physics 663 - university of chicagotheory.uchicago.edu/~smaria/sony_pcg/support/det5.pdf · 2002....

Physics 663, lecture 8 1

Physics 663

Par t icle Physics Phenomenology

May 7, 2002


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


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


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


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.



Ce = -0.5Cγ = +0.5



• 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



• 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



• 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


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



• 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



• Examples:– lead-scint illat or

– lead-liquid ar gon

– silicon-t ungst en

Sampling Calor imet er 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



• Example: SLD Calor imet er– 2 mm Pb

– 2.75 mm Ar gon

– 56 layer s = 21 X0

Lead- liquid ar gon



• 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


Elect r omagnet ic-shower Det ect or sSilicon- t ungst en


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:



• Aver age shower pr of iles

• Fluct uat ions about t heaver age ar e ver y lar ge



• Shower cont ainment



• 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



• 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


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



• 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



• 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




• 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



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 - university of chicagotheory.uchicago.edu/~smaria/sony_pcg/support/det5.pdf · 2002....

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