, lecture 8 6
Elect r omagnet ic Cascades
Physics 663, lecture 8 7
Elect r omagnet ic Cascades
Ce = -0.5Cγ = +0.5
Physics 663, lecture 8 8
Elect r omagnet ic Cascades
• The t r ansver se pr of iles of elect r omagnet ic cascades ar e nicelyr espr esent ed by t he Molier e r adius (RM)
RM = X0 Es / Ec (Es = 21 MeV) .
• Typical r elat ions– ~ 10% of ener gy out side RM
– ~ 99% of ener gy wit hin 3.5 RM
– shower char act er ized by nar r ow
cor e t hat br oadens as t he showerdevelops
Tr ansver se Pr of iles
Physics 663, lecture 8 9
Elect r omagnet ic Cascades
• The lengt hs of shower sscale as 1/ Ec
– t his r esult s f r om t hef act t hat when t hepar t icles of t heshower r each t hecr it ical ener gy,r adiat ion ceases andt he ener gy isdeposit ed asionizat ion.
Lengt hs of shower s
Physics 663, lecture 8 10
Elect r omagnet ic Cascades
• Maximum occur s at a dept h t hat incr eases logr it hmically wit hpr imar y ener gy
• The number of shower par t icles at t he maximum is pr opor t ional t ot he pr imar y ener gy
• t he t ot al t r ack-lengt h int egr al is pr opor t ional t o t he pr imar yener gy
• Fluct uat ions in t he t ot al ener gy deposit ed about t he aver agevar ies inver sely wit h t he squar e r oot of t he number of par t icles int he shower , or inver sely as t he squar e r oot of t he pr imar y ener gy
Review of Main Qualit at ive Feat ur es
Physics 663, lecture 8 11
Elect r omagnet ic-shower Det ect or s
• Each calor imet er will det ect a specif ic r esponse which ispr opor t ional t o t he shower development , but may var y f r omt echnique t o t echnique
– ener gy deposit ion– t r ack lengt h– t hr eshold ener gy
Not e: at ver y high ener gy t heser esolut ions will be limit ed by t hesize of t he const ant t er m
Physics 663, lecture 8 12
Elect r omagnet ic-shower Det ect or s
• Lead Glass• NaI• BGO• BaF2
• CeF3
• CsI
• eg BaBar , 5760 cr yst als int he bar r el– 820 in t he endcap
Homogeneous Calor imet er s
Physics 663, lecture 8 13
Elect r omagnet ic-shower Det ect or s
• Examples:– lead-scint illat or
– lead-liquid ar gon
– silicon-t ungst en
Sampling Calor imet er s
Physics 663, lecture 8 14
Elect r omagnet ic-shower Det ect or s
• Example: CDF bar r el– 0.5 cm t hick scint illat or
– 0.32 cm Pb absor ber
– 31 layer s = 18 X0
Lead- scint illat or
Physics 663, lecture 8 15
Elect r omagnet ic-shower Det ect or s
• Example: SLD Calor imet er– 2 mm Pb
– 2.75 mm Ar gon
– 56 layer s = 21 X0
Lead- liquid ar gon
Physics 663, lecture 8 16
Elect r omagnet ic-shower Det ect or s
• SLD Luminosit y Monit or– 3.5 mm t ungst en
– 3.5 mm gaps f or inser t ion of silicon diode det ect or s
– 23 layer s = 21 X0
Silicon- t ungst en
Physics 663, lecture 8 17
Elect r omagnet ic-shower Det ect or sSilicon- t ungst en
Physics 663, lecture 8 18
Hadr on-shower Development
• Hadr on shower s ar e mor e complicat ed– nuclear int er act ions absor b ener gy f r om t he shower– t his loss of ener gy t ypically r emoves 30% of t he incident
par t icle ener gy, but f luct uat ions in t he number and nat ur e oft he nuclear int er act ions give t his loss lar ge f luct uat ion
– t her ef or e, t he ener gy r esolut ion is much wor se t han f orelect r omagnet ic calor imet er s
• t he best is about 35% / √E• many of t he best calor imet er s achieve only 50-70% / √E
• not e: an addit ional const ant t er m can be lar ge (see compensat ion)
• Scale lengt h:
• Shower maximum:
Physics 663, lecture 8 19
Hadr on-shower Development
• Aver age shower pr of iles
• Fluct uat ions about t heaver age ar e ver y lar ge
Physics 663, lecture 8 20
Hadr on-shower Development
• Shower cont ainment
Physics 663, lecture 8 21
Hadr on-shower Development
• The r eponse of a calor imet er t o t he elect r omagnet iccomponent (pr imar ily f r om π0 s) is much dif f er ent t han t her esponse t o t he char ge hadr ons. Fluct uat ions f r om showert o shower in t he f r act ion of ener gy deposit edelect r omagnect ically t r anslat es int o ener gy r esolut ionf luct uat ions, unless t he calor imet er is “compensat ing”
• Compensat ing r ef er s t o t he r est or ing of a balance in t hecalor imet er r esponse t o EM and char ged ener gy deposit ion– t his can be achieved by boost ing t he signal when ener gy is lost
t hr ough nuclear br eakup - t he or iginal t echnique of Ur aniumcalor imet r y (Willis et al)
– or by suppr essing t he r esponse when ener gy is deposit ed byelect r omagnet ic sub-shower s
Physics 663, lecture 8 22
Hadr on-shower Development
• The hadr onic component shower s have been shown t o be welldescr ibed by (E/ E0)m-1
– 0.80 < m < 0.85– E0 ~ 1 GeV f or pions
– E > f ew t ens of GeV
• Then t he r at io of t he r esponse of t he calor imet er t o t het wo component s is
• wher e e/ h is t he int r insic r esponse
• Calor imet er s wit h e/ h close t o one ar e t hen “compensat ing”and t end t o have t he best ener gy per f or mance
Physics 663, lecture 8 23
Hadr on-shower Det ect or s
• I t was discover ed in t he 1980’s t hat t he pr oper combinat ionof scint illat or and ur anium achieved t he best compensat ingcalor imet er .
• This was implement ed by ZEUS at HERA– 3.3 mm U, 2.6 mm scint illat or
35% / √E + 1% f or hadr ons
17% / √E + 1% f or elect r ons
Physics 663, lecture 8 24
Hadr on-shower Det ect or s
Physics 663, lecture 8 25
Hadr on-shower Det ect or s
• Since t he t r acker of a det ect or is mor e pr ecise t han t hecalor imet er in det ect ing char ged par t icles, a measur ementof j et ener gies based on t he “ener gy f low” can give bet t erj et ener gy measur ement s t han a calor imet er alonemeasur ement .
Ener gy f low calor imet er s
Physics 663, lecture 8 26
Hadr on-shower Det ect or s
• To do t his well r equir es a separ at ion of t he signals in t hecalor imet er f r om char ged and neut r al par t icles
Ener gy f low calor imet er s
Physics 663, lecture 8 27
Hadr on-shower Det ect or s
• The linear collider pr oj ect s ar e st udying a silicon-t ungst encalor imet er f or t his:– densest calor imet er
• conf ines shower s
– most gr anular segment at ion• allows r eadout of det ails
– builds on exper ience wit h siliconcalor imet er s at SLD and LEP
Ener gy f low calor imet er s
Physics 663, lecture 8 28
Det ect or s
• I nt er act ion of Char ged Par t icles and Radiat ion wit h Mat t er
– I onizat ion loss of char ged par t icles
– Coulomb scat t er ing– Radiat ion loss by elect r ons
– Absor pt ion of J�-r ays in Mat t er
• Det ect or s of Single Char ged Par t icles– Pr opor t ional count er s, Spar k and st r eamer chamber s, Dr if t chamber s,
Scint illat ion count er s, Cer enkov count er s, Solid-st at e count er s,
– Bubble chamber s
• Shower Det ect or s and Calor imet er s
– Elect r omagnet ic-shower det ect or s– Hadr on-shower det ect or s
• Ref er ences: Donald H. Per kins, I nt r oduct ion t o High Ener gy Physics, Four t h Edit ion• Par t icle Dat a Gr oup: pdg.lbl.gov